ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Cause of bending fracture and control of inclusions in high-strength fasteners made of Al-bearing high carbon steel
Tao ZhangHu LongGuoguang Cheng Junyu GuoZhongyu LeiZhongzhong Xun
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JOURNAL OPEN ACCESS Advance online publication

Article ID: ISIJINT-2023-126


In this paper, the cause of bending fracture of high-strength fasteners after electroplating and the effect of T.Ca, T.O, and T.S contents in Al-bearing high carbon steel on the type, size, and shape of inclusions were studied. The fracture surface of fastener exhibited stepwise cracks and a lot of intergranular facets associated with ductile tearing, which were typical of hydrogen embrittlement. The agminated elongated MnS inclusions in the center of fasteners could aggravate the susceptibility of hydrogen embrittlement. Thermodynamic calculation showed that the ideal modification of MnS inclusions needed to meet the conditions that the inclusions in molten steel before solidification should be C12A7, and the mass ratio of CaS/MnS at the end of solidification was 23.7. Based on the above conditions, the quantitative relationships between the contents of T.Ca, T.O, and T.S were determined. Among them, the T.O content in steel increased with the increase of S content. Therefore, to suppress the formation of type B-stringer shaped inclusions and improve the cleanliness of steel, the sulfur content in steel should not be high.

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© 2023 by The Iron and Steel Institute of Japan

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