Effect of Nitrogen on Microstructure and Toughness of Coarse Grain Heat Affected Zone in Vanadium Microalloyed Steel
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摘要: 采用焊接热模拟的方法,研究了氮含量对实验钢焊接粗晶热影响区(CGHAZ)显微组织和韧性的影响规律。结果表明:随着氮含量的增加,CGHAZ的组织从晶界铁素体、贝氏体和侧板条铁素体转变成针状铁素体、多边形铁素体和少量的贝氏体,且铁素体晶粒细化;CGHAZ韧脆转变温度(FATT50)先降低后升高,屈服强度升高。氮含量从0.004 4%增加到0.009 4%时,有效晶粒尺寸减小,导致CGHAZ的FATT50降低;氮含量从0.009 4%增加到0.019 0%时,CGHAZ中固溶氮、屈服强度增量对FATT50的综合作用大于晶粒的细化作用,导致FATT50升高。Abstract: Microstructures and toughness of coarse grain heat affected zones(CGHAZ) in experimental steels with different nitrogen contents are studied by welding thermal simulation.Resultsindicate that with the increase of nitrogen content, CGHAZ microstructure changes from grain boundary ferrite, bainite and side lath ferrite to acicular ferrite, polygonal ferrite and a small amount of bainite, with the ferrite grains refined. The ductile-brittle transition temperature(FATT50) of CGHAZ steel decreases first and then increases, meanwhile the yield strength rises. When the nitrogen content increases from 0.004 4% to 0.009 4%, the effective grain size decreases and the FATT50 of CGHAZ decreases. When the nitrogen content increases from 0.009 4% to 0.019 0%, the combined influence of solid solution nitrogen and yield strength increment on FATT50 is greater than that of grain refinement, leading to the increase of FATT50.
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Keywords:
- vanadium micro alloyed steel /
- nitrogen /
- microstructure /
- toughness
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