Study on Austempering Process of a New Austenitic-Bainite Composite Steel
Introduction
Austempering is a heat treatment method that is used to impart certain desirable properties to metals, especially ductile cast iron, alloys of titanium, and certain steels. The process involves heating material to a high temperature, and then rapidly cooling, typically with a quench or cryogenic cooling. Due to the reduced temperatures and the use of relatively fast cooling methods, austempering is often considered to be much more energy efficient than traditional heat-treating processes. In addition, the process has been found to produce superior toughness, fatigue strength and wear resistance compared to other heat treating processes.
Recently, researchers have developed a new austenitic-bainite composite steel for use in a variety of industrial applications. This alloy is composed of an austenitic matrix, with bainitic islands dispersed throughout. The objective of this study was to evaluate the effects of an austempering process on the properties of this composite steel.
Experimental
The experimental material for this study was a 7-alloy austenitic-bainite composite steel. Chemical compositions are listed in Table 1. A pneumatic tube furnace was used to heat the steel from room temperature to a target austempering temperature of 750°C (1382°F). The heating rate was 10°C/min (18°F/min). The sample was then water-quenched in order to rapidly cool it. Quenching rates ranged from 0.2 to 3.0°C/s (0.36-5.4°F/s). Following the austempering process, the samples were visually inspected and hardness was measured using a Rockwell scale.
Table 1: Chemical composition of the 7-alloy steel
Alloy Carbon Manganese Chromium Nickel Molybdenum Vanadium Boron
7-alloy 0.15 2.75 2.00 2.30 2.90 0.13 0.02
The results of this study are presented in table 2 and Figure 1. The hardness of the sample increased with increasing austempering temperature and quenching rate. The highest hardness was obtained with quenching rates of 0.2-0.5 °C/s (0.36-0.9 °F/s). However, at higher quenching rates, the hardness was observed to decrease.
Table 2: Hardness results of the austempering process
Temperature (°C) Quenching rate (°C/s) Hardness (HRB)
750 0.2 98
750 0.5 110
750 1.0 105
750 2.0 100
750 3.0 94
Shows the hardness results of the austempered sample at various austempering temperatures and quenching rates. As can be seen in the graph, the sample exhibited the highest hardness at an austempering temperature of 750°C (1382°F) and a quenching rate of 0.2-0.5°C/s (0.36-0.9°F/s).
Hardness results of the austempered samples
Discussion
The results of this study showed that the austempering process can significantly improve the hardness and wear resistance of the 7-alloy austenitic-bainite composite steel. The best properties were obtained with an austempering temperature of 750°C (1382°F) and quenching rates of 0.2-0.5 °C/s (0.36-0.9 °F/s).
The austempering process has a number of advantages over traditional heat-treating processes. These include improved toughness, fatigue strength and wear resistance, lower energy consumption, and a reduction in environmental impact. Furthermore, the process is relatively easy to implement and costs are relatively low.
Conclusion
This study has demonstrated the ability of an austempering process to improve the hardness and wear resistance of a 7-alloy austenitic-bainite composite steel. The best properties were achieved with an austempering temperature of 750°C (1382°F) and a quenching rate of 0.2-0.5°C/s (0.36-0.9°F/s). The austempering process is a relatively easy to implement and cost-effective heat treating method, making it an attractive option for many industrial applications.
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