Influence of thermal fatigue on the impact strength of Orvar Supreme hot-work tool steel

摘要

The paper presents the results of investigation of thermal fatigue of Orvar Supreme steel (equivalent of WCLV steel) on a test stand designed by the Metal Forming Institute. The stand consisted of the following main elements: induction heater, cooling system of pyrometers. Thermal cracks have been made on rectangular samples with the dimensions close to those of standard impact test pieces but without notch. The heating cycles of the sample have been performed at the temperature of 500°C, 600°C, and 650°C. The number-of cycles was 1 thousand and 5 thousand. Non-destructive measurements of the total length of thermal cracks on the sample edge have been performed by means of a computer tomograph by the Institute of Casting in Cracow. Charpy impact test has been performed at the temperature of 500°C, 600°C and 650°C on samples subjected to a thousand and 5 thousand heating cycles. In the tests, Charpy pendulum machine with initial impact energy of 300 J has been used. The crack depths have been measured on the cross sections of samples after impact tests and the test results have been analysed. The tests have been performed on samples subjected to cyclic heating at the temperature of 600°C and 650°C. As a result of the cyclic heating of the samples up to the temperature of 500°C, at 5 thousand cycles, thermal cracks have not been found. Heating has caused increase of the impact energy as compared to toughened samples. At the temperature of 600°C, the effect of hardness increase has taken place, which has resulted in reduction of the energy necessary to break the impact test piece. The longest cracks have been obtained on the samples subjected to 5 thousand heating cycles at 650°C.