Microstructure Evolution and Tensile Properties of Cold-Rolled and Annealed Fe-30Mn-0.14C-7Cr-0.26Ni Steel

The carbide precipitation, microstructure evolution, and tensile properties of Fe-30Mn-0.14C-7Cr-0.26Ni (in wt pct) steel after cold rolling to 95 pct reduction followed by annealing at temperatures ranging from 600 degrees C to 900 degrees C for 1 hour were investigated. The results show that, when the annealing temperature is increased from 600 degrees C to 900 degrees C, the grain size increases from 0.65 +/- 0.30 to 5.75 +/- 3.87 mu m. When the annealing temperature is 600 degrees C, Cr23C6 carbides begin to precipitate. When the annealing temperature is increased from 600 degrees C to 800 degrees C, the average size of carbides increases from 39 to 69 nm. When the annealing temperature is increased to 900 degrees C, no carbides are produced due to the increased solubility of C in the austenite matrix. Ultrafine grains (similar to 0.8 +/- 0.58 mu m) with a large amount of nanoscale carbides (similar to 53 +/- 21.8 nm) were obtained after annealing at 700 degrees C, resulting in a good combination of yield strength (679 MPa) and total elongation (38.4 pct). The fraction of deformation twins within the samples under different tensile strains was calculated, and it was revealed that grain refinement can seriously inhibit the generation of deformation twins. In addition, it has been found that grain refinement strengthening, precipitation strengthening, and dislocation strengthening have significant effects on yield strength, while the effects of solution strengthening and lattice friction are relatively weaker.