焊缝金属中Mn含量对螺旋埋弧焊管焊缝性能的影响-《焊管》

文章信息/Info

Title:: The Effect Of Weld Metal Manganese Content On The Microstructure,Mechanical Properties And Hot Crack Susceptibility Of Helically Welded Linepipes

Author(s):: Edited and Translated by ZHANG Hong; LIU Ke-yong; ZHAO Yu-yue; ZHAO Bo; (Ｓteel Ｐipe Ｍanufacturing Ｃo.,Ltd.，of CNPC Bohai Equipment Manufacturing Co.,Ltd.,Qingxian 062658,Hebei,China)

Keywords:: weld metal; hot crack sensitivity; submerged arc welding; acicular ferrite; primary ferrite; M/A islands; ferrite with aligned second phase

摘要:: 为了研究焊丝中的Mn含量对螺旋焊管焊缝金属的微观组织、力学性能和热裂纹敏感性的影响，选取了3种w(Mn)分别为0.88%，1.05%和1.54%的焊丝，在X70螺旋焊管的生产和试验条件下进行焊接，获得的焊缝金属中w(Mn)分别为1.26%，1.44%和1.67%。通过光学显微镜及扫描电镜的金相学检查分析显示：提高焊缝金属的Mn含量，能降低各相（针状铁素体（ＡＦ）、先共析铁素体（ＰＦ）和侧板条铁素体（ＦＳＰ））的晶粒尺寸。而且随着针状铁素体不断增加，先共析铁素体（主要是晶界铁素体）和侧板条铁素体的体积分数会降低。同时力学性能试验结果显示：Mn含量越高，焊缝金属的强度和硬度就越高。冲击韧性和延伸率，观测发现有一个最佳值。Mn含量最大的焊缝金属具有较低的韧性，这归因于淬透性的增加及马奥岛（Ｍ/Ａ）及晶界碳化物在针状铁素体位置的形成。对长度超过1000m的螺旋焊管焊缝金属的分析显示：当焊缝金属中w(Mn)增加到1.4%时，热裂纹形成的可能性从0.005%减少到0.001%。

Abstract:: In order to study the effect of Mn content on the microstructure,mechanical properties and hot crack of helical line pipes weld metal.Three different wires with 0.88,1.05 and 1.54 wt% of Mn content were selected,and welding was performed in both exdperimental and production process condition of X70 helical linepipe.As a result,1.26,1.44 and 1.67 wt% of Mn in weld metal wasobtained respectively.Metallographic examinations using optical and scanning electron microscopy showed that increasing the amount of Mn in weld meta can decrease the grain size of all phases(acicular ferrite,primary ferrite and ferrite with aligned second phase).Moreover,in the expense of increasing acicular ferrite,the volume fraction of primary ferrite(mostly grain boundary ferrite) and ferrite with aligned second phase decreased.Also,the results of mechanical properties indicated that the higher the amount of Mn,the higher the strength and hardness of weld metal,but in the case of impact toughness and tensile elongation,an optimum level was observed and lower toughness in the highest Mn content weld metal is attributed to the increasing hardenability and thus formation of martensite/retained austenite islands and grain boundary carbides in coincident sites of acicular ferrite grains.Moreover,analysis on more than 1000m helical line pipes weld metal length showed that increasing weld metal Mn content up to 1.4wt%,the possibility of forming hot crack will reduce from 0.005% to 0.001%.