Study On Stabilizing Heat Treatment Of TP321 After Welding

TP321,namelyS32168,Chinese brand is 06Cr18Ni11 Ti.Elements Ti is added to the 304 steel in order to enhance its ability of intergranular corrosion resistance and high temperature resistance.Is widely used in boiler,power generation,petroleum,chemical industry,synthetic fiber,food,paper and other industries,especially the hydrogenation process system of petrochemical plant piping.Around the world,there are some controversial about whether TP321 austenitic stainless steel must be stabilized heat treatment.A lot of literature summarized on the material heat treatment after welding,but some sources outlined in reasoning,some sources outlined in scientific experiments,but the project is relatively fragmented,not systematic and in-depth.This paper reviews the development and research of austenitic stainless steel material,and summarizes the influence factors about performance of austenitic stainless steel.A series of basic performance test of TP321 raw materials are made,such as: chemical composition,mechanical properties,impact experiments.Argon arc welding primer and the consumable electrode gas shielded welding was carried out on the material after make sure that the materials are qualified.And then carrying out the 600?/4h stress relief heat treatment and 900?/4h stabilizing heat treatment of the raw material.For welded joint sample of welding state,600?/4h,and 900?/4h heat treatment,we do a series of experiments such as: hardness testing?basic mechanical properties test ? impact test.We analysis the relationship between the sensitized precipitation and impact value.We also did a lot of microscopic experiment: for example intergranular corrosion test and residual ferrite analysis of raw material and weld metal;grain size analysis of the base material and the heat affected zone;microscopic analysis of the fusion zone.Understand the grain growth in the heat affected zone and so on.Through a series of experiments,we found that :After 600?/4h stress relieving heat treatment and 900?/4h stabilization processing,the material's strength grade had no improvement,no large crystals precipitated,also did not occur sigma phase shift,did not produce intergranular corrosion,grain size did not change.The different is,after 900?/4h stabilization heat treatment,the material's plasticity and toughness is improved,although not very obvious.But after 600?/4h stress relieving heat treatment the material's hardness is larger.Overall comparison of 900 degree /4h after stabilization treatment than 600 /4h to stress treatment effect is good,but the contrast effect is not very obvious.For the project,the temperature of heat treatment rise one degree centigrade,whether it is from the time or money,the cost is still quite large.From the experimental results of some references and other cases,but also related to the welding stress in the high temperature state of the release,as well as the effect of micro defects in the weld,there will be the hidden defects of welding micro defects.So in general,it is recommended to change stabilize the heat treatment into a stress treatment.