Hot-work Steel Research Articles

Optimization of EDM Process Parameters Using Statistical Analysis and Simulated Annealing Algorithm

Nowadays, electrical discharge machining (EDM) has become one of the most extensively used nontraditional material removal processes. Its unique feature of using thermal energy to machine hard-tomachine electrically conductive materials is its distinctive advantage in the manufacturing of moulds, dies and aerospace components. However, EDM is a costly process and hence proper selection of its process parameters is essential to reduce production cost and improve product quality. In this study the effect of input EDM process parameters on AISI2312 hot worked steel, widely used in mold manufacturing, is modeled and optimized. The proposed approach is based on statistical analysis on the experimental data. The input parameters are peak current (I), pulse on time (Ton), pulse off time (Toff), duty factor (η) and voltage (V). Material removal rate (MRR), tool wear rate (TWR), and surface roughness (SR) are the most important performance characteristics of the EDM process. The experimental data are gathered using Taguchi L36 design matrix. Taguchi robust design technique was applied to obtain the signal to noise ratio (S/N ratio) for the quality characteristics being investigated. In order to establish the relations between the input and the output parameters, various regression functions have been fitted on the evaluated S/Ns data based on output characteristics. The significance of the process parameters on the quality characteristics of the EDM process was also evaluated quantitatively using the analysis of variance (ANOVA) method. Then, statistical analyses and validation experiments have been carried out to select the best and most fitted models. In the last section of this research, simulated annealing (SA) algorithm has been employed for optimization of the performance characteristics. Using the proposed optimization procedure, proper levels of input parameters for any desirable group of process outputs can be identified. A set of verification tests is also performed to verify the accuracy of optimization procedure in determining the optimal levels of machining parameters. The results indicate that the proposed modeling technique and simulated annealing algorithm are quite efficient in modeling and optimization of EDM process parameters. doi: 10.5829/idosi.ije.2015.28.01a.20

Formation mechanism of surface scale defects in hot rolling process

Thick oxide scale on steel may result in serious surface defects on hot-worked products. Yield efficiency and productivity of processes are considerably deteriorated by formation of defects. It is highly demanded to establish a way to produce hot-worked steels free from surface defects by controlling oxide scale. The oxide scale shows various behaviors in hot rolling; (a) uniform deformation with matrix steel, (b) cracking, (c) fragmentation, (d) indentation to matrix steel, etc. Through observations using glass coating, it is found that the behavior strongly depends on the rolling temperature as well as the scale thickness before rolling. Temperature drop due to contact with cold rolls is found to cause the cracking and a major reason for the thickness dependence. It is found that the scale cracking is predictable using the estimated scale temperature and the ductile-brittle transition temperature of Wustite (FeO). Then, methodology to produce hot rolled steels without surface defects in industrial processes is presented.

A New High Speed Friction Test for Extrusion Processes

A new axial friction set up for high speed friction was successfully developed and tested at the Extrusion Research and Development Center of TU Berlin. The friction behavior between the Aluminium alloy EN-AW 6060 and the hot-working steel 1.2344 at 300 °C and 400 °C was studied. The experiments were carried out with a relative friction speed from 0.1 to 50 mm/s, and a normalized contact/normal pressure of σn/kf ~ 0 and 1.5. The friction stress curves were depicted and compared with the Tresca friction model. A similar tendency between them was found, however all the theoretical results were around 15 and 30 % higher than the experimental results. In general, higher friction forces were found at 300 °C. Moreover, the effect of normal stress on the friction stress could be studied. By increasing the normalized normal stress from 0 to 1.5 kf the friction stress increases around 30 % at 300 °C and 10 % at 400 °C. A strong adhesion effect was observed especially at 400 °C, which represents around the 90 % of the total friction stress. The friction results can be reproduced using a friction factor of m= 0.85 at 300 °C and m= 0.7 at 400 °C.

