硅对铁素体耐热不锈钢韧脆转变行为的影响

铁素体耐热不锈钢18Cr-Al-Si具有优良的导热性能及良好的耐高温气体腐蚀性能，同时复合添加铝和硅元素又确保了其具有优异的抗高温氧化性，该钢是应用于超(超)临界电站锅炉连接件的一种新型耐热钢材料。以往，对于连接件材料的加工主要采用传统的水切割加工成型方法，但生产效率较低且成本较高；采用室温冲压加工成型的方法时，由于该类铁素体耐热不锈钢板脆性较大，容易在钢板厚度中心处产生裂纹；而采用带温冲压加工(即在韧性温度区间加工)时，则可避免钢板中心开裂的问题。为了提高连接件材料的生产效率，需要优化和确定该钢带温加工工艺参数。采用系列温度夏比冲击试验方法并借助扫描电子显微镜(SEM)、透射电子显微镜(TEM)及能谱仪(EDS),研究了硅含量(质量分数为0%～0.9%)对18Cr-Al-Si钢韧脆转变行为的影响。结果表明，随着硅含量的增加，各试验温度下的冲击吸收功逐渐降低、韧脆转变温度(DBTT)升高、微观断口中解理面数量增多、韧窝面积逐渐减少。硅元素对退火后的18Cr-Al-Si钢微观组织及析出物影响较大，随着硅含量的增加，钢中铁素体晶粒尺寸逐渐增加，M₂₃C₆

Effects of Si on ductile-to-brittle transition behavior of a ferritic heat-resistant stainless steel

The 18Cr-Al-Si ferritic heat-resistant stainless steel has excellent thermal conductivity and good high-temperature resistance for gas corrosion, and compounded addition with Al and Si elements to ensure its excellent resistance to high-temperature oxidation. This steel is a new type of material used for key structural connectors of supercritical and ultra critical power station boilers. In the past, the traditional water-jet forming method was mainly used for the processing of the connector material, but the production efficiency was low and the cost was high. When the room temperature stamping forming method is adopted, because the ferritic heat-resistant stainless steel plate is brittle, it is easy to generate cracks in the center of the thickness of the steel plate. When using warm stamping processing (ie processing in the toughness temperature range), the problem of cracking in the center of the steel plate can be avoided. In order to improve the production efficiency of the connecting parts, it is necessary to optimize and determine the technological parameters of the warm processing of the steel. The effect of ductile-brittle transition behavior of silicon content(mass fraction is 0%-0.9%)18Cr-Al-Si steel was studied by means of a series of Charpy impact test methods and by means of scanning electron microscope (SEM), transmission electron microscope(TEM) and energy dispersive spectrometer(EDS).The results show that with the increase of silicon content,the impact absorption energy at each test temperature gradually decreases,the ductile-brittle transition temperature(DBTT)increases, the proportion of cleavage plane area in the micro fracture gradually increases,and the dimple area gradually decreases.The silicon element has a great influence on the microstructure and precipitates of the annealed 18Cr-Al-Si steel. With the increase of silicon, the ferrite grain size in the steel gradually increases, and the M₂₃C₆ carbide gradually changes from small-sized strips or blocks. become long or large. The larger ferrite grain size and the precipitation of elongated or massive M₂₃C₆ carbides are the main factors that deteriorate the impact toughness of the steel.