中国微合金化技术与含铌钢发展30周-of Evolution(15)

中国微合金化技术与含铌钢发展30周-of Evolution

High Strength Microalloyed Linepipe: Half a Century of Evolution

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Table 10: Chemical Composition of 30” O.D. X-65 31.8 mm Linepipe (Blue Stream Project)

[55].

Steelmaking and Manufacturing Developments

At their inception microalloyed (HSLA) steels were based on Open Hearth or Basic Electric Arc steelmaking. Thus there were limitations on reducing carbon contents (to improve solubility of niobium and titanium) and impurity levels were very high. Typical sulfur and phosphorus levels were around 0.025 percent and sometimes twice this level. This level of sulfur had a very detrimental on notch toughness especially when combined with the very high oxide contents of semi-killed steel.

Sequential technical demands for improved linepipe referenced earlier in Table 3 eventually led to dramatic improvements in steel cleanness, reduction in impurities such as phosphorus and sulfur, as well as reduced nitrogen and hydrogen contents. These developments occurred very rapidly in the 1970’s and 1980’s especially in Japan [56-58] Figure 14 and were similarly adopted in Europe. The benefit of reduced sulfur on Charpy shelf energy is presented in Figure 15.

Figure 14: Progress in improving impurity removal through 1985.