Effect of Restraint on Root Cracking of Steel Welds
Effect of Restraint on Root Cracking of Steel Welds
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抑制钢焊缝根部裂纹的效果
DOI：
10.2207/qjjws1943.33.6_446
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发表时间：
1964
期刊：
影响因子：
--
通讯作者：
S. Matsui
中科院分区：
文献类型：
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作者：
Masaki Watanabe;K. Satoh;S. Matsui
焊接裂纹的控制是焊接工程师们最关心的问题之一。焊接裂纹的产生与冷却过程中的焊接应力、焊缝金属和热影响区的性能有关。因此，焊接裂纹问题不仅要从冶金学的角度，而且要从焊接应力的角度来探讨。本文研究了拘束对焊接裂纹的影响。3和4设计用于评估钢焊缝根部裂纹的敏感性。利用该装置，开发了如图1所示的“刚性约束焊接开裂试验（RRC试验）”，其使得试样的长度在冷却期间保持恒定。RRC试验方法类似于铃木博士及其合作者开发的用于研究高强度钢焊缝根部开裂的TRC试验。然而，作者的试验方法与TRC试验的不同之处在于：在TRC试验中，在焊接后几分钟或立即施加恒定载荷，因为重点只放在高强度钢焊缝的延迟根部开裂上。另一方面，作者的试验方法非常重要，原因有两个：（1）通过在焊接和冷却期间保持试样长度恒定，使反作用载荷逐渐增加;（2）通过改变约束标距长度（l），允许约束强度有很大程度的可调节性（见图1）。这可能与约束焊缝的实际行为非常相似，作为冷却过程中以及冷却至室温后约束条件下焊缝裂纹的试验方法是合理的。试验是在低碳钢和抗拉强度为60和80 kg/mm ~ 2的高强度钢的焊接件上进行的，所得结果如下。(1)在RRC试验中，随着约束标距的变化，收缩率和反力的大小变化很大，在很宽的温度范围内发生焊接裂纹。反作用载荷随冷却而逐渐增大，较高的约束强度通常有利于裂纹的萌生或缩短裂纹形成所需的时间。(2)在低碳钢焊接件中，焊接裂纹仅在冷却过程中产生，冷却至室温后未观察到裂纹萌生。(3)另一方面，在高强度钢焊接件中，不仅在冷却期间而且在冷却至室温之后观察到裂纹萌生。(4)即使在较低的反应应力水平下也观察到这种延迟开裂。延迟开裂的最小反应应力水平HT-80钢为33 kg/mm ~ 2，HT-60钢为60 kg/mm ~ 2。HT-80钢焊接后的孕育期为1-10小时，HT-60钢焊接后的孕育期为20小时。(5)对于低碳钢、HT-60钢和HT-80钢，在300-370 mm、450-500 mm和550-600 mm范围内没有裂纹萌生。
Control of weld cracking is one of the most important problems for welding engineers. Weld cracking is influenced by welding stress during cooling as well as properties of weld metal and heat affected zone. The problems of weld cracking, therefore, should be explored not only from metallurgical strandpoint but also from standpoint of welding stress. In this report research was focused on the influence of restraint on weld cracking.A new test apparatus as shown in Figs. 3 and 4 was designed for evaluation of sensitivity for root cracking of steel welds. With this apparatus, "Rigid Restraint Weld Cracking test (RRC test)" as shown in Fig. 1 was developed, it is such that the length of a specimen is kept constant during cooling. The RRC test method is similar to the TRC test developed by Dr. Suzuki and his collaborators for the researches on root cracking of high strength steel welds. However the authors' test method differs from the TRC test as follows : In the TRC test a constant load was applied at a few minutes or immediately after welding because emphasis was laid on only delayed root cracking of high strength steel welds. The authors' test method is very significant, on the other hand, for the two reasons which (1) it gives gradual increase of reaction load by keeping the length of a specimen always constant during welding and cooling and also (2) it permits a wide degree for adjustability in the restraint intensity by changing the gauge length of restraining (l), (See Fig. 1). This may be much similar to the actual behavior of restrained welds and will be reasonable as the test method for weld cracking under restraint during cooling as well as after cooled to room temperature.Experiments were carried out on the weldments of a mild steel and high strength steels of 60 and 80 kg/mm2 tensile strength level.The results obtained are as follows.(1) In the RRC test, shinkage rate and magnitude of reaction stress were widely changed with changing the gauge length of restraining, and weld crack occurs in wide range of temperature. Reaction load increases gradully with cooling, and higher intensity of restraint usually favours crack initiation or decreases the time required for cracking.(2) In mild steel weldments, weld crack occurs only during cooling and no crack initiation is observed after cooled to room temperature.(3) In high strength steel weldments, on the other hand, crack initiation was observed not only during cooling but also after cooled to room temperature.(4) This delayed cracking was observed even at lower reaction stress level. Minimum reaction stress level for the delayed cracking is 33 kg/mm2 for HT-80 steel and 60 kg/mm2 for HT-60 steel. The incubation period was measured 1-10 hours for HT-80 steel and 20 hours for HT-60 steel after welding.(5) Critical gauge length (lcr) of restraing, over which no crack initiation was observed, was 300-370 mm for mild steel, 450-500 mm for HT-60 steel and 550-600 mm for HT-80 steel.