High-surface-quality cold-rolled steel sheet for mechanical gasket and production method thereof

Abstract

The invention relates to a cold-rolled steel plate for a high-surface-quality mechanical gasket and a production method of the cold-rolled steel plate. The technical problem that an existing cold-rolled steel plate for manufacturing the mechanical gasket is poor in plate shape is mainly solved. According to the technical scheme, the cold-rolled steel sheet for the high-surface-quality mechanical gasket comprises the following chemical components in percentage by weight: 0.09%-0.12% of C, less than or equal to 0.030% of Si, 0.35%-0.45% of Mn, less than or equal to 0.020% of P, less than or equal to 0.020% of S, 0.02%-0.05% of Al, 0.030%-0.045% of V, 0.010%-0.015% of N and the balance of Fe and inevitable impurity elements, the tensile strength of the cold-rolled steel plate with the thickness of 0.30-0.50 mm is 690-840 MPa, and the wave height within 1 m in the rolling direction of the cold-rolled steel plate is smaller than or equal to 2.0 mm. The cold-rolled steel sheet is suitable for manufacturing mechanical gaskets.

Description

Technical Field

[0001] The invention relates to a cold-rolled steel plate and a production method thereof, in particular to a cold-rolled steel plate for a mechanical gasket with high surface quality and a production method thereof, belonging to the technical field of iron-based alloys. Background Art

[0002] The key performance requirements of cold-rolled steel plates for gaskets are high tensile strength, good toughness and good plate shape to ensure that the gasket fits well; the gasket is bent 90° during production and the deformation is not large. If the toughness is not enough, there is a risk of cracking during the production of the gasket; the tensile strength of cold-rolled steel plates for gaskets is required to be above 690MPa.

[0003] In the prior art, cold-rolled steel sheets for gaskets often use ordinary low-carbon steel chemical composition. To ensure high strength, cold-rolled steel sheets in hard coil state are used. However, such steel sheets will produce uneven deformation during the cold rolling process, causing internal stress in the cold rolled coil. The uneven distribution of internal stress will cause the strip to warp, or the shape of the steel sheet will change during subsequent processing due to the uneven distribution of internal stress, which cannot ensure a good plate shape and affects the use.

[0004] The Chinese patent application document with publication number CN1280206A discloses an ultra-low carbon microalloy high-strength steel, whose specific chemical composition (weight %) is: C: 0.003-0.015%, Si: 0.1-0.5%, Mn: 1.0-1.6%, P≤0.03%, S≤0.03%, Nb: 0.02-0.06%, Ti: 0.005-0.04%, and the rest is Fe; on the basis of ordinary low-carbon microalloy steel, the C content of the steel is appropriately adjusted and reasonable process means are used to make the yield strength of the microalloy steel of a simple composition system reach 800MPa; the technology reduces the C content and cooperates with hot rolling continuous multiple passes of rapid large reduction rate rolling strain inducing ultrafine ferrite precipitation and dynamic recrystallization of ferrite, thereby obtaining an ultrafine ferrite structure; the corresponding product is a hot-rolled product, and the chemical composition contains high Nb and Ti alloy elements, and the cost is high.

[0005] The existing cold-rolled steel plates used for mechanical gaskets have high production costs, poor steel plate shape, and wave height within 1m along the rolling direction of the steel plate is greater than 2mm. Summary of the invention

[0006] The invention provides a cold-rolled steel plate for mechanical gaskets with high surface quality and a production method thereof, mainly solving the technical problem of poor shape of the existing cold-rolled steel plate used for making mechanical gaskets.

[0007] The applicant has found that the tensile strength R of cold-rolled steel sheets for mechanical gaskets mThe pressure is above 690MPa, the elongation after fracture is 3%-10%, the wave height within 1m along the rolling direction of the steel plate is ≤2mm, and no cracking will occur during the production of gaskets, which meets the preparation requirements of mechanical gaskets.

[0008] The present invention utilizes the principle that vanadium and nitrogen elements form V (C, N) alloy compounds to strengthen steel, and utilizes the principle that fine V (C, N) alloy compounds dispersedly distributed during annealing hinder grain growth, thereby meeting the requirements of high strength and high plate shape for steel used in mechanical gaskets without increasing production costs.

