Method for estimating fracture stress at break of oxide film and apparatus for estimating fracture stress

摘要

PROBLEM TO BE SOLVED: To accurately estimate fracture stress when an oxide film is fractured, the oxide film formed on the surface of a steel material in a state where stress is being applied to the steel material.SOLUTION: To a solution 3 that has conductivity and to which a steel material 10 is not eluted, the steel material 10 on the surface of which an oxide film is formed is immersed; while a fracture test is executed by applying predetermined stress Ts to the steel material 10 immersed to the solution 3 by a test machine 9, a natural potential P1 of the steel material 10 is measured; in a state where the stress Ts is applied to the steel material 10, an inflection point Q1 of the natural potential P1 of the steel material 10 is specified; and stress Ts corresponding to the inflection point Q1 is estimated as fracture stress at the time when the oxide film is fractured.