STEEL MATERIAL SURFACE QUALITY EXAMINING METHOD

摘要

A method for simply and reliable examining the weldability of a steel material, for example the oxidization scale of a hot-press steel material. (i) Two measurement terminals that can be pressed under a constant pressing pressure of 8.7 to 208 N/mm<2> are pressed against a member made by a hot-pressing a hot-rolled steel sheet (cold-rolled steel sheet), a constant current of 30 A or less is made to flow between the measurement terminals to measure the voltage between the measurement terminals. (ii) The steel material is subjected to a spot-welding test, and it is judged that this welding is acceptable or not. (iii) With reference to the voltage between the measurement terminals measured about the steel material judged as acceptable, a range of the voltage or resistance between the measurement terminals leading to favorable result of the spot-welding test is determined. (iv) The voltage between the measurement terminals about a steel material is measured in spot welding of actual operation, the spot weldability of this steel material is predicted and judged according to whether the measured voltage value is within the range.