Microalloy Precipitation Control in Development of TMCP

This paper reviewed the development of microalloying technology, mainly took place in Japan. This is neither comprehensive survey nor scrutiny on a specific subject in the microalloying technology, but rather a summary of personal development experience in this field. Because too many papers have been already published on improvement of the base metal properties by microalloying and/or TMCP, I intentionally focused on the application side of microalloying to the HAZ and the weld metal. But every phase was surveyed by the common metallurgical effect of microalloying elements: that is, the kinetics of carbo-nitrides. Firstly the reason for the usefulness of microalloying is explained in relation with the TMCP. Secondly precipitation, growth, and dissolution kinetics of microalloying carbo-nitrides and their application to the HAZ property control are reviewed. Lastly, the influence of steel design on the weld metal property is introduced, by exemplifying the SAW material design of line pipes.