Аналіз деформаційного зміцнення ADI при температурах ізотермічного загартування

The effect of isothermal hardening temperature on the mechanical properties of ADI materials is investigated. The heat treatment of the test samples amounted to heating above the temperature of transformation of the ferrite component in austenite and isothermal hardening at temperatures from 280 to 380 °C. In the indicated temperature ranges, the plastic characteristics and strength parameters of the samples were studied depending on the heat treatment conditions. Particular attention is paid to the strain hardening parameters. It was found that at isothermal hardening temperatures in the range of 330-360 °C with plastic deformation, the TRIP effect appears, the appearance of which is accompanied by a high hardening rate due to the conversion of residual austenite to martensite. Plastic characteristics change with increasing quenching temperature. At 280 °C, the strength and hardness of the metal is maximum, and the plastic properties are minimal. The mechanical properties of the studied bainitic iron, quenched at various temperatures, satisfy ASTM 897-90 requirements except for samples quenched at 400 °С. Hardness, yield strength, and tensile strength decrease with increasing quenching temperature, ductility and impact strength increase. During compression, two sections of hardening are observed: in the region of small deformations, the rate of change of stress is higher, the lower the temperature of quenching, in the region of large deformations, on the contrary, the rate of hardening is much higher in materials quenched at higher temperatures. The effect is explained by a change in the hardening mechanism from dislocation - at small strains to the TRIP effect at large.