Latest METALLURGY ENGINEERING Interview Questions and Answers
1. What is Iron Ferrite, Define what is it used for, and where is it found?
Well, a few definitions match your question. First, “ferrite” is the name metallurgists give to the body-centered-cubic phase of iron and its alloys. The ‘body-centered-cubic’ phrase refers to the way the atoms are arranged in the lattice, to distinguish it from “austenite” which is the face-centered-cubic arrangement. Generally, ferrite is a pretty pure iron- the core iron used in electrical transformers, for example, is ferritic-but there are also some stainless steels that are ferritic. These iron-chromium alloys would have 12 to 18% chromium in them, and used for expensive exhaust systems in automobiles, for example. Iron is not found in nature, as are, say, chunks of copper, but must be refined by a blast furnace or other smelting technique.
2. Which metals do not react with lithium Bromide ad why?
For solving the problem you should have the electro negativity of Li and B and calculate the difference between the two quantities, and for the next step for any metal, you should calculate the difference between its electro negativity and bromine’s. Then if the result was higher than first value, one may say that this metal will react with the material otherwise it will not. However, you should have this in mind that the given procedure is true only in standard condition. However, in practice, many other factors will affect. Now I give you the calculations:
Electro negativity for Li = 1
Electro negativity for Br = 1.14
1.14 – 1 = .14
Now we consider a metal, let say Mg. Its Electro negativity is 1.2, so the difference is 1.2-1.14= .06, which is less than .14, so it will not react in standard conditions. Let say Fe, its Electro negativity is 1.8, the difference is 1.8 – 1.14 = .64 which is greater than .14, and it may react and form FeBr2.
3. Define what is widman statten structure?
Primary Widman statten ferrite either directly grows from the austenite grain surfaces, whereas secondary Widmanst¨atten ferrite develops from any allotriomorphic ferrite that may be present in the microstructure.
Widmanst¨atten ferrite can form at temperatures close to the Ae3 temperature and hence can occur at very low driving forces; the under cooling needed amounts to a free energy change of only 50 J mol. This is much less than required to sustain diffusion less transformation. Because Widmanst¨atten ferrite forms at low under cooling (and above the T0 temperatures),
It is thermodynamically required that the carbon is redistributed during growth.
4. Why duplex or super duplex stainless steels are welded with low heat input type electrode?
Duplex and super duplex stainless steel; but in general it’s true for welding of all types of austenitic stainless steels -and you must know that we can assume duplex s. steels as austenitic s. steels cause the amount of austenite is 50% of the matrix equal to ferrite- to use a low heat input process. In addition, the reason is general in austenitic s. steels as well. That is because the weld decays. Austenitic s. steels containing about 0.1% carbon or more are often susceptible to inter granular corrosion in the weld HAZ, which is known as “Weld Decay”. In these types of S .Steels the higher the heat input, the more severe the weld decay. However, here is a fact that all duplex stainless steels have a carbon content of less than 0.1%. Therefore, the severity of weld decay may be lighter, but still exists, and sensitization takes place more rapidly as the carbon content is increased.
5. For Define what reason would an aluminum casting, when applied with a powder coated paint finish, cause a poor finish to the paintwork.
Porosity is related to air or gas entrapment during the melting or casting process. When the metal cools and solidifies a small hole is left in the casting. Good out gassings of the melt and good foundry practice can eliminate much of this. Porosity can also be caused by lack of flow into the mold, which is a function of the alloy, superheat (temperature above the melting point), complexity of the mold and a few other factors. Another problem might be entrapment of impurities or slag in the melt. This results in a “dirty” casting. Some aluminum alloys can be particularly prone to these problems. Porosity can be eliminated by careful slag control in the melt, filters, and pour techniques.
I am not sure if the problems are particularly Indian versus British but the people who are doing the casting. I have seen excellent Indian, British, U.S., and Mexican castings as well as bad ones for these nations.
6. Is it possible to determine the heat treatment condition in Stainless Steel (ASTM A 479 Gr XM-19) by checking the microstructure?
Clearly, you have some specific alloy issues possibly relating to an engineering or design problem you are working on. It appears to me then you are seeking some free consultation. I will cover some basics but you need to be talking to a local metallurgical engineer who can help with the specifics of your problem.
First, you mention two different alloys A-479 is a type 405 ferritic alloy, 11.5 – 14.5 Cr, 0.8 C, and no nickel. This single-phase BCC alloy is not heat treatable. The XM-19 alloy is a type 209 austenitic stainless steel, sometimes called Nitronic 50, 20.5 – 23.5 Cr, 0.6 C, 4 – 6 Mn, 11.5 – 13.5 Ni, plus all kinds of minor alloying elements. This stable, single-phase FCC alloy is also not heat treatable but gets its strengthening from cold work.
7. Why is Chromium Molybdenum steels used to build pressure vessels? Define what is special about the properties of Chromium Molybdenum steels that make them ideal for pressure vessels?
The primary users of pressure vessels and piping are the chemical, petroleum, and electric power industries. The classification of pressure vessels regarding the material is based on the working environment and service temperature.
For ordinary-temperature service, the ultimate strength of steels remains relatively constant over the temperature range from -30 to 345, consequently the plain carbon steels are the most commercial.
For low-temperature service, to ensure safe performance, the steel must be resistant to the initiation and propagation of a crack under all service conditions. In thick sections, plain carbon steels produced according to fine-grain practice and normalized or quenched and tempered are used for service to -45 degrees centigrade. Low-carbon high nickel steels are used for service down to -195. Austenitic chromium-nickel steels, aluminum, and special copper and aluminum-base alloys have been found to be particularly suitable for applications close to absolute zero. Because austenitic steels have a face-centered cubic (FCC) crystal structure, they retain toughness to very low temperature.
