Steel for aluminum formwork pull tabs in construction engineering and production method thereof

Abstract

The present invention relates to the field of metallurgical technology, and in particular to a steel for aluminum formwork tabs for construction projects and a production method. The raw material of the aluminum formwork tab is selected from medium carbon steel, and the mass percentage content of its chemical components includes: C: 0.52-0.58%; Si: 0.17-0.20%; Mn: 0.80-0.95%; Cr: 0.14-0.20%; P≤0.030%; S≤0.030; the remainder is Fe. The production method comprises the following steps: selecting a steel type that meets the chemical composition requirements → stack cooling continuous casting billet → continuous casting billet heating → furnace back high-pressure water descaling → rough rolling and rough descaling → finishing rolling, finishing descaling and finishing descaling head → laminar cooling → coiling → stack cooling → mechanical shelling → pickling → cleaning, rinsing → passivation → cold rolling → trimming → coiling. The steel for aluminum formwork tabs for construction projects provided by the present invention has good forging and punching performance, and fully meets the quality requirements of steel for aluminum formwork tabs for construction projects.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to steel for aluminum template pull tabs for construction engineering and a production method thereof. Background Art

[0002] With the rapid development of my country's construction industry, the pull-tab aluminum alloy formwork system has gradually replaced the traditional wooden formwork system and has been used more and more widely. The system has good overall safety, simple construction, high precision of formwork materials and finished products, high quality, and a large number of turnovers. It has obvious advantages in reducing resource consumption and environmental protection. The pull-tab aluminum alloy formwork system has greatly improved the overall construction level of construction projects, innovated the construction process of residential buildings, and played an important role in standardizing the construction process and promoting the healthy development of the construction industry.

[0003] The aluminum formwork tab is a thin steel sheet with a thickness of 2.0mm or less, and its length is determined by the thickness of the wall column. During concrete construction, the aluminum formwork on both sides can be tightly "pulled" to prevent the formwork from expanding or exploding during construction, thus ensuring the quality of construction. After the concrete solidifies, the aluminum formwork on the wall is removed, and the tab is left in the concrete, with both ends extending out of the wall. After all the aluminum formwork is removed, the extended part of the tab is broken. The tab is designed with a V-shaped structure for stress concentration, and the break is 5mm inside the wall, so there is no need to worry about the impact on subsequent decoration processes.

[0004] The construction industry standard JG / T 522-2017 "Aluminum Alloy Formwork" does not specify the material to be used for aluminum formwork tabs. It only gives examples of Q235, Q355B, and 45 steel bells, but they must meet their use requirements. At present, aluminum alloy formworks are widely used in China, but there are few reports and studies on the production methods of steel for aluminum formwork tabs, and no unified specifications have been formed. As a result, the mechanical properties of steel for aluminum formwork tabs vary greatly, and there are sometimes cracks of varying sizes on the edges, fractures due to forging and punching, and the extended part of the tab is not easy to break. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a method for producing steel for aluminum formwork tabs for construction projects. The steel for aluminum formwork tabs for construction projects provided by the present invention has good forging and punching properties and fully meets the quality requirements for steel for aluminum formwork tabs for construction projects.

[0006] The technical solution adopted by the present invention to solve the technical problems existing in the known technology is:

[0007] The primary purpose of the present invention is to provide a steel for aluminum formwork pull tabs in construction projects. The raw material of the aluminum formwork pull tab is medium carbon steel, and the chemical components thereof, measured by mass percentage, include: C: 0.52-0.58%; Si: 0.17-0.20%; Mn: 0.80-0.95%; Cr: 0.14-0.20%; P≤0.030%; S≤0.030; and the balance is Fe.

[0008] The present invention selects medium carbon steel because it has high tensile strength. The higher the Si content, the greater the viscosity of the iron oxide scale, and the worse the descaling property of the iron oxide scale. Therefore, the added Si content should take into account the viscosity of the iron oxide scale and the descaling property of the iron oxide scale. A certain amount of Si element is added to the steel, and after high temperature heating, Si atoms, O atoms, and Fe ions undergo a series of complex reactions to generate Fe 2 SiO 4 , the oxide layer structure is FeO and Fe 2 SiO 4 The mixed liquid phase of the iron oxide scale will pin the scale, increase the adhesion of the scale, and make it difficult to remove it completely during subsequent descaling, resulting in scale indentation defects in the finished product. Therefore, when designing the chemical composition of the steel grade, in order to improve the stripping properties of the primary and secondary scales, the method of reducing the Si content is used to reduce the liquid Fe 2 SiO 4 Generation of.

