Production method of low-yield-ratio galvanized ultra-deep drawing steel DC56D + Z for automobiles

Abstract

The invention discloses a production method of low-yield-ratio automobile galvanized ultra-deep drawing steel DC56D + Z. The production method is characterized by comprising the following steps: a steelmaking process; a hot rolling process; pickling and rolling; a hot galvanizing process; the galvanized ultra-deep drawing steel DC56D + Z comprises the following chemical components in percentage by mass: less than or equal to 0.0020 wt% of C, less than or equal to 0.010 wt% of Si, 0.08-0.15 wt% of Mn, less than or equal to 0.015 wt% of P, less than or equal to 0.010 wt% of S, 0.020-0.055 wt% of Alt, 0.055-0.070 wt% of Ti, less than or equal to 0.0030 wt% of N and the balance of Fe and inevitable impurities. According to the method, a certain amount of Ti element is added into ultra-low carbon steel to fix C and N interstitial atoms in a steel base, and the interstitial-atom-free IF steel is obtained by cooperating with the optimized process, so that the deep drawability of the steel is improved.

Description

Technical Field

[0001] This invention belongs to the field of material forming technology, and specifically relates to a production method for DC56D+Z galvanized ultra-deep drawing steel for automobiles with a low yield strength ratio. This material is used for stamping automotive rear wheel arch outer panels, side panel outer panels, and other parts. Background Technology

[0002] Galvanized ultra-deep drawing DC56D+Z steel strip is suitable for manufacturing complex automotive parts due to its advantages such as good deep drawing performance, uniform coil properties, and strong anti-powdering ability of galvanization. Components such as rear wheel arch panels and side panel panels are prone to necking and cracking during stamping due to large deformation, leading to part failure and scrap. Based on actual production conditions, reducing the yield strength ratio of the steel strip is an effective way to mitigate necking and cracking in stamped parts. To adapt to market development and meet customer needs, and considering the production situation of the manufacturing unit, based on ultra-low carbon interstitial steel, the composition of automotive DC56D+Z products has been optimized. Through reasonable control of smelting, hot rolling, pickling, and hot-dip galvanizing processes, a low yield strength ratio galvanized ultra-deep drawing steel DC56D+Z for automotive applications has been developed. Summary of the Invention

[0003] The purpose of this invention is to provide a production method for low yield strength ratio galvanized ultra-deep drawing steel DC56D+Z for automobiles. This method involves adding a certain amount of Ti to ultra-low carbon steel to fix the interstitial C and N atoms in the steel matrix, and through optimized processes, obtaining interstitial atom-free IF steel, thus improving the deep drawing performance of the steel. The mechanical properties of the produced dedicated DC56D+Z steel strip all meet user requirements: yield strength 130-170MPa, tensile strength 260-330MPa, and elongation after fracture A... 80mm ≥41%, r 90 ≥2.1, n 90 ≥0.21, the product yield strength ratio reaches 0.47-0.49.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a method for producing DC56D+Z, a low yield strength ratio galvanized ultra-deep drawing steel for automobiles, comprising:

[0006] Steelmaking process: molten iron—converter smelting—RH refining—slab continuous casting;

[0007] Hot rolling process: slab 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 flow cooling → coiling; wherein, the slab is heated in the furnace at a controlled temperature of 1160-1200℃; heating time of 160-230min; homogenization temperature of 1170-1200℃; homogenization time of 25-56min; furnace exit temperature of 1170-1200℃; the roughing mode adopts 3+5; the finishing temperature range is controlled at 890-950℃ and the coiling temperature range is 700-740℃ during the hot rolling stage, and a pre-dispersed cooling method is selected;

[0008] Pickling and rolling process: pickling and uncoiling → welding → tension leveling → pickling → rinsing → drying → edge trimming → continuous rolling mill cold rolling → slitting → coiling; the reduction rate of steel strip in the pickling and rolling stage is 67-82%, and the pickling and rolling reduction rate of the test steel strip reaches 80%;

[0009] Hot-dip galvanizing process: hot-dip galvanizing uncoiling → welding → inlet looper → cleaning → annealing furnace → zinc pot → post-galvanizing cooling → water quenching → intermediate looper → finishing machine → straightening machine → roller coating machine → dryer → air cooling device → outlet looper → edge trimming → surface inspection → oiling → sampling → coiling; wherein, the heating and soaking zone outlet temperature of the annealing process is controlled at 810-850℃, and the elongation of the finishing machine is 0.70-0.80%;

[0010] The chemical composition of the galvanized ultra-deep drawing steel DC56D+Z, by weight percentage, is as follows: C≤0.0020wt%, Si≤0.010wt%, Mn:0.08-0.15wt%, P≤0.015wt%, S≤0.010wt%, Alt:0.020-0.055wt%, Ti:0.055-0.070wt%, N≤0.0030wt%, with the remainder being Fe and unavoidable impurities.

