Influence of Carbides Precipitated by Low-temperature Tempering on the Room-temperature Mechanical Properties of Grade 91 Steel

The precipitation behavior of carbides in modified 9Cr-1Mo steel (Grade 91) subjected to low-temperature tempering and the influence those on mechanical properties at room temperature were investigated. An as-quenched sample (AQ) contained a small amount metal carbide (MC) its martensite microstructure. On 300–500°C, intended suppress recovery growth dislocation substructure, three types formed; these identified as Fe4C, hP8-type Fe3C, oP16-type Fe3C by using replica samples for transmission electron microscopy extracted-residue analyses. Samples double 500°C 5 min then 300°C 1 h (DLTT) large amounts compared with AQ sample, but had similar lath width. hardness DLTT was higher than that whereas tensile strength slightly lower regardless strain rate. reason strengthening did not increase is considered be early formation microvoids due delamination carbide/matrix interfaces during testing.