Medium carbon steel s50c and method for manufacturing the same

Abstract

This application discloses a medium carbon steel S50C and its preparation method. The method includes: cold rolling the steel coil using an 18-roll single-stand reversible rolling mill, including: adjusting the rolling mode of the 18-roll single-stand reversible rolling mill to a double-sided wave mode, with a rolling intensity of 1IU~20IU, to obtain cold-rolled strip steel; performing a full-hydrogen bell-type annealing treatment on the cold-rolled strip steel, including: placing the cold-rolled strip steel in a bell-type annealing furnace and heating it in a reducing atmosphere, so that the cold-rolled strip steel reaches a first preset temperature plateau during the heating stage and holds it at that temperature for a first preset time; and performing bell-type annealing treatment on the cold-rolled strip steel after the heat holding treatment in a reducing atmosphere to obtain bell-type annealed medium carbon steel S50C. The preparation method of carbon steel S50C in this application embodiment can reduce the width and color depth of residual oxide color at the edge of the cold-rolled strip steel, and improve the overall surface quality of the medium carbon steel S50C cold-rolled strip steel.

Description

Technical Field

[0001] This application belongs to the field of cold-rolled strip steel production technology, and particularly relates to a medium carbon steel S50C and its preparation method. Background Technology

[0002] Cold-rolled S50C, as a medium carbon steel, is widely used in the manufacture of automotive parts, hardware tools, and precision electronic components due to its excellent strength and plasticity. When the strip is precision stamped into parts, it often requires electroplating. If there is a color difference on the surface of the parts due to annealing, it will greatly affect the product quality. Due to differences in the processing, cold-rolled S50C medium carbon steel generally has a certain degree of color difference on its surface, which is caused by oxidation at the edges of the strip. Therefore, the oxidation color defect at the edges of cold-rolled S50C medium carbon steel strip must be improved to ensure that the color of the entire sheet is uniform after electroplating of the parts. However, there is currently no good solution. Summary of the Invention

[0003] This application provides a medium carbon steel S50C and its preparation method, which can reduce the width and color depth of residual oxide color on the edge of the strip and improve the overall surface quality of the medium carbon steel S50C strip.

[0004] In a first aspect, this application provides a method for preparing medium carbon steel S50C, comprising: The steel coil is cold rolled using an 18-roll single-stand reversible rolling mill, including: adjusting the rolling mode of the 18-roll single-stand reversible rolling mill to a double-sided wave mode, wherein the rolling strength of the double-sided wave mode is 1IU~20IU, so as to obtain cold-rolled strip steel. The process of performing all-hydrogen bell-type annealing on cold-rolled strip steel includes: placing the cold-rolled strip steel in a bell-type annealing furnace and heating it in a reducing atmosphere, so that the cold-rolled strip steel reaches a first preset temperature plateau during the heating stage and holds it at that temperature for a first preset time; and then performing bell-type annealing on the cold-rolled strip steel after the holding treatment in a reducing atmosphere to obtain bell-type annealed steel coils of medium carbon steel S50C.

[0005] According to the embodiments of the first aspect of this application, the method for preparing medium carbon steel S50C further includes: adding a set of edge cleaning nozzles on each side of the exit of an 18-roll single-stand reversible rolling mill for cleaning the emulsion and rolling oil on the edge of the strip.

[0006] According to an embodiment of the first aspect of this application, an additional set of edge purging nozzles is added to each side of the exit of an 18-roll single-stand reversible rolling mill, wherein the pressure of the nozzles is 3000 kN / m. 2 ~6000KN / m 2 .

[0007] According to an embodiment of the first aspect of this application, after the cold rolling process is completed and before the cold-rolled strip is re-coiled, felt is used to clean the surface of the cold-rolled strip at the exit of the 18-roll single-stand reversible mill to reduce the residue of emulsion and rolling fluid on the surface of the cold-rolled strip.

[0008] According to an embodiment of the first aspect of this application, the volume content of the rolling oil in the felt is ≤5%.

[0009] According to an embodiment of the first aspect of this application, by replacing or degreasing the felt, the volume content of rolling oil in the felt is ≤5%.

[0010] According to an embodiment of the first aspect of this application, cold-rolled strip steel is placed in a bell-type annealing furnace and heated in a reducing atmosphere to allow the cold-rolled strip steel to reach a first preset temperature plateau during the heating stage. The first temperature plateau is 200°C to 300°C, and the first preset duration is 2 hours to 4 hours.

[0011] According to an embodiment of the first aspect of this application, the reducing atmosphere may be any one or a mixture of two of H2 and N2.

