The metallographic study has been carried out on the steel having the chemical composition 16%Cr-3%Si-4%Ni-4%Cu-0.44%N-Bal Fe which had been melted in magnesia crucible under ten atmospheric nitrogen by the induction heating and had been cast under the same pressure, and various factors in the steel to obtain a high strength PH type stainless steel have been clarified. The result is summarized as follows:<BR>(1) Thorough soaking at about 1100°C and repeated light deformations at the temperature in the initial stage of the forging are necessary in order to hot-work without forming cracks in the cast ingot.<BR>(2) The variation in nitrogen concentration occurs on the surface of the steel due to heating atmospheres; in the heating in vacuum and in argon—the denitrogenization, and in the heating in one atmospheric nitrogen—the nitrogen absorption. The weight increase due to the heating in air arises from both the oxidation and the nitrogen absorption on the surface of the steel.<BR>(3) The microstructure of the steel water-quenched at 1100°C after held for 10 min consists of austenite having a small amount of insoluble nitride particles. The austenite is still stable even if cooled to −180°C. The higher the solution-quenching temperature, the less the amount of the insoluble nitride becomes.<BR>(4) Precipitants, probably as Cr₂N and Cu-rich solid solution, form in the austenite by the tempering at 500°∼550°C after the solution-quenching. If the tempering at 500°∼550°C is prolonged, a small amount of martensite is found to be formed at below −100°C by the subsequent subzero-cooling after the tempering. Both the precipitation and the ferrite formation from the austenite are found to proceed during the tempering at 700°C simultaneously. By the subsequent cooling from the tempering temperature, the remaining austenite transforms into martensite at temperatures considerably higher than room temperature.<BR>(5) On tempering of the solution-quenched steel, the strength increases, while the ductility decreases, the values being relatively low; σ_B=93 kg/mm², σ_s=80 kg/mm², δ=18.5%. 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 at 1100°C, followed by the reheating at 450°C for 60 min to relieve the internal stress. When hot-cold rolled 33% in the above treatment, the final tensile-properties are found to be σ_B=129∼121 kg/mm², σ_s=109∼116 kg/mm², δ=22∼23%. Stronger magnetism and lower σ_s are obtained by the hot-cold working in the earlier stage of the tempering.