The effect of grain size on 550 ~650 °C 360 〜165 MPa stress rupture property of 316H austenitic stainlees steel 28 mm plate is studued and its rupture mode is analyzed. At 550 °C and by 360 MPa or 335 MPa stress

the stress rupture life of the fine grain (44. 5 μm ) plate only reaches 48. 92% or 51.98% of the coarse grain (89. 6 μm) plate. Wedge crack on the grain boundaries led to the rupture. Tlie grain size has more influence on the stress rupture property

and higher stress makes the effect increase furtherly. However

at 650 °C and by 165 MPa

the stress rupture life of the fine grain (44.5 μm ) plate reaches 91.35% of the coarse grain (89.6 μm)plate. In this case

the grain size has a less influence on the stress rupture property

and microscopic damage occurring during stress-rupture is caused by the growth and coalescence of cavities on grain boundaries.