Heat treating response of 0.6 C steels for saw chain applications

Abstract

Steels used in saw chain applications require a combination of strength, toughness, and wear resistance. The focus of this project is to develop improved steels for saw chain applications by utilizing alloying and processing techniques to improve upon the current generation of saw chain steels. This is accomplished by studying the relationship between heat treatment processing and the corresponding microstructures and properties of two medium carbon low alloy steels. The first alloy is designated OCS 01 and is similar to a lean alloyed 8660 steel. The second alloy is a high silicon 9260 alloy, chosen for its ability to produce austenite containing microstructures in the carbon and hardness range of interest for current saw chain steels. Austempering, quenching and tempering (Q&T), and quenching and partitioning (Q&P) (9260 only) processing methods were simulated. For Q&P processing, the volume fraction of retained austenite decreased with time at higher partitioning temperatures, due to decomposition of the austenite to ferrite and iron carbides. Higher austempering temperatures decreased the time to reach bainitic transformation stasis, and increased the volume fraction of retained austenite. The austenite carbon content increased with time for each Q&P partitioning temperature evaluated. Vickers hardness measurements showed a consistent decrease in hardness with increased time and temperature when partitioning or tempering, as well as a decrease in hardness with increased isothermal austempering temperature. Charpy impact testing showed that the Q&P processing conditions of the 9260 alloy offer a significant improvement in Charpy impact energy absorbed at room and low ( 29 °C ( 20 °F)) temperature when compared to the 9260 austempered and Q&T conditions at equivalent hardness. DSRW wear testing showed that the Q&P 9260 conditions have improved low-impact abrasive wear resistance at equivalent hardness when compared to all other conditions evaluated. 9260 Q&P conditions had greater combinations of wear performance and Charpy impact performance when compared to the austempered and Q&T 9260 conditions. Tensile testing results showed that select 9260 processing conditions offer improved tensile properties (yield strength, peak stress, uniform elongation, and/or total elongation) when compared to the OCS-01 processing conditions. Increased amounts of retained austenite were observed to increase the total elongation of 9260 Q&P conditions, and increase the product of tensile strength and total elongation. A 9260 Q&P condition was identified, which offers improved combinations of tensile strength, uniform elongation, total elongation, and wear performance when compared to the OCS-01 conditions evaluated.