[0009] In addition, the Cr element has an oxidation-inhibiting effect. Cr forms Cr at the interface between the iron oxide scale and the iron matrix. 2 O 3 and FeCr 2 O 4 Protective oxidation products slow down the diffusion rate of Fe and O elements, thereby achieving the purpose of inhibiting oxidation. Therefore, the present invention adopts the method of increasing the Cr content to increase the hardenability, thereby reducing the pearlite lamellar spacing and improving the tensile strength.

[0010] Another object of the present invention is to provide a method for producing steel for aluminum formwork pull tabs for construction engineering, comprising the following steps:

[0011] S1. Select steel grades that meet the chemical composition requirements;

[0012] S2. Pile cooling continuous casting billet: The continuous casting billet is pile cooled to room temperature by offline pile cooling method; this step can promote the release of hydrogen in the steel and avoid defects such as cracks caused by hot delivery of the continuous casting billet;

[0013] S3, sending the continuous casting billet cooled to room temperature in S2 into a heating furnace for heating; the temperature of the heating section is 1100-1200° C., the temperature of the soaking section is 1200-1250° C., and the heating time is 90-120 min;

[0014] S4. Post-furnace high-pressure water descaling: descaling pressure ≥ 16MPa, the iron oxide scale can be effectively removed in one step;

[0015] S5, rough rolling and rough descaling; the rough rolling adopts the full continuous rolling method, including 8 continuous rolling, 1 rolling per pass, and the single pass reduction rate of rough rolling and flat rolling is 15-40%; after rolling, high-pressure water descaling is used, and the descaling pressure is ≥15MPa to remove the secondary iron oxide scale;

[0016] S6, finishing rolling, finishing descaling and finishing descaling and head clearance; finishing rolling adopts a full continuous rolling method, including 11 continuous rolling passes, 1 rolling per pass, and the directions of the rollers are arranged as follows: 1 vertical-1 flat-2 flat-2 vertical-3 flat-4 flat-5 flat-6 flat-7 flat-8 flat-9 flat; conventional hot-rolled strip finishing rolling is generally 1 vertical + 7 flat for a total of 8 passes, or there is no vertical rolling, only 7 flat rolling passes. The present invention has 2 vertical rolling passes and 9 flat rolling passes, which can more accurately control the width of the strip, reduce the burden of width control in finishing rolling, and reduce edge defects. The flat rolling deformation is distributed in 9 passes, which can further reduce the motor load, the deformation is more uniform, the finishing speed can be increased, and the output is increased. After 1 vertical rolling, high-pressure water is used for descaling, and the descaling pressure is ≥16MPa to remove secondary iron oxide scale; finishing descaling and head clearance;

[0017] The finishing rolling start temperature is 980-1050℃; the finishing rolling temperature is 840~890℃; the finishing rolling speed is 11.5-14.0m / s; the finishing rolling threading time is 15-18s; the finishing rolling flat rolling single pass reduction rate is 10-40%; the finishing rolling 1st and 2nd vertical rolls are rolled with vertical roll pass type, and the pass reduction is ≤20mm;

[0018] S7, laminar cooling: after finishing rolling, laminar cooling method is adopted, with fast cooling in the front section and fine adjustment in the back section, and the cooling rate is 50-80℃ / s;

[0019] S8, coiling; when coiling, turn off the cooling water of the coil in advance, and start to turn off the cooling water of the coil when the previous steel is thrown; control the coiling temperature at 600-640℃; coiling tension at 20-25kN;

[0020] S9, stack cooling: the strip is stacked and cooled for more than 24 hours after it comes off the production line, and the strip temperature is below 100℃;

[0021] S10, mechanical shell removal; using multiple bending rollers for descaling;

[0022] S11, pickling the steel strip after shell removal with hydrochloric acid;

[0023] S12. The pickled steel strip is cleaned and rinsed with condensed water; the cleaning and rinsing temperature is 60-90℃;

[0024] S13, the rinsed steel strip is passivated with a sodium nitrite aqueous solution with a mass concentration of 1-3%;

[0025] S14, cold rolling; using a single-stand rolling mill or a continuous rolling mill, rolling 4-6 times, with a total reduction rate of 39-58%;

[0026] S15, trimming;

[0027] S16, roll up.

