The stability of the martensitic microstructure in ferritic/martensitic G91 steel at operating temperatures up to 700 °C might be improved by means of ausforming thermomechanical treatments. The goal sought is to promote the formation of a high number density of MX nanoprecipitates in the martensitic microstructure obtained after a subsequent tempering. This work is focused on the effect of the ausforming temperature. The results show that the lower the ausforming temperature is the higher is the dislocation density obtained in ausformed fresh martensite and the larger the number density of MX carbonitrides after tempering is. Creep strength, evaluated by Small Punch Creep Tests has allowed us to conclude that the best creep resistance was obtained for the steel ausformed at the lower temperature due to the higher pinning force for dislocation motion triggered by the distribution of MX. The creep results obtained on the ausformed samples were compared with those after the conventional heat treatment, showing that the high density of MX carbonitrides after an ausforming thermomechanical treatment is a promising processing to raise the operation temperature of this steel.

铁素体/马氏体G91钢在高达700°C的工作温度下的马氏体显微组织的稳定性可能会通过奥氏体热机械处理而得到改善。寻求的目标是促进在随后的回火后获得的马氏体微观结构中形成高密度的MX纳米沉淀。这项工作集中在奥氏体温度的影响上。结果表明，奥氏体化温度越低，奥氏体化新鲜马氏体中获得的位错密度越高，回火后MX碳氮化物的数量密度越大。蠕变强度 由Small Punch Creep Tests评估的结果使我们得出结论，由于MX的分布触发了位错运动的较高的钉扎力，因此在较低温度下对奥氏体钢可获得最佳的抗蠕变性。将在奥氏体样品上获得的蠕变结果与常规热处理后的蠕变结果进行了比较，表明在奥氏体热机械处理之后，高密度的MX碳氮化物是提高该钢工作温度的有前途的工艺。