A 440MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel and its manufacturing method

Abstract

The invention discloses a 440MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel, the chemical composition of which is as follows by weight: C: 0.006-0.010%, Si: ≤0.03%, Mn: 1.00-1.20%, P: 0.085-0.100%, S≤0.005%, Als: 0.020-0.045%, Nb: 0.012-0.020%, Ti: 0.04-0.06%, B: 0.0010-0.0015%, N≤0.0035%, and the rest is Fe and unavoidable impurities; wherein the elements are fully The invention is defined as follows: 8C+3N+2S≤Ti+2Nb≤10C+3N+2S, 60B≤P≤80B, calculated according to the corresponding weight percentage of each element; the present invention adds the P element to the IF steel, and through composition and process optimization control, obtains a P-containing hot-dip galvanized iron alloy high-strength IF steel with a yield strength of 310-360 MPa, a tensile strength of 440-490 MPa, an elongation of 32-40%, an r value (average plastic strain ratio) ≥1.7, a secondary processing brittle transition temperature of below ‑45°C, high surface quality, high formability, and good cold brittleness.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and in particular relates to a 440MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel and a manufacturing method thereof. Background Art

[0002] Hot-dip galvanized iron alloy coated steel sheet (GA steel sheet) offers superior corrosion resistance, paintability, and weldability compared to hot-dip pure zinc sheet (GI), and is widely used in Japanese sedans. Traditionally, Japanese sedan exterior panels have primarily used IF steel, but with the trend toward lightweight vehicles, high-strength steels are gradually replacing traditional IF steel. Currently, automotive manufacturers primarily use BH steel to replace traditional IF steel. However, BH steel's inferior deep-drawing properties and aging issues limit its application. Therefore, to address this challenge, high-strength IF steel containing phosphorus (P) has emerged.

[0003] P-containing high-strength IF steel is a traditional IF steel with the strengthening element P added. It not only improves the strength, but also retains the characteristics of interstitial-free atom steel and has excellent stamping performance. At the same time, the interstitial-free atoms in the steel also solve the aging problem of BH steel, so it is widely used in automotive exterior panels. However, the P element will segregate at the grain boundaries, seriously hindering the zinc-iron alloy reaction, making the zinc-iron alloy reaction difficult. In addition, the segregation of the P element will also weaken the grain boundaries, affecting the secondary processing brittleness of the steel plate and causing the cold brittleness temperature to rise. At the same time, the addition of alloying elements will reduce the formability of the steel plate. How to improve the strength while ensuring the formability has become a technical problem that needs to be solved urgently.

[0004] Patent CN201610233053.7 "A 440MPa grade cold-rolled high-strength IF steel and its production method" adds a large amount of Si as a strengthening element, and there are obvious differences in the hot rolling and cold rolling processes. Its overall yield strength is low, and there is no mention of solving the secondary processing brittleness problem.

[0005] Patent CN201711112729.8 discloses "a 440MPa grade cold-rolled strip steel and its production method" and also adds a small amount of Si element as a strengthening element, but does not restrict the N and S elements. It cannot effectively solve the surface and secondary processing brittleness problems. It can only produce continuous annealing plates with low surface requirements, and the overall yield strength is low. Summary of the Invention

[0006] In order to solve the above problems, the present invention provides a P-containing hot-dip galvanized iron alloy high-strength IF steel with a tensile strength of 440 MPa and

[0007] ˉ

[0008] Its manufacturing method has a yield strength of 310-360MPa, a tensile strength of 440-490MPa, an elongation of 32-40%, and an r-value (average plastic strain ratio) ≥1.7. By matching the composition and process, it not only ensures the surface quality of the steel plate, but also has excellent forming performance. The secondary brittle transition temperature can reach below -45°C, which well meets the use requirements of automobile exterior panels.

[0009] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0010] A 440MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel, the chemical composition of which is as follows by weight percentage:

[0011] C: 0.006-0.010%, Si: ≤0.03%, Mn: 1.00-1.20%, P: 0.085-0.100%, S≤0.005%, Als: 0.020-0.045%, Nb: 0.012-0.020%, Ti: 0.04-0.06%, B: 0.0010-0.0015%, N≤0.0035%, and the rest are Fe and unavoidable impurities; the elements also meet the following restrictions: calculated according to the corresponding weight percentage of each element, 8C+3N+2S≤Ti+2Nb≤10C+3N+2S, 60B≤P≤80B.

