Tailoring the Hardening Behavior of 18CrNiMo7‐6 via Cu Alloying

Abstract

In order to improve the rolling contact fatigue (RCF) behavior of gear steels, a concept to increase their damage tolerance is developed alternatively to the conventional approach of improving the degree of steel cleanliness. For that purpose, Cu is used as a main alloying element in order to trigger the precipitation of nano‐sized Cu precipitates which shall improve the strain‐hardening rate of the martensitic matrix of Cu‐alloyed 18CrNiMo7‐6 steel surrounding a non‐metallic inclusion during plastic deformation. In this way, early component failure may be avoided and the maintenance costs of, e.g., wind energy converters may be kept low. The experimental analysis shows that nano‐sized Cu precipitates influence the material's strength, ductility, and strain‐hardening behavior under tension, depending on their coherence. Among others, the latter is related to strain‐induced martensitic transformation of coherent Cu. The structure of the Cu precipitates is studied by TEM and SANS analysis. The Cu‐alloyed steel also shows an increased hardening‐exponentCHT studied by cyclic hardness test (CHT) PHYBALCHT. Fatigue tests of specimens with coherent precipitates show cyclic hardening until a critical stress amplitude. Above that, stress amplitude cyclic softening is detected. An increased damage tolerance could be obtained for a 1 mass‐% Cu‐alloyed 18CrNiMo7‐6 steel.

Cyclic Indentation of Iron: A Comparison of Experimental and Atomistic Simulations

“…This confirms that the hardening-exponent CHT (e II ) obtained from PHYBAL CHT can be compared with the cyclic hardening behavior of materials in uniaxial fatigue loading conditions [12]. Further studies by Bambach et al [14] have demonstrated a successful application of the PHYBAL CHT (e.g., to determine optimized heat treatment conditions of high strength steel for maximum damage tolerance during fatigue loadings). The present paper, however, focuses on understanding the local microstructural changes during cyclic indentation with help of MD simulations.…”

Effect of Crucible Material for Ingot Casting on Detrimental Non‐Metallic Inclusions and the Resulting Mechanical Properties of 18CrNiMo7‐6 Steel

“…The low strength zones were assumed to be a result of the scatter of carbon content in the solidified structure. 4) Metallographic characterization of non-metallic inclusions is a powerful tool to describe the steel quality. However, information on oxygen level in the melt and the NMI distribution and sizes in the solidified steel is not sufficient.…”

“…The influence of inclusions on the mechanical behaviorespecially the fatigue behavior -was investigated as well. [4] The mechanical behavior of metallic materials is highly controlled by non-metallic inclusions in different ways. Non-metallic inclusions in solid steel act as stress raisers and promote fracture during quasi-static, dynamic, or cyclic loading.…”

On the Mn–C Short-Range Ordering in a High-Strength High-Ductility Steel: Small Angle Neutron Scattering and Ab Initio Investigation

“…SANS is a well-established, non-destructive method to obtain structural information about the arrangement of atoms and magnetic moments on a mesoscopic scale, from near atomic (nanometer) to near optical (micrometer) sizes, in condensed matter systems and materials from a wide range of applications. Such arrangements may be macromolecules [20], self-assembled polymeric systems [21], biomolecular aggregates [22], precipitates and SRO in metallurgical materials [23,24] or porosities in geological and construction materials [25]. Neutrons interact with matter via short-range nuclear interactions and, thus, detect the nuclei in a sample rather than the diffuse electron cloud observed by X-rays.…”