Microstructure investigation and flow behavior during thixoextrusion of M2 steel grade

•Typical microstructure for thixoforging process can be obtained by directly heating on the hot formed and annealed stated.•Morphology varies with the penetration of the punch during forming.•Successful thixoforging process can be performed with low liquid fraction.•Material flow mechanisms are proposed.

The microstructure investigation and flow behavior during thixoforging of M2 steel parts were investigated. Partial remelting was performed at processing temperatures ranging from 1290 °C to 1340 °C corresponding to a liquid fraction range between 10% and 30% (according to differential scanning calorimetry measurements and quantitative image analyses). A conventional microstructure for thixoforming process was obtained: spherical solid grains surrounded by liquid phase. The microstructure across the heated billets was relatively homogeneous with bigger grain size near the surface. Successful thixoextrusion for producing parts was finally achieved at processing temperatures. By investigating the microstructure and load-displacement curves, different mechanisms in various forming stages were proposed.