NON-DESTRUCTIVE QUANTITATIVE EVALUATION METHOD FOR PLASTICITY OF STEEL PRODUCT

摘要

PROBLEM TO BE SOLVED: To quantitatively evaluate the degree of residual distortion as plasticity by measuring a magnetic field of the surface of a steel product to determine a distribution range in terms of a difference between the maximum and the minimum values of a magnetic signal within a zone of a specified size. SOLUTION: A specified tensile load is applied to a test object 10 is applied to measure the degree of residual distortion with a type displacement meter or the like. The surface magnetic field of the test object 10 after loaded is measured, for example, by a superconducting quantum interference device fluxmeter having a concentric type secondary differentiation detection coil and zoned by 55 cm2 to define a difference between the maximum value and minimum value within the zone. A distribution range as a difference between the maximum and minimum values of a space differential value of each zone positioned on a specified line in the longitudinal direction of a narrow part 10b of the test object 10 correlates with the degree of residual distortion in a plastically deformed area. Therefore, for example, the surface of a steel material of the existing structure is scanned by the fluxmeter to extract a space differential value of each zone on a line along the direction of drawing the steel product. Thus, by learning the distribution range of the space differential values, the residual distortion can be obtained quantitatively.