MARTENSITIC STAINLESS STEEL AND METHOD FOR MANUFACTURING SAME

摘要

A martensitic stainless steel provided includes C: 0.01 - 0.1% and Cr: 9 - 15%, and the retained austenite phase has a thickness not more than 100 nm in such a manner that the X-ray integral intensities of 111gamma and 110alpha satisfy the formula (a): 0.005 <= 111gamma/(111gamma + 110alpha) <= 0.05 Such a metal structure can be obtained by the following procedure: the steel is heated at a temperature of the Ac>3< point or more, and then cooled from 800 °C to 400 °C at a cooling rate of not less than 0.08 °C/sec and further cooled down to 150 °C at a cooling rate of not more than 1 °C/sec. The martensitic stainless steel according to the present invention has a relatively high carbon content and a greater toughness in spite of a high mechanical strength, and further exhibits an excellent corrosion resistance, so that it is particularly effective as the material for constructing a deep oil well.