Oxidation and Thermal Fatigue Behaviors of Two Type Hot Work Steels During Thermal Cycling

Thermal fatigue test has been carried out on widely used hot work steel 4Cr5MoSiVl and a low alloyed steel 3Cr3MoV in temperature range of 200 to 700 °C. Tempering resistance, as well as high temperature hardness/strength of steel specimens, works as a dominating material parameter on thermal fatigue resistance. During the heating period, high hardness can depress the inelastic deformation. This deformation is the origination of tensile stress, which acts as the driving force of heat checking during the cooling period. The cyclic strain-oxidation interaction can speed up the damage on surface defects, which plays an obvious role in initiation of thermal cracks. On 4Cr5MoSiVl steel specimens, borders between the matrix and inclusions such as titanium compounds, or lager carbides such as primary carbides, are focused by strain and attacked by oxidation, and are main initiating places of cracks. While on 3Cr3MoV steel specimens, larger strain causes plastic deformation concentrating around grain boundaries. Then the following oxidation accelerates this grain boundary damage and creates cracks.

BÖHLER W405 ISOBLOC

Abstract Böhler (or Boehler) W405 is a hot work steel with a great combination of hardness, strength, toughness, ductility, and thermal conductivity to resist typical damage mechanisms in applications. This datasheet provides information on composition, physical properties, and elasticity. It also includes information on forming and heat treating. Filing Code: TS-722. Producer or source: Böhler-Uddeholm North America.

Effect of laser surface alloying on structure of a commercial tool steel

This research project presents the investigation results of laser remelting and alloying especially the laser parameters and its influence on the structure and properties of the surface of the 32CrMoV12-28 hot work steel, using the High Power Diode Laser (HPDL). As a result of the performed research structure changes were determined concerning the grain size and reinforcement ceramic particle distribution in the steel surface layer. The reason of this work was to determine the optimal laser treatment parameters, particularly the laser power applied to achieve good layer mechanical properties for protection of this hot work tool steel from losing their work stability and to make the tool surface more resistant to action in hard working conditions. The remelted layers which were formed in the surface of investigated hot work steel were examined metallographically and analysed using light and scanning electron microscope as well as X-Ray diffraction.

Thermal Fatigue Behavior of Nitrocarburized and Low Pressure Nitrided Modified JIS SKD61 Hot Work Mold Steel

A novel method using induction heating equipment was employed to investigate the thermal fatigue behaviors of two hot-work steels, JIS SKD61 and modified JIS SKD61, vacuum hardened treated to 45 HRC. Selected specimens, austenitized at 1298K for 25min, gas quenched to room temperature and tempered at 873K, were salt bath nitrocarburized at 843K for 80min and low pressure nitrided at 813K for 6h, respectively. Microstructure, microhardness, X-ray diffraction and thermal fatigue tests were conducted. The results show that the thermal fatigue properties of the 898K tempered specimen were better than those of other treated specimens. The reason is that the hardened processes would give high tensile strength, which improved the tool material thermal fatigue resistance. The thermal fatigue properties of modified JIS SKD61 specimen, including mean crack length and crack distribution density, were better than those of JIS SKD61 specimen. Low pressure nitriding treatment with a homogeneous nitrided layer could better maintain thermal fatigue resistance than the nitrocarburized steel.

Thermal Fatigue Behavior Evaluation of Shot-Peened JIS SKD61 Hot-Work Mold Steel

Thermal fatigue cracking is one of the most important failure mechanisms in hot work die steels. Shot-peening can be used in a much wider field to obtain higher static strength, as well as better fatigue resistance. This study investigates the shot-peening effect on the microstructure and mechanical properties of hardened JIS SKD61 hot-work steel. The thermal fatigue test is based on cyclic induction heating and water cooling. A non-peened specimen with a hardness of 510HV0.05 was used as the reference material. The scanning electron microscopic observations showed craters on the surface and a severely worked hardened area in the shot-peened specimen subsurface. The microhardness values of the shotpeened surface are about 720 and 750HV0.05 for the Almen intensity of 15A (typical shot-peened specimen) and 18A (severe shot-peened specimen), respectively. The work hardening depths of typical shot-peened and severe shot-peened specimens are about 20 and 30µm, respectively. The thermal fatigue properties of shot-peened specimens, including the mean crack length and crack distribution density, are better than those of non-peened specimens. Only a slight improvement in thermal fatigue properties occurred for the severe shot-peened specimen compared with typical shot-peened specimen. [doi:10.2320/matertrans.M2013019]

