摘要
通过OM,TEM和EBSD等分析手段,并结合热膨胀测试法,研究了Cu对690 MPa级HSLA钢焊丝熔敷金属组织转变及组织细化的作用,并对细化机理进行了探讨.研究结果表明,熔敷金属的组织主要由板条状贝氏体(LB)、粒状贝氏体(GB)和残余奥氏体(AR)组成,Cu含量从0.24%增加到0.53%时,马氏体/奥氏体(M/A)组元数量由0.62%减少到0.31%,并且形状也由小块状、条状向颗粒状转变;残余奥氏体数量增多;同时,组织的亚结构得到明显细化,贝氏体板条块尺寸和板条平均宽度分别从2.18和0.39μm减少到1.99和0.36μm,可阻碍裂纹扩展的大角度晶界的比例也由68.5%增加到71.0%.通过对晶粒细化原因进行分析发现,Cu能降低奥氏体转变温度,增加奥氏体的稳定性,使相变时铁素体自由能(G_α)和奥氏体自由能(G_γ)差值增大,减小临界晶胚尺寸;同时,相变温度的降低也降低了C的扩散速率,使已形核的晶胚长大速率减慢,最终细化了亚晶粒结构.
The effect of Cu on microstructure transformation and microstructure refining of the weld metal of 690 MPa grade HSLA steel was investigated by OM, TEM, EBSD and thermal expansion instrument, and the mechanism of microstructure refining was discussed. Experimental results indicate that microstructure of weld metal is composed of granular bainite, lath bainite and residual austenite. The addition of Cu content from 0.24% to 0.53% in weld metal can decrease phase transition temperature, which induces the reduction of martensite-austenite （M/A） amount from 0.62% to 0.31%, the variation of M/A shape from small bulk and bar to granular shape, the increase of residual austenite amount, and the remarkable refining of microstructure. The increase of Cu content from 0.24% to 0.53% results in the decrease of the mean size of lath block from 2.18 to 1.99 μm, the decrease of the width of lath from 0.39 to 0.36 μm, and the increase of the amount of large angle boundary, which can inhibit crack propagation, from 68.5% to 71.0%. Analysis indicates that Cu can decrease phase transition temperature, increase the stability of austenite, raise the pontential difference between ferrite free energy （Gα） and austenite free energy （Gγ）, reduce the critical size of crystal nucleation.Meanwhile, low phase transition temperature can retard the diffusion rate of carbon atom and slower the growth rate of crystal grains. These factors result in the refining of substructure.
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2012年第11期1281-1289,共9页
Acta Metallurgica Sinica
基金
国家重点基础研究发展计划资助项目2010CB630800~~
关键词
HSLA钢
熔敷金属
相变温度
组织转变
组织细化
HSLA steel, weld metal, phase transition temperature, microstructure transformation, microstructure refining