8. Define what is the different between ferrite percentage and ferrite number?
Ferrite Number is an arbitrary standardized value designating the ferrite content of an austenitic stainless steel weld metal. It should be used in place of percent ferrite or volume percent ferrite on a direct replacement basis.
FN has been adopted as a relative measure for quantifying ferritic content using standardized magnetic techniques. The FN approach was developed in order to reduce the large variation in ferrite levels determined on a given specimen when measured using different techniques in different laboratories. FN approximates the “volume percent ferrite” at levels below 8 FN; above this level, deviation occurs.
A number of instruments are commercially available for determining the ferrite content of welds, including the Magne gage, Severn gage, and ferrite scope.
9. Is brass magnetic?
- Brass is alloy of copper and zinc, of historical and enduring importance because of its hardness and workability.
- However, brass is not magnetic, the basic magnetic elements are Iron, Cobalt and Nickel and their alloys. Then there are the new ceramic materials, which exhibit magnetic capabilities.
10. Why is steel vital in the construction of an aircraft?
In the aircraft business, carbon steels provide the airframe structure, landing gear, and by alloying with nickel, chromium, and other elements it makes up most of the aircraft gas turbine engine materials. Titanium is used in some cases for the aircraft structure because it is less dense but also much more expensive.
11. How do 304 stainless steel and 316 stainless steel weld to each other? I am hoping my medical device prospect will be able to weld a component made in 316 SS via metal injection molding toa 304 SS tube.
Both are austenitic stainless so, yes they can be easily welded but, and this is a big but, they can and are very different animals. You have not provided much information on the 304 and 316 alloys. 304 is a very common alloy that has a very wide range of compositions, this is like asking for a Chevy where you can get either a corvette or a fiesta. 316 is a little closer range of alloys but there are 316L, 316LN, 316F etc.
12. Define what other events in history might have affected the growth of Metallurgy?
This question demands a deep historical research. Now I can point out the World War II as a historical event that causes a great progress in metallurgy. For example, it was during WWII that Germans started manufacturing single body ships with the help of welding. However, in the cold waters of north the ships cracked and split into to parts and cracks initiated in the welds! In addition, that was when they realized that in cold environments metals tend to be brittle and welding could increase this tendency. It was the beginning of a great progress in welding techniques and mechanical metallurgy.
13. Define what is the strongest metal?
If there is any specific metal with the highest strength, I got no information about that. Everyday a new high technology material with unique characteristics is introduced. Now, the concentration is on composite materials. I guess the highest strength must belong to a composite material likely with a titanium alloy or as the matrix. Alternatively, maybe a super alloy is the strongest one. I got no more information.
14. How would a salt and water solution clean a penny but a vinegar and salt solution will not clean a penny? Define what is the cause of this?
I have been thinking about this overnight but I am not a chemist so I am unsure of the reactions. I do know that the penny gets shiny when you remove oxygen and impurities like sulfur from the surface. So lets reason together on this….The salt breaks down into hydrogen and chlorine in the water and produces a slightly acidic, HCl, solution. This breaks down the copper oxide pretty well. I do know the chlorine works well to clean of the copper oxide, I use “comet cleaner” with chlorine to clean brass. Now the vinegar has an acetic acid, but this is carbon, hydrogen and oxygen and I think that the salt combines with this to form a slightly basic solution and generates CO2. I would be interested in seeing if the vinegar salt solution with water added would improve the cleaning capability.
15. Are the grain boundaries a continuation of regular lattice structure from one grain to another? Explain.
They are called boundaries because this is where one crystal interacts with another. The lattice structure does not continue across the interface without mismatch. While there is some lattice, interaction or sharing it is not complete and there are many defects associated with the boundaries. The degree of mismatch determines if the boundary is a high angle boundary (lots of mismatch) or a low angle boundary (very little mismatch) A tilt boundary is an example of a low angle boundary. This is also one of the reasons that diffusion along grain boundaries is so much higher then through the bulk crystal.
16. Which method has more procity in cast part? Which method has more strength in cast part?
The sand casting will have more porosity in the final product. The die cast will also have higher strength both because of the lower degree of porosity and because of the finer grain size. While I have not been directly involved in the production of cylinder blocks there are a number of reasons for the preference of die-casting versus sand casting. Die-casting provided a finer finish, greater tolerance, better repeatability, and generally higher quality casting. They used sand casting of the iron blocks and still do in many cases and initially the used this same method for aluminum. However, the lower melting point of aluminum allows them to do the die casting method.
17. A plain carbon steel contains 45 wt% of proeutectoid ferrite. Define what is its average carbon content in weight percent? I know that you need to use a tie line in the phase diagram, but my book does not really give a good example to go by
The calculation is so easy if you have the iron-carbon diagram in your mind. Proeutectoid ferrite is ferrite formed before eutectoid transformation. At 0.8 wt% carbon, we got 100% austenite before the transformation and at 0.02wt% carbon, we got 100% ferrite, and between these two values of carbon content, we have different amounts of proeutectoid ferrite.
Considering that, we have x wt% carbon we calculate proeutectoid ferrite using the tie line.
Proeutectoid ferrite amount = (0.8-x)/ (0.8-0.02)*100=45
==> x=0.45 wt%
You can check it with eyes. At the middle of the tie line, we must have 50% austenite, 50% ferrite; and it is at (0.8-0.02)/2=0.38%C.
We have 45% ferrite, which is less than 50% so we are closer to eutectoid point (0.8%C); so the carbon content must be more than 0.38%.
