High‐vanadium high‐speed steel (HVHSS), known for its exceptional wear resistance, is widely used in industries such as steel production, bearing manufacturing, and the manufacture of cutting tools ...and high‐end components. To address the need for improved performance under challenging service conditions, the fabrication of HVHSS is investigated using spark plasma sintering (SPS) as an alternative to traditional casting methods. The research focuses on analyzing the microstructural changes in HVHSS samples produced by SPS under various sintering temperatures. These samples are then compared with those of cast HVHSS in terms of their microstructures, mechanical properties, and wear resistance. The study found that at a sintering temperature of 900 °C, the SPS‐fabricated HVHSS achieved a relative density of 98.1%. The fine and evenly dispersed carbides (mainly M7C3 and VC) in the matrix increased the microscopic hardness to 654.1 HV, which is higher than that of the cast sample. Notably, the wear resistance is significantly enhanced, showing increases of 15.48 cm−3 and ≈18% in absolute and relative terms, respectively. These results show that SPS fabrication is a major technique for enhancing the wear resistance and optimizing the microstructure of HVHSS.
In this study, HVHSS is synthesized via SPS powder metallurgy, demonstrating favorable outcomes. Compared to the cast HVHSS, the SPS‐fabricated HVHSS notably refined carbide size and distribution, enhanced absolute wear resistance by 15.48 cm−3, and improved relative wear resistance by ≈18%. At the sintering temperature of 900 °C, the ideal fine carbide dispersion distribution can be obtained.
For laser‐based powder bed fusion (PBF‐LB) of high carbon steels, preheated build platforms can reduce thermal stresses and crack formation inside the generated material. Furthermore, the heat ...distribution during PBF‐LB is affected by laser energy input and heat transfer into the surrounding area. Depending on the preheating temperature and the thermal conditions during PBF‐LB, thermal gradients and different thermal exposure times of the manufactured layers can lead to in situ heat treatment effects. As a result, gradients in microstructures and properties are observed in the manufactured material. The effects are investigated on AISI M2 high‐speed steel (1.3343). Specimens are manufactured at platform preheating temperatures between 200 and 700 °C. Base plate and surface temperatures in the building layer are monitored by thermocouples and pyrometry. Local variations in the material microstructure and properties are determined and the effects of temperature distribution on microstructure and hardness are discussed.
Depending on the preheating temperature and the thermal conditions during laser‐based powder bed fusion (PBF‐LB), thermal gradients and different thermal exposure times can lead to in situ heat treatment effects of high‐speed steels manufactured by PBF‐LB/M. These are investigated at preheating temperatures up between 200 and 700 °C herein.
Effectiveness of deep cryogenic treatment on carbide precipitation Jovičević-Klug, Patricia; Jovičević-Klug, Matic; Podgornik, Bojan
Journal of materials research and technology,
November-December 2020, 2020-11-00, 2020-11-01, Letnik:
9, Številka:
6
Journal Article
Recenzirano
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The study discusses the effectiveness of deep cryogenic treatment (DCT) on selected steels and its effectiveness on carbide precipitation. The investigation of DCT influence on the precipitation of ...different carbide types in three selected high-speed steels (M2, M3:2 and M35) has been carried out by a combination of x-ray diffraction (XRD), scanning electron microscopy (SEM), fractography, energy-dispersive X-ray spectroscopy (EBSD) and transmission electron microscopy (TEM). Three different steels with different chemical composition were selected in order to observe and correlate DCT induced carbide precipitation phenomena with varying concentration of alloying elements (Co, Cr, Mo, V and W). The study discloses the DCT effect on carbide distribution, morphology, size, and the mechanism of their formation. Using thermodynamic modeling the precipitation and origin of specific carbides is discussed and confirmed. This research proves that DCT has an impact on precipitation of carbides by increasing their volumetric fraction (overall up to 23%, up to 140% for M23C6), density (up to 30% for MC and M6C carbides), reducing their mean size and inducing a more homogeneous distribution of them. Low-cobalt-bearing steels exposed to DCT display an increased volume fraction of M23C6 carbides that presumably originate from the precipitation of additional embryos formed during DCT. However, selected steel with high Co content showed no significant changes in the volumetric fraction of carbides after DCT. The impact of preexisting M2C carbides and their decomposition on the final carbide formation is also discussed.
