Study On The Corrosion Resistance For QPQ Technology Of Steel 08Al

The QPQ(Quench Polish Quench) complex salt bath treatment is a type of very advanced technology for surface strengthening. It is used widely in the field of manufacturing engineering and in the mechanical and automobile industry to increase surface wear resistance, to enhance fatigue strength and to improve the corrosion resistance of the treated components. The QPQ surface-treatment process includes a nitriding (or lower-temperature nitro-caburizing) salt bath process and an oxidizing salt bath process. The specimens were treated in a QPQ salt bath, where the treated surface is consist of a composite layer and a tight Fe₃O₄ film. The QPQ process is particularly suitable for all kinds of low-carbon steel, cast iron and powder-metallurgy components. After QPQ treatment, plain-carbon steel can be used instead of stainless steel, whilst the QPQ process can also substitute for anti-corrosion and anti-oxidizing processes such as blacking, phosphorescing, chromium plating, etc.In this article, the QPQ complex salt bath treatment was applied for surface modified of steel 08A1. Effect of different process parameters on corrosion resistance for QPQ treated work-pieces was researched. The treated surface microstructure was observed by using SEM, meanwhile, the thickness and the quality of the compound-layer were also analyzed. The phase composition of oxide film was analyzed by XRD. The micro-hardness of diffusion layer was measured by Digital Micro Hardness Tester. The corrosion resistance of QPQ treated steel 08A1 was investigated through soaking and salt spray tests.The results indicated that: Steel 08A1 was treated at a constant nitriding temperature of 540°C and 560°C for 3h ,the peak micro-hardness of composite layer was HV660, which was about the 4 times of base material, the depth of composite layer was 52μm, but the depth of diffuse layer of 560°C was more further than 540°C. There is a spongy composite layer about 52.8μm deep, which was obtained at a nitriding temperature of 540°C for 3h and can be oxidized into a tight Fe₃O₄ film. Steel 08A1 were heated to 540°C in a QPQ salt bath, nitride for 3 h, and then oxidized at 360°C for 30 min, which can keep on rustproof state for 168h in the salt spray, and then, adding polishing process and double-oxidized at 400°C for 30min, the treated steel 08A1 will increase the anti-corrosion value and can keep on rustproof state for 192h in the salt spray.