A Metallographic Study of Steel Weldments

为了弄清钢焊接件的金相组织与各种性能的关系，对几种钢在不同气氛下进行了焊接，并观察了其组织。还对焊接件进行了机械和腐蚀试验。研究结果如下：(1)在加压Ar-CO_2混合气体气氛中对一种低碳钢进行了电弧焊接。焊缝金属的显微组织取决于大气压和气体成分，对力学性能有很大的影响。纯铁和铁合金在不同含氧气氛下进行了弧焊，研究了弧焊过程中氧的吸收和脱氧机理。观察到焊缝金属中形成的氧化物夹杂物具有基本的信息，因为它们在钢焊缝组织的形成中起着非常重要的作用。(3)三角洲-铁素体相变及其晶格…用透射电子显微镜观察了304L型奥氏体不锈钢焊缝金属在高温下的显微组织特征。焊缝金属中的形态变化和西格玛析出强烈依赖于焊缝金属中的初始铁素体组织。铁素体和奥氏体间的非共格晶界容易产生Sigma析出。利用光学显微镜、扫描电子显微镜和透射电子显微镜研究了304不锈钢焊接热影响区的晶界碳化物析出和晶间腐蚀，从结晶学的角度探讨了晶界原子结构对晶界碳化物析出和腐蚀的影响。结果表明，不锈钢焊接热影响区的晶界碳化物析出和腐蚀与晶界的结晶性质密切相关，增加材料中有序晶界的比例可以防止奥氏体不锈钢焊缝的腐蚀。较少

In order to make clear the relationships between metallographic structure and various properties of steel weldments, several steels were welded in different atmospheres and the microstructures were observed. Also mechanical and corrosion tests were performed for the weldments. The results are as follows.(1) A mild steel was arc-welded in pressurized Ar-CO_2 gas mixture atmospheres. The microstructure of weld metal depended on the atmospheric pressure and gas composition, and affected strongly the mechanical properties. An oxygen content of weld metal showed an optimum toughness.(2) Purified iron and iron alloys were arc-welded in various atmospheres containing oxygen to study the oxygen absorption and deoxidation mechanism during arc welding process. The oxide inclusions formed in the weld metal were observed to have fundamental informations, because they play very important roles in formation of the microstructure of steel welds.(3) Delta-ferrite transformations and their crystallogra … More phic characteristics in a type 304L austenitic stainless steel weld metal at elevated temperatures were observed mainly by transmission electron microscopy. The morphology change and sigma precipitation strongly depended on the initial ferrite structure in the weld metal. Incoherent boundary between ferrite and austenite resulted easily in sigma precipitation. These facts suggested that the boundary coherency affects strongly on the transformation in the weld metal.(4) Grain boundary carbide precipitation and intergranular corrosion in the weld heat affected zone of a type 304 stainless steel were investigated using optical, scanning and transmission electron microscopy to discuss effects of grain boundary atomic structure on precipitation and corrosion from a crystallographic viewpoint. The results suggested that grain boundary carbide precipitation and corrosion in stainless steel weld HAZ depend sensitively on the crystallographic character of grain boundaries, and that weld decay in austenitic stainless steel can be prevented by increasing the percentage of ordered boundaries in the material. Less