[0028] The present invention can also be further implemented by the following measures:

[0029] In the aforementioned production method of steel for aluminum formwork pull tabs for construction projects, in the continuous casting billet heating step, the air-fuel ratio is controlled at 0.60-0.70 to reduce decarburization.

[0030] The lower the air-fuel ratio, the lower the total decarburization depth of the steel. Controlling the total decarburization depth index can improve the fatigue life of the steel. The total decarburization depth is usually required to be ≤80μm, but the present invention can achieve ≤25μm.

[0031] The aforementioned production method of steel for aluminum formwork pull tabs for construction projects, wherein the rough rolling process in S5 includes the arrangement of the roller directions: 1 vertical - 1 flat - 2 flat - 2 vertical - 3 flat - 4 flat - 3 vertical - 5 flat; the rough rolling adopts a compact full continuous rolling arrangement, and compared with ordinary 3 / 4 continuous rolling and 1 / 2 semi-continuous rolling, the rolling time is 30-60 seconds shorter. It solves the problems of large temperature drop of the steel billet and large temperature difference between the head and the tail, and correspondingly solves the problem of large fluctuations in mechanical properties, and solves the problem of easy scrapping due to low head temperature. It can also improve production efficiency and produce strip steel with longer billets and heavier coils. It can also reduce the thickness of iron oxide scale and increase the yield rate. After 1 vertical rolling, high-pressure water is used for descaling, and the descaling pressure is ≥15MPa to remove secondary iron oxide scale; for rough rolling of 1 vertical, 2 vertical, and 3 vertical, vertical roller hole rolling is used, and the reduction per pass is: ≤40mm;

[0032] The production method of the steel for aluminum formwork pull tabs in the aforementioned construction project, wherein the rough rolling start temperature in S5 is 1090-1150°C; the rough rolling final rolling speed is ≥2.0m / s; the rough rolling threading time is 35-40s; the intermediate billet travels on the intermediate roller for 39-42s; and the intermediate billet thickness is 26-30mm.

[0033] The aforementioned method for producing steel for aluminum formwork pull tabs for construction projects, wherein the head of the strip steel in S6 is descaled by passing through a descaling box for a delay of 2 seconds;

[0034] The production method of the steel for aluminum formwork pull tabs of the aforementioned construction project, wherein, after the finishing rolling F1~F9 working rolls are replaced, the rolling mileage is controlled at 50-100km.

[0035] The aforementioned production method of steel for aluminum formwork pull tabs for construction projects, wherein the mass concentration of the hydrochloric acid pickling solution in S11 is 24-26%, the pickling temperature is 60-70°C, and the pickling speed is ≤2.0m / s.

[0036] The aforementioned production method of steel for aluminum formwork pull tabs for construction projects, and the steel for aluminum formwork pull tabs for construction projects prepared by the method, have the following properties: breaking force 26-30kN, elongation after fracture ≥4.5%; plate shape: plate convexity ≥0, qualified rate 100%; edge crack rate: 0; protruding part breakage rate 100%; pickling yield rate ≥99.50%; no surface rust.

[0037] The aforementioned production method of steel for aluminum formwork pull tabs for construction projects, wherein the hot-rolled strip steel prepared by the method is an intermediate product, and the metallographic structure of the hot-rolled strip steel is as follows: F+P; the total decarburization layer depth of the hot-rolled strip steel is ≤25μm; the thickness of the oxide scale of the hot-rolled strip steel is ≤10μm; the tensile strength of the hot-rolled strip steel is ≥800MPa, and the elongation after fracture is ≥15.0%; and the quality requirements for steel for aluminum formwork pull tabs for construction projects are fully met.

[0038] The present invention has the advantages and positive effects:

[0039] 1. In terms of chemical composition design: In order to improve the peelability of primary and secondary iron oxide scales, the method of reducing Si content is adopted to reduce the liquid Fe 2 SiO 4 The generation of

[0040] The method of increasing the Cr content is used to increase the hardenability, thereby reducing the pearlite interlamellar spacing and improving the tensile strength. In addition, the Cr element has an oxidation inhibitory effect. Cr forms Cr at the interface between the iron oxide scale and the iron matrix. 2 O 3 and FeCr 2 O 4 Protective oxidation products slow down the diffusion rate of Fe and O elements, thus achieving the purpose of inhibiting oxidation;

[0041] The present invention selects medium carbon steel with high tensile strength.

