S50C high-carbon steel and production method and application thereof

Abstract

The invention belongs to the technical field of steel smelting, and particularly relates to a production method and application of S50C high-carbon steel. The production method comprises the following steps that a high-pulling-speed sheet billet is sheared through a pendulum shear and then directly enters a soaking pit furnace, descaling, finish rolling, laminar cooling, coiling and air cooling are conducted, and S50C high-carbon steel is obtained; in the soaking step, the charging temperature ranges from 850 DEG C to 950 DEG C, and the heating rate ranges from 3.5 DEG C / min to 10.0 DEG C / min; the furnace temperature of the soaking furnace is 1150-1200 DEG C, and the soaking time is 19-40 minutes; in the coiling step, the coiling temperature is 570 DEG C to 620 DEG C. According to the production method of the S50C high-carbon steel, under the combination of the heating temperature, the heating time, the initial rolling temperature of finish rolling, the outlet temperature of finish rolling, the rolling speed of finish rolling and the coiling temperature, the thickness of oxide scale can be remarkably reduced, and strip steel surface layer grain boundary oxidation is improved; and the pickling surface quality and efficiency are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and specifically relates to S50C high carbon steel and a production method and application thereof. Background Art

[0002] S50C high carbon steel is mainly used in automotive parts, chains, knives, etc. After pickling and cold rolling, S50C is used in automotive parts and requires excellent microstructure, fine grains, no decarburization, no grain boundary oxidation, no obvious segregation bands; fatigue performance requirements, high steel cleanliness requirements; high dimensional accuracy requirements, especially the thinning of the edge thickness; and high surface quality.

[0003] Due to the high carbon content, high carbon steel is prone to grain boundary oxidation on the surface of slabs or strips, and the adhesion of iron oxide scale increases, which increases the difficulty of descaling after heating the slabs and the difficulty of pickling hot-rolled strips. In order to improve rolling stability and reduce the deformation resistance of hot rolling and cold rolling to ensure good plate shape and dimensional accuracy, hot rolling process parameters such as heating temperature and coiling temperature are often set higher, but this results in thicker strip iron oxide scale thickness and difficulty in pickling due to grain boundary oxidation, which is prone to pickling "white spots" (surface iron oxide scale is not pickled clean), which seriously affects the surface quality of the product and the production efficiency of the pickling unit. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a production method and application of S50C high carbon steel to solve at least one aspect of the above technical problems.

[0005] The present invention is achieved through the following technical solutions:

[0006] A first aspect of the present invention provides a method for producing S50C high carbon steel, comprising the following steps:

[0007] After the high-speed thin slab is sheared by the swing shear, it directly enters the soaking furnace, descaling, finish rolling, laminar cooling, coiling and air cooling to obtain S50C high carbon steel;

[0008] The high-drawing speed thin slab consists of the following components in mass fraction:

[0009] C: 0.47% ~ 0.53%, Si: 0.15% ~ 0.35%, Mn: 0.6% ~ 0.9%, S ≤ 0.015%, P ≤ 0.02%, Als: 0.015% ~ 0.045%, Cr ≤ 0.25%, the balance is Fe and other unavoidable impurities;

[0010] In the soaking step, the temperature of the furnace is 850°C to 950°C, the heating rate is 3.5°C / min to 10.0°C, the temperature of the soaking furnace is 1150°C to 1200°C, and the soaking time is 19min to 40min.

[0011] In the coiling step, the coiling temperature is 570°C to 620°C.

[0012] In some possible implementations, the high-drawing-speed thin slab has a thickness of 55 mm to 70 mm.

[0013] In some possible implementations, in the descaling step: the inlet descaling pressure is 19 MPa to 24 MPa, and the outlet descaling pressure is 28 MPa to 34 MPa.

[0014] In some possible implementations, in the finishing rolling step, the starting rolling temperature is 1000° C. to 1050° C., the finishing rolling stand outlet temperature is 850° C. to 900° C., and the rolling speed is 5.5 m / s to 10.5 m / s.

[0015] In some possible implementations, the outlet temperature of the finishing mill stand is 850°C to 880°C.

[0016] In some possible implementations, in the finishing rolling step, the total reduction ratio of the finishing rolling is 90% to 97.6%.

[0017] In some possible implementations, in the laminar cooling step, the cooling rate is 15° C. / s to 50° C. / s.

[0018] In some possible implementations, in the laminar cooling step, a front-stage sparse cooling mode is adopted. In this case, the cooling rate is reduced and the plasticity of the steel strip is improved.

[0019] In the front section sparse cooling mode, the laminar cooling headers are opened at intervals.

