Hot-rolled steel plate for fine blanking of automobile engine gasket and manufacturing method of hot-rolled steel plate

Abstract

The invention discloses a hot-rolled steel plate for fine blanking of automobile engine washers and a manufacturing method of the hot-rolled steel plate, and mainly solves the technical problems that the surface of an existing steel plate for the automobile engine washers is decarburized, the steel plate is cracked in stamping forming, and the yield strength is low. According to the technical scheme, the hot-rolled steel plate for the fine blanking automobile engine gasket comprises the following chemical components in percentage by weight: 0.69%-0.73% of C, 0.05%-0.15% of Si, 0.55%-0.65% of Mn, less than or equal to 0.015% of P, less than or equal to 0.003% of S, 0.4%-0.6% of Cr, 0.002%-0.010% of Al, less than or equal to 0.0012% of O and the balance of iron and inevitable impurities. The metallographic structure of the hot-rolled steel plate is pearlite and a small amount of ferrite; one-side decarburized layer depth of the hot-rolled steel plate is not more than 1.0% * steel plate thickness. The hot-rolled steel plate is mainly used in the fields of automobile fine blanking part manufacturing and the like.

Description

Technical Field

[0001] The invention relates to a hot-rolled steel plate and a manufacturing method thereof, in particular to a hot-rolled steel plate for fine-blanking automobile engine gaskets and a manufacturing method thereof, belonging to the technical field of iron-based alloys. Background Art

[0002] Fasteners are a common type of parts used in machinery, electronics, and automobile structures, mainly including bolts, nuts, washers, gaskets, etc. Washers are a type of fasteners in the shape of an oblate ring, placed between the supporting surface of bolts, screws or nuts and the surface of connected parts, and play the role of increasing the contact surface area, reducing the pressure per unit area, protecting the surface of the connected parts from damage, and preventing the nuts from loosening; at the same time, they protect adjacent equipment, parts, screws, and shock absorbers.

[0003] Therefore, the gasket material is required to have high strength, high enough plasticity when tightened, be able to withstand sufficiently large stress and alternating load when repeatedly tightened, and have good fatigue performance. In the early days, 50, 65Mn and other materials were commonly used for automotive gasket parts. The hardness and strength of the products were low after heat treatment, quenching and tempering. In addition, early high-carbon steel was mostly produced by small and medium-sized electric furnace smelting, die casting, and narrow strip rolling mills. In recent years, with the rapid development of converters and refining steelmaking technology outside the furnace, converters, refining outside the furnace, large slab continuous casting, and continuous wide coil rolling mills have become the mainstream. Compared with the traditional billet narrow strip mode, it has the characteristics of high steel cleanliness, uniform organizational properties, and good toughness.

[0004] Patent application CN103194588A discloses a heat treatment process for 65Mn spring washers, and discloses the heat treatment process for washer parts, namely the temperature, time, rules for adding atmosphere-protecting charcoal during the quenching and tempering process, and how to prevent decarburization during the heat treatment process; the material used is conventional 65Mn material.

[0005] Patent CN105018835A discloses a medium-high carbon hot-rolled steel plate with excellent fine blanking performance and a production method thereof, wherein the chemical composition by weight is as follows: C: 0.50-0.65%, Si: 0.50-1.60%, Mn: 0.50-1.70%, Ca: 0.0030-0.0070%, B: 0.0008-0.0050%, Al: 0.015-0.030%, P≤0.015%, S≤0. 0.008%; the rest is Fe and unavoidable impurities; Si element is used to increase the activity of carbon atoms and improve the spheroidizing annealing ability; and the fine blanking steel plate is obtained by spheroidizing annealing in a bell furnace; it is a fine blanking steel plate that has been hot-rolled and spheroidized annealed. Although the blanking quality meets the requirements, the hardness is very low; and the high silicon content design of more than 0.50% produces a large amount of iron oxide scale during the hot rolling process of the steel plate, forming surface pits and pits, which greatly reduces the surface quality and specification accuracy of the steel plate. Summary of the invention

[0006] The invention discloses a hot-rolled steel plate for fine-blanking automobile engine gaskets and a manufacturing method thereof, which mainly solves the technical problems of surface decarburization, cracking of steel plate stamping and low yield strength of existing steel plates for automobile engine gaskets.

