Effect of High Nitrogen Addition on Microstructure and Mechanical Properties of As-cast M42 High Speed Steel

Abstract

This study systematically investigated the influence of high nitrogen (N) addition (0.205 wt.%) on microstructure and mechanical properties of as-cast M42 high speed steel. The results demonstrate that the conventional and high-nitrogen M42 cast ingots are mainly composed of martensite, retained austenite and various precipitates (M 2 C, M 6 C as well as MC in M42 cast ingot or M(C, N) in M42N cast ingot). The addition of N could increase the retained austenite content, trigger the transformation of MC to M(C, N), favor the formation of M 2 C at the expense of M 6 C, and improve the distribution uniformity of M 6 C at the macroscopic scale. Moreover, the addition of N could lead to the reduction of the secondary dendrite arm spacing as well as the decrease of the thickness and area fraction of eutectic carbides, and improve the distribution uniformity of eutectic carbides at the microscopic scale. The M(C, N) particles form directly from the liquid phase prior to the formation of primary austenite, which could act as the heterogeneous nuclei of primary austenite and thus promote the refinement of the as-cast microstructure. The addition of N slightly decreases the macro-hardness and ultimate compression strength of the cast ingot but increases its ductility, which could be ascribed to the increase of retained austenite content and the reduction in the amount of eutectic carbides. Therefore, high N addition can significantly improve the as-cast microstructure of M42 high speed steel, which is promising for the further enhancement of the mechanical property and service life of the final product.KEY WORDS: M42 high speed steel; pressurized metallurgy; nitrogen; as-cast microstructure; precipitates; mechanical property. N i J J J J J D

Evolutions of Micro- and Macrostructure by Cerium Treatment in As-Cast AISI M42 High-Speed Steel

“…This result is consistent with our previous reports. [1,12] In this paper, the bright white region is called as the M 6 C region. As shown in Figure 9(a), M 6 C regions of Ce0 steel are mainly distributed in the center of the cross section and exhibit a large block-like morphology.…”

“…Therefore, Ce 2 O 2 S and Ce 2 O 3 can serve as heterogeneous nucleation sites for primary austenite during solidification, which is beneficial to the refinement of the dendrite structure. [12,21] In addition to heterogeneous nucleation, the constitutional supercooling and intermetallic phases also have significant effects on the dendrite structure. Due to the low solubility of Ce in austenite phase, the addition of Ce will strongly segregate and enrich into the liquid phase at the dendrite forefront during solidification, [21,41,42] which is confirmed by the experimental result that Ce segregates into the interdendritic regions ( Figure 6(h)).…”

“…Consequently, the lattice disregistry between eutectic carbides (M 2 C and M 6 C) and Ce-containing inclusions (Ce 2 O 2 S and Ce 2 O 3 ) were calculated. Based on our previous study, [12] the structure of M 2 C carbide is close-packed hexagonal (HCP) with the lattice parameter a = 0.302 nm and c = 0.472 nm, the structure of M 6 C carbide is face-centered cubic (FCC) with the lattice parameter a = 1.116 nm. As shown in Table V,…”

“…[2,[8][9][10][11] In addition, the difference in the cooling rate from the center to the edge of the cast ingot results in a serious non-uniform distribution of M 6 C eutectic carbides at the macroscopic scale. [1,12] Therefore, improving the as-cast structure is of significance for M42 HSS to obtain the superior overall performance.…”

Effects of Nitrogen on the Microstructure and Mechanical Properties of Fe–28Mn–10Al–0.8C Low‐Density Steel

“…[5][6][7][8][9][10] Many researchers have confirmed that nitrogen can improve the mechanical properties of various steels. [11][12][13][14][15][16][17][18] Gu and Wang et al [11,15] reported that nitrogen could promote the precipitation of V(C, N) and (Ti, Nb)(C, N) and could refine the grains of Cr-Mo-V die steel and pipeline steel. Feng et al [16] concluded that the addition of nitrogen inhibited the formation of δ-ferrite and refined the prior austenite grains in high-nitrogen martensitic stainless steel.…”