Papers by Keyword: High Speed Steel

Abstract: In cutting aluminum alloy 6061, continuous chips have a negative influence on the machining operation. Usually, Pb is added in order to break continuous chips. However, from the standpoint of environmental protection, it is necessary to improve chip breakability without adding Pb. One effective measure to improve chip breakability is by adding Si to aluminum alloy 6061. However, the influence of Si content on tool wear has not been fully examined. In this study, in order to clarify the influence of a diamond-like carbon (DLC) coating layer with a Cr-based interlayer, namely (Al,Cr)N, on cutting performance, aluminum alloys having different Si contents were turned. The substrate of the tool material was high-speed steel (1.4%C). The tool wear and the surface roughness were experimentally investigated. The following results were obtained: (1) In cutting two kinds of Al-Si alloys, namely the Al-2%Si alloy and Al-4%Si alloy, the progress of wear of the DLC/(Al,Cr)N-coated tool was slower than that of the DLC-coated tool. Therefore, the (Al,Cr)N interlayer was effective for decreasing the tool wear of the DLC-coated tool. (2) The wear progress of the two kinds of DLC-coated tools in cutting of Al-4%Si alloy was faster than that in cutting of Al-2%Si alloy. (3) In cutting of Al-2%Si alloy with the (Al,Cr)N/DLC-coated tool, the surface roughness was almost constant in the range of a cutting distance from 0.1 km to 9.5 km.

Abstract: Microstructure and mechanical properties of W9Mo3Cr4V high speed steel fabricated by spray deposition have been studied. Spray deposited W9Mo3Cr4V high speed steel has a typical equiaxed structure which is finer and more homogeneous with a grain size of 20-30 micrometer compared with conventional casted counterparts. There are pores in the matrix of the deposited steel, which involve gas porosity, filling porosity and solidification shrinkage. As-deposited high speed steel is mainly composed of martensite, austenite and carbides which comprise MC carbide and M₆C carbide. Mechanical properties show that the hardness and bending strength of the as-deposited steel are higher than that of the conventionally casted ones. However, impact toughness of the high speed steel is lower than that of the conventionally casted steel, which can be attributed to the existence of porosities and M₆C carbides which reduce the impact toughness of high speed steels.

Abstract: Rolls in the steel industry withstand very high loads, thermal cycling leading to thermal fatigue, and severe environmental. How to improve the wear resistance and elongate the service life of rolls matters a lot in reducing the consumption of rolls. In recent years, because of its better red-hardness and wear property, high speed steel (HSS) was used to manufacture the new type composite rolls. As a surface treatment technology, laser cladding can fabricate coating to improve the wear resistance of substrate. In this paper, the substrates for laser cladding were nodular cast iron rolls, Nd:YAG solid pulsed laser and continuous wave CO₂ laser were both used to explore the feasibility of preparation HSS coatings. The Nd:YAG laser cladding results that the coated layers combined metallurgically with the substrate with a lot of microcracks. The average microhardness up to 600 HV is about 2 times as high as that of the substrate. The CO₂ laser cladding results that: fully dense and crack free clad surfaces of high speed steel with an excellent metallurgical bonding were deposited. The average microhardness up to 900 HV is about 3 times as high as that of the substrate. The high-temperature (500 °C) wear rate is 40% of nodular cast iron’s in 30 min.

Abstract: The M3 type high speed steel billets with / without Nb addition were prepared via spray forming. The effects of cooling rate and Nb on the microstructures and property of the M3 type high speed steel were investigated. The results show that the as-cast steels contain coarse primary dendrites and M₂C eutectic carbide, but the equiaxed grains and fine carbides are formed in the spray-formed steels. It can be seen that carbide precipitation and grain growth were suppressed by high cooling rate. The Nb additions can change the types of primary carbides. The solidified carbide microstructure was effectively changed from M₂C to M₆C type during the cooling of hot spray-formed billet. Niobium improves the microstructural thermostability of the M3 type high speed steel during heat treatments.

