新型耐热钢NF709的研究进展

随着锅炉蒸汽参数的提高,对受热面管材的要求愈发苛刻,新型奥氏体耐热钢以其高蠕变强度、优良的抗腐蚀和氧化性能逐步取代马氏体耐热钢应用到高参数机组的过热器和再热器,但其导热性差、膨胀系数大、合金元素含量高等问题,易导致焊接缺陷。此外,奥氏体耐热钢在长期服役过程中有可能析出σ和Cr2N等有害相,降低材料的高温性能。因此,增加奥氏体耐热钢中Cr和Ni含量,通过多元合金化,以Z相、MX相和M23C6相共同复合强化,并借助合理的冷热成型加工工艺,获得适宜的晶粒尺寸和表面质量,进一步提高组织稳定性及高温性能,以满足更高蒸汽参数超超临界锅炉的过热器和再热器使用要求。

Research Progress of a New Type of Heat-resistant Steel NF709

With the improvement of the boiler steam parameters, the requirements for the tube of the heated surface are becoming more and more severe. New austenitic heat-resistant steels gradually replace martensitic heat-resistant steels for high-parameter unit superheaters and reheaters due to their high creep strength, excellent corrosion resistance and oxidation resistance. However, the problems of poor thermal conductivity, large expansion coefficient and high content of alloy elements are easy to cause welding defects. In addition, the austenitic heat-resistant steel may precipitate the harmful phase such as sigma and Cr2N during the long term service, reducing the high temperature properties of the material. Therefore, the content of Cr and Ni in the austenitic heat-resistant steel is increased, and through multi-alloying, the Z-phase, MX-phase, and M23C6-phase are jointly compounded. The suitable grain size and surface quality are obtained with the help of a reasonable cold and heat forming process. Further the stability of the tissue and the high temperature performance is improved to meet the requirements of the superheater and reheater for the ultra supercritical boiler with higher steam parameters.