Production method of bake hardening steel for passenger car trunk outer plate

Abstract

The invention discloses a production method of bake-hardening steel for a passenger car trunk outer plate, and belongs to the technical field of ferrous metallurgy steelmaking processes. The method comprises the following procedures of steelmaking, hot rolling, cold rolling and annealing. The casting blank comprises the following chemical components in percentage by mass: 0.0010% < = C < = 0.0040%; less than or equal to 0.03% of Si; 0.30% or less of Mn; 0.020% < = P < = 0.050%; s < = 0.008%; alt is greater than or equal to 0.020%; the bake-hardened steel with the mechanical properties meeting the requirements that the yield strength is 180-240 MPa, the tensile strength is 290-390 MPa, the ductility is larger than or equal to 34.0%, r90 is larger than or equal to 1.5, n90 is larger than or equal to 0.16, and BH2 is larger than or equal to 30 MPa can be obtained by controlling the technological parameters of the steelmaking procedure, the hot rolling procedure, the annealing procedure and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of steel metallurgy and steelmaking technology, and in particular relates to a production method of bake-hardened steel for passenger car luggage compartment outer panels. Background Art

[0002] In the automotive industry, most parts require a certain degree of deformation capability, leading to the widespread use of IF steel. However, the disadvantage of interstitial-free steel is its low yield strength, making it unsuitable for parts requiring dent resistance. Based on IF steel, bake-hardened steel has been developed, which increases its strength during the baking process after deformation, thus achieving both deformation capability and dent resistance. The purpose of this patent is to explore the key components and process points that influence the performance and surface quality of bake-hardened steel, and to produce products that meet user requirements. Summary of the Invention

[0003] The present invention aims to provide a method for producing bake-hardened steel for passenger car luggage compartment outer panels. The produced bake-hardened steel for passenger car luggage compartment outer panels has the following mechanical properties: yield strength of 180-240 MPa, tensile strength of 290-390 MPa, elongation ≥34.0%, r90 ≥1.5, n90 ≥0.16, and BH2 ≥30 MPa.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention provides a method for producing bake-hardened steel for passenger car luggage compartment outer panels, comprising the following steps: steelmaking step - hot rolling step - cold rolling step - annealing step; and is characterized in that:

[0006] In the steelmaking process, a cast ingot is obtained, and the chemical composition of the cast ingot is controlled to be as follows by mass percentage: 0.0010%≤C≤0.0040%; Si≤0.03%; Mn≤0.30%; 0.020%≤P≤0.050%; S≤0.008%; Alt≥0.020%; Ti≥0.010%, N≤0.0050%, and the remainder is Fe and unavoidable impurities;

[0007] The hot rolling process includes: heating the ingot - high-pressure water descaling - fixed width press - E1R1 roughing mill rolling - E2R2 roughing mill rolling - insulation cover - flying shear - high-pressure water descaling - F1-F7 finishing mill rolling - dense laminar cooling - coiling; wherein: during the heating of the ingot, the heating temperature is controlled to be 1220-1260°C, the heating time is 180-240 minutes, the soaking temperature is controlled to be 1230-1260°C, the soaking time is controlled to be 30-60 minutes, the furnace temperature is controlled to be 1230-1260°C, the finishing temperature of the finishing rolling is controlled to be 880-930°C, the coiling temperature is controlled to be 600-650°C, and the cooling method is the front concentrated cooling method;

[0008] The annealing process includes: controlling the annealing heating temperature to be 780-820° C., the annealing soaking temperature to be 780-820° C., and the leveler elongation to be 0.8-1.1%.

[0009] Furthermore, the mechanical properties of the bake-hardened steel for the passenger car luggage compartment outer panel produced meet the following requirements: yield strength 180-240 MPa, tensile strength 290-390 MPa, elongation ≥ 34.0%, r 90 ≥1.5, n 90 ≥0.16, BH2≥30MPa.