Influence of Hard Milling on the Surface Integrity of Hot Working Steel

The efficiency of forming and moulding processes highly depends on the surface quality of the manufactured tools, dies and moulds. The capability of these tools is significantly defined by the tooling material, the geometrical precision and the integrity of the sub-surface. Machining of hot working steels in their hardened state is a major challenge for multi-axis hard milling processes in the tooling sector. In this study the machining and the related impact to the generated sub-surface was investigated. The most utilized hot working steels, especially in the field of die casting, 1,2343, 1,2344, 1,2367 and 1,2340 were considered. It was observed that mainly by choosing appropriate cutting parameters, ploughing-related sub-surface deformation as well as cutting, tearing and deformation of the microstructure and local machining-related sub-surface hardness-increase can be significantly decreased in contrast of choosing “worst case” scenarios in terms of centre milling and milling with worn milling tools.

Laser Cladding of CPM Tool Steels on Hardened H13 Hot-Work Steel for Low-Cost High-Performance Automotive Tooling

This paper summarizes our research on laser cladding of high-vanadium CPM® tool steels (3V, 9V, and 15V) onto the surfaces of low-cost hardened H13 hot-work tool steel to substantially enhance resistance against abrasive wear. The results provide great potential for fabricating high-performance automotive tooling (including molds and dies) at affordable cost. The microstructure and hardness development of the laser-clad tool steels so obtained are presented as well.

Advances in Surface Engineering: Alloyed and Composite Coatings

The use of composite and alloyed coatings is a widely used strategy for obtaining desired properties in a surface coating. Several advantages are envisaged by use of these coatings. Some of these include a desirable change in fracture toughness, wear resistance, corrosion resistance, as well as electrical and thermal properties. It is known that no single material can provide all the properties. The selection of the constituents and their relative amounts determines the properties of the coatings, and hence, this provides a way for tailoring the properties of the composites. The interaction of the composite mixture during the spray process is interesting to study because the constituents may have different deposition efficiencies and process optimization needs to be carried out to get the desired composition in the coating. Instead of pure metals, alloyed coatings offer higher wear and corrosion resistance. Amorphous and nanocrystalline coatings are potential candidates for applications in severe conditions. Amorphous materials are typically multicomponent and are known to have high corrosion resistances. Similarly, pitting corrosion is expected to be discouraged by use of nanocrystalline coatings. To capture the recent advances in this area, a symposium with the same title as this article was held at the TMS 2012 Annual Meeting and Exhibition in Orlando, Florida. The symposium included 54 presentations with several invited talks from U.S. and international researchers. Talks concerning wear resistance, indentation behavior, development of residual stresses, and electrochemical behavior of composite and alloy coatings were presented over five sessions. This included several processing methods such as laser deposition, electrochemical techniques, thermal spraying, spark plasma sintering, and physical and chemical vapor deposition techniques. There was a huge interest in many of the talks, and attendance was good compared with previous years. The discussion in this JOM issue on surface engineering highlights some of the current views and presents six papers touching on these topics. The first paper by Boris D. Bryskin and co-workers titled ‘‘Chemical Vapor Deposition of Iridium and Rhodium Coatings from Hydridotetrakis (triflourophosphine) Complexes’’ presents a study on iridium and rhodium coatings on molybdenum substrates by chemical vapor deposition. These coatings are important in applications because of their inertness. They show the use of new organometallic complexes that result in pure coatings without contamination of carbon and oxygen, which is otherwise difficult to obtain from conventional precursors. The second paper by J. Chen and L. Xue on ‘‘Laser Cladding of CPM Tool Steels on Hardened H13 HotWork Steel for Low-Cost High-Performance Automotive Tooling’’ presents studies on laser cladding H13 tool steels with high-alloy, high-vanadium tool steels. It improves the surface of molding and extrusion dies leading to improved performance. The paper discusses the microstructure and hardness of the coatings and the effect of hardening and tempering treatments on the evolution of hardness. The third paper by M. Aghaie-Khafri and M. Mohamadpour Nazar Abady presents a study on the chromo-boronizing treatment of DIN1.2714 steel. The authors show the multilayers of Fe and Cr borides, namely, CrB, Cr2B, FeB, and Fe2B, which have high hardness. Kinetic analysis of the layer formation is also provided along with the effect of the treatment on the corrosion resistance. The fourth paper by Mingdong Bao and co-workers titled ‘‘The Tribological Behavior of Plasma Sprayed Al-Si Composite Coatings Reinforced with Nanodiamond’’ discusses the microstructure and tribological behavior of Al-Si coatings reinforced JOM, Vol. 64, No. 6, 2012

