Study On The Corrosion Resistance Of TRIP Steel

The corrosion of steel spreads over the each field of national economy developments, and the loss is enormous. It is extremely important to improve the corrosion resistance of steel. TRIP (Transformation Induced Plasticity) steel is known to combine high strength levels with high ductility and therefore is very attractive for the automotive industry. However, no systematic study about the corrosion resistance of TRIP steel has hitherto been made. It is necessary to investigate the corrosion mechanism of TRIP steel to meet the corrosion resistance requirements of materials of new age. This article investigates corrosion behavior of four kinds of low-carbon Si-Mn TRIP steels in different environments.Immersion test, atmospheri ccorrosion test (salt spray test, dry-wet cycle immersion test) and soil corrosion test were conducted in laboratory. Corrosion dynamic analysis was performed by gravimetric, spectrophotometry, potentiodynamic polarization method. Optical microscopy (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and electro-probe microanalysis (EPMA) were used to systematically investigate the microstructures, surface morphologies, as well as the composition and distribution of alloy elements of corrosion products of the corrosive specimens. The microstructures and mechanical properties of TRIP steel were evaluated by austempering immediately after intercritical annealing.Stable rust layer formation mechanism of TRIP steel is also been discussed. The results have shown that the corrosion rate of steel A is the highest among four kinds of TRIP steels. The corrosion rate of steel C is higher than those of steel B and D. The corrosin rates of four kinds of steels were reduced significantly with increasing corrosion time. The corrosion rate of steel C in soil corrosion test is highest. The composition of corrosion product and the enrichment of alloying elements in the rust layer resulted in the rust layer compactness, which could contribute to the improvement of the corrosion resistance of the sample. Steel D has the best mechanical properties. The mechanical properties of steel B are better than those of steel C. Steel A exhibits the worst performance. The alloying elements can improve the corrosion resistance and mechanical properties of TRIP steel. Protective rust layer protects the substrate of TRIP steel containing a complex mix of multiphase. The enhancement of corrosion performance of TRIP steel is attributed to the additions of alloying elements, and the alloying elements increase the compactness of the rust layers. Therefore electrochemical characteristic of TRIP steel is improved.A systematic investigation of the corrosion resistance and stable rust layer formation mechanism of TRIP steel is not only important to the design of properties and microstructure, but also significant to apply TRIP steel in industrial practice.