PSI - Issue 43

Maroš Eckert et al. / Procedia Structural Integrity 43 (2023) 318–323 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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the improvement or development of new products. These empirical models, by their very nature, often conform to certain groups of materials that exhibit similar hot deformation behaviours. It is not possible to derive universal constitutive models that would suit all materials, processes and processing conditions, Barlat et al (2007). At present, analyzes of metallic materials in terms of hot deformation are performed on dilatometric devices. The work of Pernis et al. (2010), Zhou et al. (2022) provide a comprehensive overview of the hot deformation of metallic materials. A standard deformation curve describing the thermal deformation of metals is shown in Fig. 1. This curve consists of two co-ordinates, the true stress and true strain, while the elastic deformation is negligible. Four characteristic points can be observed in the profile of the deformation curve, whereby the point [0; σ 0 ] represents the beginning of the plastic deformation. In this context the stress σ 0 can be considered as the compression stress limit. The subsequent point, characterized by coordinates [ε p ; σ p ], represents the maximum stress value of the stress-strain curve and it is designated as the peak stress (Spigarelli et al. 2003, Solhjoo 2009). Analogously, the deformation value, where the deformation curve reaches the maximum, is referred to as the peak deformati on ε p . Furthermore, the point coordinates [ε i ; σ i ] defines the inflection point of the deformation curve. Finally, at the point [ε ss ; σ ss ] the curve reaches a steady state, at which a dynamic equilibrium occurs between hardening and softening process in a deformed material. Dilatometry makes it possible to perform the pressure tests under defined conditions, in terms of temperature, strain and strain rate in order to acquire high temperature deformation stress- strain curves (Jurči et al. 2019, Yang et al. 2 019, Jurči 2012).

Fig. 1. Typical hot deformation curve of steels

This work focuses on the analysis of the use of a constitutive model based on the Arrhenius equation. Of all the available models, this model, designed in the 1960s, best describes the behavior of the material at higher temperatures and over a wide range of strain rates. It is based on a phenomenological approach using the Arrhenius equation, transformed into a constitutive equation that expresses the actual stress and strain rate at different temperatures using the Z parameter, known as the Zener-Hollomon parameter (Zener et al. 1944). This parameter represents a thermally compensated strain rate that is widely used to characterize the hot work behavior of materials (Shang et al. 2018). 2. Experimental Work 2.1. Experimental Material Tool steel 100MnCrW4 for universal hardening oil was chosen as the experimental material. The alloying elements are manganese, chromium and tungsten. Tools made of this steel have good wear resistance due to the tungsten content, which is also contributed by the higher chromium content. The steel shows good hardenability, fine structure, and high toughness. Another important feature is very good dimensional stability after heat treatment. The chemical composition with the limit values allowing the relevant standard are given in Table 1. The basic microstructure of annealed steel contains fine carbides in a ferritic matrix and tempered martensite.

Table 1. Chemical composition of tool steel 100MnCrW4 ISO 4957 C Mn

Si

Cr

W

V

Min. Max.

0,85 0,95 0,91

1,80 2,20 1,83

0,10 0,40 0,32

0,40 0,65 0,50

0,40 0,70 0,64

0,05 0,20 0,18

Spectral analysis