Abstract: A simulation model of a punch grinding process has been used to determine optimal parameters to reduce grinding cycle time and achieve a constant-temperature no-burn situation. Two basic outputs of the simulation model include arc length of contact and specific material removal rate that are both time-variant. A thermal model is included in the simulation to calculate maximum grinding temperature rise. The simulation-based optimization can help to avoid thermal damage, which includes thermal softening, residual tensile stress, and rehardening burn. The grindability of high speed steel (HSS) is presented in terms of specific grinding energy versus undeformed chip thickness and maximum temperature rise versus specific material removal rate. It is shown that for a given specific material removal rate lower temperatures are achieved when grinding fast and shallow. Higher temperatures, characteristic for slow and deep grinding, soften the material leading to a lower specific grinding energy, especially if grinding is timid. Lowest values of specific grinding energy can be achieved in fast and shallow grinding at aggressive grinding conditions.

Abstract: CBN diffusion coating on the ball nose end mills made of AISI-M35 high speed steel (HSS) has been produced thermo-chemically. The microstructure and component depth profiles of the CBN diffusion layer have been studied by scanning electron microscopy and energy dispersive X-ray spectrometry. The results on laboratory cutting tests of ball nose end mills made of AISI-M35 HSS with and without complex CBN diffusion coating are also introduced in the paper. The relationship between wear kinetics and tool life has been established. It was shown that under the used cutting conditions the tool life of the mills with the coating was a factor of 1.6 higher than that of the mills without the coating. The higher tribological stability of the coating in cutting process was supported by metallographic observations of the worn surfaces using scanning electron microscopy.

Abstract: High speed steel based ceramic preforms with three-dimensionally interpenetrated micropores were fabricated using the mixture of TiH2, CaCO3 and stearic acid as pore-forming agent. A self-made vacuum high pressure infiltration furnace was used to infiltrate the preforms with Pb-Sn based solid lubricants to create almost fully dense self-lubrication composites. The microstructure and properties of HSS-based self-lubrication composites were investigated as a function of sintered porosity. A quantitative analysis of microstructure was correlated with crushing strength，microhardness and wear rate to understand the influence of pore size, shape and distribution on mechanical and tribological behavior. Crushing strength and microhardness decreased with an increase in porosity. Meanwhile the decrease in microhardness with increasing porosity was slightly. The friction coefficient of HSS-based self-lubrication composites decreased with increasing the volume fraction of lubricant due to the self-lubrication and unique micropore structure. Within the range of lubricant volume fraction from 0% to 14%, the wear rate of the composites decreased steadily with the increase of lubricant content in the composites. Micropore structure and lubricant volume fraction play an important role in determining wear resistance of the composites whereas the measured bulk properties seem to be of minor importance.

Abstract: The present work has investigated the effect of aluminum on the solidification microstructure of M2 high speed steel. The results show that the as-cast structure is refined and the networks of M2C eutectic carbides are distributed more homogeneously with the addition of aluminum. Meanwhile, the morphology of M2C changes from the fibrous shape to the plate-like one. Despite of the same crystal structure, the microstructure differs greatly between the two carbides. Compared with the fibrous M2C, micro-twining is formed in the plate-like M2C, resulting in the orientation changes between different plates. It is expected that the solid/liquid interface structure of M2C may evolve from the non-faceted into the faceted due to the addition of aluminum.

Abstract: The present work has investigated the influence of calcium on the microstructure and properties of AISI M2 high speed steels. The results show that the as-cast structure consists of the iron matrix and networks of M2C eutectic carbides, which are greatly refined in the ingot modified by calcium. Meanwhile, the morphology of M2C evolves from the plate-like shape into the fibrous one. Compared with the plate-like M2C, the fibrous M2C is less stable at high temperatures, which promotes the spheroidization and refinement of carbides. Therefore, M2 steels modified by calcium obtain higher hardness and red-hardness after heat treatment than those without the addition of calcium.

Abstract: Giga-cycle fatigue behavior of notched specimens with stress concentration factor, Kt of 1.5, 2.0 and 2.5 for 0.65 mass% carbon matrix high speed steel, YXR3 with Rockwell C scale hardness number of 60.7 is investigated. The higher the stress concentration factor the lower the giga-cycle fatigue strength is. The emphasis is placed upon the subsurface crack initiation observed on all notched specimens. Crack initiation mode of high speed steel is discussed with respect to fracture surface morphology.