中国微合金化技术与含铌钢发展30周-of Evolution(5)

中国微合金化技术与含铌钢发展30周-of Evolution

24 中国含铌钢技术发展30周年国际研讨会论文集

In retrospect the carbon content was still relatively high since carbon contents have steadily decreased, Figure 3, as strengths have increased and larger amounts of microalloying elements have become necessary. The current limit on the combined microalloying content Nb+V+Ti for steels with yield strength >60 ksi is 0.15 percent [18-19]. Individual limits are presented in Figure 4.

Figure 3: Relationship between carbon content and yield strength for high strength pipeline

steels [16].

Figure 4: Comparison of limits for vanadium and niobium for different pipe grades.

There has been a steady increase in available yield strengths from 52 ksi in the 1950’s to 120 ksi today Figure 5.