CONTROL OF STRING SHAPED NON-METALLIC INCLUSIONS OF CaO-Al2O3 SYSTEM IN X80 PIPELINE STEEL PLATES

WANG Xinhua; LI Xiugang; LI Qiang; HUANG Fuxiang; LI Haibo; YANG Jian

doi:10.3724/SP.J.1037.2012.00505

Acta Metall Sin >

2013 , Vol. 49 >Issue 5: 553 - 561

DOI: https://doi.org/10.3724/SP.J.1037.2012.00505

CONTROL OF STRING SHAPED NON-METALLIC INCLUSIONS OF CaO-Al₂O₃ SYSTEM IN X80 PIPELINE STEEL PLATES

WANG Xinhua ,
LI Xiugang ,
LI Qiang ,
HUANG Fuxiang ,
LI Haibo ,
YANG Jian

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1)School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083
2)Shougang Technical Research Institute, Beijing 100042

Received date: 2012-08-30

Revised date: 2013-02-05

Online published: 2013-05-11

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Abstract

The string shaped B type non-metallic inclusions in API (American Petroleum Institute) X80 pipeline steel plates, produced by the BOF-LF-RH-Ca treatment steelmaking route, were mainly of CaO-Al₂O₃ system with lower melting temperatures. The formation reasons are as follows: (1) there existed many small sized liquid inclusions of CaO-Al₂O₃ system in liquid steel after the secondary refining and Ca treatment. These small inclusions could aggregate to larger ones of 10- 20μm in continuous casting and be deformed into string shaped inclusions in steel plates during rolling. (2) for the larger sized and low melting temperature CaO-Al₂O₃ inclusions, in Ca treatment, their surface layers could be modified into high melting temperature CaO, CaS or CaO-CaS system, but the centers remained to be CaO-Al₂O₃ system. During rolling, these inclusions could also be elongated to string typed ones because of their soft CaO-Al₂O₃ centers. A new strategy for control of B type inclusions in X80 pipeline steel plates was adopted. The key of the control was shifted from removing low melting temperature inclusions of CaO-Al₂O₃ system after Ca treatment to remove as much as possible inclusions especially large sized inclusions before the Ca treatment. With the new strategy, the amount of inclusions after RH refining was remarkably decreased and the efficiency of Ca treatment significantly improved. The non-metallic inclusions found in steel plates were all of high melting temperature CaO-CaS system and theseverity of B-type inclusions has been lowered from ≤2.0 to 0.

Key words： X80 pipeline steel; non-metallic inclusion; B type inclusion; secondary refining; Ca treatment

Cite this article

WANG Xinhua , LI Xiugang , LI Qiang , HUANG Fuxiang , LI Haibo , YANG Jian . CONTROL OF STRING SHAPED NON-METALLIC INCLUSIONS OF CaO-Al₂O₃ SYSTEM IN X80 PIPELINE STEEL PLATES[J]. Acta Metall Sin, 2013 , 49(5) : 553 -561 . DOI: 10.3724/SP.J.1037.2012.00505

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