[0010] Furthermore, the steelmaking process includes: converter top and bottom blowing smelting - RH - slab continuous casting process; wherein:

[0011] The tapping temperature of the converter is ≥1650℃, and the tapping temperature drop requirement is ≤80℃;

[0012] Deep decarburization is performed based on the composition and temperature of the RH molten steel supplied by the converter. After decarburization, aluminum particles are added for deoxidation and alloying according to the oxygen content. After circulating for more than 5 minutes, ferromanganese, ferrotitanium and other alloys are added to adjust the composition. After the composition adjustment is completed, ensure that the vacuum cycle is ≥5 minutes;

[0013] In the slab continuous casting, the superheat of the intermediate ladle is controlled within a range of 20 to 40° C. during the casting process of the casting machine, and the production casting speed is 1.0 to 1.8 m / min.

[0014] Furthermore, the cold rolling process includes: pickling uncoiling - welding - straightening - pickling - rinsing - drying - trimming - continuous rolling mill cold rolling - coiling;

[0015] The annealing process includes: uncoiling - welding - entrance looper - cleaning - annealing furnace - zinc pot - post-plating cooling - water quenching - intermediate looper - skin pass mill - roller coater - dryer - exit looper - trimming - surface inspection - oiling - sampling - coiling - weighing - packaging.

[0016] Furthermore, the thickness of the ingot is 230 mm, the thickness of the ingot after hot rolling is 3.0 mm, and the thickness after cold rolling is 0.65 mm.

[0017] Furthermore, the chemical composition of the ingot is as follows by mass percentage: C 0.0031%; Si 0.003%; Mn 0.22%; P 0.033%; S 0.003%; Alt 0.039%; Ti 0.014%, N 0.0015%, and the remainder is Fe and unavoidable impurities.

[0018] Furthermore, the chemical composition of the ingot is as follows by mass percentage: C 0.0030%; Si 0.003%; Mn 0.19%; P 0.036%; S 0.004%; Alt 0.039%; Ti 0.013%, N 0.0018%, and the remainder is Fe and unavoidable impurities.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] The preparation method of bake-hardening steel for passenger car trunk outer panels provided by the above technical solution adopts a new composition design and controls process parameters such as steelmaking process, hot rolling process, cold rolling process, annealing process, etc. (the characteristics of the product are that it adopts solid solution strengthening of manganese and phosphorus, takes low-cost design into consideration, mainly adds titanium to control interstitial atoms, and pays attention to surface quality control during the production process). A product that meets user needs and has good bake hardening value is obtained. It has been proven in actual use that the performance is suitable, and its mechanical properties meet the following requirements: yield strength of 180-240MPa, tensile strength of 290-390MPa, elongation ≥34.0%, r 90 ≥1.5, n 90 ≥0.16, BH2≥30MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below with reference to the accompanying drawings.

[0022] Figure 1 The distribution range of the yield strength test results of the bake hardening steel obtained according to the method of the present invention is shown in FIG.

[0023] Figure 2 The distribution range of the tensile strength test results of the bake hardening steel obtained according to the method of the present invention is shown in FIG.

[0024] Figure 3 The distribution range of the elongation test results of the bake hardening steel obtained according to the method of the present invention is shown in FIG.

[0025] Figure 4 The distribution range of the r-value test results of the bake hardening steel obtained according to the method of the present invention.

[0026] Figure 5 is the distribution range of the n value test results of the bake hardening steel obtained according to the method of the present invention.

[0027] Figure 6 is the distribution range of the bake hardening value test results of the bake hardening steel obtained according to the method of the present invention. DETAILED DESCRIPTION

[0028] Based on user needs for bake-hardening steel, the present invention provides a method for preparing bake-hardening steel for passenger car trunk outer panels that meets user needs by adopting new composition design and metallurgical process parameters (characterized by the product adopting solid solution strengthening of manganese and phosphorus, considering low-cost design, mainly adding titanium to control interstitial atoms, and paying attention to surface quality control during the production process).

