Improvement of the cold resistance of the 09G2S steel by programmed hardening combined with additional medium-temperature tempering

The article discusses a method of improving the cold resistance of steels of a ferrite-pearlite class. It has been established that the process of programmed hardening, combined with an additional medium temperature tempering, has a positive effect on the cold resistance of thermally improved 09G2S steel. The mechanical properties of steel grade 09G2S were determined before and after additional tempering at mediumtemperature. It is shown that the new technology allows the critical temperature of brittleness, determined by the criterion of the energy intensity of failure, to be shifted to lower temperatures by 15°C, and at the same time to increase the impact strength of 09G2S steel three times more at a temperature of minus 90°C without changing its strength properties.

The Effect of Hot-Mounting on the Microstructure of an As-Quenched Auto-Tempered Low-Carbon Martensitic Steel

The effect of hot-mounting for metallographic studies of as-quenched low-carbon martensitic steels has been studied. Hot-mounting is typically carried out at 150–200 °C, i.e., a low-temperature tempering regime. Cold- and hot-mounted specimens from an as-quenched low-carbon auto-tempered steel were examined using a scanning electron microscope and their hardness levels were also compared. It was found that hot-mounting causes additional tempering that manifests as the appearance of new precipitates in those regions that are free of auto-tempered cementite. The observations were rationalized using DICTRA simulations to calculate the potential growth of cementite. Hot-mounting was also shown to cause a small but statistically significant increase in the hardness of the martensite.

The Effects of Post-Sintering Treatments on Microstructure and Mechanical Properties of Mn-Mo Steel

The effect of heat treatment on density, hardness, microstructure and tensile properties of Fe-0.85Mo-1.3Mn-0.6C sintered steel were investigated. Pre-alloyed Astaloy 85Mo, ferromanganese and UF4 graphite powders were mixed for 60 minutes in a Turbula mixer and then pressed in single-action die at 660MPa to produce green compacts (according to PN EN ISO 2740).The compacts were sintered in a specially designed semi-closed container at 1120 or 1250°C for 60 minutes in N2. The chemical composition of the sintering atmosphere was modified by adding getter and/or activator into the container. Two different types of heat treatment in nitrogen were carried out: sinteraustempering at 525°C for 60 minutes; and sinterhardening with additional tempering at 200°C for 60 minutes. The slightly better combination of strength and plasticity of steel for both sintering temperatures were achieved after sinterhardening+tempering variant. Average values of 0.2% offset yield stress, ultimate tensile strength and elongation after sintering in 1250°C, were 415MPa, 700MPa, and 2.0%, respectively.