Low Alloy Tool Steel Research Articles

Energy-Efficient Application of CrN Coating on Low-Alloy Tool Steel: Comparative Analysis of Technological Processes

Abstract This research examines the technological processes of applying CrN coating on low-alloy tool steel, focusing on the comparison between hardening-tempering-coating (HTC) and hardening-coating (HC) processes, with an emphasis on energy savings. The study investigates the chemical composition, microstructure, mechanical properties, fractography, residual stress, and corrosion resistance of the coated tool steel. Notably, the results indicate no significant differences in the microstructural, mechanical, and corrosion properties between the HTC and HC processes, suggesting that tempering may be excluded without compromising the quality. This study introduces a novel approach to tool steel coating, which improves energy efficiency while maintaining high-quality outcomes. The findings highlight potential improvements in industrial applications, offering an energy-efficient alternative that does not sacrifice the performance or durability of the tool steel. This advancement could lead to significant improvements in manufacturing efficiency and sustainability.

Evolution of iron carbides during tempering of low-alloy tool steel studied with polarized small angle neutron scattering, electron microscopy and atom probe

The magnetic scattering of iron carbides in low-alloy tool steel was investigated ex-situ by polarized small angle neutron scattering measurements after tempering the steel at 550 °C and 600 °C. Magnetic features could be detected in the as-quenched sample resulting in a negative interference term, believed to be either θ-Fe 3 C, η-Fe 2 C, or ε-Fe 2-3 C. During tempering the evolution of cementite could be studied by the variation of the interference term and in γ-ratio, which is the ratio of the magnetic to nuclear scattering length density contrast. From scanning transmission electron microscopy (STEM) and atom probe tomography, it is evident that cementite (θ-Fe 3 C) is present directly when reaching the tempering temperature of either 550 °C or 600 °C. At longer tempering times, cementite gets enriched with substitutional elements like chromium and manganese, forming an enriched shell on the cementite particles. STEM and energy dispersive x-ray spectrometry show that the chemical composition of small cementite particles approaches that of Cr-rich M 7 C 3 carbides after 24 h at 600 °C. It is also seen that small non-magnetic particles precipitate during tempering and these correspond well with molybdenum and vanadium-rich carbides. • SANSPOL was used to separate the signal between cementite and alloy carbides. • The evolution of magnetic properties was recorded with SANSPOL. • The evolution of cementite during tempering was captured with APT and TEM. • Partitioning of substitutional elements in cementite could lead to in-situ transformation.

The “Expanded” Phases in the Low-Temperature Treated Stainless Steels: A Review

Low-temperature treatments have become a valuable method for improving the surface hardness of stainless steels, and thus their tribological properties, without impairing their corrosion resistance. By using treatment temperatures lower than those usually employed for nitriding or carburizing of low alloy steels or tool steels, it is possible to obtain a fairly fast (interstitial) diffusion of nitrogen and/or carbon atoms; on the contrary, the diffusion of substitutional atoms, as chromium atoms, has significantly slowed down, therefore the formation of chromium compounds is hindered, and corrosion resistance can be maintained. As a consequence, nitrogen and carbon atoms can be retained in solid solutions in an iron lattice well beyond their maximum solubility, and supersaturated solid solutions are produced. Depending on the iron lattice structure present in the stainless steel, the so-called “expanded austenite” or “S-phase”, “expanded ferrite”, and “expanded martensite” have been reported to be formed. This review summarizes the main studies on the characteristics and properties of these “expanded” phases and of the modified surface layers in which these phases form by using low-temperature treatments. A particular focus is on expanded martensite and expanded ferrite. Expanded austenite–S-phase is also discussed, with particular reference to the most recent studies.

Experimental Evaluation of the Methods of Laser Cementation of Low-Alloy Tool Steels

The methods of laser cementation of low-alloy tool steels by laser radiation are discussed. The results of experimental investigation of various cementation methods are presented, and the optimum cementation method providing reproducible results and commercial use is determined.

Increasing the Intensity of Cementation Process of Tool Low-Alloy Steels by Surface Laser Treatment

This work considers the questions of low-alloy tool steel cementation by laser treatment. The model of surface layer carbon saturation from the laser-induced plasma is shown. It is described that the diffusion process in the laser treatment can not be explained only by the influence of temperature gradient. The results of the experimental work confirmed the increasing intensity of the process surface layer saturation with carbon. The work describes the influence of the laser emission power on surface layer microstructure formation. The test results of the hardened samples showed an approximately two-time increase in durability.

