Ultralow yield ratio high-phosphorus atmospheric corrosion resistant steel and preparation method thereof

Abstract

This invention relates to the field of metallurgical technology, specifically to an ultra-low yield strength ratio, high-phosphorus, atmospheric corrosion-resistant steel and its preparation method. The preparation method includes: placing a cut billet into a slow-cooling pit, with the initial slow-cooling temperature ≥500℃ and the final slow-cooling temperature not lower than 300℃; heating the slow-cooled billet, controlling the billet's exit temperature from the furnace to 1140~1170℃, and the furnace time coefficient to be 10~11 min / cm; employing a two-stage rolling process, with the billet undergoing the first stage of rolling after descaling, and the surface temperature of the rolled piece at the start of the second stage of rolling being T2=(T+1600 / H-1.8H)℃, and the rolled steel plate not being water-cooled; and then placing the rolled steel plate between steel plates at 500~600℃ for at least 48 hours to achieve stacking cooling. This invention utilizes a fine, uniform microstructure and phosphorus and chromium compounds to improve the material's corrosion resistance, meeting the requirements for corrosion resistance and high toughness of steel used in building and engineering structures in coastal atmospheric environments.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to an ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel and its preparation method. Background Technology

[0002] Steel plates exposed to air for extended periods will corrode and deteriorate, and the cost of rust prevention constitutes a significant portion of the later maintenance expenses for buildings and steel bridges. Steel plates with excellent corrosion resistance, under certain conditions, can be painted without coating, greatly reducing the operation and maintenance costs of steel structures and offering significant economic and environmental benefits. Therefore, corrosion-resistant steel has a significant advantage over ordinary steel in the application of large-scale steel structure projects such as bridges and building structures.

[0003] Chinese patent application CN 109161793 A discloses a low yield strength ratio high strength weathering steel. The finished product obtained by this method has a thickness of 6~12mm, which is relatively thin and has a narrow range of applications. It is necessary to use precious elements such as Cu, Ni, Cr, Nb and Ti at the same time, resulting in high alloy cost.

[0004] Chinese patent application CN 113201687 A discloses a 420MPa grade weathering bridge steel, whose chemical composition and mass percentage are as follows: C 0.05%~0.07%, Si 0.25%~0.50%, Mn 1.10%~1.70%, P≤0.020%, S≤0.010%, Cu 0.28%~0.35%, Ni 0.20%~0.30%, Cr 0.45%~0.55%, Mo≤0.10%, Nb 0.008%~0.030%, Ti 0.010%~0.030%, V 0.005%~0.015%, Als 0.020%~0.035%, Ca 0.0020%~0.0050%, O≤0.0040%, N The alloy composition of this weathering bridge steel is complex, ranging from 0.0025% to 0.0080%, with the balance being Fe and unavoidable impurities. This results in high production costs. Furthermore, the high yield strength ratio (between 0.78 and 0.82) significantly impacts bridge safety and seismic resistance. Summary of the Invention

[0005] To address the technical problems of high production costs and high yield strength ratio in weathering steel due to the large amount of precious elements used, this invention provides an ultra-low yield strength ratio, high phosphorus, atmospheric corrosion resistant steel and its preparation method. It employs a lower carbon content and adds inexpensive phosphorus and chromium alloying elements. The fine, uniform microstructure and phosphorus and chromium compounds are used to improve the material's corrosion resistance, giving it high toughness, high corrosion resistance, and easy weldability. This meets the corrosion resistance and high toughness requirements for building and engineering structures in coastal atmospheric environments.

[0006] In a first aspect, the present invention provides a method for preparing ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel. The chemical composition and weight percentage of the ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel are as follows: C: 0.05%~0.07%, Si: 0.10%~0.20%, Mn: 1.20%~1.35%, 0.060%≤P≤0.080%, S≤0.003%, Als: 0.010%~0.040%, Cr≤0.80%, Cu≤0.50%, Ni≤0.50%, Ti≤0.020%, with the balance being Fe and unavoidable impurities.

[0007] The preparation method includes at least the following steps:

[0008] The cut billet is placed in a slow cooling pit. The initial slow cooling temperature of the billet is ≥500℃, and the final slow cooling temperature is not lower than 300℃.

[0009] The billet after slow cooling is heated, and the billet exiting the furnace is controlled at 1140~1170℃, with a furnace time coefficient of 10~11min / cm.

[0010] A two-stage rolling process is adopted. After descaling the billet, the first stage of rolling is carried out. When the second stage of rolling begins, the surface temperature of the rolled piece is T2=(T+1600 / H-1.8H)℃, where T=870+11.2[%C]-1.8[%Si]+18[%Mn]+1.6[%Al]-1.2[%Cr], and H is the thickness of the steel plate in mm. The steel plate is not water-cooled after rolling.

[0011] After rolling, the steel plate is placed between steel plates at 500~600℃ for cooling, and the cooling time is not less than 48 hours.