[0007] The technical solution adopted by the present invention is a hot-rolled steel plate for fine blanking automobile engine gaskets, whose chemical composition weight percentage is: C: 0.69%-0.73%, Si: 0.05%-0.15%, Mn: 0.55%-0.65%, P≤0.015%, S≤0.003%, Cr: 0.4%-0.6%, Al: 0.002%-0.010%, O≤0.0012%, and the rest is iron and unavoidable inclusions.

[0008] The metallographic structure of the hot-rolled steel plate of the present invention is pearlite + a small amount of ferrite; the lower yield strength R of the hot-rolled steel plate with a thickness of 2.5 to 5.0 mm is eL 540~700MPa, tensile strength R m 960~1120MPa, elongation after fracture A 50 mm 18% to 26%; the depth of single-sided decarburization layer of hot-rolled steel plate is ≤1.0%×steel plate thickness; according to the American Society for Testing and Materials "ASTM E45-13 Standard Test Method for Determination of Inclusion Content in Steel", method A is used for inspection, and non-metallic inclusions A, B, C, and D in hot-rolled steel plates are ≤1.5 level.

[0009] The reasons why the chemical composition of the hot-rolled steel sheet for fine blanking automobile engine gaskets of the present invention is limited to the above range are as follows:

[0010] Carbon: Carbon is an element that affects the hardness of the material after annealing and quenching. If the carbon content is too low, the hardness required by the part will not be obtained after quenching; if the carbon content is too high, the material hardness is too high, which is not conducive to subsequent fine stamping. The carbon content range used in the present invention is 0.69% to 0.73%.

[0011] Silicon: As a solid solution strengthening element, silicon has a certain strengthening effect when dissolved in the steel strip matrix, and can significantly improve the elastic limit of the material; at the same time, as a deoxidizer during smelting, it plays a role in deoxidation and desulfurization. However, when it is contained in large quantities, it will harden the ferrite phase and significantly reduce the processing performance. In addition, Si in steel will produce rust-red iron oxide scale defects on the surface of the steel plate during the hot rolling process, affecting the user's subsequent pickling surface; therefore, the Si content is controlled in the range of 0.05% to 0.15%;

[0012] Manganese: Manganese is a good deoxidizer and desulfurizer. A certain amount of manganese in steel can eliminate or improve the hot working properties of steel and significantly improve hardenability. However, when the content is too much, it will cause component segregation, resulting in uneven structure, a sharp drop in material forming properties, and subsequent processing is not useful; the present invention limits the Mn content to 0.55% to 0.65%.

[0013] Phosphorus: Phosphorus is an impurity element. It segregates at grain boundaries and reduces processing performance. It is hoped to reduce its content as much as possible to improve forming performance. However, considering the control capability of process equipment and dephosphorization cost, the present invention limits P to ≤ 0.015%.

[0014] Sulfur: Sulfur is an impurity element, which forms inclusions such as MnS in steel, affecting the formability. It is desirable to reduce its content as much as possible; considering the actual control capability and desulfurization cost, the present invention limits S to ≤ 0.003%.

[0015] Chromium: Chromium is a carbide-forming element that can increase the hardenability of steel and is the main alloying element for corrosion resistance and oxidation resistance. It can also inhibit the grain size of the structure during the cooling process after hot rolling and improve the strength and hardness of the material. However, excessive content will increase the alloy cost and also reduce the processing performance. Taking comprehensive considerations, the present invention sets the Cr content to 0.4% to 0.6%.