[0042] 2. In order to reduce the risk of steel head wearing and roller damage during the finishing rolling process, the finishing descaling is performed at the head. At the same time, the hardness of the F6-F9 working rolls is selected to be HSD 80-85.

[0043] 3. Because the finishing rolling is not equipped with hydraulic bending roll and roll shifting device, in order to ensure that the convexity of the finished plate is positive and the plate shape meets the production of cold rolling, the rolling mileage is limited. After the finishing rolling F1-F9 working rolls are replaced, the rolling mileage is controlled at 50-100km. If the rolling mileage is less than 50km, the plate convexity is prone to negative value, and if the rolling mileage is greater than 100km, the surface quality of the strip will deteriorate.

[0044] 4. The present invention utilizes 5 passes of vertical roller pass rolling, namely 1 pass, 2 passes, and 3 passes in rough rolling and 1 pass and 2 passes in finishing rolling, which improves the stability of vertical rolling, avoids rapid cooling of the corners of the ingot, uneven deformation, cracks, and folding defects; at the same time, the vertical roller pass removes scales on the edges to reduce secondary iron oxide scale.

[0045] 5. The present invention reduces the rough rolling threading time, increases the roller speed, reduces the travel time of the intermediate billet on the intermediate roller, increases the finishing rolling speed, reduces the finishing rolling threading time, and thus reduces the oxidation of steel during rolling; increasing the rolling speed also has the characteristics of high rolling efficiency and high machine hour output.

[0046] 6. The present invention closes the reel cooling water in advance to eliminate quenching cracks caused by the chilling of the steel head.

[0047] 7. The continuous casting billet of the present invention adopts a stack cooling process to eliminate internal stress and avoid the occurrence of cracks.

[0048] 8. The finished strip steel of the present invention adopts a stack cooling process to eliminate internal stress, reduce the aging period, improve the plasticity of the steel, and stabilize the mechanical properties.

[0049] 9. The yield rate of the present invention after pickling reaches 99.50%, which is higher than the 99.0% level in the same industry.

[0050] 10. The present invention does not require annealing and leveling after cold rolling, and can be directly stamped after cold rolling, thus saving production costs.

[0051] 11. The steel for aluminum formwork pull tabs for construction projects obtained by the present invention has good forging and punching properties.

[0052] 12. The present invention adopts passivation treatment to ensure that the surface of the finished product is free of rust.

[0053] 13. The steel used for the aluminum formwork pull tab of the construction project of the present invention replaces Q355B and No. 45 steel grades. The national standard of Q355B requires a tensile strength of 470-630MPa, and the national standard of No. 45 steel grade requires a tensile strength of ≥600MPa. The tensile strength of the steel used for the aluminum formwork pull tab of the construction project of the present invention is ≥800MPa, which is higher than that of Q355B and No. 45 steel grades. While ensuring high strength, the elongation after fracture of the present invention is ≥4.5%. After all aluminum formworks are removed, the extended part of the pull tab is easy to break, which fully meets the requirements of aluminum formwork prefabrication construction. DETAILED DESCRIPTION

[0054] In order to further understand the content, features and effects of the present invention, the following embodiments are given as examples and described in detail as follows:

[0055] The invention discloses a method for producing steel for aluminum template pull tabs for construction projects, comprising the following steps: selecting a steel type that meets chemical composition requirements → stack cooling continuous casting billets → heating continuous casting billets → descaling with high-pressure water after the furnace → rough rolling and rough descaling → finishing rolling, finishing descaling and finishing descaling → laminar cooling → coiling → stack cooling → mechanical shelling → pickling → cleaning and rinsing → passivation → cold rolling → trimming → coiling.

[0056] Example 1

[0057] Step 1: Select the steel grade that meets the chemical composition requirements:

[0058] The steel used for the aluminum template pull tab is medium carbon steel, and the chemical composition, measured by mass percentage, includes the following chemical components:

[0059] Table 1 Chemical composition Unit: (%)

[0060]

[0061] Step 2: Stacking and cooling continuous casting billets:

[0062] The continuous casting billet adopts the offline stack cooling method to promote the release of hydrogen in the steel and avoid defects such as cracks caused by hot delivery of the continuous casting billet; it can only enter the heating furnace after being stack cooled to room temperature; the cross-sectional dimensions of the continuous casting billet are: width 330mm, thickness 165mm.

