Cold Work Tool Steel Research Articles

Determination of Surface and Hole Quality in Drilling of AISI D2 Cold Work Tool Steel Using MPMR, MARS and LSSVM

This paper adopts Minimax Probability Machine Regression (MPMR), Multivariate Adaptive Regression Spline (MARS), and Least Square Support Vector Machine (LSSVM) for prediction of surface and hole quality in drilling of AISI D2 cold work tool steel with uncoated titanium nitride (TiN) and titanium aluminum nitride (TiAlN) monolayer- and TiAlN/TiN multilayer-coated-cemented carbide drills. MPMR is a probabilistic model. MARS is a nonparametric regression technique. LSSVM is developed based on statistical learning algorithm. Cutting tool (t), Feed rate (fr)(mm/rev), and Cutting speed (v)(m/min) have been adopted as inputs of MPMR, MARS, and LSSVM. The output of MPMR, MARS, and LSSVM is Surface roughness (rs) (μm) and Roundness error (re) (μm). A comparative study has been presented between the developed models. The results show that the developed model gives excellent performance.

Influence of Solution Nitriding of Supersolidus–Sintered Cold Work Tool Steels on their Hardenability

Abstract Powder metallurgical steel grades offer higher quality and performance compared to cast and forged steel grades due to their finer microstructure without segregations or textures. Because high-alloyed, cold work tool steels cannot be compacted by solid-state sintering, hot isostatic pressing is state of the art. This process, however, is comparatively expensive and there is thus a high demand for alternative densification processes. Supersolidus liquid-phase sintering represents an alternative to hot isostatic pressing for densification of these steels to theoretical density. During sintering, the steel powder interacts with the sintering atmosphere, which can be a vacuum, hydrogen, hydrogen plus nitrogen, or nitrogen. In a nitrogen atmosphere, there may be nitrogen uptake by the sintered material, which changes the chemical composition of the steel and thus results in a decrease in the sintering temperature. The aim of this work is to investigate the influence of nitrogen uptake on the hardenability of a high-alloyed and supersolidus-sintered cold work tool steel. Computational thermodynamics using the Calphad method were applied to calculate the optimal parameters for direct quenching from the sintering temperature. In addition, the tempering response was investigated as a function of the heat-treatment parameters. It was found that nitriding exerts a significant influence on the hardenability, which is also dependent on the cooling rate from the sintering temperature to the quenching temperature. Hardenability was predicted qualitatively on the basis of equilibrium carbon concentrations of the austenitic matrix calculated with the Calphad method.

The Interface Morphology of Thixo-Joined Cold Work Tool Steel

Cold-work tool steel is considered to be a nonweldable metal due to its high percentage content of carbon and alloying elements. The application of a new process of the semi-solid joining of two parts of AISI D2 cold-work tool steel is proposed using a partial remelting method. Samples were heated in an argon atmosphere up to 1275°C which corresponded to about 20% of liquid fraction and held for 10 minutes. Metallographic analyses along the joint interface showed a smooth transition from one to the other and neither oxides nor micro-cracking was observed. The current work successfully confirmed that avoidance of a dendritic microstructure in the semi-solid joined zone and high bonding quality components can be achieved without the need for force or complex equipment when compared to conventional welding processes.

냉간금형강의 미세조직과 기계적 특성: STD11과 8%Cr 강의 비교

Abstract A comparative study was performed on the microstructures and the mechanical properties of STD11and 8Cr steel. The specimens were quenched from 1030 o C and tempered at 240C and 520C. Vickers hard-ness, impact toughness and tensile tests were conducted at various tempering temperatures. Microstructuralcharacterization to measure grain size, volume fraction of retained austenite and distribution of carbides was car-ried out by using SEM, EBSD, TEM and X-ray diffraction techniques. Due to finer M 7 C 3 carbides dispersed, 8Crsteel showed larger impact toughness and plasticity than STD11 irrespective of the tempering temperature. While8Cr steel had lower hardness in as-quenched state and after tempering at 240 o C owing to smaller carbide con-tent and more retained austenite, it was harder after tempering at 520 o C due to larger precipitation hardeningfrom finer M 23 C 6 .(Received August 25, 2014; Revised September 12, 2014; Accepted September 18, 2014)Key words : Cold-work tool steel, 8Cr steel, STD11, Microstructure, Mechanical property

