Production method of rare earth zinc-plated phosphorus-added steel adapting to low-temperature environment service

Abstract

The invention discloses a production method of rare earth galvanized phosphorized steel adapting to low-temperature environment service. The production method comprises the following steps: a steelmaking process: KR desulfurization, converter treatment, RH (Ruhrstahl Heraeus) refining and slab continuous casting; in the hot rolling process, the heating temperature of a plate blank is 1180-1220 DEG C, the finish rolling temperature of finish rolling is greater than or equal to 900 DEG C, and the coiling temperature is 690-720 DEG C; acid rolling process; according to the galvanization process, the outlet temperature of a galvanization annealing and / or soaking section is 800-840 DEG C, the outlet temperature of a slow cooling section and the ductility of a temper mill are 0.9-1.20%, the ductility of a withdrawal and straightening machine is smaller than or equal to 0.06%, the production line speed is 90-130 m / min, and the temperature of a zinc pot is controlled to be 460 + / -10 DEG C. The material disclosed by the invention can meet the requirement of stamping automobile fender parts in a cold environment (-40 DEG C) in northern areas, and has the advantages of low yield ratio (less than 0.6), high corrosion resistance, excellent forming performance and good flatness.

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 rare earth galvanized and phosphorus-coated steel suitable for service in low temperature environment. Background Art

[0002] In recent years, with the rise of many domestic enterprises, China's automobile sales market has ushered in fierce competition. Automobiles are no longer a simple means of transportation. Users pay more attention to beauty, comfort and energy saving, and the demand for steel for complex deformed parts has increased. For this reason, in addition to technical upgrades, automobile production also uses materials that are constantly changing. The lowest temperature in the north can reach more than -30 degrees Celsius in winter. In this way, materials are prone to brittle fracture during stamping of automobile parts in low temperature environments, resulting in an increase in the cracking ratio, affecting the production efficiency and qualified rate of users. In order to meet the needs of users for large deformation stamping in low temperature environments, rare earth galvanized phosphorus-reinforced steel has been developed. The demand for 180MPa grade phosphorus-reinforced steel for appearance parts on the market is the largest. There is no production experience in China for 180MPa grade rare earth phosphorus-reinforced steel, which is a blank product. Rare earth phosphorus-reinforced steel can meet the requirements of stamping in extremely cold areas. It has a low yield strength ratio (yield strength ratio is less than 0.6), high corrosion resistance, excellent forming performance and good flatness, and is favored by the majority of users. In order to achieve the above indicators, we at Baosteel have carried out research on the metallurgical process route for 180MPa grade rare earth galvanized automotive steel.

[0003] The existing literature and patent research are as follows:

[0004] The search patent "A method for reducing the yield ratio of thick-gauge phosphorus-reinforced steel 250P1" describes a method for reducing the yield ratio of thick-gauge 250P1 phosphorus-reinforced steel. The strength level written in this patent is 250MPa, and the yield ratio is controlled below 0.7. No rare earth elements are added in the design of the chemical composition. This patent studies the strength level of 180MPa, and the yield ratio is controlled below 0.6.

[0005] Search patent "A 170MPa grade cold-rolled phosphorus-added IF high-strength steel and its production method", the present invention discloses a 170MPa grade cold-rolled phosphorus-added IF high-strength steel, the chemical composition weight percentage C≤0.004%; Si≤0.03%; Mn: 0.50-0.60Wt%; P: 0.050-0.065%; S≤0.01%; Als: 0.030-0.050%; Ti: 0.01-0.10%; the rest is iron and inevitable trace elements. The process flow is: blast furnace molten iron smelting → converter molten steel smelting → LF molten steel refining treatment → RH molten steel refining treatment → CSP thin slab continuous casting and rolling → pickling cold rolling → bell furnace annealing → leveling → inspection packaging and storage. The present invention follows the LF-RH process, which is obviously different from other conventional production methods, and has the advantages of short production cycle, low production cost and stable quality. This patent mainly studies cold-rolled annealing products, and the production process is different from this patent, and the component control is also different. Summary of the invention