18. Is nickel considered a non-sparking metal?
Monel and nickel form almost identical spark streams. The sparks are small in volume and orange in color. The sparks form wavy streaks with no sparklers.
So is not as bright as sparks of ferrous alloys. Therefore, that is a way to identify nickel and monel.
19. Define what kind of cleaning substance or treatments keep or help prevent cast iron from rusting?
Cast iron is a mixture of graphite (carbon) flakes in a matrix of steel (iron with carbon in solution). The graphite, which has the shape of corn flakes, does not contribute much to strength. If anything, it makes the cast iron some Define what porous or sponge like. The graphite does makes it easy to machine and has a dampening effect on the cast iron. However, it also makes for a lot of surface area, which allows plenty of air (oxygen) to get to the iron and form rust.
20. Define what is the difference between Stainless steel and Alloy Steel?
Stainless steels have at least 11 to 12% chromium in the alloy. Why 11 to 12% minimum you might ask? That much is required to provide a continuous layer of protective chromium oxide on the surface. Alloy steel just means that there are additional elements added to the iron-carbon. So to answer your second question; Yes, stainless steels are by definition alloy steels.
21 Define what affect would increasing the charpy impact toughness on an object have on the surface of an object it strikes if all else remains the same? Would it cause more damage to the object it strikes?
Charpy toughness is a measure of the metals ability to resist tearing or to absorb energy during an impact. Generally, we achieve that by altering the microstructure to be more ductile. In the quenched and tempered alloys (steels) for example, that involves tempering to convert the hard brittle martensite to softer more ductile bainite or a ferrite carbide mixture. Therefore, we are making a softer metal; therefore, if it affects another object it would tend to deform more. There would be less damage to the object being struck because the striking object would deform more and distribute its load across more of the surface of the object being struck.
22. Define what medal conducts heat best?
- In physics, thermal conductivity, (showed by the Latin capital of land), is the intensive property of a material which relates its ability to conduct heat.
- Thermal conductivity is the quantity of heat, Q, transmitted through a thickness L, in a direction normal to a surface of area A, due to a temperature gradient (delta T), under steady state conditions and when the heat transfer is dependent only on the temperature gradient.
- In general, thermal conductivity tracks electrical conductivity metals being good thermal conductors. There are exceptions: the most outstanding is that of diamond, which has a high thermal conductivity, between 1000, and 2600 W/mk, while its electrical conductivity is low.
23. Do you know Define what metal might be considered the “most environmental”? I say aluminum because it can be recycled others on my team say brass.
Due to the consumption of a large amount of fossil energies to purify, ferrous alloys are not environmental. USA has stopped most of its steel mills, and the strategy is to concentrate mills in the developing countries. In non-ferrous alloys, let us consider only the mostly used alloys, which are copper alloys (including copper, brass, and bronze) and aluminum alloys. Because the rest are produced so much less than mentioned alloys that they are not actually a threat to the environment, furthermore, they are mostly extracted during refining Fe, Al, and Cu. Production of Cu and AL involves melting and electrolyzes procedures. However, the energy per kilogram pure Al needs is much higher than even Fe, but the most of the energy is electrical and much cleaner than that used for Fe. For Cu, through pirometallurgy methods a large amount of energy is gained autogenously, i.e. exothermal reactions occurred during copper making process supply a large amount of energy needed, but it involves producing products that are not environment. There are hydrometallurgy methods to produce copper, which are more environment-friendly.
24. Define what are Ceramics?
The word ceramic is derived from the Greek word keramikos, “having to do with pottery”. The term covers inorganic non-metallic materials whose formation is due to the action of heat. Up until the 1950s or so, the most important of these were the traditional clays, made into pottery, bricks, tiles and the like, along with cements and glass.
Historically, ceramic products have been hard, porous, and brittle. Technical Ceramics can also be classified into three distinct material categories:
Oxides: Alumina, zirconia
Non-oxides: Carbides, borides, nitrides, silicides
Composites: Particulate reinforced combinations of oxides and non-oxides.
Ceramic materials can be crystalline or amorphous. They tend to fracture before any plastic deformation takes place, which results in poor toughness in these materials. Additionally, because these materials tend to be porous, the pores and other microscopic imperfections act as stress concentrators, decreasing the toughness further, and reducing the tensile strength. These combine to give catastrophic failures, as opposed to the normally much more gentle failure modes of metals.
25. When austenitized, carbon steel is quenched, why is the BCC crystal elongated into a body-centered tetragonal crystal structure?
Martensite crystals ideally have planar interfaces with the parent austenite. The preferred crystal planes of the austenite on which the martensite crystals form are designated habit planes, which vary according to alloy composition. In steels, the parent phase is usually austenite with a face-centered cubic (fcc) crystal structure, but the crystal structure of the product phase may be body-centered cubic (bcc). Under special conditions, steels undergo martensitic transformations in which the crystal structure of the product phase reverts to that of the parent. Most medium-carbon and high-carbon steels form martensite with a bct crystal structure, because carbon atoms occupy only one of the three possible sets of octahedral interstitial positions.
Allotropy means the property by which certain elements (like Fe) may exist in more than one crystal structure. Iron exists in two allotropic forms: BCC and FCC. In other words at 700°C (1290°F) it undergoes an allotropic transformation from FCC to BCC (in quenching, i.e. iron has FCC structure above this temperature and BCC structure below that).