[0063] Step 3: Heating of continuous casting billet:

[0064] The temperature of the heating section is 1100-1200°C, the temperature of the soaking section is 1200-1250°C, and the heating time is 90-120 minutes. To reduce decarburization, the air-fuel ratio is controlled at 0.60-0.70.

[0065] Step 4: Descaling with high pressure water after the furnace:

[0066] The descaling pressure is 18MPa, and the oxidized iron scale can be effectively removed in one step.

[0067] Step 5, rough rolling and rough descaling:

[0068] The rough rolling adopts the full continuous rolling method, including 8 continuous rolling passes, 1 rolling per pass, and the roll direction is arranged as follows: 1 vertical-1 flat-2 flat-2 vertical-3 flat-4 flat-3 vertical-5 flat; high-pressure water descaling is used after 1 vertical rolling, and the descaling pressure is 16MPa to remove the secondary iron oxide scale; the rough rolling 1, 2 and 3 vertical rolls are rolled with vertical roll pass type, and the pass reduction is ≤40mm; the single pass reduction rate of rough rolling and flat rolling is 15-40%;

[0069] The rough rolling start temperature is 1090~1150℃; the rough rolling threading time is 37s; the intermediate billet thickness is 28mm; the intermediate billet travel time on the intermediate roller is 40s; the rough rolling final rolling speed is 2.3m / s;

[0070] Step 6: Finish rolling, finish descaling and finish descaling:

[0071] The finishing rolling adopts the full continuous rolling method, including 11 continuous rolling passes, 1 rolling pass in each pass, and the arrangement of the roll direction is: 1 vertical-1 flat-2 flat-2 vertical-3 flat-4 flat-5 flat-6 flat-7 flat-8 flat-9 flat;

[0072] After finishing rolling, high-pressure water is used for descaling at a pressure of 18MPa to remove secondary iron oxide.

[0073] Fine descaling allows the head to pass through the descaling box with a delay of 2 seconds for descaling;

[0074] Finishing rolling flat rolling single pass reduction rate: 10-40%; finishing rolling 1 and 2 passes adopt vertical roller pass rolling, pass reduction: ≤20mm;

[0075] The finishing rolling start temperature is 990-1050℃; the finishing rolling final rolling temperature is 840~890℃; the finishing rolling final rolling speed is 11.5-14m / s; the finishing rolling threading time is 16s;

[0076] The hardness of the finishing rolling F6-F9 working rolls is HSD 80-85;

[0077] After the finishing rolling F1-F9 working rolls are replaced, the rolling mileage is controlled at 50-100km.

[0078] Step 7: Laminar cooling:

[0079] After finishing rolling, laminar cooling method is adopted, with rapid cooling in the front section and fine adjustment in the back section. The cooling rate is 50-80℃ / s, and the coiling temperature is controlled at 600-640℃.

[0080] Step 8: Coiling method:

[0081] The coiling tension is 23kN. The coil cooling water is turned off in advance during coiling. The coil cooling water is turned off when the previous steel is thrown. After coiling, a hot-rolled strip with a thickness of 3.3mm and a width of 355mm is obtained.

[0082] Step 9: Stack cooling:

[0083] After the strip comes off the production line, it is cooled in the stack for more than 24 hours and the strip temperature is below 100℃.

[0084] Step 10: Mechanical shell removal:

[0085] Descaling is performed using multiple curved rollers.

[0086] Step 11, pickling:

[0087] Use hydrochloric acid for pickling, the mass concentration of hydrochloric acid is 24-26%, the pickling temperature is 60-70℃, and the pickling speed is 1.3m / s.

[0088] Step 12: Cleaning and rinsing:

[0089] Condensed water is used for cleaning and rinsing, and the cleaning and rinsing temperature is 60-90℃.

[0090] Step 13: Passivation:

[0091] Use 2% mass concentration sodium nitrite aqueous solution for rust prevention treatment.

[0092] Step 14: Cold rolling:

[0093] A single-stand rolling mill or a continuous rolling mill is used, with 4 rolling passes and a total reduction rate of 39-58%.

[0094] Step 15: Cutting edges:

[0095] Use a slitting machine to trim the edges, removing 2mm on each side.

[0096] Step 16: Roll up to obtain the finished product.

