M2 Tool Steel Research Articles

Economic machining analysis of using coated cutting tools machining M42 tool steel at unusually low cutting speeds

Nanostructured coated cutting tools are increasingly being used to machine difficult-to-cut materials. This is especially so in machining hardened tools, exotic alloys and fissile materials. This paper describes the recent developments concerned with machining hardened M42 tool steel that is used to simulate the conditions that pertain to the unusually low-speed machining of fissile materials. An experimental analysis of the wear of coated cutting tools and how the experimentally determined tool life is used to select the most appropriate coating according to the number of components to be machined is presented. The research shows that tools coated with a non-titanium-based coating are superior to those already used for machining hardened tool steels at low cutting speeds.

Mechanical and tribological properties of multicomponent Ti–B–C–N thin films with varied C contents

Multicomponent thin films of Ti–B–C–N with different C contents (C target current ranging from 0.0 to 4.0 A) were deposited onto unheated Si(100) wafers (for mechanical analyses) and M42 tool steels (for tribological measurements) by reactive close-field unbalanced dc-magnetron sputtering in an Ar–N 2 gas mixture. These films were characterized and analyzed in terms of their microstructure by X-ray diffraction, their hardness by microindentation measurements, their surface root-mean-square roughness by atomic force microscopy, and their friction and wear behaviors by Rockwell-C testing, microscratch testing, dynamic impact testing and pin-on-disc tribometer. It was found that the mechanical and tribological properties of multicomponent films (typically 1.6 ± 0.2 μm in thickness) were closely related to the C content (varied from 4.4 at.% to 42.0 at.%). For the best multicomponent film with 12.4 at.% C content, a high hardness of 27 GPa was achieved and the best cohesive and adhesive strength was evidenced in terms of critical load values of L C1 (~ 37 N), L C2 (>75 N), and the highest adhesive strength (HF1). Moreover, by dynamic impact testing the multicomponent film could endure impact cycles up to 2 × 10 5 without adhesive failure. However, when the C content was further increased up to 42.0 at.%, the hardness, cohesive and adhesive strength were decreased due to the formation of amorphous structure. It was also found that the pin-on-disc test under dry conditions showed that the frictional coefficients decreased with C content. The frictional coefficients obtained at a load of 2 N were kept at ∼0.57 without C incorporation and decreased to ~0.18 at C current of 4.0 A. The tribological properties of the Ti–B–C–N films with different C contents are also explained in terms of mechanical properties and wear mechanisms.

Co-sintering of M2/17-4PH Powders for Fabrication of Functional Graded Composite Layers

Stepwise-graded composite layer of M2 tool steel and 17-4PH stainless steel was fabricated by a simple powder layering technique and the isothermal and nonisothermal sintering response of the bilayer were examined. It was shown that the materials exhibit poor compatibility during co-sintering, i.e., the amount of mismatch shrinkage is significant. An improved compatibility was obtained by adding 0.2 wt% B to the stainless steel powder. Formation of relatively dense layer at the bonding zone indicated an enhanced densification rate at the interface. Microstructural studies showed formation of a ferritic interface in M2/17-4PH composite and elongated grains with an intergranular boride phase and martensitic matrix at the bonding zone of M2/17-4PH + B. Increasing the sintering temperature broadened the interface width along with formation of more ferrite and coarser grains at the interface. Mechanical tests indicated higher shear strength and hardness of the interface zone in the composite compared with the individual layers.

Lubrication of Steel/Steel Contacts by Choline Chloride Ionic Liquids

There is a growing interest in the use of ionic liquids to provide lubrication for challenging contacts. This study is an initial assessment of the application of two ionic liquids based on choline chloride cations to be used as ionic liquid lubricants for engineering contacts, in this case steel on steel. These ionic liquids, termed ethaline and reline, have anions of ethylene glycol and urea, respectively, and are available at relatively low costs and in high quantities. In order to assess the lubrication performance of the ionic liquids, lubricated reciprocating sliding wear tests were conducted between M2 tool steel samples and a steel stylus. Initial tests conducted at a sliding speed of 0.005 m s−1 and 30 N showed that ionic liquids could provide low friction lubrication, comparable to that of SAE 5W30 friction modifier free engine oil under the same test conditions; however, lubrication was lost after short sliding distances. Further testing with higher sliding speed/lower load and varying sample surface textures showed that ionic liquid lubrication could be better maintained in high-speed/low-load testing and by increasing the roughness and therefore surface area of the sample. It was also observed that the choline chloride/urea ionic liquid formed a residual film when tested on iron silicate peened samples, and that this film may promote lubrication.

