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

为了明确钢焊件的金相组织与各种性能之间的关系，对几种钢在不同气氛下进行了焊接，并对焊件进行了力学和腐蚀试验，结果如下。低碳钢在Ar-CO_2混合气体强气氛下进行电弧焊，焊缝金属的显微组织取决于大气压力和气体成分，并影响焊缝金属的力学性能。 (2)在各种含氧气氛中对纯铁和铁合金进行电弧焊，研究电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础信息。在钢焊缝显微组织的形成中起着非常重要的作用。(3) 304L 型奥氏体不锈钢焊缝金属中的 δ 铁素体相变及其晶相特征高温下的形貌变化和强烈的σ析出很大程度上取决于焊缝金属中的初始铁素体结构，铁素体和奥氏体之间的不相干边界很容易导致σ析出。 (4)采用光学、扫描等方法研究了304不锈钢焊缝热影响区的晶界碳化物析出和晶间腐蚀。和透射电子显微镜从晶体学角度讨论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中的晶界碳化物析出和腐蚀敏感地依赖于晶界的晶体学特征，并且焊缝腐蚀。在奥氏体不锈钢中，可以通过增加材料中有序边界的百分比来防止。