Fabrication of high borated austenitic stainless steel thick plates with enhanced ductility and toughness using a hot-roll-bonding method

The increase in casting slab thickness causes sharp increase in both the size and uneven distribution of brittle eutectic borides in high borated austenitic stainless steel, thus remarkably deteriorating the hot workability and the final room-temperature mechanical properties. Hence, it is undesirable to produce thick plates by rolling an extra-thick slab. Here it is reported that a specially designed hot-roll-bonding method for producing Fe–19Cr–15Ni-1.2B austenitic stainless steel thick plates using the conventional thick slab as starting materials. The main aim is to obtain refined and uniformly distributed borides so as to improve the room-temperature ductility and toughness by increasing total rolling compression ratio via hot-roll-bonding. It was validated that double-layered thick slabs could be successfully hot-roll-bonded though massive brittle ceramic (Cr,Fe)2B particles exist at the contacting interlayer interfaces. The hot-roll-bonding mechanism was clarified in terms of severe plastic flow, recrystallization and interface-diffusion. The effects of total rolling compression ratio on the morphological change and size distribution of (Cr,Fe)2B particles in both the mono-layered plates and the double-layered composite plates were investigated in details with the consequent effects on room-temperature comprehensive mechanical properties. It was found that the initial large and brittle (Cr,Fe)2B broke into more spheroidal and refined particles and significantly enhanced the ductility and toughness with increasing the total rolling compression ratio up to 10. The present work provides not only a practicable method to fabricate high borated austenitic stainless steel thick plates but also a promising way to improve the ductility and toughness of other metals containing a large number of hard and brittle particles.