Sliding/rolling wear performance of plasma nitrided H11 hot working steel

H11 steel discs were tested by considering sliding/rolling friction under dry and lubricated conditions. The H11 discs were plasma nitrided at 500°C and 550°C for 9h. Wear tests were conducted at different slip ratios of 1.79%, 10.53% and 22.22%. The test loads were 100N, 150N and 200N. It was determined that plasma-nitrided H11 discs had a surface hardness of 1200–1400HV0.1. Plasma nitriding produced wear performance much higher than those of the un-nitrided but hardened samples. The wear mechanism of the plasma-nitrided discs was a mixture of adhesive wear, abrasive wear and plastic yielding.

Effect of duty cycle on residual stress and tribology behaviour of TiCx nanostructure coating deposited by PACVD method

In this paper, nanostructured TiCx was coated onto H11 hot working steel by pulsed dc plasma assisted chemical vapour deposition method, and various duty cycles were carried out in order to observe the influence of this parameter on residual stress and tribology behaviours. The duty cycles were 33, 40 and 50% at 510°C operating temperature. Therefore, wear behaviour, hardness and chemical analyses of TiCx nanostructure coating were characterised, and it was found that the residual stresses in the coating were compressive, which were −1·1516, −0·1323 and −0·1752 MPa at three different duty cycles, i.e. 33, 40 and 50% respectively. According to the results, the coating that was applied at 40% exhibited superior wear resistance and possessed the lowest friction coefficient of ∼0·06 in a pin-on-disc test against WC–Co.

Numerical and Experimental Investigations on the Service Life Estimation for Hot-Forging Dies

Hot forging dies are exposed during service to a combination of cyclic thermo-mechanical, tribological and chemical loads. Besides abrasive and adhesive wear on the die surface, fatigue crack initiation with subsequent fracture is one of the most frequent causes of failure. In order to extend the tool life, the finite element method (FEM) may serve as a means for process design and process optimisation. So far the FEM based estimation of the production cycles until initial cracking is limited as tool material behaviour due to repeated loading is not captured with the required accuracy. Material models which are able to account for cyclic effects are not verified for the fatigue life predictions of forging dies. Furthermore fatigue properties from strain controlled fatigue tests of relevant hot work steels are to date not available to allow for a close-to-reality fatigue life prediction. An industrial forging process, where clear fatigue crack initiation has been observed is considered for a fatigue analysis. For this purpose the relevant tool component is modelled with elasto-plastic material behaviour. The predi

The Study of EDM Parameters in Finishing Stage on Electrode Wear Ratio Using Hybrid Model

In this study, the influence of different electro discharge machining parameters (current, pulse on-time, pulse off-time, arc voltage) on the electrode wear ratio as a result of application copper electrode to hot work steel DIN1.2344 has been investigated. Design of the experiment was chosen as full factorial. Artificial neural network has been used to choose proper machining parameters and to reach certain electrode wear ratio. Finally a hybrid model has been designed to reduce the artificial neural network errors. The experiment results indicated a good performance of proposed method in optimization of such a complex and non-linear problems.

