论文部分内容阅读
常规TMCP工艺生产的C-Mn钢厚板出现-40℃低温冲击脆化现象,为了确定引起脆化的微观组织因素,通过实验室重复冲击实验、微观组织的定量化统计分析、断口观察发现钢板不同部位的铁素体晶粒尺寸分布和珠光体含量有极大差别,解理脆性断裂试样铁素体晶粒粗大且服从对数正态分布,珠光体含量高于20%,而韧性断裂试样具有细小均匀的铁素体晶粒,晶粒尺寸服从正态分布,珠光体分布均匀、含量低于10%。经验公式计算表明脆性断裂试样的铁素体晶粒尺寸和珠光体含量使韧脆转变温度比韧性断裂试样高约60℃,因此可以确定铁素体晶粒尺寸和珠光体含量是影响钢的低温脆性的主要因素。靠近钢板表面部位具有与脆性断裂试样类似的微观组织特征,而靠近厚度中间部位具有与韧性断裂类似的微观组织特征,这使得表面与厚度中间部位韧脆转变温度近60℃的差异。厚度方向微观组织差异是由钢板轧后的不同厚度发生相变的过冷度差异引起的,而低温终轧是导致钢板表面温度低而在空冷阶段先发生相变的工艺因素。
Conventional TMCP production of C-Mn steel plate appeared -40 ℃ low temperature impact embrittlement phenomenon, in order to determine the cause of embrittlement microstructure factors through repeated laboratory impact experiments, quantitative analysis of microstructure, fracture observation found that steel Ferritic grain size distribution and pearlite content in different parts are very different, cleavage brittle fracture specimen ferrite grain coarse and obey logarithm normal distribution, pearlite content higher than 20%, and ductile fracture The sample has fine and uniform ferrite grains, the grain size obeys the normal distribution and the pearlite distributes evenly, the content is less than 10%. The empirical formula calculation shows that the ferrite grain size and the pearlite content of the brittle fracture specimen make the ductile-brittle transition temperature about 60 ° C. higher than that of the ductile fracture specimen, so that it can be confirmed that the ferrite grain size and the pearlite content are influences on the steel The main factor of low temperature brittleness. The microstructure near the surface of the steel plate is similar to that of the brittle fracture specimen, and the microstructure near the middle of the thickness has the same microstructure characteristics as the ductile fracture, which makes the difference of the ductile-brittle transition temperature between the surface and the middle of the thickness nearly 60 ℃. The difference of microstructure in the thickness direction is caused by the difference of supercooling between the different thicknesses after the sheet rolling, while the low temperature finish rolling is the process factor that causes the surface temperature of the steel sheet to be low and the phase transformation occurs first in the air cooling stage.