Production method of passenger car back door inner plate special steel DX56D + Z

Abstract

The invention discloses a preparation method of special steel DX56D + Z for an inner plate of a back door of a passenger car. The special steel DX56D + Z for the inner plate of the back door of the passenger car comprises the following chemical components in percentage by mass: less than or equal to 0.0020% of C, less than or equal to 0.015% of P, less than or equal to 0.015% of S and the balance of Fe. S is less than or equal to 0.02%; the content of Mn is 0.05 to 0.15 percent; less than or equal to 0.010% of P; s < = 0.008%; t is 0.055 to 0.075 percent; n < = 0.0035%; 0 < = 0.0030%, with the balance being Fe and inevitable impurities; and the technological parameters of the steelmaking procedure, the hot rolling procedure, the galvanizing procedure and the like are controlled, the DX56D + Z with the mechanical properties meeting the requirements that the yield strength ranges from 110 MPa to 160 MPa, the tensile strength is larger than or equal to 260 MPa, the ductility is larger than or equal to 41.0% and r is larger than or equal to 2.3 can be obtained, and the method can be used for production of the passenger car back door inner plate, is appropriate in performance and can be widely applied and popularized.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy and steelmaking technology, and in particular relates to a production method of special steel DX56D+Z for passenger car rear door inner panels. Background Art

[0002] The ultra-deep drawn hot-dip galvanized DX56D+Z product for the inner panel of the rear tailgate of passenger cars is one of the high-end varieties of automobile plates that are more difficult to produce. The strip steel is required to have excellent stamping formability and performance stability. In order to meet the development needs of high-end manufacturing and high-end efficiency creation, combined with the production concept of energy saving and cost reduction of the production unit, the composition system of DX56D+Z is designed based on the principles of ultra-low carbon and adding pure titanium. Through scientific composition design and reasonable smelting, hot rolling, acid rolling and hot-dip galvanizing process control, special steel for the inner panel of the rear tailgate of passenger cars is developed to meet the needs of users.

[0003] Deep drawing series steel is the type of steel used most frequently by car manufacturers. Since the matching of materials and molds is the key to successful use, customized design based on user needs is the innovation point of this type of product.

[0004] Compared with the comparative patent "A Production Method of a Special Steel DC06-M for Passenger Car Doors", the comparative patent is produced on a continuous annealing line, while this patent is produced on a galvanizing line. Due to the differences in the length and configuration of the furnace areas of the two production lines, if the galvanized product is to meet the user's needs for large deformation stamping, the interstitial atomic carbon and strengthening element manganese must be controlled more strictly in terms of composition design; in addition, the inner panel of the rear door of a passenger car requires a high plastic strain ratio, and the factor that affects this index is the texture, so high-temperature coiling and high-temperature annealing are adopted at the same time to ensure this index. Summary of the invention

[0005] The purpose of the present invention is to provide a production method of special steel DX56D+Z for passenger car back door inner plate, and the mechanical properties of the produced special steel meet the user requirements: yield strength 110-160MPa, tensile strength ≥260MPa, elongation ≥41.0%, r ≥2.3.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention discloses a production method of a special steel DX56D+Z for a rear back door inner plate of a passenger car, comprising the following steps: a steelmaking step, a hot rolling step, a cold rolling step, and a galvanizing step; wherein:

[0008] In the steelmaking process, a cast billet is obtained, and the chemical composition of the cast billet is controlled to be: C≤0.0020%; Si≤0.02%; Mn 0.05-0.15%; P≤0.010%; S≤0.008%; Ti0.055-0.075%; N≤0.0035%; O≤0.0030%, and the rest is Fe and unavoidable impurities;

[0009] The hot rolling process includes: heating of 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 in the heating of the ingot, the heating temperature is controlled to be 1160-1220°C, the heating time is 150-250min, the soaking temperature is 1170-1220°C, the soaking time is 20-55min, the furnace temperature is 1170-1200°C, the final rolling temperature of the finishing rolling is controlled to be 900-950°C, the coiling temperature is 700-750°C, and the cooling method is the front dispersion cooling method;

[0010] In the galvanizing process, the galvanizing heating temperature is controlled to be 800-850° C., the galvanizing soaking temperature is controlled to be 800-840° C., and the leveling machine elongation is controlled to be 0.6-0.8%.

[0011] Furthermore, the mechanical properties of the special steel DX56D+Z for the rear back door inner panel of a passenger car meet the following requirements: yield strength 110-160 MPa, tensile strength ≥ 260 MPa, elongation ≥ 41.0%, and r ≥ 2.3.

[0012] Furthermore, the steelmaking process includes: converter top and bottom combined blowing smelting - LF - RH - slab continuous casting.

[0013] Furthermore, the steel-tapping temperature of the converter is ≥1670°C, and a top slag modifier is added according to the oxygen content of the molten steel and the amount of slag; the LF refining furnace performs heating and temperature raising operations according to the molten steel in-situ temperature, and adds lime and modifier to perform top slag modification treatment.

