and the average value of the three locations was made the area ratio of fine 1 u03bcm or less in terms of the equivalent circle diameter holes of each sample further the average value of respective samples the front end center part and rear end of the coil was calculated and was made the area ratio of the fine holes of each test no samples with 250 mm length were taken from the front end center part and rear end of the coil respectively were applied with deformation strain of 6 by a tensile test machine and were taken out from the chuck air was thereafter blown to the sample and the scale on the surface of the steel wire material was blown out the appearance before and after application of the strain was photographed by a digital camera and the area ratio of the remaining scale was calculated by comparing the both by image analysis nos 1 2 4 28 30 32 34 35 37 39 41 42 44 45 of tables 4 5 are examples satisfying the requirements of the present invention the scale thickness and the area ratio of the fine holes inside the scale are appropriate and therefore the md property is excellent on the other hand in nos 3 29 33 36 40 43 46 47 the md property deteriorated because.