[0011] Furthermore, the thickness of the cast billet is 230 mm.

[0012] Furthermore, the internal microstructure of the galvanized ultra-deep drawing steel strip DC56D+Z is ferrite.

[0013] Furthermore, the ferrite structure has a grain size of 8-9.

[0014] Furthermore, the mechanical properties of the low yield strength ratio automotive galvanized ultra-deep drawing steel DC56D+Z all meet the following requirements: yield strength 130-170MPa, tensile strength 260-330MPa, and elongation after fracture A. 80mm ≥41%, r 90 ≥2.1, n 90 ≥0.21, the product yield strength ratio reaches 0.47-0.49.

[0015] Furthermore, the chemical composition of the galvanized ultra-deep drawing steel DC56D+Z, by weight percentage, is as follows: C: 0.0017wt%, Si: 0.003wt%, Mn: 0.13wt%, P: 0.011wt%, S: 0.009wt%, Alt: 0.038wt%, Ti: 0.068wt%, N: 0.0015wt%, with the remainder being Fe and unavoidable impurities.

[0016] Furthermore, the chemical composition of the galvanized ultra-deep drawing steel DC56D+Z, by mass percentage, is as follows: C: 0.0016wt%, Si: 0.002wt%, Mn: 0.11wt%, P: 0.008wt%, S: 0.008wt%, Alt: 0.046wt%, Ti: 0.061wt%, N: 0.0015wt%, with the remainder being Fe and unavoidable impurities.

[0017] Furthermore, the chemical composition of the galvanized ultra-deep drawing steel DC56D+Z, by mass percentage, is as follows: C: 0.0014wt%, Si: 0.002wt%, Mn: 0.11wt%, P: 0.006wt%, S: 0.008wt%, Alt: 0.038wt%, Ti: 0.062wt%, N: 0.0025wt%, with the remainder being Fe and unavoidable impurities.

[0018] Furthermore, the chemical composition of the galvanized ultra-deep drawing steel DC56D+Z, by mass percentage, is as follows: C: 0.0020wt%, Si: 0.004wt%, Mn: 0.14wt%, P: 0.001wt%, S: 0.010wt%, Alt: 0.047wt%, Ti: 0.067wt%, N: 0.0013wt%, with the remainder being Fe and unavoidable impurities.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0020] This invention, to ensure that the produced DC56D+Z steel strip possesses low yield strength and good plasticity, strictly controls the C and N atomic content in the steel and uses Ti alloying element to coordinate with C and N elements, eliminating interstitial atoms in the steel, thus making the DC56D+Z steel strip age-free and achieving product performance stability. It also optimizes metallurgical process parameters and controls the C and P element content in the steel. By controlling the hot rolling, pickling, and hot-dip galvanizing annealing processes, the steel strip achieves a low yield strength, resulting in a low yield-to-tensile strength ratio in the finished steel coil. For complex automotive parts, products with a low yield-to-tensile strength ratio and low yield strength have a mitigating effect on cracking during the stamping process of complex parts such as rear wheel arch panels and side panel panels. Lower yield strength facilitates metal flow during the forming process. The product's mechanical properties all meet the following requirements: yield strength 130-170MPa, tensile strength 260-330MPa, and elongation after fracture A. 80mm ≥41%, r 90 ≥2.1, n 90 ≥0.21, the product yield strength ratio reaches 0.47-0.49. Attached Figure Description

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

[0022] Figure 1 The metallographic structure of the finished product in Example 1. Detailed Implementation

[0023] In response to users' actual needs for low yield strength galvanized ultra-deep drawing steel DC56D+Z, this invention provides a low yield strength ratio galvanized ultra-deep drawing steel DC56D+Z for automobiles and its production method.

[0024] include:

[0025] 1. Smelting process

[0026] 1.1 Desulfurization pretreatment: KR hot metal desulfurization technology is adopted. It is required that the sulfur content at the end point after deep desulfurization is within 0.002%. KR desulfurization is carried out by mechanical stirring. After desulfurization, the desulfurization slag is completely removed. The area of ​​hot metal slag removal is required to be greater than 95% to prevent high sulfur slag from being added into the converter and causing sulfur reversion.