[0009] The present invention eliminates internal stress through annealing to solve the problem of poor steel plate shape; after annealing, the grain structure of the strip steel material is often coarse and the strength is reduced, so the problem of coarse grain structure and low strength of the strip steel must be solved. The solution is to add vanadium (V) and nitrogen (N) elements to the chemical composition of the strip steel material to form a V (C, N) alloy compound, which can solve the problem of coarse grain structure and reduced material strength of the strip steel during annealing.

[0010] The technical solution adopted by the present invention is:

[0011] A cold-rolled steel plate for high-surface-quality mechanical gaskets, the chemical composition of which is as follows by weight: C: 0.09%-0.12%, Si≤0.030%, Mn: 0.35%-0.45%, P≤0.020%, S≤0.020%, Al: 0.02%-0.05%, V: 0.030%-0.045%, N: 0.010%-0.015%, and V / N is 3.0, and the remainder is Fe and unavoidable impurity elements.

[0012] The metallographic structure of the cold-rolled steel sheet of the present invention comprises 30% to 50% of ferrite + fibrous ferrite + pearlite by area fraction; the yield strength R of the cold-rolled steel sheet with a thickness of 0.30 to 0.50 mm is P0.2 650~800MPa, tensile strength R m 690~840MPa, elongation after fracture A 50 mm It is 3% to 10%, and the wave height within 1m along the rolling direction of the cold-rolled steel plate is ≤2.0mm.

[0013] The reasons why the chemical composition of the cold-rolled steel sheet for high surface quality mechanical gaskets of the present invention is limited to the above range are as follows:

[0014] Carbon: Since C is a strengthening element, it exists in the form of interstitial atoms and cementite in steel. In order to strengthen the material, a certain amount of C needs to be added to the material to improve the strength. However, if the element is too high, the plastic deformation resistance of the material increases, which is not conducive to the plate shape control of the product. Since the cold-rolled steel sheet of the present invention has a high requirement for the plate shape, the C content of the present invention is 0.09% to 0.12%, and the strength of the product is guaranteed by the comprehensive effect of other strengthening elements and production processes.

[0015] Silicon: Silicon is also a strength element in the material, but Si easily causes red iron oxide scale to be produced during hot rolling, and it is difficult to clean it off, resulting in poor surface quality of the steel sheet, and thus poor surface quality of the steel sheet after cold rolling. Therefore, the lower the content of Si in the present invention, the better, and it is controlled as much as possible to be below 0.030%.

[0016] Manganese: Mn is a strengthening element of the material like C. Proper addition of Mn to the material is conducive to improving the strength. At the same time, adding a small amount of Mn can combine with S to form MnS, reduce surface hot brittleness, and avoid surface quality problems. However, adding too much will increase the plastic deformation resistance of the material, and defects such as wave shape are easily generated during the rolling process of the steel plate, which is not conducive to the shape control of the steel plate. Therefore, the present invention controls Mn to 0.35% to 0.45%.

[0017] Sulfur and phosphorus: Sulfur forms sulfide inclusions in steel, which reduces the ductility and toughness of the steel. Although phosphorus is also a strengthening element, it increases the cold brittleness of the steel. The lower the two elements are controlled, the better. However, considering the cost, after testing, the present invention limits P≤0.020% and S≤0.020%, which can meet the requirements.

[0018] Aluminum: The role of aluminum in the present invention is to deoxidize. Aluminum is a strong oxidizing element, and it forms Al2O3 with oxygen in steel, which is removed during steelmaking. Too much aluminum will form too much Al2O3 inclusions, and continuous casting is easy to block the pouring nozzle. It can be seen from the test that the original aluminum content can ensure the quality requirements. Therefore, the aluminum content of the present invention is maintained at the original 0.02% to 0.05%.

