No abstract

A low‐carbon, high‐strength steel is treated by different quenching and partitioning (QP) and quenching and tempering (QT) routes in a salt bath furnace, and its wear performance is evaluated by impact abrasive wear tests. It is observed as compared with the traditional QT steel; the QP steel manifests better wear performance at the quenching temperature of 220 °C. Stable film‐like retained austenite (RA) and fine martensite laths improve the wear resistance of the QP steel at the quenching temperature of 220 °C, whereas unstable blocky RA formed in the QP steel at the quenching temperature of 190 °C decrease the wear resistance. In addition, the lower critical impact stress for crack initiation at the higher impact energy decreases the wear resistance; however, the relative wear resistance is improved greatly at the higher impact energy due to the better fracture toughness of the QP steel. Moreover, the correlation of wear loss, hardness, and KIC is modeled to compare the wear resistances of the test steel after different heat treatments.

The microstructure and wear performance of a low-carbon steel treated by austempering below and above martensite start temperature (Ms) were investigated. The results show that the bainite, fresh martensite (FM) and retained austenite (RA) were observed in samples austempered above Ms. Except for the three above phases, the athermal martensite (AM) was also observed in samples austempered below Ms. The bainite transformation was accelerated and finer bainite was obtained due to the AM formation in samples austempered below Ms. In addition, the strength and hardness were improved with the decrease of the isothermal temperature and time, whereas the total elongation decreased with the increasing isothermal time and the decreasing isothermal temperature. Moreover, the materials austempered below Ms exhibited better wear performance than the ones treated above Ms, which is attributed to the improved impact toughness by the finer bainite and the enhanced hardness by AM. The best wear resistance was obtained in the samples austempered at 300 °C below Ms for 200 s, due to the highest hardness and considerable impact toughness.

The investigations on wear resistance, mechanical properties, and microstructure of three steels with different additions of chromium (Cr) and nickel (Ni) are conducted. Continuous cooling treatment is conducted to obtain martensitic/bainitic dual‐phase microstructure, and wear behavior is analyzed. The results indicate that Ni addition has no significant influence on the strength, hardness, and elongation but improves the low‐temperature impact toughness and reduces the weight loss due to the decrease in spalling wear. In addition, composite addition of Cr and Ni enhances strength, hardness, and elongation but decreases low‐temperature impact toughness. Although the weight loss of sample with the composite addition of Cr and Ni is small in the early stage of wear, the lower impact toughness results in the increase in chiseling wear, and the wear rate increases in the later stage of wear.

Unlike medium‐carbon and high‐carbon steels, the effect of the high‐temperature deformation process on the bainite transformation of low‐carbon steels is yet to be fully understood. Processes with varying high‐deformation temperatures and reductions are designed to investigate the bainitic transformation of low‐carbon steel. The results indicate that compared with the undeformed samples, for all deformation temperatures (850, 950, and 1050 °C) in the austenite temperature range, a small reduction of 5% accelerates the bainite transformation rate corresponding to the samples, and this can be attributed to the increase in the driving force. The promoting effect is increased with a decrease in deformation temperature. However, a relatively large reduction of the samples by 25% and 50% decreases the bainite transformation rate, and the inhibiting effect increases with decreasing deformation temperature. In addition, the amount of bainite increases at 1050 °C under all strains, and the amount is higher than the amount observed in undeformed samples. For the deformation temperature of 850 °C, the bainite amount increases under conditions of small reduction (5%), whereas the bainite amount decreases under large strain conditions (50% at 850 and 950 °C). The results provide a theoretical basis for optimizing the processing parameters associated with the production of low‐carbon bainite steels.