STE355钢焊后显微组织中的粒贝及其对韧性的影响

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

摘要: 研究焊接热模拟工艺参数(峰值温度T_max和焊后冷却时间t_8/5)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T_max和t_8/5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T_max及t_8/5参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。

Abstract: 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.