Engineering steel grade can be used in a wide variety of applications because there are so many different combinations of alloying elements that achieve different properties. With such a wide variety of alloying elements and combinations, choosing an engineering steel grade can be difficult. This article will explain some considerations when choosing an engineering steel for your next project.
Some elements, such as chromium and boron, increase the steel’s hardenability. Since most engineering steels are able to be hardened, forming is typically done in the annealed state of the material. Engineering steels that are annealed and have lower amounts of alloys and carbon are typically more formable than those with higher amounts of carbon and other alloying elements. AISI 4130 is a good example of an engineering steel that when annealed has relatively good formability when compared with other engineering steels.
Similar to formability, some of the elements added to engineering steels can be detrimental to welding. Be wary of additions of sulfur and boron if you require an engineering steel to be welded as both can induce cracking. Also, if the carbon content in the engineering steel is high, care must be taken to slow the rate of cooling to avoid cracking. The welding of most engineering steels should be performed in the annealed state. AISI 4130 is an example of a very weldable engineering steel. AISI 6150 on the other hand, while weldable, must follow strict preheat and post heat procedures to avoid weld cracking.
The addition of sulfur and phosphorous can help increase the machinability of an engineering steel, while the addition of boron and chromium can decrease machinability. Machining of engineering steels is typically performed in the annealed state because the reduced hardness helps the machining process, but it can also be done after heat treatment. In the annealed condition, AISI 4130 and AISI 8620 are examples of engineering steels that can be machined readily. AISI 4340 is more difficult to machine than AISI 4130 and AISI 8620, even in the annealed state.
If corrosion needs to be inhibited (and coating is not an option) then it is important to find an engineering steel grade that has increased corrosion resistance. Engineering steel grades with a higher amount of elements such as chromium, copper, nickel, and molybdenum will generally have a greater resistance to corrosion.
One of the main benefits of engineering steel is that it can be easily heat treated. Heating and quenching engineering engineering steels such as AISI 4340 and AISI 6150 can result in very high tensile strengths and hardnesses throughout the thickness of the material when compared with low carbon steel. AISI 8620 is a steel that is commonly carburized which is a form of case hardening. Once carburized, it is very hard and abrasion resistant on the outside layer of the material, but inside the outer “case” it is still ductile and tough.
Depending on the alloying elements used, very high tensile strengths can be achieved. The strength achieved with engineering steel depends on what elements the steel is made up of as well as the heat treated state the engineering steel is in. Engineering steels that are annealed or normalized will have lower strengths than the same ones that are heated and rapidly quenched. It is best to look at a material data sheet to determine what strengths a particular engineering steel can achieve.
Here are some common types of engineering steels and how they are used: