Cyclic Crack Growth in Chemically Tailored Isotropic Austenitic Steel Processed by Electron Beam Powder Bed Fusion.

Matthias Droste,Horst Biermann,Thomas Niendorf,Sebastian Henkel,Christina Burkhardt,Johannes Günther,Ruben Wagner

doi:10.3390/ma14216544

Abstract

The present study analyzes the cyclic crack propagation behavior in an austenitic steel processed by electron beam powder bed fusion (PBF-EB). The threshold value of crack growth as well as the crack growth behavior in the Paris regime were studied. In contrast to other austenitic steels, the building direction during PBF-EB did not affect the crack propagation rate, i.e., the crack growth rates perpendicular and parallel to the building direction were similar due to the isotropic microstructure characterized by equiaxed grains. Furthermore, the influence of significantly different building parameters was studied and, thereby, different energy inputs causing locally varying manganese content. Crack growth behavior was not affected by these changes. Even a compositional gradation within the same specimen, i.e., crack growth through an interface of areas with high and areas with low manganese content, did not lead to a significant change of the crack growth rate. Thus, the steel studied is characterized by a quite robust cyclic crack growth behavior independent from building direction and hardly affected by typical parameter deviations in the PBF-EB process.

Highlights

Introduction and Matthias MarklAustenitic stainless steels are widely used in industry due to their outstanding corrosion resistance and their combination of high ultimate tensile strength and excellent ductility
These results indicate that an adequate adjustment of the process parameters enables chemical variations in the same part, even if it is built out of the same powder feedstock, see [19]
The austenitic stainless steel X5CrMnNi16-7-6 was processed by PBF-EB and assessed in cyclic crack growth experiments

Summary

Introduction

Introduction and Matthias MarklAustenitic stainless steels are widely used in industry due to their outstanding corrosion resistance and their combination of high ultimate tensile strength and excellent ductility. In contrast to other austenitic steels like AISI 316L, the CrMnNi steel exhibits a primary ferritic solidification leading to a solid–solid phase transformation bcc→fcc upon cooling [10]. Due to adjacent scan tracks and further layers added on top, i.e., the layer-wise PBF-EB production principle, the material gets heated up several times [10]. This process’ inherent cyclic heat treatment provokes repetitive phase transformations and is supposed to induce an isotropic microstructure with nearly equiaxed grains of about 30 μm size and without a pronounced crystallographic texture [10]. No special scan strategy is needed, i.e., this alloy offers a Received: 5 October 2021

Methods

Results

Conclusion