Metallurgical investigation into the failure of a chopper blade used for cutting of hot-rolled steel coils

In the present work, failure investigation of a chopper blade received from an integrated steel plant has been presented. Chopper blades are used in chopping machines for cutting trimmed edges of hot-rolled coils into pieces to convert them into scrap. These blades are manufactured from hot forged or rolled billets or flats of high carbon high chromium cold work tool steel. The investigation consists of visual examination, chemical analysis, microstructural analysis through optical and scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and hardness measurement. The chemical analysis confirmed the steel as equivalent to D2 grade in AISI notation. Carbide volume fraction of the broken blade was in the normal range of 10–15% as commonly observed in D2 tool steel. Microstructural examination under light and scanning electron microscopy showed non-uniform distribution of large eutectic primary carbides of irregular morphology forming strings or bands in tempered martensite matrix preferentially aligned in a specific direction. The uneven carbide arrangement in the matrix made the structure highly anisotropic and susceptible to localized stress concentration. The carbides were identified mainly as M23C6 type. Cracks were observed to initiate at the edges of the blade and propagate to the interior through clustered zones of carbides. SEM study suggests that the crack initiation was associated with decohesion of carbide particles in the cluster which culminated into final fracture by the mechanism of void coalescence and subsequent crack growth.

Improvement of an industrial tool life for minting the circulating coins

The material used to produce one baht coin in the Royal Thai Mint has been changed from cupronickel (75% Cu and 25% Ni) to nickel-electroplated steel, not only for economic reasons but also for the durable properties of the latter. As a result, the higher hardness value of the new material (110 HV30 versus 80 HV10) combined with the high accuracy requirements of the coin detail have reduced the durability and lifetime of coining tools. The number of coins produced by a single coining tool was reduced from approximately 300,000 to only 40,000 coins. However, the tool life can be increased if proper selections of tool material and hard thin film coating technique are made. Two types of tool material were selected: cold working tool steel, 0.97% C and warm working tool steel, 0.5% C. CrN, TiN and TiCN coatings were examined using physical vapour deposition (PVD). It was determined that the type of tool material, the type of coating material, the coating temperature and the coating thickness influenced the lifetime of a coining tool. For the conditions studied, a 3-µm-thick TiN coat on warm working tool steel produced under a coating temperature of 400°C provided the maximum tool life up to 1.22 million strokes.

Semi-Solid Joining of D2 Cold-Work Tool Steel

Cold-work tool steel is considered to be a non-weldable metal due to its high percentage content of carbon and alloying elements. To address this problem the application of a new process of semisolid joining using a direct partial remelting method was developedto achieve a spherical join structure between two parts of AISI D2 cold-work tool steel. Since the surface oxidation of this metalis very high, the control of the atmosphere during joining had to be considered. Samples were heated in an argon atmosphere at two different temperatures of 1250°C and 1275°C for 10 minutes. Metallographic analyses along the joint interface showed that an increase in temperature promoted the final joining properties and also that at a liquid fraction of 15% joining was not fully practicable. However, a20% liquid fraction can produce a very good joint and microstructure as compared to the other experimental liquid fraction. Metallographic analyses along the joint interface showed a smooth transition from one to the other and neither oxides nor microcracking was observed. The current work confirmed that avoidance of a dendritic microstructure in the semisolid joined zone and high bonding quality components can be achieved without the need for force or complex equipment when compared to conventional welding processes.

Comparison of Fuzzy Logic and Neural Network for Modelling Surface Roughness in EDM

Surface roughness is the main indicator of technological performances of a component for electrical discharge machining (EDM). EDM process of manganese alloyed cold-work tool steel was modelled. In this paper we used the fuzzy logic (FL) and neural network (NN) to predict the effect of machining variables (discharge current and pulse duration) on the surface roughness of manganese alloyed cold-work tool steel in order to improve and increase its range of application. The experiments are carried out on manganese alloyed cold-work tool steel, processed with electrodes made of copper. The values of surface roughness predicted by these models are then compared. All models show good agreement with experimental results. When compared to the NN and FL models, the NN model has shown a significant forecast improvement. The results indicate that the NN model is an effective algorithm to forecast the surface roughness in EDM.

