抄録
In the application field of self-drilling-tapping screws and joint parts like a high strength steel pin etc., high corrosion resistance as well as high strength property are required even in martensitic stainless steels, because commercial martensitic stainless steels have a large disadvantage in terms of corrosion resistance in comparison with austenitic stainless steels like SUS304. In this investigation, effects of alloying elements and microstructures on both of hardness and corrosion resistance in martensitic stainless steels are examined to improve the corrosion resistance of commercially applied high strength martensitic stainless steels. The results obtained are as follows.
(1) Corrosion resistance of martensitic stainless steels is improved to the level as same as SUS304 by suppressing the formation of δ-ferrite which leads to the promotion of Cr-carbide precipitation, and also by increasing the P. I. value; Pitting Index (=Cr+3%Mo+16%N) to 18 or more.
(2) On the hardening of martensite, carbon has 2.5 times larger effect than nitrogen, hence the hardness of as-quenched martensite can be linearly plotted to the value; (2.5C+N).
(3) Carbon contributes the significant hardening of martensite through the promotion of introduction of transformation twin and the refining of block structure.