[0097] The finished steel for aluminum formwork tabs of construction projects of the present invention has a thickness of 1.7 mm. In addition, the steel for aluminum formwork tabs of construction projects prepared by the method has the following key indicators: mechanical properties of tab steel: breaking force 28-30 kN, elongation after fracture 5.0%; plate shape: plate convexity ≥ 0, qualified rate 100%; edge crack rate: 0; protruding part breakage rate 100%; pickling yield rate 99.55%; punching rate: 100%; no surface corrosion. The hot-rolled strip is an intermediate product, and the metallographic structure of the hot-rolled strip is: F+P; the total decarburization layer depth of the hot-rolled strip is 18.5 μm; the thickness of the hot-rolled strip oxide scale is 8.4 μm; the tensile strength of the hot-rolled strip is 820-850 MPa, and the elongation after fracture is 16.0-22.0%; it fully meets the quality requirements of steel for aluminum formwork tabs of construction projects.

[0098] Example 2

[0099] Step 1: Select the steel grade that meets the chemical composition requirements:

[0100] The steel used for the aluminum template pull tab is medium carbon steel, and the chemical composition, measured by mass percentage, includes the following chemical components:

[0101] Table 2 Chemical composition Unit: (%)

[0102]

[0103] Step 2: Stacking and cooling continuous casting billets:

[0104] The continuous casting billet adopts the offline stack cooling method to promote the release of hydrogen in the steel and avoid defects such as cracks caused by hot delivery of the continuous casting billet; it can only enter the heating furnace after being stack cooled to room temperature; the cross-sectional dimensions of the continuous casting billet are: width 380mm, thickness 165mm.

[0105] Step 3: Heating of continuous casting billet:

[0106] The temperature of the heating section is 1100-1200°C, the temperature of the soaking section is 1200-1250°C, and the heating time is 90-120 minutes. To reduce decarburization, the air-fuel ratio is controlled at 0.60-0.70.

[0107] Step 4: Descaling with high pressure water after the furnace:

[0108] The descaling pressure is 19MPa, and the oxidized iron scale can be effectively removed in one step.

[0109] Step 5, rough rolling and rough descaling:

[0110] The rough rolling adopts the full continuous rolling method, including 8 continuous rolling passes, 1 rolling per pass, and the roll directions are arranged as follows: 1 vertical-1 flat-2 flat-2 vertical-3 flat-4 flat-3 vertical-5 flat;

[0111] After rough rolling, high-pressure water descaling is used at a pressure of 16 MPa to remove secondary iron oxide scale.

[0112] The starting temperature of rough rolling is 1090~1150℃; the final rolling speed of rough rolling is 2.0m / s; the strip threading time of rough rolling is 39s; the walking time of intermediate billet on the intermediate roller is 41s; the single pass reduction rate of rough rolling and flat rolling is 15-40%; the rough rolling of 1st, 2nd and 3rd vertical rolls adopts vertical roller hole rolling, and the pass reduction is ≤40mm; the thickness of intermediate billet is 30mm.

[0113] Step 6: Finish rolling, finish descaling and finish descaling:

[0114] The finishing rolling adopts the full continuous rolling method, including 11 continuous rolling passes, 1 rolling pass in each pass, and the roll direction is arranged as follows: 1 vertical-1 flat-2 flat-2 vertical-3 flat-4 flat-5 flat-6 flat-7 flat-8 flat-9 flat;

[0115] After finishing rolling, high-pressure water descaling is used at a pressure of 19 MPa to remove secondary iron oxide scale.

[0116] Fine descaling allows the head to pass through the descaling box with a delay of 2 seconds for descaling;

[0117] The starting temperature of finishing rolling is 980-1050℃; the final rolling temperature of finishing rolling is 840~890℃;

[0118] Finishing rolling speed: 11.5-13.0m / s; finishing rolling threading time: 17s; finishing rolling flat rolling single pass reduction rate: 10-40%;

[0119] Finish rolling 1 and 2 adopts vertical roller pass rolling, and the reduction per pass is ≤20mm;

[0120] The hardness of the finishing rolling F6-F9 working rolls is HSD 80-85;

[0121] After the finishing rolling F1-F9 working rolls are replaced, the rolling mileage is controlled at 50-100km.

