日本金属学会誌

J. Japan Inst. Metals, Vol. 2, No. 7 (1938),
pp. 341-351

Effect of Heat-Treatment on the Yield Point of Special Steels

Nobutaka Yamamoto1

1住友金屬工業株式會社製鋼所

Abstract:

The structural Ni-Cr steel, which has been quenched and tempered, takes various forms of stress-strain diagram at the yield point. In this investigation the effect of heat treatment (such as tempering temperature, tempering time, cooling velocity from tempering temperature, double-quenching, quenching velocity) on the form of stress-strain diagram of some special steels was studied. To measure the elongation in the tensile test Martens-Mirror-Extensometer has been used. The kinds of special steels used in the test were low Ni-Cr steel, 3% Ni-Cr steel, Ni-Cr-Mo steel, Cr-Mo steel and carbon steel.
The result of the test may be summarized as follows:
(1) The forms of stress-strain diagram of Low Ni-Cr steel and 3% Ni-Cr steel was just the same as that of low carbon steel, when test pieces were tempered at about 70° below the Ac1 point; however, the yielding phenomenon disappeared, when the tempering treatment was conducted at about 20° below the Ac1 point. The disappe-aring phenomenon of yield point was even more noticeable as the Ni content of the steel increased, and the same aring phenomenon of yield point was even more noticeable as the Ni conten of the steel increased, and the same phenomenon took place even at a lower tempering temperature as the carbon content increased.
The length of time in which the test piece was held at tempering temperature, and its cooling velocity from the tempering temperature have had almost no effect on the form of stress-strain diagram.
(2) The yield point and yielding phenomenon of Ni-Cr-Mo steel and Cr-Mo steel did not diminish, even when the tempering treatment was conducted at a temperature just below the Ac1 point. It is deduced therefore that Molybdenum acts to prevent the diminution of the yield point.
(3) In the case of carbon steel, the yield point, did not diminish, even. when test pieces were tempered at a temperature just below the Act point.
(4) The low Ni-Cr steel which has been double quenched and tempered is generaly believed to have no yielding phenomenon at the yield point, but it is ascertained that the low Ni-Cr steel shows a typical yielding phenomenon.
(5) Mildly quenched Ni-Cr and low Ni-Cr steel did not show the yielding phenomenon even when tempered at such a temperature, as may readily shows the yield point in the case of severely quenched test piece.


(Received 1938/02/02)

Keywords:


PDF(Free)PDF (Free)     Table of ContentsTable of Contents

Please do not copy without permission.