[0020] In some possible implementations, the step of preparing the high-drawing-speed thin slab includes:

[0021] The molten steel is subjected to continuous casting and slab cleaning steps to obtain the high-drawing-speed thin slab.

[0022] In some possible implementations, in the continuous casting step, the casting speed is 3.5 m / min to 4.5 m / min.

[0023] A second aspect of the present invention provides S50C high carbon steel produced by the production method of S50C high carbon steel provided by the present invention, wherein the average thickness of the oxide scale of the S50C high carbon steel is less than 10 μm.

[0024] In some possible implementations, the average thickness of the iron oxide scale is 6.5 μm to 10 μm.

[0025] In some possible implementations, the thickness of the S50C high carbon steel is 1.8 mm to 6.0 mm.

[0026] A third aspect of the present invention provides an application of the S50C high carbon steel provided by the present invention in the field of automotive parts.

[0027] The S50C high carbon steel and the production method thereof provided by the present invention have at least the following beneficial technical effects compared with the prior art:

[0028] (1) The production method of S50C high carbon steel provided by the present invention can significantly reduce the thickness of iron oxide scale and improve the surface grain boundary oxidation of the strip steel under the combination of heating temperature, heating time, start rolling temperature of finishing rolling, outlet temperature of finishing rolling, rolling speed of finishing rolling and coiling temperature.

[0029] (2) In the production method of S50C high carbon steel provided by the present invention, in the equalization step, the shorter heating time reduces the decarburization of the surface layer of the steel strip, reduces the concentration gradient of C atoms and the diffusion dynamics, is beneficial to the control of the oxidation within the grain boundaries of the surface layer of the steel strip after coiling, and is beneficial to the removal of surface oxide scale by pickling.

[0030] (3) In the production method of S50C high carbon steel provided by the present invention, in the finishing rolling step, a lower start rolling temperature is controlled, the rolling speed is increased, and a lower final rolling temperature range is maintained, which is beneficial to reducing the thickness of the oxide scale and achieving the purpose of easy pickling of the S50C high carbon steel.

[0031] (4) The production method of S50C high carbon steel provided by the present invention has a suitable coiling temperature which is beneficial to reducing the grain boundary oxidation (internal oxidation) of the surface layer of the strip steel in the middle of the steel coil after coiling, reducing the bonding force between the iron oxide scale and the matrix, and improving the pickling property, thereby obtaining excellent surface quality of high carbon steel that is easy to pickle.

[0032] (5) The S50C high carbon steel provided by the present invention has an average thickness of surface iron oxide scale of 6.5 μm to 10 μm, and the bonding force between the iron oxide scale and the substrate is weak, and it is easy to be pickled. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present drawings or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present drawings. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0034] Figure 1a is the thickness of the oxide scale of the S50C high carbon steel in Example 1 of the present invention;

[0035] Figure 1b This is the interface morphology of the steel substrate and the oxidized iron scale in Example 1 of the present invention (grain boundary oxidation);

[0036] Figure 1c This is a surface electron microscope scanning image in Example 1 of the present invention;

[0037] Figure 1d This is a macroscopic surface quality diagram after pickling in Example 1 of the present invention;

[0038] Figure 2a is the thickness of the oxide scale of the S50C high carbon steel in Comparative Example 1 of the present invention;

[0039] Figure 2b This is the interface morphology of the steel substrate and the iron oxide scale in Comparative Example 1 of the present invention (grain boundary oxidation);

[0040] Figure 2c This is a surface electron microscope scanning image in Comparative Example 1 of the present invention;

[0041] Figure 2d This is a macroscopic surface quality diagram after pickling in Comparative Example 1 of the present invention.

[0042] The purpose, features and advantages of this figure will be further described in conjunction with the embodiments with reference to the accompanying drawings. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is described and illustrated in conjunction with the embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments provided by the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0044] Obviously, the following descriptions are only some examples or embodiments of the present invention, and for those of ordinary skill in the art, the present invention can also be applied to other similar scenarios without creative work. In addition, it can also be understood that although the efforts made in such a development process may be complex and lengthy, for those of ordinary skill in the art related to the contents disclosed in the present invention, some changes in design, manufacturing or production based on the technical contents disclosed in the present invention are just conventional technical means, and should not be understood as the contents disclosed in the present invention being insufficient.

[0045] However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially the same structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the following description is provided for those skilled in the art to fully understand the present invention and is not intended to limit the subject matter described in the claims.

[0046] If not otherwise specified, all embodiments and optional embodiments of the present invention may be combined with each other to form a new technical solution, and all technical features and optional technical features of the present invention may be combined with each other to form a new technical solution.

