(1) Rolling production process and its formulation
The combination of a series of processing procedures in which an ingot or billet is rolled into a rolled material that meets the technical requirements is called the rolling production process. Organizing the rolling production process is first to obtain products that meet the quality requirements or technical requirements, but also to consider efforts to increase output and reduce costs. Therefore, how to produce high-quality, high-yield, and low-cost rolled materials that meet technical requirements is the general task and general basis for formulating the rolling production process. While in-depth understanding of the technical requirements of rolling materials, we must also fully grasp the inherent characteristics of metals and alloys, especially the characteristics of processing technology and changes in structure and properties, that is, inherent internal laws. Then, use these laws to take effective technical means and correctly formulate the production process, so as to achieve the goal of producing products that meet the technical requirements.
(2) Standards and technical requirements for rolled products
The technical requirements of the rolled material are the specifications and technical properties proposed for the rolled material in order to meet the needs of use, such as shape, size, surface state, mechanical properties, process properties, physical and chemical properties, internal metal structure and chemical composition, etc. Requirements. It is proposed by the user according to the requirements of the use, and then formulated according to the possibility of the actual production technology level and the economic efficiency of production at that time. It is embodied as a product standard. The technical requirements for rolled products have a certain range, and with the improvement of the production technology level, this requirement and the extent to which it may be met are also increasing. The task of rolling workers is to continuously improve the level of production technology to meet the higher requirements of use as much as possible. The product standards of rolled products generally include content (specification) standards, technical conditions, test standards and delivery standards. Variety standards mainly stipulate requirements for the shape and dimensional accuracy of rolled products. The shape should be correct, and there should be no defects such as crooked cross-section, uneven length and uneven surface. The dimensional accuracy refers to the size of the possible dimensional deviation. It will not only affect the performance, but also has a great relationship with the saving of metal materials. The so-called negative tolerance rolling is rolling within the range of negative deviation, which is essentially equivalent to doubling the requirements for rolling accuracy, which naturally saves a large amount of metal and can also reduce the weight of the metal structure. However, it should be pointed out that some rolled materials (such as tool steel) have to go through processing procedures during use, and they often have to be delivered according to a positive deviation. In addition to product specifications, product technical requirements also specify other technical requirements, such as surface quality, steel properties, structure and chemical composition, and sometimes include certain test methods and test conditions.
(3) Application of rolling technology in iron production
The surface quality of the product directly affects the service performance and life of the rolled material. The product requires few surface defects, smooth and clean surface. The most common surface defects are surface cracks, scars, heavy skin and iron oxide skin. There are many reasons for the surface defects, which are closely related to ingot (slab), heating, rolling and cooling. Therefore, we must pay attention to the whole production process. The requirements for the properties of the rolled material are mainly the mechanical properties, process properties (bending, stamping, welding performance, etc.) and special physical and chemical properties (magnetism, corrosion resistance, etc.) of the rolled material. The most common ones are mechanical properties (strength properties, plasticity, toughness, etc.), and sometimes hardness and other properties are also required. These properties can be determined by tensile test, impact test and hardness test.
The rolling material is also required to have sufficient plasticity and toughness when used. The elongation includes the deformation rate of uniform deformation and local deformation during stretching. Its value varies with the length of the sample, and the reduction of area is The local maximum deformation degree can be understood as the local deformation capacity that the metal can withstand under the condition that the component is not damaged. It has nothing to do with the length and diameter of the sample. Therefore, the reduction of area can better indicate the true plasticity of the metal. Therefore, many scholars suggest to measure the plasticity of metals according to the reduction of area. In actual work, the elongation is still the most widely used index because it is relatively simple to measure the elongation, and sometimes it is also required to give an index of the reduction of area. The impact toughness of a material is expressed by the work expended when the sample is broken. It is the most sensitive quality index to changes in the internal structure of the metal, reflecting the ability to resist brittle fracture or crack propagation at high strain rates. Small changes in the internal structure of metals are difficult to show in static tests, but they have a great impact on impact toughness. When the deformation speed is extremely large, it is very difficult to measure the stress-strain curve, so the energy required to break the sample is often used to comprehensively express the strength and plasticity of the metal material at high strain rates. It must be pointed out that the factors that promote the increase of strength are often not conducive to plasticity and toughness. To increase the strength and toughness of the material, that is, to improve its comprehensive mechanical properties, the material must have a fine-grained structure.
Post time: Mar-30-2021