MIG Weldability Of Fe-Mn-Al-C Low Density Steel And Process Impact

Low-density steel not only has the characteristics of high strength and good plasticity,but also has the huge advantage of reducing weight.Therefore,it has broad application prospects in the fields of ships,weapons and aerospace.However,the current research on low-density steel mainly focuses on the composition design and preparation of lowdensity steel,and the systematic research on the weldability of low-density steel is urgently needed.In this paper,welding method of gas-shielded gas welding is used to conduct welding test on Fe-Mn-Al-C low-density steel,and the structure and properties of welded joints are studied.Thereby establishing a connection between welding materials,welding test parameters and welding joint structure and performance.The effects of welding wire composition and active gas on the welding of Fe-MnAl-C low-density steel were studied.Welding tests were carried out on three different welding wires at different active gas ratios.Using X-ray non-destructive testing method to detect the weld metal,the results show that the weld has no obvious welding defects.After the active gas CO2 is added,the surface of the welding seam is obviously oxidized.The metallographic microscope,scanning electron microscope and XRD were used to study the microstructure and structure of the welded joint,and the hardness and strength of the welded joint were tested.For the ER120S-G wire weld,with the increase of the proportion of active gas,the austenite content increases,the ferrite content decreases,the grain boundary carbide content increases,and the tensile strength decreases from 742 MP to 644 MPa.It is believed that CO2 gas transitions to the weld metal during the welding process,and it will also cause alloying elements to burn,thereby deteriorating the performance of the joint.For the ER307 Mo wire weld,the structure of the weld is austenite,ferrite and Al N phase.With the addition of active gas,the austenite content increases,the ferrite content decreases,and the tensile strength increases from 805 MPa to 827 MPa.It is considered that the reason is that an oxide layer is formed on the surface of the weld,which prevents the nitrogen element from overflowing.Secondly,the active gas will change the direction of Marangoni convection and improve the fluidity of the molten pool.For ER2594 welding wire,pure argon welding is used,and the Al N phase is distributed in an aggregated state.After adding active gas,the Al N phase is distributed evenly.The tensile strength was increased from 826 MPa to 913 MPa,and the elongation after fracture was increased from 8.2% to 14.2%.Using dual-phase steel welding wire and 95%Ar+5%CO2 shielding gas,the effect of welding heat input on the structure and performance of the welded joint was studied.As the welding heat input increases,the austenite content increases and the ferrite content decreases,which has no obvious effect on the size and distribution of the Al N phase.The hardness and yield strength of the welded joint gradually decrease,and the tensile strength fluctuates in a small range.It is believed that it may be caused by martensite during the stretching process.When the welding current is 260 A,the welding voltage is 32.0V,and the heat input is 20.80 k J/cm,the performance of the joint is optimal.Oblique Y-shaped welding crack test was used to study the welding suitability of welding wire and lowdensity steel.The results show that the joint crack rate and surface crack rate are both 0,indicating that the duplex stainless steel ER2594 and Fe-Mn-Al-C low-density steel have good weld match.