[0012] According to an embodiment of the first aspect of this application, cold-rolled strip steel is placed in a bell-type annealing furnace and heated in a reducing atmosphere. The reducing atmosphere used is hydrogen, and the hydrogen flow rate is 10 m³ / s. 3 ~50m 3 .

[0013] According to the embodiment of the first aspect of this application, the cold-rolled strip steel that has undergone heat preservation treatment is subjected to bell-type furnace annealing in a reducing atmosphere, with a heating rate of 5℃ / min to 50℃ / min, an annealing temperature of 600℃ to 850℃, a heating time of 12s to 170s, and an annealing time of 50h to 150h.

[0014] According to an embodiment of the first aspect of this application, cold-rolled strip steel that has undergone heat preservation treatment is subjected to bell-type furnace annealing in a reducing atmosphere. The reducing atmosphere used is hydrogen, and the hydrogen flow rate is 25 m³ / s. 3 ~50m 3 .

[0015] Secondly, this application provides a medium carbon steel S50C, which is prepared according to the method for preparing medium carbon steel S50C provided in the first aspect embodiment. By mass percentage, the medium carbon steel S50C includes the following components: C: 0.43wt.%~0.58wt.%, Si: 0.1wt.%~1.0wt.%, Mn: 0.5wt.%~1.5wt.%, P: ≤0.02wt.%, S: ≤0.02wt.%, with the remainder being Fe and unavoidable impurities.

[0016] The medium carbon steel S50C and its preparation method in this application embodiment use an 18-roll single-stand reversible rolling mill to cold roll the steel coil. During the cold rolling process of the strip, the rolling mode of the 18-roll single-stand reversible rolling mill is changed, and edge purging at the mill exit is increased to remove emulsion and rolling oil at the exit edge. Then, annealing is carried out in a full hydrogen annealing furnace, which can effectively reduce the thinness of the strip edge and the residual emulsion, rolling oil and moisture on the edge and the entire strip surface. It also significantly reduces the width and color depth of the residual oxide color on the strip edge and improves the overall surface quality of the medium carbon steel S50C strip. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart of the preparation method of medium carbon steel S50C provided in the embodiments of this application; Figure 2 It is the edge oxidation color of the existing medium carbon steel S50C strip product.

[0019] Figure 3 This is a physical image of the medium carbon steel S50C strip product provided in Embodiment 1 of this application.

[0020] Figure 4 These are physical images of the medium carbon steel S50C strip products provided in Embodiments 2 and 3 of this application.

[0021] Figure 5 These are physical images of the medium carbon steel S50C strip products provided in Embodiments 4 and 5 of this application.

[0022] Figure 6 This is a physical image of the medium carbon steel S50C strip product provided in Embodiment 6 of this application.

[0023] Figure 7 This is a picture of the S50C medium carbon steel strip product provided in Comparative Example 1.

[0024] Figure 8 This is a picture of the S50C medium carbon steel strip product provided in Comparative Example 2. Detailed Implementation

[0025] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0026] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0027] As pointed out in the background section, the inventors of this application have discovered that the color difference on the surface of the part is an inherent annealing color difference. This is because during the annealing process, the alloying elements at the edges accumulate on the surface and combine with oxygen on the surface to form an oxidation color difference.

[0028] To address the problems of the prior art, this application provides a medium carbon steel S50C and its preparation method. The following is a description of the medium carbon steel S50C and its preparation method provided in this application.

[0029] Figure 1 A schematic flowchart of the preparation method of medium carbon steel S50C provided in the embodiments of this application is shown.

[0030] like Figure 1 As shown, an embodiment of the first aspect of this application provides a method for preparing medium carbon steel S50C, comprising: The steel coil is cold rolled using an 18-roll single-stand reversible rolling mill, including: adjusting the rolling mode of the 18-roll single-stand reversible rolling mill to a double-sided wave mode, wherein the rolling strength of the double-sided wave mode is 1IU~20IU, so as to obtain cold-rolled strip steel. The process of performing all-hydrogen bell-type annealing on cold-rolled strip steel includes: placing the cold-rolled strip steel in a bell-type annealing furnace and heating it in a reducing atmosphere, so that the cold-rolled strip steel reaches a first preset temperature plateau during the heating stage and holds it at that temperature for a first preset time; and then performing bell-type annealing on the cold-rolled strip steel after the holding treatment in a reducing atmosphere to obtain bell-type annealed steel coils of medium carbon steel S50C.

