High-carbon High-speed Steels Research Articles

Directed energy deposition and characterization of high-carbon high speed steels

Directed energy deposition (DED) of two high-carbon high speed steel alloys Febal-C-Cr-Mo-V and Febal−x-C-Cr-Mo-V-Wx was performed by using a 4 kW Nd:YAG laser source. The purpose of additive manufacturing was design and evaluation of thermally stable – high temperature wear resistant alloys. High temperature (500 °C) pin-on-disc tests were conducted to investigate the effect of carbides phase fraction on friction and wear. Strain scanning of the powder and additively manufactured materials was carried out by Neutron diffraction.Microstructures of both alloys consisted of a martensitic matrix with networks of primary and eutectic carbides. Micro-hardness (0.5 HV) measurement of all multilayer laser deposits, showed a micro-hardness greater than 700 HV, with no detrimental effect of repetitive laser thermal cycling. Febal−x-C-Cr-Mo-V-Wx showed a better high temperature wear resistance due to greater phase fraction of VC and Mo2C carbides. Fracture surfaces of post-heat treated tensile samples of Febal-C-Cr-Mo-V and Febal−x-C-Cr-Mo-V-Wx revealed brittle failures with minimal plasticity. Neutron strain mapping of the metal powders and the additively manufactured materials resulted in a weak diffraction signal and peak widening effect. These results could be explained either by an effect of strong crystallographic texture in the bulk or by the presence of nano- or semi-crystalline phases.

高炭素高速度鋼系合金の組織および硬さに及ぼす窒素の影響

高炭素高速度鋼系合金の組織および硬さに及ぼす窒素の影響

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

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 (Fe–1.9%C–0.5%Mn–4.9%Cr–5.0%Mo–5.0–7.2%V–0.4–1.4%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 M2C carbides containing mainly Fe and Mo among the austenite (γ) dendrites. Redistribution of alloying elements during the solidification sequence of primary γ, γ + MC and M2C 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 723–873 K showed secondary hardening. Furthermore, hardening of the specimens was most apparent when specimens containing large amounts of retained γ 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 γ matrix at quenching temperature, the degree of transformation from retained γ to martensite, and the precipitation and distribution of secondary carbides.

A Study on the Effects of Heat Treatment to the High-Carbon HSS Roll

High-carbon high-speed steels (HSS) are extremely abrasion resistant materials due to their high hardness MC type carbide and high hardness martensitic matrix. Different microstructures and mechanical behaviours were obtained after the quenching and tempering temperatures of HSS roll were changed. With air cooling and sodium silicate quenching, when the austenitizing temperature reaches 1273K, the metal matrix all transforms into the martensite, Afterwards, the eutectic carbides dissolve ceaselessly into the metal matrix and its continuous network distribution changes into broken network. The peak hardness temperature of high-carbon HSS is around 1323K, and the second hardening temperature is around 793K. No significant change in tensile strength and elongation percentage was observed unless the tempering temperature is beyond 753K. The tensile strength is increased obviously and the elongation percentage is decreased slightly beyond 753K. However, the tensile strength is decreased and the elongation percentage is increased when the temp exceeds 813K. The high-carbon HSS roll presents excellent abrasion resistance at 793K-813K.

Investigations on Heat Treatment of a High-Speed Steel Roll

High-carbon high-speed steels (HSS) are very abrasion-resistant materials primarily due to their high hardness MC-type carbide and high hardness martensitic matrix. The effects of quenching and tempering treatment on the microstructure, mechanical properties, and abrasion resistance of centrifugal casting high-carbon HSS roll were studied. Different microstructures and mechanical properties were obtained after the quenching and tempering temperatures of HSS roll were changed. With air-cooling and sodium silicate solution cooling, when the austenitizing temperature reaches 1273 K, the metallic matrix all transforms into the martensite. Afterwards, the eutectic carbides dissolve into the metallic matrix and their continuous network distribution changes into the broken network. The second hardening temperature of high-carbon HSS roll is around 793 K. No significant changes in tensile strength and elongation percentage are observed unless the tempering temperature is beyond 753 K. The tensile strength increases obviously and the elongation percentage decreases slightly beyond 753 K. However, the tensile strength decreases and the elongation percentage increases when the tempering temperature exceeds 813 K. When the tempering temperature excels 773 K, the impact toughness has a slight decrease. Tempering at 793-813 K, high-carbon HSS roll presents excellent abrasion resistance.

