Solidification microstructure and M2C carbide decomposition in a spray-formed high-speed steel

Abstract

The solidified carbide morphology, the decomposition behavior of the M 2 C carbide, and the carbide distribution after forging of an Fe-1.28C-6.4W-5.0Mo-3.1V-4.1Cr-7.9Co (wt pct) high-speed steel prepared by spray forming have been investigated. The spray-formed microstructure has been characterized as a discontinuous network of plate-shaped M 2 C carbides and a uniform distribution of fine, spherical MC carbides. The metastable M 2 C carbides formed during solidification have been fully decomposed into MC and M 6 C carbides after sufficient annealing at high temperatures. Initially, the M 6 C carbides nucleate at M 2 C/austenite interfaces and proceed to grow. In the second stage, the MC carbides form either inside the M 6 C carbides or at the interfaces between M 6 C carbides. With this increasing degree of decomposition of the M 2 C carbide, the carbides become more uniformly distributed through hot forging, which produces a significant increase in ultimate bend strength. The decomposition treatment of M 2 C carbide has been found to be most important for obtaining a fine homogeneous carbide distribution after hot forging.

Morphology and Properties of M2C Eutectic Carbides in AISI M2 Steel

“…Many researchers have studied the decomposition process of lamellar M 2 C, which can be described by the following formula M 2 CϩFe(g)→M 6 CϩMC. 8,9) In contrast, the properties and decomposition process of rod-like M 2 C have been rarely reported so far. Little is known about the effect of morphology change of M 2 C on the microstructure and mechanical properties of final products.…”

“…8,9) Compared with M 6 C, MC is rich in vanadium and can also be signified as VC. The differences of thermal stability between the lamellar and rod-like M 2 C are investigated in this section.…”

Ferramentas De Usinagem Em Aço Rápido Aisi M2 Obtido Por Conformação Por “spray”.

“…É o caso de ligas que têm intervalo de solidificação grande, de difícil controle da solidificação e materiais altamente ligados de difícil controle microestrutural [45] .…”

“…Os aços rápidos, em particular, se caracterizam por um longo intervalo de solidificação e reações eutéticas complexas, que resultam em segregação dos elementos de liga e formação de diferentes tipos de carboneto durante a solidificação [44,[45][46][47] .…”

“…A técnica de conformação por "spray", permite a minimização destes problemas, e tem se mostrado tão eficiente quanto à técnica da metalurgia do pó, com a vantagem de que, o material pode ser obtido em uma única operação, o que proporciona redução de custos [45] .…”