ABSTRACT

The impact of Nb contents on grain refinement in a simulated coarse-grained heated-affected zone (CGHAZ) in steels was investigated. The austenite grain grew in multiple directions and then impinged against each other during the α→γ transformation. Subsequently, austenite grains coarsened via the coalescence of small grains and boundary migration. With the increased Nb content, the austenite in CGHAZ became coarser due to the decreased quantity and increased size of Nb precipitates. Furthermore, the austenite decomposed into bainite during the cooling process. Compared with the low-Nb specimen, the crystallographic grain size in CGHAZ of high-Nb specimen is slightly coarser, relating to the coarser prior austenite grain. However, higher Nb content delays the bainite transformation start temperature, leading to multiple variants selection of bainite, increasing the refinement ratio.

摘要

研究了 Nb 含量对钢中模拟粗晶热影响区 (CGHAZ) 晶粒细化的影响。奥氏体晶粒在多个方向生长，然后在α→γ转变过程中相互碰撞。随后，奥氏体晶粒通过小晶粒的聚结和边界迁移而粗化。随着Nb含量的增加，由于Nb析出物的数量减少和尺寸增加，CGHAZ中的奥氏体变得更粗大。此外，奥氏体在冷却过程中分解为贝氏体。与低Nb 试样相比，高Nb 试样的CGHAZ 晶体晶粒尺寸稍粗，这与原奥氏体晶粒较粗有关。然而，较高的Nb含量延迟了贝氏体转变开始温度，