Residual Stresses in Different Heat Treated Workpieces after Turning

Abstract

The use of short process chains for the realization of complex and high performance components is a reasonable approach to achieve sustainable products and to reduce energy consumption. In the Collaborative Research Center SFB/TR TRR30 which is supported by the German Research Foundation DFG this approach is investigated applying thermo-mechanically forming processes. In this way, combining hot metal forming and heat treatment steps in a single process, tailored materials properties together with appropriate geometries are achieved [1, 2] . However, still additional machining operations, e. g. turning operations in case of shafts, are needed to achieve proper workpiece finish. Due to locally varying mechanical properties, undesired changings of the process conditions occur, leading to varying surface and subsurface properties, e.g. the residual stress state. It is well known that residual stresses have a major impact on the components properties during service [3]. In this paper, a survey is given about near surface residual stress states after exterior dry turning of differently heat treated cylindrical workpieces made of steel AISI 6150.

Turning Residual Stresses in Functionally Graded Steel Components

“…In this context, residual stresses play an important role for strength and lifetime of the produced parts. A survey about near surface residual stress states after hard turning of differently heat treated quenched and tempered steel AISI 6150 (51CrV4) is given in [3]. In the present paper, results of similar investigations carried out of Jominy end quench samples are reported and compared with results of samples with homogeneous microstructures.…”

“…The pronounced hardness fluctuations especially in regions of lower hardness can be attributed to the inhomogeneous microstructure of the starting condition of the material. Note that maximum hardness values close to the end face of the material are quite higher than the highest hardness of the materials investigated in [3] (see Fig. 2).…”

“…2 results of residual stress analyses in axial direction after hard turning applying different process parameters of identical materials states taken from [3] are summarized. In this case cylindrical specimen with homogeneous microstructures of differently annealed martensite, characterized by the hardness values indicated, were machined.…”

“…In Tab. 1 the process parameters used for the turning operations are listed, which are identical to those of experiments in [3]. From the hardened and turned Jominysamples 5 mm thick segments were prepared by longitudinal cutting for hardness testing and microstructural investigations.…”

In situ X-Ray Diffraction Investigation of Surface Modifications in a Deep Rolling Process under Static Condition

“…If the FWHM increase would only have been resulting from plastic deformation, no change should have take place after unloading. Therefore, the strong increase of FWHM below the contact point during loading can be attributed to inhomogeneous elastic strains, either of 1 st kind (strain inhomogeneity in the illuminated zone, e. g. over thickness or within the 50 µm beam size) or/and of 2 nd kind (intergranular strains between crystallites during load, as seen by Morooka et al [7]. Due to the mechanical energy input, already present dislocations can decrease due to annihilation effects, while new dislocations are created, which results in an almost constant FWHM for this material state.…”