HIGH STRENGTH LOW ALLOY

A special class of sheet and strip products is high strength steel. High strength steels come in a wide, and often confusing, array of types. The strength of these steels is “high” relative to the strength of low carbon steel. The products are purchased to guaranteed mechanical property requirements, with generalized chemical requirements. Most grades are available as hot rolled, cold rolled, and coated products.

Structural Steel (SS) is a class of steels strengthened primarily by carbon and manganese. These steels come up to 50 ksi (340 MPa) minimum yield strength.

High Strength Low Alloy Steel (HSLA, HSLA-F) is strengthened via additions of microalloys: niobium, vanadium and titanium. Since they generally have lower carbon than the SS steels, their ductility is superior. Strength levels range up to 80 ksi (550 MPa) minimum yield strength.

Ultra High Strength Steels are often referred to as Complex Phase high strength. This class of steels is strengthened by introducing bainite and martensite into the structure to achieve minimum yields as high as 120 ksi (830 MPa). Ductility is limited due to the brittle nature of the martensite and bainite.

Advanced High Strength Steels are characterized by a wide spread between yield and tensile strength and are most suited to applications where tensile strength is the key consideration. Types include Dual Phase (DP) and Transformation Induced Plasticity (TRIP). In both, a second phase of martensite and/or bainite result in high tensile strength. Unlike conventional high strength steels, the number designation refers to the minimum tensile strength; thus, DP590 is a dual phase steel with 590 MPa (85.7 ksi) minimum tensile strength.

Recovery Annealed High Strength Steels are available up to about 140 ksi (970 MPa) yield strength. After cold rolling, a low temperature stress relief anneal is applied to enable limited cold forming.