[0031] The method for preparing medium carbon steel S50C provided in this application embodiment uses an 18-roll single-stand reversible rolling mill to cold roll the steel coil. During the cold rolling process of the strip, the rolling mode of the 18-roll single-stand reversible rolling mill is changed, and edge purging at the mill exit is increased to remove emulsion and rolling oil from the exit edge. Then, annealing is carried out in a full hydrogen annealing furnace, which can effectively reduce the thinness of the strip edge and the residual emulsion, rolling oil and moisture on the edge and the entire strip surface. It also significantly reduces the width and color depth of residual oxide color on the strip edge, and improves the overall surface quality of medium carbon steel S50C strip.

[0032] In the method for preparing medium carbon steel S50C provided in this application embodiment, the rolling mode of the original 18-roll single-stand reversible rolling mill in the cold rolling process is changed from the middle wave mode to the double wave mode. Exemplarily, the rolling intensity of the double wave mode is controlled at 1 IU, 2 IU, 3 IU, 5 IU, 7 IU, 9 IU, 10 IU, 12 IU, 14 IU, 15 IU, 17 IU, 19, and 20 IU. The double wave mode can effectively prevent the strip edge from becoming too thin. It should be noted that in the rolling process of this application, the entire process adopts the double wave mode.

[0033] In the method for preparing medium carbon steel S50C provided in this application embodiment, the emulsion is used to cool the surface of the strip steel, and the rolling oil is used to lubricate the rolls.

[0034] In some embodiments, a set of edge purging nozzles is added on each side of the exit of the 18-roll single-stand reversible rolling mill to purge the emulsion and rolling oil from the edge of the strip.

[0035] In some embodiments, the preparation method of medium carbon steel S50C further includes: after the cold rolling process is completed and before the cold-rolled strip is recoiled, using felt to clean the surface of the cold-rolled strip at the exit of an 18-roll single-stand reversible mill to reduce the residue of emulsion and rolling fluid on the surface of the cold-rolled strip.

[0036] In some embodiments, the volume content of rolling oil in the felt is ≤5%.

[0037] In some embodiments, the volume content of rolling oil in the felt is ≤5% by replacing or degreasing the felt.

[0038] In some embodiments, when using felt to degrease cold-rolled strip steel in the rewinding pass at the mill exit, the number of felt degreasing cycles is increased, that is, the number of felt degreasing cycles is changed from once to two or three times, so that the volume content of rolling oil on the felt meets the requirement of ≤5%. Of course, it is understood that the felt can be replaced in order to make the felt more effective in degreasing cold-rolled strip steel.

[0039] In some embodiments, an additional set of edge purging nozzles is added to each side of the exit of the 18-roll single-stand reversible rolling mill, wherein the pressure of the nozzles is 3000 kN / m. 2 ~6000KN / m 2 This pressure allows for the purging of air, reducing the residue of emulsion and rolling oil in cold-rolled strip during the cold rolling process.

[0040] In some embodiments, the cold-rolled strip is placed in a bell-type annealing furnace and heated in a reducing atmosphere to reach a first preset temperature plateau, which is 200°C to 300°C, for a first preset duration of 2 to 4 hours. This is to volatilize water vapor on the surface of the cold-rolled strip and reduce the oxidizing atmosphere within the all-hydrogen bell-type annealing furnace.

[0041] In some embodiments, the reducing atmosphere may be any one or a mixture of two of H2 and N2.

[0042] In some embodiments, the cold-rolled strip steel is placed in a bell-type annealing furnace and heated in a reducing atmosphere. The reducing atmosphere used is hydrogen, and the hydrogen flow rate is 10 m³ / s. 3 ~50m 3 .

[0043] In some embodiments, the cold-rolled strip steel that has undergone heat preservation treatment is subjected to bell-type furnace annealing in a reducing atmosphere, with a heating rate of 5℃ / min to 50℃ / min, an annealing temperature of 600℃ to 850℃, a heating time of 12s to 170s, and an annealing time of 50h to 150h.

[0044] In some embodiments, the cold-rolled strip steel that has undergone heat preservation treatment is subjected to bell-type furnace annealing in a reducing atmosphere, wherein the reducing atmosphere used is hydrogen, and the hydrogen flow rate is 25 m³ / s. 3 ~50m 3 During the bell-type furnace annealing stage, the hydrogen flow rate during the heating and holding stages is increased, specifically from 10m³ / h. 3 / hour increased to 25m 3 ~50m 3Every hour, to maintain a reducing atmosphere within the bell-type furnace and reduce oxidation on the edge surface of the cold-rolled strip, the hydrogen flow rate is increased during the heating and holding stages, with flow rates of 25, 27, 28, 30, 32, 34, 35, 36, 38, 40, 42, 45, 48, 49, or 50 m³ / h. 3 .

[0045] Secondly, embodiments of this application provide a medium carbon steel S50C, which is prepared according to the method for preparing medium carbon steel S50C provided in the first aspect embodiment.

