High Strength Low Alloy Steels
High strength low alloy (HSLA) steels are a group of low carbon steels that utilise small amounts of alloying elements to attain yield strengths in excess of 275 MPa in the as-rolled or normalised conditions. These steels have better mechanical properties than as rolled carbon steels, largely by virtue of grain refining and precipitation hardening. Because the higher strength of HSLA steels can be obtained at lower carbon levels, the weldability of many HSLA steels is at least comparable to that of mild steel. Due to their superior mechanical properties, they allow more efficient designs with improved performance, reductions in manufacturing costs and component weight reduction to be produced.. Applications include oil and gas pipelines, automotive beams, offshore structures and shipbuilding.
Maraging steels differ from conventional steels in that they are hardened by a metallurgical reaction that does not involve carbon. These steels are strengthened by intermetallic compounds such as Ni3Ti and Ni3Mo that precipitate at about 500°C. These steels typically have very high nickel, cobalt and molybdenum contents while carbon is essentially an impurity and its concentration is kept as low as possible in order to minimise the formation of titanium carbide which can adversely affect mechanical properties. Ultrahigh strengths may be obtained with these steels, and weldability is good. Toughness is superior to all low alloy carbon steels of similar strength, particularly the low temperature toughness. Although they are expensive, they are easy to machine and heat treat, so that some economies result in component production.