Microstructural transformation and hardenability of supercooled austenite in high-carbon low-alloy wear-resistant steel
The supercooled austenite of a HCL wear-resistant steel is typically initiated in a two-step process. Initially, austenite is cooled at a sufficiently slow rate in order to reach a bainite transformation point. During the second step, it is cooled more rapidly until the martensite transformation occurs. The strength and hardness of the resulting steel is highly dependent upon the extended tempering or quenching temperature range reached. In order to obtain adequate material properties, the steel must be quenched to below the bainite transformation point.
While it is possible to obtain excellent properties in a HCL wear-resistant steel through the supercooled transformation process, it is also possible to obtain inadequate properties due to inadequate hardenability. Hardenability is a term used to refer to the amount of austenite that is retained in the steel upon cooling, and is typically enhanced through alloying elements such as nickel and molybdenum. Inadequate hardenability results in the premature transformation of austenite into ferrite-carbide or bainite, along with a higher retained austenite fraction. The high retained austenite fraction results in reduced mechanical properties, including decreased strength and hardness.
In order to ensure adequate hardenability and to result in favorable mechanical properties, it is often necessary to utilize an appropriate heat treatment process. This process typically involves pre-heating, austenitizing and quenching, followed by a tempering treatment. During the pre-heating stage, the desired temperature ranges for the austenitizing and quenching stages are determined. The quenching stage is the most critical when it comes to the supercooled austenite transformation process. The steel is quenched rapidly and uniformly, leading to the desired transformation of the supercooled austenite.
The hardenability of the HCL wear-resistant steel is therefore dependent on the quenching temperatures achieved, as harder steel can be produced when the formations of alloy carbides are promoted in the microstructure. The transformation process results in the formation of martensite, along with other microstructural components such as bainite, ferrite and/or pearlite in various proportions depending on the quenching temperature and time.
The microstructure resulting from the supercooled austenite transformation process is typically comprised of a heterogeneous mixture of primary and secondary phases. The primary phases, such as martensite or bainite, are the main contributors to the final steel properties, while the secondary phases, such as pearlite or fractured carbides, help to further refine the microstructure. The tool wear resistance and fatigue strength of the steel are improved when the retained austenite fraction is reduced.
In summary, the supercooled austenite transformation process is essential to obtaining the desired physical and mechanical properties in an HCL wear-resistant steel. The hardenability of the steel is primarily determined by the quenching temperature achieved, which can vary depending upon the alloying elements present in the material. In order to obtain the maximum hardness and wear resistance, the retained austenite fraction must be minimized. The supercooled austenite transformation process results in a heterogeneous mixture of primary and secondary microstructural components, helping to refine the material properties.
Conatct us