[0016] Aluminum: The role of aluminum in the present invention is to deoxidize and combine free nitrogen. Aluminum is a strong oxidizing element and forms Al with oxygen in steel. 2 O 3 It is removed during steelmaking. However, too much aluminum will form too much Al 2 O 3 Inclusions, on the one hand, are easy to block the pouring nozzle during continuous casting, and on the other hand, the Al 2 O 3 Too many or too large inclusions will deteriorate the fine blanking processing performance of the material; after comprehensive consideration, the present invention sets the Al content Al: 0.002% to 0.010%.

[0017] Oxygen: It is a harmful element in steel. It is mainly FeO, MnO, SiO 2 、Al 2 O 3 The presence of inclusions such as O will reduce the strength and plasticity of the steel, especially the fatigue strength and impact toughness. Therefore, it is hoped to reduce them as much as possible, but it is impossible to eliminate them completely, which will lead to a significant increase in manufacturing costs. Considering the actual control ability of the refining process, the present invention limits O to 0.0012%.

[0018] A method for manufacturing a hot-rolled steel plate for fine-blanking automobile engine gaskets, the method further comprising:

[0019] The molten steel is continuously cast to obtain a continuous casting slab, and the inclusion level in the continuous casting slab is controlled. According to the American Society for Testing and Materials "ASTM E45-13 Standard Test Method for Determining Inclusion Content in Steel", method A is used for testing, and the non-metallic inclusions of A, B, C, and D in the continuous casting slab are ≤1.5 level; the weight percentage of the chemical composition of the continuous casting slab is: C: 0.69% to 0.73%, Si: 0.05% to 0.15%, Mn: 0.55% to 0.65%, P≤0.015%, S≤0.003%, Cr: 0.4% to 0.6%, Al: 0.002% to 0.010%, O≤0.0012%, and the rest are iron and unavoidable inclusions;

[0020] The heating furnace heats the continuous casting slab in a reducing atmosphere environment, the excess air coefficient is 0.90-0.95, the continuous casting slab is heated at 1200-1240°C for 180-240min and then hot rolled, the hot rolling is a two-stage rolling process, the rough rolling is 6-pass continuous rolling, the rolling is performed above the austenite recrystallization temperature, and the rough rolling end temperature is 1020-1060°C; the intermediate slab thickness is 34-40mm; the finishing rolling is 7-stand continuous rolling, and the finishing temperature of the finishing rolling is 830-870°C; after finishing rolling, the thickness of the steel plate is controlled to be 2.5-5.0mm, the laminar cooling adopts front-stage cooling, and the cooling rate is 25-35°C / S; the hot-rolled steel plate is obtained by coiling at a coiling temperature of 580-620°C;

[0021] The hot rolled steel coil is slowly cooled after coiling, and the cooling rate of the hot rolled steel coil to 200° C. is 4 to 8° C. / h.

[0022] Furthermore, during continuous casting, the superheat of the molten steel in the tundish is controlled to be 15-25°C, and the drawing speed of the continuous casting slab is 1.1-1.2 m / min, with good results.

[0023] The key technology of the present invention is mainly achieved through the rational regulation and matching technology of composition design, steelmaking and refining, and hot rolling process. Through simulation calculation and experimental verification, the steel composition system A of the present invention is 3Point is 760.3℃, A 1 The hot rolling process adopted by the present invention is based on the steel composition system of the present invention and the phase transition point calculated by experimental simulation.

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

[0025] 1. Setting of continuous casting superheat and casting speed

[0026] In order to improve the internal quality of the ingot and reduce component segregation and looseness, it is necessary to control the continuous casting superheat and pulling speed; therefore, the present invention sets the superheat of the molten steel in the tundish to 15-25°C and the pulling speed of the continuous casting slab to 1.1-1.2 m / min, which has a good effect.