[0029] The preparation method specifically includes the following steps: steelmaking step - hot rolling step - cold rolling step - annealing step; wherein:

[0030] The steelmaking process includes: converter top and bottom blowing smelting - RH - slab continuous casting process;

[0031] The tapping temperature of the converter is ≥1650℃, and the tapping temperature drop requirement is ≤80℃;

[0032] Deep decarburization is performed based on the composition and temperature of the RH molten steel supplied by the converter. After decarburization, aluminum particles are added for deoxidation and alloying according to the oxygen content. After circulating for more than 5 minutes, ferromanganese, ferrotitanium and other alloys are added to adjust the composition. After the composition adjustment is completed, ensure that the vacuum cycle is ≥5 minutes;

[0033] In the slab continuous casting, the superheat of the intermediate ladle is controlled within a range of 20 to 40° C. during the casting process of the casting machine, and the production casting speed is 1.0 to 1.8 m / min.

[0034] The thickness of the above-mentioned ingot is 230 mm, and the hot-rolled thickness is 3.0 mm;

[0035] The hot rolling process includes: billet heating - high-pressure water descaling - width-fixing press - E1R1 roughing mill rolling - E2R2 roughing mill rolling - flying shear - high-pressure water descaling - F1-F7 finishing mill rolling - dense laminar cooling - coiling. This process uses a walking beam furnace to heat the billet (heating process see Table 1). Roughing uses a reciprocating rolling process of two stands R1 and R2. To achieve good surface quality, roughing is fully descaled, and the descaling pressure must be greater than 190 bar. Finishing uses the F1-F7 continuous rolling process. The inter-stand cooling water of the finishing mill requires ≥4 stands. The high-speed steel rolls used in F1-F4 must not have any oxide film peeling on the roll surface. The cooling method before coiling is front-concentrated. The specific hot rolling process is shown in Table 2.

[0036] Table 1: Slab heating system

[0037]

[0038] Table 2: Hot rolling process

[0039]

[0040] The cold rolling process includes: pickling uncoiling - welding - straightening - pickling - rinsing - drying - trimming - continuous rolling mill cold rolling - coiling;

[0041] The annealing process includes: uncoiling, welding, entry looper, cleaning, annealing furnace, zinc pot, post-plating cooling, water quenching, intermediate looper, skin pass mill, roller coater, dryer, exit looper, trimming, surface inspection, oiling, sampling, coiling, weighing, and packaging. To achieve good surface quality, the chrome plating rollers are replaced during production. After the rollers are replaced, at least eight rolls of non-exterior plate are prepared to confirm the quality.

[0042] The specific process system of the annealing process is shown in Table 3.

[0043] Table 3: Annealing process

[0044]

[0045] The present invention is described in detail below through specific examples. The examples are only intended to help understand the present invention but are not intended to limit the present invention.

[0046] Example

[0047] 1. According to the above steelmaking process requirements, the actual slab chemical composition (mass percentage) is shown in Table 4 below.

[0048] Table 4: Chemical composition (%)

[0049]

[0050] 2. According to the above hot rolling process requirements, the hot rolling thickness is 3.0 mm, and the actual process is shown in Table 5.

[0051] Table 5: Rolling process

[0052]

[0053] 3. According to the above annealing process requirements, the finished product thickness is 0.65mm, and the actual process is shown in Table 6.

[0054] Table 6: Annealing process

[0055]

[0056] 4. The mechanical properties of representative steel strip products obtained through the above process are shown in Table 7. The test method refers to GB / T 228.1. Figure 1-6 As shown in the figure, the distribution range of the mechanical properties (yield strength, tensile strength, elongation, r value, n value, bake hardening value) of the bake hardened steel obtained according to the method of the present invention is shown. It can be seen that the mechanical properties produced by the above process meet the user's requirements: yield strength 180-240MPa, tensile strength 290-390MPa, elongation ≥34.0%, r value ≥34.0%, and n value ≥34.0%. 90 ≥1.5, n 90≥0.16, BH2≥30MPa.

[0057] Table 7: Mechanical properties

[0058]

[0059] In summary, the steel strip products obtained by the process have suitable mechanical properties and can be widely promoted and used.

