Materials Transactions Online

Transactions of the Japan Institute of Metals, Vol. 14 No. 4 (1973) pp.314-319
© 1973 The Japan Institute of Metals

Influence of High Hydrostatic Pressure on the Flow Stress of 18-8 Stainless Steel*

Atsushi Oguchi** and Susumu Yoshida**

An austenitic 18-8 stainless steel was tested in tension under hydrostatic pressure and the influence of hydrostatic pressure on its stress-strain behaviour was discussed. Tensile tests under constant pressures of 12000 kg/cm2 and atmos-pheric pressure and tests during which the ambient pressure was changed from 12000 kg/cm2 to atmospheric pressure and vice versa were carried out at room temperature. Also, the change in incuctance of a coil wound around the specimen was measured to evaluate the amount of α-martensite induced by plastic deformation. The results obtained are as follows: (1) Pressurizing at 12000 kg/cm2 gives no effect on the stress-strain relation of the annealed specimen at atmospheric pressure. (2) In the magnetic measurement, α-martensite cannot be observed over the range of less than about 10 % strain, whereas at a larger strain it begins to be induced and its amount increases similarly with increasing strain under both 12000 kg/cm2 and atmospheric pressure. But ε-martensite is observed by X-ray diffraction when the specimen is deformed under 12000 kg/cm2. (3) When the specimens are deformed under a constant pressure of 12000 kg/cm2, the increase in flow stress against that at atmospheric pressure is very large at the beginning of deformation, decreases with increasing strain, and then becomes almost constant (about 12 %) above about 15 % strain or more. (4) When the ambient pressure is changed between atmospheric pressure and 12000 kg/cm2 on the way of deformation, the flow stress changes 0 to 4 % at small strains and, about 12 % (pressure raising) and 19 % (pressure releasing) at 30 to 40 % strain. (5) The phenomena mentioned above in (3) and (4) can be explained by the fact that ε-martensite is induced rapidly at the beginning of deformation resulting in work-hardening under high hydrostatic pressure, while it easily transforms to α-martensite under a low tensile stress at atmospheric pressure at large strains.

(Received November 20, 1972)

* This paper was published originally in Japanese in J. Japan Inst. Metals, 36 (1972), 550.

** National Research Institute for Metals, Meguro-ku, Tokyo, Japan.

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