[0019] Vanadium and nitrogen: Based on the principle of vanadium and nitrogen elements strengthening the performance of steel, the composition of vanadium and nitrogen is designed. First, it is to control the production cost. If other alloys, such as titanium and niobium, are selected, they are imported alloys with high costs. Vanadium is an alloy deposit with relatively abundant domestic resources, and nitrogen can be obtained by blowing nitrogen into the bottom of the converter or the bottom of the ladle during the converter smelting or refining stage, and adding a small amount of manganese nitride alloy to increase the nitrogen content in the molten steel. Therefore, the production cost has not increased significantly. Secondly, vanadium combines with carbon and nitrogen in steel to promote the precipitation of V (C, N). The appearance of this alloy compound, during the stress relief annealing process, the fine and dispersed V (C, N) alloy compounds hinder the growth of grains, refine the grains of the strip, and improve the strength and toughness of the strip. However, the content of vanadium and nitrogen cannot be increased too much, otherwise the hardness of the strip will be too high and the toughness will be reduced, and there is a risk of cracking when making gaskets. Therefore, after experiments, the present invention controls the V content to 0.030% to 0.045%, the N content to 0.010% to 0.015%, and satisfies the vanadium and nitrogen content: V / N is 3.0.

[0020] A method for producing a cold-rolled steel sheet for mechanical gaskets with high surface quality, the method comprising:

[0021] The molten steel is continuously cast to obtain a continuous casting slab, wherein the weight percentage of the molten steel components is: C: 0.09% to 0.12%, Si≤0.030%, Mn: 0.35% to 0.45%, P≤0.020%, S≤0.020%, Al: 0.02% to 0.05%, V: 0.030% to 0.045%, N: 0.010% to 0.015%, and V / N is 3.0, and the balance is Fe and unavoidable impurity elements;

[0022] The continuous casting slab is heated in a heating furnace and then hot rolled. The heating temperature of the continuous casting slab is 1190-1210°C, and the heating time of the continuous casting slab is 200-220 minutes. The hot rolling is a two-stage rolling process. The rough rolling is performed above the austenite recrystallization temperature, and the rough rolling end temperature is 1030-1050°C; the finishing rolling end temperature is 870-890°C, and the finishing rolling reduction rate is 93%-94%. After finishing rolling, the steel plate thickness is 2.3-2.8 mm, and the laminar cooling adopts the rear cooling, the cooling rate is 10-30°C / s, and the coiling temperature is 550-570°C to obtain the hot rolled steel plate.

[0023] After the hot-rolled steel coil is unrolled, it is pickled, cold rolled, and annealed in a vertical continuous annealing furnace to obtain a finished cold-rolled steel plate with a thickness of 0.30 to 0.50 mm, and the cold rolling reduction rate is 82 to 87%; the hardened strip steel after cold rolling is annealed in a vertical continuous annealing furnace, the annealing temperature of the strip steel in the soaking section of the vertical continuous annealing furnace is 590 to 600° C., and the annealing time of the strip steel in the soaking section is 50 to 80 seconds.

[0024] The reasons for the production process adopted by the present invention are as follows:

[0025] 1. Setting of heating temperature and heating time for continuous casting slab

[0026] The setting of heating temperature and time of continuous casting slab is to ensure that alloy elements such as C, N, V, Mn in the continuous casting slab are fully diffused and dissolved, and coarse carbide particles are dissolved and evenly distributed in the steel. Too low temperature and too short heating time cannot achieve the above purpose; at the same time, too low temperature cannot guarantee the end temperature of finishing rolling. A medium slab heating temperature is adopted, and the target temperature is 1200℃. If the temperature is too high and the heating time is too long, the surface of the slab will be severely oxidized, which is not conducive to the final product performance and surface quality of the steel plate, and also consumes energy and increases manufacturing costs. Therefore, the present invention sets the heating temperature of the continuous casting slab to 1190-1210℃ and the heating time to 200-220min.

[0027] 2. Setting of finishing temperature

[0028] The finishing temperature setting of the present invention has two effects. On the one hand, by rolling the material in the austenite non-recrystallization zone, flat austenite grains with deformation bands inside are obtained, which are transformed into fine ferrite grains in the subsequent laminar cooling process, which plays a role in refining grains and reducing band segregation. On the other hand, if the finishing temperature is too low, the strength of the hot-rolled product is too high, and the rolling load of the cold rolling unit will inevitably increase. Rolling waves are very likely to occur during the cold rolling process, resulting in poor product plate shape. Moreover, after the rolling load of the cold rolling unit increases, the production efficiency of the unit will inevitably be reduced, and the product manufacturing cost will increase. Therefore, the present invention sets the finishing temperature of 870-890°C.

