Influence of the Deformation Rate of Different Tests on Hot Cracking Formation

Abstract

Referring to the ISO standardization of hot cracking test procedures with externally loaded specimens, three different and fundamental test procedures are assessed with the help of experiments and finite element analyses to find out the influence of different deformation rates on the test results of three well known stainless steels.

A comparison is made between the hot tensile test carried out with help of the Gleeble system using the Moscow procedure of the Standard of Russian Federation, the American instructions for the Hot Ductility Curve as well as the PVR-test (controlled deformation crack test) created in Austria. These main test procedures have generally been used for more then 30 years.

While within the American Hot Ductility Curve Test a round tensile specimens is torn after heating by thermal resistance to a test temperature some degrees below liquation at a tension speed of about 50 mm/s, the Russian method heats all round tensile specimens to the same maximum temperature just above the melting point and loads each specimen at another tension speed between 0.01 and 0.1 mm/s for approximation of the critical tension speed.

For tensile test comparison, the PVR test is carried out on round specimens with a diameter of 10 mm. A TIG melt run is simultaneous welded longitudinally at a superposed tension speed linearly increasing from zero to 1 mm/s in welding direction. The length position of the first crack appearing at the specimen defines the critical tension speed.

Three different stainless steels have been subjected to these test procedures. The test results of the different procedures precisely correlate within the materials ranking, but differ in the amount of evaluated test criteria.