抄録
A metallographical study has been carried out on the steel melted and cast under the 10 atmospheric pressure of nitrogen. The chemical composition of this steel is 16% Cr-3% Si-4% Ni-4% Cu-0.44% N-Bal Fe. Various factors have been clarified to obtain a high strength PH type stainless steel. The results may be summarized as follows:
(1) Thorough soaking at about 1100°C and repeated light deformations at the temperature in the initial stage of forging are necessary to hot-work without forming cracks in the cast ingot.
(2) The microstructure of the steel water-quenched from 1100°C after held for 10 min consists of austenite having a small amount of insoluble nitride particles. The austenite is still stable even after cooled down to −180°C. The higher the solution-quenching temperature, the less the amount of the insoluble nitride becomes.
(3) On tempering of the solution-quenched steel, the yield strength increases remarkably, and the ductility decreases. To make the steel strong and tough, it is adequate to hot-cold work during the tempering at 700°C of the steel water-quenched from 1100°C and subsequently reheat at 450°C for 60 min to relieve the internal stress. When 33% hot-cold rolled by the above treatment, the steel shows such an excellent final tensile properties as σB=129∼121 kg/mm2, σS=109∼116 kg/mm2 and δ=22∼23%.
