对填充ER309焊丝的1Cr18Ni9Ti/Q235异种钢接头二型边界形成机理进行了研究. 结果表明，二型边界是由碳钢侧不均匀混合区内Ni质量分数为5% ~ 6%的位置所形成的凝固界面向焊缝中心一侧迁移而形成的. 当部分熔合区和不均匀混合区内Ni质量分数小于5% ~ 6%的区域(N区)为熔池凝固提供δ相基底，或者部分熔合区提供γ相基底且N区提供δ相基底的情况下，碳钢侧熔合边界附近均会形成二型边界；当部分熔合区提供δ相基底且N区提供γ相基底，或者部分熔合区和N区均提供γ相基底的情况下均不会形成二型边界.
Formation mechanism of the type-II boundary of 1Cr18Ni9Ti/Q235 dissimilar steel joint with the filler metal of ER309 was studied. The results showed that the type-II boundary was formed by the migration of the solidified boundaries γ/γ from the position of the 5% ~ 6% Ni mass fraction in the unmixed zone to weld center. Under the condition that the partial fusion zone and the zone of Ni mass fraction less than 5% ~ 6%(N zone) in the unmixed zone provided the substrate of δ phase, or the partial fusion zone provided the substrate of γ phase and N zone provided the substrate of δ phase, the type-II boundary all could form near the fusion boundary of the carbon steel side. The type-II boundary could not form under the condition that the partial fusion zone provided the substrate of δ phase and N zone provided the substrate of γ phase, or the partial fusion zone and N zone provided the substrate of γ phase.
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