Abstract
This work presents the results of phase transformation kinetics during continuous cooling in newly developed high strength low-alloy steel (HSLA). Initial theoretical calculations for the determination of heat treatment parameters were conducted. To determine the structural constituents formed due to the austenite decomposition the dilatometry approach was used. The material was cooled down from the austenitization temperature of 1000 °C with cooling rates between 0.1 °C/s to 60 °C/s. Then, light and scanning electron microscopy investigations were carried out. The microstructure after cooling at rates between 0.1 °C/s up to 1 °C/s is mainly ferritic with some fraction of granular bainite. Increasing the cooling rate led to formation of a higher fraction of bainitic ferrite. At 60 °C/s the microstructure was mainly bainite with some fraction of ferrite. To determine the presence of retained austenite, color etching using Klemm solution was used. The results show that the increase of cooling rate decreases the amount of retained austenite in the microstructure of the steel. Hardness measurements were made to determine the changes in the mechanical properties as a function of the cooling rate.
Highlights
The Ae1 and Ae3 temperatures are 686 and 836 ◦ C, respectively
Cementite formation starts at 707 ◦ C, and the highest amount of it is at 660 ◦ C and is equal to 2.4%
The results present the dilatometric curves, which present the relative change in length (RCL) as a function of temperature
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Developed construction materials need to have a high strength, ductility, resistance to cracking— at low temperatures. In the case of steels intended for forging, it is very important to ensure adequate hardenability and machinability and at the same time limited cost determined by the concentration of alloy elements. Many of the listed properties require a different material development approach because their simultaneous fulfillment is a very difficult challenge for material science engineers [1,2,3]
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