混粒に関する研究(I)

鋼質におよぼす混粒の影響について(その1)

抄録

The duplex-grains of austenite were divided into the "uniform duplex-grains" and the "non-uniform duplex-grains" with regard to its grain distribution pattern and the "duplexgrains in the McQuaid-Ehn grain size" and the "duplex-grains in actual grain size" with regard to the method of revealing them. Thus the effect of duplex-grain structures on properties of steel was studied quantitatively.
Carbon steels with 0.30, 0.70, 1.00%C and Ni-Cr-Mo case hardening steels with 0.20%C were used, and with most of these steels impact transition characteristics was investigated systematically, but with some steels tensile properties were also investigated.
Results of these investigations and some considerations are summarized as follows;
(1) Steels of the "non-uniform duplex-grains" in the McQuaid-Ehn grain size present similar duplex-grain structures also in actual grain size. Steels of the "uniform duplexgrains" in the Mc-Quaid-Ehn grain size, on the other hand, do not always develop duplexgrain structures in actual grain size, but ordinarily present fine-grained structures in it, unless its austenitizing conditions are so high temperature and so long time.
(2) Strength and ductility of steels are strongly influenced by their grain distribution pattern in the actual grain size; steels of higher degree of duplexity have lower strength and ductility and steels of the "non-uniform duplex-grains" have much less strength and ductility than those of the "uniform duplex-grains".
(3) Steels of the "non-uniform duplex-grains" in the McQuaid-Ehn grain size, therefore, are most undesirable with regard to strength and ductility, and steels of the "uniform duplexgrains" in the McQuaid-Ehn grain size, on the contrary, have ordinarily almost same degree of strength and ductility in actual heat treating conditions as that of steels of "fine-grains" in the McQuaid-Ehn grain size.