[0047] Example 1

[0048] Embodiment 1 provides a method for producing S50C high carbon steel, the steps are as follows:

[0049] (1) A continuous casting slab with a thickness of 65 mm is selected. The continuous casting slab is composed of the following components by mass fraction:

[0050] C: 0.49%, Si: 0.25%, Mn: 0.7%, S≤0.015%, P≤0.02%, Als: 0.025%, Cr: 0.15%, and the balance is Fe and other inevitable impurities.

[0051] (2) The continuous casting slab is placed in a soaking furnace for soaking. The furnace temperature is 900°C. The continuous casting slab is heated at a heating rate of 7.5°C / min. The soaking furnace temperature is 1180°C and the soaking is performed for 25 minutes.

[0052] (3) Descaling: The slab is descaled after being heated. The inlet pressure during descaling is 20 MPa and the outlet pressure is 30 MPa.

[0053] (4) Finish rolling: After descaling, 7-stand finish rolling was adopted, with the starting rolling temperature of 1020°C, the total reduction rate of 96.1%, the rolling speed of 8.0 m / s, and the final rolling temperature of 880°C.

[0054] (5) Laminar cooling: The front-stage sparse cooling mode is used for laminar cooling, and the cooling rate is 25°C / s.

[0055] (6) Coiling: The cooled strip is coiled at a coiling temperature of 600°C.

[0056] This embodiment also provides a S50C high carbon steel, which is produced by the production method of the S50C high carbon steel of this embodiment. The thickness of the produced S50C high carbon steel is 2.5 mm. Figure 1a As shown, the average thickness of the surface iron oxide scale is 7.5 μm (for example, the thickness of 1-1 in the figure is 4.98 μm, the thickness of 1-2 is 6.15 μm, the thickness of 1-3 is 8.30 μm, and the thickness of 1-4 is 10.15 μm); Figure 1b As shown, there is no obvious grain boundary oxidation on the surface; Figure 1c As shown, there is basically no iron oxide scale remaining on the surface, and it is relatively smooth; Figure 1d As shown, the macroscopic surface quality of the strip after pickling is good.

[0057] Example 2

[0058] Example 2 proposes a method for producing S50C high carbon steel, the steps are basically the same as those of Example 1, except that:

[0059] (2) The continuous casting slab is placed in a soaking furnace for soaking. The furnace temperature is 850°C. The continuous casting slab is heated at a heating rate of 9.2°C / min. The temperature of the soaking furnace is 1200°C and the soaking is carried out for 30 minutes.

[0060] (3) Heat balancing: The slab is descaled after heat balancing. The inlet descaling pressure is 23 MPa and the outlet descaling pressure is 28 MPa.

[0061] (4) Finish rolling: After descaling, 7-stand finish rolling is adopted, the starting rolling temperature is 1050°C, the total reduction rate is 96.9%, the rolling speed is 9.5m / s, and the final rolling temperature is 900°C.

[0062] (5) Laminar cooling: The front-stage sparse cooling mode is used for laminar cooling, and the cooling rate is 45°C / s.

[0063] (6) Coiling: The cooled strip is coiled at a coiling temperature of 620°C.

[0064] This embodiment also provides an S50C high carbon steel, which is produced by the production method of the S50C high carbon steel of this embodiment. The thickness of the produced S50C high carbon steel is 2.0 mm, and the average thickness of the surface oxide scale is 6.8 μm.

[0065] Example 3

[0066] Example 3 proposes a method for producing S50C high carbon steel, the steps are basically the same as those of Example 1, except that:

[0067] (2) The continuous casting slab is placed in a soaking furnace for soaking. The furnace entry temperature is 950°C. The continuous casting slab is heated to a soaking temperature of 1150°C at a heating rate of 3.5°C / min for 40 minutes.

[0068] (3) Heat balancing: The slab is descaled after heat balancing. The inlet descaling pressure is 19 MPa and the outlet descaling pressure is 34 MPa.

[0069] (4) Finish rolling: After descaling, 7-stand finish rolling is adopted, the starting rolling temperature is 1010°C, the total reduction rate is 90%, the rolling speed is 7.5m / s, and the final rolling temperature is 860°C.

[0070] (5) Laminar cooling: The front-stage sparse cooling mode is used for laminar cooling, and the cooling rate is 20°C / s.

[0071] (6) Coiling: The cooled strip is coiled at a coiling temperature of 590°C.

[0072] This embodiment also provides an S50C high carbon steel, which is produced by the production method of the S50C high carbon steel of this embodiment. The thickness of the produced S50C high carbon steel is 3.5 mm, and the thickness of the surface iron oxide scale is 8.6 μm.

