Fe-36%Ni合金搅拌摩擦焊接头组织与性能的改善

Improvement on microstructure and properties of friction stir welded joint of Fe-36%Ni alloy

随着能源业的发展,Fe-36%Ni合金作为结构材料的应用需求越来越广,而电弧焊时存在严重的热裂纹和再热裂纹问题。采用搅拌摩擦焊方法焊接Fe-36%Ni合金可以有效地避免电弧焊带来的裂纹问题,获得成形良好的接头。但已有研究获得的焊缝组织均有晶粒粗化的特点,导致其接头力学性能低于母材。因此,需要解决晶粒粗化问题,寻找组织与性能获得改善的方法。采用控制焊接工艺的方法改善Fe-36%Ni合金搅拌摩擦焊接头的组织和性能。结果表明,在较低的焊接速度下,调整搅拌头转速更适合于控制Fe-36%Ni合金搅拌摩擦焊接头的晶粒尺寸。搅拌头低转速带来较低的焊接热输入,使焊缝具有晶粒尺寸与母材相当或较母材晶粒细化的组织。晶粒尺寸是接头力学性能的主导因素。在400 r/min和2 mm/s的焊接工艺下可获得与母材晶粒尺寸相近、强度和硬度相当、断后伸长率也较高的接头。

With the development of the energy industry,Fe-36wt%Ni alloy,as a construction material,has great potential in manufacturing liquefied natural gas storage and transportation equipment.However,it has very high hot cracking susceptibility during the conventional arc welding process.Friction stir welding of Fe-36wt%Ni can effectively avoid cracking problems occurred in fusion welding.However,due to the coarse grain in stir zone,the mechanical properties of Fe-36wt%Ni joint are lower than that of the base metal.Therefore,it is necessary to improve the microstructure and mechanical properties of friction stir welded joint of Fe-36wt%Ni alloy.The effect of welding parameters on microstructures and the mechanical properties were investigated.It reveals that the grain size in stir zone of Fe-36wt%Ni alloy joint mainly affect by the rotational speed when the welding speed is relatively low.Lower rotational speeds produce the lower heat input and results in the finer grain size in stir zone and higher hardness,yield strength and tensile strength of welded joint.The optimized microstructure and mechanical properties for engineering application of friction stir welding of 3 mm-thick Fe-36wt%Ni alloy were obtained with the welding parameter of 400 r/min of rotational speed and 2 mm/s of welding speed.