Effect of Nitrogen on the Microstructure and Hardness of High-Carbon High-Speed Tool Steel Type Alloys

Abstract

The effect of nitrogen addition on the microstructure formation and hardness during solidi cation and heat treatment was investigated and the possibility of nitrogen as an alloying element was discussed in terms of alloy chemistry for high-carbon high-speed tool steel type cast alloys. Nitrogen with a concentration from 48 ppm to 1542 ppm was successfully introduced by mixing Cr 2 N into a molten alloy. Analysis of the diffraction pattern revealed that the primary V 2 CN carbonitride crystallized upon the addition of nitrogen, whereas eutectic carbides mainly formed in N-free specimens. The chemical composition of the carbonitride is also affected by the addition of nitrogen. With increasing quenching temperature, the Vickers hardness gradually increased to a peak and then decreased. Nitrogen addition helps to increase the hardness similarly to carbon. A N-containing specimen also exhibited superior secondary hardening after tempering. It is known that a large amount of residual austenite nally transforms to a hard martensite phase after tempering. According to the results of XRD analysis, nitrogen addition increases the volume fraction of retained austenite in the matrix at a higher holding temperature. Furthermore, the precipitation of nanosize carbonitride was observed around the primary V 2 CN carbonitride in addition to the standard precipitation. Therefore, this carbonitride precipitation may induce the superior secondary hardening and ultimately increase the macrohardness of N-containing specimens.

Effect of Alloying and Microalloying Elements on Carbides of High-Speed Steel: An Overview

“…Compared to layered M 2 C, fibrous M 2 C is easily disintegrated into more stable M 6 C and MC during forging and annealing. Hara et al [64] investigated the effect of N on the solidification structure of high-speed steel. They successfully introduced nitrogen at a concentration ranging from 48 ppm to 1542 ppm, as found in high-speed steel, by mixing Cr2N into the molten alloy.…”

Carbide Characteristics of High Vanadium High-speed Steel Manufactured by Electroslag Remelting

“…As the solubility product of VN is much smaller than that of VC, vanadium nitride is much more thermodynamically stable than vanadium carbide in austenite 24,25) and then the former is preferentially precipitated. Through the thermodynamic calculation and experimental measurement, a certain amount of N in HSS promotes the formation of primary M(C,N) which includes higher content of N than that of C, while in the eutectic MC, the content of N is much fewer than that of C. [26][27][28] The maximum contents of V, C and N in MC are 77.89%, 9.20% and 4.05% respectively and the average contents of Cr, Mo and W in MC are about 5.60%, 7.19% and 9.57% respectively. In fact, a certain difference of the contents of alloy elements in primary lumpy MC and eutectic strip-like MC occurs and a new scale bar of V content is used to clearly display the difference as shown in Fig.…”

Improved High‐Temperature Softening Resistance and Wear Resistance of AISI M42 High‐Speed Steel by N‐Alloying

“…[17][18][19][20][21][22][23][24] Recent studies have shown that adding N to HSS could produce some beneficial effects on its properties. For instance, Hara et al [25] and Halfa et al [26] reported that N-alloying could increase the secondary hardness of high-carbon HSS and M41 HSS owing to the precipitation of carbonitrides. Mattar et al reported that the room-temperature wear resistance of M41 HSS was improved by N-alloying owing to the increase of hardness and precipitate concentration.…”