[Alloy Steel] Designation, Properties, Processing and Applications

Hello friends. Today’s article is it is kind of a general lecture on alloy steel designation and some processing methods which we use for making or for processing bulk materials and that we will discuss today in the Civil Experience blog article

Here, you will learn about:

• Types of alloy steel
• Properties of alloy steel
• Production and processing of alloy steel
• Applications and application areas of alloy steel

Alloy designation first, an alloy which is most important and widely used is steel and in steel, there are different alloy steel grade is available

These are given by designation provided by these 2 agencies AISI is the American Iron and Steel Institute and SAE is the Society of Automotive Engineers. Because these 2 agencies are responsible for making the grades or making the designation for the grades for different materials

Types of Alloy Steel

There are various subcategories of alloy steel which include:

1. Low-alloy steel
2. High-strength low alloy (HSLA) steel
3. High-alloy steel
4. Stainless steel
5. Microalloyed steel
6. Advanced high-strength steel (AHSS)
7. Maraging steel
8. Tool steel

Generally, low alloy steels contain less than 8 wt.% non-iron elements, whereas high-alloy steels contain more than 8 wt.% non-iron elements. Both have typically superior mechanical alloy steel properties in comparison to carbon steels.

Society of Automotive Engineers (SAE) Designation

There are different numbers are given here and then, xxx is written. As shown in below table

SAE Designation	Major Alloying
1xxx	Carbon
2xxx	Nickel
3xxx	Nickel-chromium
4xxx	Molybdenum
5xxx	Chromium
6xxx	Chromium-vanadium
7xxx	Tungsten
8xxx	Nickel-chromium-molybdenum
9xxx	Silicon-manganese

Where

The first digit here actually specifies the major alloying element

Let take an example for better understanding, if it is only plain carbon steel, only carbon is added as an alloying element. Then, it will be having the first digit as 1 and then, there are 3 more digits remaining there. So, the first digit is to specify if it is one, which means, it is going to the Carbon; main alloying.

If it is 2, Nickel will be there as a major alloying element Of course, carbon will also be there, but now the main alloying element is Nickel and which actually dictates the alloy steel properties. 

Then, 3 series is Nickel-chromium. 4 series is Molybdenum and 5 series is plain only Chromium and 3 series it was both Nickel and Chromium were there 6000 series Chromium-vanadium. 7000 is Tungsten; 8000 is Nickel-chromium-molybdenum and 9000 is Silicon-manganese

This is one of the important alloys for magnetic application as we discussed that silicon, steel is one of the most important alloys for any transformer application or soft magnetic material application

In plain carbon steel, we are not going into details of all these things because it is a very long list and each one has some variation in the composition and then their usage

Type of Plain Carbon Steel Material

If you take plain carbon steel; now, you can see in that 4 number series another number is added here. Now it is 0. So, in this case, it is only plain carbon steel in some cases you will have some other number also. So, these are depending upon what kind of another chemical treatment is given

In some cases it is kind of the defrustize or disulphuric it is added or removed and so on So, depending upon that this number will keep on changing

10xx – Plain carbon steel

The plain carbon steel also depending upon what type of treatment was given to the steel, the number will come in the second digit place. Right now, it is simply plain carbon steel that is a 0 here and now, still, the 2 number are left here. So, if it is plain carbon steel, you are only dealing with Carbon. So, these last 2 digits will be responsible for telling us the composition of the alloy.

The first 2 digits indicate the grade of carbon steel. What alloy steel grade? And the last 2 numbers indicate the approximate middle of the carbon range. 

For example, in the degrade designation if it is written as 1035. Then, it represents the carbon range of 0.32% to 0.38%. So, it is a range and you should take an average of that

It will come somewhere around 0.35% Carbon So, that is why in the alloy steel designation it is written as 1035 So, this is how you will get usually the if you want to go and buy plain carbon steel in the market, this the type of designation you have to specify.

