Evolution of Microalloyed Linepipe Steels with Particular Emphasis on the “Near Stoichiometry Low Carbon, 0.10 Percent Niobium “HTP Concept
Microalloyed linepipe steels were first introduced in 1959 at strength levels around 52-60 ksi1 2. The steels were generally strengthened by niobium or vanadium used singly. As strengths levels increased to X-70 in the early 1970’s niobium and vanadium were used in combination and controlled rolling was introduced on a broad basis. Higher strengths decrease tolerance for impurities and non-metallic inclusions which required improved steelmaking practices. Sulfur, carbon, and nitrogen were reduced and continuous casting was increasingly applied which required improved ladle refining and deoxidation practices.Niobium-molybdenum steels were introduced by IPSCO in 19723 and by Italsider in 19744. Steels with higher niobium contents were also introduced in the early 1970’s but available steelmaking technologies limited the use of optimum niobium to carbon ratios,i.e.those approaching stoichiometry. Nevertheless the steels benefited from the effect of niobium in retarding austenite recrystallization at relatively high rolling temperatures and they developed attractive combinations of strength and toughness in old manufacturing facilities using simple (relaxed) rolling schedules. Fluctuations in the price of molybdenum and vanadium in the past decade and expanded application of API Grade X-80 linepipe, have led to more widespread use of niobium contents up to 0.11 percent, in combination with 0.02-0.03 percent carbon (near stoichiometry) thus maximizing the effects of solute niobium during rolling, in lowering transformation temperature, and thereby reducing reliance on other alloying, often expensive, elements. The history of these developments will be presented and applications of the concept will be summarized.
GRAY J.Malcolm
Microalloyed Steel Institute Inc.,5100 Westheimer Ste 540,Houston, TX 77056 USA
国际会议
The 6th International Conference on High Strength Low Alloy Steels(第六届高强度低合金钢国际会议HSLA Steels2011)
北京
英文
90-93
2011-05-31（万方平台首次上网日期，不代表论文的发表时间）