[0027] 1.2 Converter Smelting: After desulfurization pretreatment, molten iron is smelted in a converter. The phosphorus content of the molten iron entering the converter is ≤0.050%. Oxygen blowing is used for decarburization and temperature rise, and the P and S content is controlled to prevent over-oxidation of the molten steel. The final temperature of the converter is controlled above 1660℃. Steel must be tapped using a reusable ladle, and the temperature drop at tapping must be less than 70℃. During the tapping process, quicklime and modifiers are added to modify the top slag.

[0028] 1.3 Refining: The RH refining furnace performs decarburization treatment based on the composition and temperature of the molten steel. After decarburization, deoxidizer and aluminum are added according to the oxygen content. After circulating for more than 3 minutes, alloys such as ferrotitanium and ferromanganese are added to adjust the composition. The pure degassing time is guaranteed to be more than 6 minutes to ensure the uniformity of the temperature and composition of the molten steel, and at the same time, it is conducive to the flotation of inclusions in the molten steel, thereby improving the cleanliness of the molten steel.

[0029] 1.4 Continuous Casting: Continuous casting is a protective process to prevent secondary oxidation of the molten steel and to avoid secondary oxidation of the steel quality. A constant casting speed is adopted, controlled at 1.0-1.8 m / min, and the superheat is controlled appropriately during casting, maintaining a superheat of approximately 20-45℃ to promote the flotation of inclusions and enabling multi-furnace casting.

[0030] 2. Hot rolling process

[0031] The billet is heated by a walking beam furnace (heating process is shown in Table 1). The roughing rolling adopts a double-stand R1 and R2 reciprocating rolling process with a 3+5 roughing mode. The finishing rolling adopts a continuous rolling process of F1-F7 with a finishing rolling temperature of 890-950℃ to ensure rolling in the single-phase austenite region. The coiling temperature is 700-740℃ to ensure normal precipitation of carbonitrides and improve deep drawing performance. The specific hot rolling process is shown in Table 2.

[0032] Table 1 Heating Regime for Cast Billets

[0033]

[0034] Table 2 Rolling Process

[0035]

[0036] 3. Pickling and rolling process

[0037] The reduction rate of steel strip during the pickling and rolling stage ranged from 67% to 82%, and the pickling and rolling reduction rate of the test steel strip reached 80%.

[0038] 4. Hot-dip galvanizing process

[0039] Annealing is performed in a vertical continuous annealing furnace, with a reducing atmosphere and a nitrogen-hydrogen mixed protective atmosphere used for cooling. The temperature range of the heating and soaking sections is 810-850℃ to ensure complete recrystallization of the grains. See Table 3 for the specific hot-dip galvanizing process.

[0040] Table 3 Hot-dip galvanizing process

[0041]

[0042] The present invention will be described in detail below through specific embodiments. These embodiments are only intended to help understand the present invention and do not limit the scope of the present invention.

[0043] Example

[0044] 1. Based on the above steelmaking process requirements, the actual chemical composition (mass percentage) of the slab is shown in Table 4 below.

[0045] Table 4. Chemical composition (wt.%) of examples

[0046]

[0047] 2. According to the above hot rolling process requirements, the hot rolling thickness is 3.5mm. The actual process is shown in Table 5.

[0048] Table 5 Hot Rolling Process

[0049]

[0050] 3. According to the above hot-dip galvanizing process requirements, the finished product thickness is 0.7mm. The actual process is shown in Table 6.

[0051] Table 6 Hot-dip galvanizing process

[0052]

[0053] 4. The room temperature tensile mechanical properties of representative steel strip products obtained through the above process are shown in Table 7. The test methods refer to GB / T 228.1. The microstructure of the finished product is equiaxed ferrite with a grain size of 8.0-9.0. The microstructure morphology is shown in Table 7. Figure 1 .

[0054] Table 7. Tensile mechanical properties of finished products at room temperature

[0055]

[0056] In summary, the product obtained through this process meets all performance requirements after performance testing, has suitable strength, and a low yield strength ratio, making it suitable for widespread use.

