Powder Metallurgy High Speed Steel Research Articles

Hot deformation behavior of the 1.15C–4.00Cr–3.00V–6.00W–5.00Mo powder metallurgy high speed steel

The deformation behavior of the 1.15C–4.00Cr–3.00V–6.00W–5.00Mo powder metallurgy (PM) high speed steel in hot working process was investigated by the isothermal compression tests carried out at the temperature of 950–1150°C and the strain rate of 0.001–1.0s−1 with the height reduction of 60%. True stress–true strain curves are investigated; the hot deformation activation energy of the steel is determined to be 750kJ/mol, and a constitutive equation is obtained. The processing maps were constructed, identification of the instability region and optimization of hot deformation parameters. It is found that the hot working process of the steel can be carried out safely in the domain of (Td: 1000–1150°C, ε̇: 0.006−0.1s−1). To obtain the homogeneous microstructure with fine grains, the hot working process should be carried out at the condition of (Topi: 1050°C, ε̇opi: 0.1s−1). The flow instability is expected in the two domains at 1030–1150°C/0.1–1.0s−1 and 1000–1075°C/0.001–0.006s−1. Furthermore, the true strain takes a great effect on processing maps in which the efficiency of power dissipation η obviously changes with the increase of strain from 0.05 to 0.90.

Study of the Surface Integrity of Powder-Metallurgy High-Speed Steel (S390) Multi-Cut by Wire Electrical Discharge Machining

The surface integrity of powder metallurgical high speed steel (S390) cut by wire electrical discharge machining (WEDM) has a great influence on the its fatigue life. In this paper, a study focused on surface integrity including white layer, surface finish, retained austenite, carbide and residual stress changed with multi-cutting has been described. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrograph (EDS) analysis were performed in the examination of the evolution of surface integrity. The experimental results reveal that the surface roughness, micro-cracks, white layer thickness and surface residual stress decrease with the increase of cutting pass, but the amount of retained austenite in the resolidified layer of the surface after the second cutting pass is the highest, compared with the other cutting passes. The content of carbides increases with the cutting pass and few carbides appear in the top section of the white layer of the first two cutting passes.

Analysis on Residual Stress in TiN Coating with Different Thicknesses

TiN coating is often coated on fine blanking tools made of with the powder metallurgy high speed steel S790 by Multi-arc ion plating. The phase variation, residual stress and microhardness of TiN coatings were respectively analyzed by X-Ray Diffraction(XRD) and Vickers hardness tester in this research. The result shows that: there is obvious preferred orientation in the crystal surface (1 1 1) and (2 2 2) of TiN coating, the residual stress of TiN coating ranges from -2 347 MPa to -1 920 MPa, and that of the substrate from -154.9 MPa to -69.21 MPa, both of which decrease with the increasing of coating thickness. The TiN coating on the S790 substrate was annealed at temperature 500°C for one hour. It was revealed that the stress state of TiN coating was better and thus the properties of the TiN coating were improved.

Effect of Deep Cryogenic Treatment on Mechanical and Tribological Properties of PM S390 MC High-Speed Steel

Abstract Application of deep cryogenic treatment instead of conventional heat treatment showed an increase in wear resistance of tools made of high speed steel which are exposed to very complex and demanding conditions in exploitation. The purpose of this study was to investigate the effect of deep cryogenic treatment in combination with plasma nitriding on the tribological properties of powder metallurgy high speed steel, grade PM S390 MC. On treated specimens hardness and fracture toughness was determined, the resistance to intensive adhesive wear (galling) and dry sliding wear (dry sliding wear resistance) were also tested. Test results show that deep cryogenic treatment in combination with plasma nitdriding contributes to better abrasive wear resistance and better galling properties of tested powder metallurgy high speed steel.

Gigacycle Fatigue Response of PM versus Ingot Metallurgy Tool Steels

In this work, the gigacycle fatigue response of several tool steel grades has been studied using an ultrasonic resonance testing device. It showed that both with ingot metallurgy (IM) and powder metallurgy (PM) tool steels, a true fatigue limit does not exist up to 10E10 cycles. PM steels resulted in significantly higher endurance strength levels than IM grades. However, there was virtually no effect of the composition and hardness of the materials, both for PM and IM grades cold work tool steels and high speed steels exhibiting virtually the same S-N curves. In the IM tool steel grades, crack initiation started at large primary carbides or carbide clusters, while in the PM grades, nonmetallic inclusions were the critical sites. In any case it is very important to avoid introducing residual stresses into the specimen surfaces during preparation, which would markedly shift the endurance strength levels.

