Smelting control technology
Traditional enameled steel uses aluminum-killed steel and ultra-low carbon steel composition systems. The steel is relatively pure and has few second-phase particles, resulting in poor hydrogen storage capacity and scale resistance. According to literature research, the addition of certain alloying elements to enameled steel can appropriately improve the steel plate's anti-scaling performance, but it still cannot meet the requirements of complex forming; moreover, due to the high carbon content in the steel, the products after firing and enameling cannot meet the requirements. Modern enamel products have high quality requirements for corrosion resistance, high temperature resistance and aesthetic appearance. The Ti-S-B-N (titanium-sulfur-boron-nitrogen) composite microalloying composition system studied in this article, combined with the control of material structure and properties, is conducive to the formation of a large number of fine two-phase particles (density reaches 1020 ~ 1021 particles/square meter) and larger The strong γ texture not only greatly improves the hydrogen storage capacity and scale explosion resistance, but also is more conducive to stamping forming.
Ti-S-B-N composite microalloying composition system
After hydrogen atoms in steel are "trapped" by the second phase in the microstructure, it is generally difficult to escape. This type of second phase is often called an irreversible hydrogen trap. Ti element and its precipitated phase have the strongest affinity with hydrogen atoms, so Ti is mainly used as the hydrogen trap forming element in enamel steel. From the perspective of the formability of the enamel steel plate, the second phase in the structure has a great influence on the formability. In addition, the stability of the second phase is also the main factor affecting the mechanical properties and scale resistance of enameled steel during the enameling process. Therefore, through reasonable component design and optimization process, the quantity, morphology and stability of the second phase in the microstructure can be controlled. This study proposes an ultra-low carbon Ti-S-B-N cold-rolled strip steel chemical composition system for enamel. Based on the ultra-low carbon design, Ti microalloying is performed to control the appropriate N, B content and Mn/S (manganese/sulfur). )Compare. The segregation characteristics of B at the grain boundaries are utilized to hinder the solid solution and diffusion of carbon atoms and promote the precipitation of a large number of fine cementite particles within the grains. B and N combine in the fine cementite to form two-phase particles and composite precipitated phases, making the steel plate have good hydrogen storage effect.
Material organization and performance control technology
Based on the ultra-low carbon Ti-S-B-N composite microalloying composition system, corresponding material structure and performance control technology is developed to solve the contradiction between the formability and scale resistance of enameled steel, as well as the key technical problem of strength reduction after enameling. Process factors have a great influence on the hydrogen penetration behavior and hydrogen storage characteristics of steel. Measures such as increasing the heating temperature, lowering the coiling temperature, and low-temperature long-term annealing can significantly increase the penetration time of hydrogen in the steel plate; taking measures such as increasing the cold rolling pressure Measures such as lowering the rate, increasing the penetration time of hydrogen in the steel plate, and reducing the hydrogen diffusion coefficient can obtain a stronger γ texture, which is beneficial to stamping forming. By analyzing the effects of the parameters of hot rolling process, cold rolling process, continuous annealing and bell annealing process on the scale resistance and mechanical properties of enamel steel, the hot rolling process and cold rolling annealing process were determined [7]. Studies have shown that appropriately increasing the contents of S, Mn and N, and adding trace amounts of B, can greatly improve the performance of enamel. Compared with B-free steel, the continuously annealed plate of B-containing enamel steel obtains a lower yield strength. Although the strain hardening index (n) has decreased, the plastic strain ratio (r) and elongation after fracture are high, and the overall performance is excellent. Research on the hot rolling process shows that when the billet is heated to 1200-1250°C and held for more than 120 minutes, the coarse precipitates in the billet dissolve into second phase particles. After multiple passes of rolling, the thickness changes from 23mm to 4mm, and the layer cooling The coiling temperature is 680 ~ 750 ℃. During the high-temperature coiling and cooling process, the dislocation density in the steel decreases, which is conducive to the re-precipitation of carbon and nitride, and is conducive to the aggregation and growth of the second-phase particles in the steel. When the cold rolling reduction rate is 80%, the larger two-phase particles precipitated in the hot rolling base material are further crushed and become smaller. Research on the continuous annealing process shows that short-term continuous annealing at high temperature is more conducive to obtaining a stronger γ texture, which is beneficial to stamping forming; while the "fine-grained structure + chain-like degraded pearlite" and fine dispersed pearlite obtained by long-term insulation at relatively low temperatures Cementite particles are more helpful in reducing the diffusion rate of hydrogen in steel and improving the anti-scaling performance of enameled steel. During the bell annealing process, as the annealing temperature increases and the holding time increases, the large two-phase particles in the cold-rolled plate continue to decompose and refine, and partially form new Ti carbonitrides at high temperatures. After finishing, precipitate particles with a size of 25 to 50 nm are dispersed in the cold roll, which are Ti carbonitrides, carbon sulfides, manganese sulfide, etc. The double electrolytic cell method was used to conduct a scale explosion resistance test on 0.80mm deep-drawn cold-rolled enamel steel DC03EK, and the anti-scale explosion sensitivity TH value was obtained to be 18.74 min/mm2. According to general test experience, when TH ≥ 6.7 min/mm2, enameled steel has stable scale explosion resistance. In addition, because the chemical composition adopts composite micro-alloying, the thermal stability of the composite precipitation phase is very strong, and the strength reduction value of the steel plate after sintering is within 30 MPa.
