Patent ID: 8357247
Filing Date: 2013-01-22
Classification: C22C,F16D

Abstract:
1. A hot-rolled and stamped sheet made of a martensitic stainless steel, the steel comprising: less than 0.050 mass % carbon, 1.0 mass % or less silicon, 2.0 mass % or less manganese, 0.04 mass % or less phosphorus, 0.010 mass % or less sulfur, 0.2 mass % or less aluminum, chromium in a range of from more than 11.5 mass % to 15.0 mass %, nickel in a range of from 0.5 mass % to 2.0 mass %, copper in a range of from more than 0.50 mass % to 4.0 mass %, niobium in a range of from 0.15 mass % to 0.6 mass %, less than 0.09 mass % nitrogen, 0.0005 mass % to 0.0050 mass % calcium, and iron and unavoidable impurities, wherein the carbon content, the nitrogen content, the niobium content, the chromium content, the silicon content, the nickel content, the manganese content, and the copper content satisfy the following relationships (1) and (2): the steel sheet being 90 percent to 100 percent martensite on a volume basis, and the remainder of the volume of the steel being ferrite, the martensite and the ferrite being formed by subjecting the steel to heating at 900° C. to 1000° C. and hardening by cooling at a cooling rate of air-cooling or higher, the steel sheet having a hardness of 32 to 38 in HRC, a hardness of 32 or more in HRC when the steel is further tempered at 650° C. for one hour, a hardness of 30 or more in HRC when the steel is further tempered at 670° C. for one hour, a Charpy impact value of 50 J/cm wherein the steel sheet is in a shape of a disc brake.