Characterization of the carbides and the martensite phase in powder-metallurgy high-speed steel

A microstructural characterization of the powder-metallurgy high-speed-steel S390 Microclean was performed based on an elemental distribution of the carbide phase as well as crystallographic analyses. The results showed that there were two types of carbides present: vanadium-rich carbides, which were not chemically homogeneous and exhibited a tungsten-enriched or tungsten-depleted central area; and chemically homogeneous tungsten-rich M 6C-type carbides. Despite the possibility of chemical inhomogenities, the crystallographic orientation of each of the carbides was shown to be uniform. Using electron backscatter diffraction the vanadium-rich carbides were determined to be either cubic VC or hexagonal V 6C 5, while the tungsten-rich carbides were M 6C. The electron backscatter diffraction results were also verified using X-ray diffraction. Several electron backscatter diffraction pattern maps were acquired in order to define the fraction of each carbide phase as well as the amount of martensite phase. The fraction of martensite was estimated using band-contrast images, while the fraction of carbides was calculated using the crystallographic data.

Development of Powder Metallurgy High Speed Steel

High speed steels (HSS) have been widely used worldwide. This paper introduced some research results of high speed steels via Powder Metallurgy process. High speed steels AHPT15 (W12Cr4V5Co5 ) were investigated via gas atomization, hot isostatic pressing, hot working and heat treatment processes. Microstructure of the steels, precipitation of carbides and the influence of nonmetallic inclusions on mechanical properties of the steels were investigated. PM HSS showed fine and uniform microstructure and exhibited excellent toughness and wear resistance, with bend strength up to 3500 MPa and hardness up to 68.0 HRC.

Microstructural characterisation of vacuum sintered T42 powder metallurgy high-speed steel after heat treatments

High-speed steel powders (T42 grade) have been uniaxially cold-pressed and vacuum sintered to full density. Subsequently, the material was heat treated following an austenitising + quenching + multitempering route or alternatively austenitising + isothermal annealing. The isothermal annealing route was designed in order to attain a hardness value of ∼50 Rockwell C (HRC) (adequate for structural applications) while the multitempering parameters were selected to obtain this value and also the maximum hardening of the material (∼66 HRC). Microstructural characterisation has been carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microstructure consists of a ferrous (martensitic or ferritic) matrix with a distribution of second phase particles corresponding to nanometric and submicrometric secondary carbides precipitated during heat treatment together with primary carbides. The identification of those secondary precipitates (mainly M 3C, M 6C and M 23C 6 carbides) has allowed understanding the microstructural evolution of T42 high-speed steel under different processing conditions.

Sintering behaviour and microstructure development of T42 powder metallurgy high speed steel under different processing conditions

High speed steel powders (T42 grade) have been uniaxially cold-pressed and subsequently densified through different sintering routes including: supersolidus liquid phase sintering (SLPS) under vacuum and different nitrogen pressures (0.2, 0.9, and 8 bar) and through solid state sintering (SSS) by hot isostatic pressing (HIP). HIP temperatures as low as 850 °C led to near full densification of the material (>98% theoretical density) with average size of M 6C and MC carbides lower than 1 μm and grain size ≈3 μm. Pressureless sintering under different nitrogen pressures (up to 0.39 wt.%N absorption) led to a significant reduction of the optimum sintering temperature (OST) and a pronounced increase in the sintering window (SW) as compared to vacuum sintering. Pressureless sintering under 8 bar N 2 led to a further reduction in OST together with the precipitation of massive eutectic structures. Therefore, the SW was judged to be negligible. The response of the as-sintered materials to the heat treatment is basically determined by the amount of C available in the matrix prior to quenching and the grain size. The highest hardness achievable for the sintering conditions evaluated ranges 700–1100 HV2 after austenitizing at 1100 °C, oil quenching and multitempering at 500–550 °C.

