Mitsubishi Jukogyo Kabushiki Kaisha

Humio Mitsuura

Fujimitsu Masuyama

High strength heat-resistant low alloy steels have a chemical composition of, on weight basis, a carbon content of 0.03-0.12%, a silicon content not higher than 1%, a manganese content of 0.2-1%, a phosphor content not higher than 0.03%, a sulfur content not higher than 0.03%, a nickel content not higher than 0.8%, a chromium content of 0.7-3%, a molybdenum content of 0.3-0.7%, a tungsten content of 0.6-2.4%, a vanadium content of 0.05-0.35%, a niobium content of 0.01-0.12% and a nitrogen content being 0.01-0.05% with the balance of iron and inevitable impurities, wherein the molybdenum content and the tungsten content satisfy the relationship 0.8%.ltoreq.(Mo+1/2W)%.ltoreq.1.5%; or a carbon content of 0.03-0.12%, a silicon content not higher than 1%, a manganese content of 0.2-1%, a phosphor content not higher than 0.03%, a sulfur content not higher than 0.03%, a nickel content not higher than 0.8%, a chromium content of 0.7-3%, a molybdenum content of 0.3-1.5%, a vanadium content of 0.05-0.35%, a niobium content of 0.01-0.12%, a nitrogen content of 0.01-0.05% and, occasionally, a further content of one or more of tungsten, in a content of 0.5-2.4%, boron, in a content of 0.0005-0.015%, aluminum, in a content not higher than 0.05%, and titanium, in a content of 0.05-0.2%, with the balance of being iron and inevitable impurities. The low alloy steels are obtained by subjecting a starting metal having the above chemical composition to a heat treatment by heating it to a temperature above 1100.degree. C. (A) and subsequent cooling to the ordinary temperature, then, subjecting the so treated metal to a plastic working at a temperature in the range from the ordinary temperature to a temperature at which no recrystallization occurs during the working or in the course of subsequent cooling and, finally, subjecting the so worked metal to a normalizing at a temperature lower than 1100.degree. C. (A) and to a tempering at a temperature below the Ac.sub.1 point.

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Nagasaki, Japan

Humio Mitsuura