Manufacturing method for improving hardness nonuniformity of cold-rolled medium-high carbon strip steel in width direction after cover annealing furnace heating

Abstract

The invention relates to the technical field of cold-rolled strip steel production processes, and discloses a manufacturing method for improving uneven hardness of cold-rolled medium-high carbon strip steel in the width direction after bell annealing furnace heating, and the manufacturing method comprises the steps of acid continuous rolling treatment, bell furnace annealing treatment and leveling process treatment on the strip steel. The method has the advantages that the operation method is simple and adjustable, the production process and the production cost are not increased, the strip shape of the strip steel is strictly controlled, the strip steel is ensured to be neat and compact in the coiling process, uneven overflow edges are avoided, and the surface hardness uniformity of the cold-rolled strip steel is improved. And meanwhile, the interior of the strip steel still keeps a relatively soft hardness state, so that the surface of the material has relatively high hardness and keeps good plasticity in the using process, the method is an effective method for improving the hardness nonuniformity of the cold-rolled medium-high carbon steel after bell-type furnace annealing, and the hardness uniformity and machinability of the strip steel can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of cold-rolled strip steel production technology, in particular to a manufacturing method for improving the uneven hardness of cold-rolled medium- and high-carbon strip steel along the width direction after heating in a hood-type annealing furnace. Background Art

[0002] Cold-rolled medium- and high-carbon steel is often used in strip stamping by downstream customers, and the stamping machine is more sensitive to the uniformity of the hardness distribution of the strip. If the hardness of the strip is unevenly distributed in the length and width directions, it is easy to cause uneven force on the stamping machine, and long-term use will reduce the service life of the stamping machine. At the same time, the uneven hardness distribution of the strip will also cause the surface of the stamped parts to warp.

[0003] In terms of improving the uniformity of strip hardness, Chinese patent application CN202111200494.4 discloses a method for manufacturing NM400 wear-resistant steel with high hardness uniformity. By adjusting the cooling temperature, ferrite is avoided in the head, middle and tail structures of the strip, thereby avoiding uneven hardness of the strip in the length direction. However, this invention belongs to the field of wear-resistant steel and is not suitable for the field of cold-rolled medium and high carbon. Chinese patent application CN202011041935.6 discloses a medium-carbon wheel steel for urban rail that improves hardness uniformity and reduces the depth of abnormal structures. By adjusting the appropriate tempering temperature and adding Mo, the hardness difference is reduced and the depth of abnormal structures is reduced. However, this invention belongs to the tempering treatment of hot-rolled strip and is not suitable for the production of cold-rolled strip. Chinese patent CN201910391481.6 discloses a production method for improving the uniformity of cross-sectional hardness of NSM30 plastic mold steel. By lowering the temperature of the soaking section of the heating furnace, reducing the time the billet spends in the soaking section, and maintaining the principle of single-pass large reduction during the steel rolling process, the uniformity of the performance in the thickness direction of the steel is improved. However, this invention belongs to the field of improving the uneven hardness of hot-rolled strip steel and has no reference to the production of cold-rolled strip steel. Based on the above domestic invention patents that have been applied for, it can be seen that the focus of invention patents on improving the uniformity of strip hardness is mainly concentrated in the hot rolling field, and there are fewer reports on invention patents on improving the uniformity of cold-rolled strip hardness, and the existing invention patents have the problem of increasing production costs and production processes.

[0004] Based on this, it is necessary to propose a method to improve the uneven hardness along the width direction of cold-rolled medium and high carbon strip steel after heating in a hood annealing furnace. Summary of the invention

[0005] 1. Technical issues to be resolved In order to solve the above technical problems, the present invention provides a manufacturing method for improving the uneven hardness of cold-rolled medium and high carbon strip steel along the width direction after heating in a hood annealing furnace, thereby solving the problem of uneven hardness of cold-rolled medium and high carbon steel after annealing in a hood furnace.

[0006] (II) Technical solution In order to achieve the above-mentioned object, the present invention discloses a manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon strip steel along the width direction after heating in a hood annealing furnace: It includes acid continuous rolling treatment, bell furnace annealing treatment and leveling process treatment of the strip.