Starch Consolidation as a New Process for Manufacturing Powder Metallurgy High-Speed Steels

The development of a new method called “starch consolidation,” suitable for the production of powder metallurgy (P/M) high-speed steel (HSS) components has been studied. Samples have been consolidated using 1.5, 3.5, and 5vol pct starch and up to 60vol pct powder. The high solid loading was achieved by stabilizing the repulsive forces with a small addition (0.01wt pct) of a dispersant (polyacrylic acid) that resulted in accurate fluidity and consolidation of the prepared slurries. After shaping of the samples, the bending strength of the green bodies was evaluated. Debinding cycles were optimized by comparing carbon and oxygen content in argon, in N2-5H2, and in pure hydrogen. The three atmospheres showed no significant differences in carbon elimination. To determine the influence of H2 in a nitrogen-rich atmosphere during sintering, tests were performed at 1230°C in a N2-5H2 and in a nitrogen atmosphere. Pure nitrogen resulted in a microstructure formed by smaller carbides. Heat treatments were performed on the samples with the compositions that gave the best combination of properties. A hardness of 800HV and a bending strength of 1475MPa were obtained.

Grindability of Conventionally Produced and Powder-Metallurgy High-Speed Steel

The factors affecting the grindability of high-speed steel (HSS) were investigated by measuring G-ratio and power consumption in surface grinding of 18 grades of HSS of different composition with an aluminium-oxide wheel. The dominant factor affecting grindability was the size of vanadium carbide. The marked difference between HSS produced by the conventional method and the powder-metallurgy method was analyzed. The relationship between power consumption, G-ratio and grindability was investigated.

Tribological evaluation of TiN and TiAlN coated PM-HSS gear cutter when machining 19MnCr5 steel

Two PVD coated powder metallurgy high speed steel (PM-HSS) gear cutters were investigated when machining helical gears made from AISI 19MnCr5 steel with hardness between 140 and 180 HV. Machining trials were carried out with gear cutters coated with TiAlN (nano layers) and TiN (mono layer). Crater and flank wears were measured and analysed after all the machining trials. Analyses of the worn tools show that the TiAlN coated gear cutter performed better than the TiN coated gear cutter. This can be attributed to its nano layers and the higher hardness of the TiAlN coating. The dominant tool wear mechanisms were adhesion, abrasion, delaminating of the coating layer and chipping of the cutting edge.

Influence of Cutting Edge Radius on the Wear Resistance of Powder Metallurgy High-Speed Steel Milling Inserts

The wear behaviour of powder metallurgy high-speed steel (PM-HSS) milling inserts is investigated experimentally. Cutting inserts with different cutting edge radii tested at various feed rates and cutting speeds were examined. The radii have been obtained either by microsandblasting or by honing. The initiation and progress of the tool wear was analysed with scanning electron microscopy (SEM) of the cutting edges. The experimental results exhibit quantitatively the effect of tool radius on the performance of milling inserts. A radius on the cutting edge prevents fast and unpredictable wear, and can lead to a great improvement of the tool life.

Processing of M2 powder metallurgy high-speed steel by means of starch consolidation

A study is made of a new method called starch consolidation (SC) for the production of powder metallurgy (P/M) high-speed steel (HSS) components. Samples of a commercial HSS, M2, were shaped by using 1.5, 3.5 and 5 vol% of starch and up to 60 vol% of powder. The high solids loading was made possible by a small addition (0.03 wt%) of dispersant (polyacrylic acid) that stabilized the repulsive forces and provided the desired fluidity to the slurries. After shaping and demoulding, the bending strength of the green bodies was evaluated. Debinding cycles were optimized by comparing the carbon content in argon, in a mixture of N 2–5H 2 and in pure hydrogen atmospheres at 450 and 600 °C. The three atmospheres caused no significant differences in carbon removal. Best results were achieved from sintering in vacuum with a debinding cycle in H 2 up to 600 °C for 30 min. Sintering tests were carried out at 1250 and 1260 °C for 30 min. The heat treatments then performed on the samples showed the best combination of properties: 1250 MPa and 888 HV.