[0006] The purpose of the present invention is to provide a method for producing rare earth galvanized phosphorus steel suitable for service in low temperature environments. The material of the invention can meet the requirements of stamping automobile fender parts in the cold environment (-40°C) in northern regions, and has a low yield strength ratio (yield strength ratio is less than 0.6), high corrosion resistance, excellent forming performance and good flatness.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for producing rare earth zinc-plated phosphorus-added steel suitable for service in low temperature environments, comprising:

[0009] Steelmaking process: KR desulfurization → converter → RH refining → slab continuous casting;

[0010] Its chemical composition by mass percentage satisfies: C≤0.003%, Si≤0.12, 0.3%≤Mn≤0.7%, 0.02%≤P≤0.060%, S≤0.015%, Alt≥0.020%, B≥0.0004% N≤0.0040%, 0.030%≤T i≤0.060%, 0.020%≤Nb≤0.040%, 0.0005%≤Ce≤0.0050%, and the rest is Fe and unavoidable impurities;

[0011] Hot rolling process: heating furnace → rough rolling high-pressure water descaling machine → fixed width press → E1 R1 rough rolling mill → E2R2 rough rolling mill → insulation cover → flying shear → finishing high-pressure water descaling machine → F1-F7 finishing mill → encrypted laminar cooling → coiler; where: slab heating temperature is 1180-1220℃, finishing rolling temperature ≥900℃, coiling temperature is 690-720℃;

[0012] Pickling process: Pickling uncoiling → welding → straightening → pickling → rinsing → drying → trimming → rolling → coiler → pickling reduction rate ≥ 70%;

[0013] Galvanizing process: hot-dip galvanizing uncoiling → welding → entrance looper → cleaning → annealing furnace → zinc pot → cooling after plating → water quenching → intermediate looper → skin pass machine → straightening machine → roller coater → dryer → air cooling device → exit looper → trimming → surface inspection → oiling → sampling → coiling; Among them: galvanizing annealing heating / soaking section outlet temperature 800-840℃, slow cooling section outlet temperature, skin pass machine elongation 0.9-1.20%, tension straightening machine elongation ≤0.06%, production line speed 90-130m / min, zinc pot temperature control 460±10℃.

[0014] Furthermore, the finished product performance meets the following requirements: yield strength is controlled at 200-215MPa, tensile strength is controlled at 370-380MPa, elongation reaches 36%-40%, r value is 2.16-2.3, n value is 0.21-0.22, and yield strength ratio is 0.50-0.57.

[0015] Furthermore, the prepared rare earth galvanized phosphorus steel adapted to low temperature environment also has excellent corrosion resistance, so that the product meets the processing requirements of automobile fenders.

[0016] Furthermore, the KR desulfurization process requires that the sulfur content of the molten iron entering the converter is less than 0.002%, and the slag cleaning area of ​​the molten iron is greater than 95%.

[0017] Furthermore, the converter smelting process: the converter endpoint control requirements: the steel tapping temperature is ≥1660℃, the normal turnover ladle is used for tapping, and the steel tapping temperature drop requirement is less than 70℃; lime and modifiers are added during the converter tapping process to modify the top slag.

[0018] Further, the RH furnace is subjected to vacuum deep decarburization treatment, and phosphorus iron alloy is added to adjust the composition to the target range. After the RH vacuum decarburization is completed, aluminum particles are added for deoxidation alloying. After a 3-minute cycle, ferrosilicon, ferromanganese, ferroniobium, ferrotitanium and ferroboron alloys are added to adjust the composition to the target range. At the end of the RH furnace vacuum treatment, 30-40 kg of rare earth ferrocerium alloy is added. After the alloy is added, the pure degassing time is ensured to be ≥ 6 minutes.

[0019] Furthermore, the continuous casting adopts constant casting speed control, and the casting speed range is 1.0-1.8m / min.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are:

[0021] The present invention is designed and developed from the whole process of chemical composition, smelting, hot rolling, cold rolling and hot-dip galvanizing, and the development process is explained in a relatively systematic and perfect manner. Not only is the production cost low, but it also meets the international ROSH and Reach environmental protection requirements. For the 0.8mm thickness specification, the yield strength is controlled at 200-215MPa, the tensile strength is controlled at 370-380MPa, the elongation reaches 36%-40%, the r value is 2.16-2.3, the n value is 0.21-0.22, and the yield strength ratio is 0.50-0.57.