[0012] The method for manufacturing the above-mentioned 440MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel comprises the following steps:

[0013] 1) After continuous casting, the billet is mechanically peeled to remove the surface iron oxide scale, and then enters the heating furnace. The heating temperature is controlled at 1200-1230℃ and the heating time is ≥150min;

[0014] 2) Rough rolling and finishing rolling; control the rough rolling temperature at 1060-1110°C for full descaling; control the finishing rolling temperature at 900-930°C;

[0015] 3) Coiling: adopt U-shaped cooling, control the coiling temperature at 620-650℃ at the head and tail, and 600-640℃ in the middle;

[0016] 4) Pickling: the pickling temperature is controlled at 80-90°C and the acid concentration is greater than 120g / l;

[0017] 5) Cold rolling: control the total cold rolling reduction rate to 65-83%;

[0018] 6) Continuous annealing; control the soaking temperature at 790-810°C;

[0019] 7) Hot dip galvanizing: control the temperature of the steel plate entering the zinc pot at 500-520℃ and the dew point of the furnace nose below -45℃;

[0020] 8) Alloying; entering the alloying furnace using alloying power control mode, the power is controlled at 1800-2000KW, the iron content of the coating is controlled at 9 to 11wt%;

[0021] 9) Finishing: Finishing rate is 1.1-1.3%, steel plate surface roughness is 0.9-2.0 μm, oiling amount is 1.5±0.5 g / m 2 .

[0022] According to the above scheme, IF steel or ordinary stamping steel is used for transition when welding the strip in step 5.

[0023] According to the above scheme, in step 6, alkali washing is performed before entering the annealing furnace to remove residual substances on the surface. After cleaning, the iron powder on the plate surface is ≤1000ppm and the oil powder is ≤100ppm;

[0024] According to the above scheme, step 6 requires turning on the nitrogen humidification equipment in the heating section furnace and controlling the dew point between 0-+15°C;

[0025] According to the above scheme, before hot-dip galvanizing in step 7, ensure the effect of the squeeze roller, and strictly prohibit the plate surface from bringing water into the zinc pot; control the Al content in the zinc liquid composition between 0.10 and 0.11 wt%;

[0026] According to the above plan, in step 8, the power is increased or decreased according to the degree of flouring of the plate, and the edge burners are fully opened.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention adds phosphorus to IF steel and, through composition and process optimization, produces a phosphorus-containing hot-dip galvanized iron alloy high-strength IF steel with a yield strength of 310-360 MPa, a tensile strength of 440-490 MPa, an elongation of 32-40%, an r-value (average plastic strain ratio) ≥ 1.7, and a secondary processing brittle transition temperature below -45°C. The steel exhibits high surface quality, excellent formability, and good cold brittleness resistance. This steel exhibits excellent overall performance and can replace traditional IF and BH steels to enhance automotive strength and safety. Furthermore, it achieves high strength and thinness, enabling low-carbon, green production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 : The matrix structure morphology of the product obtained in Example 1 of the present invention.

[0030] Figure 2 : Surface coating morphology of the GA product obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The following examples further illustrate the technical solutions of the present invention but are not intended to limit the scope of protection of the present invention.

[0032] The specific embodiment provides a method for manufacturing a 440MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel:

[0033] 1) The chemical composition by weight is as follows: C: 0.006-0.010%, Si: ≤0.03%, Mn: 1.00-1.20%, P: 0.085-0.100%, S≤0.005%, Als: 0.020-0.045%, Nb: 0.012-0.020%, Ti: 0.04-0.06%, B: 0.0010-0.0015%, N≤0.0035%, and the remainder is Fe and unavoidable impurities; wherein the elements also meet the following restrictions: calculated by weight percentage of each element, 8C+3N+2S≤Ti+2Nb≤10C+3N+2S, 60B≤P≤80B; after smelting and refining according to the set composition, the elements such as P, S, B, and N are strictly controlled;

[0034] 2) After continuous casting, the billet is mechanically peeled to remove the surface oxide scale to ensure the subsequent surface quality; then it enters the heating furnace, the heating temperature is controlled at 1200-1230℃, and the heating time is ≥150min;