26. Which is stronger, Tungsten or Titanium?
Tungsten has high tensile strength and good creep resistance. At temperatures above 2205 OC (4000 OF), tungsten has twice the tensile strength of the strongest tantalum alloys and is only 10% denser. However, its high density, poor low-temperature ductility, and strong reactivity in air limit its usefulness. Maximum service temperatures for tungsten range from 1925 to 2480 “C (3500 to 4500 OF), but surface protection is required for use in air at these temperatures.
Wrought tungsten (as cold worked) has high strength, directional mechanical properties, and some room-temperature toughness. However, re crystallization occurs rapidly above 1370 “C (2500 OF) and produces a grain structure that is crack sensitive at all temperatures.
27. Define what is a silver and deming drill bit?
Silver and Denim is the name of a manufacturing company. This company could trace its history back to 1854, although the “Silver & Deming” name does not date back that far. The titular heads were Albert R. Silver and John Deming. Silver & Deming made a variety of machines that were primarily aimed at wheelwrights: hob-boxing machines, spoke-tenoning machines, etc.
Silver & Deming apparently invented the large-size twist drill bit with a turned-down shaft so they can be used in a chuck smaller than the bit’s cutting diameter. They did not patent this idea, so the idea was quickly copied by others, but these bits are still called “Silver & Deming drills”.
28. How much gold is in a troy ounce?
Troy ounce defined by the troy system of mass. In troy weight, there are 12 ounces in a pound, and a troy pound is 5760 grains (about 373.24 g), rather than 7000 (about 453.59 g). Note: at roughly 31.10 g, the troy ounce is about 10 per cent more than the more-common avoirdupois ounce. These troy ounces are now used only when weighing precious metals like gold and silver. One ounce of gold is always 31.1 g.
29. How to calculate heat affected zone in weld?
Heat affected zone is measured regarding the microstructure changes in the weld. For example in steels, this is the area around the weld zone, which has undergone a transformation. In other words, this is the area, which had been austenitized. For calculating the HAZ after welding, for steels, it is better to macroetech the section of the weld HAZ can be easily recognized by the contrast it makes with the base metal and the weld metal.
30. Why is it so hard to find literature on the wear resistance of titanium?
Titanium in elemental form is so soft it does not even register on a Rockwell C scale. With that being said, I would guarantee that you are using a titanium alloy of some type, most likely a Titanium-Aluminum-Vanadium alloy. These types of alloys can be processed to hardness in the low 40’s HRC. In terms of concentrating on wear resistance, hardness is Define what you are going to want to focus on. I looked in one of my books and found the mechanical properties for various titanium alloys. The book, which you may be interested in purchasing a copy of, has all of the different properties of many materials, including entire chapters on titanium and titanium alloys. Below is the Amazon link to purchasing this book.
31. Is it possible to use metallurgical inverted microscope to other designation?
A microscope is a microscope for most purposes. First, make sure the light source on the scope is useful in seeing Define whatever it is you want to see. Certain items are seen well in certain lights. The second thing, as I am sure you have already realized, is that you will have a tough time determining where on the sample you are looking, as it is up side down. For this reason, I even prefer a non-inverted scope even for metallurgical tasks. In summary, if you are ok with the sample being upside down, and the light source is sufficient, there is no reason it will not work to the magnification that scope is specified.
32. When using mercury to recover very, fine gold from ore, Define what is the best way to separate the gold laden mercury from the ore?
A centrifugal system would certainly separate the mercury assuming you could maintain a fluidized bed and that there were not large differences in the sizes of the particles in the slurry. Depending on the volume involved, a vibratory table might be better. There are many other methods, but I would need to know the relative size / volume / solid-liquid ratio information in order to make a useful recommendation. You need to take special precautions in any case to preclude the release of mercury into the environment. This is very east to do I can help you there as well if you care to divulge the nature of your processing circuit.
33. Is there any way through hardening and anodizing some type of aluminum, it could be as hard as steel? I have hardened steel rollers that run up and down on a ramp along with spring pressure. Alternatively, if you are familiar with snowmobiles, the rollers run on the helix on the secondary clutch.
Aluminum, while it is incredible for some applications due to it being lightweight, is a very soft and weak metal. There really is not any way to get it any where near the hardness of steel. Define what people are doing for applications requiring lightweight, but strong materials is going with some new age alloys, mostly consisting of titanium and nickel.
34. Define what is the minimum temperature for stress relieving of ASTM A 519 Gr.4130 material and please tell us where we can find the location.
Stress relieving of alloy steels (like 4130) has no temperature outlined in the spec of the material. However, it is common practice to stress relieve 4130 between 1050 and 1200 F. This is high enough to relieve the stress with out being hot enough that the material has an austenitic phase change, which occurs around 1350 F.
35. Define what are Metallurgical microscopes?
A metallurgical microscope is an inverted scope with light sources designed for magnifying structures of metallographically prepared specimens. The magnification is no different from most normal upright scopes. Companies including Nikon and Olympus produce the scopes and you will be able to find a plethra of information about the scopes on their websites. I would also consider contacting their sales reps to ask specific technical questions about the scopes.
36. Is there a possibility of inducing stress cracking in an insulated stainless road tanker vessel (20 tonne capacity) if the vessel is subject to rapid filling (10 tonne /hr) with liquid methane (-160 C) assuming the vessel is at ambient. If so, where could I obtain suggested cooling rates?
Assuming a two-hour load time, insulation in good condition and steel in good condition with no existing stress cracks at the welds, and a “pre-cool” period prior to rapid loading, the unit should hold up OK.
If you start with an ambient unit, and you have an inrush of liquid methane, the initial boiling of the methane in the unit will be very vigorous until the inner surfaces are cooled down. This violent boiling will result in liquid being ejected from the unit if care is not taken, and could result in damage to the insulation and liner. It would be best to load a small amount of the liquid methane into the unit and let it boil away, collecting the fumes and re-compressing if possible, thereby cooling the inner components of the unit. This will lessen the initial thermal shock and reduce the likelihood of stress cracking.