[0029] 3. Setting of finishing rolling reduction rate

[0030] The finishing reduction rate is controlled at 93-94%. The main reason is that a larger intermediate billet thickness can reduce heat dissipation and increase heat storage inside the slab. At the same time, a larger finishing reduction rate produces more deformation energy, ensuring that the finishing outlet material is rolled in the austenite non-recrystallization zone, improving the uniformity of the organization and performance of the hot-rolled steel plate, thereby improving the performance uniformity of the steel plate after cold rolling annealing.

[0031] 4. Setting of cold rolling reduction rate

[0032] The cold rolling reduction rate is controlled at 82-87%, mainly because the steel for mechanical gaskets has high requirements on the shape of the steel plate. When the reduction rate exceeds 87%, the load of the cold rolling mill increases significantly, the process stability is poor, and it is easy to cause poor shape of the steel plate; using a lower reduction rate, less deformation energy can be stored in the steel plate, reducing the recrystallization driving force, and the recrystallization temperature can be appropriately increased. After the subsequent vertical continuous annealing, the number of recrystallized grains in the steel plate structure is small, which is beneficial to improving the tensile strength of the steel plate, and the insulation temperature in the vertical continuous annealing process can be appropriately increased, which is beneficial to reducing the temperature transition of the vertical continuous annealing unit, improving the production efficiency of the cold rolling unit and the vertical continuous annealing unit, and helping to reduce the product manufacturing cost. Therefore, the present invention sets the cold rolling reduction rate to 82-87%.

[0033] 5. Setting of continuous annealing process

[0034] The cold-rolled hard coil is annealed, and the annealing stability of the present technology is designed based on the principle that the annealing temperature can eliminate the internal force of the strip, the principle that the temperature near the recrystallization temperature is used as the control range of the annealing temperature so that the grains of the strip will not be coarse, and the principle that the narrow annealing temperature control range can achieve stable annealing performance. In order to effectively eliminate internal stress, the annealing temperature is studied. After comprehensive consideration, the present invention sets the annealing temperature of the strip in the soaking section of the vertical continuous annealing furnace to 590-600°C, and the annealing time of the strip in the soaking section to 50-80s. The determination of the annealing temperature and the mechanism of annealing to refine the grains are as follows:

[0035] The role of annealing is to eliminate the internal stress of the material, but after the internal stress is eliminated, the grains of the material will grow and coarsen at the annealing temperature, thereby reducing the strength of the material. The solution is to add 0.03% to 0.045% of V and 0.010% to 0.015% of N to the chemical composition of the material as before. Due to the combination of these two elements, a V (C, N) alloy compound will be formed. The alloy compound will precipitate on the ferrite crystal interface at the annealing temperature, which will hinder the growth of ferrite, thereby inhibiting the growth of ferrite grains in the material during annealing. Therefore, it plays a role in refining the grains to a certain extent, thereby improving the strength of the strip.

[0036] However, if the annealing temperature is too high, the grains of the steel strip will become coarse at high temperatures, which is a prominent problem. For example, the role of the alloy compounds in the steel strip in refining the grains is not significant, and it does not play a role in refining the grains. If the annealing temperature is too low, it will not promote the elimination of internal stress, and it will not solve the problem of poor shape of cold-rolled steel strip for gaskets. If the annealing temperature range is too wide, it will cause unstable performance of cold-rolled steel strip. Therefore, the selection of annealing temperature can not only eliminate internal stress, but also ensure stable performance.

[0037] According to research, if the annealing temperature is kept near the recrystallization temperature (610±30℃) of the material, that is, the annealing temperature is reduced by 10℃-20℃ based on the average recrystallization temperature (610℃), it can not only promote the grain refinement of the strip steel, but also prevent the grain structure of the strip steel from becoming coarse due to high temperature, and at the same time ensure the stability of the strip steel performance after annealing. This is the reason why the annealing temperature of the present invention is set at 590~600℃, that is, the annealing temperature Where t is the annealing temperature, is the average value of the recrystallization temperature, which is set at 610°C here.

