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 i n such a manner that the X-ray integral intensities of 111.gamma. and 110.alph a. satisfy the formula (a): 0.005 <= 111.gamma./(111.gamma. + 110.alpha.) &l t;= 0.05 Such a metal structure can be obtained by the following procedure: the steel is heated at a temperature of the Ac3 point or more, and then cooled from 80 0 ~C to 400 ~C at a cooling rate of not less than 0.08 ~C/sec and further cool ed 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 strengt h, and further exhibits an excellent corrosion resistance, so that it is particularly effective as the material for constructing a deep oil well.