Induktive Erwärmung von partikelverstärkten Stahlpresslingen in den thixotropen Temperaturbereich

The producers of powder metallurgy components are constantly making efforts to improve manufacturing processes and to extend the present ranges of their applications. One way to increase the complexity of powder metallurgy components is the combination of powder metallurgy and thixoforging. In contrast to the conventional process route, the powder‐pressed raw parts are heated up to the thixotropic temperature range in order to realise complex components in one process step. Additionally, the powder metallurgy combined with ceramic particles allows to produce Metal Matrix Composite (MMC) materials with improved mechanical properties compared to conventional materials. In this work basic experiments of the pressing and inductive heating of particle‐reinforced steel parts are examined.     

Effect of quenching temperature on microstructure and performance of Al‐bearing cast boron steel

The effects of quenching temperature on microstructure and performance of Al‐bearing cast boron steel (ACBS) containing 0.25–0.45%C, 1.5–1.8%B and 1.4–1.6%Al were investigated by means of the optical microscopy (OM), the scanning electron microscopy (SEM), X‐ray diffraction (XRD), Rockwell hardness and Vickers micro‐hardness tester. The results show that the solidification structures of cast steel consist of high hardness boride, ferrite, pearlite and a small quantity of martensite when 1.5–1.8%B and 1.4–1.6%Al are added into the carbon steel. The metallic matrix of ACBS changes into single martensite from the mixed structure of ferrite, pearlite and martensite along with the increase of quenching temperature. The increase of quenching temperature also leads to the transformation of boride from continuous shape to isolated shape. Moreover, the micro‐hardness of matrix and macroscopical hardness increase with the increase of quenching temperature. When the quenching temperature excels 1000°C, the hardness has a slight decrease. ACBS has good comprehensive properties after heat treatment at 1000°C.     

Materials characterization and mechanical properties of graded tool steels processed by a new co‐spray forming technique

In order to meet the requirements of micro cold forming tools, a new co‐spray forming process has been applied to produce graded materials from two different tool steels in this study. The two steel melts were atomized and co‐sprayed simultaneously onto a flat substrate, resulting in a flat graded deposit when the two sprays were overlapped. To eliminate porosity and break up carbide network, the graded deposits were further hot rolled. The resultant graded tool steels were investigated with respect to porosity, element distribution, microstructure, hardness, strength, and toughness. The degree of overlapping of the two sprays determined the concentration gradient of the chemical elements in the deposits. The overlapping of the spray cones also contributed to low porosity in the gradient zone of the deposits. The porosity in the graded deposits could be essentially eliminated by means of hot rolling. The carbides and grain structures of the hot rolled tool steels were fine and homogeneous. By means of combining different tool steels in a single deposit, different microstructures and properties were combined.     

TRIP and phase evolution for the pearlitic transformation of the steel 100Cr6 under. step‐wise loads

The investigation of complex material behaviour of steel like transformation‐induced plasticity (TRIP) and stress‐dependent phase transformation (SDPT) is a large field of current research. The simulation of the material behaviour of work‐pieces in complex situations requires a knowledge as deep as possible about such phenomena. In addition, there are effects in the case of non‐constant stress which cannot be explained by the widely used Leblond model for TRIP. Therefore, we consider a TRIP model taking into account back stress due to TRIP itself. Based on experimental data for the isothermal pearlitic transformation of the steel 100Cr6 (SAE52100) under step‐wise loads we calculate material parameters for the extended TRIP model. Regardless of the preliminary character of the performed tests, all experiments show a back‐stress effect with a decrease of the TRIP strain after unloading.     

Overview and comparison of various test methods to determine formability of a sheet metal cut‐edge and approaches to the test results application in forming analysis

This paper presents an overview of published test methods for determination of formability of a sheet metal cut‐edge. The presented test methods were developed to evaluate formability of a sheet metal edge that was produced by shear cutting. Due to high local strains, hardening, or even microcracks, the cut‐edge might have less formability than the base material. The presentation of the tests is structured according to the three steps each test can be divided into: cutting, forming and evaluation. Similarities and differences concerning these steps were worked out. Additionally, a classification of the tests is made regarding their strain gradients in the vicinity of the cut‐edge. For this, finite element models of exemplary tests were built up using LS‐DYNA explicit and analyzed accordingly. Evaluation approaches that go beyond the common hole expansion ratio (HER) from the hole expansion test (HET) standardized in the ISO 16630 are also described. The tests can be used not only for a quantitative comparison of materials and cutting processes with regard to the cut‐edge formability but to determine input data for the finite element analysis (FEA) of forming processes to allow a simulation based cut‐edge failure prediction. The paper also presents appropriate procedures on the transfer of the test results into the FEA of forming of a workpiece with a cut‐edge.