A lecture given by K. Fang, at the Adventures in the Physical Metallurgy of Steels (APMS) conference held in Cambridge University. Nanostructured bainite is incredibly difficult to weld because of its high carbon concentration. Here an innovative method is presented to resolve the weldability. High-carbon nanostructured bainite steel is very difficult to be well welded due to poor weldability. By adopting a new technology called regeneration treatment, the welded joint has similar microstructures and mechanical properities to base metal. The effect of regeneration time (0h-120h) and temperature (230°C-270°C) on microstructures and mechanical properities was also investigated. Results show that microstructures in fusion and austenitised zones consist of two phases when regeneration time is long enough, which are nano-scale bainite ?lms separated by carbonâ€"enriched ?lms of retained austenite. However, volume fraction of retained austensite in fusion zone is a little lower than austenitised zone. With regeneration temperature increasing, volume fraction of retained austensite increases and thickness of slender platelets shows the same changing trend. The changes of microstructures have important effect on mechanical properities. By tensile and hardness test, the strength of fusion zone is lower than austenitised zone, but both increases with regeneration temperature decreasing while the elongation decreases. And the micro hardness increases when regeneration temperature decreasing. The strength of obtained welds reaches to as high as 1.7-2.1 GPa and corresponding hardness 550HV-650 HV.