[0038] In addition, the metallographic structure of the hardened coil steel is improved after annealing, the degree of fiberization of the structure is reduced, and the strength and toughness of the steel are improved (that is, the performance and elongation of the steel are improved).

[0039] The metallographic structure of the cold-rolled steel sheet produced by the method of the present invention comprises 30% to 50% of ferrite + fibrous ferrite + pearlite in terms of area fraction; the yield strength R of the cold-rolled steel sheet with a thickness of 0.30 to 0.50 mm is P0.2 650~800MPa, tensile strength R m 690~840MPa, elongation after fracture A 50 mm It is 3% to 10%, and the wave height within 1m along the rolling direction of the cold-rolled steel plate is ≤2.0mm.

[0040] Compared with the prior art, the present invention has the following positive effects: 1. This technology uses vanadium and nitrogen elements that are easily available and low in cost to strengthen the steel plate. Vanadium combines with carbon and nitrogen in the steel to precipitate fine and dispersed V (C, N) alloy compounds. The fine and dispersed V (C, N) alloy compounds achieve precipitation strengthening on the one hand, and precipitate on the ferrite grain boundary on the other hand. During the stress relief annealing process, the fine and dispersed V (C, N) alloy compounds hinder the growth of grains, refine the grains of the steel plate, and improve the strength of the steel plate. The yield strength of the steel plate R P0.2 650~800MPa, tensile strength R m 690~840MPa, elongation after fracture A 50 mm 2. This technology uses continuous annealing furnace to eliminate the internal force of the strip and obtain a good steel plate shape. The wave height within 1m along the rolling direction of the cold-rolled steel plate is ≤2.0mm, which meets the requirements of high plate shape for mechanical gasket steel. 3. The present invention does not require the use of a flattening unit, and has a good plate shape, which reduces energy consumption and production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a metallographic photograph of the cold-rolled annealed steel plate according to Example 1 of the present invention. DETAILED DESCRIPTION

[0042] The present invention is further described below in conjunction with specific embodiments 1-6, as shown in Tables 1-4.

[0043] Table 1 shows the chemical composition (by weight percentage) of the steel according to the embodiment of the present invention, with the remainder being iron and unavoidable impurities.

[0044] Table 1 Chemical composition of the steel of the present invention, unit: weight percentage.

[0045]

[0046]

[0047] The molten steel meeting the chemical composition requirements is obtained by converter smelting. After deep desulfurization and composition fine-tuning in the LF ladle refining furnace refining process, the molten steel is continuously cast to obtain a continuous casting slab; the continuous casting slab has a thickness of 210 to 230 mm, a width of 900 to 1600 mm, and a length of 8500 to 11000 mm.

[0048] The cut-to-length slab produced by steelmaking is directly sent to the heating furnace for reheating, and then sent to the hot rolling mill for rolling after being removed from the furnace and descaled. The rolling is controlled by the rough rolling and finishing rolling mills, and the coiling is carried out after laminar cooling. The laminar cooling adopts the rear cooling method to produce hot-rolled steel coils. The thickness of the hot-rolled steel plate is 2.3-2.8 mm. The hot rolling process control parameters are shown in Table 2.

[0049] Table 2 Hot rolling process control parameters of the embodiment of the present invention

[0050]

[0051] The hot rolled steel coils are unrolled and pickled, and then cold rolled on a 5-stand cold rolling mill, with a cold rolling reduction of 82% to 87%. The hardened strip steel after cold rolling is annealed in a vertical continuous annealing furnace, and the annealing temperature of the strip steel in the soaking section of the vertical continuous annealing furnace is 590 to 600°C, and the annealing time of the strip steel in the soaking section is 50 to 80 seconds. The control parameters of the cold rolling and annealing processes are shown in Table 3.

