A study on the effect of the solution treatment temperature on austenite decomposition and mechanical property changes in a series of Fe-30Mn-9Al-xC alloys has been undertaken.
These alloys after solution treatment above 1000℃ show typical austenitic microstructures except an alloy (x=0.49) with a duplex structure of austentite and δ-ferrite phases because of its lower carbon and higher Al concentration.
To attain satisfactory heat treatment condition for high austenite stability and high mechanical properties, hardness tests have been also conducted and the results indicate that the optimum treatment procedure is 1100℃ solution treatment and subsequent aging at 500℃. The tensile tests of all the alloys which are solution-treated at 1100℃ and aged at 500℃ exhibit high yield strength, ultimate tensile strength and satisfactory elongation.
The austenitic decomposition rate during aging above 600℃ is higher when the preceeding solution treatment temperature has been lower.
The precipitate phase on aging above 600℃ has been identified as cubic (Fe, Mn)$_3Alc$ carbide of perovskite structure.
All the alloys have manifested the precipitation hardening on aging at 500℃.
In the alloy with high carbon content (x=0.84), a carbide phase of submicron size seems to have precipitated at the grain boundaries on aging at 500℃. This particular alloy has shown intergranular fracture in tension test with negligible small elongation.