[0046] In some embodiments, medium carbon steel S50C comprises the following components by weight percentage: C: 0.43wt.%~0.58wt.%, Si: 0.1wt.%~1.0wt.%, Mn: 0.5wt.%~1.5wt.%, P: ≤0.02wt.%, S: ≤0.02wt.%, with the remainder being Fe and unavoidable impurities.

[0047] In some embodiments, the thickness of medium carbon steel S50C cold-rolled strip is 0.3mm to 10mm, and the width is 900mm to 2250mm.

[0048] The technical solutions and effects of this application will be further illustrated below through specific embodiments and comparative examples.

[0049] In the following embodiments, the chemical composition of medium carbon steel S50C cold-rolled strip is as follows (by weight percentage): C: 0.43wt.%~0.58wt.%, Si: 0.1wt.%~1.0wt.%, Mn: 0.5wt.%~1.5wt.%, P: ≤0.02wt.%, S: ≤0.02wt.%, with the remainder being Fe and unavoidable impurities; the strip thickness is 0.3~10mm, and the width is 900~2250mm.

[0050] Example 1 A method for preparing medium carbon steel S50C, wherein the medium carbon steel S50C uses S50C hot-rolled substrate as raw material. The chemical composition and content of the S50C hot-rolled substrate include: C: 0.48 wt.%, Si: 0.36 wt.%, Mn: 0.95 wt.%, S: 0.003 wt.%, P: 0.015 wt.%, with the remainder being Fe and unavoidable impurities. The strip steel has a specification of 2.3 mm × 2250 mm × total length. The method includes: An 18-roll single-stand reversible rolling mill is used to cold-roll strip from pickled hot-rolled steel coils. This includes: adjusting the rolling mode of the 18-roll single-stand reversible rolling mill to a double-sided wave mode with a rolling strength of 15 IU to obtain cold-rolled strip; and adding a set of edge-blowing nozzles on each side of the 18-roll single-stand reversible rolling mill exit to blow away the emulsion and rolling oil from the strip edges. The nozzle pressure is 3000 KN / m. 2 ; After the cold rolling process is completed and before the cold-rolled strip is recoiled, felt is used to clean the surface of the cold-rolled strip at the exit of the 18-roll single-stand reversible mill. By degreasing the felt to make the rolling oil content of the felt 5%, the surface of the cold-rolled strip is effectively cleaned, reducing the emulsion and rolling liquid residue on the surface of the cold-rolled strip. The cold-rolled strip steel is subjected to all-hydrogen bell-type annealing treatment, which includes: placing the cold-rolled strip steel in a bell-type annealing furnace and heating it in a reducing atmosphere. The reducing atmosphere used for the heating treatment is hydrogen, and the hydrogen flow rate is 10 m³ / s. 3 This ensures that the cold-rolled strip reaches the first preset temperature plateau, 200°C, during the heating stage, and is held at that temperature for the first preset duration, i.e., 4 hours. The cold-rolled strip steel, after heat preservation treatment, is subjected to bell-type furnace annealing in a reducing atmosphere. The reducing atmosphere used for the heating process is hydrogen, with a hydrogen flow rate of 25 m³ / h. 3 The heating rate was 8℃ / min, the annealing temperature was 650℃~700℃, the heating time was 56.25s, and the annealing time was 55h, to obtain medium carbon steel S50C bell furnace annealed steel coils.

[0051] Example 2 A method for preparing medium carbon steel S50C, wherein the medium carbon steel S50C uses S50C hot-rolled substrate as raw material. The chemical composition and content of the S50C hot-rolled substrate include: C: 0.51 wt.%, Si: 0.11 wt.%, Mn: 1.01 wt.%, P: 0.020 wt.%, S: 0.0012 wt.%, with the remainder being Fe and unavoidable impurities. The strip steel has a specification of 1.8 mm × 2250 mm × total length. The method includes: An 18-roll single-stand reversible rolling mill is used to cold-roll strip from pickled hot-rolled steel coils. This includes: adjusting the rolling mode of the 18-roll single-stand reversible rolling mill to a double-sided wave mode with a rolling strength of 15 IU to obtain cold-rolled strip; and adding a set of edge-blowing nozzles on each side of the 18-roll single-stand reversible rolling mill exit to blow away the emulsion and rolling oil from the strip edges. The nozzle pressure is 3500 KN / m. 2 ; After the cold rolling process is completed and before the cold-rolled strip is recoiled, felt is used to clean the surface of the cold-rolled strip at the exit of the 18-roll single-stand reversible mill. By degreasing the felt to reduce the rolling oil content of the felt to 5%, the surface of the cold-rolled strip is effectively cleaned, reducing the emulsion and rolling fluid residue on the surface of the cold-rolled strip. The cold-rolled strip steel is subjected to all-hydrogen bell-type annealing treatment, which includes: placing the cold-rolled strip steel in a bell-type annealing furnace and heating it in a reducing atmosphere. The reducing atmosphere used for the heating treatment is hydrogen, and the hydrogen flow rate is 10 m³ / s. 3 This ensures that the cold-rolled strip reaches the first preset temperature plateau, 200°C, during the heating stage, and is held at that temperature for the first preset duration, i.e., 4 hours. The cold-rolled strip steel, after heat preservation treatment, is subjected to bell-type furnace annealing in a reducing atmosphere. The reducing atmosphere used for the heating process is hydrogen, with a hydrogen flow rate of 25 m³ / h. 3 The heating rate was 20℃ / min, the annealing temperature was 700℃~735℃, the heating time was 25s, and the annealing time was 60h, to obtain medium carbon steel S50C bell furnace annealed steel coils.