[0052] Table 3 Cold rolling and annealing process control parameters of the embodiment of the present invention

[0053]

[0054] The cold rolled steel sheet obtained by the above method is Figure 1 The metallographic structure of the cold-rolled steel sheet of the present invention includes ferrite + fibrous ferrite + pearlite in an area fraction of 30% to 50%; the yield strength R of the cold-rolled steel sheet with a thickness of 0.30 to 0.50 mm is P0.2650~800MPa, tensile strength R m 690~840MPa, elongation after fracture A 50 mm It is 3% to 10%, and the wave height within 1m along the rolling direction of the cold-rolled steel plate is ≤2.0mm.

[0055] The cold-rolled steel sheet obtained by the present invention was subjected to tensile and microstructural testing according to the tensile test method for metallic materials (GB / T 228.1) and the microstructural evaluation method for steel (GB / T 13299). The properties of the cold-rolled steel sheet are shown in Table 4.

[0056] Table 4 Mechanical properties of cold-rolled steel sheets according to the present invention

[0057]

[0058] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A cold-rolled steel sheet for mechanical gaskets with high surface quality, the chemical composition weight percentage of which is: C: 0.09% to 0.12%, Si≤0.030%, Mn: 0.35% to 0.45%, P≤0.020%, S≤0.020%, Al: 0.02% to 0.05%, V: 0.030% to 0.045%, N: 0.010% to 0.015%, and V / N is 3.0, the balance is Fe and unavoidable impurity elements; the yield strength R of the cold-rolled steel sheet with a thickness of 0.30 to 0.50 mm P0.2 650~800MPa, tensile strength R m 690~840MPa, elongation after fracture A 50mm It is 3% to 10%, and the wave height within 1m along the rolling direction of the cold-rolled steel plate is ≤2.0mm.

2. The cold-rolled steel sheet for mechanical gaskets with high surface quality as claimed in claim 1, characterized in that: The metallographic structure of the cold-rolled steel sheet includes 30% to 50% of ferrite+fibrous ferrite+pearlite in terms of area fraction.

3. A method for producing a cold-rolled steel sheet for mechanical gaskets with high surface quality, characterized in that: The method includes: The molten steel is continuously cast to obtain a continuous casting slab, wherein the weight percentage of the molten steel components is: C: 0.09% to 0.12%, Si≤0.030%, Mn: 0.35% to 0.45%, P≤0.020%, S≤0.020%, Al: 0.02% to 0.05%, V: 0.030% to 0.045%, N: 0.010% to 0.015%, and V / N is 3.0, and the balance is Fe and unavoidable impurity elements; The continuous casting slab is heated in a heating furnace and then hot rolled. The heating temperature of the continuous casting slab is 1190-1210°C, and the heating time of the continuous casting slab is 200-220 minutes. The hot rolling is a two-stage rolling process. The rough rolling is performed above the austenite recrystallization temperature, and the rough rolling end temperature is 1030-1050°C; the finishing rolling end temperature is 870-890°C, and the finishing rolling reduction rate is 93%-94%. After finishing rolling, the steel plate thickness is 2.3-2.8 mm, and the laminar cooling adopts the rear cooling, the cooling rate is 10-30°C / s, and the coiling temperature is 550-570°C to obtain the hot rolled steel plate. After the hot-rolled steel coil is unrolled, it is pickled, cold rolled, and annealed in a vertical continuous annealing furnace to obtain a finished cold-rolled steel plate with a thickness of 0.30 to 0.50 mm, and the cold rolling reduction rate is 82% to 87%; the hardened strip steel after cold rolling is annealed in a vertical continuous annealing furnace, the annealing temperature of the strip steel in the soaking section of the vertical continuous annealing furnace is 590 to 600°C, and the annealing time of the strip steel in the soaking section is 50 to 80s.

4. The method for producing a cold-rolled steel sheet for mechanical gaskets with high surface quality as claimed in claim 3, characterized in that: The metallographic structure of the cold-rolled steel sheet includes 30% to 50% ferrite + fibrous ferrite + pearlite in terms of area fraction; the yield strength R of the 0.30 to 0.50 mm thick cold-rolled steel sheet is P0.2 650~800MPa, tensile strength R m 690~840MPa, elongation after fracture A 50mm It is 3% to 10%, and the wave height within 1m along the rolling direction of the cold-rolled steel plate is ≤2.0mm.

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