| Layer metal cladding plates not only possess excellent properties of various materials, but also save rare and precious material leading to cost saving, therefore, they are in widespread usage. Hot roll-cladding, increasingly replacing explosive cladding, becomes the major method for plate cladding production. As a kind of hot roll-cladding methods, vacuum hot roll-cladding not only solves problems such as low efficiency, serious pollution and production size construction appeared in the traditional explosive cladding, but also avoids severe oxidation in cladding interface during direct hot-rolled cladding, which makes vacuum hot roll-cladding a significant method for high-quality wide clad plate production. Interface inclusion is a key element affecting the interfacial properties of the vacuum hot roll-cladding plates. Based on this, ultra-thick steel plates, stainless clad steel plates and titanium clad stainless steel plates were produced by vacuum hot roll-cladding in this thesis. In view of these materials, generation and evolution mechanism of interface inclusions, effect of interface inclusions on cladding properties and effect of cladding technology on interface inclusions were researched systematically and thoroughly. The main work and the research results of this thesis are as follows:(1) Ultra-thick steel plates were produced by vacuum hot roll-cladding, and generation mechanism of cladding interface inclusion were studied and analyzed. The results show that interface oxides generated at cladding interface are the selective and internal oxides which are chemically generated in combination of both residual oxygen in the surface and elements in high oxygen affinity near interface in the heating process.(2) Effect of assembly vacuum degree and rolling reduction ratio on interface inclusions in ultra-thick cladding plates was studied, and impact of interface inclusion morphology on interfacial cladding properties was also analyzed. Results show that assembly vacuum degree directly affects the quantity and size of cladding interface inclusions. The higher assembly vacuum degree is, the less interface oxides are generated, the smaller oxides are, therefore, the higher strength of cladding interface is, and the better ductility is. During the rolling process interface inclusions are crushed and dispersed, and the higher rolling reduction rate is, the more serious the interface inclusion is crushed, the more dispersive the inclusions'distribution is, the less effect on the bonding properties is. When the reduction ratio of high-vacuum assembly is no less than 50%, the interface properties of ultra-thick cladding plates can achieve a considerable level as that of the matrix.(3) Stainless clad steel plates were produced by vacuum hot roll-cladding, and generation mechanism of cladding interface inclusion was studied and analyzed. The results show that during the heating process, most interface inclusions generated in the stainless steel side, in the stainless steel side Cr and O are chemically combined to generate Cr2O3, which is then displaced by of elements such as Al, Si, Mn with corresponding higher-stability oxides, therefore new mixed oxides form.(4) Impact of assembly vacuum degree and rolling reduction ratio on interface inclusions in stainless steel cladding plates was researched, and effect of interface inclusion morphology on interfacial cladding properties was also analyzed. Results show that the higher assembly vacuum degree is, the less interface oxides are generated, the smaller oxides are, the higher interface shear strength is, and the better ductility is. Assembly interface properties in both low and high vacuum environment could meet ASTM standard requirements. The higher rolling reduction rate is, the more serious the interface inclusion is crushed, the more dispersive the inclusions' distribution is, and the higher interface shear strength is. When the reduction ratio of high-vacuum assembly is more than 20%, the interface strength can meet ASTM standard requirements.(5) Titanium clad stainless steel plates were produced, and the generation characteristics of Intermetallic Compounds (IMC) without an interlayer were researched. Effect of cladding temperature on generation of IMC and effect of IMC on cladding properties were also studied. Results show that a variety of brittle IMC such as Fe2Ti, FeTi, Cr2Ti and NiTi2 generate at the interface. As the temperature increases, thickness of IMC increases, and the interface shear strength is higher. In the cladding temperature range of 800-950?, the interface strength could not meet ASTM standard requirements.(6) Ni interlayer was added to produce vacuum hot roll-cladding titanium/ stainless steel cladding plates, and effect of Ni interlayer on interface IMC in vacuum hot roll-cladding titanium clad stainless steel plates were studied. Results show that Ni interlayer can effectively prevent the diffusion between titanium and stainless steel, preventing titanium and stainless steel to generate IMC. Ni and stainless steel do not generate IMC, and brittle IMC of TiaNi, TiNi and TiNi3 generate in the Ti-Ni interface. As the cladding temperature increases, the IMC becomes thicker, and the interface shear strength decreases. Addition of Ni interlayer effectively enhanced interface bonding strength, and when cladding temperature is no more than 900?, the interface shear strength can meet standard requirements.(7) Nb intermediate layer was added to produce vacuum hot roll-cladding titanium clad stainless steel plates, and effect of Nb intermediate layer on interface IMC in vacuum hot roll-cladding titanium clad stainless steel plates were studied. Results show that Nb interlayer can effectively prevent the interdiffusion between titanium and stainless steel, preventing titanium and stainless steel to generate IMC. Ti-Nb interface do not generate IMC. When temperature is no more than 900?, Nb and stainless steel do not generate IMC. When the temperature is more than 900?, Nb and stainless steel interface generate FeNb brittle inter-metallic compound and decrease interface strength. In the temperature range of 850-1000?, addition of Nb intermediate layer makes strength of titanium clad stainless steel plates meet standard requirements, and interface strength at 900? achieves maximum of 397MPa.(8) Bonding mechanism and process control theory of vacuum hot roll-cladding was analyzed. Interfacial bonding process is as follows:lots of gaps and residual air exist at cladding interface of assembly. During heating process, some of interface form initial bonding points. During rolling process, interface gaps are bridged, and large area of actual physical contact form at the interface, and the interface atoms are activated to generate metal bond. Diffusion and recrystallization happen and form firm metallurgical bonding at interface during rolling and cooling process. The process control principle is as follows, during the heating process, some metal elements and oxide reacts to generate interface oxides, the higher the vacuum degree is, the weaker the oxidation is. During the rolling process, interface oxides are embedded in the matrix and was crushed and diffused. The higher the reduction ratio is, the more severe the crush is, and more diffuse the distribution is. Diffusion makes interface form metallurgical bonding, causing some metals to generate inter-metallic compounds or Kirkendall holes which weaken interface bonding strength. Interface diffusion can be adjusted by controlling the temperature and adding an intermediate layer, thereby decreasing interfacial strength weakening effect caused by the inter-metallic compounds and Kirkendall holes. |
PDF Full Text Request