[0022] According to the chemical composition, hot rolling process, acid rolling process and galvanizing process of the present invention, a steel strip having good mechanical property stability, good corrosion resistance and other indicators and meeting excellent stamping forming performance indicators in a low temperature environment can be manufactured. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the accompanying drawings.

[0024] Figure 1 Metallographic structure of the product;

[0025] Figure 2 For salt spray corrosion photos;

[0026] Figure 3 For the fender. DETAILED DESCRIPTION

[0027] A method for producing rare earth zinc-plated phosphorus-added steel suitable for service in low temperature environments, specifically comprising:

[0028] 1Smelting process

[0029] KR desulfurization process: The sulfur content of the molten iron entering the converter is required to be less than 0.002%, and the slag removal area of ​​the molten iron is greater than 95% (the surface of the molten iron is cleaner after slag removal).

[0030] Converter smelting process: converter endpoint control requirements: tapping temperature ≥ 1660℃, use normal turnover ladle to tap steel, tapping temperature drop requirement is less than 70℃. Add lime and modifier to modify the top slag during converter tapping.

[0031] RH process:

[0032] The RH furnace is used for deep vacuum decarburization, and phosphorus iron alloy is added to adjust the composition to the target range. After the RH vacuum decarburization is completed, aluminum particles are added for deoxidation and alloying. After a 3-minute cycle, ferrosilicon, ferromanganese, ferroniobium, ferrotitanium and ferroboron alloys are added to adjust the composition to the target range. At the end of the RH furnace vacuum treatment, 30-40 kg of rare earth ferrocerium alloy is added. After the alloy is added, the pure degassing time is ensured to be ≥ 6 minutes.

[0033] Continuous casting process: The casting machine adopts constant casting speed control, and the casting speed range is 1.0-1.8m / min;

[0034] 2 Hot rolling process

[0035] The ingot was heated in a walking beam heating furnace (the heating process is shown in Table 1), the rough rolling adopted the 3+3 mode, the finishing rolling adopted F1-F7 continuous rolling, the cooling method was front concentrated, the finishing rolling mill was F2-F4, the roll gap lubrication opening amount was controlled at 140-180 ml / min, the inter-stand cooling water was turned on F1 and F2, and the water volume was set to 50%. The specific hot rolling process is shown in Table 2.

[0036] Table 1 Billet heating system

[0037]

[0038] Table 2 Rolling process

[0039]

[0040] 3Galvanizing process

[0041] The outlet temperature control of each section of the galvanizing annealing furnace is shown in Table 3. The elongation settings of the leveling machine and the tension leveling machine are shown in Table 4. At the same time, the tension before and after the leveling machine is controlled at 40-50KN.

[0042] Table 3 Galvanizing annealing process

[0043]

[0044] Table 4 Leveling machine and tension leveling machine process

[0045]

[0046] (6) Example Analysis

[0047] 1 Steelmaking ingredients

[0048] According to the above steelmaking process requirements, the actual slab chemical composition (mass percentage) is shown in Table 5.

[0049] Table 5 Chemical composition of examples wt.%

[0050]

[0051] 2. Finished product performance

[0052] 2.1 Mechanical properties

[0053] The room temperature tensile mechanical properties of the finished product of 0.8 mm are shown in Table 6. The yield and tensile strength of the product are stable, and the yield strength ratio is small. The fluctuation range of the product manufactured by the rare earth phosphorus steel with a thickness of 0.8 mm according to the present invention can be controlled within 15 MPa. Stable product performance and low yield strength ratio are important factors for product stamping and meet the requirements of product stamping under harsh environmental conditions.

[0054] Table 6 Tensile mechanical properties of finished products

[0055]

[0056] 2.2 Metallographic structure

[0057] The metallographic structure is ferrite, the grains are small and uniform, and the structure morphology is Figure 1 .

[0058] 2.3 Salt spray corrosion

[0059] After 72 hours of corrosion, the product has no red rust or other defects on the surface, meeting the user's requirements. Figure 2 .

[0060] 2.4 Usage

[0061] The products manufactured according to the present invention can be processed by users in cold regions such as fender parts. Figure 3 As shown, the stamping condition is good and meets the user's requirements.