Effect of copper addition on the characteristics of high-carbon and high-chromium steels

The effect of Cu addition on the microstructures and the tempering behavior of cold-work tool steels was investigated. 8% Cr steels with varying amount of Cu added from 0.22 to 2.56wt% were prepared, then hardened by quenching and tempering. The alloys with different Cu contents showed similar fraction and size of M7C3 carbide. Therefore, it could be known that the addition of Cu did not affect the formation of M7C3 carbide which formed at high temperatures where Cu existed as a solute element. While increased Cu content reduced prior austenite grain size, the as-quenched hardness decreased due to increased volume fraction of retained austenite. During tempering at 520°C, Cu addition generally led to higher hardness due to delayed softening, while after prolonged duration the softening rate was more diminished at the lowest Cu content. It was observed that Cu suppressed the formation of M23C6 precipitate during tempering. Prior formation and coarsening of Cu precipitate could lead to enhanced tempering resistance in the early stages of tempering, whereas after prolonged duration, the effect was diminished due to the insufficient hardening caused by the suppressed precipitation of M23C6. By balanced co-precipitation of Cu and M23C6 with refined grain size, the hardness and the impact toughness could be optimized at around 1wt% of Cu addition.

Influence of Tool Steel Hard Phase Orientation and Shape on Galling

Conventionally manufactured cold work tool steel is often used in sheet metal forming as die material. Due to the forging process, the as-cast network structure of carbides is broken into elongated particles. Depending on the tool cross-section, the orientation and shape of carbides in the active tool surface is different. In the present research, the influence of tool steel hard phase orientation and shape on galling was investigated. D2 type tool steel was cut in three different orientations and tested in lubricated sliding conditions against AISI 304 austenitic stainless steel. Tests were performed using a Slider-On-Flat-Surface and galling was detected by changes in friction and post-test microscopy. The lubricant was Castrol FST8 using 5 g/m2 sheet material. Results showed a strong correlation between sliding distance to galling and tool steel hard phase orientation and shape at low loads, whereas high load contact resulted in early galling in all cases. Material transfer was observed mainly to the tool steel matrix. The worst performance was observed for specimens cut so that the tool steel hard phase, M7C3 carbides in the D2 steel, were oriented along the sliding direction, which resulted in longer open tool matrix areas contacting the sheet material.

Boriding of high carbon high chromium cold work tool steel

High-carbon high-chromium cold work tool steels are widely used for blanking and cold forming of punches and dies. It is always advantageous to obtain an increased wear resistant surface to improve life and performance of these steels. In this connection boriding of a high-carbon high-chromium cold work die steel, D3, was conducted in a mixture of 30% B4C, 70% borax at 950 °C for two, four and six hours. Case depth of the borided layer obtained was between 40 to 80 μm. After boriding, the surface hardness achieved was between 1430 to 1544 HV depending upon the process time. X-ray diffraction studies confirmed the formation of a duplex compound layer consisting of FeB and Fe2B. It is generally considered that FeB is undesirable because of its inherent brittleness. Post boriding treatment (homogenization) transformed the compound layer into single-phase layer of Fe2B, while surface hardness decreased to 1345-1430 HV. Pin-on-disc wer test showed that wear resistance of the borided samples was superior as compared to non-borided material and increased with boriding time.

Effect of test parameters on the micro-abrasion behavior of PVD CrN coatings

Micro-abrasion wear test is a widely used method in measurement of abrasive wear resistance of thin hard coatings. During the test, selection of test parameters has great importance in determination of the wear behavior of the material under investigation correctly. Therefore, in this study, the effect of test parameters on the micro-abrasion behavior of CrN coating was investigated by the fixed-ball micro-scale abrasion test and modeled by response surface methodology. The coating was deposited on AISI D2 cold work tool steel using industrial cathodic arc evaporation system. The wear tests have been performed using SiC abrasive slurry. Analysis of worn craters was conducted by scanning electron microscope (SEM). It was found that the models obtained from ANOVA tables for wear volume and wear rate of CrN coating are significant and have high correlation coefficients. The rotation speed has higher influence on the wear volume of CrN coating, whereas the normal load has higher influence on the wear rate. The higher normal load increases the wear volume and decreases the wear rate. The effect of rotation speed changes according to the value of applied speed. Grooves take place by two-body abrasion in all of the craters obtained at different rotation speed and normal load values. Depth of parallel grooves in CrN coating and AISI D2 substrate decreases with the normal load and with the rotation speed.