It is plain carbon steel. So, now, depending upon carbon percentage, it will be low carbon steel or high carbon steel and so on So, you will know that what type of material you want for a certain application.

Type of Aluminium Material

Now, coming to aluminium another very important material used in a large number of Engineering alloy steel applications. So, these are the widely used materials. These two class of materials in kind of daily product. So, Aluminum is another very important alloy So, they also have a large number of series depending upon what is the alloying element

If you remember the temper designation, we have already discussed when we were discussing hit treatment of Aluminum copper alloys that we can give different suffix to specify that what is the heat treatment was given to the materials, that is already discussed now.

The remaining numbers which are there will tell you about the alloy steel composition So, the compotation will be there and the temper designation will be there. So, combined them, you will able to know which material we are talking about

What is the alloy steel composition that? What is the treatment is given to that particular material or in your case whatever application you what that material?

Your design purpose, you came to know that what kind of strength you want, what kind of if possible some ductility should be there? So, from that, you can go back to that particular material and see which material is able to satisfy your conditions and what should be the heat treatment given to that material to get those alloy properties

Then as an engineer, it is always important for us to understand that what are the cost benefit analysis has to be there. So, what is the cost of that particular material and how much it is going to benefit for whatever application you want that material So, this cost-benefit analysis will always be there for any engineer? 

Because there is a large number of material some alloy steel elements are expensive. So, you will have to see whether you need that kind of composition or not or you can leave it with material that does not have this expensive element as an alloying element.

1000 Series Aluminium

It can still serve your purpose So, in aluminium, you have 1000 series aluminium. These are basically pure aluminium. So, nothing is added, commercially pure.

Some impurities will always be there. So, it will only 99% aluminium content will be there. Now depending upon the processing, it can be 99.9 or 99.99 for different from different manufacturers you will get different purity. 

Of course, the cost will be also will be dependent that on what kind of purity you want in a particular material And since there is no alloying element

Here. If you want to kind of change the alloy steel properties of this material, it can be only done with work hardening.

Basically, you can do a court ruling or some working operation to introduce a Large number of dislocation in the material and thereby, you can have work hardening in the material. So, because there are no alloying elements, I can only do work hardening in these or if you are possible, you can have grain size refinement So, grain size strengthening can also be there.

2000 Series Aluminium

If the 2000 series are alloyed with copper, one of the important alloys initially people studied a lot to understand the ageing phenomena in aluminium and that is why you can see it can be precipitation harden to very high strengths

They were used as aerospace alloys for a very long time because they had high strength due to precipitation and of course, aluminium is a lightweight material. So, preferred for aerospace applications, but due to stress corrosion cracking problem, these susceptible it is where you can have stress concentration and under corrosive environment

You have stress corrosion cracking and that is why they were later replaced now by 7000 series alloys. We will see what these 7000 series alloys are there. But, once copper alloys were very popular aluminium copper alloys.

3000 Series Aluminium

Then, we have 3000 series, in this, it is, in this case, it is allowed with manganese, again manganese will go into solid solutions. So, these alloys can be work-hardened

4000 Series Aluminium

4000 Series Aluminium in which we add silicon into aluminium And these are some of the very important alloys, alloys because they give you very good casting ability; you can do casting very easily and these are now used for making cylinder head. You can understand they have a very complex shape with all these things around them for better cooling and they have to be cast.

You can understand that material has to flow in those complex shape when you are doing the alloy steel casting. So, since it has good flowability and to get into those mould shapes. That is why this kind of alloy aluminium-silicon alloys are used for making cylinder blocks nowadays. 

5000 Series Aluminium

The next craze for 5000 series allowed with magnesium. 

It offers superb corrosion resistance. So, wherever you need a good corrosion resistance for example, in a marine application, where the, for example, the ship is in saline water. So, corrosion will be very fast in this kind of conditions, there this aluminium magnesium alloy is very good. They have very good corrosion resistance and out of this 5083 alloy is one of the more popular alloys which is used in the marine application and because it has the highest strength in non-heat-treatable alloys. 