In situ characterization of backstress effects on the austenite-to-bainite phase transformation

An in situ examination of the backstress and postforming effects was carried out in a low-alloy tool steel undergoing an isothermal austenite-to-bainite phase transformation. The findings shed light on the combined role of superimposed stresses and load reduction on the nucleation, selection and growth of bainitic variants throughout the phase transformation.

Improvement of press dies used for the production of diamond composites by means of DUPLEX-PVD-coatings

In the machining of hard materials such as glass or stone, cemented carbides have been recently replaced by diamond tools, consisting of a metallic carrier, on to which diamond segments are brazed. One of the most economic ways for the production of diamond segments is the cold compaction of the mixture of a metallic powder and diamond particles. Due to a highly abrasive sliding contact between diamond particles and the die walls, the wear rate of the press dies is very high. As a result of a low lifetime of the press dies, they must be replaced in short time periods. To avoid the costly and time-consuming substitution of the press dies, in this work PVD-coatings were deposited on the inner surface of the pre-plasma nitrided press dies (DUPLEX treatment). Thereby, various high and low alloy tool steels were treated by means of plasma nitriding process. Subsequently, a nanocomposite TiAlN coating (nc-TiAlN) was deposited by means of a high ionization magnetron sputtering device on nitrided and non-nitrided steel substrates. The mechanical and tribological properties of these coating systems were studied by means of several standard tests such as nanoindentation, ball-on-disc and scratch test. The most wear resistant coating system was chosen to employ on the inner surface of the press dies. The wear resistance of the press dies developed in this study was tested under real loading condition during compaction of the mixture of diamond particles and cobalt powder. It was revealed that employing plasma nitrided tool, steels coated with nanocomposite TiAlN decreases the wear rate of the press dies up to 76%.

Active screen plasma nitriding – an overview

Extensive researches carried out over the past few years have shown that the novel active screen plasma nitriding (ASPN) technique can be used to treat low alloy steels, stainless steels, tool steels and other steels to achieve identical nitriding effects as the conventional DC plasma nitriding technology. Importantly, the ASPN technique provides the possibilities of treating non-electrical conducting materials such as steel with an oxidised surface and polymeric materials which are unattainable with a conventional DC plasma system. Experimental results presented in this overview further demonstrate that sputtering and deposition play important roles in nitrogen mass transfer in ASPN. In order to achieve a desirable metallurgical response, materials for the active screen and the amount of bias applied to the component have to be considered in applications of active screen plasma processing. The distance between the screen and the component surface also needs to be considered if the components to be treated are placed in a floating potential.

Parametric study of relative erosion of cathode and anode of SAE L7 low alloy tool steel in EDM using grey relational concept in L9 orthogonal array

In EDM, dissimilar erosion of anode and cathode occur due to the effect of polarity even if both the electrodes interface each other under similar working condition and EDM process parameters. Dissimilar erosion is due to the difference in governing physical process associated with anode and cathode, unequal spatial source of heat that develops at both ends of electrodes, and unequal energy sharing. In this context, dielectric and thermo-physical properties of electrode material act as the concomitant parameters. Since dielectric is common in interfacing both the electrodes, considering common electrode material for both anode and cathode of SAE L7 low alloy tool steel, in the present paper, an experimental investigation based on L9 orthogonal array has been done to characterise spark-eroded craters formed on both anode and cathode surfaces. Due to the stochastic nature of machining, the observations of crater morphology fail to provide complete information regarding the parametric effects. Hence, grey relational analysis has been used to establish the significance of the process parameters based on Fisher test of grey relational coefficients. Finally, confirmatory experiments have been done to understand the nature of the relative erosion of anode and cathode with respect to EDM process parameters.

