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Improved formability and higher heat-resistance are increasingly demanded to materials used for hot end parts of automotive exhaust gas system in order to meet stricter emission regulations. A heat-resistant ferritic stainless steel and pipe with high formability was developed by refining the microstructure of hot rolled and annealed sheets. The newly developed steel showed a remarkable improvement in various forming properties such as limit drawing ratio, limit expansion ratio of pipe, and thickness reduction ratio of pipe after bending in comparison with conventional steels.

Organic composite coated steel sheets retain their excellent corrosion resistance during cyclic corrosion tests (CCT). To clarify the corrosion behavior of these sheets during CCT, variations in corrosion products and coating components were examined. Moreover, the contribution of the corrosion products, organic composite coating, and chromate film to corrosion resistance was examined by AC impedance measurements. Formation of crystalline ZnCl2·4Zn(OH)2 and amorphous zinc carbonate were detected by X-ray diffraction (XRD) and Fourier transformation infrared spectroscopy (FT-IR). Crystalline ZnCl2·4Zn(OH)2 is formed during CCT on and under the organic composite coating. The corrosion products formed on the coating contain silicates from the silica in the organic composite coating. Consequently, the contents of zinc and silica in the coating decrease, while nickel and chromium in the chromate film and carbon in the coating remain constant during CCT.

Modifications in the properties of galvannealed steel sheet have been made to meet the needs of the automotive industry. The press formability (powdering and flaking) of the galvannealed steel sheet is very sensitive to the phase composition and coating weight of the coating. The allowable coatings for a satisfactory anti-powdering property may fail to provide the anti-flaking property, showing a high coefficient of friction due to the existence of a soft phase, ζ, at the surface. In this study, the effects of an inorganic film on the surface of the galvannealed coating were studied improving press formability. It was found that a thin borax film was effective to minimize surface friction and to improve unti-flaking properties. Short electrode life is another problem, as it limits continuous spot welding of the galvannealed steel sheet. During welding, electrode tips (Cu) are consumed by an interaction with the coating and the steel substrate.

Operating temperatures in many bearing applications exceed 100 °C. Conventional bearing steel (SAE52100,SAE5120,Etc.) will begin to experience a reduction in life due to dimensional instability, and reduced surface hardness, at these temperatures. High speed tool steel (such as AISI-M50) can operate in temperatures up to 300°C but is very costly. SAE52100 can be heat stabilized up to 300°C to improve the dimensional stability, but this process can severely decrease the surface hardness and fatigue life. There are many applications where the high operating temperature is greater than 100°C but less than 200°C. A new material has been developed, based on SAE52100, with improved dimensional stability, and surface hardness, for this medium operating temperature range.

The corrosion mechanism of zinc coated steel sheets in automotive bodies was studied in field vehicle tests and several types of accelerated tests. Perforation corrosion starts in unpainted areas of lapped parts, and proceeds in the following steps: i) galvanic protection by the Zn coating, ii) protection by corrosion products, and iii) corrosion of the steel substrate and perforation. Although the corrosion processes were the same in all the cases tested, the corrosion rate depended significantly on the environment, such as atmospheric exposure conditions and the part of the automotive body. In accelerated corrosion environments, Zn coating is largely ineffective against perforation corrosion because galvanic protection and protection by corrosion products cannot be maintained over the long term.

Al2O3 -dispersed Zn-Co-Cr alloy electroplated has been developed for automobile use. Optimum coating composition ranges from 0.5 to 2.0wt% for Co, 0.3 to 1.0wt% for Cr, and 0.1 to 2.0wt% for Al2O3. The coating showed excellent corrosion resistance with and without paint. Superior anti-corrosive property of the coating results from the formation of the mechanically and chemically stable corrosion products, ZnCl2 −4Zn (OH)2, and the passivation in anodic polarization. The coating also showed good stone chipping resistance as well as paintability, formability, and weldability. Accordingly Al2O3 -dispersed Zn-Co-Cr alloy electroplated is suitable for application to both unexposed and exposure parts, including interior and exterior surfaces.