高强钢焊缝热裂纹断口形貌的研究

On Fracture Morphology of HotCracking in HighStrength Steel Weld Using HighSpeed Photography and Data Processing

研究了变拘束试验方法条件下产生的焊缝热裂纹断口形貌的形成机理及影响因素。结果表明，该方法所导致的热裂纹断口形貌分为四种类型：Ａ型区、Ｄ型区、ＤＦ型区及Ｆ型区。而四个区的形成机理和尺寸大小主要和试验中的应变速率相关。在较高的应变速率条件下，ＤＦ型区、Ｆ型区尺寸明显减小，而Ｄ型区尺寸增大。

We are the first in P.R. China to study systematically the effect of strain rate on hot cracking of welds, using advanced technology. We found that, in hot cracking of highstrength steel welds, the strain rate influences significantly the follwing items: (1) the rate of crack propagation, (2) the fracture morphology and its four different types of regions, (3) the formation mechanism of each type of region. The SEM pictures in Fig.1 show the four types of regions of the fracture surface: Fig.1(a), Atype (arant); Fig.1(b), Dtype (dendrite); Fig.1(c), DF type (dendriteflat); Fig.1(d), Ftype (flat). Using highspeed photography and data processing and analyzing the results so obtained, we found that strain rate influences significantly but quite differently the crackpropagation rates in the four regions. After careful analysis, we deem that the effect of strainrate on crack propagation is due to that high strainrate facilitates innergrain deformation and thus increases the ability of steel to deform under high temperature. SEM pictures in Fig.2 show the marked difference of the four regions under two different strain rates: the relatively high 19%·s -1 (Fig.2(a)) and the usual 11%·s -1 (Fig.2(b)).