[0027] 2. Setting of continuous casting slab heating temperature, heating time and heating atmosphere

[0028] The setting of heating temperature and time of continuous casting slab not only ensures the full diffusion and solid solution of alloying elements such as C, Si, Mn in the continuous casting slab, the dissolution of coarse carbide particles and the uniform distribution in the steel, but also controls the degree of oxidation and decarburization of the slab and the stability of subsequent production, especially thin-gauge rolling; too low temperature and too short heating time cannot meet the above requirements. If the temperature is too high and the heating time is too long, due to the high carbon content in the steel, the oxidation and decarburization of the slab surface is serious, which is not conducive to the final performance and surface quality of the steel plate, and also consumes energy; the setting of heating atmosphere mainly controls the degree of oxidation and decarburization of the slab. Therefore, the present invention sets the heating temperature of continuous casting slab to 1200-1240℃, the heating time to 180-240min, and adopts reducing atmosphere for heating, with an excess air coefficient of 0.90-0.95.

[0029] 3. Setting of finishing temperature

[0030] The finishing temperature setting of the present invention has two functions. 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, thereby reducing the effect of band segregation. On the other hand, considering the high strength of this product and the influence of the rolling load on the impact of the rolling rollers, the stability of the plate and the plate shape control, the final rolling temperature is determined to be 830-870°C by comprehensive consideration.

[0031] 4. Setting of laminar cooling mode and cooling speed after finishing rolling

[0032] The present invention mainly considers that laminar cooling after finishing rolling can promote the rapid transformation of austenite in the material structure after finishing rolling into fine lamellar pearlite and ferrite, and the grains are refined, the structure is uniform, and the band segregation is reduced. Therefore, the present invention sets the laminar cooling method after finishing rolling to adopt the front-stage cooling process, and the cooling rate is set to 25-35°C / S.

[0033] 5. Setting of hot rolling coiling temperature

[0034] For high carbon steel products, the hot rolling coiling temperature mainly affects the material's structure, performance and subsequent spheroidizing annealing effect. A medium to low coiling temperature can make the grains moderately refined and uniform, which is beneficial to subsequent cold rolling. If the coiling temperature is too high, the grains will be coarse and the structure will be uneven. If the coiling temperature is too low, the strength of the hot rolled material will increase significantly, the brittleness of the steel plate will increase, resulting in large residual stress and poor plate shape, which is not conducive to further uncoiling and cold rolling processing. Therefore, the present invention sets the hot rolling coiling temperature to 580-620°C.

[0035] 6. Setting of cooling speed of hot rolled steel coil

[0036] By controlling the slow cooling of the steel coil after it comes off the line and entering the slow cooling wall, and setting the slow cooling time, not only can the uniformity of the organizational properties be effectively improved, but also the residual stress of the steel plate can be reduced, the plate shape can be improved, and the subsequent cold processing of the user can be facilitated; the present invention sets the cooling rate of the hot-rolled steel coil to 200°C to 4-8°C / h.

[0037] The metallographic structure of the hot-rolled steel plate produced by the method of the present invention is pearlite + a small amount of ferrite; the lower yield strength R of the 2.5-5.0 mm thick hot-rolled steel plate is eL 540~700MPa, tensile strength R m 960~1120MPa, elongation after fracture A 50mm It is 18% to 26%; the depth of single-sided decarburization layer of hot-rolled steel plate is ≤1.0%×steel plate thickness; non-metallic inclusions A, B, C, and D in hot-rolled steel plate are ≤level 1.5.

[0038] Compared with the prior art, the present invention has the following positive effects: 1. The present invention adopts a high-carbon, chromium-added composition design, matches the design of coupling steelmaking and hot rolling processes, obtains a hot-rolled steel plate with good microstructure and appearance quality, improves the material's own strength and the hardness and wear resistance of parts heat treatment, and better solves the problem of low strength and poor fatigue performance of existing products, meeting the user's subsequent deep processing and use requirements. 2. The present invention mainly adopts a low-aluminum, low-oxygen, low-sulfur design and a combination of LF+RH double refining processes and matches appropriate continuous casting process control to improve the purity of steel and improve the shape and size of non-metallic inclusions, etc., to meet the intrinsic quality requirements of high-quality materials of end users. 3. The present invention not only improves the degree of decarburization on the surface of the steel plate, meets the user's high requirements for the product surface, but also obtains a hot-rolled steel plate with uniform and refined grain structure and moderate strength and toughness, solves the problem of unwinding and forming cracking of users, and is conducive to the user's subsequent cold rolling processing, spheroidizing annealing, and uniform material heat treatment structure and performance requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a metallographic structure photograph of the hot-rolled steel plate in Example 5 of the present invention, and its magnification is 500 times.

