Solidification Microstructures and Quench/Temper Hardness of Tantalum Added High-Carbon High-Speed Steel Type Cast Alloy

Abstract

The influence of Ta addition on the solidification microstructure, solute distribution and hardness after quenching and tempering treatments was investigated for a high-carbon high-speed steel type cast alloy (Fe1.9%C0.5%Mn4.9%Cr5.0%Mo5.07.2%V0.41.4%Ta). The compositions of V and Ta were systematically changed to improve the distribution of hard MC carbides in the hypoeutectic range. Electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) identified an oval microstructure as MC carbides containing mainly V and Ta, and a lamellar structure as M 2 C carbides containing mainly Fe and Mo among the austenite (£) dendrites. Redistribution of alloying elements during the solidification sequence of primary £, £ + MC and M 2 C eutectic structure could be calculated from the Scheil-Gulliver equation and the initial composition. The macro-hardness of the quenched specimens gradually increased with increasing quenching temperature until a maximum was reached. This indicates that macro-hardness of the quenched specimens depends on both the amount and hardness of martensite matrix. All specimens which were tempered at 723873 K showed secondary hardening. Furthermore, hardening of the specimens was most apparent when specimens containing large amounts of retained £ were tempered at an optimum temperature. For example, the hardness of specimens with added Ta increased to around 900 HV after tempering at 823 K. These results suggest that the macro-hardness of tempered specimens is governed by the maximum amount of carbon in the £ matrix at quenching temperature, the degree of transformation from retained £ to martensite, and the precipitation and distribution of secondary carbides.

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

“…The same characteristics are obtained in the study of HSS with Fe-1.9%C-4.8%Cr-4.5%Mo-7.4%V. 17) Different from the obvious dendritic structure with coarse grains and poor distribution uniformity in ESR-C in Fig. 1(a), more uniform and finer grains are obtained in ESR-E which shows obvious equiaxed crystal morphology as shown in Fig.…”

“…Figure 6 shows the compositional analysis of lumpy and strip-like MC by EPMA. As high V content promotes the formation of primary V-enrich MC instead of primary γ , 3,17,23) it clearly indicates that the MC is rich in V, C, N and certain contents of Mo, W, oppositely, the contents of Cr and Fe in MC is very low. It is also found that N is mainly presented in the interior of lumpy MC in Fig.…”

Thermodynamic and experimental study of 30 wt-%Cr-containing {Co, Fe or Ni}-based alloys with very high contents in Ta and C

“…as carbides' alloys [5][6][7] . Tantalum carbides are also used to strengthen copper-based alloys 8 , alloyed steels 9,10 , titanium-based 11 and molybdenum-based 12 alloys. Besides coating techniques and sintering route, TaC carbides can precipitate during solidification, and are in equiaxed alloys and even in directionally solidified alloys 13 .…”

Effect of MC Type Carbides on Wear Resistance of High Wear Resistant Cast Iron Rolls Developed for Work Rolls of Hot Strip Mills

“…[12][13][14] Hence, the effects of elements such as V, Nb, and Ta on the formation of MC-type carbides in the solidification process have been reported. 15,16) It has also been reported that the addition of a small amount of Ti can lead to the formation of TiC and Ti(CN), which become the crystallization nuclei of VC and NbC granules. 17,18) Figure 2 shows examples of the microstructures of the enhanced indefinite chilled rolls (NiGr-E2) developed by utilizing these findings.…”