热模拟Q890高强钢焊接过程中组织转变的原位观察

采用高温激光共聚焦显微镜对6 mm厚Q890高强钢板进行了焊接热模拟试验。通过原位观察研究了不同焊接热输入条件下钢板显微组织的形核和核长大过程。结果表明:焊接后在t_8/5为300 s的条件下冷却的钢板奥氏体晶界析出块状铁素体,室温组织为先共析铁素体、粒状贝氏体和少量板条贝氏体;在t_8/5为60 s的条件下冷却的钢板,贝氏体转变从奥氏体晶界开始,室温组织主要为针状铁素体、板条贝氏体和粒状贝氏体;在t_8/5为30 s的条件下冷却的钢板,板条贝氏体呈缠结互锁状,室温组织主要为板条贝氏体和板条马氏体;在t_8/5为15 s的条件下冷却的钢板室温组织为板条马氏体及少量板条贝氏体。通过采用高温激光共聚焦显微镜进行焊接热模拟试验并结合组织转变的原位观察来判定高强钢钢焊接性能是可行的。

In-situ Observation of Structural Transformation in Q890 High-strength Steel During Thermally Simulated Welding

The thermally simulated welding test for 6-mm-thick Q890 high-strength steel plates was carried out by means of a high-temperature laser scanning confocal microscope(HT-LSCM).The nucleation and growth of microstructure in the steel plate on the condition that weld heat inputs were different was investigated by in-situ observation.The results indicated that(a)block ferrite precipitated from the austenite grain boundaries,and the microstructure consisted of proeutectoid ferrite,granular bainite and a small amount of lath bainite at room temperature,for the steel plate cooled on the condition that t_8/5 was equal to 300 s after the welding test;(b)the bainite transformation commenced from the prior austenite boundary,and the microstructures were predominantly acicular ferrite,lath bainite and granular bainite at room temperature,for the steel plate cooled on the condition that t_8/5 was equal to 60 s after the welding test;(c)the lath bainite was interlocked with tangles,and the microstructures at room temperature were predominantly lath bainite and lath martensite,for the steel plate cooled on the condition that t_8/5 was equal to 30 s after the welding test;and(d)the microstructure at room temperature consisted of lath martensite and a small amount of lath bainite for the steel plate cooled on the condition that t_8/5 was equal to 15 s after the welding test.It is feasible to determine the weldability of high-strength steel by thermally simulated welding test which is performed by HT-LSCM in conjunction with in-situ observation of structural transformation.