37. Define what metal cord transfers electricity, and how can i tell?
As far as I am concerned, copper is known as a good and cheap conductor of electricity. Although there are some other elements, such as silver, with higher conductivities copper is preferred due to its being rather cheap. Sometimes because of weight considerations, aluminum is also used even though it has a lower conductivity compared to copper.
38. Define what is meant by hardening ability of metals?
It is the ability of a metal to become hard (and inevitably brittle) under a given cooling rate. Therefore, the higher the hardenability of an alloy, the lower the cooling rate required to harden the metal. We have more heard about the hardenability in steels rather than other alloys. This is because in steels, there are different phases which can appear subject to the applied cooling rate below the critical temperature (the eutectoid temperature) as well as the alloying elements present in that grade of steel. Most of alloying elements in steel improve its hardenability by decreasing the critical cooling rate required to obtain the hardest possible phase i.e. martensite.
39. Can 1026 steel be welded?
Weldability of Iron-Carbon alloys is a function of their carbon content and decreases as their carbon increases. Plain carbon steels can be roughly categorized into 3 main groups: 1- low carbon plain steels which have less than 0.2wt% carbon and are the most wieldable and heat treatable carbon steels, 2- medium carbon plain steels with a carbon content of 0.2-0.5wt%C, and 3- high carbon plain steels with more than 0.5wt%C. The 1026 steel is a medium carbon steel (10 at the beginning implies its being a plain carbon steel and 26 at the ending denotes that it has 0.26wt%C). Thus, 1026 steel falls into the second category which although are not as wieldable as those of the first group, still are quite wieldable? Post heating (in order to establish controlled cooling) can reduce the risk of its becoming hard and brittle after welding operation.
40. Define what is the chemical composition of ceramic and Define what is its atomic density?
There are literally thousands of different ceramic products. They have widely varying atomic structures and characteristics.
41. Which of different types of cast irons is stronger? Is their strength superior to steels?
Generally, steels are considered to have better mechanical properties and ductility. However, there are some types of cast irons like ductile iron, which, in contrast to other types of cast irons, are not brittle. The strength of these ductile irons can be enhanced by controlling their matrix via an austempering heat treatment. This Austempered Ductile Irons (ADI) has very good mechanical properties comparable to those of some grades of steel. However, keep in mind that in spite of lower mechanical properties and being brittle, cast irons have good fluidities and are cheaper than steels. By the way, there are some special purpose gray and white irons, which are frequently used for special applications like where resistance to corrosion, wear, and heat is required.
42. How one can differentiate between 304 & 316 grades of Steel (Physically)?
There is no physical distinction between these two grades of stainless steels since there are very similar compositionally. However, it might be possible to differentiate them rapidly by comparing their electrical resistance (measurable via an ohmmeter), indeed with some considerations in order to minimize the errors. I assume you already know that the most reliable method of telling them from each other would be to perform a chemical analysis of them using EDS and other spectroscopy methods.
43. Define what is the melting point of E70 steel, 304,308,316 stainless steels? In addition, Define what is the hottest part of the flame in a fire?
You may find the melting range of some frequently used stainless steels below. Steel is an alloy and instead of a unique melting point, has a melting range, which is the range in which under equilibrium conditions, liquid, and solid phases coexist.
304: 1400-1450 (oC)
308: 1400-1420 (oC)
316: 1375-1400 (oC)
44. How is metal heavy?
Not all metals are heavy. Hydrogen is a metal, and is the lightest element known. Lithium, also a metal is the third lightest element there are many heavy elements that are not metals. If you “Google” the definition of “metal” you will note the properties that qualify a substance as a metal. Mass (weight) is not the important factor. Common metals are heavy because they have a dense electron structure.
45. Does case harden steel properties detoriates over time? Especially for guns, parts like bolt carrier, the brand new parts has been kept for 10 year and properly oiled. I am worried about its surface hardness to take the blow during firing.
Hardened steel does not generally deteriorate over moderate periods, especially not as short as ten years, providing it have been protected from corrosion. Strong magnetic fields and electric fields generated through or around the steel can have an effect, but this is highly unlikely. If your bolt carrier has been kept protected and oiled it should be fine. I have a shotgun that was made in 1740 which has lost none of its hardness as well as steel swords dating back to the 1600’s that are still hard and sharp. You should not have a problem.
46. Does the extrusion process for A355 AND A356 alloy effect on the amount of impact energy?
Yes, it does. I am not an expert in these things, but I do know that the parameters of the extrusion process directly affect the crystalline matrix of the alloy, which in turn governs the physical characteristics of the alloy. As the differences can be quite significant, I would recommend checking with qualified references for pertinent details. I know that quenching and max temperatures are big issues. Good luck, sorry I could not be of greater assistance.
47. Define what is the difference between plaster used in gold investment casting and ceramic used in the process of investment casting of automobile engine parts and turbine blades etc. when both are used in the lost-wax method?
In general, the plaster used in gold investment casting is standard “plaster of Paris” or other such material it has a fine but inconsistent grain size and, for the most part, water based. The other parts you mentioned are generally a higher precision, the casting material is of a fine but consistent grain, high temperature, hard, and not always water based. This is especially important for turbine blades as the material from which they are cast is more difficult to fine finish than other metals and the precision is extremely important due to the speed of rotation. It would be safe to say that the latter could be used in place of the former but not the former in place of the latter. Hope this is helpful.
