不锈钢与碳钢焊接接头力学性能研究

Study on Mechanical Properties of Weld Joints of Stainless Steel and Carbon Steel

随着工程应用场景日趋复杂,结构在承载力、耐腐蚀性和经济性等方面面临更高的要求,单一金属材料已经很难满足工程所有使用要求。不锈钢是一种绿色高性能材料,强度和耐腐蚀性良好,且有利于我国实现“双碳”目标;碳钢价格低廉、应用较广,但耐腐蚀性较差。为了提高材料的利用率、节约成本,在工程上常常将不锈钢与碳钢焊接。目前在核电站中由于设备的工作环境和工作介质的不同,通常会采用奥氏体不锈钢与碳钢进行焊接;在建筑幕墙中,一般室外墙板、驳接件、玻璃幕墙支撑体系会采用不锈钢,而内部龙骨和主题钢桁架柱采用碳钢,因此会有大量不锈钢与碳钢焊接的需求。由于不锈钢与碳钢两种材料的化学成分和物理性能不同,焊接时会出现问题,比如:熔点差异使得金属流失、线膨胀系数差异可能导致焊缝出现裂纹、化学成分差异使焊接过程出现脆性化合物等等,所以目前国内大部分规范并不支持不锈钢与碳钢焊接。现有关于不锈钢与碳钢焊接的研究主要集中于Q235B钢和奥氏体不锈钢,没有对常见的不锈钢和碳钢进行系统研究。为此,将S30408、QN1803、S22053不锈钢与Q235B、Q355B碳钢采用对接焊缝连接,对6种不同组合、48个不锈钢与碳钢焊接接头的金相组织、硬度、强度和断口形貌等力学性能进行系统的试验研究。试验表明:不锈钢与碳钢焊接接头在熔合线附近出现明显的增碳层和脱碳层;热影响区晶粒增大,出现马氏体等脆性组织使得热影响区的硬度大于金属母材;不锈钢与碳钢焊接接头拉伸试件断裂在碳钢一侧,抗拉强度与其碳钢母材抗拉强度一致,屈服强度低于碳钢母材,延伸率显著降低;由于脱碳层的形成,使得碳钢熔合线附近的硬度和韧性下降;不锈钢与碳钢焊接接头拉伸断口均出现韧窝,为韧性断裂。

The engineering application scenarios are becoming more and more complex,and the structure is facing higher requirements in terms of bearing capacity,corrosion resistance and economy.It is difficult for a single metal material to meet all engineering requirements.Stainless steel is a kind of green high-performance material,which is conducive to the realization of the goal of'double carbon'in China,and has good strength and corrosion resistance.Carbon steel is widely used because of its low price,but its corrosion resistance is poor.In order to improve the utilization of materials and save costs,stainless steel and carbon steel are often welded in engineering.At present,due to the different working environment and working medium of the equipment in the nuclear power plant,austenitic stainless steel and carbon steel are usually used for welding;in the building curtain wall,the general outdoor wall panels,connectors,glass curtain wall support system will use stainless steel,while the internal keel and the theme steel truss column will use carbon steel,so there will be a large number of stainless steel and carbon steel welding.However,the current domestic specifications do not support the welding of stainless steel and carbon steel.Due to the different chemical composition and physical properties of the two materials,the welding of stainless steel and carbon steel encounters problems.For example,the difference in melting point causes metal loss,the difference in linear expansion coefficient may lead to cracks in the weld,and the difference in chemical composition causes brittle compounds in the welding process.Since the existing research mainly focuses on the welding of Q235B steel and austenitic stainless steel,there is no systematic study on the common types of stainless steel and carbon steel.The S30408,QN1803,S22053 stainless steel and Q235B,Q355B carbon steel are connected by butt weld.The mechanical properties such as metallographic structure,hardness,strength and fracture morphology of 6 different combinations and 48 stainless steel and carbon steel welded joints were systematically studied through experiments.The results show that there are obvious carburized layer and decarburized layer in the welded joint of stainless steel and carbon steel near the fusion line.The grain size of the heat affected zone increases,and the brittle structure such as martensite appears,so that the hardness of the heat affected zone is greater than that of the metal base metal.The tensile specimens of stainless steel and carbon steel welded joints fractured on the side of carbon steel.The tensile strength was consistent with the tensile strength of the carbon steel base metal.The yield strength was lower than that of the carbon steel base metal,and the elongation was significantly reduced.Due to the formation of decarburized layer,the hardness and toughness near the fusion line of carbon steel decrease,the tensile fractures of stainless steel and carbon steel welded joints show dimples,which are ductile fractures.