Experimental Research On The Effect Of Strain Hardening On Stress Corrosion Of 304 And 316L Austenitic Stainless Steel

Austenitic stainless steel with excellent corrosion resistance, mechanical properties and process performance, are widely used in various industrial sectors. Strain hardening make full use of the plastic properties of austenitic stainless steel, so the yield strength is improved, thereby increase the allowable stress, reduce the weight of the container, finally, realize the pressure vessel lightweight design goals. However, strain hardening make austenitic stainless steel microstructure and properties too many greater changes, which is likely to induce stress corrosion brittle fracture. Therefore researching the effect of strain hardening on stress corrosion of austenitic stainless steel 304 and 316Lhave important practical applications, and provide reference for the strain hardening process parameters screening.In this paper,304 and 316L stainless steel base metal and welded joints are used for the study, which are widely used materials for the pressure vessel. Produce strain hardening by single stretch at room temperature, through make a series of basic tests, such as, deformation martensite checking, hardness testing, metallurgical analysis, then research on the influence of strain hardening on material microstructure and mechanical properties. By the slow strain rate tensile test, the effect of strain hardening on the stress corrosion properties and mechanism of 304 and 316L stainless steel is studied, The main conclusions are as follows:(1) After strain hardening,304 stainless steel produced lath deformation martensite, as the strain increased, the deformation martensite content and micro-hardness increased significantly,316L stainless steel has a higher level of stacking fault energy and nickel equivalent, so in the strain hardening process produces only a very small amount of deformation martensite.(2) The 304 and 316L stainless steel welded joints in the strain-hardening process does not produce deformation martensite, the microstructure are columnar austenite and wormlike σ ferrite, forming duplex structure, the pattern of weld crystallization are all F-A (ferrite-austenitic crystal) mode, and the content of 304 welds 8 ferrite are greater than 316L.(3) The effect of strain hardening on stress corrosive property of 304 stainless steel can be divided into three areas:material strengthening, martensitic transformation and dislocations and defects, when the amount of strain hardening is less than critical value, the effect of material strengthening are dominant, the sensitivity of stress corrosion will decline slightly, when the amount of strain hardening is more than critical value, The main factors of 304 base metal is martensitic transformation, the sensitivity of stress corrosion will rise sharply, the main factors of 304 welded joints is the increasing of dislocations and defects, the sensitivity of stress corrosion will rise, as the weld have continuous network 8 ferrite block crack propagation channel, that lead to a lower sensitivity to stress corrosion.(4) The effect of strain hardening on stress corrosive property of 316L stainless steel can be divided into two areas:material strengthening and dislocations and defects, when the amount of strain hardening is less than critical value, the effect of material strengthening are dominant, the sensitivity of stress corrosion will decline slightly, when the amount of strain hardening is more than critical value, with the increasing of dislocations and defects, the sensitivity of stress corrosion will rise, but always at a low level, both the 316L base metal and weld are all contain 2% molybdenum, greatly improved resistance to chloride stress corrosion.