拉伸变形对经济型双相不锈钢S32001组织和耐蚀性的影响

Effect of tensile strain on microstructure and corrosion resistance of a lean duplex stainless steel S32001

经济型双相不锈钢S32001具有与304不锈钢相当的耐点蚀能力。得益于其高塑性、良好的耐应力腐蚀和焊接性能,新近开发的高伸长率的经济型双相不锈钢S32001不锈钢常被应用于需要冷成型的建筑和化工能源等领域,因此了解冷成型对组织和耐腐蚀性能等方面的影响具有重要意义。对S32001进行了不同形变量的拉伸试验,通过光学显微镜、扫描电子显微镜和电子背散射衍射分析了其形变前后的组织和腐蚀形貌。采用电化学工作站、酸性介质腐蚀和晶间腐蚀试验分析了不同拉伸形变量下的耐腐蚀性能。随着拉伸形变量的增加,S32001的微观组织出现由位错塞积到形变马氏体的转变。这种应变诱发马氏体可导致S32001钢的TRIP效应,从而获得较高的塑性。与此同时,点蚀电位从退火态的327 mV下降到拉伸断裂状态的297 mV,这可能与应变诱发马氏体的负作用有关。由于S32001双相不锈钢具有优异的抗硫酸和晶间腐蚀能力,随着拉伸形变增加,两者腐蚀速率只是轻微上升。

S32001 is a lean duplex stainless steel with the similar pitting corrosion resistance as 304 austenitic stainless steel.Such steel was recently developed with good ductility,excellent stress corrosion resistance and weldability and had been applied in construction and building,chemical and energy industry with its excellent performance and lower cost.The cold forming processes often occur to those applications and therefore it is of importance to understand the effect of cold form on the microstructure and the corrosion resistance,etc.The tensile tests with different strains were made for a lean duplex stainless steel S32001 to simulate the cold forming processing.The microstructure and the surface morphology after corrosion under both the solution annealed and the tensile deformed states were analyzed by means of optical microscope,scanning electron microscope and electron backscattered diffraction.The corrosion resistance,such as the pitting potential,the sulfuric acid corrosion rate and the intergranular corrosion rate were evaluated via electrochemical workstation,sulfuric acid corrosion and intergranular corrosion tests,respectively.As the tensile strain increases,the dislocation piled microstructure appears and the strain induced martensite appears later.Such strain induced martensite may lead to TRIP effect of S32001 steel and as a result,the high ductility was gained.Notably,the pitting potential was markedly reduced from 327 mV under the solution annealed to 297 mV under the tensile broken state,which may be explained by the negative effect of strain induced martensite.The sulfuric acid corrosion rate and the intergranular corrosion rate rise very slightly with increase of tensile strain which is attributed to the excellent sulfuric acid corrosion resistance and intergranular corrosion resistance of the S32001l stainless steel.