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The conditions for acicular ferrite formation and the overall transformation behaviour of mild and low-alloy steel weld metals are discussed in terms of deoxidation and alloying practice, solidification microstructure, and operational conditions. Selected weld metal microstructure and composition data are critically reviewed, and new semi-empirical correlations for predictions of the final mechanical properties of the weldment under various welding conditions are presented. The results of this review provide a systematic basis for future research which is required if a sound theoretical treatment of weld metal microstructure development is to be obtained. IMR/155A grain boundary ferrite; B polygonal ferrite; C Widmanstatten ferrite; 0 acicular ferrite; E upper bainite; Flower bainite and/or martensite

A strategy for use of microalloyed steels in long products, including bar and forging steels, is presented based on alloying and processing characteristics applicable to this class of steels. The approach, which defines in temperature/composition space specific composition and processing temperatures for different product types, helps guide selection of microalloy additions for specific applications. Results of several recent product developments characteristic of thermomechanically processed and heat treated bar steels are also presented to illustrate opportunities available for the expanded use of microalloy additions in long products.

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