[0035] 3) Carry out rough rolling, control the rough rolling temperature at 1060~1110℃, in order to ensure the descaling effect, require that the descaling water is fully opened to ensure complete descaling; control the finishing rolling temperature at 900~930℃;

[0036] 4) After finishing rolling, coiling is carried out. In order to ensure the uniformity of the performance of the head and tail, U-shaped cooling is adopted. The coiling temperature of the head and tail is controlled at 620-650℃, and the coiling temperature of the middle part is 600-640℃;

[0037] 5) Pickling is performed. The pickling temperature is required to be controlled at 80-90°C and the acid concentration is required to be greater than 120g / l;

[0038] 6) Cold rolling is carried out. According to different thickness specifications, the total cold rolling reduction rate is controlled at 65-83%. Since it is P-containing steel, IF steel or ordinary stamping steel is used for transition during welding and threading. High-strength steel transition is strictly prohibited.

[0039] 7) Continuous annealing: Ensure the alkali washing effect before entering the annealing furnace, clean the residual substances on the surface of the pickling, and ensure that the iron powder on the plate surface is ≤1000ppm and the oil powder is ≤100ppm after cleaning; control the soaking temperature at 790-810℃, and turn on the nitrogen humidification equipment in the heating section of the furnace, and control the dew point between 0-+15℃;

[0040] 8) Hot-dip galvanizing: Ensure the effect of the squeeze roller before hot-dip galvanizing. It is strictly forbidden to bring water into the zinc pot; the temperature of the steel plate entering the zinc pot is controlled at 500-520℃, and the dew point of the furnace nose is below -45℃; the Al content in the zinc solution is controlled between 0.10 and 0.11wt%;

[0041] 9) After hot-dip galvanizing, the steel enters the alloying furnace for alloying. The alloying power control mode is adopted, and the alloying power is controlled at 1800-2000KW. The power is increased or decreased according to the degree of plate flouring. The edge burners are required to be fully open, and the iron content of the coating is controlled at 9-11wt%;

[0042] 10) Perform finishing: the finishing rate is 1.1-1.3%. The surface roughness of the steel plate after alloying is controlled at 0.9-2.0 μm, and the oiling amount is 1.5±0.5 g / m 2 .

[0043] The mechanism and function of each element and main process in the present invention:

[0044] C: The most basic solid solution strengthening element. To ensure interstitial-free steel, an ultra-low carbon design is adopted. However, to ensure the strength of high-strength IF steel, the C content is controlled between 0.006-0.010%.

[0045] Si: A ferrite-strengthening element, the addition of Si can significantly improve product strength. However, during hot rolling, Si promotes the formation of iron oxide scale, deteriorating surface quality and affecting the effectiveness of subsequent pickling processes. Furthermore, as the Si content increases, Si enrichment becomes apparent during hot-dip galvanizing annealing, making it prone to plating defects on the steel sheet surface, seriously impacting surface quality. Furthermore, the combined effects of Si and P make alloying high-strength IF steel difficult. Therefore, the present invention controls the Si content to below 0.03%.

[0046] Mn: Manganese dissolves in ferrite, causing solid solution strengthening and significantly increasing the material's hardness and strength. However, excessive Mn content can deteriorate the steel's weldability. Therefore, while maintaining strength, the Mn content is preferably controlled within the range of 1.00-1.20%.

[0047] Al: The most effective deoxidizing element. However, as the AlS (solid-solution Al) content increases, the number of inclusions in the steel increases, and the size of these inclusions also increases. Therefore, the AlS content should be properly controlled, preferably within a range of 0.020-0.045%.

[0048] Nb and Ti: They exhibit precipitation strengthening effects, effectively fixing interstitial atoms such as C and N, and refining grains, thereby increasing the strength and ductility of the steel. Furthermore, Nb can increase the reaction window of IF steel zinc-iron alloys, facilitating production control. However, Nb is expensive, and Nb-Ti composite strengthening is generally employed. However, adding too much Nb or Ti weakens the strengthening effect, increasing alloy cost and affecting secondary processing brittleness. Therefore, the present invention preferably uses 0.012-0.020% Nb and 0.04-0.06% Ti.

