Research On Welding Properties Of Fe-Mn-Al-C Low Density Steel

In recent years,the rapid development of the automotive industry has become an inevitable trend for the future development of the automotive industry.Fe-Mn-Al-C low-density steel has become a potential materials for automobile lightweight,because of its excellent properties,but the welding performance is an important index to measure whether it can be successfully applied to automobile production.The main reason for the difficulty in welding Fe-Mn-Al-C low-density steel is the high alloy content,but there are few studies on the influence of alloy elements on welding performance.Based on the above analysis,the research contents and conclusions of this article are as follows:In this paper,the effects of peak temperature and line energy on the microstructure and properties of 12Al-12 Mn steel and 10Al-12 Mn steel HAZ are studied by welding thermal simulation method.The results show that the peak temperature is The influence of the microstructure in the affected zone is small,but as the temperature increases,the grain size and the proportion of small-angle grain boundaries decrease,and the hardness increases;when the peak temperature is 1300 ° C,The grain size is the largest,and the grain boundaries are basically large-angle grain boundaries.At this time,the hardness is the lowest and it is the softened area of the entire heat affected zone.With the increase of the welding line energy,the grain size of the coarse grain zone of 12Al-12 Mn steel decreases,The hardness increases;while the structure of the coarse grain region of10Al-12 Mn steel has not changed,all are austenite,and the grain size decreases and the hardness increases.In this paper,the test results obtained from the welding thermal simulation are used as a guide.The TIG welding process with low heat input is used to weld the test steel.The microstructures of welded joints of 10Al-12 Mn steel,12Al-12 Mn steel and 12Al-16 Mn steel were studied by means of OM,SEM,EBSD and XRD.In particular,the effects of Al content and Mn content on the microstructure and mechanical properties of welded joints were studied.the result shows:(1)After the three component test steels are welded,the weld joint forms a weld zone and a heat-affected zone.The weld zone is organized as dendritic crystals perpendicular to the direction of the weld.But The heat-affected zone has typical characteristics and can be divided into the fusion zone,coarse grain zone and part of the phase transition zone,the normalizing zone is not obvious.With the increase of Al and Mn content,the dendrite spacing of columnar crystals in the weld zone decreases,the number of annealing twins in the structure of the heat affected zone increases,and the grain size decreases.(2)The growth mechanism of the test steel weld zone is related to the Mn and Al content.As the Al content increases,the growth mechanism of the weld zone near the fusion zone changes from epitaxial growth to a mixed mode of epitaxial and nonepitaxial growth As the Mn content increases,the growth mechanism of the weld zone near the fusion zone does not change.However,the growth mechanism of the threecomponent test steel in the weld zone far from the fusion zone is competitive growth.As the Al content increases,the competitive growth mechanism weakens,and as the Mn content increases,the competitive growth mechanism increases.(3)The hardness distribution of the test steel welded joints has the same law.The base metal is the highest and the weld zone is the lowest,it is the softened area of the entire welded joint.With the increase of the Al and Mn content,the overall hardness of the welded joint is slightly In addition,the composition of the entire welded joint of the test steel is unevenly distributed.After tensile deformation,they all fracture at the weld,and the fracture mechanisms are brittle fractures.As the Al content increases,the tensile strength and elongation of the test steel decrease,and as the Mn content increases,the tensile strength and elongation increase,and the mechanical properties of the test steel are improved.This paper uses solution treatment to dissolve the welded samples.The results show that as the solution temperature increases,the size of the columnar crystals in the weld seam increases.The hardness and tensile strength of the joint gradually decrease,the yield strength decreases first and then increases,while the elongation gradually increases.