[0007] Preferably, the chemical composition of the strip steel is as follows in weight percentage: C: 0.5%~1.0%, Si: 0.1%~0.50%, Mn: 0.1%~1.4%, P: ≤0.02%, S: ≤0.02%, of which Cr+Ni+Mo: ≤2.0%, Al: ≤0.06%, and the rest is Fe and unavoidable impurities.

[0008] Preferably, the strip steel has a thickness of 0.3-10 mm and a width of 900-2250 mm.

[0009] Preferably, the acid continuous rolling treatment includes the following steps: using a shallow trough turbulent pickling process so that the acid solution forms a turbulent channel in the pickling tank under the drive of the high-speed running strip to accelerate the penetration into the interior of the strip iron oxide scale. After cleaning, use deionized water to rinse to neutrality, dry, and then cold roll to obtain the strip after acid continuous rolling treatment.

[0010] Preferably, the acid solution is a 80-100 g / L hydrochloric acid solution, the pickling speed is 60-220 m / min, the cleaning temperature is 70-80° C., and the reduction rate of the strip during the cold rolling process is 10%-60%.

[0011] Preferably, the bell-type furnace annealing treatment uses a full-hydrogen bell-type annealing furnace to anneal the strip steel, including heating, insulation and cooling processes.

[0012] Preferably, during the heating and insulation process, the flow rate of the inlet hydrogen is 25-35 m / s. During the heating process, the heating rate is 5-10°C / h, and the temperature is heated to 600-740°C. The insulation time is 10-20 hours. During the cooling process, a furnace table variable frequency fan is used to form a convection cycle in the full hydrogen hood annealing furnace.

[0013] Preferably, the flattening process adopts a flattening rolling method, wherein the flattening elongation is 1% to 10%.

[0014] Preferably, the leveling rolling force in the leveling process is adjusted to 200~1200kgf.

[0015] Furthermore, in order to ensure that the thickness of the finished product remains unchanged after the flattening process, the thickness compensation at the mill outlet is adjusted in the acid continuous rolling process. The compensation amount varies according to the change in the flattening rolling elongation, and the thickness compensation range is 0 to 300 μm.

[0016] 3. Beneficial technical effects Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention achieves the purpose of improving the uniformity of the surface hardness of the cold-rolled strip by performing thickness compensation at the cold-rolling exit and appropriately increasing the rolling elongation in the leveling process. The operation method is simple and adjustable, and the production process and production cost are not increased. The surface of the strip is more obviously hardened by the leveling process, the rolling accuracy and stability of the strip are improved, the shape of the strip is strictly controlled, and the strip is ensured to be neat and tight during the coiling process to avoid uneven overflow edges. At the same time, the inside of the strip still maintains a relatively soft hardness state, so that the surface of the material has both high hardness and good plasticity during use. It is an effective method to improve the hardness non-uniformity of cold-rolled medium and high carbon steel after hood furnace annealing.

