700℃超超临界锅炉用钢HR6W焊接接头性能的试验研究

介绍了HR6W材料的化学成分和力学性能及焊接填充材料,进行了环向对接焊接试验,焊接接头按JB/T 4730标准进行RT检测,接头做了拉伸、弯曲、冲击、硬度试验和金相分析。试验结果表明:材料焊接性能良好,接头性能能满足材料要求,焊接接头在700℃高温持久试验外推1.0×105 h强度能满足材料在700℃工况条件下长期使用运行,为700℃超超临界机组锅炉高温受热面选用材料做好了技术储备。

高效超超临界机组用材HR3C和HR6W的热腐蚀行为及机理研究

为对比熔盐环境下典型耐热钢HR3C和铁镍基合金HR6W的热腐蚀行为及机理,在高温腐蚀试验系统上开展了750℃和810℃条件下1 000 h的熔盐腐蚀试验,利用扫描电镜、X射线衍射仪及能谱分析仪等表征了腐蚀产物成分与分布。结果表明:HR6W的腐蚀增重和腐蚀产物厚度均低于HR3C的;试验早期耐热材料的腐蚀主要受离子扩散控制,后期保护膜失效材料主要以失稳腐蚀为主。材料表面腐蚀产物主要为块状尖晶石结构和瘤状团聚物。产物主要为(Fe,Cr)2O3和Fe2O3,并有少量(Ni,Mn) Cr2O4。温度对于腐蚀过程的影响主要体现在提高反应离子活性与扩散速率,加速腐蚀的快速进行生成对应的腐蚀产物。模拟熔盐以熔融态盐膜形式沉积在耐热材料表面发生热腐蚀行为,且腐蚀层疏松多孔、层次分明,呈复合结构,即腐蚀外层为富Fe氧化物,腐蚀内层为富Cr氧化物,基体内侧出现明显内硫化区域。铁镍基合金HR6W的抗腐蚀性能优于耐热钢HR3C。

超超临界HR6W钢平板钨极氩弧焊接焊缝的微观组织和性能

为检验超超临界钢焊接工艺及焊缝接头的可靠性,通过万能拉伸实验研究了超超临界锅炉用钢HR6W平板钨极氩弧对接焊缝的焊接工艺及焊接接头性能,利用光学显微镜、扫描电子显微镜分析了其微观组织。结果表明:对于10 mm厚新型超超临界HR6W钢,采用小电流I=50 A打底焊,焊接速度为10~12 mm/min,再将焊接电流增大至70 A,进行单面焊双面成型,焊接速度为15 mm/min,最后在焊缝背面采用小电流I=40 A,焊接速度为12 mm/min,增焊一道焊缝进行焊接变形矫正,可以得到焊缝成形美观,微观组织均匀,变形小,焊缝无裂纹,拉伸性能、冲击韧性和弯曲性能优良的焊接接头。

超超临界HR6W钢TIG焊接残余应力和变形有限元预测

采用钨极氩弧焊接(TIG)方法对超超临界HR6W钢厚板进行对接焊接,采用数值模拟方法分析焊接过程温度场,预测焊缝残余应力和焊接变形分布。结果表明,随着焊接道次增多,焊接变形逐渐增大,焊接变形为典型的角变形,以焊接线为中心线,呈对称分布,最大变形不超过1mm;随着焊接道次的增加,焊缝平均拉应力和压应力均先增大,后减小;焊缝中部区域存在残余压应力,焊缝首端和末端区域存在残余拉应力。

The Effect of Cold Working on Creep Rupture Strength and Microstructure of Ni-23Cr-7W Alloy

In order to clarify the reason why the creep rupture time of pre-strained Ni-23Cr-7W Alloy (HR6W) is longer than that of the non-pre-strained HR6W, microstructures of HR6W after a series of creep tests were investigated. The creep tests were conducted at 750°C, 90 and 100 MPa. In the pre-strained samples, the grain boundary shielding ratio by precipitates was larger than that of the non-pre-strained sample. In addition, in the pre-strained samples the size of the M23C6 carbide in the grains was finer than in the non-pre-strained sample. The W content in the M23C6 carbide in the pre-strained samples tended to be larger than in the non-pre-strained sample. Therefore, the Ostwald ripening of the carbide was delayed and the size of M23C6 carbide was thought to be fine for a long time. These observations show that creep strength in the pre-strained samples is higher than that of the non-pre-strained sample because of both precipitation strengthening inside of the grains and grain boundaries.