[0040] Figure 2 This is a photograph of the surface decarburization layer of the hot-rolled steel plate in Example 5 of the present invention. The depth of the surface decarburization layer is 18.7 μm, and the magnification is 500 times. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with Examples 1 to 5, as shown in Tables 1 to 3.

[0042] Table 1 shows the chemical composition (by weight percentage) of the steel of the present invention, and the rest is Fe and unavoidable impurities.

[0043] Table 1 Chemical composition of the steel of the present invention, unit: weight percentage.

[0044]

[0045] Molten steel meeting the basic requirements of chemical composition is obtained by converter smelting, the molten steel is refined in LF ladle furnace, vacuum cycle degassing is carried out in RH vacuum furnace, and continuous casting is carried out to obtain continuous casting slabs; during continuous casting, the superheat of molten steel in the tundish is controlled to be 15-25°C, and the drawing speed of the continuous casting slab is 1.1-1.2 m / min; the inclusion level in the continuous casting slab is controlled, and according to the American Society for Testing and Materials "ASTM E45-13 Standard Test Method for Determining Inclusion Content in Steel", method A is used for inspection, and non-metallic inclusions A, B, C, and D in the hot-rolled steel plate are ≤1.5 level; the thickness of the continuous casting slab is 210-230 mm, the width is 900-1500 mm, and the length is 8500-11000 mm.

[0046] The cut-length slab produced by steelmaking is sent to the heating furnace for heating, and after being removed from the furnace and descaled, it is sent to the hot rolling unit for rolling. The rolling is controlled by the rough rolling and finishing rolling units, and the coiling is carried out after laminar cooling. The laminar cooling adopts the front cooling, and the hot-rolled steel coil is coiled; the hot-rolled steel coil after coiling enters the slow cooling wall for slow cooling to obtain the finished hot-rolled steel coil. The cooling rate of the hot-rolled steel coil to 200℃ is 4-8℃ / h; the thickness of the hot-rolled steel plate is 2.5-5.0mm; the hot rolling process control parameters are shown in Table 2.

[0047] Table 2 Hot rolling process control parameters of the embodiment of the present invention

[0048]

[0049]

[0050] The hot rolled steel sheet obtained by the above method is Figure 1 and Figure 2 The metallographic structure of the hot-rolled steel plate is pearlite + a small amount of ferrite; the non-metallic inclusions in the hot-rolled steel plate are A, B, C, D ≤ 1.5 grade; the lower yield strength R of the 2.5-5.0 mm thick hot-rolled steel plate eL 540~700MPa, tensile strength R m 960~1120MPa, elongation after fracture A 50mm It is 18% to 26%; the depth of decarburization layer on one side of hot-rolled steel plate is ≤1.0%×steel plate thickness.

[0051] The hot-rolled steel plate obtained by the present invention was subjected to a tensile test according to "GB / T 228.1-2010 Tensile test of metallic materials Part 1: Room temperature test method", and the microstructure was detected according to the steel microstructure evaluation method (GB / T 13299). The mechanical properties of the hot-rolled steel plate are shown in Table 3.

[0052] Table 3 Mechanical properties of hot-rolled steel sheets according to the present invention

[0053]

[0054] From the performance in Table 3, it can be seen that the hot-rolled steel plate for fine blanking automobile engine gasket obtained by the present invention has high strength, good toughness, low surface decarburization, and fine inclusions, which fully meets the quality requirements of users for subsequent processing and heat treatment.

