日本金属学会誌

J. Japan Inst. Metals, Vol. 31, No. 7 (1967),
pp. 846-850

Effect of Al upon Phase Changes in 17-7 PH Steel (On the Nature of Age-Hardening of 17-7 PH Steel, I)

Natsuo Yukawa1, Masayoshi Mizutani2 and Hiroyasu Saka1

1Department of Metallurgy, Faculty of Engineering, Nagoya University, Nagoya
2Toyota Central Research and Development Laboratories Inc., Nagoya

Abstract:

In order to clarify the nature of age-hardening of 17-7 PH steel, the constitution of alloys containing 16∼19%Cr, 7%Ni, 0∼10%Al and the remainder Fe was investigated physico-metallurgically, through which the sectional diagram of the (17Cr-7Ni-Fe)-Al system was determined.
In this system, there exist δ (α) (bcc), α ' (ordered bcc of CsCl type based on NiAl) and γ (fcc) phases, of which the γ phase last transforms to martensite (αM) by quenching from 1050°C. On aging between 400°C and 600°C, α ' precipitates from both αM and δ matrices.
In commercial 17-7 PH steel containing about 0.07%C, M23C6 is formed in addition to the above-mentioned phases. In this case, however, γ is so stable that it is retained to room temperature during cooling from 1050°C. On annealing this metastable γ at about 800°C, it transforms to αM by subsequent cooling owing to the precipitation of M23C6. On further aging between 400°C and 600°C, α ' as well as M23C6 precipitates from αM and δ matrices, but the amount of the latter is negligibly small.


(Received 1967/1/6)

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