These are non-heat-treatable; they do not show precipitate precipitation within the grain. So, either they are in the solid solution or if any precipitate is also forming, they will form at the grain boundary.

These are cannot be hardened using precipitation. You cannot do the ageing of these alloys. So, these are called non heat-treatable alloys, but the 5083 alloy has the highest strength in a non-heat-treatable class of materials or in aluminium and then they have a very good corrosion resistance that is why they are used in marine applications.

6000 Series Aluminium

Then the 6000 series is there alloyed with both magnesium and silicon. So, 6000 series alloy possesses good machinability and weldability; can be precipitation harden what not to the high strength of 2000 or 7000 series. So, it cannot be as good as aluminium copper alloys or 7000 series alloys. 606 is one of the most commonly used general-purpose aluminium alloys.

If you see any you know general-purpose aluminium, wherever it is used. Most probably, it will be 6061 alloy which contains both magnesium and silicon. 

7000 Series Aluminium

Then comes the 7000 series is a very important alloy because it is it comes under the high strength category. These are called high strength aluminium alloys and these are now nowadays used in a large number of applications.

Especially aerospace application, where you need high strength and because you have aluminium as the base material the alloy steel density will also below the weight of that particular component below. So, that is what is needed and coupled with that you have, you get a very high strength in these materials.

For example, in the case of some mobiles also when they were advertising that this is made of aluminium and the cover is made of aluminium. These are all high strength aluminium alloys which usually comes under 7000 series.

It can be precipitation hardened to the very high strength of any aluminium alloy. For example, for 7608 alloys, the hardness which you can achieve is 700 Mega Pascal ultimate tensile strength which is fairly good strength, it is close to any steel normally. So, this kind of strength you can achieve in aluminium alloys by doing very careful alloying zinc and magnesium.

8000 Series Aluminium

Then, comes 8000 series alloyed with other elements which are not covered by other series and in this class one of the most important alloys are aluminium-lithium alloys and the importance of these alloys is that lithium is a very low-density material. The weight of the lithium per unit volume will be very low in any structural material.

If you are adding lithium in aluminium the overall weight reduction is very good and this one of the very important alloys 8090 aluminium alloy, aluminium-lithium alloy. 

Again, used in aerospace alloy steel applications because you want to reduce the weight of the body whatever whether it is an aeroplane or any other aerospace body. So, aluminium lithium alloys are very important and in this 8090 is one of the most important alloys.

8000 series, you will see in a large number of different alloying with different alloy steel elements because it is given for kind of a general-purpose alloy and where alloying elements are can be a quite different type of alloying elements can be there.

Material Processing

Then, will come to material processing just to give you an overall idea that how will you get a different type of materials. So, we are not going in the processing back from over to the main material which you get. So, we are not going into that processing right now because a lot of processing is done in secondary processing also.

For example, if you want to recycle steel or you really want to recycle aluminium. So, that is already been extracted refined and you have the material in the use alloy steel composition.

These are again re-melted and you do casting. So, a lot of these industries are also there and some industries are there which starts from the over itself and then, do the refining and later on do the other processing. So, right now we are not going into that part, we will do starting from the casting so that my material is already refined or if you have recycling already taken from a recycler and you know that we have segregated it into aluminium and steel scrap differently

The first process by which we do is alloy steel casting. So, you basically melt the material and furnaces and then, you pour it into the same ingots. So, we are not kind of concentrating here on a different type of castings. Bulk material processing that you do casting in ingots

Then, you will go to Secondary some forming processes. So, these are either primary you can divide into Primary forming processes or Secondary forming processes. 

The Primary forming process is usually done at high temperature. So, that is why they are called Hot forging, Hot rolling or Hot extrusion. 

The purpose of this particular state after casting is and if you remember when we were discussing solidification and what type of microstructure you get during solidification. 