[0052] Example 3 A method for preparing medium carbon steel S50C, wherein the medium carbon steel S50C uses S50C hot-rolled substrate as raw material. The chemical composition and content of the S50C hot-rolled substrate include: C: 0.51 wt.%, Si: 0.35 wt.%, Mn: 0.54 wt.%, S: 0.0012 wt.%, P: 0.018 wt.%, with the remainder being Fe and unavoidable impurities. The strip steel has a specification of 1.5 mm × 2250 mm × total length. The method includes: An 18-roll single-stand reversible rolling mill is used to cold-roll strip from pickled hot-rolled steel coils. This includes: adjusting the rolling mode of the 18-roll single-stand reversible rolling mill to a double-sided wave mode, with a rolling strength of 15 IU to obtain cold-rolled strip; and adding a set of edge-blowing nozzles on each side of the 18-roll single-stand reversible rolling mill exit to blow away the emulsion and rolling oil from the strip edges, wherein the nozzle pressure is 4000 KN / m. 2 ; After the cold rolling process is completed and before the cold-rolled strip is recoiled, felt is used to clean the surface of the cold-rolled strip at the exit of the 18-roll single-stand reversible mill. By performing two degreasing treatments on the felt to reduce the rolling oil content of the felt to 5%, the surface of the cold-rolled strip is effectively cleaned, reducing the residue of emulsion and rolling fluid on the surface of the cold-rolled strip. The cold-rolled strip steel is subjected to all-hydrogen bell-type annealing treatment, which includes: placing the cold-rolled strip steel in a bell-type annealing furnace and heating it in a reducing atmosphere. The reducing atmosphere used for the heating treatment is hydrogen, and the hydrogen flow rate is 10 m³ / s.3 This ensures that the cold-rolled strip reaches the first preset temperature plateau, 200°C, during the heating stage, and is held at that temperature for the first preset duration, i.e., 4 hours. The cold-rolled strip steel, after heat preservation treatment, is subjected to bell-type furnace annealing in a reducing atmosphere. The reducing atmosphere used for the heating process is hydrogen, with a hydrogen flow rate of 25 m³ / h. 3 The heating rate was 45℃ / min, the annealing temperature was 820℃~850℃, the heating time was 14s, and the annealing time was 80h, to obtain medium carbon steel S50C bell furnace annealed steel coils.

[0053] Example 4 A method for preparing medium carbon steel S50C, wherein the medium carbon steel S50C uses S50C hot-rolled substrate as raw material. The chemical composition and content of the S50C hot-rolled substrate include: C: 0.45 wt.%, Si: 0.73 wt.%, Mn: 0.98 wt.%, S: 0.0018 wt.%, P: 0.018 wt.%, with the remainder being Fe and unavoidable impurities. The strip steel has a specification of 1.5 mm × 2250 mm × total length. The method includes: An 18-roll single-stand reversible rolling mill is used to cold-roll strip from pickled hot-rolled steel coils. This includes: adjusting the rolling mode of the 18-roll single-stand reversible rolling mill to a double-sided wave mode, with a rolling strength of 15 IU to obtain cold-rolled strip; and adding a set of edge-blowing nozzles on each side of the 18-roll single-stand reversible rolling mill exit to blow away the emulsion and rolling oil from the strip edges, wherein the nozzle pressure is 4000 KN / m. 2 ; After the cold rolling process is completed and before the cold-rolled strip is recoiled, felt is used to clean the surface of the cold-rolled strip at the exit of the 18-roll single-stand reversible mill. By performing two degreasing treatments on the felt to reduce the rolling oil content of the felt to 5%, the surface of the cold-rolled strip is effectively cleaned, reducing the residue of emulsion and rolling fluid on the surface of the cold-rolled strip. The cold-rolled strip steel is subjected to all-hydrogen bell-type annealing treatment, which includes: placing the cold-rolled strip steel in a bell-type annealing furnace and heating it in a reducing atmosphere. The reducing atmosphere used for the heating treatment is hydrogen, and the hydrogen flow rate is 10 m³ / s. 3 This ensures that the cold-rolled strip reaches the first preset temperature plateau, 200°C, during the heating stage, and is held at that temperature for the first preset duration, i.e., 4 hours. The cold-rolled strip steel, after heat preservation treatment, is subjected to bell-type furnace annealing in a reducing atmosphere. The reducing atmosphere used for the heating process is hydrogen, with a hydrogen flow rate of 25 m³ / h. 3The heating rate was 50℃ / min, the annealing temperature was 830℃~850℃, the heating time was 12.6s, and the annealing time was 100h, to obtain medium carbon steel S50C bell furnace annealed steel coils.