Mechanical and tribological properties of Ti/TiAlN duplex coatings on high and low alloy tool steels

In this research work, different steels were hardened using plasma nitriding process in an Arc-PVD device. Afterwards, on both non-nitrided and plasma nitrided substrates, different Ti/TiAlN multilayer coatings were deposited by a magnetron sputtering device. Scratch tests were performed on the duplex systems in order to characterize their adhesive properties. The failure modes of individual coating systems under various normal loads were described using light optical microscope. Furthermore, to study the effect of plasma nitriding on the friction coefficient and wear rate of the systems, ball-on-disc tests were carried out. It was shown that high and low alloy tool steels obtained different levels of hardness after plasma nitriding process. The results of scratch tests showed that both Ti/TiAlN multilayer coatings have a higher adhesion to plasma nitrided steels compared to non-nitrided steels. In addition, plasma nitriding of the substrates resulted in an increase in the wear rates of multilayer coatings. It was also revealed that the adhesion and the tribology of multilayers depend strongly on the amount of titanium interlayers. An increase of the thickness of titanium interlayers enhanced the adhesion of multilayers. However, increasing the thickness of titanium interlayers decreased the hardness and wear resistance of multilayers.

Short cycle hardening and tempering behaviour of low alloy tool steel 60WCrV7

AbstractThe effect of short heat treatment cycles, typical of induction or laser hardening, on the low alloy steel 60WCrV7, was simulated using a quench dilatometer. The heat treated material was examined using optical and scanning electron microscopy, microhardness testing, X-ray diffraction and microimpact testing. The effects of variation in austenitising time and temperature as well as tempering parameters on the hardness and toughness obtained are reported, and the metallurgical reasons for this behaviour are discussed. The results provide conclusions for optimum rapid cycle heat treatments and reveal significant potential for strongly reduced heat treatment cycles, which may have applications in areas besides surface hardening.

Active screen plasma nitriding of materials

The rapid development and the uptake of plasma nitriding technology into industrial surface engineering have slowed down in recent years. This is attributed to some of the inherent shortcomings of conventional dc plasma technology, for example, difficulties in maintaining a uniform chamber temperature, instability of the plasma and potential surface damage to parts caused by arcing. Efforts in overcoming these problems have led to the development of active screen plasma nitriding (ASPN) technology. This review demonstrates that with all its technological and environmental advantages, ASPN can be used to treat low alloy steels, tool steels, stainless steels and other steels which can conventionally be nitrided with dc plasma technology. In addition, ASPN can be used to treat non-conducting materials such as oxidised steels and polymeric materials which are not suitable for a dc plasma nitriding system. In the longer term, environmental friendly and technologically advanced plasma nitriding will outperform conventional salt bath and gaseous methods. Active screen plasma nitriding is a novel way of possibly achieving the full potential of plasma technology for thermochemical surface engineering.

TEM study on the surface white layer in two turned hardened steels

The structure of surface white layers was examined using transmission electron microscopy. Surface specimens were machined from a BS 817M40 steel (0.4C 1.2Cr 1.4Ni 0.2Mo) of 52 HRC and a low alloy tool steel (0.8C 1.7Cr 0.4Mo) of 58 HRC, with unworn and worn alumina/TiC composite cutting tools. Thin foil specimens were prepared such that the direction of observation was normal to the machined surface. The as-tempered microstructure of both steels was lath martensite. The structure of the machined surfaces of both steels was characterised by very fine, mis-orientated cells, less than 100 nm in size. The accompanying selected area electron diffraction patterns indicated the presence of retained austenite, the volume fraction of which increased with cutting tool wear. A refinement in the size of cementite particles was also evident. In the surface of the BS 817M40 steel machined with a worn cutting tool, there was evidence to suggest a degree of recrystallization. This may be accounted for by a transition from dynamic recovery to dynamic recrystallization during surface generation; a phenomenon which is favoured by the decrease in the work materials stacking fault energy as a result of the reverse martensite transformation.

Mechanical behavior of borides formed on borided cold work tool steel

In this study, some mechanical properties of borided cold work low-alloy tool steels were investigated. Boronizing was performed in a solid medium consisting of Ekabor-I powders at 1000°C for 2, 4 and 6 h. The substrate used in this study was high-carbon, low-alloy tool steel essentially containing 1.18 wt.% C, 0.70 wt.% Cr, 0.30 wt.% Mn, 0.10 wt.% V and 0.25 wt.% Si. The presence of borides (FeB+Fe 2B) formed on the surface of steel substrate was confirmed by optical microscope and X-ray diffraction (XRD) analysis. The hardness of the boride layer formed on the surface of the steel substrate and unborided steel substrate were 1854 and 290 kg/mm 2, respectively. Experimental results revealed that longer boronizing time resulted in thicker boride layers. Optical microscope cross-sectional observation of the borided layers revealed denticular morphology. The fracture toughness of the boride layers measured by means of a Vickers indenter with a load of 3 N was in the range of 2.52–3.07 MPa m 1/2.

