APPLICATION OF NANO-SCALE PRECIPITATE ENGINEERING OF TiN-NbC COMPOSITE IN 32mm K60-E2 GRADE PLATE ROLLING

摘要

A cost effective alloy design based on niobium microalloying was developed by Shagang for the production of 32 mm gage K60-E2 steel plate for manufacturing LSAW pipes of 1422 mm diameter. Two metallurgical challenges are (i) to meet enhanced CTOD toughness and (ii) to ensure consistent DWTT performance in accordance with the specification laid out by Gazprom Vniigaz. Nano-scale precipitate engineering of TiN-NbC composite offers a novel method based on microstrutural engineering for integrated design and processing to refine the austenite grain size in upstream processing of heavy gage plate before pancaking in order to improve DWTT performance. Accelerated growth of NbC precipitates engineered at austenite grain boundary is effective in catalyzing the nucleation of acicular ferrite. The increase in acicular ferrite fraction in target microstructure is the key to achieve enhanced CTOD toughness in base plate. This paper deals with the application of nano-scale precipitate engineering of TiN-NbC composite precipitates in plate rolling in order to obtain consistent fracture toughness at low temperature in 32 mm gage plate of K60-E2 grade, as measured by CTOD and DWTT performance.