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...

Niobium in Steels

Niobium in Steels  Niobium (Nb) (atomic number 41 and atomic weight 92.91) has density of 8.57 gm/cc. The element is also known as Columbium (Cb). Melting point of Nb is 2467 deg C and boiling point is 4740 deg C. Cb was discovered in 1801 by Charles Hatchett, who named the element to signify the American origin. This name was used in USA while Europe used the name niobium for the same element. To end this confusion, the name niobium was chosen for element 41 at the 15th Conference of the Union of Chemistry in Amsterdam in 1949. A year later this name was officially adopted by the International Union of Pure and Applied Chemistry (IUPAC) after 100 years of controversy, despite the chronological precedence of the name Columbium. Columbium name is still used in many places in USA. The phase diagram of the Fe-Nb binary system is at Fig 1. Fig 1 Fe-Nb phase diagram  The use of Nb dates back to 1925 when it was used to replace tungsten (W) in tool steel production. By the 1930s, Nb was being used to prevent corrosion in stainless steels. The ability of Nb to maintain fine grain sizes in steels at higher temperatures has been known since 1940s and steels that take advantage of this effect have been commercially produced for many years. In recent years, however, Nb is being known more as one of the most important element for the micro alloying. Nb plays an important role in HSLA (high strength low alloy) steels. Nb also has important applications in tool steels, wear and abrasion resistant steels, steels for high temperature service, stainless steels and super alloys. Many of these uses depend on the strong affinity of Nb for carbon (C) and/or nitrogen (N). Addition agents...