How to improve the mechanical properties of cold-rolled low-carbon rigid strip through heat treatment process?
Publish Time: 2025-05-26
Cold-rolled low-carbon rigid strip is a basic material widely used in many industrial fields. Common uses include annealing strip, galvanized strip, anti-theft doors and windows, filing cabinets, storage shelves and steel pipes. It has certain strength and hardness, but due to the work hardening during the cold rolling process, its plasticity and toughness decrease, which is not conducive to further processing and forming. Therefore, heat treatment process becomes an important means to improve its organizational structure and optimize mechanical properties.1. Basic characteristics and processing difficulties of cold hardened stripCold-rolled low-carbon rigid strip is made by cold rolling ordinary low-carbon steel at room temperature, and its carbon content is usually controlled between 0.05% and 0.15%. Due to the strong deformation effect during the cold rolling process, the internal grains of the material are elongated and the dislocation density increases, which brings higher hardness and strength, but at the same time, there will be obvious problems such as increased brittleness and reduced elongation.Although the cold hardened strip in this state has some direct application possibilities, such as for some structural parts with low forming requirements, in most cases, it still needs to be restored to its plasticity and machinability through heat treatment to meet the needs of subsequent manufacturing processes.2. The core goal of heat treatment process: softening and recrystallizationFor the heat treatment of cold hardened strip, the most commonly used process is annealing. The purpose of annealing is to eliminate the internal stress accumulated during the cold rolling process by heating and slowly cooling the material, and to promote the recrystallization of the material, so that the originally deformed grains grow again into uniform and fine new grains, thereby significantly improving the toughness and ductility of the material.Specifically, the annealing process generally includes the following stages:Heating stage: heating the steel strip to a certain temperature range (usually 600℃~700℃), so that the microstructure inside the metal begins to change.Insulation stage: maintaining a constant temperature for a period of time to ensure that the structure in the entire material volume is fully restored and the required recrystallization effect is achieved.Slow cooling stage: slowly cooling to avoid the generation of new residual stress and ensure that the material has good comprehensive mechanical properties.Through this whole set of heat treatment process, the cold hardened strip can obtain higher elongation, better stamping performance and lower yield strength ratio, which is very suitable for deep processing products, such as anti-theft door panels, file cabinet frames or storage shelf structural parts.3. Different application scenarios have different requirements for heat treatment parametersAlthough annealing is the main means to improve the performance of cold hardened strips, in actual production, according to the performance requirements of different downstream products, the specific parameters of the heat treatment process need to be finely adjusted:For steel strips for anti-theft doors and windows, it may be necessary to retain a certain strength while improving the forming ability, so low temperature and short-time annealing will be selected to moderately restore plasticity without significantly reducing hardness; in the field of file cabinets or storage shelves, more attention is paid to the deep drawing performance and welding adaptability of the material, and full recrystallization annealing is often used to make it have the best ductility; as the raw material for steel pipe production, the cold hardened strip needs to consider the subsequent high-frequency welded pipe or seamless pipe manufacturing process, and has high requirements for its surface quality and transverse and longitudinal performance consistency, so the furnace temperature and atmosphere must be strictly controlled during the annealing process to avoid oxidation or decarburization.4. Significant improvement in mechanical properties after heat treatmentAfter reasonable heat treatment, the mechanical properties of cold-rolled low-carbon rigid strip will change significantly: the tensile strength decreases slightly, but it will not affect its basic bearing capacity as a structural part; the yield strength decreases significantly, making the material easier to process and shape; the elongation is greatly improved, from the original 3%-5% to more than 20%, which greatly enhances the processing capabilities such as stamping and bending; the hardness uniformity is enhanced, which is conducive to improving the consistency and stability of the finished product quality. These changes in performance not only improve the efficiency of material use, but also save mold loss and energy consumption costs for downstream manufacturing industries, with significant economic benefits.As an important metal material, cold-rolled low-carbon rigid strip has certain strength advantages in its original state, but it has limitations in processability and service life. Through scientific and reasonable heat treatment processes, especially annealing treatment, its organizational structure can be effectively improved, plasticity and toughness can be improved, thereby expanding its application value in various fields such as anti-theft doors and windows, filing cabinets, storage shelves, and steel pipes.