Regeneration technique for welding nanostructured bainite

High-carbon steels which are transformed into extremely fine bainite plates embedded in a matrix of carbon-enriched austenite have recently been developed, and have found commercial application in the manufacture of engineering components. However, because of the large carbon concentration, they cannot be welded and this limits the scope for their exploitation. A method is reported here by which the mixture of bainitic ferrite and retained austenite is regenerated to prevent the austenite that is generated by the heat input during welding, from transforming into brittle martensite. The microstructures of the fusion and austenitised zones were characterised by X-ray diffraction, scanning electron microscopes and transmission electron microscopy. Tensile and micro-hardness tests were carried out to evaluate the mechanical properties. The results show that a bead-on-plate weld with the tensile strength of 1850 MPa and the hardness of 600 HV can in principle be been achieved; these properties almost match those of the base metal.

► The regeneration treatment is used for welding nanostructured bainite steel.
► Nanostructured bainite is obtained again in the welded joint with regeneration.
► Cracks are eliminated by regeneration treatment.
► Weak parts of welded joint transfer to tempered zone by regeneration treatment.
► A weld joint with ultimate tensile strength of 1850 MPa has been achieved.