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Recently engin output and vehicle speed are much improved and there received much requests for better brake system with high performance and safety. In order to meet these reguests research work was initiated to develop new retavder system as auxiliary brake, and new compact & light weight retarder without requiring electricity consumption was successfully developed by using very strong parmanent magnet of Nd-Fe-B base for the first time in the world. This new retarder was marketed in the last January for the heavy duty truck followed medium duty tyuck in this April. This new retarder well matched with market needs has been highly commented upon beyond engineer expectation, and it is believed that this new system will be popularized very rapidly in Japan.

Hot rolled steel sheets having tensile strength of about 300MPa with excellent press formability have been developed by using RH-degassing process and hot rolling technology. The basic chemical composition of new steel is chosen as extra low carbon, low manganese and low nitrogen to improve ductility. In addition, controlled cooling on runout table or micro-alloying of niobium is applied to prevent the grain coarsening, which is caused by leaner compositions. These steel sheets have high elongation and excellent press formability. Furthermore, these steel sheets exhibit a high resistance to cold-work embrittlement. These properties are compared with those of DQ grade mild steel sheets and interstitial free steel sheets. In this paper, the metallurgical basis of these new steel sheets and their characteristics are described.