[0062] In summary, the performance indicators and formability of this product meet the user's requirements and have been supplied in batches.

[0063] 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 method for producing rare earth galvanized and phosphorus-coated steel suitable for low temperature environment, characterized in that: include: Steelmaking process: KR desulfurization → converter → RH refining → slab continuous casting; Its chemical composition by mass percentage satisfies: C≤0.003%, Si≤0.12, 0.3%≤Mn≤0.7%, 0.02%≤P≤0.060%, S≤0.015%, Alt≥0.020%, B≥0.0004%N≤0.0040%, 0.030%≤Ti≤0.060%, 0.020%≤Nb≤0.040%, 0.0005%≤Ce≤0.0050%, and the rest is Fe and unavoidable impurities; Hot rolling process: heating furnace → rough rolling high-pressure water descaling machine → fixed width press → E1R1 rough rolling mill → E2R2 rough rolling mill → insulation cover → flying shear → finishing rolling high-pressure water descaling machine → F1-F7 finishing mill → encrypted laminar cooling → coiler; where: slab heating temperature is 1180-1220℃, finishing rolling temperature ≥900℃, coiling temperature is 690-720℃; Pickling process: Pickling uncoiling → welding → straightening → pickling → rinsing → drying → trimming → rolling → coiler → pickling reduction rate ≥ 70%; Galvanizing process: hot-dip galvanizing uncoiling → welding → entrance looper → cleaning → annealing furnace → zinc pot → cooling after plating → water quenching → intermediate looper → skin pass machine → straightening machine → roller coater → dryer → air cooling device → exit looper → trimming → surface inspection → oiling → sampling → coiling; Among them: galvanizing annealing heating / soaking section outlet temperature 800-840℃, slow cooling section outlet temperature, skin pass machine elongation 0.9-1.20%, tension straightening machine elongation ≤0.06%, production line speed 90-130m / min, zinc pot temperature control 460±10℃.

2. The method for producing rare earth galvanized and phosphorus-coated steel suitable for low temperature environment according to claim 1, characterized in that: The finished product performance is achieved: the yield strength is controlled at 200-215MPa, the tensile strength is controlled at 370-380MPa, the elongation reaches 36%-40%, the r value is 2.16-2.3, the n value is 0.21-0.22, and the yield strength ratio is 0.50-0.

57.

3. The method for producing rare earth galvanized and phosphorus-coated steel suitable for low temperature environment according to claim 1, characterized in that: The prepared rare earth galvanized phosphorus steel adapted to low temperature environment also has excellent corrosion resistance, so that the product meets the processing requirements of automobile fenders.

4. The method for producing rare earth galvanized and phosphorus-coated steel suitable for service in low temperature environment according to claim 1, characterized in that: KR desulfurization process: The sulfur content of molten iron entering the converter is required to be less than 0.002%, and the slag cleaning area of ​​molten iron is required to be greater than 95%.

5. The method for producing rare earth galvanized and phosphorus-coated steel suitable for low temperature environment according to claim 1, characterized in that: Converter smelting process: Converter endpoint control requirements: steel tapping temperature ≥ 1660℃, use normal turnover ladle to tap steel, and the tapping temperature drop requirement is less than 70℃; lime and modifier are added during the converter tapping process to modify the top slag.

6. The method for producing rare earth galvanized and phosphorus-coated steel suitable for service in low temperature environment according to claim 1, characterized in that: The RH furnace is used for deep vacuum decarburization, and phosphorus iron alloy is added to adjust the composition to the target range. After the RH vacuum decarburization is completed, aluminum particles are added for deoxidation and alloying. After a 3-minute cycle, ferrosilicon, ferromanganese, ferroniobium, ferrotitanium and ferroboron alloy are added to adjust the composition to the target range. At the end of the RH furnace vacuum treatment, 30-40 kg of rare earth ferrocerium alloy is added. After the alloy is added, the pure degassing time is ensured to be ≥ 6 minutes.

7. The method for producing rare earth galvanized and phosphorus-coated steel suitable for low temperature environment according to claim 1, characterized in that: Continuous casting adopts constant casting speed control, and the casting speed range is 1.0-1.8m / min.

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