Direct fabrication of high-performance high speed steel products enhanced by LaB 6

Abstract

A direct fabrication technology (DFT) without smelting has been developed for fabricating sophisticated high speed steel products with low pollution, near-net shaping and short process. The steel consisting of (wt. %): 6.4W, 5.0Mo, 4.2Cr, 3.1V, 8.5Co and 1.28C, was fabricated as exemplary material. The activated and reactive sintering of green compacts under vacuum with low activation energy, redox reaction enhanced diffusion and the construction of concentration gradient of alloying elements around pores, promotes the nearly full densification (>99.40%). Also, the DFT steels show high purity and superior mechanical properties. Minor strengthening agent LaB 6 (0.1 wt. %), which is easily to be accurately introduced in DFT, obviously increases the hot hardness, temper resistance, bend strength and toughness of DFT M3:2. The strengthening effect of boron atoms and La-rich complexes are proposed to directly result in the high hot hardness and temper resistance of LaB 6 containing steel.

Microstructure and mechanical properties of high carbon M2 powder metallurgy high-speed steel prepared by the carbide addition

“…The diffusion coefficient of chromium is much higher than that of tungsten, chromium and vanadium. Therefore, chromium carbide is the first to dissolve, and completely dissolved at 1180°C, which is consistent with the report [14]. The evolution of M 6 C and M 2 C carbides is mainly affected by tungsten and molybdenum.…”

“…During the sintering process, the types of carbides had undergone an interesting evolution, and the original carbides gradually transformed into composite carbides. Zhang et al [14] pointed out that M 6 C carbides start to form at 1000°C. In this paper, it is observed that a large amount of white M 6 C carbides in the samples after sintered at 1180°C.…”

“…Sun et al [13] explored the sintering characteristics of HSS powder with different particle size, and pointed out that the sintering densification degree of fine powder was higher at the same temperature. In recent years, Zhang et al [14,15] provided a new way for improving the sinterability of PM HSS by mechanical milling iron powder and carbide powder, and prepared high-performance PM HSS products with the help of grain boundary purification effect of LaB 6 . Although M2 HSS is the most widely used HSS brand at this stage, there is no report on the preparation of M2 PM HSS by carbide addition.…”

Effects of Nano TiC on the Microhardness and Friction Properties of Laser Powder Bed Fusing Printed M2 High Speed Steel

“…The frictional wear mechanism of pure M2HSS with different TiC addition was described as follows. The wear resistance of the pure M2HSS material relied mainly on fine carbide grains such as WC, MoC, and VC, which were diffusely distributed in the matrix [44][45][46][47][48][49][50][51][52][53] with a grain size in the matrix ranging from 1 to 2 μm. When the grinding ball was applied to the sample surface with a normal load and shear force, the grains of M2HSS were pulled off, and the fragmentation is shown in Figure 12a.…”

In-situ VN reinforced powder metallurgy M30 steels prepared from water atomized powers via pressureless sintering

“…Therefore, many efforts have been reported focusing on the preparation of HSS with water atomised powders. The studies on how to achieve pressureless sintering of HSS have received extensive attention due to their low cost [11,12]. Giménez et.al studied the microstructure characteristics of HSS fabricated by HIP, vacuum sintering, and nitrogen sintering [13].…”