[0054] Example 5 A method for preparing medium carbon steel S50C, wherein the medium carbon steel S50C uses S50C hot-rolled substrate as raw material. The chemical composition and content of the S50C hot-rolled substrate include: C: 0.49 wt.%, Si: 0.33 wt.%, Mn: 0.72 wt.%, S: 0.0013 wt.%, P: 0.017 wt.%, with the remainder being Fe and unavoidable impurities. The strip steel has a specification of 2.3 mm × 2250 mm × total length. The method includes: An 18-roll single-stand reversible rolling mill is used to cold-roll strip from pickled hot-rolled steel coils. This includes: adjusting the rolling mode of the 18-roll single-stand reversible rolling mill to a double-sided wave mode, with a rolling strength of 15 IU to obtain cold-rolled strip; and adding a set of edge-blowing nozzles on each side of the 18-roll single-stand reversible rolling mill exit to blow away the emulsion and rolling oil from the strip edges, wherein the nozzle pressure is 4000 KN / m. 2 ; After the cold rolling process is completed and before the cold-rolled strip is recoiled, felt is used to clean the surface of the cold-rolled strip at the exit of the 18-roll single-stand reversible mill. By performing two degreasing treatments on the felt to reduce the rolling oil content of the felt to 5%, the surface of the cold-rolled strip is effectively cleaned, reducing the residue of emulsion and rolling fluid on the surface of the cold-rolled strip. The cold-rolled strip steel is subjected to all-hydrogen bell-type annealing treatment, which includes: placing the cold-rolled strip steel in a bell-type annealing furnace and heating it in a reducing atmosphere. The reducing atmosphere used for the heating treatment is hydrogen, and the hydrogen flow rate is 10 m³ / s. 3 This ensures that the cold-rolled strip reaches the first preset temperature plateau, 200°C, during the heating stage, and is held at that temperature for the first preset duration, i.e., 4 hours. The cold-rolled strip steel, after heat preservation treatment, is subjected to bell-type furnace annealing in a reducing atmosphere. The reducing atmosphere used for the heating process is hydrogen, with a hydrogen flow rate of 25 m³ / h. 3 The heating rate was 40℃ / min, the annealing temperature was 720℃~750℃, the heating time was 13s, and the annealing time was 75h, to obtain medium carbon steel S50C bell furnace annealed steel coils.

[0055] Example 6 A method for preparing medium carbon steel S50C, wherein the medium carbon steel S50C uses S50C hot-rolled substrate as raw material. The chemical composition and content of the S50C hot-rolled substrate include: C: 0.57 wt.%, Si: 0.45 wt.%, Mn: 0.75 wt.%, S: 0.0013 wt.%, P: 0.016 wt.%, with the remainder being Fe and unavoidable impurities. The strip steel has a specification of 2.5 mm × 2250 mm × total length. The method includes: An 18-roll single-stand reversible rolling mill is used to cold-roll strip from pickled hot-rolled steel coils. This includes: adjusting the rolling mode of the 18-roll single-stand reversible rolling mill to a double-sided wave mode with a rolling strength of 15 IU to obtain cold-rolled strip; and adding a set of edge-blowing nozzles on each side of the 18-roll single-stand reversible rolling mill exit to blow away the emulsion and rolling oil from the strip edges. The nozzle pressure is 4500 KN / m. 2 ; After the cold rolling process is completed and before the cold-rolled strip is recoiled, felt is used to clean the surface of the cold-rolled strip at the exit of the 18-roll single-stand reversible mill. By performing two degreasing treatments on the felt to reduce the rolling oil content of the felt to 5%, the surface of the cold-rolled strip is effectively cleaned, reducing the residue of emulsion and rolling fluid on the surface of the cold-rolled strip. The cold-rolled strip steel is subjected to all-hydrogen bell-type annealing treatment, which includes: placing the cold-rolled strip steel in a bell-type annealing furnace and heating it in a reducing atmosphere. The reducing atmosphere used for the heating treatment is hydrogen, and the hydrogen flow rate is 10 m³ / s. 3 This ensures that the cold-rolled strip reaches the first preset temperature plateau, 200°C, during the heating stage, and is held at that temperature for the first preset duration, i.e., 4 hours. The cold-rolled strip steel, after heat preservation treatment, is subjected to bell-type furnace annealing in a reducing atmosphere. The reducing atmosphere used for the heating process is hydrogen, with a hydrogen flow rate of 25 m³ / h. 3 The heating rate was 36℃ / min, the annealing temperature was 770℃~800℃, the heating time was 16s, and the annealing time was 120h, resulting in bell-type furnace annealed steel coils of medium carbon steel S50C.