[0060] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for producing bake-hardened steel for passenger car trunk outer panels, comprising the following steps: steelmaking, hot rolling, cold rolling, and annealing; characterized in that: In the steelmaking process, a casting billet is obtained, and the chemical composition of the casting billet is controlled to be: 0.0010%≤C≤0.0040%; Si≤0.03%; Mn≤0.30% in terms of mass percentage; 0.020％≤P≤0.050％； S≤0.008%; Alt≥0.020%; Ti ≥ 0.010%, N ≤ 0.0050%, the rest is Fe and unavoidable impurities; The hot rolling process includes: heating the ingot - high-pressure water descaling - width-fixing press - E1R1 roughing mill rolling - E2R2 roughing mill rolling - insulation cover - flying shear - high-pressure water descaling - F1-F7 finishing mill rolling - dense laminar cooling - coiling; wherein: during the heating of the ingot, the heating temperature is controlled to be 1220-1260°C, the heating time is 180-240 minutes, the soaking temperature is controlled to be 1230-1260°C, the soaking time is controlled to be 30-60 minutes, the furnace temperature is controlled to be 1230-1260°C, the finishing temperature of the finishing rolling is controlled to be 880-930°C, and the coiling temperature is controlled to be 600-650°C, and the cooling method is the front concentrated cooling method; The annealing process includes: controlling the annealing heating temperature to be 780-820° C., the annealing soaking temperature to be 780-820° C., and the leveler elongation to be 0.8-1.1%.

2. The method for producing bake-hardened steel for passenger car trunk outer panels according to claim 1, characterized in that: The mechanical properties of the bake-hardened steel for the passenger car luggage compartment outer panel produced meet the following requirements: yield strength 180-240MPa, tensile strength 290-390MPa, elongation ≥34.0%, r 90 ≥1.5, n 90 ≥0.16, BH2≥30MPa.

3. The method for producing bake-hardened steel for passenger car trunk outer panels according to claim 1, characterized in that: The steelmaking process includes: converter top and bottom combined blowing smelting - RH - slab continuous casting process; wherein: The tapping temperature of the converter is ≥1650℃, and the tapping temperature drop requirement is ≤80℃; Deep decarburization treatment is carried out according to the composition and temperature of the RH molten steel supplied by the converter. After decarburization, aluminum particles are added for deoxidation and alloying according to the oxygen content. After circulating for more than 5 minutes, ferromanganese and ferrotitanium are added to adjust the composition. After the composition adjustment is completed, ensure that the vacuum cycle is ≥5 minutes; In the slab continuous casting, the superheat of the intermediate ladle is controlled within a range of 20 to 40° C. during the casting process of the casting machine, and the production casting speed is 1.0 to 1.8 m / min.

4. The method for producing bake-hardened steel for passenger car trunk outer panels according to claim 1, characterized in that: The cold rolling process includes: pickling uncoiling - welding - straightening - pickling - rinsing - drying - trimming - continuous rolling mill cold rolling - coiling; The annealing process includes: uncoiling - welding - entrance looper - cleaning - annealing furnace - zinc pot - post-plating cooling - water quenching - intermediate looper - skin pass mill - roller coater - dryer - exit looper - trimming - surface inspection - oiling - sampling - coiling - weighing - packaging.

5. The method for producing bake-hardened steel for passenger car trunk outer panels according to any one of claims 1 to 4, characterized in that: The thickness of the ingot is 230 mm. The thickness of the ingot after hot rolling is 3.0 mm, and the thickness after cold rolling is 0.65 mm.

6. The method for producing bake-hardened steel for passenger car trunk outer panels according to claim 1, characterized in that: The chemical composition of the ingot is as follows by mass percentage: C 0.0031%, Si 0.003%, Mn 0.22%, P 0.033%, S 0.003%, Alt 0.039%, Ti 0.014%, N 0.0015%, and the remainder is Fe and unavoidable impurities.

7. The method for producing bake-hardened steel for passenger car trunk outer panels according to claim 1, characterized in that: The chemical composition of the ingot is as follows by mass percentage: C 0.0030%; Si 0.003%; Mn 0.19%; P 0.036%; S 0.004%; Alt 0.039%; Ti 0.013%; N 0.0018%; the remainder being Fe and unavoidable impurities.

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