We said that they contain dendrites and the sub dendrite cast structure basically they have. Then, they also have a lot of heterogeneity in composition. So, heterogeneity in composition can be eliminated by doing a homogenization process, but to break this entity cast structure, I have to do processing where I can impose very high deformation.

That is why they are done at high temperature where you can introduce more deformation in the material at one go. So, in this case, you want to have very high deformation. So, we either it can be done by forging or it can be done by rolling process or it can be done by extrusion process. Then, we go to the secondary forming processes, usually, you do a lot of rolling at this stage. So, cold rolling is going to be there 

If you want strips of any sheet then strip rolling will be there, if you want different shapes of material; for example, you want a rail you want I beam. Then rolling to give different shapes are there. So, these are the final stages of processing. So, you have the Casting and Primary forming process; then, Secondary forming process. 

This is a very broad alloy steel classification here. You can have much more refined classification also in between different processes are done.

Ingot Casting

For example, after any forming process maybe there can be aniline in between to kind of do a stress-relieving or to do in case of precipitation hardening to dissolve the precipitate and make a solid solution and so on and then, you have you may have heat treatment later on also.

Casting if you see just you are concentrating here on the ingot casting because casting itself is a big subject and you can see very big Ingots are there.

It is already lying on a rail and you can understand that the what will be the dimension of this cast. So, basically from a big laden, where tons of molten metal is there, it is poured into this kind of ingots where you get the shape of ingots may be a rectangular shape or round shape depending upon what processing you want to do later on and then, you do later forming operations if this is kind of a batch process, you can see single ingot will be there and then, it will be taken to for other processing.

Continuous Casting

Now a day's another very useful casting process is called Continuous casting. So, you can see that in this you have a continuous metal is coming in form of different shapes of ingots and it is a continuous process. 

You put molten metal in some die and then, the molten metal will flow down by vertical force or by due to gravity and then, it will be when it starts solidifying it will be kind of taken out and taken on on some rails to which will be cut in different shapes later on.

Then, you do the Secondary processing by doing rolling or extrusion or whatever end product you want from that this is a continuous process. This is a batch process whereas this is a continuous process.

Hot Rolling Process

Then, after casting we do rolling one of the processes. It can be other processes also. So, hot rolling is done for heavy reduction basically to break your cast structure. Once you do that in hot rolling the problem is because the material will be hot, there will be a lot of oxidation takes place. So, you have scale on the surface.

Also when it cools down, it will have some distortion in the material the surface finish will not be very nice. So, we cannot do a hot process as the last process after which the materials go to the customer.

Cold Rolling Process

But we can do it as an intermediate process where we want a very large reduction to break the cast structure. So, these are done in the initial processes and later on, when the material is supposed to go out to the customer we do cold rolling. So, for producing sheet strips with a high-quality surface finish, in this case, you get a very good surface finish and closer dimensional tolerances which is not possible with a hot rolling process. 

But, initial processing is required at the higher temperature. We can also get I beam this is I beam and railroad rails are fabricated using grooved rolls. So, either you can do a groove rolling as you can see in this case, we want to have I beam.

You can see multiple rolls are there to make this particular shape; whereas in simple strip rolling, you need only 2 rolls and the material will be taken through those rolls. 

It is like your sugar cane you must have seen, if you want to take out sugarcane juice, you put sugarcane between 2 rolls and that is squeeze with it and you take out the squeezed sugarcane from the other side. So, basically the same process, 2 rolls are there and the material will go through these rolls. So, the initial material will have a higher thickness, after going through the role depending upon the separation between the roll the thickness will be reduced and because you are putting it so, much strain maybe the strain will be enough to do to have some recrystallisation in the material. 

You will get very fine grain material after the reduction and these can be again processed using some grooved rolls to get a certain shape depending upon your requirement.

Forging Process

Forging is another very important process. So, it can be open die forging or closed die forging if you want a certain shape. 

Then, you can have closed die forging. So, the die itself will have that shape and then, you are forging it and the material which will take the shape of the die or you can I have an open die forging has being shown here right now and you can see the size of the rolling size of the forging machine and the size of the material which is being forged. So, if you have Automatic crankshafts, piston connecting rods, railroad wheels are made by forging.

