Heating Defects and Control

Introduction During the heating process of the hot rolled steel strip, nonuniform heating environment can easily cause non-uniformity defect, which seriously affects the quality of the steel product. The common cumulation mark defects are the surface discoloration, cracking, tension marks, etc. Therefore, it is of great practical significance to research the surface heating defects and the corresponding control measures in order to reduce the appearance rate of the defects. 1. Analysis of heating defects 1.1 Definition of heating defects According to the Dictionary of Iron and Steel, the heating defects caused by the limitation of the heating process and equipment parameters are referred to as the heating defects. This refers to the uneven color, formation of tension marks, cracking and other defects on the surface of the strip. Generally, high temperature causes the strip to expand and generates tensile force, while the low temperature causes the strip to contract and generates compressive force, thus resulting in this kind of defect. 1.2 Causes of heating defects The heating defects are generally caused by the following factors: ①Uniformity of the heating environment: Improper design of the heating system, inappropriate matching of the parameters, improper adjustment of the parameters, unbalanced heating of the furnace, etc. can easily cause the temperature nonuniformity of the furnace and non-uniform heating of the material, resulting in local charcoal burning and, serious heating defects. ② Heat damage: The temperature regulation of the heat treatment process is improper, resulting in local overheating of the coils, which can form harmful phases, causing corrosion on the surface, such as white rust. ③ Variation of the chemical composition of the material: The excessive sulfur and phosphorus in the material can easily cause the coil to harden and fracture due to the intermittent heating. 2. Control of heating defects 2.1 Design and adjustment of heating device The heating temperature, linear velocity and other parameters need to be well adjusted to ensure uniformity of temperature. For the design of the heating device, attention should be paid to the location of heating points and insulation, as well as the number of heating wires, the caliber of the heating wire, the distance between heating wires and the shape of the heating wire. In addition, measures should also be taken to adjust the temperature regulation time and improve the air supply situation. 2.2 Improvement of material quality It is necessary to strictly examine the chemical composition of the material, so as to detect and avoid the problems generated by sulfur, phosphorus and other elements in time. 2.3 Specifications for heat treatment All types of heat treatment shall have a detailed heating process and requirements, and the parameters of different types of strip shall be different. 3. Conclusion The heating defects on the surface of the strip easily cause a huge loss to the product quality. Therefore, it is very necessary to take scientific measures to prevent and reduce the occurrence of the heating defects. The design of the heating device, the adjustment of the heating parameters, the quality of the material, and the specifications of the heat treatment must be coordinated with each other to ensure the quality of the product.