S30408不锈钢角焊缝低温力学性能试验

Experimental Study on Mechanical Properties of Fillet Weld Connections of S30408 Stainless Steel in Low Temperature

焊接接头作为压力容器的重要组成,其低温下的力学性能直接影响容器的安全性.目前针对奥氏体不锈钢焊接接头的力学性能研究主要集中在对接焊缝连接件,且试验温度多为常温和-196℃,对角焊缝在不同温度下的研究较少.为了研究S30408不锈钢角焊缝接头的低温力学性能,采用100 t万能试验机,在-60~20℃的温度范围内,进行了一批正面和侧面角焊缝接头试件低温下的拉伸试验,绘制其在各温度下的应力-应变曲线,以及焊缝强度、变形和破坏特征.采用热场发射扫描电子显微镜JSF对断口形貌进行了观测研究,分析其组织特点.试验结果表明:-60℃相较于20℃,正面角焊缝构件屈服强度提高了18%、抗拉强度提高了25%,侧面角焊缝构件分别提高了约35%和30%,低温强化效应显著;正面角焊缝构件的抗拉强度与侧面件的比值略小于理论值1.5;正面角焊缝受到拉力和剪力共同作用,20℃时其弹性模量为198 GPa,侧面构件仅受剪力作用,其弹性模量约102 GPa;弹性模量随温度降低增长缓慢,正面构件的弹性模量最大增幅为6%,侧面构件为9%;正面角焊缝的断口呈多边形韧窝形貌,侧面为剪切型韧窝形貌,温度降低,韧窝数量均减少,颜色变浅,塑性变形能力减弱,但仍旧为韧性断裂.

As an essential part of a pressure vessel,the mechanical properties of welded joints at low temperatures directly influence the vessel’s safety.At present,most research on mechanical properties of stainless steel welded joints focuses on butt weld at the experimental temperature range between room temperature and-196℃.However,fillet weld at different temperatures has been scarcely investigated.To study the low-temperature mechanical properties of the S30408 stainless steel fillet weld joint,the low-temperature tensile tests were performed on 15 transverse and longitudinal fillet weld joint specimens in the temperature range-60—20℃using a 100t universal testing ma-chine.Besides,the stress-strain curves,weld strength,deformation,and failure characteristics were measured.The fracture morphology was observed using a thermal field-emission scanning electron microscope,and microstructure characteristics were analyzed.The results show that-60℃compared to 20℃,the yield and tensile strength of the transverse fillet weld increased by 18%and 25%,respectively,and that of the longitudinal fillet weld increased by 35%and 30%,respectively.Low temperature hardening effect is remarkable.The ratio of the tensile strength of the transverse fillet weld member to the longitudinal member is slightly less than the theoretical value of 1.5.The results show that the combined action of tensile and shear forces influence the transverse fillet weld.The elastic modulus of the transverse fillet weld is 198 GPa at 20℃and the longitudinal member is 102GPa under the action of shear force.The elastic modulus increases gradually with decreasing temperature.The elastic modulus of the transverse member increases by a maximum of 6%and the longitudinal member by 9%.The fracture surface of the front fillet weld has polygonal dimple morphology,and the longitudinal one has shear dimple morphology.The number of dimples de-creases with the decreasing temperature,the color lightens,and the plastic deformation ability weakens;however,the fracture is still ductile.