[0056] Comparative Example 1 A method for preparing medium carbon steel S50C, wherein the medium carbon steel S50C uses S50C hot-rolled substrate as raw material. The chemical composition and content of the S50C hot-rolled substrate include: C: 0.49 wt.%, Si: 0.32 wt.%, Mn: 0.71 wt.%, S: 0.0013 wt.%, P: 0.018 wt.%, with the remainder being Fe and unavoidable impurities. The strip steel has a specification of 2.3 mm × 2250 mm × total length. The method includes: The strip of hot-rolled steel coil after pickling is cold-rolled using an 18-roll single-stand reversible rolling mill, including: cold rolling the 18-roll single-stand reversible rolling mill in the medium wave mode, with a rolling strength of 15IU, to obtain cold-rolled strip. After the cold rolling process is completed and before the cold-rolled strip is recoiled, felt is used to clean the surface of the cold-rolled strip at the exit of the 18-roll single-stand reversible mill. By performing two degreasing treatments on the felt, the rolling oil content of the felt is reduced to 5%, so as to effectively clean the surface of the cold-rolled strip and reduce the emulsion and rolling liquid residue on the surface of the cold-rolled strip. The process of performing all-hydrogen bell-type annealing on cold-rolled strip steel includes: placing the cold-rolled strip steel in a bell-type annealing furnace for bell-type annealing in a reducing atmosphere, wherein the reducing atmosphere used for the heating process is hydrogen gas with a flow rate of 10 m³ / h. 3 The heating rate was 25℃ / min, the annealing temperature was 650℃~680℃, the heating time was 18s, and the annealing time was 55h, to obtain medium carbon steel S50C bell furnace annealed steel coils.

[0057] Comparative Example 2 A method for preparing medium carbon steel S50C, wherein the medium carbon steel S50C uses S50C hot-rolled substrate as raw material. The chemical composition and content of the S50C hot-rolled substrate include: C: 0.57 wt.%, Si: 0.45 wt.%, Mn: 0.75 wt.%, S: 0.0013 wt.%, P: 0.022 wt.%, with the remainder being Fe and unavoidable impurities. The strip steel has a specification of 2.5 mm × 2250 mm × total length. The method includes: An 18-roll single-stand reversible rolling mill is used to cold-roll strip from pickled hot-rolled steel coils. This includes: adjusting the rolling mode of the 18-roll single-stand reversible rolling mill to a double-sided wave mode with a rolling strength of 15 IU to obtain cold-rolled strip; and adding a set of edge-blowing nozzles on each side of the 18-roll single-stand reversible rolling mill exit to blow away the emulsion and rolling oil from the strip edges. The nozzle pressure is 4500 KN / m. 2 ; After the cold rolling process is completed and before the cold-rolled strip is recoiled, felt is used to clean the surface of the cold-rolled strip at the exit of the 18-roll single-stand reversible mill. By performing two degreasing treatments on the felt to reduce the rolling oil content of the felt to 5%, the surface of the cold-rolled strip is effectively cleaned, reducing the residue of emulsion and rolling fluid on the surface of the cold-rolled strip. The cold-rolled strip steel is subjected to all-hydrogen bell-type annealing treatment, which includes: placing the cold-rolled strip steel in a bell-type annealing furnace and heating it in a reducing atmosphere. The reducing atmosphere used for the heating treatment is hydrogen, and the hydrogen flow rate is 10 m³ / s. 3No first preset temperature platform of 200℃ is set; The cold-rolled strip steel, after heat preservation treatment, is subjected to bell-type furnace annealing in a reducing atmosphere. The reducing atmosphere used for the heating process is hydrogen, with a hydrogen flow rate of 15 m³ / s. 3 The furnace was set at 25℃ / min, with an annealing temperature of 650℃~680℃, a heating time of 18s, and an annealing time of 55h to obtain medium carbon steel S50C bell-type furnace annealed steel coils.

