Microstructure And Mechanical Property Of Stainless Steel Clad Plate Made By Vacuum Hot Roll-Cladding

With the rapid development of electric power, building, automobile, shipbuilding industry, the use of stainless steel clad plate continues to expand, and the demand for stainless steel clad plate is increasing with good market prospects. It can bring about immeasurable economic and social benefits to use stainless steel clad plate, due to the lower costs by decreasing 70%～80% Cr and Ni content and the superior properties that combine the advantages of both materials.Vacuum hot roll-cladding is used for preparation of stainless steel clad plate in this paper. The interface was investigated, which is the key part of the stainless steel clad plate and affects the microstructures and properties. The effects of vacuum hot roll-cladding on the microstructures, inclusions types, element diffusion and properties of the interface were discussed, by clarifying the evolution of microstructures, diffusion mechanism of elements and formation mechanism of inclusions. Meanwhile, the effects of reduction ratio and heat treatment on the interface of stainless clad steel plates made by vacuum hot roll cladding were studied. Main progress is as following:(1) The stainless steel and carbon steel are composited by vacuum hot roll-cladding in the laboratory conditions. An interface with good metallurgical bonding and without obvious defects is obtained between both materials.(2) The microstructures and the morphologies of inclusions in the interface of the stainless steel clad plate after hot roll-cladding are observed by optical microscopy, scanning electron microscopy and transmission electron microscopy. The interface morphology of stainless steel clad plate composed of martensite and a small amount of austenite is serrated. The interface of stainless steel clad plate can be divided into four regions which are stainless steel substrate, recombination region of interface, decarburized zone and carbon steel substrate, respectively. The recombination region is located in the stainless steel side of the interface, whose width is about 10μm.(3) The inclusion composition and element distribution of the interface of the stainless steel clad plate are analyzed by scanning electron microscopy and energy dispersive spectrometer. Small inclusions, mainly sulfide and oxide inclusions, are distributed in the interface of the stainless steel clad plate. The sulfide inclusions can be confirmed as manganese sulfide inclusions with spherical or elongated shape, while the dispersed small particles mainly consist of Al2O3, Si-Mn-O and Si-Mn-Al-O mixed oxide.The diffusion region of Cr, Ni and C element appears near the interface of stainless steel clad plate. The hardness of the interface increases resulting from the formation of Cr and Ni enriched layer, which is due to the diffusion of Cr and Ni element from stainless steel to carbon steel during hot rolling. Uphill diffusion phenomenon of C element, resulting in the enrichment of C element in the interface region, occurs when it migrates to the stainless steel side, which is caused by the interaction of Cr and Ni element. In contrast, the migration of C element to the stainless steel side can cause the appearance the decarburization area, whose hardness is lower.(4) The mechanical properties of interface of stainless steel clad plate interface are tested by shear test. The binding properties of the interface of stainless steel clad plate are excellent with the interfacial shear strength 395MPa, which is far larger than the national standard. The fracture mode of the interface is ductile, resulting in better plasticity.(5) The microstructures and properties of stainless steel clad plate are studied by the process of reduction ratio of 60% and 80%. Effective metallurgical bonding has been achieved by the two kinds of reduction ratio in the interface and unbounding or micro-cracks and other defects are not found. The larger the reduction ratio is, the smaller the grain size and interface inclusion are. However, the stainless steel side with the reduction ratio of 60% appears intergranular corrosion, which is due to chromium depleted of the grain boundary region of austenite resulting from carbon precipitation from supersaturated austenite to form chromium carbide along the grain boundaries. The second phase particles precipitate from grain boundary and lead to the increase of the interface hardness of stainless steel side. With the increase of the reduction ratio, the diffusion distance of Cr and Ni becomes small in the interface, and the interface bonding strength increase.(6) The effects of heat treatment on the microstructures and properties of stainless steel clad plate are investigated. The grain size increases with increasing the heat treatment temperature, and the inter-crystalline corrosion of stainless steel is gradually reduced. The shear strength, as well as the plasticity, of stainless steel clad plate is improved after heat treatment. As the heat treatment temperature increase, the interfacial shear strength increase gradually. The fracture mode is ductile, which results in good plasticity.