Dynamic Strain Ageing of A533b Class 1 Nuclear Pressure Vessel Steel

摘要

The dynamic strain aging behavior of A533B nuclear grade low alloy steel was evaluated as a function of initial heat treatment, based on determination of the tensile properties at temperatures in the range 50 to 100 C and strain rates varying from 8.3 x 0.00001 to 5.3 x 0.001/s. Residual levels of interstitial nitrogen present in the steel under standard heat treatment conditions are sufficient to induce measurable susceptibility to dynamic strain aging, as evidenced by serrated yielding and flow in the temperature range 150 to 275 C and peaks in proof and ultimate tensile strength in the range 250 to 300 C. The temperatures dependence for onset of serrations is associated with an activation energy higher than that for simple diffusion of nitrogen in ferrite, and it is suggested that the process is controlled by nitrogen manganese atom interactions. Modified heat treatments which result in coarse prior austenite grain sizes lead to diminution of the strain aging effects, whereas quenching treatments give enhanced strengthening, principally in the temperature range 50 to 250 C.