Surface preparation of powder metallurgical tool steels by means of wire electrical discharge machining

The surface of two types of powder metallurgical (PM) tool steels (i.e., with and without nitrogen) was prepared using wire electrical discharge machining (WEDM). From each grade of tool steel, seven surfaces corresponding to one to seven passes of WEDM were prepared. The WEDM process was carried out using a brass wire as electrode and deionized water as dielectric. After eachWEDM pass the surface of the tool steels was thoroughly examined. Surface residual stresses were measured by the X-ray diffraction (XRD) technique. The measured stresses were found to be of tensile nature. The surface roughness of the WEDM specimens was measured using interference microscopy. The surface roughness as well as the residual stress measurements indicated an insignificant improvement of these parameters after four passes of WEDM. In addition, the formed recast layer was characterized by means of scanning electron microscopy (SEM), XRD, and X-ray photoelectron spectroscopy (XPS). The characterization investigation clearly shows diffusion of copper and zinc from the wire electrode into the work material, even after the final WEDM step. Finally, the importance of eliminating excessive WEDM steps is thoroughly discussed

Critical Aspects of High Performance Manufacturing of Structural Sintered Steel

Steel is the dominant material for the production of structural parts. By means of powder metallurgy (PM) processing, manufacturers have been able to manufacture steel parts with appreciable dimensional accuracy and proper mechanical properties. Nevertheless, end user demands on part manufacturers are not only suggesting the need for components with better mechanical properties, but also a lower final cost. Such requirements can question the competitiveness of the powder metallurgy process compared with the other well established manufacturing routes. Therefore, to fulfil the end user demands, in this thesis, some critical aspects of the powder metallurgy process for manufacturing structural steel components have been studied. The focus of the study is on compaction and sintering. Two powder metallurgical tool steels (Vancron 40 and Vanadis 10) commonly used in compaction dies were investigated. By means of optical, stereo and scanning electron microscopy in addition to X-ray diffraction analysis, the die materials were characterised and the wear mechanisms identified. Interference microscopy and X-ray photoelectron spectroscopy were used to examine the surface of the dies. The die made of Vancron 40 exhibited a much longer lifetime than the Vanadis 10 die. This discrepancy was mainly due to higher tendencies of oxide formation in the former material as compared to that of the latter. Vancron 40 suffered from mild abrasive, while Vanadis 10 exhibited strong adhesive wear leading to galling.In this thesis, some sintering aspects of water atomised chromium alloyed steel powders have also been dealt with. To simulate microstructures and mechanical properties acquired after sintering, a modern thermodynamic and kinetics software (JMatPro) was used. A good correlation between the simulation results and the available experimental data was found. Having developed a methodology for simulating microstructure development and mechanical properties; carbon content and cooling rate sensitivity analyses were performed. Moreover, to have better understanding of the reactions occurring between the powder compact and the sintering gas atmosphere, with the aid of another thermodynamic computer program (HSC Chemistry) the equilibrium partial pressures of the atmosphere constituents were modelled

Critical Aspects of High Performance Manufacturing of Structural Sintered Steel

Steel is the dominant material for the production of structural parts. By means of powder metallurgy (PM) processing, manufacturers have been able to manufacture steel parts with appreciable dimensional accuracy and proper mechanical properties. Nevertheless, end user demands on part manufacturers are not only suggesting the need for components with better mechanical properties, but also a lower final cost. Such requirements can question the competitiveness of the powder metallurgy process compared with the other well established manufacturing routes. Therefore, to fulfil the end user demands, in this thesis, some critical aspects of the powder metallurgy process for manufacturing structural steel components have been studied. The focus of the study is on compaction and sintering. Two powder metallurgical tool steels (Vancron 40 and Vanadis 10) commonly used in compaction dies were investigated. By means of optical, stereo and scanning electron microscopy in addition to X-ray diffraction analysis, the die materials were characterised and the wear mechanisms identified. Interference microscopy and X-ray photoelectron spectroscopy were used to examine the surface of the dies. The die made of Vancron 40 exhibited a much longer lifetime than the Vanadis 10 die. This discrepancy was mainly due to higher tendencies of oxide formation in the former material as compared to that of the latter. Vancron 40 suffered from mild abrasive, while Vanadis 10 exhibited strong adhesive wear leading to galling.In this thesis, some sintering aspects of water atomised chromium alloyed steel powders have also been dealt with. To simulate microstructures and mechanical properties acquired after sintering, a modern thermodynamic and kinetics software (JMatPro) was used. A good correlation between the simulation results and the available experimental data was found. Having developed a methodology for simulating microstructure development and mechanical properties; carbon content and cooling rate sensitivity analyses were performed. Moreover, to have better understanding of the reactions occurring between the powder compact and the sintering gas atmosphere, with the aid of another thermodynamic computer program (HSC Chemistry) the equilibrium partial pressures of the atmosphere constituents were modelled

