The Effect of Heat Treatment on the Mechanical Properties of 17-7PH Stainless Steel

Abstract

The effect of heat treatment on the mechanical properties of 17-7PH (17% Cr, 7% Ni, 1% Al) stainless steel was investigated at room temperature. The specimens were given the following heat treatment conditions: (a) Solution treatment: 1050°C×15min, a.c. (b) Intermediate treatment: 760°C∼975°C×15min, a.c. (c) Subzero treatment: -78°C×8hr. (d) Aging treatment: 425°C∼575°C, 0∼70hr, a.c. The results obtained can be summarized as follows:(1) Austenite in the solution treatment could be transformed into martensite by intermediate and subzero treatments, so that tensile strength, yield strength, plane-bending fatigue limit and hardness increased, but elongation considerably decreased.(2) After subzero treatment, the mechanical properties of this steel increased a little with increasing intermediate temperature.(3) In the relation between aging conditions and hardness, the lower the aging temperature, the longer was the aging time that showed a maximum value of hardness, but its value rose high.(4) When the aging conditions continued within the temperature range of 425°C to 575°C for 2 hours, the maximum mechanical properties could be obtained at 500°C. In this case, there was hardly the effect of intermediate temperature except elongation.(5) When the specimens intermediate-treated at 950°C were aged at 500°C, these tensile strength, yield strength, fatigue limit and hardness were remarkably increased in the early stage of aging and showed the maximum values in 2 hours. But these elongation was nearly constant up to 7 hours.(6) In the condition of subzero treatment or aging treatment the ratio of the fatigue limit to the tensile strength was about one-third.