焼結鋼におけるCuの代替としてのBおよびCの添加

抄録

Copper is one of the most important alloying elements in sintered steel parts. However, reduction or removal of copper in the parts which are mainly used in automobiles is desirable for the promotion of recycling of steel from scrapped cars.
Calculation with a thermodynamic software and observation of slumping in shape of small compacts have indicated a low melting point near 1400K(1127°C)in the(lmass%Cr-0.7mass%Mn-0.3mass%Mo)steel-2.5mass%B-lmass%C powder mixture. The temperature is comparable to the melting point of copper or 1357K(1084°C). Thus, boron with carbon is a candidate replacement for copper at temperatures no higher than 1423K(1150°C)which can be easily reached in a conventional mesh belt furnace.
The addition of 2 mass% of the low-melting-point mixture or the combined addition of 0.05mass%B and lmass%C to the Cr-Mn-Mo steel has been proved to be effective in activating sintering. The addition has provided a reduction of sharp corners in the periphery of small pores, leading to a dimple fracture and an improvement in tensile strength of a basic Cr-Mn-Mo-lmass%C sintered steel by 15%.