STE355钢焊后显微组织中的粒贝及其对韧性的影响

研究焊接热模拟工艺参数(峰值温度Tmax和焊后冷却时间t8/5)对低碳微合金Ti—Nb钢(STE355钢)热影响区(HAZ)显微组织及冲击韧度的影响。选用干涉层腐蚀法，在光学金相显微镜下清晰显示出了显微组织中的粒贝及M—A组元。观察了Tmax和t8/5不同的热模拟试样中粒贝及M—A组元的形态及分布特征，研究了不同Tmax及t8/5参数对显微组织及冲击韧度的影响，并用电子显微镜进行了观察和验证。结果表明，热模拟峰值温度的升高，或冷却趋缓，都使显微组织变粗、韧性降低。沿晶铁素体和晶内铁素体片的长大、增厚，粒贝中块状M—A岛的长大，都对韧性的改善不利。

Granular bainite in microstructures after welding and its effects on impact toughness in STE355 steels

The effects of technology parameters of stimulated welding thermal cycle (peak temperature T max and cooling time t 8/5 ) on microstructures and impact toughness of HAZ in low carbon microalloying Ti Nb steel STE355 were studied.The microstructures were etched by special interference technology and granular bainite and M A constitucents were shown clearly in optical microscope.The observations were proved by electron microscope.The results show that coarsening of microstructures and decrease of toughness must take place with raising T max and increasing t 8/5 (lowering cooling rate).Growing and thickening of ferrite in boundary and in grains and growing of M A constituents are detrimental to toughness improvement.