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We have developed a lead-free, free-machining 0.1 - 0.8% C steel for machine structural use, which demonstrates machinability almost equivalent to lead-containing free-machining steels. This free-machining steel is characterized by controlling the sulfide shape by Ca-Al deoxidation, and, unlike conventional Ca-deoxidized steels (1) and Al-deoxidized CaS free-machining steels (2), its machinability is improved with the aid of manganese-calcium sulphides which precipitate wrapping calcium-aluminate oxides. In order that these duplex inclusions generate, it is essential that the activity balance between [O] and [S] be controlled to 15 ≦ aS/aO ≦ 100. The free-machining steel which satisfies this activity balance has an outstanding machinability and fatigue strength, which are equivalent to lead containing steels. It has been under consideration to apply this novel free-machining steel to automotive parts such as crank shafts and connecting rods.

A lately established melting-refining-casting process for special steel and their qualities are described in this paper. The process consists of electric arc furnace melting, ladle furnace refining, vacuum degassing and continuous casting in this order. Such a complicated process has been put in the practice for the first time to manufacture particularly automobile steels. One of the advantages of this process is the reduction of impurities such as oxygen and sulfur Oxygen is evacuated during vacuum degassing treatment and sulfur is controlled through ladle furnace refining. As a consequence, cold formability is improved significantly. Mechanical reliability can be increased as well, and especially, it should be noteworthy that stress corrosion cracking of high strength fastners is able to be prevented by the reduction of sulfur. Consistent quality is an another major advantage of the process.

In hardfacing of automobile engine valves made of heat resisting steel such as 21-4N, conventional oxy-acetylene gas welding has been currently conducted manually by well trained operators because of using cast Stellite rods as the filler. In accordance with the strong demands of automatic welding, we newly developed an automatically controlled Plasma Powder Welding (PPW) system. This system is characterized by the application of a high thermal density plasma arc as heat source and by using powder filler which melts more easily than bar cast rods. Moreover, this PPW system has been applied to the automotive engine valve production line and resulted in the great contribution to manpower saving.

ABS sensor rings for automotive use are becoming smaller and thinner because of the demand for low cost and light weight. Such small thin parts are easier to break as they must withstand the same severe conditions as larger heavier parts. Superior elongation properties, after corrosion testing, are necessary for avoiding breakage and to obtain superior corrosion resistance. We have, therefore, developed such high performance P/M stainless steel with superior elongation and corrosion resistance. Conventional stainless steel has uniform pores on its inner surface which makes allows water penetration thus making corrosion worse and decreasing elongation. It is possible to increase corrosion resistance by changing pore structure (e.g. decrease continual pores) through the addition of special alloys that accelerate the sintering process.