关键词: 超快冷, 含Nb钢, 析出, 显微组织, 相变

Abstract: To further improve the strength and reduce development cost of Nb bearing steel, the effects of three cooling methods, including ultra fast cooling, ultra fast cooling added laminar cooling and laminar cooling, on microstructure evolution and mechanical properties of Nb bearing steel have been investigated by hot rolling experiment at laboratory. The results indicate that：Compared with the experimental steel adopting laminar cooling technology, the experimental steel adopting ultra fast cooling technology obtains acicular ferrite and bainite, the grain size is refined, the dislocation density increases significantly, the size of precipitations is refined and mechanical properties improve remarkably. The main strengthening mechanisms under ultra fast cooling condition include phase transformation strengthening, refine grain strengthening, dislocation strengthening and precipitation strengthening. Under the ultra fast cooling added laminar cooling, with the decrease of final cooling temperature, the strength of experimental steel increases resulting from the decrease of soften phase fraction and increase of harden phase fraction. With the decrease of ultra fast cooling ending temperature, the strength of experimental steel increases and the elongation decreases slightly due to the decrease of polygonal ferrite fraction, grain refining and the increase of acicular ferrite fraction. The above results lay the theoretical foundation for developing low cost Nb bearing steel under ultra fast cooling condition.

Key words: microstructure, Nb bearing steel, phase transformation, precipitation, ultra fast cooling