| 409L stainless steel is one kind of low chromium ferritic stainless steel(FSS),which with corrosion resistance,cold forming,good welding and high temperature oxidation resistance.The plasticity and toughness of 409 L are better than those of high chromium FSS.It is also an economical and environmental material without or containing trace nickel.The 409 L is widely used in automotive industry,chemical equipment,building materials,food and medical fields,but the heat affected zone of welded joints has coarse grain,low plasticity and toughness,and is prone to crack corrosion.These defects will limit the popularization and application of FSS,so it is of great significance to improve the properties of welded joints.In this study,14 groups of rare earth element Ce and stable element Ti were added into the 409 L welded joints by tungsten inert gas(TIG)welding.Microstructure observation,tensile test,low temperature impact test and thermal cycle test were carried out on all kinds samples.The influence of Ce/Ti on the microstructure and mechanical properties of 409 L stainless steel welded joints were explored by comparing mechanical properties,statistical analysis of test data,and study of impact fracture morphology and composition.The results show that Ce/Ti in 409 L stainless steel welded joint can refine grain,purify structure,improve the plasticity and impact toughness of welded joints.When the addition of Ce/Ti is 0.24% and 0.72% respectively,the mechanical properties of the welded joint is the best.The yield strength of the welded joint is 372.1MPa,the tensile strength is 538.6MPa,the impact energy is 27.5J,and the impact energy of heat treatment is 61.5J.The yield strength,tensile strength,impact energy and heat treatment impact energy are increased by 127.2%,41.9%,841.8% and 123.6%,respectively.However,when the addition of Ce is 0.45% and Ti is 0.18%,the mechanical properties of welded joints are the worst.The characteristics of fracture structure of welded joints are brittle fracture and ductile fracture,mainly brittle-ductile mixed fracture.The brittle fracture is composed of many cleavage planes and steps,and has a large number of river patterns.The ductile fracture is distributed with dense dimples,the dimples are large and deep in parabolic shape.After thermal cycling treatment,the number of oxide particles decreases and the impact toughness increases,which indicates that heat treatment can improve the mechanical properties of welded joints. |
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