48. We make aluminum moulds by press casting, can u suggest any thing so that the moulds should shine after casting?
Shininess of castings depends on the surface quality of cast parts. Casting surface finish is always a function of mold surface and characteristics. The selection of mold materials and the accuracy of mold finish maintained in premium casting operations ensure that specified requirements are met. Sometimes there is the possibility of increasing surface finish of castings by increasing their surface tension. This is done for aluminum alloys by allowing formation of oxide inclusions, the most important of which is Al2O3, in the molten metal. The increase in surface tension prevents molten metal from penetrating into the mold depressions since as you know surface finish improves when the melt solidifies in contact with air. However, such a resolution is accompanied by decrease in mechanical properties of castings, as oxides will act as stress concentration sites.
By the way, I have not heard about usage of grain refiners as shine promoters for aluminum castings, though their application in such cases may rely on the same mechanism.
49. Define what is the grain size of lead as an element and as an alloy such as lead tin alloy?
Grain size in alloys and pure elements is a function of their solidification rate. The higher the solidification rate, the smaller the grains are. Determination of grain size in pure elements is rather difficult since it is difficult to locate the grain boundaries; there is no segregation and composition distinction in the case of micro structural features in pure elements. However, in the case of alloys such as Pb-Sn alloys, composition difference between the primary dendrites and the eutectic matrix allows for grain size measurement. As most of Pb-Sn alloys exhibit a dendritic structure surrounded in a eutectic matrix, the dendrite arm spacing is used instead of grain size. For some alloy systems, there are relationships to correlate grain size to solidification rate. In the case of pure Pb and Pb-Sn alloy as well as most other alloys, primary dendrite arm spacing (at normal solidification rates like those applicable through sand and even die casting) is of order some microns and can be decreased to some nanometers by Rapid Solidification processes like melt spinning. The solidification rate in the case of such processes can reach 1,000,000,000 [0C/s]. These processes have the capability of producing “Amorphous” structures in the case of some special alloys where grain size becomes meaningless. For more information on lead alloys, you are advised to refer to the 2nd volume of ASM handbooks, which is on non-ferrous alloys and contains a section devoted to lead alloys.
50. How can you find out Define what kind of stainless steel was used in making a stainless object?
Usually, one can simply guess the general type of stainless steel i.e. tell if it is ferritic (or martensitic) or austenitic though there are some other types of stainless steels like precipitation hardening and duplex types which have some specific applications. To find the category to which you are stainless belongs, you only need a magnet. If the magnet attracts your steel, then it is a ferritic (martensitic) type otherwise austenitic. Austenitic steels have high nickel or manganese contents, which are both austenite stabilizer elements. However, you need to perform further examinations to tell the exact grade of your steel. These examinations might be micro structural, compositional etc. Usually purchasers of stainless use a quantometer to find chemical composition of stainless steels; then they compare the compositions with the standards and find their type. Please note that only limited grades of stainless steels like 410, 420, 201, 304, and 316 are frequently used and usually one only needs to tell these from each other.
51. Will aluminum alloy like 380 or 356 settle? Meaning while in “Liquid form” above melting point will the heavier elements like copper, Fe, Silicon, zinc etc. settle to the bottom of the liquid/molten aluminum after a period.
Yes settling, due to gravity, of heavier elements takes place in the molten state in the absence of any convection. As you know, severity of settling depends on the density difference among alloying elements. For instance, in the case of A356 alloy, the main elements Al and Si have rather similar densities and settling of Al is too sluggish. Nevertheless settling of heavy elements like Cu may lead to their accumulation in the bottom of container after a rather short time, provided there is NO convection. In practice, settling in the molten state is not too likely and will not be problematic.
In contrast, during soaking in the semi-solid state, settling would be considerable since presence of a network of primary dendrites interferes with convection in the liquid phase. My own experiments have evidenced considerable settling of Zn in the case of ZA27 alloy (Zn-28.5wt%Al-2.5wt%Cu) after a soaking time of 55 minutes in the semi-solid state (452C). Normally for this alloy primary dendrites are Al-base (refer to Al-Zn binary phase diagram) but due to Zn settling, primary phase in the bottom of container had changed to a Zn-base phase which will only form when zinc content is more than 98wt% or so. Primary dendrites at the upper part of container were Al-base
52. How is solution annealing carried out? Define what type of furnace is required? Does one need to be heat in a Salt Bath?
Solution annealing is carried out by heating up the alloy to a temperature in which typically only one phase is stable. This temperature depends on the alloy to be solution heat-treated; for precipitation hardenable Al-Cu base alloys, solution-annealing temperature is ~550C in which only alpha phase persists and for some precipitation hardenable steel grades like precipitation hardening martensitic stainless steel 17-4PH, this is something like 1050C where only gamma (austenite) phase exists.
Solution annealing is the second stage of a two-stage process; the second stage is precipitation hardening which is performed by heating the alloy to a temperature far below the solution annealing temperature, in which very small precipitates begin to form. This leads to enhancement of mechanical properties of the alloys and desired properties mainly high strength are reached only at the end of the precipitation hardening stage, whereas after solution annealing, material is rather soft. The precipitation hardening temperature for Al-Cu base alloys is something around 180C, while that of 17-4PH stainless steel is around 500C. Such materials are mainly used in aerospace applications where materials having high strength/weight ratios are required.
53. How much gold concentration should be in the organic phase (DBC) before reduction by oxalic acid solution? Is it effective on purity of gold in reduction step? Define what is the ratio of DBC to oxalic acid solution in this step?
