Improvement of High Temperature Strength of Type 304 Stainless Steel by Small Additions of Titanium and Niobium

Abstract

A heat of type 304H steel which shows the highest creep-rupture strength in the tests of our laboratory has considerably iigh creep-rupture strength at long times and seems to have even higher strength than that of type 316H steel. If such 403H steel is always available, the profit m ould be expected very much to reduce the construction cost of boiler plants.
The difference of the strength in commercial heats can be explained by that of the electron microscopic structure, showing that the heat of higher strength has very fine and good distribution of M₂₃C₆type carbides and they have a resistance to coalesce to longer times-due to the presence of small amounts of titanium and niobium. An experimental heat of type 304 steel containing 0.16%C, 0-10%Ti and 015% Nb had much higher creep-rupture strength than that of type 316H steel and showed itself to be very much economical new stainless steel for high temperature use. And also it was found that at C/(Ti+Nb) atomic ratio of about 4 the maximum high temperature strength is obtained and precipitated carbides distribute themselves very finely and uniformly.