Development and Investigation of Mechanical Properties of Hot Forging Dies by Bulk Forming and Thermomechanical Treatment
Final Report Abstract
Forging tool steels are exposed to a complex load spectrum that includes high thermal and mechanical stresses. This leads to wear, plastic deformation and crack formation in the die. In order to minimize the primary damage mechanisms of crack formation and wear, a compromise between high hardness and high toughness is required. Ausforming offers the potential to resolve this conflict of objectives through grain refinement and to achieve hardening without sacrificing ductility. In order to determine and evaluate the potential of ausforming of tools for hot forging, a process chain for the production of dies was developed with the aim of increasing the tool life. The focus here was on tool geometries with primarily mechanical stress, which favours crack formation. The investigations into the applicability of ausforming in the production of tools made from the hot-work tool steel X38CrMoV5-1 were divided into the experimental determination of suitable process routes and the production and testing of a crack-prone die engraving. Comparative mechanical material tests and optical analyses of the microstructure were used to evaluate the process chain. First, the thermal process route was characterised using simplified upsetting tests. Based on this, ausforming was used to produce cups with different degrees of deformation, which were tested for load-bearing capacity under cyclic swelling stress state. The resulting forming parameters and the thermal process route consisting of heating, cooling and tempering conditions were used to produce die inserts. Finally, these were subjected to tool life tests in order to investigate the application behaviour with regard to thermomechanical fatigue cracking under operating conditions. In the model tests on the simplified cup geometry, an increase in hardness due to ausforming was observed compared to conventional production, which had a detrimental effect on crack resistance. The reference samples, which were only forged and heat-treated, achieved a higher number of load cycles. A comparison of different thermomechanical process routes showed that lower degrees of deformation and tempering temperatures have a favourable effect on fatigue resistance, but also lead to lower hardness. Scaling to larger die inserts from 7 mm to 15 mm bottom thickness results in differences in the thermal equalisation processes and therefore in the transformation behaviour and thus the achievable material properties. Tests in forging trials have shown that austenitic hardening can achieve a significantly longer service life than conventionally produced and formed dies.
Link to the final report
https://oa.tib.eu/renate/handle/123456789/21415
Publications
-
Manufacturing of High-Performance Forging Dies by Ausforming. METAL Conference Proeedings, 2020, 203-208. TANGER Ltd..
BEHRENS, Bernd-Arno; BRUNOTTE, Kai & TILL, Michael
-
Adjusting Mechanical Properties of Forging Dies Produced by Ausforming. ESAFORM 2021-24th International Conference on Material Forming. Liège: ULiège Library
Behrens, Bernd-Arno et al.
-
Transfer of Ausforming Parameters TO SCALED Forging tools. METAL 2021 Conference Proeedings, 2021, 247–252.
BEHRENS, Bernd-Arno; BRUNOTTE, Kai; PETERSEN, Tom; RELGE, Roman & TILL, Michael
