Study On Welding And Heat Treatment Technology Of Custom 455 Precipitation Hardening Stainless Steel

As a new type of martensitic precipitation hardening stainless steel,Custom 455 has excellent corrosion resistance and ultra-high strength.Its components and weldments can be widely used in many application fields such as aerospace,marine manufacturing and so on.In order to optimize the welding and heat treatment process parameters of stainless steel and promote the use of Custom 455 in industry,this paper adopts tungsten inert gas welding(TIG),which is simple to operate,widely used and cost-effective,as the welding method,studies the effects of different welding process parameters on the microstructure and properties of the joint,analyzes the results and optimizes the better parameters,Subsequently,the post weld heat treatment process parameters of Custom 455 welded joint are debugged,which has strong practical significance.In this paper,the Pulsed Current tungsten inert gas welding(PCTIG)test scheme of Custom 455 stainless steel is designed.ER-630 welding wire with a diameter of 1.2 mm is used to study the effects of peak current Ip,base current Ib,duty cycle Rw,pulse frequency f and wire feeding speed v1 on weld formation,microstructure distribution and joint properties.Minitab software is used to analyze the data of the results,get the best set of parameters,and compare the microstructure and mechanical properties of Custom 455 stainless steel welded joints welded by PCTIG and CCTIG under the same heat input.The results show that the sample welded with the best process parameters of pulse argon arc welding(PCTIG)obtained by orthogonal test has a good weld shape,the tensile strength is 1097mpa(joint strength coefficient 90%),the elongation is 7%(70% of base metal),and the average hardness of joint weld is 326hv(94% of base metal).Compared with the CCTIG welded joint under the same heat input,due to the stirring effect of pulse current on the molten pool,the dendrite is broken,resulting in the refinement of its structure.The PCTIG welded joint has higher tensile strength,higher elongation and higher average hardness in the weld area.The effects of different solution holding time,aging holding time and aging holding temperature on the microstructure and properties of welded joints were studied.The results show that under the solid solution holding time of 20 min,40min and 60 min,the 40 min sample has better seawater corrosion resistance,less retained austenite(reversed austenite)in the structure and better comprehensive mechanical properties(the tensile strength of the three joints were 1552 MPa,1571 MPa and 1567 MPa respectively,and the elongation is 4.5%,4%and 3% respectively.The average hardness of the weld area is 259 HV,272 HV,and 264 HV,respectively).Under the aging holding time of 2h and 4h,the welded joint has better seawater corrosion resistance,less retained austenite(or reversed austenite)in the structure,finer structure and better comprehensive mechanical properties(under the same tensile strength,the elongation reaches 6%,50% higher than 4% of 4h sample,and the joint hardness is 526 hv,93%higher than 4h sample).At the aging temperatures of 480℃,520℃ and 560℃,the seawater corrosion resistance of the material increases with the increase of aging temperature;The reverse austenite in the weld increases gradually,and the grain size and dendrite spacing increase continuously;The precipitates increase and grow gradually;The tensile strength of Custom 455 stainless steel welded joint and base metal decreases gradually,the elongation increases gradually,and the hardness decreases gradually(the tensile strength of the three joints are 1569 MPa,1370MPa and 1189 MPa respectively,and the elongation is 6%,7% and12% respectively.The average hardness of the weld area is 526 HV,484 HV and 398 HV respectively).