炭素鋼における表面脱炭深さの非破壊測定に関する研究

Abstract

For nondestructively inspecting the existence of a decarburized layer and its depth in a carbon steel, we investigated the electric inspection method of tubing and bar stock.If a steel bar stock which has a known depth of decarburized layer on its Surface is placed in the field of a exciting coil, which is energized by alternating current of high freequency, circumferential alternating current are induced in the steel bar.These induced currents, distributed near the suface of the bar, set up a magnetic field opposing the magnetic field of the exiter. The flux density between the coil and the bar is therefore a function of the resistance of the material and of the distance from the mean path of the current with in the material.The measurement of the magnetic flux is effetive by means of search coil located with in the magnetic flux and in close proximity to the steel bar.The voltage induced in the search coil is measured by a valve voltmeter, and from these results the decarburized depth versus induced voltage reletionship is obtined.Using this relationship, we can nondestructively inspect the existence of a decarburized layer and its depth in a steel bar stock.This experiment was carried out with the specimens of 0.61% carbon steel, 12mm diameter, 155mm in length, and its decarburized depth 0-0.5mm. The experimental result obtained are as follows, (1) When the exciting current are 40-80mA, the sensitive results are obtainable.(2) The suitable frequency of exiting current are selected from the range of 400-1200cycle/ sec according to the depth of decarburized layers, which ranges from 0 to 0.5mm.(3) This method is useful for picking up some decarburized ones from many heat treated parts which have same dimension.