| AISI430(1Cr17) as a representative of the ferritic stainless steel is widely used in automotive, kitchen, appliances, construction, environmental protection and other fields.It is a resource-saving stainless steel. Many applications of ferritic stainless steel have higher requirements on surface quality. In the production process, the surface quality control has become an important production index, directly affects the performance and quality of the finished products of ferritic stainless steel. Besides, the intergranular corrosion has a great influence on the surface quality of the stainless steel.This paper focuses on the susceptibility to intergranular corrosion of430ferritic stainless steel production process. Simulation of hot-rolled, coiling and short annealing process tests and actual industrial validation was investigated to find the reasonable production process to avoid the susceptibility of intergranular corrosion. Conducted in-depth analysis and research on the "gold dust" phenomenon of the cold-rolled stainless steel surface.It was shown that the microstructure of430ferritic stainless steel after hot rolled is ferrite+residual martensite and a small amount of carbide.The martensite decomposed after annealing into ferrite and carbides, making the lower hardness and improved plastic of the steel. The double loop-electrochemical potentiokinetic reactivation (DL-EPR) could be able to evaluate the susceptibility to intergranular corrosion of430ferritic stainless steel. It is found that the optimal operating condition for the DL-EPR test is in an electrolyte composed solution of0.05mol/L H2SO4+0.001mol/L KSCN+0.10mol/L Na2SO4with a potential scaning rate of5.0mV/s(anodic) and1.67mV/s(reverse).The phenomenon of "gold dust" of ferritic stainless steel has a direct relationship with the intergranular corrosion. The results showed that:when430ferritic stainless steel was sensitized in hot rolling, intergranular corrosion will happened in the pickling process, it will eventually lead to the generation of "gold dust" defects on the cold-rolled surface. The main measures to prevent "gold dust" is to avoid the steel sensitization, reduce carbon and nitrogen content and alloying elements.The intergranular corrosion of430ferritic stainless steels is easily appeared in hot rolling. Gleeble simulation of hot rolling tests showed that when the final deformation temperature of900,950℃and colding was water-cooled, the intergranular corrosion susceptibility was smaller,and the Ra values of the corresponding DL-EPR test in less than10%. Intermediate test line rolling experiment showed that the susceptibility of intergranular corrosion existed at different temperatures after hot rolling, which the air cooling is more severe of sensitivity with the DL-EPR test Ra value was higher than the water-cooled. Intergranular corrosion phenomenon of430ferritic stainless steel is difficult to avoid even on water-cooling conditions, and the hot rolling temperature has little effect on the DL-EPR test Ra value.Susceptibility to intergranular corrosion of430ferritic stainless steels after hot rolling could be improved and eliminated through following processes after hot rolling, such as coiling and annealing. Simulate a coiling test results show that intergranular corrosion tendency of430ferritic stainless steel can be reduced and eliminated with a treatment in the650～800℃×4h, water-cooled. Simulate a short annealing results show that the intergranular corrosion the sensitivity has been good suppression and improvement after a short annealing treatment with750～850℃×10min, slow cooling. Industrial validation results gave an optimal process,which is coiling at700℃or a short-term annealing of775℃×10min after hot rolling, are able to effectively mitigate and avoid the emergence of430ferritic stainless steel to intergranular corrosion sensitivity. |
PDF Full Text Request