[0073] Example 4

[0074] Example 4 proposes a method for producing S50C high carbon steel, the steps are basically the same as those of Example 1, except that:

[0075] (2) The continuous casting slab is placed in a soaking furnace for soaking. The furnace entry temperature is 890°C. The continuous casting slab is heated to a soaking temperature of 1200°C at a heating rate of 9.5°C / min for 25 minutes.

[0076] (3) Heat balancing: The slab is descaled after heat balancing. The inlet descaling pressure is 24 MPa and the outlet descaling pressure is 32 MPa.

[0077] (4) Finish rolling: After descaling, 7-stand finish rolling is adopted, the starting rolling temperature is 1050°C, the total reduction rate is 93.1%, the rolling speed is 6.5m / s, and the final rolling temperature is 860°C.

[0078] (5) Laminar cooling: The front-stage sparse cooling mode is used for laminar cooling, and the cooling rate is 30°C / s.

[0079] (6) Coiling: The cooled strip is coiled at a coiling temperature of 570°C.

[0080] This embodiment also provides an S50C high carbon steel, which is produced by the production method of the S50C high carbon steel of this embodiment. The thickness of the produced S50C high carbon steel is 4.5 mm, and the thickness of the surface iron oxide scale is 9.1 μm.

[0081] Comparative Example 1

[0082] Comparative Example 1: Production method of S50C high carbon steel, the steps are as follows:

[0083] (1) A continuous casting slab with a thickness of 65 mm, the continuous casting slab is composed of the following components in mass fractions:

[0084] C: 0.50%, Si: 0.24%, Mn: 0.75%, S≤0.015%, P≤0.02%, Als: 0.028%, Cr: 0.16%, and the balance is Fe and other inevitable impurities.

[0085] (2) The continuous casting slab is placed in a soaking furnace for soaking. The furnace temperature is 900°C. The continuous casting slab is heated at a heating rate of 10.5°C / min. The soaking furnace temperature is 1250°C and the soaking is performed for 25 minutes.

[0086] (3) Descaling: The slab is descaled after being heated. The inlet pressure during descaling is 20 MPa and the outlet pressure is 30 MPa.

[0087] (4) Finish rolling: After descaling, 7-stand finish rolling was adopted, with the starting rolling temperature of 1100°C, the total reduction rate of 96.1%, the rolling speed of 6.0 m / s, and the final rolling temperature of 900°C.

[0088] (5) Laminar cooling: The front-stage concentrated cooling mode is used for laminar cooling, and the cooling rate is 45°C / s.

[0089] (6) Coiling: The cooled strip is coiled at a coiling temperature of 700°C.

[0090] The thickness of the S50C high carbon steel obtained in the comparative example production is 2.5 mm. Figure 2a As shown, the average thickness of the surface iron oxide scale is 13.5 μm (for example, the thickness of 2-1 in the figure is 16.59 μm, and the thickness of 2-2 is 11.62 μm); Figure 2b As shown, there is obvious grain boundary oxidation on the surface (for example, the oxidation depth of 2-3 in the figure is 15.88 μm, the oxidation depth of 2-4 is 13.91 μm, the oxidation depth of 2-5 is 13.15 μm, and the oxidation depth of 2-6 is 3.43 μm); Figure 2c As shown, there is residual iron oxide scale (including iron oxide scale cracks) on the surface; Figure 2d As shown, there are "white spots" on the surface of the strip after pickling.

[0091] Comparative Example 2

[0092] Comparative Example 2 proposes a method for producing S50C high carbon steel, the steps are basically the same as those of Example 1, except that:

[0093] (2) The continuous casting slab is placed in a soaking furnace for soaking. The furnace entry temperature is 870°C. The continuous casting slab is heated to a soaking temperature of 1220°C at a heating rate of 8°C / min for 40 minutes.

[0094] (3) Heat balancing: The slab is descaled after heat balancing. The inlet descaling pressure is 20 MPa and the outlet descaling pressure is 30 MPa.

[0095] (4) Finish rolling: After descaling, 7-stand finish rolling is adopted, the starting rolling temperature is 1080°C, the total reduction rate is 93.1%, the rolling speed is 4.5m / s, and the final rolling temperature is 880°C.

[0096] (5) Laminar cooling: The front-stage concentrated cooling mode is used for laminar cooling, and the cooling rate is 35°C / s.

[0097] (6) Coiling: The cooled strip is coiled at a coiling temperature of 680°C.

[0098] The thickness of the S50C high carbon steel obtained in the comparative example production is 4.5 mm, and the average thickness of the surface oxide scale is 14.5 μm.