Investigation of the adhesion of NbN coatings deposited by pulsed dc reactive magnetron sputtering using scratch tests

Scratch tests have been used to investigate the adhesion of niobium nitride (NbN) coatings that were deposited by pulsed dc reactive magnetron sputtering at target currents of 1.5, 2.5, and 3.5 A onto M2 tool steel and silicon wafer. The coating adhesion on each material substrate was investigated using a progressive load scratch tester (PLST) and a multi-pass scratch tester (MPST). Microhardness tests and scanning electron microscopy (SEM) were also used to examine the hardness and microstructure of the NbN coatings. These results have indicated that the structural, mechanical, and adhesion properties of the NbN coatings improve with increasing target currents. While performing PLST and MPST tests, the highest adhesion and lowest friction force were obtained for the coatings deposited at a target current of 3.5 A. In addition, the triboscobic behaviors that were observed from the MPST of the coatings indicated that the target currents affect the friction behavior of the coatings.

Effects of CPII implantation on the characteristics of diamond-like carbon films

A diamond-like carbon film (DLC) was successfully synthesized using a hybrid PVD process, involving a filter arc deposition source (FAD) and a carbon plasma ion implanter (CPII). A quarter-torus plasma duct filter markedly reduced the density of the macro-particles. Graphite targets were used in FAD. Large electron and ion energies generated from the plasma duct facilitate the activation of carbon plasma and the deposition of high-quality DLC films. M2 tool steel was pre-implanted with 45 kV carbon ions before the DLC was deposited to enhance the adhesive and surface properties of the film. The ion mixing effect, the induction of residual stress and the phase transformation at the interface were significantly improved. The hardness of the DLC increased to 47.7 GPa and 56.5 GPa, and the wear life was prolonged to over 70 km with implantation fluences of 1 × 10 17 ions/cm 2 and 2 × 10 17 ions/cm 2, respectively.

Erosive wear of hardfaced Fe–Cr–C alloys at elevated temperature

Many engineering components are subjected to erosive wear at elevated temperature. As erosive wear at elevated temperature is governed by the synergistic effect of erosive wear and oxidation, it is possible to modify surfaces of the components in order to achieve improved performances. In view of the above, two different types of hardfacing alloys of Fe–Cr–C were designed incorporating Nb, Mo and B to ensure improved performances at elevated temperature. In order to achieve the above objective, mild steel was hardfaced with these alloys under optimised gas metal arc welding (GMAW) condition. The microstructures of the hardfaced coating was characterised with the help of optical microscopy (OM) and scanning electron microscopy (SEM). The mechanical properties of these coatings were obtained by means of micro indenter. Erosive wear of these coatings was evaluated for four different temperatures, for two different impact angles and at one impact velocity. The morphologies and the transverse sections of the worn surfaces are examined with SEM. The erosive wear of these coatings were compared with conventional M2 tool steel. Results indicate that erosion rate of these coatings increases with increase of test temperature and impact angles. Among various coatings, Fe–Cr–C coating containing higher amount of Nb, Mo and B exhibits best erosion resistance particularly at elevated temperature.

Solid–liquid structural break-up in M2 tool steel for semi-solid metal processing

The success of semi-solid metal processing mostly depends on the formation of suitable starting microstructure, which must consist of solid metal spheroids in a liquid matrix. Various methods of obtaining this structure have been established; they include recrystallisation and partial melting (RAP), strain-induced melt-activated (SIMA), or simple mechanical stirring, to name a few. These methods, as widely discussed, have mostly been applied with light alloys, mainly aluminium based. This article discusses solid–liquid structural break-up in M2 tool steel subjected to a direct re-melting procedure from the as-annealed condition. The role of carbide dissolution in the grain boundary liquation of the steel is described. This leads to the production of near spheroidal solid grains in a liquid matrix, a microstructure suitable for the thixoforming process. Microstructural examination revealed that carbide particles contained in bands at 1220 °C slowly disappeared with temperature. At 1300 °C, the solid grains seemed to be free from carbides. Most of the carbides had now re-precipitated at the grain boundaries. Thixoforming carried out at 1340 and 1360 °C revealed the thixotropic properties of the semi-solid metal slurries. The results indicate a widening of the range of potential routes to thixoformable microstructures.

