Heat treatment of the increased stability die steel

Abstract

In the work, the heat treatment conditions of 4H4N5M4F2 die steel for hot deformation are investigated. The physico-mechanical properties of the investigated ingot steel were determined after quenching 1100 ± 5 °С and tempering. Given the importance of cooling regimes after tempering, various cooling regimes (in oil, in a furnace, in air) were investigated. Physical-mechanical properties of cast steel 4X4H5M4F2 after tempering at 550 ± 5 °C and 600 ± 5 °C were determined. The optimal tempering regime for steel at 550 ± 5 °C with air cooling was established: the ultimate strength of 1860 MPa and the yield strength of 1760 MPa. The optimal tempering regime for steel at 600 ± 5 °C with air cooling has been established: the ultimate strength is 1600 MPa, the yield strength is 1500 MPa, and the heat resistance is 48.5 HRC. It was established that twofold hardening and tempering of steel at 600 ± 5 °C temperature with oil cooling leads to an increase in its fracture toughness (75 J/cm2) compared with the fracture toughness after air cooling (30 J/cm2). It is established that the temperature range of tempering brittleness of the studied steel is 465 ‑ 495 °С. The optimized temperature regime of tempering of the investigated steel (590 ± 5 °С) made it possible to increase the impact strength by a factor of two (up to 30 J/cm2) in the temperature range 465 ‑ 495 °С. A pilot test of the punch tool made from the investigated steel was carried out. During hot pressing of the AK7ch aluminum alloy, the life of the dies was at the level of forged steel 4Kh5MF1S with a nitrided surface layer, which was used at the factory. After the operation of both matrices (hot deformation), samples were cut and tested for hardness and toughness. The latter turned out to be higher for the forged steel, however, the service life of the matrices from both steels was at the same level.

Keywords

• die steel
• composition
• thermal treatment
• structure
• mechanical properties.