[0058] The preparation process parameters and test results of Examples 1-6 and Comparative Examples 1-2 were statistically analyzed and recorded in Table 1 below.

[0059] Table 1

[0060] As can be seen from the comparison of the edge oxidation color difference of medium carbon steel S50C cold-rolled strip in Examples 1-6 and Comparative Examples 1-2 in Table 1, for cold-rolled medium and high carbon steel S50C, the edge oxidation color difference defect of annealed strip can be reduced by combining measures such as changing the cold rolling mode, increasing the number of mill exit purging nozzles, increasing the number of felt degreasing pairs in the rewinding pass, increasing the low temperature holding platform of the bell furnace annealing, and increasing the hydrogen flow rate during the heating and holding stages. Through the adjustment of the above measures, the width of the edge oxidation color difference of annealed strip has been significantly reduced, meeting the customer's requirements.

[0061] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A method for preparing medium carbon steel S50C, characterized in that, include: The steel coil is cold rolled using an 18-roll single-stand reversible rolling mill, including: adjusting the rolling mode of the 18-roll single-stand reversible rolling mill to a double-sided wave mode, wherein the rolling strength of the double-sided wave mode is 1IU~20IU, so as to obtain cold-rolled strip steel. The process of performing all-hydrogen bell-type annealing on cold-rolled strip steel includes: placing the cold-rolled strip steel in a bell-type annealing furnace and heating it in a reducing atmosphere, so that the cold-rolled strip steel reaches a first preset temperature plateau during the heating stage and holds it at that temperature for a first preset time; and then performing bell-type annealing on the cold-rolled strip steel after the holding treatment in a reducing atmosphere to obtain bell-type annealed steel coils of medium carbon steel S50C.

2. The method for preparing medium carbon steel S50C according to claim 1, characterized in that, Also includes: A set of edge purging nozzles is added to each side of the exit of the 18-roll single-stand reversible rolling mill to purge the emulsion and rolling oil from the edge of the strip.

3. The method for preparing medium carbon steel S50C according to claim 1, characterized in that, Also includes: After the cold rolling process is completed and before the cold-rolled strip is recoiled, felt is used to clean the surface of the cold-rolled strip at the exit of the 18-roll single-stand reversible mill to reduce the residue of emulsion and rolling fluid on the surface of the cold-rolled strip.

4. The method for preparing medium carbon steel S50C according to claim 3, characterized in that, The volume content of rolling oil in felt is ≤5%; Optionally, the volume content of rolling oil in the felt can be ≤5% by replacing or degreasing the felt.

5. The method for preparing medium carbon steel S50C according to claim 1, characterized in that, The process involves placing the cold-rolled strip steel in a bell-type annealing furnace and heating it in a reducing atmosphere, so that the cold-rolled strip steel reaches a first preset temperature plateau during the heating stage. The first temperature plateau is 200℃~300℃, and the first preset duration is 2 hours~4 hours.

6. The method for preparing medium carbon steel S50C according to claim 1, characterized in that, The reducing atmosphere may be any one or a mixture of two of H2 and N2.

7. The method for preparing medium carbon steel S50C according to claim 1, characterized in that, The process involves placing the cold-rolled strip steel in a bell-type annealing furnace and heating it in a reducing atmosphere. The reducing atmosphere used is hydrogen, and the hydrogen flow rate is 10 m³ / s. 3 ~50m 3 .

8. The method for preparing medium carbon steel S50C according to claim 1, characterized in that, The cold-rolled strip steel that has undergone heat preservation treatment is annealed in a bell-type furnace in a reducing atmosphere. The heating rate is 5℃ / min to 50℃ / min, the annealing temperature is 600℃ to 850℃, the heating time is 12s to 170s, and the annealing time is 50h to 150h.

9. The method for preparing medium carbon steel S50C according to claim 1, characterized in that, The cold-rolled strip steel, after heat preservation treatment, is subjected to bell-type furnace annealing in a reducing atmosphere. The reducing atmosphere used is hydrogen, and the hydrogen flow rate is 25 m³ / s. 3 ~50m 3 .

10. A medium carbon steel S50C, characterized in that, The medium carbon steel S50C is prepared according to any one of claims 1-9, and by mass percentage, the medium carbon steel S50C contains the following components: C: 0.43wt.%~0.58wt.%, Si: 0.1wt.%~1.0wt.%, Mn: 0.5wt.%~1.5wt.%, P: ≤0.02wt.%, S: ≤0.02wt.%, with the remainder being Fe and unavoidable impurities.

Images