Yield strength tempered martensite

The austenitic-ferritic steels, because of their two structural components also known as duplex steels, are chromium-nickel steels with chromium contents of about 21%-27%, and nickel contents of 4%-5%. They are usually made with about 3% molybdenum, nitrogen additions and a carbon content of < 0.03%. They reach the category of temperable martensitic steels with values for the 0.2% yield point of > 450 N/mm and are thus clearly above the austenitic steels. Worth mentioning are the good viscosity parameter values and the favourable fatigue strength properties of these steels, even in corrosive mediums. 

Figure 16.5 Comparison of (a) yield strength and (b) total elongation versus test temperature for conventional 9% Cr-2% W (Grade 92) ferritic-martensitic steel and two experimental heats of 9% Cr-2% WMnV next-generation steel designed using computational thermodynamics. Heat treatment conditions include both standard normalized and tempered (N T) and hot-roU thermomechanical treatment (TMT) conditions [87].

Alloys with Less Than 10 wt.% Mn. Alloys containing less than 10% Mn show transformation behavior similar to that of the Fe Ni alloys For Mn contents of 8 to 10%, the as-cooled structure is a dislocated lath martensite. Both the yield and tensile strengths of the alloys increase with Mn concentration. The ductile-brittle transition temperature, however, is high therefore, these alloys are unsuited for cryogenic service in the as-cooled conditions. As with Fe-Ni alloys, a tempering treatment in the two-phase (a + y) region causes a decrease in the ductile-brittle transition temperature of ferritic Fe-Mn alloys This beneficial tempering... 

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