PSI - Issue 43

Michal Krbaťa et al. / Procedia Structural Integrity 43 (2023) 270 – 275 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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formed). Most elements, e.g., Mn , Si , Al , Cu , Ni , prolongs the decay time of austenite. Alloying elements other than Al and Co modify M s and increase the proportion of retained austenite. As the proportion of carbon in the steel increases, the effect of the additives will be even more pronounced. In addition, carbide-forming elements ( Cr , W , V , Mo ) significantly change the shape of the diagram - they separate the pearlitic and bainitic degree of transformation. At the interface of these transformations, the decay slows down and at the same time increases the stability of subcooled austenite (Liu et al. 2017, Anijdan et al. 2012, Leach et al. 2019, Kawulok et al. 2020). 2. Experimental Work 2.1. Experimental Material X37CrMoV5-1 Steel is suitable for highly stressed tools operating at elevated temperatures. The chemical composition of a given tool steel and the basic mechanical properties can be found in Table 1. Seven cooling rates of 10, 5, 1, 0.5, 0.1, and 0.05 °C/s were used for the steel under investigation. The samples were heated to an austenitization temperature of 1000 °C where the endurance at the austenitization temper ature was set for 10 min. Table 1. Chemical composition of steel (wt.%) and basic mechanical and physical properties of steel X37CrMoV5-1 ISO 4957 C Mn Si Cr Mo V Min 0.33 0.25 0.80 4.80 1.10 0.40 Max 0.41 0.50 1.20 5.50 1.50 0.70 * air cooled The basic microstructure of the tool steel was fine-grained, consisting of a ferritic matrix with a high content of globular carbides rich mainly in Cr , V and Mo . 3. Result and Discussions 3.1. Analysis of dilatation curves for tool steel X37CrMoV5-1 In Fig. 2 shows a selected heating curve on which the start and end of the austenitization temperature A c1 and A c3 are shown by means of tangent lines. As we can see in this figure, the initial temperature of austenitization A c1 started at 861 °C and the end of austen itization A c3 was at 929 °C. These values are also confirmed by the derivation of the given dilatation curve on which it is possible to read these temperatures even more accurately. These austenitization temperatures were determined as the average of all seven measurements in order to obtain the most accurate determination of these temperatures. Spectral analysis 0.37 0.38 1.15 5.20 1.46 0.49 Mechanical and physical properties Tensile strength (MPa) Modulus of elasticity (GPa) Thermal conductivity (W·m -1 ·K -1 ) Hardness * (HV) Heat capacity (J·kg -1 ·K -1 ) Value > 615 200 25 660 465

Fig. 2. Determination of transition temperatures A c1 and A c3 with continuous heating to 1 °C/s