[0122] Step 7: Laminar cooling:

[0123] After finishing rolling, laminar cooling method is adopted, with rapid cooling in the front section and fine adjustment in the back section. The cooling rate is 50-80℃ / s, and the coiling temperature is controlled at 600-640℃.

[0124] Step 8: Coiling method:

[0125] The coiling tension is 25kN. The coil cooling water is turned off in advance during coiling. The coil cooling water is turned off when the previous steel is thrown. After coiling, the hot-rolled strip with a thickness of 3.4mm and a width of 403mm is obtained.

[0126] Step 9: Stack cooling:

[0127] After the strip comes off the production line, it is cooled in the stack for more than 24 hours, and the strip temperature is below 100℃.

[0128] Step 10: Mechanical shell removal:

[0129] Descaling is performed using multiple curved rollers.

[0130] Step 11, pickling:

[0131] Use hydrochloric acid for pickling, the mass concentration of hydrochloric acid is 24-26%, the pickling temperature is 60-70℃, and the pickling speed is 1.6m / s.

[0132] Step 12: Cleaning and rinsing:

[0133] Use condensed water, washing and rinsing temperature 60-90℃

[0134] Step 13: Passivation:

[0135] Use 1-3% mass concentration of sodium nitrite aqueous solution for rust prevention.

[0136] Step 14: Cold rolling:

[0137] Use single-stand rolling mill or continuous rolling mill, rolling 5 times, total reduction rate 39-58%

[0138] Step 15: Cutting edges:

[0139] Use a slitting machine to trim the edges, removing 1mm on each side.

[0140] Step 16: Roll up to obtain the finished product.

[0141] The finished steel for aluminum formwork tabs of construction projects of the present invention has a thickness of 1.8 mm. In addition, the steel for aluminum formwork tabs of construction projects prepared by the method has the following key indicators: mechanical properties of tab steel: breaking force 28-30 kN, elongation after fracture 5.5%; plate shape: plate convexity ≥ 0, qualified rate 100%; edge crack rate: 0; protruding part breakage rate 100%; pickling yield rate 99.50%; punching rate: 100%; no surface corrosion. The hot-rolled strip is an intermediate product, and the metallographic structure of the hot-rolled strip is: F+P; the total decarburization layer depth of the hot-rolled strip is 20 μm; the thickness of the oxide scale of the hot-rolled strip is 9.0 μm; the tensile strength of the hot-rolled strip is 830-860 MPa, and the elongation after fracture is ≥ 17.0-23%; it fully meets the quality requirements of steel for aluminum formwork tabs of construction projects.

[0142] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for producing steel for aluminum formwork pull tabs for construction projects, wherein the raw material of the aluminum formwork pull tab is medium carbon steel, and the mass percentage content of the chemical composition is: include: C： 0.52-0.58%； Si: 0.17-0.20%; Mn: 0.80-0.95%; Cr: 0.14-0.20%; P≤0.030%; S≤0.030; the balance is Fe; Characterized in that the production method comprises the following steps: S1. Select steel grades that meet the chemical composition requirements; S2. Pile cooling continuous casting billet: The continuous casting billet is pile cooled to room temperature by offline pile cooling method; this step can promote the release of hydrogen in the steel and avoid crack defects caused by hot delivery of the continuous casting billet; S3, sending the continuous casting billet cooled to room temperature in S2 into a heating furnace for heating; the temperature of the heating section is 1100-1200°C, the temperature of the soaking section is 1200-1250°C, and the heating time is 90-120 minutes; S4. Post-furnace high-pressure water descaling: descaling pressure ≥ 16MPa, the iron oxide scale can be effectively removed in one step; S5, rough rolling and rough descaling; the rough rolling adopts the full continuous rolling method, including 8 continuous rolling, 1 rolling per pass, and the single pass reduction rate of rough rolling and flat rolling is 15-40%; after rolling, high-pressure water descaling is used, and the descaling pressure is ≥15MPa to remove the secondary iron oxide scale; S6, finishing rolling, finishing descaling and finishing descaling and head cutting; finishing rolling adopts full continuous rolling method, including 11 continuous rolling passes, 1 rolling per pass, and the roll direction is arranged as follows: 1 vertical-1 flat-2 flat-2 vertical-3 flat-4 flat-5 flat-6 flat-7 flat-8 flat-9 flat; finishing rolling adopts high-pressure water descaling after 1 vertical, and the descaling pressure is ≥16MPa to remove secondary iron oxide scale; finishing descaling and head cutting; S7, laminar cooling: after finishing rolling, laminar cooling method is adopted, with fast cooling in the front section and fine adjustment in the back section, and the cooling rate is 50-80℃ / s; S8, coiling; when coiling, turn off the cooling water of the coil in advance, and start to turn off the cooling water of the coil when the previous steel is thrown; control the coiling temperature at 600-640℃; coiling tension at 20-25kN; S9, stack cooling: the strip is stacked and cooled for more than 24 hours after it comes off the production line, and the strip temperature is below 100℃; S10, mechanical shell removal; using multiple bending rollers for descaling; S11, pickling the steel strip after shell removal with hydrochloric acid; S12. The pickled steel strip is cleaned and rinsed with condensed water; the cleaning and rinsing temperature is 60-90℃; S13, the rinsed steel strip is passivated with a sodium nitrite aqueous solution with a mass concentration of 1-3%; S14, cold rolling; using a single-stand rolling mill or a continuous rolling mill, rolling 4-6 times, with a total reduction rate of 39-58%; S15, trimming; S16, roll up.

