热处理对GH3128合金接头组织及力学性能的影响

 核能已经逐渐取代化石能源成为新一代能源,作为重要构件的高温气冷堆中间换热器得到了广泛关注。由于GH3128合金具有较好的焊接性、较高的高温抗氧化性能和组织稳定性,有望成为超高温气冷堆中间换热器的候选材料,但基于换热器结构复杂性以及密封性的要求,焊接是其生产和制造的关键成形手段。采用脉冲钨极氩弧焊(GTAW)对GH3128合金2 mm板材进行对接焊,研究了热处理对焊接焊接接头显微组织以及应力的影响。结果表明,在优化焊接工艺参数下,固溶态板材接头表现出最高的强塑性,室温及高温拉伸断裂位置均为母材。由于热轧态与固溶态板材接头热影响区在焊接过程中产生残余应力,导致该区硬化,在高温变形过程中残余应力诱发热影响区μ相析出,对接头持久、蠕变性能造成不利影响。焊后热处理消除了接头热影响区的残余应力,减少了持久、蠕变过程中μ相的析出,接头持久寿命得以改善。在1 200 ℃下,残余应力可为焊后热处理过程中静态再结晶提供激活能,接头热影响区发生再结晶,硬度下降,接头塑性变形能力不协调,导致室温拉伸与950 ℃拉伸断裂位置均为焊接接头。对固溶态板材试样进行不同的焊后热处理,EBSD扫描结果分析发现,接头经过1 100 ℃×10 min热处理后,残余应力明显消失,温度升高至1 140 ℃后,热影响区开始发生再结晶。

Effect of heat treatment on microstructure and mechanical properties of super alloy GH3128 weld joint

With the increasing demand of electricity and awareness of environmental protection,nuclear is gradually replacing fossil. As the core component of ULTRA-high temperature gas cooled reactor (UHTR),intermediate heat exchanger (IHX) has also attracted extensive attention. The superalloy GH3128 is expected to become candidate material for ultra-high temperature gas cooled reactor intermediate heat exchanger (UHTRIHX) due to well weldability,excellent mechanical properties,superior thermal stability and outstanding creep resistance. The welding process is necessary for heat exchanger for production and manufacture. Due to the high degree of heat input concentration and the speedy cooling rate welding. During the subsequent high-temperature service process,brittle phase precipitation and recrystallization occur in this zone,which affects the mechanical properties and long-term service life. Therefore,the GTAW welding of superalloy GH3128 sheet was conducted,the microstructure evolution,residual stress and mechanical properties of weld joint was investigated. The results show that under the optimization of welding parameters,solid-solution plate joint shows the highest tensile strength and plasticity,both room temperature and high temperature tensile fracture position were the base metal. Residual stress in the HAZ was exist without post weld heat treatment (PWHT). The hardens,and the residual stress induces μ phase precipitate in the during high temperature deformation,the precipitation of μ phase deteriorates the creep rupture properties of weld joint. Post-weld heat treatment eliminated residual stress of the joint,precipitation of μ phases was decrease during high temperature deformation,and improved the creep rupture time of weld joint. Under the Temperature of 1 200 ℃,the residual stress can provide activation energy for recrystallization,recrystallization occured in the heat affected zone of the joint during the post-weld heat treatment process. The hardness decreases,and the plastic deformation was ununiform,induced the room temperature and 950 ℃ tensile fracture position was welded joints. After different post-welding heat treatment of the solid solution plate specimen,the EBSD results showed that after the joint heat treated at 1 100 ℃×10 min,the residual stress and strain disappeared,and with the temperature raised to 1 140 ℃,the heat affected zone began to recrystallize.