This paper elucidates that on eddy-current measurement method can effectively be used in in-process measurement of the case depth in LASER surface heat treatment process.
In LASER heat treatment process of steels, the thin layer of substrate is rapidly heated to the austenitizing temperature and subsequently cooled at a very fast rate due to the self-quenching effect. Consequently, it is transformed to martensitic structure which has low magnetic permeability. The eddy-current measurement method proceeds by measuring the sensing coil's electrical impedance which varies with the changes in permeability.
In this paper, the eddy-current electromagnetic field is analyzed by the finite element methods. The numerical solutions show that the eddy-current measurement method can feasibly be used to measure the changing case depth and the sensitive frequency ranges from 10KHz to 20KHz.
Also, this paper introduces the experimental result of the actual measurement. The experimental results show that the relationship between the eddy-current sensor output and the changes in case depth is almost linear.