[0049] Nitrogen: Excessive nitrogen content can degrade the elongation and weldability of high-strength steel. Furthermore, nitrogen forms compounds with niobium (Nb) and titanium (Ti), reducing the combined strengthening effects of these elements. Therefore, the nitrogen content in this invention is required to be below 0.0035%.

[0050] S: A harmful element in steel. When the S content is too high, it easily forms MnS inclusions, which impair the plasticity of the steel plate, cause anisotropy in performance, and reduce the r-value. S, along with C and N, forms compounds with Nb and Ti, seriously affecting the secondary processing brittleness of the steel. Therefore, the S content needs to be reasonably controlled. The present invention preferably has an S content of less than 0.005%. Furthermore, to ensure the interstitial atom fixation effect of Nb and Ti, and to prevent excess Nb and Ti from forming compounds with C, N, and S, which affects the secondary brittleness of the steel and increases the brittle transition temperature, according to actual production experience, it is necessary to ensure that 8C+3N+2S≤Ti+2Nb≤10C+3N+2S.

[0051] P: P is also an effective solid solution element, which can effectively improve the strength of steel. However, phosphorus is the most important element affecting the secondary processing brittleness of IF steel. In IF steel, due to the lack of competition from solid solution carbon at the grain boundary position, phosphorus segregation at the grain boundary occurs faster and more easily than in non-IF steel, causing grain boundary embrittlement, which in turn leads to secondary processing brittleness. In addition, during galvanizing, if the P content is too high, a large amount of explosive structure ξ phase will be formed in the initial coating, making the zinc-iron alloy reaction difficult and causing the coating's anti-powdering ability to deteriorate. Preferably, the P content of the present invention is controlled between 0.085 and 0.100%.

[0052] B is also an effective solid-solution element. When a certain amount of B is added, the solid-solution B not only preferentially segregates at grain boundaries, reducing the adverse effects of P segregation at grain boundaries, but also increases the number of small-angle grain boundaries, effectively hindering crack propagation and thus improving secondary processing brittleness. However, excess B can result in high yield strength and poor stamping performance. Therefore, the preferred B content is 0.0010-0.0015%, and the requirement is 60B≤P≤80B. This ensures both improved secondary processing brittleness and good stamping performance of the steel plate.

[0053] The reason for choosing mechanical peeling of continuous casting billets is that it can effectively remove surface iron oxide and other defects to ensure subsequent surface quality.

[0054] The reason why the heating temperature is controlled at 1200-1230℃ and the heating time is ≥150min is that this not only ensures that the steel plate is burned through and is conducive to the uniform distribution of alloy elements, but also the lower heating temperature can save a lot of energy costs.

[0055] The reason why the descaling water is required to be fully opened during hot rolling to ensure complete descaling is to ensure the surface quality of the galvanized original sheet. If the hot rolling scale remains, it will lead to uneven alloying after galvanizing, seriously affecting the surface quality of the coating.

[0056] The reason why the final rolling temperature is selected as 900-930℃ is that the high final rolling temperature is conducive to the precipitation of Nb and Ti compounds, and more effectively refines the grains, thereby improving the material's formability and secondary processing brittleness.

[0057] The reason for choosing a higher coiling temperature of 600-650℃ is that the high coiling temperature is conducive to the precipitation of carbides and refinement of grains; U-shaped cooling is adopted to ensure the uniformity of head and tail performance, and avoid the deterioration of plate shape due to inconsistent head and tail strength during the pickling process, which affects the subsequent hot-dip galvanizing and zinc-iron alloy reaction process.

[0058] The pickling temperature is required to be controlled between 80 and 90°C, and the acid concentration must be greater than 120g / l. This is because pickling effectively removes iron oxide scale. Poor pickling results in residual iron oxide scale, which can then be pressed into the substrate during pickling, causing surface defects such as missed plating and seriously affecting the surface quality of the steel plate.

[0059] The reason why IF steel or ordinary stamping steel is used for transition during pickling and welding is strictly prohibited because the P element is easily concentrated at the welding point, resulting in weakened strength at the welding position. If it is transitioned with high-strength steel, the strength difference before and after is too large, which can easily lead to steel coil breakage during pickling.

