加工後時効熱処理を施した原子炉用低炭素ステンレス鋼の時効析出と残留応力の変化

摘要

Changes in residual stress and precipitation phenomena were studied, during aging for an austenitic stainless steel, SUS316L, cold-rolled with various degrees of reduction and surface ground by transmission electron microscopy and synchrotron radiation (SR) diffractmetry. After aging at 573 K, two kinds of precipitates were observed in the cold-rolled specimens. They were identified as M_7C_3 and M_(23)C_6 by SR diffraction and electron diffraction measurements. The precipitate M_7C_3 was formed both in grain interiors and at grain boundaries, while the precipitate M_(23)C_6 was formed in grain interiors. Precipitation was promoted with increasing cold-rolling reduction. Additionally, segregation of phosphorous was expected along grain boundaries. Residual stresses measured at a synchrotron radiation facility, SPring-8, showed that the compressive stress detected in cold-rolled specimens was changed into tensile stress with proceeding of aging. On the other hand, the tensile stress induced by surface grinding was decreased.%オーステナイト系ステンレス鋼は耐食性に優れているため，ステンレス鋼の中でも大量に，かつ広範囲に使用されている．しかし，オーステナイト系ステンレス鋼の優れた耐食性は，表面に形成される不動態皮膜によって維持されているため，不動態が局部的に損なわれるとその箇所で局部腐食が起こる．