Patent ID: 7186304
Filing Date: 2007-03-06
Classification: C22C,C23C,F16C

Abstract:
1. A process for forming a martensitic stainless steel which is case hardened comprising the steps of: forming an article from a material consisting essentially of from 8.0 to 18 wt % chromium, cobalt up to 16 wt %, vanadium up to 0.5 wt %, molybdenum up to 8.0 wt %, nickel up to 8.0 wt %, manganese up to 4.0 wt %, silicon up to 2.0 wt %, tungsten up to 6.0 wt %, titanium up to 2.0 wt %, niobium up to 4.0 wt % and the balance iron; and producing a hardened case containing from 0.2 to 0.55 wt % carbon and from 0.2 to 1.2 wt % nitrogen on said article; said hardened case producing step comprising carbo-nitriding said article to form at least one of a hard martensite phase and nitride precipitates, wherein said carbo-nitriding step comprises forming said at least one of a hard martensite phase and nitride precipitates by heating said material in an atmosphere containing carbon and nitrogen at a temperature in the range of 1650 degrees Fahrenheit to 2000 degrees Fahrenheit for a time in the range of from 40 to 200 hours.