Hardness effect on thermal fatigue damage of hot-working tool steel

• At high temperature, the behavior of the both steel is similarly.
• The modulus of elasticity does not influenced by hardness.
• The increase of the hardness decreases the crack propagation rate.
• Heat treatment has not major effects on the crack initiation period.

Thermal cracks in die-casting are often caused by thermal fatigue loading, surface stresses, low material strength and surface irregularities. During the process cycle, alternate heating and cooling leads to thermal fatigue. Mechanical and thermal stress fluctuations initiate fine cracks on the cavity surface that grow larger and ultimately lead to failure of the die. Hardness or surface heat treatment can extend the die life time. The aim of this work is to study the thermal fatigue damage of AISI H13 tool steels that underwent different heat treatments. The results prove that the thermal fatigue resistance is closely related to the initial hardness. In fact, thermal fatigue tests prove that increases in the hardness of the steel lead to decreases in the crack growth rate. However, it seems that the heat treatment does any not major effect on the crack initiation period of thermal fatigue cracks.