By forging because you are doing we are putting a lot of compressive load on the material and already we have seen that the compressive stresses in the material are very good for their later application. 

The first thing is you kind of remove the defects, by forging if there are defects you are kind of closing those defects and you are imposing some residual stresses compressive residual stresses in the material and also the microstructure gets refined, you also introduce a lot of dislocation alloy steel density.

Overall you have very dense material with minimal defects and very good microstructural properties and so, this forging is a very important process for any to make any product where you need very high stresses will be there. 

Application, For example, crankshaft and piston connecting rod you can see continuously it are experiencing fluctuating loads. 

Railroad wheels you can understand that. So, much load is there and they are rotating. So, again continues fatigue loading is there. In all these conditions, you need forged material So, cast material will just break under the load. 

By forging we are breaking the cast structure, refining the microstructure, introducing a lot of strain hardening in the material to get a very high strength material.

Extrusion Process

Extrusion is another very important process to make rods or tube. So, if you put a mineral here called a mandrel, you can get a tube out of that.

Extrusion

There will be a hollow section in the centre and the material around it or if you do not put the mandrel you will get it in rod shape. So, in this case, you have a die here, it is a cross-section is shown here and we are applying force from the other side; squeeze the material out from here.

A lot of in household we have this kind of technique to make certain what we call namkeen to make using this kind of tools. It is similar to that. 

Extrusion is basically you are putting force from the other side to squeeze the material out from the open and here in the die and the cross-section is reduced during the process and also you are imposing a lot of strain in the material.

It is getting work to harden if temperature and strain are sufficient you will have requested microstructure and so on. So, this is an axis-symmetric process. So, to make a rod to make a tube, it is a very nice process to make a tube or rod through the extrusion process. 

Powder Metallurgy Processes

Another very important processing is what we call is Powder metallurgy processes and usually, in the case of ceramics, you cannot do any other processing like casting melting casting and then, other forming operations. 

In the case of Powder metallurgy alloys, these basic ceramics can be processed only using Powder metallurgy processes or if you have material that is hard to deform or will have high temperature with their melting point is very high.

Then, it will be very difficult to melt it and take it into a ladle; the ladle will be of a low-temperature material. How you are going to store a liquid metal into these ladles. It is very difficult. So, for higher temperature materials, ceramic for hard to form materials we have very good technical Powder metallurgy. 

In this case, you process the material in solid-state. So, you have the powder you pour the powder or whatever shape you want final shape you want for the product; you make a die of that putting powder there and you can consolidate it.

Basically, you have metal powder for ceramic powders whichever powder you want you to do mixing, you can add additives also; lubricants and binder.

Then, you apply compaction. So, you make a compact of that and then we do Sintering. So, Sintering means you have to heat this compacted powder to some high temperature below the melting point to increase the diffusion process. 

When you do the compact the powders are only in kind of a mechanical contact. There they are not metallurgically bonded to each other. So, to have this metallurgical bond, we need to take it to a high temperature. So, that diffusion is possible and then powder each individual powder particle gets attached to the next one and overall you get a product.

Then, depending upon the application you can have secondary processes either you can have machining or some other finishing operation and then, you have finished the product. So, a very important technique for some type of material where it is very difficult to melt them or to form them.

Now, I just took here 2 alloy steel examples that how now the material is being celebrated. Celebrated in the since I think in the importance of a certain subject can be gauged from if that particular product is advertised like that this is made by made of certain materials

Then, the material you know the material has come to a certain stage. For example, earlier if you want a good sound system the advertisement will say that it is its Dolby sound system or it is a Stereo sound system or it has a high fidelity sound system.

You know these are important things when it is advertised. So, for me, the importance of material comes when the materials or that specification comes in the advertisement of the product. So, I am just taking here 2 examples; where the materials are celebrated because they are being advertised that because of this material you are getting some special properties or some special product we are getting. For example, Car bodies.