[0017] (2) The present invention uses an acid solution for cleaning, which can remove surface oxides and pollutants, promote the peeling of surface iron oxide, and ensure the surface quality of the strip. In the cold rolling process, there is no temperature drop and temperature unevenness in hot rolling, and extremely thin strips can be produced, while having good surface finish, flatness and dimensional accuracy as well as excellent mechanical properties and processing properties. The acid continuous rolling process not only improves production efficiency, but also significantly reduces production costs, while improving the quality and output of the strip. In the hood furnace annealing process, hydrogen is used as a protective gas, which can reduce the generation of oxidation and pollutants during the annealing process, thereby improving the quality and stability of the product. Further, the temperature uniformity and stability during the annealing process can be guaranteed, thereby improving production efficiency. During the insulation process, the unstable atoms on the grain boundaries are rearranged due to thermal motion, and new equiaxed grains are formed through the process of nucleation and growth, that is, recrystallization occurs. During the cooling process, high-purity hydrogen forms a strong convection cycle in this space through the furnace table variable frequency fan. Impurities on the surface of the strip are removed with the flowing hot hydrogen. At the same time, the oxides on its surface react with hydrogen to be reduced, avoiding uneven hardness caused by too fast or too slow cooling. After the cold-rolled strip is annealed in a full hydrogen bell furnace, the hardening and internal stress caused by cold rolling deformation can be eliminated, so that the strip has good mechanical properties and ductility. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0019] Example 1 A manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon strip steel along the width direction after heating in a hood annealing furnace comprises the following steps: (1) The steel strip is subjected to acid continuous rolling treatment: the chemical composition and mass percentage of the steel strip are: C: 0.5%, Si: 0.1%, Mn: 0.1%, S: 0.001%, P: 0.01%, Al: 0.03%, Cr: 0.1%, Mo: 0.02%, Ni: 0.01%, and the rest are Fe and unavoidable impurities. The specification of the steel strip is 0.3 mm × 900 mm × full length. A shallow groove turbulent pickling process is adopted to make the acid solution form a turbulent channel in the pickling tank under the drive of the high-speed running steel strip to accelerate the penetration into the inner part of the steel strip oxide scale. After the cleaning is completed, it is rinsed with deionized water to neutrality, wherein the acid solution is 80 g / L hydrochloric acid solution, the pickling speed is 60 m / min, and the cleaning temperature is 70 ° C. After drying, it is cold rolled again. The reduction rate of the steel strip during the cold rolling process is 30%, and the steel strip after acid continuous rolling treatment is obtained; (2) Hood annealing treatment: A full hydrogen hood annealing furnace is used to anneal the strip, including heating, insulation and cooling processes. During the heating and insulation processes, the flow rate of the inlet hydrogen is 25 m / s. During the heating process, the heating rate is 5 °C / h, and the temperature is heated to 700 °C. The insulation time is 13 h. During the cooling process, a furnace table variable frequency fan is used to form a convection cycle in the full hydrogen hood annealing furnace. (3) Leveling process: In the leveling process, the leveling rolling method is adopted, the leveling elongation is 1%, and the leveling rolling force in the leveling process is adjusted to 200 kgf to obtain improved strip steel.

[0020] Example 2 A manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon strip steel along the width direction after heating in a hood annealing furnace comprises the following steps: (1) The steel strip is subjected to acid continuous rolling treatment: the chemical composition and mass percentage of the steel strip are: C: 0.55%, Si: 0.19%, Mn: 0.65%, S: 0.002%, P: 0.01%, Al: 0.03%, Cr: 0.15%, Mo: 0.05%, Ni: 0.02%, and the rest are Fe and unavoidable impurities. The specification of the steel strip is 2.5 mm × 2250 mm × full length. A shallow groove turbulent pickling process is adopted to make the acid solution form a turbulent channel in the pickling tank under the drive of the high-speed running steel strip to accelerate the penetration into the inner part of the steel strip oxide scale. After the cleaning is completed, it is rinsed with deionized water to neutrality, wherein the acid solution is 85 g / L hydrochloric acid solution, the pickling speed is 80 m / min, and the cleaning temperature is 75 ° C. After drying, cold rolling is carried out, and the strip reduction rate during the cold rolling process is 40%, thereby obtaining the steel strip after acid continuous rolling treatment; (2) Hood annealing treatment: A full hydrogen hood annealing furnace is used to anneal the strip, including heating, insulation and cooling processes. During the heating and insulation processes, the flow rate of the inlet hydrogen is 30 m / s. During the heating process, the heating rate is 8°C / h, and the temperature is heated to 715°C. The insulation time is 14 hours. During the cooling process, a furnace table variable frequency fan is used to form a convection cycle in the full hydrogen hood annealing furnace. (3) Leveling process: In the leveling process, the leveling rolling method is adopted, the leveling elongation is 4%, and the leveling rolling force in the leveling process is adjusted to 750 kgf to obtain improved strip steel.