[0057] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing a zinc-coated super deep drawing steel DC56D+Z for low yield ratio automotive vehicles, characterized in that, include: Steelmaking process: molten iron—converter smelting—RH refining—slab continuous casting; Hot rolling process: slab 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 flow cooling → coiling; wherein, the slab is heated in the furnace at a controlled temperature of 1160-1200℃; heating time of 160-230min; homogenization temperature of 1170-1200℃; homogenization time of 25-56min; furnace exit temperature of 1170-1200℃; the roughing mode adopts 3+5; the finishing temperature range is controlled at 890-950℃ and the coiling temperature range is 700-740℃ during the hot rolling stage, and a pre-dispersed cooling method is selected; Pickling and rolling process: pickling and uncoiling → welding → tension leveling → pickling → rinsing → drying → edge trimming → continuous rolling mill cold rolling → slitting → coiling; the reduction rate of steel strip in the pickling and rolling stage is 67-82%, and the pickling and rolling reduction rate of the test steel strip reaches 80%; Hot-dip galvanizing process: hot-dip galvanizing uncoiling → welding → inlet looper → cleaning → annealing furnace → zinc pot → post-galvanizing cooling → water quenching → intermediate looper → finishing machine → straightening machine → roller coating machine → dryer → air cooling device → outlet looper → edge trimming → surface inspection → oiling → sampling → coiling; wherein, the heating and soaking zone outlet temperature of the annealing process is controlled at 810-850℃, and the elongation of the finishing machine is 0.70-0.80%; The chemical composition of the galvanized ultra-deep drawing steel DC56D+Z, by weight percentage, is as follows: C≤0.0020wt%, Si≤0.010wt%, Mn:0.08-0.15wt%, P≤0.015wt%, S≤0.010wt%, Alt:0.020-0.055wt%, Ti:0.055-0.070wt%, N≤0.0030wt%, with the remainder being Fe and unavoidable impurities.

2. Process for the production of a low yield ratio zinc-coated super deep drawing steel DC56D+Z for automotive applications according to claim 1, characterized in that, The thickness of the cast billet is 230mm.

3. Process for the production of a low yield ratio zinc-coated super deep drawing steel DC56D+Z for automotive applications according to claim 1, characterized in that, The internal microstructure of the galvanized ultra-deep drawing steel strip DC56D+Z is ferrite.

4. Process for the production of a low yield ratio zinc-coated super deep drawing steel DC56D+Z for automotive applications according to claim 3, characterized in that, The ferrite structure has a grain size of 8-9.

5. A method of manufacturing a low yield ratio zinc-coated super deep drawing steel DC56D+Z for automobiles according to claim 1, characterized in that, The mechanical properties of the low yield strength ratio automotive galvanized ultra-deep drawing steel DC56D+Z all meet the following requirements: yield strength 130-170MPa, tensile strength 260-330MPa, elongation after fracture A 80mm ≥41%, r 90 ≥2.1, n 90 ≥0.21, the product yield strength ratio reaches 0.47-0.

49.

6. The production method of DC56D+Z galvanized ultra-deep drawing steel for automobiles with low yield strength ratio according to claim 1, characterized in that, The chemical composition of the galvanized ultra-deep drawing steel DC56D+Z, by weight percentage, is as follows: C: 0.0017wt%, Si: 0.003wt%, Mn: 0.13wt%, P: 0.011wt%, S: 0.009wt%, Alt: 0.038wt%, Ti: 0.068wt%, N: 0.0015wt%, with the remainder being Fe and unavoidable impurities.

7. A method of manufacturing a low yield ratio zinc-coated super deep drawing steel DC56D+Z for automobiles according to claim 1, characterized in that, The chemical composition of the galvanized ultra-deep drawing steel DC56D+Z, by weight percentage, is as follows: C: 0.0016wt%, Si: 0.002wt%, Mn: 0.11wt%, P: 0.008wt%, S: 0.008wt%, Alt: 0.046wt%, Ti: 0.061wt%, N: 0.0015wt%, with the remainder being Fe and unavoidable impurities.

8. The production method of low yield strength ratio galvanized ultra-deep drawing steel DC56D+Z for automobiles, as described in claim 1, is characterized in that, The chemical composition of the galvanized ultra-deep drawing steel DC56D+Z, by weight percentage, is as follows: C: 0.0014wt%, Si: 0.002wt%, Mn: 0.11wt%, P: 0.006wt%, S: 0.008wt%, Alt: 0.038wt%, Ti: 0.062wt%, N: 0.0025wt%, with the remainder being Fe and unavoidable impurities.

9. A method of manufacturing a low yield ratio zinc-coated super deep drawing steel DC56D+Z for automobiles according to claim 1, characterized in that, The chemical composition of the galvanized ultra-deep drawing steel DC56D+Z, by weight percentage, is as follows: C: 0.0020wt%, Si: 0.004wt%, Mn: 0.14wt%, P: 0.012wt%, S: 0.010wt%, Alt: 0.047wt%, Ti: 0.067wt%, N: 0.0013wt%, with the remainder being Fe and unavoidable impurities.

Images