[0099] In order to verify the progress of a S50C high carbon steel and a production method thereof provided in an embodiment of the present invention, the S50C high carbon steel of the embodiment and the comparative example was subjected to metallographic examination, and the average thickness of the obtained oxidized iron scale is shown in Table 1 below. Taking Example 1 and Comparative Example 1 as examples, the thickness of the oxidized iron scale is shown in the attached manual. Figure 1a and 2a As shown; the S50C high carbon steel of the embodiment and the comparative example was pickled and its pickling rate was detected. The results of the pickling rate are shown in Table 1 below.

[0100] The steps of pickling are as follows:

[0101] The steel strips of the embodiment and the comparative example are pickled in the same push-pull pickling production line; including the steps of steel coil unrolling, straightening, pickling tank, accumulation pit, tension roller, coiling, etc.; the hydrochloric acid concentration in the pickling tank is 75g / L~240g / L (there are three pickling tanks for pickling, and the hydrochloric acid concentrations in the three pickling tanks are 70g / L~120g / L, 160g / L~200g / L, and 200g / L~240g / L, respectively), and the temperature is 70°C~85°C.

[0102] Table 1

[0103] Average thickness of iron oxide scale (μm) Pickling speed (m / min) Example 1 7.5 100 Example 2 6.8 100 Example 3 8.6 100 Example 4 9.1 100 Comparative Example 1 13.5 30 Comparative Example 2 14.5 30

[0104] From Table 1 above, we can at least draw the following conclusions:

[0105] 1) The production method of S50C high carbon steel provided in the embodiment of the present invention maintains the same acid concentration and temperature as other low carbon steel grades during production on a push-pull pickling line, and the pickling speed can reach more than 100m / min, greatly improving the production efficiency of the pickling unit.

[0106] 2) The S50C high carbon steel provided in the embodiment of the present invention has an average thickness of surface iron oxide scale of 6.5 μm to 10.0 μm, no obvious grain boundary oxidation on the surface of the strip, weak bonding between the iron oxide scale and the matrix, easy pickling, and good surface quality.

[0107] It should be noted that the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the technical solution of the present invention are all included in the technical scope of the present invention. In addition, without departing from the scope of the main purpose of the present invention, various modifications that can be thought of by those skilled in the art to the embodiments and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present invention.

Claims

1. A method for producing S50C high carbon steel, characterized in that: The steps include: After the high-speed thin slab is sheared by the swing shear, it directly enters the soaking furnace, descaling, finish rolling, laminar cooling, coiling and air cooling to obtain S50C high carbon steel; The high-drawing speed thin slab consists of the following components in mass fraction: C: 0.47% ~ 0.53%, Si: 0.15% ~ 0.35%, Mn: 0.6% ~ 0.9%, S ≤ 0.015%, P ≤ 0.02%, Als: 0.015% ~ 0.045%, Cr ≤ 0.25%, the balance is Fe and other unavoidable impurities; In the soaking step, the temperature of the furnace is 850°C to 950°C, the heating rate is 3.5°C / min to 10.0°C / min, the temperature of the soaking furnace is 1150°C to 1200°C, and the soaking time is 19min to 40min. In the coiling step, the coiling temperature is 570°C to 620°C.

2. The method for producing S50C high carbon steel according to claim 1, characterized in that: In the finishing rolling step, the starting rolling temperature is 1000° C. to 1050° C., the finishing rolling stand outlet temperature is 850° C. to 900° C., and the rolling speed is 5.5 m / s to 10.5 m / s.

3. The method for producing S50C high carbon steel according to claim 1, characterized in that: In the descaling step, the inlet descaling pressure is 19MPa-24MPa, and the outlet descaling pressure is 28MPa-34MPa.

4. The method for producing S50C high carbon steel according to claim 1, characterized in that: In the laminar cooling step, the cooling rate is 15°C / s to 50°C / s.

5. The method for producing S50C high carbon steel according to any one of claims 1 to 4, characterized in that: The thickness of the high-drawing speed thin slab is 55 mm to 70 mm.

6. The method for producing S50C high carbon steel according to any one of claims 1 to 5, characterized in that: The drawing speed for preparing the high-drawing-speed thin slab is 3.5 m / min to 4.5 m / min.

7. A S50C high carbon steel produced by the production method of S50C high carbon steel according to any one of claims 1 to 6, characterized in that: The average thickness of the oxide scale of the S50C high carbon steel is less than 10 μm.

8. The S50C high carbon steel according to claim 7, characterized in that: The thickness of the S50C high carbon steel is 1.8 mm to 6.0 mm.

9. Use of the S50C high carbon steel as claimed in claim 7 or 8 in the field of automobile parts after pickling and cold rolling.

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