The Study of EDM Parameters in Finishing Stage on Electrode Wear Ratio Using Hybrid Model

In this study, the influence of different electro discharge machining parameters (current, pulse on-time, pulse off-time, arc voltage) on the electrode wear ratio as a result of application copper electrode to hot work steel DIN1.2344 has been investigated. Design of the experiment was chosen as full factorial. Artificial neural network has been used to choose proper machining parameters and to reach certain electrode wear ratio. Finally a hybrid model has been designed to reduce the artificial neural network errors. The experiment results indicated a good performance of proposed method in optimization of such a complex and non-linear problems.

Thermal fatigue of hot working steel after hybrid surface treatment

AbstractThe application of surface treatment methods like ion nitriding, physical vapour deposition (PVD) coatings and their combination in duplex treatments effectively reduces the occurrence of oxidation, corrosion, erosion and wear processes. However, it is still uncertain whether nitriding and duplex treatment have any real effect on the decrease in the nucleation and growth of thermal fatigue cracks on the surface. This paper presents the results of thermal fatigue investigations of a nitrided layer and different composite layers ‘nitrided layer/PVD coating’ (TiN, CrN and TiAlN) obtained on the EN X40CrMoV5·1 hot working steel. The ion nitrided only and three different duplex treated substrates were compared, based on the intensity of the thermal fatigue cracks observed after testing. The nitrided layer and composite layers investigated were obtained with the use of the hybrid surface treatment technology consisting of ion nitriding followed by arc evaporation coating deposition. Apparatus based on h...

Direct Extrusion of Circular Profiles with Surface Composite Produced by Friction Stir Processing

In this research, a new application of friction stir processing (FSP) in producing surface composite on circular billets was introduced. Al/Cu composite was fabricated by FSP on the surface of a 1050 aluminium cylinder with the diameter of 60 mm. Then this cylinder with surface composite was extruded with the extrusion ratio of 1.7. Finally, microstructure and microhardness were investigated before and after the extrusion. H13 hot work steel was used as the material of the tool whose pin diameter and length were 6 mm and shoulder diameter was 18 mm. The rotation and traverse speed of the tool were 1000 rpm and 25 mm/min respectively. The microstructural investigations show that the thickness of the composite layer decreases and a uniform layer of the composite remains on the surface after the extrusion. Also the microhardness measurements demonstrated that the hardness of the composite layer was higher than the base metal and the microhardness of all zones increased after the extrusion.

Effects of duty cycle on microstructure and corrosion behavior of TiC coatings prepared by DC pulsed plasma CVD

Titanium carbide coatings are deposited on hot-work steel (H11) by plasma-assisted chemical vapor deposition (PACVD) and the dependence of the corrosion behavior on fabrication parameters is investigated. Grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FESEM), Raman and electrochemical tests are used to study the structure as well as corrosion behaviors. Grazing incidence X-ray diffraction reveals the (200) plane implying that the TiC coatings are deposited via the kinetics-limited crystal growth mechanism and under thermodynamically stable conditions. The SEM results indicate that the formation of a homogeneous and uniform titanium carbide nanostructure coatings. Potentiodynamic and electrochemical impedance tests performed in 0.5M H2SO4 and 0.05M NaCl show that the TiC coating produced using a 40% duty cycle possesses high corrosion resistance in both media. The Rp values of the TiC coating (50% duty cycle) in 0.05M NaCl and the other TiC coating (40% duty cycle) in 0.5M H2SO4 are approximately four and sixteen orders of magnitude higher than that of the bare steel, respectively. Our results reveal that the duty cycles not only affect the structure and morphology of the coatings but also influence the electrochemical properties.

Improved tribological properties of TiC with porous nanostructured TiO 2 intermediate layer

The mismatch in the thermal expansion coefficients between TiC coatings and steel substrates and residual stress in the TiC degrade the tribological properties. In this work, a porous nanostructured TiO 2 coating is deposited as an intermediate layer on hot-work steel (H 11) before final deposition of the TiC film. This intermediate layer is expected to reduce the interfacial energy, decreases the thermal mismatch between TiC and steel, and improves the tribological properties. Grazing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and pin-on-disk are used to study the structure as well as tribological properties such as friction, wear, and hardness. Our results reveal that the porous TiO 2 interlayer improves the friction, wear, hardness, and elastic modulus of the system.