Role of Martensite-Austenite Component of Bainitic Structure in Formation of Properties of Pipe Steel. 3. Effect of Martensitic Transformation of Austenite in the MA-Component of Bainite on the Ductility of Steel

The behavior of low-carbon pipe steel containing 2 and 6 vol.% martensitic-austenitic component in the structure is studied under step forming, expanding and unbending of the pipe using the method of finite-element simulation. The effect of martensitic transformation in the MA-component on the ductility of the steel after processing and unbending of the pipe depending on the volume fraction of the MA-particles in the structure and on the test conditions (the direction of cutting of the samples and the stresses at the start of martensitic transformation) is studied. It is shown that the presence of untransformed austenite in the MA-component can restore partially the ductility of the steel lost due to the plastic deformation during processing of the pipe.