Effect of Ausforming Temperature on the Microstructure of G91 Steel

The development of thermomechanical treatments (TMT) has a high potential for improving creep-strength in 9Cr-1Mo ferritic/martensitic steel (ASTM T/P91) to operate at temperatures beyond 600 °C. To maximize the number of nanoscale MX precipitates, an ausforming procedure has been used to increase the number of nucleation sites for precipitation inside the martensite lath. Relative to standard heat treatments (consisting of austenitization at about 1040 °C followed by tempering at about 730 °C) this processing concept has enabled achieving a microstructure containing approximately three orders of magnitude higher number density of MX precipitates having a size around four times smaller in ASTM T/P91 steel. On the other hand; this TMT has little effect on the size and number density of M23C6 particles. The optimized microstructure produced by this TMT route proposed is expected to improve the creep strength of this steel.The authors acknowledge financial support to Spanish Ministerio de Economia y Competitividad (MINECO) in the form of a Coordinate Project (MAT2016-80875-C3-1-R). The work presented here is done within the Joint Program on Nuclear Materials of the European Energy Research Alliance Pilot Project CREMAR. The authors also would like to acknowledge financial support to Comunidad de Madrid through DIMMAT-CM_S2013/MIT-2775 project.We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)