Metallurgy Interview Preparation Guide

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Presence of silicon promotes graphitisation reaction.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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%.

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.

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 somewhat 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.

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.

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.

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.

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.