[0014] Furthermore, the RH furnace performs deep decarburization according to the composition and temperature of the molten steel in place; after decarburization, aluminum particles are added for deoxidation and alloying according to the oxygen fixation conditions, and titanium iron and manganese iron alloys are added after a 5-minute cycle to adjust the composition to the target value; after the composition adjustment is completed, ensure that the vacuum cycle is ≥10 minutes.

[0015] Furthermore, in the slab continuous casting, the superheat of the intermediate ladle is controlled in the range of 25 to 45° C. during the casting process of the casting machine, and the production casting speed is 1.0 to 1.8 m / min.

[0016] Furthermore, the thickness of the ingot is 230 mm, the thickness of the ingot after hot rolling is 3.8 mm, and the thickness of the ingot after cold rolling is 0.8 mm.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are:

[0018] The preparation method of the special steel DX56D+Z for the rear back door inner panel of a passenger car of the present invention adopts a new component design and controls process parameters such as a steelmaking process, a hot rolling process, a cold rolling process, and a galvanizing process, so as to obtain a product that meets user needs and has a certain deformation ability, and is proved by actual use to have suitable performance, and its mechanical properties meet the following requirements: yield strength 110-160MPa, tensile strength ≥260MPa, elongation ≥41.0%, and r ≥2.3.

[0019] For the galvanized products of stamped back door inner panels, compared with the door panel products of continuous retreat, the key point is to control the skin pass elongation, which affects the yield strength and surface quality of the products at the same time. On the one hand, the skin pass elongation is an important process parameter affecting the yield strength of the product. A large amount of production data shows that for deep drawing steel, the skin pass elongation increases by 0.1%, the yield strength increases by about 3-5MPa, and the tensile strength is not significantly improved, which leads to an increase in the yield strength ratio, which is not conducive to product deformation. Therefore, from the perspective of controlling the yield strength, a low skin pass elongation should be selected. On the other hand, the skin pass elongation affects the surface roughness and surface quality of the galvanized sheet. If the skin pass elongation is low, it affects the control of the surface roughness. In addition, the steel strip surface appears shiny and slipping, which does not meet the delivery conditions of the automobile sheet. Therefore, the biggest difficulty in the research process of the present invention is to explore a reasonable skin pass control range, and combine the control of tension and rolling force to ensure that the product can meet the delivery requirements and ensure that there is no cracking problem during the stamping process. The above technical solution of the present invention achieves the above purpose. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings.

[0021] Figure 1 The yield strength test result distribution range of the special steel DX56D+Z for the rear back door inner panel of a passenger car obtained according to the method of the present invention is shown in FIG.

[0022] Figure 2 The distribution range of the tensile strength test results of the special steel DX56D+Z for the rear back door inner panel of a passenger car obtained according to the method of the present invention.

[0023] Figure 3 The distribution range of the elongation test results of the special steel DX56D+Z for the rear back door inner panel of a passenger car obtained according to the method of the present invention.

[0024] Figure 4 The distribution range of the r-value test results of the special steel DX56D+Z for the rear back door inner panel of a passenger car obtained according to the method of the present invention. DETAILED DESCRIPTION

[0025] In view of users' actual demand for special steel for passenger car rear door inner panels, the present invention provides a method for preparing special steel for passenger car rear door inner panels that meets users' demand by adopting new component design and optimizing metallurgical process parameters.

[0026] The preparation method specifically includes the following steps: steelmaking step - hot rolling step - cold rolling step - galvanizing step; wherein:

[0027] The steelmaking process includes: converter top and bottom combined blowing smelting - LF - RH - slab continuous casting;

[0028] The tapping temperature of the converter is ≥1670°C, and a top slag modifier is added according to the oxygen content of the molten steel and the amount of slag;

[0029] The LF refining furnace performs heating and temperature raising operation according to the molten steel in-situ temperature, and adds lime and modifier to perform top slag modification treatment;

[0030] The RH furnace performs deep decarburization according to the composition and temperature of the molten steel. After decarburization, aluminum particles are added for deoxidation and alloying according to the oxygen setting conditions. Titanium iron, manganese iron and other alloys are added for 5 minutes to adjust the composition to the target value. After the composition adjustment is completed, ensure that the vacuum cycle is ≥10 minutes;

[0031] In the slab continuous casting, the superheat degree of the intermediate ladle is controlled within the range of 25 to 45° C. during the casting process of the casting machine, and the production casting speed is 1.0 to 1.8 m / min.

[0032] The thickness of the above-mentioned ingot is 230 mm, and the hot-rolled thickness is: 3.8 mm;

[0033] The hot rolling process includes: heating of the ingot - high-pressure water descaling - fixed width 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 heating furnace to heat the ingot (heating process see Table 1), rough rolling uses double-frame R1 and R2 reciprocating rolling, finishing rolling uses F1-F7 continuous rolling process, and the cooling method is front dispersed cooling method. The specific hot rolling process is shown in Table 2.

