Abstract
The influences of austenitizing conditions on the microstructure of AISI M42 high-speed steel were investigated through thermodynamic calculation, microstructural analysis, and in-situ observation by a confocal scanning laser microscope (CSLM). Results show that the network morphology of carbides could not dissolve completely and distribute equably in the case of the austenitizing temperature is 1373 K. When the austenitizing temperature reaches 1473 K, the excessive increase in temperature leads to increase in carbide dissolution, higher dissolved alloying element contents, and unwanted grain growth. Thus, 1453 K is confirmed as the best austenitizing condition on temperature for the steel. In addition, variations on the microstructure and hardness of the steel are not obvious when holding time ranges from 15 to 30 min with the austenitizing temperature of 1453 K. However, when the holding time reaches 45 min, the average size of carbides tends to increase because of Ostwald ripening. Furthermore, the value of Ms and Mf decrease with the increase of cooling rate. Hence, high cooling rate can depress the martensitic transformation and increase the content of retained austenite. As a result, the hardness of the steel is the best (65.6 HRc) when the austenitizing temperature reaches 1453 K and is held for 30 min.
Highlights
High-speed steels (HSS) have been widely used to make engineering cutting tools in quenched and high-temperature tempered conditions due to their high hardness, wear resistance, and favorable high-temperature properties [1,2,3]
The mechanical properties of AISI M42 HSS are determined by the martensitic matrix and distribution of carbides
The AISI M42 high-speed steel scrap was melted in vacuum induction furnace and refined through electroslag remelting (ESR) furnace
Summary
High-speed steels (HSS) have been widely used to make engineering cutting tools in quenched and high-temperature tempered conditions due to their high hardness, wear resistance, and favorable high-temperature properties [1,2,3]. The cast structure of high-speed steel can be improved by subsequent heat treatment processes such as annealing, quenching, and tempering. High-speed steels have a ferrite matrix with plenty of undissolved carbides. Following quenching, they contain martensite, retained austenite, and undissolved carbides. It is known that microstructural factors like distribution of carbides, as well as characteristics of the martensitic matrix, play important roles in optimizing the properties of high-speed steel such as hardness, wear resistance, fracture toughness, and thermal-fatigue behavior
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