Effect of Rare Earth on Microstructures and Properties of High Speed Steel With High Carbon Content

The effects of rare earth (RE) on the microstructures and properties of high carbon high speed steel (HCHSS) were investigated. The results show that when suitable RE is added to the HCHSS, the effect of RE on the austenite and eutectic carbides is obvious. The austenite grain and coarse eutectic structure are refined, and flake carbides in the eutectic structures become short and fine. After heat treatment, most of the eutectic carbides are spheroidized and distributed in a uniform manner. The hardness and red hardness of modified HCHSS are slightly increased; impact toughness is greatly increased by 37. 81% and reaches 10. 17 J/cm2. The mechanism by which RE improves the structures and properties of HCHSS is also analyzed.

Structures and properties of high-carbon high speed steel by RE-Mg-Ti compound modification

The effects of rare earths (RE)-Mg-Ti compound modification on the structures and properties of high-carbon high speed steel (HSS) were researched. The impact toughness (αk), the fracture toughness (K1c) and threshold of fatigue crack growth (ΔKth) are tested. The thermal fatigue test is done on a self-straining thermal fatigue tester, the wear test is done on a high temperature wear test machine. The results show that the matrix can be refined by the RE-Mg-Ti compound modification, the eutectic carbides are inclined to spheroidicize and are distributed evenly, the morphology and distribution of eutectic carbides are unproved by appropriate RE-Mg-Ti complex modification. After RE-Mg-Ti compound modification, a little effects can be found on the strength, hardness and red hardness, but the fracture toughness (K1c) and threshold of fatigue crack growth (ΔKth) are improved in the meantime, the impact toughness (αk) is increased by over one time, and the resistance to thermal fatigue and wear resistance at an elevated temperature are remarkably improved.

Characteristics of High-carbon High Speed Steel Rolls for Hot Strip Mill.

In the field of hot strip mill finishing train, the demands for not only high quality of sheet product shape and sheet surface condition but also high productivity and energy saving in rolling are increasing. In this circumstance, we have developed completely new type compound roll which is composed of high-carbon high speed steel of outer shell and forged steel of core material to meet the requirement of high reliability as well as high wear resistance.After many experiments, the first trial of this new compound high-carbon high speed steel rolls was made in 1987 in finishing train of hot strip mill. Since then more than one hundred fifty new compound rolls have been used in hot strip mill finishing train. These new compound rolls are contributing the high productivity of rolling and the improvement of sheet products.

Basic Characteristics and Microstructure of High-carbon High Speed Steel Rolls for Hot Rolling Mill.

Work roll life of hot rolling mills is strongly affected by roll material. Recently, high-carbon high speed steel rolls have been developed to improve further work roll life.In this paper, relationship between basic characteristics of roll and microstructure in high-carbon high speed steels were investigated. After specimens with the several chemical compositions made by casting, forging, and powder process were prepared, wear test, friction test, heat crack test, flexure test were conducted.Consequently, it was revealed that basic characteristics of roll were strongly dependent upon the amount, shape, size of carbide, that is, wear resistance mainly increases with an increase in the amount of carbide, seizure resistance increases as the size of carbide is larger except at a large amount of carbide, heat crack resistance and toughness increase as the shape of carbide is the more spherical and the size of that is the smaller.Moreover, it became clear from the above results that 3.0wt%C-10.0wt%V high speed steel made by powder process is one of the most desirable roll material as has a large amount of fine spherical carbide.As a result of model rolling test, it was found that wear resistance of the above material is about five times that of high Cr cast iron.

Selection of the optimum hardening and tempering cycles for high-carbon high-speed steels

Together with improvement in the combination of basic properties, the increased carbon content leads to an increase in the quantity of residual austenite after hardening and an increase in its resistance to tempering. As the result of this, the selection of the optimum hardening and tempering cycles for obtaining a high combination of properties and providing good production properties becomes important.

Structure and properties of high-speed steels after cold treatment

1. After cold treatment in liquid nitrogen the mechanical properties of the steels are somewhat lower than after standard heat treatment. The cutting properties are not impaired in this case. In the course of the cold treatment the retained austenite is more completely transformed, particularly in high-carbon high-speed steels. However, use of this treatment to reduce the number of temperings is possible only in cases where the lower mechanical properties do not impair the cutting properties. 2. The main reason for the lower mechanical properties of high-speed steel subjected to the cold treatment is the smaller quantity of secondary martensite when retained austenite is transformed in the process of standard tempering.