Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
Characteristics of HAZ Microstructure in Ti-B Treated Steel for Large Heat Input Welding
Yasuhide OHNOYoshihiro OKAMURAShoichi MATSUDAKoichi YAMAMOTOToshio MUKAI
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1987 Volume 73 Issue 8 Pages 1010-1017


Recently the needs for 50 kgf/mm2 tensile strength steels with good HAZ toughness under the welding condition of large heat input have been increasing. A new type of 50 kgf/mm2 tensile strength steel containing small amounts of Ti and B was developed for this purpose.
The steel is charactarized by the microstructure in the HAZ which consists mainly of the intragranular ferrite plates(IFP) without the high carbon martensite islands and the small amount of the grain boundary allotriomorphs.
The toughness of IFP is very good due to its fine ferrite grain. Complex precipitates of TiN-MnS-Fe23(CB)6 act as nuclei of IFP and B addition suppresses the growth of grain boundary allotriomorphs. The authors suppose a mechanism that a carbon depleted zone formed around Fe23(CB)6 assists ferrite nucleation as the reason why IFP is produced effectively by these complex precipitates.

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© The Iron and Steel Institute of Japan
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