Abstract
The characteristic of toughness in weld heat affected zone (HAZ) of multi-pass welded high strength steel was investigated in this study. In multi-pass HAZ, some kinds of microstructure are distributed and toughness can be affected by this microstructure distribution. Therefore, in this report, the distribution of microstructure in HAZ of multi-pass welded 60 kgf/mm2 class high strength steel was investigated.
The main results obtained were as follows.
(1) It was confirmed that HAZ was heated above the reverse transformation temperature once, twice or three times by weld thermal cycles. But it was found that the microstructure in HAZ could be almost simulated by single or double thermal cycles.
(2) Peak temperature of weld thermal cycle could be divided into three regions according to its effect on microstructure. That is, (I) α-γ dual phase region, (II) low hardenability region and (III) hardenability recovered region.
(3) Microstructure was relatively uniform in the outer and the intermediate part of HAZ. But, in the inner part (that is, near the fusion line), three kinds of microstructures were ditsributed.
