Development of Evaluation Procedures for the Fracture Mecharical Characterization of Welds at Cryogenic Temperatures

大型超导磁体支撑结构承重构件的制造需要厚壁焊接。这些焊件必须能够承受液氦温度(4K)下的高应力。因此，焊接件的低温断裂韧性是重要的设计参数。本研究项目研究了厚壁焊件断裂力学特性的评定方法。1.用25 mm厚的紧凑型拉伸(1TCT)试件在4K下进行了弹塑性断裂韧性(JIC)试验，评价了下一代聚变反应堆磁体用锻造JN1型奥氏体不锈钢厚壁焊件的断裂韧性和温升。焊缝由钨极惰性气体保护焊(TIG)采用Inconel625型填充金属焊接而成。用Au/0.07%Fe-Chromel热电偶测量了裂纹尖端附近的温升。WE…生产的JN1型奥氏体不锈钢通过200 mm厚的焊接深度在五个位置进行了更多的LD测试和分析。考察了氮含量对J_lt；IC&gt；的影响，发现温升与J积分塑性分量的增加之间具有良好的相关性。2.在4K下对1TCT试件进行J_lt；IC&gt；试验，以确定氮含量、夹杂物含量和二次裂纹对锻造JJ1型奥氏体不锈钢厚板焊接件J_lt；IC&gt；的影响。试件由TIG焊接件在200 mm厚的锻板上加工而成。用0.5TCT和1TCT试件在4K下进行了J&lt；IC&gt；试验，以评价用于大型螺旋装置超导线圈系统的SUS316型奥氏体不锈钢电子束焊的断裂韧性。通过75 mm厚的焊接深度，对SUS316型奥氏体不锈钢焊缝进行了三个位置的试验和分析。研究了试件尺寸、预裂温度和铁素体含量对J&lt；IC&gt；的影响。4.采用J&lt；IC&gt；试验和声发射测试相结合的方法对奥氏体不锈钢焊缝进行了4K下的表征。通过小冲孔试验估算了奥氏体不锈钢焊缝在4K下的断裂韧性。较少

The fabrication of load-bearing members of large superconducting magnet support structures requires the welding of thick section. These weldments must be capable of withstanding high stresses at liquid helium temperature (4K). Therefor, the cryogenic fracture toughness of the weldments is important design parameter.In this research project, evalustion procedures for the fracture mechanical characterization of thick section weldments are investigated.1.Elastic-plastic fracture toughness (JIc) tests were performed with 25-mm-thick compact tension (1TCT) specimens at 4K evaluate the fracture toughness and the temperature rise of thick section weldment in forged JN1 type austenitic stainless steel plate for the fusion reactor magnets of the next generation. The weld was produced by tungsten inertgas (TIG) are welding using Inconel 625 type filler metals. Au/0.07%Fe-Chromel thermocouples were used to measure the temperature rise near the crack tip. The JN1 type austenitic stainless steel we … More ld was tested and analyzed at five locations through the depth of 200-mm-thick welding. The effect of nitrogen content on J_<IC> is examined, and the excellent correlation between temperature rise and increase in plastic component of J-integral is found.2.J_<IC> tests were carried out with 1TCT specimens at 4K to establish the effects of nitrogen content.inclusion content and secondary cracking on J_<IC> of thick section weldment in forged JJ1 type austenitic stainless steel plate. The test specimes were machined from TIG weldment in 200-mm-thick forged plate. Temperatures of base metal specimen were also measured during straining at 4K,and a two dimensional finite element analysis was used to interpret the experimental measurements.3.J_<IC> tests were carried out with 0.5TCT and 1TCT specimens at 4K to evaluate the fracture toughness of SUS316 type austenitic stainless steel slectron-beam weld for the superconducting coil systems in the Large Helical Device. The SUS316 type austenitic stainless steel weld was tested and analyzed at three locations through the depth of 75-mm-thick welding. The effects of specimen size, precracking temperature and ferrite content on J_<IC> are examined.4.J_<IC> tests supplemented with acoustic emission measurement were conducted to characterize austenitic stainless steel welds at 4K.5.Small punch tests were performed to estimate the fracture toughness of austenitic stainless steel welds at 4K.The effect of loading rate to small punch test results is examined. Less