Thomas Hirsch

Effect of different surface states before plasma nitriding on properties and machining behavior of M2 high-speed steel

Abstract In the present work the effect of different surface conditions on the plasma nitriding response of AISI M2 high-speed steel was investigated. Samples and drills were prepared to different surface finishes prior to plasma nitriding: ground and sandblasted. Polished samples were used as a reference surface state. The plasma nitriding was performed at temperatures of 400 and 500 °C for two gas mixtures: 5 and 76 vol.% N2 in hydrogen. The surfaces were characterized before and after plasma nitriding concerning the microstructure, roughness, microhardness, chemical composition, phase composition and residual stress states. Machining tests were carried out with drills, during which drilling forces and flank wear were measured. A significant effect of the surface state prior to nitriding on the residual stress states and properties of the nitrided layer and untreated core has been observed. Thinner nitrided layers on ground and sandblasted samples were attributed to high compressive residual stress states and a stress-affected diffusion of nitrogen and carbon. In the machining tests, sandblasted drills exhibited the best performance. Lower nitrogen concentrations in the gas atmosphere gave the lowest drill flank wear for sandblasted surfaces, while higher nitrogen concentrations led to a reduction in drilling forces and torque.

Nitrided layer embrittlement due to edge effect on duplex treated AISI M2 high-speed steel

Plasma nitriding prior to TiN deposition on single-point turning tools made of high-speed steel (HSS) AISI M2 has been carried out in order to investigate the improvement of machining performance. Optical and scanning electron microscopy, microhardness test, glow discharge optical emission spectroscopy (GDOES) and X-ray diffraction (XRD) were used to characterize the nitrided layer. Machining tests using a tool life criterion of 0.3 mm average width of the flank wear land were carried out to evaluate the service performance of the composite tools. The results have indicated that careful attention must be taken when comparing flat coupons to complex shaped substrates. In plasma nitriding systems without auxiliary heating, nitrogen incorporation depends on the plasma current density and, therefore, temperature, which can be significantly higher at the tool edges, forming an excessive deep and brittle diffusion case, reducing the service life of the duplex treated tool. The results also indicated that using brighter plasma nitriding, the TiN hard coating machining performance could be improved dramatically.

Analysis by design of experiments of distortion potentials in drawn and induction hardened wire

In this investigation a DoE (Design of Experiments) analysis of distortion for a typical manufacturing process of pre-straightened, cold drawn and induction hardened AISI 1045 cylindrical steel bars was carried out. A careful characterization of the material, including residual stress states and geometrical changes, was done for the different manufacturing steps. In order to identify effects and correlations on distortion behavior, the investigated variables included the drawing process itself with two different drawing angles, a stress relief treatment, which was applied to one part of the samples, and, finally, induction hardening with two different case depths. Main and statistically significant effects on the distortion of the induction hardened samples were found to be in this order, the drawing angle, the stress relief treatment and the induction hardening depth. It was also found that the distortion potentials are transmitted from the drawing process to further manufacturing steps and, consequently, from one production site to the next.

Combined Neutron and X-Ray Diffraction Analysis for the Characterization of a Case Hardened Disc

The present work has been executed within the framework of the collaborative research center on Distortion Engineering (SFB 570) in order to evaluate the residual stress state of a disc after carburizing and quenching as well as to validate a simulation procedure. The combined use of X-ray and neutron diffraction analysis provided information about the residual stress states in the whole cross section. However, the stress free lattice spacing d0 for the neutron diffraction experiments is problematic and induces systematic uncertainties in the results and the application of a force balance condition to recalculate d0 might be a solution for improving the reliability of the results. Comparison of experimental results with simulation showed that an overall satisfying agreement is reached but discrepancies are still present.

Experimental characterization and simulation of a wire drawing process and related distortion potentials

Abstract In this investigation a DoE (Design of Experiments) analysis of distortion for a typical manufacturing process of pre-straightened, cold drawn and induction hardened AISI 1045 cylindrical steel bars was carried out. A careful characterization of the material, including residual stresses and geometrical changes was done for the different manufacturing steps. The variables included the drawing process itself with two different drawing angles, a stress relief treatment which was applied to one part of the samples and finally an induction heat treatment with two different case depths applied to identify effects and correlations on distortion. Simulation of the drawing process was also used as tool to clarify possibilities and limits of this kind of analysis, depending on the available input data. Different influences on the distortion of the induction hardened samples were found and discussed, as for example the marked dependence of the distortion on drawing angle.