[0055] 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 hot-rolled steel plate for fine blanking of automobile engine gaskets, wherein the chemical composition by weight is as follows: C: 0.69% to 0.73%, Si: 0.05% to 0.15%, Mn: 0.55% to 0.65%, P≤0.015%, S≤0.003%, Cr: 0.4% to 0.6%, Al: 0.002% to 0.010%, O≤0.0012%, and the rest is iron and unavoidable inclusions; the metallographic structure of the hot-rolled steel plate is pearlite + a small amount of ferrite; the depth of the single-sided decarburization layer of the hot-rolled steel plate is ≤1.0%×the thickness of the steel plate; according to the American Society for Testing and Materials "ASTM E45-13 Standard Test Method for Determining the Content of Inclusions in Steel", the non-metallic inclusions of A, B, C, and D in the hot-rolled steel plate are ≤1.5 grade.

2. The hot-rolled steel plate for fine blanking automobile engine gasket according to claim 1, characterized in that: Lower yield strength R of 2.5~5.0mm thick hot rolled steel plate eL 540~700MPa, tensile strength R m 960~1120MPa, elongation after fracture A 50mm It is 18% to 26%.

3. A method for manufacturing a hot-rolled steel plate for fine blanking automobile engine gaskets, characterized in that: The following steps are involved: The molten steel is continuously cast to obtain a continuous casting slab, and the inclusion level in the continuous casting slab is controlled. According to the American Society for Testing and Materials "ASTME45-13 Standard Test Method for Determining Inclusion Content in Steel", method A is used for inspection, and the non-metallic inclusions of A, B, C, and D in the continuous casting slab are ≤1.5 level; the weight percentage of the chemical composition of the continuous casting slab is: C: 0.69% to 0.73%, Si: 0.05% to 0.15%, Mn: 0.55% to 0.65%, P≤0.015%, S≤0.003%, Cr: 0.4% to 0.6%, Al: 0.002% to 0.010%, O≤0.0012%, and the rest are iron and unavoidable inclusions; The heating furnace heats the continuous casting slab in a reducing atmosphere environment, the excess air coefficient is 0.90-0.95, the continuous casting slab is heated at 1200-1240°C for 180-240min and then hot rolled, the hot rolling is a two-stage rolling process, the rough rolling is 6-pass continuous rolling, the rolling is performed above the austenite recrystallization temperature, and the rough rolling end temperature is 1020-1060°C; the intermediate slab thickness is 34-40mm; the finishing rolling is 7-stand continuous rolling, and the finishing temperature of the finishing rolling is 830-870°C; after finishing rolling, the thickness of the steel plate is controlled to be 2.5-5.0mm, the laminar cooling adopts front-stage cooling, and the cooling rate is 25-35°C / S; the hot-rolled steel plate is obtained by coiling at a coiling temperature of 580-620°C; The hot rolled steel coil is slowly cooled after coiling, and the cooling rate of the hot rolled steel coil to 200° C. is 4 to 8° C. / h.

4. The method for manufacturing a hot-rolled steel sheet for fine blanking automobile engine gaskets according to claim 3, characterized in that: During continuous casting, the superheat of the molten steel in the tundish is controlled to be 15-25°C, and the drawing speed of the continuous casting slab is 1.1-1.2 m / min.

5. The method for manufacturing a hot-rolled steel sheet for fine blanking automobile engine gaskets according to claim 3, characterized in that: The metallographic structure of hot-rolled steel plate is pearlite + a small amount of ferrite; the lower yield strength R of 2.5-5.0mm thick hot-rolled steel plate eL 540~700MPa, tensile strength R m 960~1120MPa, elongation after fracture A 50mm It is 18% to 26%; the depth of decarburization layer on one side of hot-rolled steel plate is ≤1.0%×steel plate thickness.

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