Hot Rolling Process and Microstructures of X70 Pipeline Steel Under Ultra-Fast Cooling

doi:10.12068/j.issn.1005-3026.2015.11.013

Abstract

Abstract: The microstructures and mechanical properties of 14.2 mm X70 pipeline steel， which undergoing ultra-fast cooling+laminar cooling and single laminar cooling after finish rolling， were compared and analyzed. The strengthening and toughing mechanisms were discussed for ultra-fast cooling methods. The results indicate that the mechanical properties of the experimental steel at both cooling methods can meet the API SPEC 5L X70 criterions. The microstructures consist of bainitic ferrite， acicular ferrite and M-A island， and the mixture microstructures of acicular ferrite and M-A island can be refined at the condition of ultra-fast cooling+ laminar cooling. The main strengthening mechanisms are grain refinement strengthening and nano-scale precipitation strengthening. The ideal cooling method after rolling for 14.2mm X70 pipeline steel is listed as: finish rolling at temperature of 820~840℃+ ultra-fast cooling to temperature of 450~500℃+laminar cooling to 350~400℃+ coiling.

Key words: ultra-fast cooling, X70 pipeline steel, acicular ferrite, M-A island, hot rolling

CLC Number:

TG142.1

KANG Jian， ZHAO Jin-hua， WANG Xue-qiang， DI Hong-shuang. Hot Rolling Process and Microstructures of X70 Pipeline Steel Under Ultra-Fast Cooling[J]. Journal of Northeastern University Natural Science, 2015, 36(11): 1576-1580.

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