Comparação entre difração de raios X e "método do furo cego" para medição de tensões residuais em barras cilíndricas

The residual stresses in the surface and subsurface of mechanical components during the manufacturing process can affect the behavior and represent a significant potential for deviations in shape and size. These residual stresses also represent one of the main potentials for the distortion (which are bending and dimensional changes) in mechanical components during the manufacture. Therefore, the determination of the distribution and the control of these residual stresses in each stage of the manufacturing process is of great importance. In this work, analysis of the variation of the residual stresses were accomplished in cold-drawed bars of AISI 1045 steel due to the manufacturing process. The bars were analyzed by X-ray diffraction (XRD) and hole-drilling (H.D) to characterize the residual stresses. Starting from the values of strains obtained, the longitudinal residual stresses were calculated for each tested point. With this work, a detailed view of the development of stress in the surface to a depth of 1mm of bars after the process steps was obtained.

Distortion Analysis in the Manufacturing of Cold-Drawn and Induction-Hardened Components

In this investigation, a design of experiments analysis of distortion for a typical manufacturing process involving pre-straightening, cold drawing, and induction hardening of AISI 1045 cylindrical steel bars was carried out. A careful characterization of the material, including residual stress states and geometrical changes, was done for the different manufacturing steps. In order to identify effects and correlations on distortion behavior, the investigated variables included the batch influence, the combined drawing process itself with two different drawing angles and two different polishing and straightening (P.S.) angles, a stress relief treatment which was applied to a part of the samples, and finally induction hardening with two different surface hardening depths. Main and statistically significant effects on the distortion of the induction-hardened samples were found to be in this order: first, the interaction between the drawing angle and batch, then the interaction between drawing angles, and finally drawing angle and induction hardened layer. It was also found that the distortion potentials are transmitted from the drawing process to further manufacturing steps and, consequently, from one production site to the next.

Effect of microstructure on electrical conductivity of Inconel 718 alloys

Abstract The microstructural evolution of Inconel 718 during aging processes has been studied through a combination of eddy current testing, X-ray diffraction analysis, and metallography and hardness measurements. Measurements were carried out in samples subjected to eight different heat treatment cycles, between 620 and 1035°C for 1–18 h. Different amounts of secondary precipitates were achieved, reaching 18% of delta phase for samples overaged at 900°C for 18 h. Results show that the different microstructures of Inconel 718 obtained have a distinguishable effect on electrical conductivity when this is measured through an appropriately sensitive technique (i.e. eddy current testing). The lowest conductivity values were observed for under aged samples (1·44% IACS). A clear increase in conductivity values was seen for all aged or overaged conditions, reaching a maximum of 1·63% IACS, when coarsening of intra granular precipitates, associated with an increase in density of globular precipitates at grain boundaries, was identified. The influence of microstructure on conductivity could be shown to be due to the competition between two effects on the scattering of electrons: matrix purification and precipitation characteristics. A combination of hardness values and electrical properties proved to be a fast and practical way of determining the stage of aging of the alloy.

Residual stress analysis of drive shafts after induction hardening

Typically, for automotive shafts, shape distortion manifests itself in most cases after the induction hardening by an effect known as bending. The distortion results in a boost of costs, especially due to machining parts in the hardened state to fabricate its final tolerances. In the present study, residual stress measurements were carried out on automotive drive shafts made of DIN 38B3 steel. The samples were selected in consequence of their different distortion properties by an industrial manufacturing line. One tested shaft was straightened, because of the considerable dimensional variation and the other one not. Firstly, the residual stress measurements were carried out by using a portable difractometer, in order to avoid cutting the shafts and evaluate the original state of the stresses, and afterwards a more detailed analysis was realized by a conventional stationary diffractometer. The obtained results presented an overview of the surface residual stress profiles after induction hardening and displayed the influence of the straightening process on the redistribution of residual stresses. They also indicated that the effects of the straightening in the residual stresses cannot be neglected.

Comparison between Neutron Diffraction measurements and numerical simulation of residual stresses of a Wire-Drawing process

In this work, a drawing processed was simulated to calculate forces and the resulting residual stresses in the material. The calculated residual stresses were compared with experimentally measured residual stresses by the Neutron Diffraction Method. The modeled process was the Wire Drawing. The necessary parameters to model the process were taken from an industrial currently used process. Rods of an AISI 1045 steel with nominal diameters of 21.46 mm were reduced to 20.25 mm by drawing with an drawing angle of 15°. Compression tests were used to determinate flow curves of the real material an used in the simulation models. The possibility to estimate drawing forces by numerical simulation was evaluated by comparing simulated results with values from empirical equations given by the literature. The results have shown a sufficient accuracy for the calculation of forces, but the comparison of residual stresses has shown differences to the experimentally determined ones that can be minimized by the consideration of high strain rates in the compression tests, anisotropy of the material and kinematic hardening.