2. The method for producing steel for aluminum formwork pull tabs for construction engineering as claimed in claim 1, It is characterized in that The air-fuel ratio in S3 is controlled at 0.60-0.

70.

3. The method for producing steel for aluminum formwork pull tabs for construction engineering as claimed in claim 1, Features: The rough rolling process in S5 includes the arrangement of the roll directions: 1 vertical - 1 flat - 2 flat - 2 vertical - 3 flat - 4 flat - 3 vertical - 5 flat; high-pressure water descaling is used after 1 vertical rolling, and the descaling pressure is ≥15MPa to remove the secondary iron oxide scale; the rough rolling of 1 vertical, 2 vertical and 3 vertical adopts vertical roll hole rolling, and the reduction per pass is ≤40mm.

4. The method for producing steel for aluminum formwork pull tabs for construction engineering as claimed in claim 1, Features: The starting temperature of rough rolling in S5 is 1090-1150°C; the final rolling speed of rough rolling is ≥2.0m / s; the strip threading time of rough rolling is 35-40s; the walking time of the intermediate billet on the intermediate roller is 39-42s; and the thickness of the intermediate billet is 26-30mm.

5. The method for producing steel for aluminum formwork pull tabs for construction engineering as claimed in claim 1, Features: In S6, the head of the strip steel passes through the descaling box with a delay of 2 seconds for descaling.

6. The method for producing steel for aluminum formwork pull tabs for construction engineering as claimed in claim 1, Features: In S7, the starting temperature of finishing rolling is 980-1050℃; the final rolling temperature of finishing rolling is 840~890℃; the final rolling speed of finishing rolling is 11.5-14.0m / s; the finishing strip threading time is 15-18s; the single pass reduction rate of finishing flat rolling is 10-40%; finishing rolling 1st and 2nd vertical rolls are rolled with vertical roll hole type, and the pass reduction is ≤20mm.

7. The method for producing steel for aluminum formwork pull tabs for construction engineering as claimed in claim 1, Features: In S7, after the finishing rolling F1-F9 working rolls are replaced, the rolling mileage is controlled at 50-100km.

8. The method for producing steel for aluminum formwork pull tabs for construction engineering as claimed in claim 1, Features: The mass concentration of the hydrochloric acid pickling solution in S11 is 24-26%, the pickling temperature is 60-70°C, and the pickling speed is ≤2.0m / s.

9. The method for producing steel for aluminum formwork pull tabs for construction engineering as claimed in claim 1, Features: The steel for aluminum formwork pull tabs of construction engineering prepared by the method has the following properties: breaking force 26-30kN, elongation after fracture ≥4.5%; Plate shape: Plate convexity ≥ 0, qualified rate 100%; edge crack rate: 0; protruding part breakage rate 100%; pickling yield rate ≥ 99.50%; no rust on the surface; The hot-rolled strip is an intermediate product, and the metallographic structure of the hot-rolled strip is: F+P; the total decarburization layer depth of the hot-rolled strip is ≤25μm; the thickness of the oxide scale of the hot-rolled strip is ≤10μm; the tensile strength of the hot-rolled strip is ≥800MPa, and the elongation after fracture is ≥15.0%; it fully meets the quality requirements of steel used for aluminum formwork pull tabs in construction projects.

Images