As the most important structural material, steel materials have always been an urgent requirement for market applications to increase their strength. Carbon is the most important and inexpensive reinforcing element of steel materials. However, an increase in carbon content affects plasticity. According to the traditional concept, increasing the carbon content to 1% or more will reduce the plasticity to a point where the structural material cannot be used, or even form a certain understanding in the material world that the steel material has a carbon content of 1% to 2.1%. Ultra-high carbon steel, which is inherently brittle and has no development value. Therefore, ultra-high carbon steels have long been excluded from practical engineering materials.
However, since the 1970s, metallurgists represented by Prof. ODSherby of Stanford University in the United States have discovered that the brittleness of ultra-high carbon steel materials is due to the difficulty of high carbon content during solidification under conventional casting conditions. The segregation of carbon and the formation of coarse carbides are avoided, and it is difficult to avoid the precipitation of coarse carbide networks in the austenite grain boundary during the conventional hot working process. If the segregation of carbon can be avoided and the structure is sufficiently refined and homogenized, ultra-high carbon steel can completely obtain excellent mechanical properties with high strength and certain plasticity. In fact, Damascus sabers, which appeared thousands of years ago, are recorded in history using their sharp edges and beautiful appearance. They are made of ultra-high carbon steel (1.5 to 2.0% carbon). The process has been lost. Sherby et al. found that through the refinement and homogenization of the structure, ultra-high carbon steel can not only obtain excellent mechanical properties that match the ultra-high strength and certain toughness plasticity of existing steel materials, but also can obtain an amazing elongation of up to 600%. Above the superplasticity. The discovery by Sherby et al. made ultra-high carbon steel a new research hotspot for materials and an important research object for the development of cheap new high-strength steels.
However, although ultra-high carbon steel is easy to obtain ultra-high strength, it is relatively difficult to maintain a good tough plasticity, and it requires a very complicated process, thereby increasing its production cost and limiting its market application.
Combining ultra-high-strength ultra-high carbon steel with other materials with better toughness to prepare composites with high strength and good enough tough plasticity is an important idea. Now, it has been reported that layered composite ultra-high carbon steel obtained by solid-phase welding ultra-high carbon steel with other ferrous metals. This composite material is usually obtained by the method of roll-bonding welding, that is, three or more layers of ultra-high carbon steel and low-carbon steel are laminated and welded together below the temperature of A1. The soldering temperature should generally not be too high to prevent the migration and diffusion of carbon at the interface of the layer, and to avoid the growth of ultra-high carbon steel grains.
The biggest advantage of layered composite ultra-high carbon steel is that it has a high impact toughness, is larger than any of its constituent materials, and the brittle transition temperature is very low, for example, 12 layers of ultra-high carbon steel-low carbon steel composite materials (each The brittle transition temperature of each 6 layers of material is -140°C. This is mainly due to the fact that the crack propagation is effectively prevented at the interface of the layer and the crack tip is passivated.
The yield strength of layered composite ultra-high carbon steel is in accordance with the mixing law. When the two materials are similar in plasticity, their plasticity follows the mixing law. However, when the plasticity difference between the two is large, the plasticity of the layered composite ultra-high carbon steel will be lower than the result of the mixing law, which may be related to the early cracks produced by materials with poor plasticity. By increasing the number of laminated ultra-high carbon steel layers and reducing the thickness of the layers, the plasticity can be further improved. Tests have shown that layered composite ultra-high carbon steel also has superplasticity. The greater the volume percentage of ultra-high carbon steel is, the smaller the lamellar spacing is and the better the superplasticity is.
However, since the 1970s, metallurgists represented by Prof. ODSherby of Stanford University in the United States have discovered that the brittleness of ultra-high carbon steel materials is due to the difficulty of high carbon content during solidification under conventional casting conditions. The segregation of carbon and the formation of coarse carbides are avoided, and it is difficult to avoid the precipitation of coarse carbide networks in the austenite grain boundary during the conventional hot working process. If the segregation of carbon can be avoided and the structure is sufficiently refined and homogenized, ultra-high carbon steel can completely obtain excellent mechanical properties with high strength and certain plasticity. In fact, Damascus sabers, which appeared thousands of years ago, are recorded in history using their sharp edges and beautiful appearance. They are made of ultra-high carbon steel (1.5 to 2.0% carbon). The process has been lost. Sherby et al. found that through the refinement and homogenization of the structure, ultra-high carbon steel can not only obtain excellent mechanical properties that match the ultra-high strength and certain toughness plasticity of existing steel materials, but also can obtain an amazing elongation of up to 600%. Above the superplasticity. The discovery by Sherby et al. made ultra-high carbon steel a new research hotspot for materials and an important research object for the development of cheap new high-strength steels.
However, although ultra-high carbon steel is easy to obtain ultra-high strength, it is relatively difficult to maintain a good tough plasticity, and it requires a very complicated process, thereby increasing its production cost and limiting its market application.
Combining ultra-high-strength ultra-high carbon steel with other materials with better toughness to prepare composites with high strength and good enough tough plasticity is an important idea. Now, it has been reported that layered composite ultra-high carbon steel obtained by solid-phase welding ultra-high carbon steel with other ferrous metals. This composite material is usually obtained by the method of roll-bonding welding, that is, three or more layers of ultra-high carbon steel and low-carbon steel are laminated and welded together below the temperature of A1. The soldering temperature should generally not be too high to prevent the migration and diffusion of carbon at the interface of the layer, and to avoid the growth of ultra-high carbon steel grains.
The biggest advantage of layered composite ultra-high carbon steel is that it has a high impact toughness, is larger than any of its constituent materials, and the brittle transition temperature is very low, for example, 12 layers of ultra-high carbon steel-low carbon steel composite materials (each The brittle transition temperature of each 6 layers of material is -140°C. This is mainly due to the fact that the crack propagation is effectively prevented at the interface of the layer and the crack tip is passivated.
The yield strength of layered composite ultra-high carbon steel is in accordance with the mixing law. When the two materials are similar in plasticity, their plasticity follows the mixing law. However, when the plasticity difference between the two is large, the plasticity of the layered composite ultra-high carbon steel will be lower than the result of the mixing law, which may be related to the early cracks produced by materials with poor plasticity. By increasing the number of laminated ultra-high carbon steel layers and reducing the thickness of the layers, the plasticity can be further improved. Tests have shown that layered composite ultra-high carbon steel also has superplasticity. The greater the volume percentage of ultra-high carbon steel is, the smaller the lamellar spacing is and the better the superplasticity is.