Variation of fatigue strength of parts manufactured by laser powder bed fusion

This study reports the variability of the fatigue strength of specimens manufactured by the laser powder bed fusion process with respect to their location on the build plate. Specimens from the right-hand and left-hand halves of the build plate were tested under high cycle fatigue. Comparison of the fatigue data suggests that the specimens manufactured on the right-hand half of the build plate have a higher fatigue strength than those manufactured on the left-hand half. One reason for the observed discrepancy in fatigue strength was the higher accumulation of spattered powder particles on the left-hand side as compared to the right-hand side of the build plate. These spattered particles are oxidised, and form defects such as inclusions within the specimen. © 2021 The Author(s

High Performance Manufacture of Sintered Steel – Critical Aspects of Tooling Performance and Sintered Microstructure

Steel is the dominant material for the production of structural parts. By means of powder metallurgy (PM) processing, manufacturers have been able to manufacture steel parts with appreciable dimensional accuracy and desirable mechanical properties. Nevertheless, end user demands on component manufacturers are not only suggesting the need for components with better mechanical properties, but also a lower final cost. Such requirements can question the competitiveness of the powder metallurgy process compared with the other well-established manufacturing routes.In this thesis the aim is to obtain a deeper understanding of some critical aspects of the powder metallurgy process which can result in the production of higher quality parts at a lower cost. Hence, the emphasis has been placed on three main areas of the Press & Sinter process: tooling performance, microstructure control and optimised component design and process selection. With regard to tooling performance, two types of powder metallurgical tool steels (i.e. alloyed with and without nitrogen) are investigated. These tool steels are commonly used in the manufacturing of compaction dies. The results show that dies made of the nitrogen alloyed (i.e. Vancron 40) material exhibit a much longer lifespan than the nitrogen free (i.e. Vanadis 10) dies. Vancron 40 typically suffers from mild abrasive, while Vanadis 10 exhibits severe adhesive wear leading to galling. This tribological discrepancy is supposed to be associated with the preferred formation of solid lubricant oxides of the Magn\ue9li type on the Vancron 40 surface as compared to Vanadis 10.Furthermore, critical aspects of the sintering operation with specific attention to the sinter-hardening process have been rigorously studied. To this end, the microstructure, mechanical and physical properties of a water atomised Cr-Mo prealloyed steel powder were simulated by utilising a modern thermodynamic and kinetic software (JMatPro). Based on the available literature for solid steel, JMatPro and finite element method (FEM) simulations, other issues such as the influence of density on cooling rate, the effect of different sintering temperatures (e.g. 1120 \ub0C and 1250 \ub0C) on austenite grain size, and consequently hardenability have been thoroughly analysed and predicted. Finally, a computer software (i.e. PM Manager) has been developed to provide designers with an easy to use tool with which the possibilities and limitations of designing and manufacturing a PM component can be readily evaluated

Optimised selection of processing routes for sintered parts manufacture: A component-oriented approach

To stay competitive, PM manufacturers have to be able to accept a wide range of components with different features and properties. Thus, it is of utmost importance for manufacturers to adapt their common process routes to new requirements as rapidly and economical as possible. The procedure of identifying the right route among all the alternatives requires abundance of experience and knowledge and is a crucial and time-consuming decision; usually made by a team of engineers. In this study, by considering the mechanical properties and design specifications of the final component, a simple methodology is developed to aid the engineer(s) in selection of the optimum PM process route. In order to sort the possible routes according to cost, a cost estimating module has been devised. The total concept is applied to a case study and its accuracy has been evaluated

Optimized Selection of Processing Routes for Sintered Parts Manufacture: A Component-Oriented Approach

To stay competitive, PM manufacturers have to be able to accept a wide range of components with different features and properties. Thus, it is of utmost importance for manufacturers to adapt their common process routes to new requirements as rapidly and economical as possible. The procedure of identifying the right route among all the alternatives requires abundance of experience and knowledge and is a crucial and time-consuming decision; usually made by a team of engineers. In this study, by considering the mechanical properties and design specifications of the final component, a simple methodology is developed to aid the engineer(s) in selection of the optimum PM process route. In order to sort the possible routes according to cost, a cost estimating module has been devised. The total concept is applied to a case study and its accuracy has been evaluated