Thermal fatigue properties of hot-work tool steels

Abstract

The Thermal Fatigue (TF) resistance rates of four martensitic chromium steel grades (DIN 1.2343, 1.2344, 1.2365 and 1.2367) are evaluated. Three parameters were used to describe the resistance to thermal cracking: the mean crack length lm, the maximum crack length lmax and the crack density ρ. A higher damage is shown by DIN 1.2343 and 1.2344 compared to DIN 1.2365 and 1.2367, the latter being characterised by higher yield strength at elevated temperature, higher resistance to thermal softening and lower toughness. An increasing number of cycles is required to nucleate the cracks in different materials, i.e., 60, 120, 180 and 240 for 1.2343, 1.2344, 1.2367 and 1.2365, respectively. During the initial incubation stage, the crack density displays an increase with increasing thermal softening and decreasing hot strength. During the rest of the test, a general increase in maximum crack length can be appreciated with increasing thermal softening and decreasing hot strength.