Microstructural aspects determining the adhesive wear of tool steels

In many machining applications, adhesion of the workpiece to the tool is a major problem. Adhesion may be reduced by changing the microstructure of the tool steel, e.g. by increasing the carbide content. The present work deals with the influence of some microstructural parameters in the adhesive wear of tool steels. The investigations were conducted using six model alloys based on the powder metallurgy high speed steel AISI M4, all of which had the same martensitic matrix composition after heat treatment. The alloys had MC carbide contents which varied between 0 and 25 mol% in 5 mol% increments. Ball-on-disc experiments were carried out in ambient air at room temperature using austenitic stainless steel and aluminum balls as counterfaces. Wear tracks on the disks were characterized using both a scanning electron microscope and an optical profiler. The results show that two main parameters determine the adhesive wear behavior: the carbide content and the distance between carbides.

Fatigue behavior of powder metallurgy high-speed steels: fatigue limit prediction using a crack growth threshold-based approach

Abstract Based on the well-known fact that fatigue lifetime of powder metallurgy high speed steels (PM-HSSs) is given by subcritical crack growth of pre-existing defects, a linear elastic fracture mechanics (LEFM) approach is implemented by assessing a fatigue limit–fatigue crack growth (FCG) threshold correlation under infinite fatigue life conditions. In doing so, critical flaw size under cyclic loading is simply defined in terms of FCG threshold. Additionally, it is assumed that the fundamental LEFM correlation among defect size, strength and threshold conditions evaluated for large cracks applies for natural flaws too. Hence, the fatigue limit value for the PM-HSS studied is predicted using the experimentally measured fracture and FCG characteristics, provided that critical flaws are similar, in terms of nature, geometry and size, under monotonic and cyclic loading. The reliability of the applied LEFM approach is sustained through the excellent agreement observed between estimated and experimentally determined fatigue limit values.

Computer aided design of PM high speed steels for vacuum and nitrogen atmospheres

Computer aided alloy design has been used to develop new highly sinterable alloys in order to fulfil the requirements for robust processing of powder metallurgy high speed steels. Three alloys (M35IG, AR-K2 and M42HVIG) have been designed and subsequently analysed in terms of the expected sintering behaviour, atmosphere interaction and microstructural features. Predicted optimum sintering temperatures are 1200°C for the vacuum sintered M35IG alloy and 1150°C for the AR-K2 and M42HVIG alloys sintered under a 90N2+9H2+ 1CH4 atmosphere. On the other hand, the expected sintering windows exceed 10°C for all the alloys and the sensitivity to small compositional changes has been minimised guaranteeing the robust processing requirements. Additionally, sintering temperatures of 1150°C allow processing in continuous belt furnaces with the inherent interest for the industrial environment. Thermo-Calc software and the TC-Fe2000 database have been used to obtain the different calculations on the multicomponent systems.

Evaluation of As-Hipped PM High Speed Steel for Production of Large-Diameter Cutting Tools

Powder Metallurgy has been presented as an important process for producing metallic materials. Specially for high speed steels, it presents many advantages, as finer microstructures and alloy compositions that could not be feasible thought other processes. For large diameter bars, powder metallurgy is important because it produces more isotropic materials, with better carbide distribution, increasing the mechanical properties and notably the toughness. The present work aimed to characterize M3:2 high speed steel produced by powder metallurgy and compare its properties with conventional M2, in bar diameters between 76 and 91 mm. The steels were hardened using austenitizing temperatures varying between 1080 and 1200 °C; tempering was performed at 560 °C. For all austenitizing temperatures, bend toughness and microstructure were analysed and isotropy was evaluated comparing toughness values in transverse and longitudinal directions. The results show that, in the same hardness levels, PM M3:2 high speed steel is tougher than conventional M2. Besides, toughness in PM material is completely isotropic while M2 present differences in relation to the sample direction. Toughness results are closely related to the microstructure of materials, as PM material has a more homogeneous and finer distribution of primary carbides. Thus, the as-HIPed powder metallurgy high speed steel is shown as an important option to improve mechanical properties with maximum isotropy.

The Sintering of Powder Metallurgy High-Speed Steel with Activating Additions

The basic laws of vacuum sintering of high-speed steel powder with activating additions of 10-30% B and 70-90% Ni are considered. It is shown that for each of the compositions an optimal temperature and time of isothermal sintering, and also initial compact density exists, above which the density of the sintered ingot does not noticeably increase.

Порошковая быстрорежущая сталь для высокопроизводительного режущего инструмента

Порошковая быстрорежущая сталь для высокопроизводительного режущего инструмента