The sides of disk-like specimens made of 5%Cr-Mo-Si steel were repeatedly heated and cooled by using a high-frequency induction surface-hardening apparatus, and the influence of heating time and heating temperature on the formation of heat-checks on the sides was studied. The results were as follows: (1) The longer the heating time (
t) and the higher the heating temperature (surface temperature θ), the more conspicuous the checks. This tendency is more apparent in the case of
N(the number of thermal cycles)=1000 than
N=100. (2) In the case of
N=1000, the mean depth and the maximum depth of checks increase with increasing heating times and heating temperature, but the total number of checks reaches a maximum at
t=2.5 sec (θ=850°) and decreases at
t=3.0 sec (θ=910°). (3) The depth of checks at any heating time is distributed according to the exponential function, but in the case of
t=3.0 sec the distribution is changed showing a lesser number of shallow checks. (4) With increasing heating time and heating temperature, the width of the checks on the cross-section of the specimen also increases.
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