Spray forming (SF) is a newly developed rapid solidification and near-net-shape technique for preparing high-speed steels (HSSs) in recent years. However, a large amount of overspray powders will be ...produced in the SF process, which brings about a serious material pollution and waste. To solve this problem, a new method of the two-step sintering and subsequent heat treatment was used to fabricate high-performance W6Mo5Cr4V2Co5Nb (825 K) HSSs using the overspray powders. The microstructural evolution and mechanical properties by the heat treatment were systematically studied. Results show that near full dense 825 K alloys with many uniformly distributed carbides are obtained by the two-step sintering. After quenching and triple tempering, the alloys consist of the martensite, M6C and MC carbides, and a small amount of retained austenite. The carbides have smaller particle size of less than 3 μm and greater sphericity than the as-sintered alloy. The diffusion of alloying elements determines the dissolution and re-precipitation of carbides. The fabricated 825 K alloy quenched at 1180 °C and triple tempered at 540 °C possesses the best mechanical properties, with a hardness of 64.2 HRC and bending strength of 2858 MPa, which is much higher than that of casting alloy with similar composition. This work provides a feasible way to recycle the overspray powders.
The aim of the study was to evaluate the corrosion properties of three different grades of high-speed steel following a heat treatment procedure involving deep cryogenic treatment after quenching and ...to investigate how these properties are connected to the microstructure and hardness of the material. The hardness of steels was measured, and microstructural properties were determined through observation of the metallographically prepared steels using scanning electron microscopy. These studies were complemented corrosion evaluation by the use of corrosion potential measurement and linear polarization measurement of steels in a sodium tetraborate buffer at pH 10. The results showed that the deep cryogenic procedure of high-speed steel changed the microstructure and consequently affected the hardness of the investigated steels to different extents, depending on their chemical composition. Corrosion studies have confirmed that some high-speed steels have improved corrosion properties after deep cryogenic treatment. The most important improvement in corrosion resistance was observed for deep cryogenically treated high-speed steel EN 1.3395 (M3:2) by 31% when hardened to high hardness values and by 116% under lower hardness conditions. The test procedure for differentiating corrosion properties of differently heat-treated tool steels was established alongside the investigation.
Concerning tooling applications, Laser Powder Bed Fusion (LPBF) enables new features such as internal cooling channels that can be implemented in cutting or shaping tools. Thus, higher cutting speeds ...are feasible thanks to the more efficient cooling that could not be obtained by channels fabricated with conventional methods. However, the alloys exploited for the cutting tools production usually contain high levels of carbon, which makes their LPBF processability challenging due to their high crack-susceptibility. In this work, an approach based on the use of basic physical/empirical indicators has been employed to map the processability of six novel high-alloyed tool steel grades. A large experimental campaign with variable energy densities, single and double passes, as well as different focal points was designed. The results exhibit highly dense but cracked parts. In particular, the LPBF processability deteriorates with increasing carbon content, suggesting that mostly chemistry, rather than process parameters, plays a key role in the determination of the LPBF feasibility. The cooling rate, cooling time between 800 °C and 500 °C, equivalent carbon content, solidification interval, martensite start temperature and volumetric energy density were employed as indicators to provide a rapid classification of processability. The work demonstrates that the combined use of the indicators can better explain the cracking behaviour of carbon-containing tool steels. At a screening level, this approach based on complementar use of physical/empirical tools, may significantly shorten the experimental effort during the design of new compositions, especially when dealing with crack susceptible alloys like carbon-containing tool steels.
An electroslag casting method is used to add rare‐earth La to M2 high‐speed steels by adding La2O3 into the molten slag. The effects of the La content on the microstructure and mechanical properties ...of M2 high‐speed steel are studied. The results show that rare‐earth La is effectively added to steel by taking advantage of the decomposition of La2O3. The rare‐earth La partially modifies the pre‐existing oxide and sulfide inclusions into small and spherical rare‐earth oxysulfide inclusions. By adding an appropriate amount of La, the as‐cast iron dendrite matrix and coarse eutectic carbides can be refined, the carbide content is reduced, the carbide network is broken, and the decomposition of M2C into M6C and MC is promoted. After heat treatment, the network breaking and spheroidalization of the carbides are further facilitated, and the carbide content is reduced. The impact toughness and bending strength of the studied samples are improved by modifying the inclusions and optimizing the microstructure.
An electroslag casting method is used to add rare‐earth La to M2 high‐speed steels by taking advantage of the decomposition of La2O3 in the molten slag. The results show that by adding rare‐earth oxides La2O3 to electroslag casting, the inclusions in the steel can be modified, and the microstructure and mechanical properties of M2 high‐speed steel can be improved.
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