Research On The Effect Of Heat Treatment On S30432 Shot Peening Layer Hardness And High Temperature Oxidation Properties

With the ultra-supercritical units gradually applicated,high temperature steamside oxidation problem of superheater and reheater tubes becomes very serious.The inner shot peening of austenitic stainless steel,is a very effective way to improve the steamside anti-oxidation capability.However,the actual production of stainless steel material must undergo heat treatment,heat treatment may affect the the properties of shot peening layer,especially the antioxidant propertie.This article designe the heat treatment test which reflect manufacture condition to study the microhardness variation of S30432 tube shot peening layer,Followed by high-temperature oxidation test analyze the changes in the Cr content with the heat treatment temperature.The influence of heat treatment on the shot peening layer of austenitic stainless steel in ultra supercritical boiler was obtained.Through these studies to determine how to choose the right way and the heat treatment temperature,the basis of ensuring the safety of the boiler structure,taking into account the high-temperature steam oxidation capacity,reduce unplanned downtime,improve operational efficiency of power plant is significant.We use the resistance furnace and infrared heating chip to heat treatment S30432 at 640?,740?,765? and 1125?×2h four temperature points.The morphology of shot peening layer was observed by SEM and oxide component was analysised by EDS after the heat treatment;The change data of microhardness in the depth of 60?m were measured by microhardness tester after heat treatment.Origin software was used to fit the 640? and 740? microhardness-time curves,and the mathematical model of the relationship between microhardness and time was established.Then samples were put into a resistance furnace for 700?×48h high temperature oxidation test,the samples were observed the layered structure oxide,section oxides,different Cr content of oxide sublayer was measured by SEM after oxidation test.The distribution of Fe?Cr?Ni?O elements in the original and heat treated state and the difference of Cr content in inner oxide layer was analyzed were analyzed by using EDS line scan after oxidation test.The research shows that:the heat treatment significantly reduces the microhardness,the rate of decrease of the hardness decreases with the time passing by,in the first 30 minutes,a large decline,finally approaching to a stable value,the higher the temperature the greater the amplitude decrease,The shot peening layer hardness is no different from the base metal after 1125?×2h heat treatment,the hardness of the other three temperature points decrease about 30-70HV0.5,and they retained peening feature.microhardness changed because of the Recovery and recrystallization of shot peening layer during the heat treatment.High temperature air oxidation test found that the heat treatment temperature significantly affect the average Cr content in the oxide layer,with the increase of the temperature,the average Cr content decreased.The oxidation resistance of the shot peening layer after PWHT of dissimilar weld was in the range of acceptable.The oxidation resistance of the shot peening layer was the lowest in the 1125? after solution heat treatment.Sub-grain structure grow,reducing the number of grain boundary to reduce the diffusion paths of Cr element to the surface of shot peening layer and leading oxidation capability degradation.