抄録
The effects of 0•003 and 0•006% B on the transformation, hardenability, quenched and tempered hardness and mechanical properties etc. of Mn-Cr and Mn-Cr-Mo high tensile steels were investigated. The results obtained were as follows.
The Ac1 points were not affected by addition B, But Ac3 points were raised while Ar points were lowered. 0•003% B was more effective to increase the hardenability than 0•006% B and as compared with no adding B the hardenability increased remarkably by addition of B. The quenched and tempered hardness was not affected by addition of B above 300°C of tempering temperature. The yielding point tensile strength and impact value increased a little by addition of B, but elongation and reduction of area were not affected.
As one of the practical making processes of B steel, 400kg ingot was made by addition of B in the ingot mould while pouring the molten steel from ladle. The properties of this 400kg ingot were uniform and the effect of B on the ingot was the same as that of B on the small ingot which was made experimentally by a small furnace.