Precise control technology for narrow composition smelting
The high content of Ti in the ultra-low carbon Ti-S-B-N composite microalloying component system causes the cold-rolled enamel steel to be easily accumulated during the casting process, affecting efficient and stable production. This is a common problem in the metallurgical industry. A special ladle top slag modifier is used, and a nitrogen-increasing and oxygen-control process is used to form a specific matching relationship between the amount of ladle top slag modifier and the oxygen blowing amount of RH (vacuum circulation degassing refining furnace). High-Ti enamel is cast with steel to accumulate flow. The problem has been significantly improved. The production efficiency of continuous casting of cold-rolled enamel steel has been greatly improved, and continuous casting of 5 furnaces can be achieved. In order to achieve precise and stable control of smelting components with extremely low carbon content, this project conducts systematic research on RH carburization and the carburization rules of the continuous casting process. In order to obtain pure molten steel during the steelmaking stage, it is necessary to strictly control the carbon and oxygen content out of the converter, reduce the pressure of the RH process, and improve the quality of the molten steel. In addition, in order to effectively control the carbon content, in the actual continuous casting process, magnesia coating material is used as the refractory material of the tundish working layer, and ultra-low carbon protective slag and alkaline covering agent are used to strictly control the carbonization of the molten steel during the continuous casting process. quantity. Through the above measures, the amount of carbon added during the continuous casting process is controlled below 6×10-6.
Anti-scaling performance testing technology and devices
The project developed an integrated technology and device for the electrochemical measurement of the hydrogen permeability of steel used for enamel, as well as a simulation experimental method and sampling method for the anti-scale explosion performance of gas shielded ion welding coating and burning enamel of large-size steel plates. The two detection technologies were applied to actual product resistance. It is used in conjunction with the scale explosion performance test to establish a quantitative relationship between hydrogen penetration data and the steel plate's scale explosion resistance, and improve the prediction accuracy of the steel plate's scale explosion resistance performance.
Hydrogen permeability testing technology and equipment
In view of the lack of special instruments for double-electrolytic cell electrochemical metallic hydrogen permeability testing, the testing process requires the temporary construction of experimental devices, and the sample surface effect and boundary effect affect the test results. This project independently developed an integrated metallic hydrogen permeability tester. This experimental device can realize functions such as sample pretreatment, electrochemical metallic hydrogen permeability measurement, data acquisition and processing, etc., forming a device for measuring metallic hydrogen permeability, which can stably, accurately, sensitively and conveniently measure hydrogen diffusion speed, diffusion time, The diffusion coefficient can meet both the national standard "Hydrogen Penetration Method for Scale Explosion Sensitivity Test of Cold-rolled Steel Plate for Enameling" (GB/T29515-2013) and the international standard "Measurement of Hydrogen Penetration and Determination of Hydrogen Absorption and Migration in Metals Using Electrochemical Technology" Method" (ISO 17081-2014) testing requirements. In addition, this instrument can be used to study hydrogen behavior on steel samples with complex structural states.