[0021] Example 3 A manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon strip steel along the width direction after heating in a hood annealing furnace comprises the following steps: (1) The steel strip is subjected to acid continuous rolling treatment: the chemical composition and mass percentage of the steel strip are: C: 0.20%, Si: 0.18%, Mn: 0.65%, S: 0.003%, P: 0.02%, Al: 0.05%, Cr: 0.15%, Mo: 0.05%, Ni: 0.02%, and the rest are Fe and unavoidable impurities. The specification of the steel strip is 3.2 mm×2250 mm×full length. A shallow groove turbulent pickling process is adopted to make the acid solution form a turbulent channel in the pickling tank under the drive of the high-speed running steel strip to accelerate the penetration into the inner part of the steel strip oxide scale. After the cleaning is completed, the steel strip is rinsed with deionized water until it is neutral. The acid solution is 95 g / L hydrochloric acid solution. The pickling speed is 100 m / min and the cleaning temperature is 75°C. After drying, the steel strip is cold rolled. The reduction rate of the steel strip during the cold rolling process is 50%, and the steel strip treated with acid continuous rolling is obtained; (2) Hood annealing treatment: A full hydrogen hood annealing furnace is used to anneal the strip, including heating, insulation and cooling processes. During the heating and insulation processes, the flow rate of the inlet hydrogen is 30 m / s. During the heating process, the heating rate is 8 °C / h, and the temperature is heated to 730 °C. The insulation time is 15 h. During the cooling process, a furnace table variable frequency fan is used to form a convection cycle in the full hydrogen hood annealing furnace. (3) Leveling process: In the leveling process, the leveling rolling method is adopted, the leveling elongation is 6%, and the leveling rolling force in the leveling process is adjusted to 1000kgf to obtain improved strip steel.

[0022] Example 4 A manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon strip steel along the width direction after heating in a hood annealing furnace comprises the following steps: (1) The steel strip is subjected to acid continuous rolling treatment: the weight percentage of the chemical composition of the steel strip is: C: 1.0%, Si: 0.50%, Mn: 1.4%, P: 0.02%, S: 0.02%, Al: 0.06%, Cr: 0.3%, Mo: 0.1%, Ni: 0.05%, and the rest is Fe and inevitable impurities. The specification of the steel strip is 10 mm×2250 mm×full length. A shallow groove turbulent pickling process is adopted to make the acid solution form a turbulent channel in the pickling tank under the drive of the high-speed running steel strip to accelerate the penetration into the inner part of the steel strip oxide scale. After the cleaning is completed, the steel strip is rinsed with deionized water until it is neutral. The acid solution is 100 g / L hydrochloric acid solution. The pickling speed is 120 m / min and the cleaning temperature is 80°C. After drying, the steel strip is cold rolled. The reduction rate of the steel strip during the cold rolling process is 55%, and the steel strip treated with acid continuous rolling is obtained; (2) Hood annealing treatment: A full hydrogen hood annealing furnace is used to anneal the strip, including heating, insulation and cooling processes. During the heating and insulation processes, the flow rate of the inlet hydrogen is 35 m / s. During the heating process, the heating rate is 10°C / h, and the temperature is heated to 740°C. The insulation time is 15h. During the cooling process, a furnace table variable frequency fan is used to form a convection cycle in the full hydrogen hood annealing furnace. (3) Leveling process: In the leveling process, the leveling rolling method is adopted, the leveling elongation is 10%, and the leveling rolling force in the leveling process is adjusted to 1200kgf to obtain improved strip steel.

[0023] Comparative Example 1 A method for improving the manufacturing of cold-rolled strip steel comprises the following steps: (1) The steel strip is cold rolled: the chemical composition and mass percentage of the steel strip are: C: 0.55%, Si: 0.19%, Mn: 0.65%, S: 0.002%, P: 0.01%, Al: 0.03%, Cr: 0.15%, Mo: 0.05%, Ni: 0.02%, and the rest are Fe and unavoidable impurities. The specification of the steel strip is 2.5 mm×2250 mm×full length. The steel strip is cold rolled. The reduction rate of the steel strip during the cold rolling process is 40%, thereby obtaining a steel strip after cold rolling; (2) Annealing treatment: Annealing treatment includes heating, heat preservation and cooling processes. During the heating and heat preservation process, the heating rate is 8℃ / h, the temperature is heated to 715℃, the heat preservation time is 14h, and the strip is naturally cooled to obtain improved strip steel.

