Observation of the mechanism of failure in short-time tests of austenitic steels at 1100°C

Conclusions

• 1. Holding the test specimens at 1100°C for 1 minute leads to the development of an initial microstructure before loading.

• 2. Intergranular cracks become apparent even during the early stages of deformation. Under the test conditions the creep process is associated with the preferential destruction of grain boundaries with comparatively small deformations of the body of the grain itself.

• 3. Total deformation before failure of the specimen under various tensile loads amounts to 17.5–25% for steel EX18H9 and 8–16% for steel 4X14H14B2M; smaller total deformation occurs in specimens with a larger grain.

• 4. Under equal conditions of tensile stress (2.5 kg/mm²) the time to failure is 5.5 min for steel EX18H9 and 24 min for steel 4X14H14B2M. In this case the grain size is of importance, inasmuch as with enlargement of the structure (characteristic of 4X14H14B2M) the length of the boundaries is diminished, which is a decisive factor in the accumulation of deformation before failure.