| 摘要 |
PURPOSE:To prevent the formation of coarse grains of austenite crystal grains by the carburizing and nitriding at high temps. after rolling by rolling carbon steels and low alloy steels wherein the contents of Al, Ti, N and the upper limit value of B are limited, under specific conditions. CONSTITUTION:The carbon steel or low alloy steel which contains 0.015-0.07% Al, 0.007-0.07% Ti and 0.013-0.03% N, and wherein the content of B is limited to <=0.0005% is used as steel for carburization or steel for carburization and nitridation. The ingots or continuous casting ingots of such carbon steel and low alloy steel are bloomed at >=1,200 deg.C and are further rolled at >=800 deg.C end temp. of rolling without reheating in the stage of rolling in succession to said treatments. After the end of the rolling, the ingots are slowly cooled so that the texture of the steel after the cooling consists essentially of ferrite and pearlite. If such steel is carburized and nitrided at a high temp. of >=950 deg.C, fine austenite texture is formed, and the generation of strain owing to heat treatment and the decrease in strength are obviated. |
