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A 5-layer laminated metal composite composed of ultrahigh-strength maraging steel and ductile 316L stainless steel was fabricated by hot pressing in vacuum and post-heat treatment. Microstructure characterization on hierarchical structure of the composite before and after heat treatment was made by optical microscopy, scanning electron microscopy and electron back-scattered diffraction technique, respectively. Meanwhile, the difference of mechanical performance on both sides of the interface was characterized by nano-hardness testing. Uniaxial tensile test showed that superior interfacial bonding was achieved due to the micro-‘bite’ structure between the two steels without obvious defects or oxides at the interface and with coordinated deformation of the two components. Thus, a laminated metal composite consisting of two different constituents with extreme difference in strength can be well fabricated.

The rapid coarsening of the M23C6carbides has been held responsible for the creep fracture in 9–12Cr martensitic heat resistant steels. A commercial P92 steel was subjected to thermal aging at a high temperature of 800 °C to investigate the ripening behavior of the M23C6carbides. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the microstructure evolution, especially the ripening process of the M23C6carbides. The new concept of the effective mean size, dependent on the critical radius, was introduced to correct the measured mean size and then the Ostwald theory was applied to describe the ripening behavior of the M23C6carbides. The ripening of the M23C6carbides was revealed to be grain boundary diffusion controlled.