Nonequilibrium Austenite Phase in Melt-quenched Fe-C-Mo and Fe-C-W Alloys

Abstract

By melt-quenching technique, nonequilibrium austenite alloys possessing high strength and hardness combined with good ductility have been found in Fe-C-Mo and Fe-C-W ternary systems. This formation region is limited to about 1.02.4 wt%C and 322 wt%Mo for Fe-C-Mo and 1.02.4 wt%C and 324 wt%W for Fe-C-W. The austenite phase has ultre-fine grains of about 0.2 μm in diameter. Their Vickers hardness and tensile strength increase with increase in the amounts of C and Mo or W, and the maximum values attain about 710 DPN and 1450 MPa for Fe-C-Mo and about 700 DPN and 1500 MPa for Fe-C-W, respectively. Elongation increases with decreasing C and Mo or W contents and reaches about 2% for Fe-1.4%C-9%Mo and Fe-1.4%C-15%W. The relatively large elongation at low concentrations of C and Mo or W results from the transformation-induced plasticity of austenite to martensite. In addition, the changes in microstructure and mechanical properties of the tempered austenitic alloys have been investigated and it has been observed that a large secondary hardening occurs in a wide range of about 600900 K for Fe-C-Mo and 500900 K for Fe-C-W. The hardening is due to bainite transformation from austenite to ferrite and M₃C in the temperature range from 500 to 700 K and due to the formation of carbide in the range from 700 to 900 K and martensite transformation after tempering. Thus the present alloys may be attractive as fine gauge high-strength materials.