Mechanical and tribological characterisation of nanostructured Ti/TiB2 multilayer films

Ti/TiB2 nanomultilayer thin films with different bilayer thicknesses λ were deposited onto unheated Si(100) wafers (for mechanical analyses) and AISI M42 tool steels (for tribological measurements) by unbalanced dc magnetron sputtering. The effects of different λ values on mechanical and tribological properties were investigated. These films were characterised and analysed in terms of their hardness by microindentation measurements, their surface root mean square roughness by AFM, their stress by an optical interference method, and their friction and wear behaviors by Rockwell-C testing, nano-/micro-scratch testing, dynamic impact testing and pin on disc tribometer. It was found that the mechanical and tribological properties of multilayer films (typically 1˙58±0˙10 µm in thickness) were closely related to λ (varied from 1˙1 to 9˙8 nm). For the best multilayer film with λ51˙9 nm, a maximum hardness of ∼32˙5 GPa was achieved and the best cohesive and adhesive strength was evidenced in terms of critical load values of LC1 (∼26 N) and LC2 (∼62 N). Moreover, by dynamic impact testing this multilayer film could endure impact cycles up to 4 × 105 without adhesive failure. However, when the λ was further decreased to 1˙1 nm, the hardness, cohesive and adhesive strength were decreased due to a high level of intermixing and lack of a layered structure. It was also found that the nanoscratch test under single pass and constant load conditions showed that the frictional coefficients decreased with λ and increased with normal load due to the ploughing effect. The enhanced hardness in the multilayer films with small λ values improved the wear resistance and lowered the frictional coefficients. These adhesive properties and wear performance are also discussed on the basis of mechanical properties and wear mechanisms.

A study on the abrasive and erosive wear behavior of arc-deposited Cr–N–O coatings on tool steel

In this study, the cathodic arc evaporation technique, by using the chromium target and controlling the flow rate of nitrogen/oxygen reactive gases, was utilized to deposit three different Cr–N–O coatings (CrN, CrN/Cr(N,O), CrN/Cr 2O 3) on AISI M2 tool steel. Two types of wear tests were applied to evaluate the abrasive and erosive wear behavior of the coated and uncoated specimens. One was the ball-on-disk abrasion test to measure the friction coefficient of these specimens. The other was the erosion test using Al 2O 3 particles (~ 177 µm in size and Mohr 7 scale) of about 5 g, and then the surface morphologies of the eroded specimens were observed. To further understand the coating effects on the two wear behaviors of M2 steel, coating structure, morphology, and adhesion were analyzed using XRD, SEM, and TEM, respectively. The results showed that surface roughness and adhesion of the double-layered coatings (CrN/Cr(N,O) and CrN/Cr 2O 3) were inferior to those of monolithic CrN, but their hardness and elastic modulus were superior to those of CrN. In the abrasive behavior, Cr–N–O coatings reduced the friction coefficient of M2 substrate. In particular, the CrN/Cr 2O 3 has the highest hardness/elastic (H/E) modulus ration, therefore the lowest friction coefficient, among all the coated-specimens tested. In the erosive behavior, the coated specimens exhibited better erosion resistance as compared to the uncoated ones, at the impingement angles of either 30 o or 90 o. Moreover, the erosion resistance of CrN/Cr(N,O) coatings was superior to that of CrN/Cr 2O 3 coatings due to its better adhesion.

Corrosion Resistance of Tool Steel Arc-Deposited Cr-N-O Double-Layered Coatings in 3.5% Sodium Chloride

Abstract In this study, the cathodic arc deposition technique was utilized to synthesize three Cr-N-O coatings (chromium nitride [CrN], CrN/Cr[N,O], CrN/chromium oxide [Cr2O3]) on AISI M2 tool steel by using the chromium target and controlling the flow rate of nitrogen/oxygen reactive gases. Polarization tests were performed to evaluate the corrosion resistance of the uncoated and coated specimens in 3.5 wt% sodium chloride (NaCl) solution. Structure and morphology of the coatings were separately analyzed using x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to better understand the coating effects on the corrosive behavior of M2 steel. The results showed that the CrN/Cr(N,O) and CrN/Cr2O3 double-layered coatings had higher surface roughness than monolithic CrN, but their dense and double-layered structures resulted in better corrosion resistance. The sequence of corrosion resistance is in the order of CrN/Cr(N,O) > CrN/Cr2O3 > CrN > uncoated M2 stee...