[0024] Comparative Example 2 A method for improving the manufacturing of cold-rolled strip steel comprises the following steps: (1) cold rolling the steel strip: the chemical composition and mass percentage of the steel strip are: C: 0.20%, Si: 0.18%, Mn: 0.65%, S: 0.003%, P: 0.02%, Al: 0.05%, Cr: 0.15%, Mo: 0.05%, Ni: 0.02%, and the rest are Fe and unavoidable impurities. The specification of the steel strip is 3.2 mm×2250 mm×full length. The steel strip is cold rolled. The reduction rate of the steel strip during the cold rolling process is 40%, thereby obtaining a cold rolled steel strip; (2) Annealing treatment: Annealing treatment includes heating, heat preservation and cooling processes. During the heating and heat preservation process, the heating rate is 8℃ / h, the temperature is heated to 715℃, the heat preservation time is 14h, and the strip is naturally cooled to obtain improved strip steel.

[0025] The improved strip steels corresponding to Example 2, Example 3, Comparative Examples 1 and Comparative Examples 2 were tested for performance, and the test results are shown in Table 1: Table 1 It can be seen from the test results in Table 1 that after acid continuous rolling treatment, hood furnace annealing treatment and leveling process treatment, the improved strip steel corresponding to Example 2 and Example 3 has uniform hardness distribution in the width direction, which is significantly better than the improved strip steel corresponding to Comparative Example 1 and Comparative Example 2. The distribution of hardness in the width direction indicates that the method of appropriately increasing the leveling elongation has a more obvious effect on improving the uneven hardness of the cold-rolled medium and high carbon strip steel along the width direction after heating in the hood annealing furnace.

[0026] Although the embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that all equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon strip steel along the width direction after heating in a bell-type annealing furnace, characterized in that: It includes acid continuous rolling treatment, bell furnace annealing treatment and leveling process treatment of the strip.

2. The manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon strip steel along the width direction after heating in a bell-type annealing furnace according to claim 1, characterized in that: The chemical composition of the strip steel is as follows by weight percentage: C: 0.5%~1.0%, Si: 0.1%~0.50%, Mn: 0.1%~1.4%, P: ≤0.02%, S: ≤0.02%, of which Cr+Ni+Mo: ≤2.0%, Al: ≤0.06%, and the rest is Fe and unavoidable impurities.

3. The manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon strip steel along the width direction after heating in a bell-type annealing furnace according to claim 1, characterized in that: The strip steel has a thickness of 0.3-10 mm and a width of 900-2250 mm.

4. The manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon strip steel along the width direction after heating in a bell-type annealing furnace according to claim 1, characterized in that: The acid continuous rolling treatment comprises the following steps: a shallow trough turbulent pickling process is used to allow the acid solution to form a turbulent channel in the pickling tank under the drive of the high-speed running strip steel to accelerate the penetration into the inner part of the strip steel oxide scale; after the cleaning is completed, deionized water is used to rinse to neutrality, and after drying, cold rolling is performed to obtain the strip steel after the acid continuous rolling treatment.

5. The manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon strip steel along the width direction after heating in a bell-type annealing furnace according to claim 4, characterized in that: The acid solution is a hydrochloric acid solution of 80-100 g / L, the pickling speed is 60-220 m / min, the cleaning temperature is 70-80° C., and the reduction rate of the strip during the cold rolling process is 10%-60%.

6. The manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon strip steel along the width direction after heating in a bell-type annealing furnace according to claim 1, characterized in that: The bell-type furnace annealing treatment adopts a full hydrogen bell-type annealing furnace to anneal the strip steel, including heating, heat preservation and cooling processes.

7. The manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon steel strip along the width direction after heating in a bell-type annealing furnace according to claim 6, characterized in that: During the heating and heat preservation process, the flow rate of the inlet hydrogen is 25-35 m / s. During the heating process, the heating speed is 5-10°C / h, and the temperature is heated to 600-740°C. The heat preservation time is 10-20 hours. During the cooling process, a furnace table variable frequency fan is used to form a convection cycle in the full hydrogen hood annealing furnace.

8. The manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon steel strip along the width direction after heating in a bell-type annealing furnace according to claim 1, characterized in that: The flattening process adopts a flattening rolling method, wherein the flattening elongation is 1% to 10%.

9. The manufacturing method for improving the uneven hardness of cold-rolled medium-high carbon steel strip along the width direction after heating in a bell-type annealing furnace according to claim 8, characterized in that: The temper rolling force during the temper rolling process is 200 to 1200 kgf.

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