It really does not matter the concentration of gold in the DBC, it will respond well to very small concentrations or it will generally load up at about 25 grams of gold in a liter of DBC. This does not present a problem, as the DBC is completely re-useable, although I generally figure on a 3% to 4% loss per cycle in handling, etc. Therefore, if your original acid had 50 grams of gold in it, you would do two extractions into DBC using a liter of the extracting solvent. You should continue to extract from the pregnant gold solution until you are sure no gold is left in it. If the pH of the acid solution is not too high a simple stannous chloride test will tell you if there is still gold in it, and that is sensitive to the ppb level.
54. Which is the only liquid in which gold is dissolved?
Since gold is very a noble metal, it does not dissolve in conventional solvents used to leach. Gold cannot be easily converted to Au2+ cations, so in practice, it becomes dissolved in the form of complex cations Au((CN)2)-, using the alkaline cyanide solutions like sodium cyanide, indeed in the presence of oxygen as oxidant(usually air agitation is used).
55. Define what is the metallurgy use? Define what is the casting and forging?
Actually, you asked a question, which requires a very long-winded answer. In summary, actually, you asked a question, which requires a very long-winded answer. In summary, metallurgy i.e., science of metals, is used to get metals with higher quality and higher in-service performance.
Casting is a forming method based on melting metals and pouring them into molds with desired shapes, so that after solidification desired properties are achieved.
Forging is a solid state forming method, which means it involves no melting. Forging stock is heated up to the appropriate temperature (it is usually so hot that appears red or white) and then application of pressure leads to plastic deformation of stock. Therefore, stock takes on the negative shape of die. Heating facilitates forming, i.e. makes possible forming at a smaller load.
Forging products usually are of higher quality and have a higher manufacturing cost compared to castings. Some parts cannot be used in the cast form because of the defects inherent to casting (most grades of steels) while some other metals are so brittle that they cannot be forged (e.g. cast irons). Indeed, there are some metals, which can be produced by either of the methods. The standard applicable to the part determines which form must be used.
56. Define what is proeutectoid ferrite and cementite?
If you are not familiar with the Fe-C binary phase diagram, please try to download it before reading the answer below, because without such prior knowledge, it might be difficult to figure out my answer. Using keywords “Fe-C”, “phase”, and “diagram” in search engines like Google, you can easily find this diagram.
As you probably know, in the iron-carbon binary phase diagram, which in addition to some other purposes is used to predict phase transformations in steels and cast irons, there, is a eutectoid reaction wherein austenite phase decomposes to a mixture of ferrite and cementite upon cooling. If there is no alloying element other than carbon, and if cooling rate is slow enough (so that there is sufficient time for diffusion transformations to take place), this reaction occurs at the temperature of ~723C and at a composition of ~0.8wt%C; a Fe-C alloy with exactly 0.8wt%C is called a eutectoid steel.
57. How does and why the recrystallization temperature of the metals affects on alloying?
The formation of new equi-axed grains in the heating process, instead of the oriented fibrous structure of the deformed metal is called re crystallizations. The temperature required for the beginning of the re crystallizations is characteristic of each metal but depends on number of factors and firstly up on the degree of deformation. The higher the degree of deformation, the lower the re crystallizations temperature will be.
In the process of the re crystallization of such metals as iron, copper, and aluminum, the new crystals sometimes grow in an oriented arrangement and the so called re crystallization texture is obtained.
The effect of foreign atoms in solid solution on the rate of re crystallization is almost apparent at very concentrations. The change in the re crystallization temperature caused by the presence of foreign atoms depends markedly up on the nature of the solute atoms.
58. How we describe strain aging based on dislocation theory?
The carbon/nitrogen atoms are important in yielding process because they interact with the dislocations and immobilize them. This locking of the dislocations is brought about because the strain energy due to the distortion of a solute atom can be relieved if it fits into a structural region where the local lattice parameter approximates to that of the natural lattice parameter of the solute. Such a condition will be brought about by the segregation of solute atoms to the dislocations, with large substitution atoms taking up lattice positions in the expanded region, and small ones in the compressed region; small interstitial atoms will tend to segregate to interstitial sites below the half-plane. Thus, where both dislocations and solute atoms are present in the lattice, interactions of the stress field can occur, resulting in a lowering of the strain energy of the system. This provides a driving force tending to attract solute atoms to dislocations and if the necessary time for diffusion is allowed, a solute atom ‘atmosphere’ will form around each dislocation.
59. Define what are the compositions of brass, how can this metal be heat-treated, Define what is the melting point of this metal?
Brass is an alloy of copper and zinc, with varying degrees of mixing. It is a substitution alloy, which means the copper and zinc elements substitute each other in microstructure matrix positions. This behavior translates into a metal which has a lower melting point in between that of its elements (Cu=1084, 83ºC, Zn=419, 58ºC) in pure state. Usually, the possibility of heat treatment will depend on Define what are you trying to achieve. For the substitution range of compositions, for example, you cannot obtain hardening from heat-treating.
60. Define what is or Define what characterize the thermodynamic state of metal (structure of metal)?
In the solid state, metals have a crystalline structure made of metal atoms, which are drawn together by low force vanderwaals interactions. The electrons form a cloud around the atom structure and migrate from one point to the other constantly.
The structured state of the atoms allows for low entropy in this state. Depending on the metal, several different structures may form, and one metal may have more than one structure at different temperatures, since its entropy depends on atom vibration as well, which is connected to the internal energy, reflected as temperature.
Crystalline structures have, usually, a straight correlation of stress in the elastic region. When traction stress is applied, the atoms are forced away from each other, up to a point where it, theoretically, should loose coherence by breaking all interactions at once and forming new surfaces. This energy level is so high that other mechanisms of energy dissipation happen first, usually connected to defects and dislocations in the crystalline structure. These mechanisms allow for the inducing of surface cracking, or plastic deformation.
