# Application of Instrumented Indentation Procedure in Assessing the Low-Cycle Fatigue Properties of Selected Heat-Treated Steels

## TL;DR

This paper explores how heat treatments affect the fatigue properties of steels using indentation tests and strain-controlled experiments.

## Contribution

The study introduces a new indentation-derived parameter P* to assess fatigue strength coefficients in heat-treated steels.

## Key findings

- The indentation force P* correlates with structural stress parameters in heat-treated steels.
- Fatigue life and cyclic stress-strain behavior vary significantly with heat treatment.
- Elastic strain-life characteristics remain parallel across different tempering temperatures.

## Abstract

The paper presents an analysis of the low-cycle fatigue (LCF) properties of C45, X20Cr13, and 34CrNiMo6 steels subjected to various heat treatment processes. Strain-controlled LCF tests were carried out with a total cyclic strain amplitude equal to 0.5, 1 and 1.5%. Fatigue life, cyclic stress-strain behavior and hardness were analyzed. Qualitative and quantitative relationships between material LCF properties resulting from the heat treatment processes, were related to the indentation force P*, which was derived experimentally by applying an instrumented indentation procedure with the use of the Vickers indenter. The proposed parameter P* and its changes ΔP* seem to be promising for the identification of the structural stress parameter σ* that is necessary for deriving values of the fatigue strength coefficients σf’ corresponding to different tempering temperatures. The common feature of all steels analyzed in this paper is that the elastic parts of the strain-life characteristics remain parallel after being subjected to different tempering temperatures.