[0060] The reason we guarantee iron powder ≤ 1000ppm and oil powder ≤ 100ppm on the plate surface after cleaning is that the segregation of the P element hinders the diffusion of Fe into the zinc layer. Therefore, P-containing steels are more difficult to react with zinc and iron than other steels. When the residual iron and oil content on the surface is too high, it further hinders the diffusion of zinc and iron reaction, which can easily lead to uneven alloying on the plate surface.

[0061] The reason why the continuous annealing temperature is 790-810°C is that at this annealing temperature, the present invention can obtain better elongation and r-value while avoiding energy waste. At the same time, at higher annealing temperatures, carbides decompose at high annealing temperatures, which can increase solid-solution carbon and further reduce phosphorus segregation, thereby ensuring that the steel plate of the present invention has a low secondary processing brittle transition temperature. The nitrogen humidification equipment in the heating section furnace is turned on, and the dew point is controlled between 0-+15°C because the present invention adds more Mn and P elements in order to improve the strength. In order to prevent the Mn and P elements from oxidizing on the surface of the substrate at the furnace nose to form an oxide film that affects the plating performance, nitrogen humidification is turned on in the heating section to achieve pre-oxidation. The oxide formed can be reduced by a hydrogen reducing atmosphere in the high-temperature section, effectively improving its wettability.

[0062] The reason why the squeezing roller effect is guaranteed before hot-dip galvanizing and the plate surface is strictly prohibited from bringing water into the zinc pot is that water on the plate surface will cause uneven reaction of P-containing steel zinc-iron alloy and deteriorate the powdering performance, seriously affecting the surface quality.

[0063] The reason the strip enters the zinc pot at a temperature of 500-520°C is to ensure that the steel plate remains at a relatively high temperature after exiting the zinc pot, which facilitates the zinc-iron alloying reaction and avoids uneven alloying. The dew point at the furnace nose is controlled below -45°C to prevent oxidation of the substrate at the furnace nose, which could hinder the zinc-iron alloying reaction and even lead to plating errors. Furthermore, an Al content of 0.11-0.11 wt% effectively reduces the formation of an inhibitory layer, ensuring a more favorable zinc-iron reaction.

[0064] The alloying power control mode is employed, with the power controlled between 1800 and 2000 kW and adjusted according to the degree of plate powdering. This is because high power control allows Fe to more easily penetrate the barrier of P and diffuse into the zinc layer, resulting in more uniform alloying. When the alloying power exceeds 2000 kW, a large amount of brittle Γ phase is easily formed, deteriorating the product's powdering resistance. The edge burners are required to operate fully to ensure uniform zinc-iron reaction and diffusion along the edges, avoiding color variations caused by uneven alloying. Research has also shown that high-strength steel zinc-iron alloy coatings with an Fe content of 9-11% exhibit optimal powdering resistance.

[0065] The reason for choosing the skin-clearing elongation of 1.1-1.3% is to eliminate the yield platform of the material. At the same time, the surface roughness of the alloyed steel plate is controlled at 0.9-2.0μm to meet the coating requirements of the user. Due to the loose structure of the zinc-iron alloy plate coating, the oiling amount needs to be increased to 1.5±0.5g / m 2 , thus ensuring rust prevention and stamping effect.

[0066] Table 1 is a list of chemical composition values ​​of various embodiments and comparative examples of the present invention.

[0067] Table 2 is a list of main process parameters of various embodiments and comparative examples of the present invention.

[0068] Table 3 is a table of performance test results of various embodiments of the present invention and comparative examples.

[0069] Table 1 Chemical composition values ​​of various embodiments and comparative examples of the present invention (wt%)

[0070]

[0071]

[0072] Table 2 Process parameters of various embodiments of the present invention and comparative examples

[0073]

[0074] Table 3 is a list of performance tests of various embodiments and comparative examples of the present invention.

[0075]

[0076] Figure 1 This is the matrix structure morphology of the product obtained in Example 1. It can be seen that the substrate has fine and uniform grains, a structure of ferrite + a small amount of carbide, and a grain size of level 9. Figure 2 The surface coating morphology of the GA product obtained in Example 1 shows that the surface coating is mainly composed of δ phase, the degree of alloying is good, and there are visible polishing marks. The coating has appropriate strength and plasticity and excellent anti-powdering performance.