Analysis of Rheological Properties of Steel near Solidus Point Using Gleeble<sup>®</sup> Simulator

The main goal of this work is the analysis of rheological properties of steel alloy at high temperatures, just below the solidus point, and in the semi-solid state with low liquid phase content. Data obtained from the analysis can form the basis of numerical simulation for designing and optimizing the thixoforming processes. The rheological properties should be known over a wide temperature range so that the simulations could also predict defects such as incomplete die filling. The analysis concerned M2 tool steel alloy. The paper also discusses development of globular microstructure in partially melted steel.

Atomic transport and chemical reaction in TiN/Ti nanolayers on plasma nitrided steel

Transport of N, O, and Ti during dc magnetron sputtering deposition of nanoscopic TiN/Ti and TiN structures on plasma nitrided M2 tool steel, as well as transport of metallic species composing the plasma nitrided steel substrates were investigated. N and O depth distributions were determined with subnanometric resolution using narrow resonant nuclear reaction profiling, whereas Ti was profiled, also with subnanometric depth resolution, by medium energy ion scattering. The surface elementary compositions of the TiN/Ti/nitrided steel and TiN/nitrided steel structures were determined by low energy ion scattering. The chemical compounds formed during deposition were accessed by X-ray photoelectron spectroscopy, indicating the presence of TiN, TiO2, Ti oxynitrides, as well as other metallic nitrides and oxynitrides, but no metallic Ti was observed. Owing to the observed intensive atom mobility, the compositions of the deposited films on plasma nitrided steel structures varied continuously on a nanoscopic scale, from the core of the steel substrate to the bulk of the stoichiometric TiN films. The Ti interlayer assists interdiffusion of all species, in contrast to the TiN film layer, which is known to be a diffusion barrier. The improved adhesion of TiN hard coatings to plasma nitrided steel under working conditions is discussed in terms of the gradual compositional change around the interfaces and the atomic mobility during their formation.

Material transfer phenomena and failure mechanisms of a nanostructured Cr–Al–N coating in laboratory wear tests and an industrial punch tool application

In this research, CrAlN and TiN coatings were deposited on AISI M2 tool steel substrate test coupons and on industrial punch tools by electron beam plasma-assisted physical vapour deposition (EB-PAPVD). The microstructure and morphology of the coatings were investigated by XRD, XPS, TEM, and SEM with EDX. Pin-on-disc tribotests were conducted on the coatings against AISI 52100 steel counterface material in order to investigate their wear performance, with particular emphasis on the material transfer phenomena during the sliding tests. After industrial trials on piercing high strength steels, the worn uncoated as well as CrAlN- and TiN-coated punches were also studied. The results showed that the nanostructured CrAlN coating exhibited less material transfer and thus better adhesive wear protection than the TiN coating under both laboratory pin-on-disc tribotests and industrial trial conditions. It was also found that the coating morphologies replicated the surface finish of the punch substrates, and that local coating spallation appeared to be initiated at machining grooves on the punches, which were detrimental to the coating lifetime.

Analysis of machining of laser hardened M42 tool steel using computational techniques

The mutual interactions between M42 tool steel and a multipoint cutting tool creates significant opportunities to understand how dry milling of laser hardened materials affects machining conditions especially at the microscale. The present work not only compares various computational approaches to the solution of shear plane and tool face temperatures during dry machining, but also discusses how the accompanying machining attributes react to large changes in the coefficient of friction caused by changes in the type of coated cutting tool used for machining in the form of changes in the coefficient of sliding friction. The paper accounts for the changes in material properties during machining as a function of increasing temperature and also shows how stresses and strains are affected by significant changes in the magnitude of the coefficient of friction.

Analysis of the heating process and development of a microstructure suitable for thixoforming of steel

The thixoforming processes of metal alloys are carried out in the semi-solid state. The thixotropy phenomenon is conditional upon the globular microstructure that occurs in shaped material. In order to design and optimise such processes, some procedures of the Gleeble® system could be applied. The main objective of this work is an analysis of the resistance heating of samples in different material tests which are possible on the Gleeble® 3800 simulator. An example of development of steel alloy microstructure during heating on the Gleeble® simulator will also be presented. M2 tool steel was submitted for analysis. In this case, obtaining the globular microstructure was carried out on the basis of the SIMA method (Strain Induced Melt Activated).

