| 摘要 |
PURPOSE:To predict the life expectancy of stainless steel easily and uniquely by measuring the length of crack in a test piece and the intergranular concentration upon elapse of a predetermined interval and then calculating the crack latent time and the lifetime based upon this. CONSTITUTION:A test piece of stainless steel material has known initial intergranular Cr concentration Cr0 at the time t0 of starting to use, and known Cr concentration (corrosion starting critical Cr concentration) Cr1 at a crack latent time t1 when a crack begins to appear. When the intergranular Cr concentration Cr2 is measured by means of a transmission electron analytic microscope and the crack length L2 is measured by means of an optical microscope upon elapse of a predetermined time t2, the latent time t1 can be determined as follows; t1= {(Cr0-Cr1)/(Cr0-Cr2) }Xt2. Subsequently, the lifetime t3 and equal determined as follows; t3=t1+(t2-t1) (L2/L3)<1/2>. (L3 represents the crack length for the lifetime t3 and equal to a crack developing speed (v) integrated from time t1 to t2). Finally, the life expectancy T=t3-t2 of steel material is determined as follows; T=(t1-t2)+(t2--t1)(L2/L3)<1/2>. |
