High Strength Carbon and Low Alloy Steels...

High Strength Carbon and Low Alloy Steels High strength carbon (C) and low alloy steels have yield strength (YS) greater than 275 N/sq mm and can be classified generally in four types namely (i) as-rolled C – Mn (manganese) steels, (ii) as rolled high strength low alloy (HSLA) steels also known as micro-alloyed steels, (iii) heat treated (normalized or quenched and tempered) C steels, and (iv) heat treated low alloy steels (Fig 1). These four types of steels have higher YSs than mild C steel in the as hot rolled condition. The heat treated low alloy steels and the as rolled HSLA steels also provide lower ductile-to-brittle transition temperatures than do C steels. Fig 1 Classification of high strength carbon and low alloy steels The four types of high strength steels have some basic differences in mechanical properties and available product forms. In terms of mechanical properties, the heat treated low alloy steels offer the best combination of strength and toughness. However, these steels are available primarily as bar and plate products and only occasionally as sheet and structural shapes. In particular, structural shapes (I and H beams, channels, or special sections) can be difficult to produce in the quenched and tempered condition since shape warpage can occur during quenching. Heat treating steels is also a more involved process than the production of as rolled steels, which is one reason the as rolled HSLA steels are an attractive alternative. The as rolled HSLA steels are also commonly available in all the standard wrought product forms (sheet, strip, bar, plate, and structural shapes). HSLA steels are an attractive alternative in structural. High strength steels are used to reduce section sizes for a given design load, which allows weight savings. Reductions in section size are also...