Effects of alloying elements in hadness modification during heat tratment of high speed steels

Abstract:

The performance of high speed steels has always been related to the hardness and toughness both from the bulk material and from the elements of the microstructure separately. The hardness of the matrix, depending on the solidification, quenching and hardening, is the focus of this study. It has been reported that, during tempering, higher carbon activity can lead to higher precipitation of secondary carbides, along with an easier decomposition of retained austenite. These two phenomena can generate an increase in the hardness of high speed steels. In order to study this, thermodynamic calculations were made to evaluate the effect of some non-carbide forming elements, such as nickel and cobalt, in carbon activity using the ThermoCalc software. Based on these calculations, some compositions were selected to be produced in pilot scale. The alloys were heat treated and the matrix hardness was measured using microindentation Vickers. The metallic matrixes of these steels were also characterized using SEM to visualize and evaluate the effects of the modifications in the products of decomposition of austenite and secondary carbides distributed on the microstructure. Carbon activity during tempering calculated from thermodynamic calculations revealed not to be the only factor involved in the hardness effect promoted by cobalt.


Reference:
ANDRADE, Roberto Silva; BRAGA, Ana Paola Villalva; CARVALHO, Felipe Moreno Siqueira Borges de; PAULO, Glauco; BOCCALINI JUNIOR, Mario. Effects of alloying elements in hadness modification during heat tratment of high speed steels. In: INTERNATIONAL TOOLING CONFERENCE, 11., 2019, Aachen, Alemanha. Proceedings… 8 p.

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