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A Metallographic Study of Steel Weldments

钢焊件的金相研究

基本信息

批准号：
63550545
负责人：
SATO Yoshihiro
金额：
$ 1.22万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1990
项目状态：
已结题

项目摘要

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

为了弄清钢焊接件的金相组织与各种性能之间的关系，对几种钢在不同的气氛下进行了焊接，并观察了其显微组织。并对焊接件进行了力学和腐蚀试验。结果如下：(1)在加压Ar-CO_2气体混合气氛中对低碳钢进行了电弧焊接。焊缝金属的显微组织受大气压力和气体成分的影响，对其力学性能有较大影响。焊缝金属的氧含量表现出最佳的韧性。(2)在不同含氧气氛下对纯化铁及铁合金进行电弧焊接，研究电弧焊接过程中的吸氧脱氧机理。焊缝金属中形成的氧化物夹杂物具有基本的信息，因为它们对钢焊缝微观结构的形成起着非常重要的作用。(3)通过透射电镜观察了304L型奥氏体不锈钢焊缝金属在高温下的δ -铁素体相变及其晶体特征。形貌变化和sigma析出与焊缝金属中铁素体的初始组织密切相关。铁素体和奥氏体之间的非共格边界容易导致sigma析出。这些事实表明，边界相干对焊缝金属的相变有很大的影响。(4)采用光学显微镜、扫描电镜和透射电镜对304型不锈钢焊接热影响区晶界碳化物析出和晶间腐蚀进行了研究，从晶体学的角度探讨了晶界原子结构对析出和腐蚀的影响。结果表明，不锈钢焊缝热影响区晶界碳化物的析出和腐蚀与晶界的结晶学特征密切相关，提高材料中有序晶界的比例可以防止奥氏体不锈钢的焊缝衰减。少