Alloy steel is steel that has been combined with other elements to create a new kind of material with different mechanical properties. Some of the most common elements that are combined with steel via alloying are aluminum, copper, boron, nickel, silicon, sulfur, titanium, etc. Bismuth and lead improve the machinability of steel, boron makes it even harder, copper helps with corrosion resistance. Nickel is one of the rare elements that has a double effect. It can improve the toughness of steel if its concentration in the alloy is between 2 and 5 percent. In the second case, the alloy has a bigger percentage of copper, between 12 and 20 and it can improve the corrosion resistance greatly. Of course, the steel itself is an alloy. It is created with iron and carbon. It is one of the strongest materials that we have as well as one of the cheapest to create. Alloy steel and high speed steel are the most important type of tool steel.
Alloy steel are divided into two alloy steel types: low alloy steel and high alloy steel. What the exact difference and definition of both are still disputed. Some consider 4% to be the cutting off point and others think its 8%. But in general, when we speak about alloy steel we think about low alloy steel.
Some of the most common types of alloy steel are 300M, 256A and etc.
When we talk about alloy steel applications we can divide alloy steel into four distinct groups:
1) Magnetic Alloys – they contain at least three elements with magnetic properties, most likely iron, nickel, and cobalt. The strongest alloys in this class have iron inside of it. This gives them magnetic properties.
2) Tool and die steel is a combination of abrasion resistance and air-hardening characteristics. The 4140 steel is counted into this category.
3) Stainless and Heat resistant – Stainless steel is steel that has been altered with elements that hinder corrosion, while heat resistant steel is steel that has been treated so it can resist very high temperatures.
4) Structural steel is probably the most known and widespread application of alloy steel. It is usually used in large buildings, to give them more structural stability. People have realized the potential of this type of alloy and many structures that are deemed very safe, even when hit by a powerful earthquake, come with some sort of structural steel.
One of the most versatile types of steel is the 4140 alloy steel. There are a wide variety of industries that use this alloy steel. It is a alloy steel that is comprised of chromium and molybdenum. The first part of the mix gives the steel much greater hardness penetration, while the second part, the molybdenum infuses the steel with a high level of strength and hardness. This makes it a great material for creating shafts, nuts, bolts, all kinds of machinery parts, gears, slides, steel collets, drill collars, etc.
Another popular and widely available type of alloy steel is the 4130 steel. Much like the previously mentioned 4140, it is also an alloy of chromium and molybdenum. But with different percentages. The carbon content in this ally is said to be around 0.30%. Since it has a relatively small amount of carbon, this makes it a very good choice for fusion weldability. Some of the most common applications for this type of steel is for structural purposes. That might include aircraft engine mounts and tubing applications.
It can be mechanized by all known conventional methods. But, it would be ideal to treat it when it is in a normalized and tempered condition.
If you are looking for a alloy steel that is easy to wield, this is probably the best option because it is known as being able to be wielded by any commercial method. The same could be said for cold working this alloy.
On the other hand, if you are looking for steel that could be aged, this alloy steel would be a very poor choice indeed. To harden it you will need to heat the oven up to 1600 F. Tempering a 4130 alloy is done between 750 F and 1050 F. Combine the temperature with an oil quench to get this steel even harder. Sometimes you can lose ductability after you harder your 4130 alloys. If you want to increase it up again you will need to temper it.
Now you have a better idea of what kind of steel to choose for your construction purpose.