304 스테인리스 鋼의 高溫에서의 表面균열 成長特性에 관한 硏究

Surface crack growth behaviors of 304 stainless steel at elevated temperatures

본 연구에서는 고온기기의 부재로 널리 사용되는 304스테인리스강을 사용하여 기기의 사용조건을 고려한 538.deg. C(1000.deg. F), 593.deg. C(1100.deg. F)및 650.deg. C(1200.deg. F)의 세가지 온도레벨하의 대기중에서 크리이프-피로시험을 실시하여 작은 인공표면결함으로부터 발생.성장하는 표면균열의 성장거동을 조사 연구하였다. 또한 주파수의 영향을 조사 하기 위하여 538.deg. C에서 고온피로시험을 실시하여 이 결과를 크리이프 및 크리이프피로 시험의 결과와 비교.검토하였다.

Creep and fatigue tests were carried out on crack growth properties of small surface cracks in 304 stainless steel at 538.deg.C, 593.deg. C and 650.deg. C in air, by using small plate specimens with a small artificial pit. All the data of the crack growth rate per hour obtained in the present tests were correlated with the maximum stress intensity factor, so that the applicability of linear fracture mechanics to the crack growth of surface cracks at elevated temperature was investigated. In the creep test, relatiion of .sigma.$\^$n/.t$\_$f/=C is obtained between failure time and nominal stress at each temperature level, where n has the value of 11-14 depending on the temperature level. In the creep and fatigue crack growth properties of surface cracks at the elevated temperatures, the maximum stress intensity factor, $_{4}$$\_$max/, is some extent applicable parameter to describe the surface crack growth rate under the present experimental conditions. The crack growth rate per hour increases when the holding time decreases, and creep crack growth rate per hour becomes the lowest limit of crack growth rate per hour in this tests.