1. Direct rolling method
Direct rolling is a common method for producing metal clad plates. It can also be divided into hot rolling composite method, cold rolling composite method, asynchronous rolling composite method and vacuum rolling composite method.
(1) Hot-rolled composite method
Hot rolling composite method is to overlap the composite and base material, weld around, and combine the composite and base material through hot rolling. Under the action of shear deformation force, the contact surface between two metals is very similar to viscous fluid, and tends to have fluid characteristics. Once the surface of the new metal appears, they will produce adhesive friction behavior, which is conducive to the fixation between the contact surface and the metal. Based on the fixation point (or core), stable thermal diffusion will be formed under the condition of high temperature thermal activation, so as to realize the welding bonding between the metals.
(2) Cold rolling compound method
Usually, the cold rolling compound method with equal roll diameter and equal roll speed is called cold rolling compound method for short. In the 1950s, the United States first began to study and put forward a three-step production process of "surface treatment+cold rolling composite+diffusion annealing". Compared with hot rolling composite method, the first pass deformation of cold rolling composite method is larger, generally reaching 60%~70%, or even higher. By virtue of large reduction, cold rolling of two or more layers of metal overlapped by cold rolling can make them produce atomic bonding or tenon fitting, and then strengthen them by diffusion annealing.
(3) Asynchronous rolling compound method
Asynchronous rolling is a strip rolling production technology that began to rise in the 1960s. It rolls metal by changing the rolling speed of the upper and lower rollers to make the linear speed of the rollers different. In the 1970s, asynchronous rolling was used for the production of composite plates, called asynchronous rolling composite method. Many countries, including China, have invested considerable efforts in basic research and industrialization. The asynchronous rolling compound method generally corresponds the harder metal to the fast roll, and the softer metal to the slow roll. Asynchronous rolling compound makes full use of the relative sliding in the "rolling zone". On the one hand, the relatively sliding interface friction generates heat, which provides energy for the interface bonding; On the other hand, relative sliding is conducive to the breaking and extrusion of the contact surface pollution layer and oxide film, and promotes the formation of fresh surface. Therefore, relative sliding is beneficial to improve the interfacial bonding strength and reduce the average rolling pressure.
(4) Vacuum rolling compound method
Generally, in the atmosphere, the metal surface is covered with an oxide film and an absorbing layer, and the surface is convex and concave, which hinders the combination of metals. In view of these conditions, the former Soviet Union first started the vacuum rolling test in 1953, and then the United States, China and Japan also began to study. The vacuum rolling composite method can be divided into two cases: hot rolling in vacuum and cold rolling. The biggest feature of hot rolling in vacuum is that because there is no oxidizing atmosphere, the metal surface does not form oxides and nitrides, which makes it easy to process the metal that is difficult to process because of oxidation in the atmosphere. The original characteristics of the new metal surface produced by plastic processing can be fully developed, and because vacuum is conducive to degassing, a clean finish machined metal surface can be obtained.
2. Explosive billet making - rolling method
Explosive billet making and rolling method is a production method of rolling the required base and composite materials to the required specification and size of composite plates and strips after explosive welding. This method is a new combined technology developed by combining the advantages of explosive bonding technology and rolling technology. Its advantages are:
(1) The explosive composite method ensures the quality of the bonding area of two or three layers of metal composite plates;
(2) The product has high dimensional accuracy and good surface quality;
(3) It increases the flexibility of production and is easy to popularize.
3. Sintering method
Sintering method is a composite method that combines powder particles with composite substrate by heating in a protective atmosphere. Protective gases mainly include hydrogen and nitrogen. The composite substrate shall be pretreated by degreasing, derusting and roughening. There are two main methods for powder preparation:
(1) Uniformly mix the powder of different pure metals;
(2) The powder of coating alloy is prepared directly. The basic principle of sintering method is that at high temperature, the atomic amplitude increases and diffusion occurs, thus forming a combination of dissimilar metal atoms. It is mainly used for the composite of composite substrate and alloy coating. Because the sintering temperature is lower than the melting point of the pure metal component with high melting point during the sintering process, the microstructure and properties of the alloy coating are very uniform, which is a useful supplement to the rolling method.
4. Cast-rolling composite method
The technological process of cast-rolling composite method is as follows: two steel plates are superimposed, the inner layer is coated with stripping agent, the four sides are welded and placed in the mold containing molten metal, the liquid metal is solidified, and the initial rolling is carried out, and finally the welded edges are cut off to obtain the composite plate. High composite strength can be achieved at appropriate temperature and pressure. This method is simple in process and low in cost, and can be used for batch production.
5. Reverse solidification method
Reverse solidification process is a thin strip continuous casting process developed by German metallurgists in 1989. This process is to let a certain thickness of base band pass through the molten steel in the reverse solidification device, make the molten steel near the surface of the base band rapidly cool, solidify on the surface of the base band to form a new phase, and roll when the new phase is still in the semi-solidified state to obtain a flat surface and uniform thickness of hot rolled strip. This method is a new fusion technology for producing bimetallic composites. But it is different from the mold casting method. Its base plate is ordinary carbon steel (solid phase), and the composite layer is stainless steel (liquid steel). It has the characteristics of high efficiency and low energy consumption. It can produce composite plates with stainless steel composite layer less than 1mm. It can realize the continuous and short process of the production process. The process is simple, the product quality is high, and it is conducive to environmental protection.
6. Electromagnetic continuous casting composite method
The method of producing composite plates by electromagnetic continuous casting is still in the research stage. The basic principle is that two kinds of molten steel with different chemical compositions are injected into the mold at the same time through different submerged nozzles. Because a horizontal magnetic field is installed at the lower part of the mold, the Lorraine magnetic force acting on the molten steel flows vertically through the horizontal magnetic field, which inhibits the mixing of the two kinds of molten steel, and the horizontal magnetic field becomes a dividing line. The molten pool of the mold is divided into upper and lower parts by the action of the magnetic force. Through the cooling effect of the mold, the molten steel in the upper molten pool solidified into the outer layer of the composite billet, and the molten steel in the lower molten pool solidified in the inner side of the shell to form the inner core of the billet.
Advantages of this method:
(1) Because the combination of stainless steel and other steel materials can be realized directly in the mold, oxidation and slag inclusion at the interface can be avoided;
(2) Because of the liquid-liquid combination, the interface bonding strength of the stainless steel composite plate produced by the reverse solidification method is higher than that by the reverse solidification method, and the activation treatment of the substrate surface is also unnecessary;
(3) No pollution, suitable for mass production.