Effect of plasma nitriding potential on tribological behaviour of AISI D2 cold-worked tool steel

The effect of the nitrogen potential on the micro-abrasive wear resistance of AISI D2 plasma nitrided tool steel was evaluated. Plasma nitriding experiments were conducted in a pulsed plasma reactor using different nitrogen potentials. The results indicate that a nitrided layer, with finely dispersed nitrides, can be formed when shorter nitriding times and higher nitrogen potentials were used. Although the thickness of this layer is small, its wear resistance is higher than that observed at longer nitriding times. Increasing the nitriding time resulted in the formation of thicker layers, albeit with grain boundary nitrides, which are deleterious to wear resistance. For untreated material, three-body abrasive wear rolling was the dominant mechanism, and for nitrided material, the mechanism transition was not clearly observed in spite of its better wear resistance.

Predicting of Machining Quality in Electric Discharge Machining using Intelligent Optimization Techniques

This paper presents the development and application of fuzzy logic, neural network and genetic algorithm in EDM (Electrical Discharge Machining) for prediction of machining quality. Machining quality is the main indicator of technological performances of a component for EDM. The experiments are carried out on manganese alloyed cold-work tool steel, processed with electrodes made of copper. Experiments were conducted by varying the discharge current and pulse duration and the corresponding values of surface roughness were measured. The values of machining quality predicted by these models are then compared. All models show good agreement with experimental results. The results indicate that the genetic programming technique gives slightly smaller deviation of the measured values of model than fuzzy logic and neural network.

Machinability investigation in hard turning of AISI D3 cold work steel with ceramic tool using response surface methodology

The hard turning process has been attracting interest in different industrial sectors for finishing operations of hard materials. In this paper, the effects of cutting speed, feed rate, and depth of cut on surface roughness, cutting force, specific cutting force, and power in the hard turning were experimentally investigated. An experimental investigation was carried out using ceramic cutting tools, composed approximately with (70 %) of Al2O3 and (30 %) of TiC, in surface finish operations on cold work tool steel AISI D3 heat-treated to a hardness of 60 HRC. Based on 33 full factorial designs, a total of 27 tests were carried out. The range of each parameter is set at three different levels, namely, low, medium, and high. Analysis of variance is used to check the validity of the model. Experimental observations show that higher cutting forces are required for machining harder work material. This cutting force gets affected mostly by feed rate followed by depth of cut. Feed rate is the most influencing factor on surface roughness. Feed rate followed by depth of cut become the most influencing factors on power; especially in case of harder workpiece. Optimum cutting conditions are determined using response surface methodology (RSM) and the desirability function approach. It was found that, the use of lower depth of cut value, higher cutting speed, and by limiting the feed rate to 0.12 and 0.13 mm/rev, while hard turning of AISI D3 hardened steel, respectively, ensures minimum cutting forces and better surface roughness. Higher values of depth of cut are necessary to minimize the specific cutting force.

Transfer of titanium in sliding contacts—New discoveries and insights revealed by in situ studies in the SEM

Titanium and its alloys generally display poor tribological properties in sliding contacts due to their high chemical activity and strong adhesion to the counter surface. The strong adhesion causes a high tendency to transfer and ultimately galling or build-up edge formation, resulting in severe surface damage. As a result, forming and machining of titanium and its alloys are generally associated with significant problems such as high friction, rapid tool wear and poor surface finish of the formed/machined surface.In the present study, in situ tests in a scanning electron microscope have been performed to increase the understanding of the mechanisms controlling the initial transfer of titanium (Grade 2) in sliding contact with tool surfaces. Tool materials included cover cold work tool steel, cemented carbide, CVD deposited Al2O3 and PVD deposited DLC. In these tests, a relatively sharp tip, representing the titanium work material, slides against a flat surface, representing the tool. The contact conditions result in plastic deformation of the work material against the tool surface, thereby simulating forming or machining. The limited and well-defined contact, along with the possibility to study the sliding in the SEM, makes it possible to correlate local surface variations to transfer of work material and frictional response. Post-test characterization of the contact surfaces was performed by high-resolution SEM, TEM, EDS and EELS.The initial friction was low and stable against all tested materials, but then gradually escalated against all surfaces except the DLC. The friction escalation was associated to increasing levels of transfer, while the DLC stayed virtually free from transfer. From these very initial sliding tests DLC is a promising tool coating in forming and machining of titanium.