Advanced High Strength Steels

Application in Car bodies

Now advanced high strength steels are being used in Car bodies. Recently you must have heard that in a lot of these crash test none of the Indian cars could qualify; almost all failed in those crash test to see that whether any impact on the car whether the passenger will survive or not. 

All these new cars which are coming, they are coming with the material which is called Advanced high strength steels. So, they have very high strength. So, by that, you can also reduce the weight of the body car body and at the same time, you have very high strength. So, both it is good for safety.

Because you have the highest and material to take the impact load and also it reduces the weight of the car. So, you have improved safety at the same time you have reduced weight. So, that is why these highly advanced high strength steels are very important and the strength is there because of the alloying element, some alloying elements are added to get very high strength in this material.

Basically, the structure is made by advanced high strength steels. The car body that it is the place which is covering the car, those are not very high strength as I told you earlier also those are interstitial free steels IF steels. 

The only structure, the main structure of the body of the car that is a high advance high steels and the remaining which is like tenels which is covering the car, they are usually IF steels.

Application in Smartphones

Another product Smartphones. one of the most important specifications given in any Smartphone is that what type of glass is used. 

These are gorilla glasses, all their trademark of a certain company. So, they are advertised like they have very high resistance to scratches. So, you will not have scratches on the screen and then, they are also now coated with nanosilver. 

They do not have any smudging will be there or a little bit antibacterial properties also or for a certain product or certain company also advertise that the body which this auto and this phone have, it contains high strength aluminium alloy.

Again as I told you that some of the highest strength aluminium alloys are used to make the bodies of these Smartphones. So, these are actually advertised during the product launch that these kind of materials are there and that for me is a very good sign that and also now, you can also understand that the metallic materials are again coming into the 4.

Earlier we people started thinking that plastic will take over the whole thing, but now we see that metallic materials are again coming becoming popular and in this kind of very fancy product also you see that usage of metallic material is increasing. 

One of the most important reasons for users increased usage of metallic material is they are recyclable. Whereas polymers, plastic that they are not we are not able to recycle them and for the environment, it is not good.

Whereas, any metallic materials can be recycled. So, once you discard them, the scrap can be again taken to some secondary processing units. 

There it will be again melted and you can again start getting a new product out of that. So, with that this, our courses are ended this is the last lecture just wanted to bring out the flavour of materials in different application and how they are processed, what are the designation of different alloys.

Short Idea About Function of Element

Element	Symbol	Function
Aluminium	Al	Alloying element in nitriding steels
Bismuth	Bi	Improves machinability
Boron	B	Improves hardenability
Chromium	Cr	Improves hardenability
		Corrosion resistance
Copper	Cu	Corrosion resistance
Lead	Pb	Improves machinability
Manganese	Mn	Prevents brittleness in combination with sulfur
		Increases hardenability
Molybdenum	Mo	Inhibits grain growth
Nickel	Ni	Increases toughness Improves corrosion resistance
Silicon	Si	Increases strength and hardenability
		Increases yield strength (spring steel)
		Increases magnetic properties
Sulfur	S	Improves machinability (free-machining steel properties)
Titanium	Ti	Reduces martensitic hardness in Cr steels
Tungsten	W	Increases hardness at high temperatures
Vanadium	V	Increases strength while maintaining ductility, promotes fine grain structure

I hope the course will be of benefit to you and it will satisfy your curiosity and also it will help you to decide when you are making any product that which materials to use.

FAQ 1: What are the Types of Alloy Steel?

There are various subcategories of alloy steel which include: 1. Low-alloy steel 2. High-strength low alloy (HSLA) steel 3. High-alloy steel 4. Stainless steel 5. Microalloyed steel 6. Advanced high-strength steel (AHSS) 7. Maraging steel 8. Tool steel

FAQ 2: Best application of Advanced High Strength Steels?

1. Application in Car bodies 2. Application in Smartphones