Steel 101

Steel 101
Butler CC – 04/16/2010
By: Jason Gulick

In the autobody industry there are many types of steel. They range from the most formable grades with a low yield strength of 140 N/mm to ultra high strength steel with a strength of 2500 N/mm.

Some grades have special processing for a specific use, such as super-clean steels used in fuel injection systems, forging grades such as a camshaft and connecting rods. A key requirement for sheet steel intended for use in automotive pressings is that it is formable, so that it can be stretched without undue thinning in a press to form complex shapes. Softer grades of steel, having low yield strength, tend to be highly formable but lack the strength needed for the main loadbearing members of a vehicle. Higher-strength steel parts may be more difficult to form, since they do not stretch so easy, but it is better for the economy for weight reduction.

Ultra High Strength steel is used specially for safety critical areas on the vehicle such as the passenger compartment to ensure the safety of the passenger in a crash. It varies between 900 and 1200 N/mm. High Strength Steels, with a good balance of strength, formability, energy absorbtion, and durability, is used for a lot of the support in the body. HSS acts as support beams in the body and is normally between 600 to 800 N/mm. Steels that vary between 100 and 300 is normally the skin of your vehicle. The body is made with these steels.

Boron is the strongest steel currently being manufactured in the autobody industry, followed by Martensitic. Boron is not easily formed or forged. It is mainly in the passengers area of the vehicle. It not that common to find this steel yet due to its recent discovery, but it is now on the manufacturing line and in the new 2010 Chevrolet Camaro. Martensitic varies in strength from 650 N/mm to 1200 N/mm, and is also very difficult to forge or mold.

Steel manufacturers can use a range of techniques to make higher-performance steels. These techniques include grain refinement, work hardening, precipitation hardening and heat treatment. Grain refinement is a method of strengthening materials by changing their average crystallite (grain) size. Work hardening, also known as strain hardening, is the strengthening of a metal by plastic deformation. This strengthening occurs because of dislocation movements within the crystal structure of the material.

Any material with a reasonably high melting point can be straightened in this fashion. Precipitation hardening, also known as age hardening, is a heat treatment technique used to increase the yield strength of malleable materials. Heat treatment is to treat metal by alternate heating and cooling in order to produce desired quality.