Monitoring of Wear Characteristics of TiN and TiAlN Coatings at Long Sliding Distances

TiN and TiAlN thin hard coatings have been widely applied on machine components and cutting tools to increase their wear resistance. These coatings have different wear behaviors, and determination of their wear characteristics in high-temperature and high-speed applications has great importance in the selection of suitable coating material to application. In this article, the wear behavior of single-layer TiN and TiAlN coatings was investigated at higher sliding speed and higher sliding distances than those in the literature. The coatings were deposited on AISI D2 cold-worked tool steel substrates using a magnetron sputtering system. The wear tests were performed at a sliding speed of 45 cm/s using a ball-on-disc method, and the wear area was investigated at seven different sliding distances (36–1,416 m). An Al2O3 ball was used as the counterpart material. The wear evolution was monitored using a confocal optical microscope and surface profilometer after each sliding test. The coefficient of friction and coefficient of wear were recorded with increasing sliding distance. It was found that the wear rate of the TiAlN coating decreases with sliding distance and it is much lower than that of TiN coating at longer sliding distance. This is due to the Al2O3 film formation at high temperature in the contact zone. Both coatings give similar coefficient of friction data during sliding with a slight increase in that of the TiAlN coating at high sliding distances due to the increasing alumina formation. When considering all results, the TiAlN coating is more suitable for hard machining applications.

The effect of nitrogen flow rate on TiBN coatings deposited on cold work tool steel

TiBN coatings have high hardness and high adhesion. Due to these excellent properties there has been increasing interest in TiBN coatings. In this study, TiBN coatings were deposited on AISI D2 cold work tool steel and silicon wafers by closed field unbalanced magnetron sputtering (CFUBMS). The structural, mechanical and adhesion properties of these coatings were analysed by X-ray diffraction, scanning electron microscopy, microhardness test, indentation test and scratch tests. TiBN coatings produced by magnetron sputtering exhibited a dense and columnar structure. These results indicate that TiB2, TiN and h-BN exist in crystalline forms at all coatings. The highest hardness was obtained at the lowest nitrogen flow rate. Very few cracks were observed at the edge of the indentation marks at the highest nitrogen flow rate. The highest critical load obtained with scratch test was identified as 102 N.

The Investigation and Growth Kinetics of TiC Coatings on AISI D3 Steel Produced by Thermo-Reactive Diffusion Technique

Abstract TiC coatings on AISI D3 cold-work tool steel were carried out by pack method thermo-reactive diffusion process (TRD) for 2 and 4 h at 950, 1 000, 1 050 and 1 100 °C, respectively. The carbide layers were evaluated based on microstructure, thickness, hardness, energy dispersive X-ray facility and X-ray diffraction analysis. Titanium carbide layer thickness on the coated specimens ranged from 6 to 23 μm, depending on treatment time and temperature. Growth kinetics of the carbide layers were analyzed measuring the depth of carbide layer as a function of temperature and time. The activation energy was estimated to be 249.42 kJ/mol. The micro-hardness value of the coating layer was obtained to be 2 470 HV in maximum.

An investigation on the suitability of different surface treatments applied to a DIN X100CrMoV8-1-1 for cold forming applications

In this work DIN X100CrMoV8-1-1 cold work tool steel samples were plasma nitrided and coated with two different films TiCN and AlCrN by plasma-assisted physical vapor deposition with cathodic arc evaporation method. The samples were characterized concerning surface roughness, chemical composition profile by Glow Discharge Optical Emission Spectroscopy (GDOES), hardness profile, coating thickness, coating adhesion, present phases and residual stresses. Friction coefficient and wear rate were measured by carrying out pin-on-disk tests. Furthermore the developed surface treatments were applied to cutting punches and industrial tests were carried out. Surface conditions (nitrided or not) prior to PAPVD did not affect roughness after coating, but coating adhesion was improved. Compressive residual stresses were increased on the previously plasma nitrided substrates when compared to those on the non-treated ones, and plasma nitriding also resulted in better load bearing capacity. Results also showed that AlCrN and the duplex AlCrN didn't present the running-in behavior as seen for TiCN and duplex TiCN. It was also possible to assure that the combination of plasma nitriding and the TiCN hard coating on top gave the best coating adhesion and the lowest wear rate, what is reflected on the cutting punches analysis after real industrial use.