Subsurface Deformation of Worn Al-Cu and Al-Mg Alloys

This paper investigates the subsurface deformation of two types of aluminium alloys with differing nature; A2124 (precipitation-hardened) and A5056 (work-hardened), sliding against an M2 tool steel slider. With block-on-ring configuration, the wear test was carried out at different loads ranging from 23 - 140N, in a dry sliding condition. Detailed secondary electron microscopy (SEM) performed on the longitudinal cross sections of the worn alloys indicates that the subsurface deformed layer beneath the worn surfaces is composed of a number of distinct layers like the mechanically mixed layer (MML), the shear deformed and bulk layers with increased hardness as the surface was approached. Deformation below the MML followed the expected behaviour of an exponential decay of strain with depth. In contrast to other studies in the literature, a linear relationship between depth of deformation and specific wear rate was not found for both alloys. This was believed to a result of the MML, which occupied a great proportion of the total depth of deformation. The relationship between the characteristics of the MMLs especially on the work hardening as a function of alloy type is also discussed.

Mechanical and tribological properties of nanostructured TiN/TiBN multilayer films

Nanostructured multilayer films of TiN/TiBN with different bilayer thicknesses ( Λ) were deposited onto Si(1 0 0) wafers (for mechanical analyses) and AISI M42 tool steels (for tribological measurements) at room temperature by reactive unbalanced magnetron sputtering in an Ar–N 2 gas mixture. The effects of different Λ values on mechanical and tribological properties were studied by atomic force microscope (AFM), scanning electron microscope (SEM), microindentation measurements, Rockwell-C tester, nano- and micro-scratch tester, impact tester, pin-on-disc tribometer, and Fourier-transform infrared spectroscopy (FTIR). It was found that the mechanical and tribological properties of multilayer films (typically 1.4 ± 0.1 μm in thickness) were closely related to Λ (varied from 1.4 to 9.7 nm). For the best multilayer film with Λ = 1.8 nm, a maximum hardness of ∼29.5 GPa was achieved and the best cohesive and adhesive strength was evidenced in terms of critical load values of L C1 (∼37 N), L C2 (>80 N) and the highest adhesion strength (HF1). Moreover, by the dynamic impact testing this multilayer film could endure impact cycles up to 4 × 10 5 without adhesive failure. It was also found that the nano-scratch test under single-pass and constant-load conditions showed that the frictional coefficients decreased with Λ and increased with normal load due to the ploughing effect. The enhanced hardness in the multilayer films with small Λ values improved the wear resistance and lowered the frictional coefficients. The frictional coefficients obtained at 5 N were kept at ∼0.5 and increased from ∼0.52 to ∼0.65 when Λ increased from 1.8 to 9.7 nm at 2 N. By FTIR analyses, the multilayer films with Λ = 1.8 and 2.2 nm showed the presence of h-BN which provided a lubricating function resulted in lower frictional coefficients and wear rates. The tribological properties of the TiN/TiBN multilayer films with different Λ values are also explained in terms of mechanical properties and wear mechanisms.

Microfinishing quenched and tempered M42 tool steels

Improvements associated with the life of cutting tools used to machine M42 tool steel are discussed in this paper. To achieve this, experiments using a variety of tool coatings are conducted on quenched and tempered M42. The limitations of the study include the employment of a short-time tool wear method. The paper presents original information on the characteristics of dry machining M42 tool steels under finish machining conditions.

Micromachining M42 tool steel using nanostructured titanium coatings

The machining of M42 tool steel is discussed in this paper. Traditionally, these materials have been machined using uncoated cutting tools with limited success. New developments in titanium-based coatings such as cation-substituted Til-x-y-zAlxCryyY2N alloys, with y = 0.03 and z = 0.02, have been shown to offer enhanced high-temperature oxidation resistance compared to presently used TiN and Til-xAlxN films that are deposited to cutting tool surfaces. Machining experiments indicated that cutting tool life is improved significantly using yttrium-doped titanium based coatings, when machining M42 tool steels.