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Technical Paper

Properties of Precoated Galvannealed Steel Sheets for Lead-Free Automotive Fuel Tank Use

The goal of this study was to identify a pre-coated steel sheet that will satisfy press formability, seam weldability, spot weldability, brazing property, external corrosion resistance and internal fuel resistance. We established an experimental method for anti-fuel resistance measurement by applying synthetic spoiled gasoline by investigating the composition of spoiled gasoline and corrosion products in the fuel tank, which was collected in North America after 160,000 kilometers' running. Newly developed lead-free pre-coated steel sheet shows excellent anti-fuel corrosion resistance in comparison with that of usual terne coated steel sheet according to this method.
Technical Paper

Fatigue Properties of Nb-Bearing Stainless Steels for High Temperature Applications in Automobile Exhaust Gas System

Exhaust manifolds have been fabricated from stainless steels such as type 409 in place of cast iron in order to reduce the weight and to increase performance of the engine. In this paper, thermal fatigue and high temperature fatigue resistances of Nb-bearing ferritic stainless steels and type 409 have been investigated. The results obtained are as follows: Nb-bearing steels were superior to type 409 in high temperature fatigue resistance. Thermal fatigue resistance depended on a restraint ratio. The fatigue life of Nb-bearing steels was longer than that of type 409 in the condition of a low restraint ratio which might be near to the actual automobile exhaust system.
Technical Paper

Evaluation of the Corrosion Rate of Zn Coated Steel Sheets for Automotive Body Use

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.
Technical Paper

Development of Vibration Damping Steel Sheets for Automobile Oil Pans

Recently, Vibration Damping Steel Sheet (VDSS) has been increasingly used for automobile parts such as dash boards and partition panels. VDSS is also used in oil pans, but the rquirements in this application are much stricter than those in other auto applications. The material must remain sound (show no wall break) and not delaminate during deep drawing press forming. In service, it must be oil tight at the welded drain nut and must maintain good adhesion characteristics at high temperatures of 60-120°C. The VDSS with a thermoplastic resin core used to date in oil pans provides poor baking durability and heat durability in high temperature service. For use in oil pans, the authors therefore developed a new VDSS material comprising two extra deep drawing class steel skin sheets (of ultra low carbon steel) and a thermosetting polyester resin core layer containing metal powder.
Technical Paper

Corrosion Behavior of a Vehicle Submitted in Service in Subtropical Marine Environment of Okinawa Island for Eight Years

A passenger vehicle in the subtropical marine environment of Okinawa Island for eight years was submitted for corrosion investigation.The precoated sheet steels such as Zn-Ni and Zn-Fe showed excellent corrosion resistance in the door hem flange and a scribed outer panel, compared to cold rolled steel. Cosmetic corrosion of a North America vehicle was more severe than that of a Okinawa vehicle, but a similar corrosion rate for perforation was shown in door hem flange. Basic zinc chloride and β-FeOOH were observed by using micro X-ray diffraction method in the initial stage of corrosion, and then these changed to ZnO and α-FeOOH, Fe304.
Technical Paper

Corrosion Behavior of Organic Composite Coated Steel Sheet

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.
Technical Paper

Characteristics of Al2O3 Dispersed Zn-Co-Cr

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.