Structure, Mechanical Properties and Fracture Surface Features of Structural Steels Subjected to Deformation-Heat Treatment

A comparative study is made of the structure, mechanical properties and crack growth micromechanisms of 09G2S, 25 and 35X steel pipes after different versions of deformation and heat treatment, including cold plastic deformation of highly tempered material by radial forging and subsequent annealing. It is established that the maximum strength of the test steels is achieved after cold radial forging (CRF) with a degree of deformation of 55% and subsequent annealing at 300 °C. It is shown that CRF and annealing at 600 °C leads to formation of an ultra-fine-grained structure as a result of which reliability properties are achieved similar to a highly tempered condition with retention of improved strength properties. Features of the structure are revealed that is formed during CRF. The micromechanism of crack growth after heat and deformation-heat treatment is studied. Analysis is provided for elements of the failure surface after dynamic tests.