Experimental method for simulating scale explosion resistance of large-size steel plates by enameling and burning
In order to increase the area of the enameled steel test area, at the same time examine the anti-scaling performance of the steel plate welded joint area, and improve the accuracy of predicting the anti-scaling performance of the steel plate, this study designed a cold-rolled enamel steel for the water heater liner. detection method. Take two inspection samples from the same batch of steel plates and use gas shielded ion welding to form a large inspection sample with a size of (90~120) mm × (180~240) mm. Coat the outer surface of the large inspection sample steel plate with For enamel, after sintering and timed alternating tests in high and low temperature chambers, observe whether scaling occurs on the upper and lower surfaces of the entire sample; the principle is that the hydrogen produced by electrolyzing water in the air through plasma arc welding dissolves into the heat-affected zone at high temperature to This considers the hydrogen storage capacity of the steel plate itself. This method is used in conjunction with electrochemical methods to accurately predict material explosion. After a large number of tests, it was determined that the standard 1mm thick sample of enameled steel meets the requirements for scale explosion resistance when the hydrogen penetration time is more than 9.5 minutes. At the same time, this study designed a sampling method for hot continuous rolling strip steel, which reduces the intensity of sampling work, improves the product yield, and speeds up the production rhythm.
High-precision shape control technology
The new high-precision shape control technology of enamel steel hot rolling and cold rolling processes developed by the project uses online real-time monitoring of gap fit, roughing and finishing rolling centering and matching control, automatic roll stringing control of the middle roll of the rolling mill, and cold rolling recoiling unit through hot continuous rolling. The lap welding machine thin strip overlay welding, the cold rolling coiler mandrel superimposed with a rubber sleeve, and the installation of a device to reduce the working vibration of the cold rolling mill coiler helper have achieved stable control of the plate shape of the finished enameled steel within 1nm.
Online real-time monitoring technology for matching gaps in hot tandem rolling mills
The functions of the online real-time monitoring technology for hot tandem rolling mill fit gaps are as follows: ① Preset the control accuracy range of the rolling mill archway size and bearing seat size, the normal value range and the normal measurement cycle range of the rolling mill archway and bearing seat fit clearance range in the online monitoring system ; ② Input and store original data including bearing seat information and rolling mill arch information to the online monitoring system; ③ Based on the original data, the online monitoring system automatically calculates and stores the matching clearance between the rolling mill arch and the online bearing seat, and outputs the rolling mill in real time The matching clearance between the archway and the online bearing seat greatly improves the timeliness and accuracy of monitoring.
Hot continuous rolling rough rolling and finish rolling centering and matching technology and devices
The centering and matching technology and devices of rough rolling and finish rolling in hot continuous rolling mainly include intermediate roller tables and side guide plates. There are multiple transmission rollers on the middle roller table, and two side guide plates are spaced apart, namely the first side guide plate and the second side guide plate. The first side guide plate is located in the middle of the middle roller table, and the second side guide plate is located in the finishing rolling mill. In front of the unit entrance and between the first side guide plate and the finishing rolling unit. The side guide plate includes a trumpet-shaped inlet, a clamping part and a guide wheel located at the intersection of the two. The guide wheel has a rotating shaft. This device does not need to change the center line of the rough rolling unit, finishing rolling unit and intermediate roller table. It corrects the deviation through the easy-to-move side guide plate. It is simple and easy to implement, and finally achieves the purpose of matching the centering of the intermediate billet with the centering of the finishing rolling table.
Optimization of rolling system of tandem cold rolling mill
Optimization of the cold rolling mill rolling system includes the following aspects: ① develop the thin strip welding method of the lap welding machine of the cold rolling recoiling unit; ② improve the cold rolling emulsion oil skimming device, cold rolling hard coil core welding device and reduce cold rolling The device that vibrates the coiler of the rolling mill; ③ Optimize the purge flow control system, the circulation system to remove crystallization in the feed line of the acid regeneration system, and the fully automatic steel coil labeling integrated system; ④ Design the superimposed glue on the core shaft of the cold rolling coiler patented groups such as sets and dials to prevent the rollers from being separated from the grinder headstock. Through the above optimization measures, the finished product plate shape is finally stably controlled within 1nm.