中国微合金化技术与含铌钢发展30周-of Evolution(10)

It should be noted that the early lower strength steels presented in Figure 5 had very poor toughness from both a fracture energy absorption and impact transition temperature viewpoint. The low absorbed energies in the Charpy test were related to high carbon and sulfur contents and poor steel cleanness, especially in the case of semi-killed steels, whilst the high Charpy and Battelle Drop Weight Tear Test transition temperatures were caused by the coarse ferrite grain sizes and high carbon contents. As a consequence, the early high strength steels often relied on normalizing to achieve adequate grain refinement. In the mid to late 1960’s the benefits of low finish rolling temperatures were discovered and thermomechanical processing was quickly introduced on a broad scale. Simultaneously, lower carbon contents were