Ductility tempered martensite

Austempering. Lower bainite is generally as strong as and somewhat more ductile than tempered martensite. Austempering, which is an isothermal heat treatment that results in lower bainite, offers an alternative heat treatment for obtaining optimum strength and ductility if the specimens are sufficiently small. 

Bolton [ ] reported that some b.c.c. Fe-Mn alloys were susceptible to tempered martensite embrittlement. Other data [ ] confirm this. The increase in the ductile-brittle transition temperature of Fe-12Mn by heat treatment at 350°C is shown in Fig. 2. This embrittlement appears to have a chemical origin whose nature is under investigation. 

To summarize, the relative hardness of the various phases discussed thus far (Brinell hardness values in parentheses) martensite (300-700) > tempered martensite (300-450) > bainite ca. 400) > fine pearlite (100-300) > coarse pearlite (100-220) > spheroidite (90-180). The hardness and brittleness of cementite is much greater than ferrite, whereas the latter has significantly greater ductility. 

Severe loss of ductility of a metal (or alloy) loss of load carrying capacity of a metal or alloy the severe loss of ductility or toughness or both, of a material, usually a metal or alloy. Many forms of embrittlement can lead to brittle fracture and many can occur during thermal treatment or elevated-temperature service (thermally induced embrittlement). Some of these forms of embrittlement, which affect steels, include blue brittleness, 885 °F (475 °C) embrittlement, quench-age embrittlement, sigma-phase embrittlement, strain-age embrittlement, temper embrittlement, tempered martensite embrittlement, and thermal embrittlement. In addition, steels and other metals and alloys can be embrittled by environmental conditions (environmentally assisted embrittlement). Forms of environmental embrittlement include acid embrittlement, caustic embrittlement, corrosion embrittlement, creep-rupture embrittlement, hydrogen embrittlement, bquid metal embrittlement, neutron embrittlement, solder embrittlement, sobd metal embrittlement, and stress-corrosion cracking. 

Tempered martensite a-Ferrite + Fe3C Very small FesC spherelike particles in an a-ferrite matrix Strong not as hard as martensite, but much more ductile than martensite... 

Tempered martensite is very strong but relatively ductile. 

Bainite has desirable strength-ductility combination but is not as strong as tempered martensite. 

Ferritic stainless steels contain more chromium than martensitic stainless steels to improve corrosion resistance. They cannot be hardened by quenching and tempering and have limited ductility in thicker sections. The base alloy is 430. They are used for heat exchanger tubes. See Figure 4-5. 

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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