碳和氮含量对大规格球扁钢组织和性能的影响

doi:10.13228/j.boyuan.issn0449-749x.20220540

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Abstract In the context of the development of large scale ships in the world,in order to meet the needs of the international market and improve transportation efficiency,China has put forward higher requirements for the specifications and performance of ship materials. As the main section bar of ships,the original composition design of bulb flat steel can no longer meet the requirements of the existing large scale strength,toughness and section uniformity. In order to meet the needs of the industry,a kind of No.18 asymmetric bulb flat steel with high strength and toughness and good cross-section uniformity has been studied,using the hot rolling + tempering process to replace the hot rolling+quenching and tempering technology to reduce costs. The experimental steel is a V-N microalloyed steel designed with three different C and N compositions,which is produced in industry and then tempered and tested in the laboratory. The strength and low-temperature toughness of the ball and flat of the bulb flat steel with different C and N contents in hot-rolled and tempered states are studied by means of transmission electron microscopy,phase analysis and other material characterization methods and mechanical property testing. On this basis,the strengthening increment is quantitatively calculated. The results showed that the microstructure of the ball and flat of hot rolled spheroidal flat steel contained polygonal ferrite(PF),pearlite(P) and acicular ferrite(GB). The microstructure combination of PF and P provided better low-temperature toughness,while GB reduced the toughness of experimental steel. After tempering at 680 ℃ for 2 h,the toughness of the three kinds of experimental steels could be greatly improved on the premise that the strength loss is small. Especially for the Low C high N steel,due to the fine grain size and the size of V (C,N) precipitated phase,the yield strength of the ball head and flat of the Low C high N steel was about 560 MPa,and the cross-section uniformity was further improved. Moreover,due to the high content of large angle grain boundaries,the low-temperature toughness was further improved,and the ductile brittle transition temperature of the ball was reduced to -58 ℃,which had excellent strength toughness matching.

Key words： bulb flat steel large size V-N microalloying mechanical property strength toughness matching

Received: 24 August 2022

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	Articles by authors
	CHEN Mi-da
	ZHANG Yun-xiang
	LIANG Feng-rui
	ZHOU Nai-peng
	CHEN Shi

Cite this article:

CHEN Mi-da,ZHANG Yun-xiang,LIANG Feng-rui等. Effect of C and N contents on mechanical properties of tempered large size bulb flat steel[J]. Iron and Steel, 2023, 58(4): 126-137.

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http://www.chinamet.cn/Jweb_gt/EN/10.13228/j.boyuan.issn0449-749x.20220540 OR http://www.chinamet.cn/Jweb_gt/EN/Y2023/V58/I4/126

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