61. When we do cardonitriding or casehardening operation for a plain carbon steel the case depth, hardness & microstructure are not alike why and Define what are the basic thing, which makes such a difference.
Usually that will depend on the time and temperature, as well as chemical composition of the furnace atmosphere you are using.
If these variables are not kept well controlled, they may cause very different results. Please note that time and temperature are correlated, the more temperature, the less time and lesser diffusion control.
62. Why we are doing post heating in alloy steel welding?
The preheating is application of heat to a base metal immediately before welding. Preheating helps reduce hardness in the metal.
In addition, the application of heat to the weld immediately after welding is post-heating .The Post heating helps reduce stress in the weld metal.
63 Define what does allotropic mean Define what does iron and steel have to do with it?
Iron is a metal with polymorphism structure. Each structure stable in the range of temperature, for example delta-iron with bcc structure in the range of 1538-1394C changes to gamma -Iron with fcc in the range of 912-1394C and gamma iron to Alfa-Iron etc. For hardening of the metal, this quality of iron is exploited.
64. How can you separate gold from mercury?
- Gold (Au) and mercury (Hg) are two separate metals. Therefore, from pure mercury you cannot extract Gold.
- Amalgamation is better suited to ores in which the gold occurs in the free and cores state. Fine particles of Gold are better treated by Cyanidation.
- Gold dissolves in aqua regia. Aqua Regia is a mixture of hydrochloric acid and nitric acid. It can dissolve gold, which single acids alone cannot do. Here we see that each of the acids separately has no effect on the gold but a mixture of the two dramatically reacts with the gold. To three samples of gold are added (1) concentrated hydrochloric acid (2) concentrated hydrochloric and concentrated nitric acids and (3) concentrated nitric acid. The gold reacts only with the concentrated acid mixture which is referred to as aqua regia (royal water)”.
65. Define what is the difference between diagrams of IT and CT in heat treatment of steels?
Isothermal Transformation (IT) and Continuous Transformation (CT) diagrams are diagrams used to investigate kinetic aspect of phase transformations and are of extensive use in steels heat treatment. In these diagrams generally called Time-Temperature-Transformation (TTT), the abscissa is time in logarithmic scale and ordinate is temperature. The C shaped curves indicate the onset and the end of diffusion (civilian) transformations e.g. pearlite or bainite formation or precipitation of carbides.
IT diagram shows Define what happens when steel is held at a constant temperature for a prolonged period. The development of the microstructure with time can be followed by holding small specimens in a lead or salt bath and quenching them one at a time after increasing holding times and measuring the amount of phases formed in the microstructure with the aid of a microscope. An alternative method involves using a single specimen and a dilatometer, which records the elongation of the specimen as a function of time. The basis for the dilatometer method is that the micro constituents undergo different volumetric changes and thus, the onset of transformations could be detected.
66. Define what is the metallurgical explanation of effects of chromium, nickel, molybdenum, and carbon in stainless steels?
Alloying elements in stainless steels can be divided into 2 main categories namely austenite and ferrite stabilizers. Austenite stabilizers must be present in austenitic as well as martensitic STSs (austenite at annealing temperature is the precursor phase for these two categories although for the latter group, it transforms to martensite before cooling down to room temperature). In order to stabilize austenite at annealing temperature, the ratio of austenite to ferrite stabilizers must be high. The strongest austenite stabilizers are N, C, Ni, Mn, and Cu whereas elements like Cr, Si, Nb, Ti, and Mo are the most important ferrite stabilizers. Ni-equivalent to Cr-equivalent ratio is an effective way to quantify the austenite formation tendency of STSs. There are different expressions for Creq and Nieq, one of which looks like this: Nieq=Ni+0.3Mn+22C+14.2N+Cu, and Creq=Cr+1.37Mo+1.5Si+2Nb+3Ti).
67. Define what are the properties and application of manganese steel?
Steel is an alloy of iron and carbon, consisting of iron phase and iron carbides. Crude steel produced from iron contains an undesirable amount of oxygen and some sulphur. Manganese plays a key role because of two important properties: its ability to combine with sulphur and its powerful deoxidation capacity. When there is insufficient manganese, the sulphur combines with iron to form a low melting point sulphide, which melts at hot rolling temperatures, causing a surface cracking phenomenon known as “hot shortness”. Desulphurization processes reduce the need for manganese in this respect. Some 30 of the manganese used today is still used for its properties as a sulphide former and deoxidant.
The other 70 of the manganese is used purely as an alloying element. These alloying uses depend on the desired properties of the steel being made. Steel, as has been noted, contains iron and carbon. At room temperature, iron crystallizes into a body-centered cubic structure named alpha iron (ferrite). At a high temperature (above 910 degrees C), the structure is transformed into a face-centered cubic form, which is called a gamma iron (austenite). When the steel is cooled down slowly, the carbon, soluble in austenite, precipitates as iron carbide called cementite, the austenite transforms to ferrite and they precipitate together in a characteristic lamellar structure known as pearlite.
68. Define what is carbide?
The epsilon carbide is transition carbide of between Fe2C and Fe3C composition, with hexagonal close packing microstructure, which forms over a range of 250-400 ºC temperature during lower-bainite transformation. This transformation happens during tempering heat treatment of quenched steels, or during slow cooling in that temperature range.
It is fine dispersed carbide in a ferrite needle-like matrix. Lower bainite has lower tensile strength (about 5-10%), but usually same hardness as martensite structures, but with a higher toughness.