[0034] Table 1: Billet heating system

[0035]

[0036] Table 2: Hot rolling process

[0037]

[0038] The cold rolling process includes: pickling uncoiling - welding - straightening - pickling - rinsing - drying - trimming - continuous rolling mill cold rolling - coiling;

[0039] The galvanizing process includes: galvanizing uncoiling - welding - entrance looper - cleaning - annealing furnace - zinc pot - cooling - water quenching - intermediate looper - skin pass machine - straightening machine - roller coater - dryer - exit looper - trimming - surface inspection - oiling - sampling - coiling - weighing - packaging.

[0040] The specific process system of the galvanizing process is shown in Table 3.

[0041] Table 3: Galvanizing process

[0042]

[0043] 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.

[0044] Example

[0045] 1. According to the above steelmaking process requirements, the actual slab chemical composition (mass percentage) is shown in Table 4 below.

[0046] Table 4: Chemical composition (%)

[0047]

[0048] 2. According to the above hot rolling process requirements, the hot rolling thickness is 3.8 mm, and the actual process is shown in Table 5.

[0049] Table 5: Rolling process

[0050]

[0051] 3. According to the above galvanizing process requirements, the finished product thickness is 0.8mm, and the actual process is shown in Table 6.

[0052] Table 6: Galvanizing process

[0053]

[0054] 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 / T228.1. Figure 1-4 As shown, the distribution range of the mechanical properties (yield strength, tensile strength, elongation and r value) of the steel strip DX56D+Z 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 requirements: yield strength 110-160MPa, tensile strength ≥260MPa, elongation ≥41.0%, r≥2.3.

[0055] Table 7: Mechanical properties

[0056]

[0057] The steel strip products obtained by the above process have been used by users and have suitable strength and can be widely promoted and used.

[0058] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A production method of DX56D+Z special steel for passenger car back door inner panel, characterized in that: It includes the following processes: steelmaking process - hot rolling process - cold rolling process - galvanizing process; among which: In the steelmaking process, a casting billet is obtained, and the chemical composition of the casting billet is controlled to be: C≤0.0020%; Si≤0.02%; Mn 0.05-0.15%; P≤0.010%; S≤0.008%; Ti0.055-0.075%; N≤0.0035%; O≤0.0030%, and the rest is Fe and unavoidable impurities; The hot rolling process includes: heating of 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 in the heating of the ingot, the heating temperature is controlled to be 1160-1220°C, the heating time is 150-250min, the soaking temperature is 1170-1220°C, the soaking time is 20-55min, the furnace temperature is 1170-1200°C, the final rolling temperature of the finishing rolling is controlled to be 900-950°C, the coiling temperature is 700-750°C, and the cooling method is the front dispersion cooling method; In the galvanizing process, the galvanizing heating temperature is controlled to be 800-850° C., the galvanizing soaking temperature is controlled to be 800-840° C., and the leveling machine elongation is controlled to be 0.6-0.8%.

2. The production method of the special steel DX56D+Z for the rear back door inner panel of a passenger car according to claim 1, characterized in that: The mechanical properties of the special steel DX56D+Z for the rear back door inner panel of a passenger car meet the following requirements: yield strength of 110-160 MPa, tensile strength ≥260 MPa, elongation ≥41.0%, and r ≥2.

3.

3. The production method of the special steel DX56D+Z for the rear back door inner panel of a passenger car according to claim 1, characterized in that: The steelmaking process includes: converter top and bottom combined blowing smelting - LF - RH - slab continuous casting.

4. The production method of the special steel DX56D+Z for the rear back door inner panel of a passenger car according to claim 3, characterized in that: The steel-tapping temperature of the converter is ≥1670℃, and the top slag modifier is added according to the oxygen content of the molten steel and the amount of slag. The LF refining furnace performs heating and temperature raising operations according to the molten steel in-situ temperature, and adds lime and modifier to modify the top slag.

5. The production method of the special steel DX56D+Z for the rear back door inner panel of a passenger car according to claim 3, characterized in that: The RH furnace performs deep decarburization according to the composition and temperature of the molten steel in place; after decarburization, aluminum particles are added for deoxidation and alloying according to the oxygen fixation conditions, and titanium iron and manganese iron alloys are added after a 5-minute cycle to adjust the composition to the target value; after the composition adjustment is completed, ensure that the vacuum cycle is ≥10 minutes.

6. The production method of the special steel DX56D+Z for the rear back door inner panel of a passenger car according to claim 3, characterized in that: In the slab continuous casting, the superheat degree of the intermediate ladle is controlled within a range of 25 to 45° C. during the casting process of the casting machine, and the production casting speed is 1.0 to 1.8 m / min.

7. The production method of the special steel DX56D+Z for the rear back door inner panel of a passenger car according to claim 1 or 3, characterized in that: The thickness of the ingot is 230 mm. The thickness of the ingot after hot rolling is 3.8 mm, and the thickness after cold rolling is 0.8 mm.

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