[0077] As can be seen from the comparative examples, comparative example 1 adds a large amount of Si alloying elements, and the surface quality is difficult to control, is not suitable for galvanized sheet production, and the yield strength is lower than the present invention, and the secondary brittleness problem is not mentioned; comparative example 2 also adds a small amount of Si elements as strengthening elements, and elements such as S and N are not restricted, and the secondary processing brittleness problem is not mentioned. In addition, the yield strength is also much smaller than the present invention; comparative example 3 also adds Si elements, but does not add B elements, and the manufacturing process does not effectively suppress the segregation of P elements, so the alloying power is high, the pulverization performance is poor, and the secondary brittleness temperature is high, and there is a greater risk in low temperature areas. The present invention is in the full process manufacturing process, under the premise of meeting mechanical properties, by precise proportioning of components, and as far as possible by process optimization to avoid the alloying uneven surface problem and the secondary processing brittleness problem brought by P element segregation, and finally obtains a kind of P hot-dip galvanized iron alloy high-strength IF steel containing P and a manufacturing method thereof with high surface quality, high formability, and good cold brittleness, and achieves obvious results. The above embodiments are only the best examples, and are not intended to limit the embodiments of the present invention.

Claims

1. A 440MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel, characterized in that The chemical composition by weight percentage is: C: 0.006-0.010%, Si: ≤0.03%, Mn: 1.00~1.20%, P: 0.085~0.100%, S≤0.005%, Als: 0.020~0.045%, Nb: 0.012~0.020%, Ti: 0.04~0.06%, B: 0.0010~0.0015%, N≤0.0035%, the rest are Fe and unavoidable impurities; the elements also meet the following restrictions: calculated by weight percentage of each element, 8C+3N+2S≤Ti+2Nb≤10C+3N+2S, 60B≤P≤80B; secondary brittle transition temperature ≤-45℃; The manufacturing method of the 440MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel comprises the following steps: 1) After continuous casting, the billet is mechanically peeled to remove the surface iron oxide scale, and then enters the heating furnace. The heating temperature is controlled at 1200~1230℃ and the heating time is ≥150min; 2) Rough rolling and finishing rolling; control the rough rolling temperature at 1060~1110℃, complete descaling; control the finishing rolling temperature at 900~930℃; 3) Coiling: adopt U-shaped cooling, control the coiling temperature at 620-650℃ at the head and tail, and 600-640℃ in the middle; 4) Pickling: the pickling temperature is controlled at 80-90°C and the acid concentration is greater than 120g / l; 5) Cold rolling: control the total cold rolling reduction rate at 65~83%; 6) Continuous annealing; control the soaking temperature at 790~810℃; 7) Hot-dip galvanizing: control the temperature of the steel plate entering the zinc pot at 500~520℃ and the dew point of the furnace nose below -45℃; 8) Alloying: When entering the alloying furnace, the alloying power control mode is adopted, the power is controlled at 1800-2000KW, and the iron content of the coating is controlled at 9~11wt%; 9) Finishing: Finishing rate is 1.1~1.3%, steel plate surface roughness is 0.9~2.0µm, oiling amount is 1.5±0.5g / m 2 .

2. The 440MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel according to claim 1, characterized in that Step 5: Use IF steel or ordinary stamping steel for transition when welding the strip.

3. The 440MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel according to claim 1, characterized in that Step 6: Alkaline washing is performed before entering the annealing furnace to remove residual substances on the surface. After cleaning, the iron powder on the plate surface is ≤1000ppm and the oil powder is ≤100ppm.

4. The 440MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel according to claim 1, characterized in that Step 6 requires turning on the nitrogen humidification equipment in the heating section furnace and controlling the dew point between 0-+15°C.

5. The 440MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel according to claim 1, characterized in that Step 7: Ensure the squeeze roller effect before hot-dip galvanizing. It is strictly forbidden to bring water into the zinc pot; control the Al content in the zinc solution between 0.10~0.11 wt%.

6. The 440MPa grade P-containing hot-dip galvanized iron alloy high-strength IF steel according to claim 1, characterized in that Step 8: Increase or decrease the power according to the degree of flouring of the plate, and fully open the edge burners.

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