Microstructure and hardness distribution of laser surface overlap coating layer

In the present work T15 high speed steel powder was coated on a low alloy tool steel by a laser surface overlap coating process to achieve a large area coating layer. The microstructure, composition, and hardness distribution of the coating layer were studied by optical microscope, scanning electron microscope, energy dispersive X -ray, and micro hardness determinations. It was shown that the composition exhibited a heterogeneous distribution which was related to convection in the molten pool during the overlap coating process. The microstructure of the coating layer exhibited a periodic feature, and a periodic hardness distribution was present. The hardness of the coating layer was between 800 and 1000 HV(100 g). After tempering at 560°C, the hardness level increased to ∼ 1100 HV (100 g) and a more homogeneous hardness distribution was obtained throughout the coating layer.

Microstructure and hardness distribution of laser surface overlap coating layer

In the present work T15 high speed steel powder was coated on a low alloy tool steel by a laser surface overlap coating process to achieve a large area coating layer. The microstructure, composition, and hardness distribution of the coating layer were studied by optical microscope, scanning electron microscope, energy dispersive X -ray, and micro hardness determinations. It was shown that the composition exhibited a heterogeneous distribution which was related to convection in the molten pool during the overlap coating process. The microstructure of the coating layer exhibited a periodic feature, and a periodic hardness distribution was present. The hardness of the coating layer was between 800 and 1000 HV(100 g). After tempering at 560°C, the hardness level increased to ∼ 1100 HV (100 g) and a more homogeneous hardness distribution was obtained throughout the coating layer.

Tribological studies of plasma source ion nitrided low alloy tool steel

Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for implanting nitrogen ions and then diffusing into metallic materials. In this work, an attempt has been made to develop a method for hardening 9SiCr low alloy tool steel at a process temperature of 250 °C by plasma source ion nitriding. The nitrided samples were characterized using optical microscopy, Auger electron spectroscopy, electron probe microanalysis and glancing angle X-ray diffraction. The wear tests were performed on a crank/connecting rod reciprocating tribometer. The dominant wear mechanisms were identified by the worn surface morphologies using scanning electron microscopy. The results indicate that the nitrided surface layers possess the improved abrasive wear resistance and increase the transition load from mild to severe wear, compared with the unnitrided samples. The formations of nitrides and nitrogen-containing solid solution are considered as the main reasons for improved tribological properties.

Butterfly martensite in industrial steels

The morphology and the conditions of formation of butterfly martensite observed in carbon tool steels, low-alloy tool steels and bearing steels have been investigated. The results indicated that the butterfly martensite in various steels in three dimensional space can be classified into two types: i.e., the butterfly martensite with tails and the butterfly martensite without tails. But in the two dimensional metallographic morphology they may be classified as three groups: i.e., the butterfly martensite with double tails, the butterfly martensite with a single tail, and the tailless butterfly martensite. The two wings of butterfly martensite comprise a whole entity and their mid-rib planes can exhibit crossing, kinking, or branching. There are ten possible stretched angles of space between the two wings of butterfly martensite. They are: 41°, 43°, 59°, 61°, 83°, 97°, 119°, 121°, 137°, and 139°. Among them, 137°, 121°, 139° and 119° appear the most frequently. The quantity of butterfly martensite increases with the increase in carbon content and in austenitizing temperature. The morphological features and the quantity of butterfly martensite are little affected by variations in alloying elements at low concentrations.

BETHALLOY

Abstract BETHALLOY is a low-alloy oil-hardening tool steel. Because of its relatively low carbon content (for tool steels), it has slightly better shock resistance than more highly alloyed types and may be used wherever wear resistance can be sacrificed for moderately increased toughness. This datasheet provides information on composition and hardness as well as fracture toughness. It also includes information on forming, heat treating, machining, and surface treatment. Filing Code: TS-308. Producer or source: Bethlehem Steel Corporation.

SIMOCH

Abstract SIMOCH is a low alloy tool steel having high shock resistance, high impact strength and excellent wear resistance. It is recommended for many hot work and cold work applications. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as fracture toughness. It also includes information on forming, heat treating, machining, and joining. Filing Code: TS-186. Producer or source: Teledyne Vasco.