[0012] Furthermore, the chemical composition of the ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel meets the marine atmospheric corrosion resistance index of 1.75≤ξ≤2.0;

[0013] ξ=(1.0-0.14[%C])×(1.005[%Si])×(1.0-0.056[%Mn])×(1.0+0.6[%P])×(1.0-0.36[%S])×(1 .0+0.30[%Cu])×(1.0+0.32[%Ni])×(1.0+0.70[%Ti])+21.28[%P]-3.5[%Ni]×[%P]+0.5[%Cr].

[0014] Furthermore, the chemical composition of the ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel meets the hardenability index of 1.50≤ф≤2.2;

[0015] ф=2.4×[%C] 1 / 2+1.4×[%Cr]+0.4×[%Ni]+2.1×[%Mo]+0.56×[%Mn]-1.68×[%Cu] 1 / 2 +1.386×[%Cu].

[0016] Furthermore, the process also includes the following steps: using a converter for smelting, top and bottom blowing, to fully decarburize and dephosphorize, so that the final carbon content is 0.045%~0.065% and the phosphorus content is 0.060%≤P≤0.080%;

[0017] LF-RH refining reduces the content of harmful elements / impurities and enables micro-alloying;

[0018] The entire casting process is protected, and a heavy pressure reduction technique is used at the end of the casting process, with a reduction ratio of 12% to 13%.

[0019] Secondly, the present invention provides an ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel produced by the above-mentioned preparation method.

[0020] Furthermore, the ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel has a yield strength ≥350MPa, tensile strength ≥630MPa, elongation after fracture ≥20%, yield strength ratio ≤0.65, and KV2 ≥47J at -40℃.

[0021] Furthermore, the thickness of ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel is ≤60mm.

[0022] Furthermore, the microstructure of the ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel is mainly composed of uniform and fine ferrite + pearlite, with the ferrite grain size being greater than grade 10.

[0023] Chemical composition is one of the important factors affecting the overall performance of a product. The chemical composition of this invention is limited as follows.

[0024] C: The main solid solution strengthening element in steel, which can significantly improve the strength of steel plates, but a high carbon content is detrimental to the welding, toughness and plasticity of steel plates. In order to effectively reduce segregation, improve the uniformity of microstructure, avoid galvanic corrosion caused by potential differences between heterogeneous phases, improve the corrosion resistance of steel, and take into account economic efficiency, the carbon content is limited to 0.05%~0.07%.

[0025] Si: Silicon is one of the effective deoxidizing and exothermic elements in the steelmaking process. It has a certain solid solution strengthening effect, which is conducive to the formation of a dense rust layer and can improve the atmospheric corrosion resistance of steel. However, excessive silicon content will reduce the surface quality, weldability and low temperature toughness of steel. Therefore, the silicon content in this invention is controlled at 0.10%~0.20%.

[0026] Mn: Manganese has a strong solid solution strengthening effect, which can significantly reduce the phase transformation temperature of steel, refine the microstructure of steel, and is inexpensive. It is an effective element for improving strength. To achieve sufficiently high tensile strength and obtain a low yield strength ratio, the content should not be less than 0.80%. However, excessive content can easily cause segregation in the cast billet, forming banded structures, reducing the weldability and toughness of the weld heat-affected zone, as well as corrosion resistance. Therefore, the manganese content in this invention is controlled at 1.20%~1.35%.

[0027] P: Phosphorus can effectively improve the atmospheric corrosion resistance of steel. When phosphorus and copper are added to steel together, they can show a better composite effect. However, excessive phosphorus content will significantly reduce the plasticity and low-temperature toughness of steel, increase the cold brittleness of steel, and deteriorate the weldability.

[0028] S: Sulfur causes hot brittleness in steel, reduces the ductility and toughness of steel, promotes the anisotropy of steel plates, and sulfide inclusions also significantly reduce the corrosion resistance of steel. The sulfur content in steel should be strictly controlled; the sulfur content in this invention is controlled at ≤0.003%.

[0029] Al: Aluminum is one of the effective deoxidizing elements in the steelmaking process. It can effectively reduce the content of inclusions in steel and refine the grains. However, if the content is too high, it can easily cause cracks on the surface of the billet. In this invention, the aluminum content is controlled at 0.010%~0.040%.

[0030] Cr: Chromium is not only an element that improves the hardenability of steel, but also one of the effective elements for improving the weather resistance of steel. It has a significant effect on improving the passivation ability of steel, and can promote the formation of a dense passivation film or protective rust layer on the steel surface. Its enrichment in the rust layer can effectively improve the selective permeability of the rust layer to corrosive media. However, excessive Cr content will increase production costs and reduce the toughness and weldability of steel.

[0031] Cu (Copper): Copper is one of the effective elements for improving the weather resistance of steel. Its high electrochemical potential ratio allows it to densify rust on the steel plate surface, promoting the formation of a stable rust layer. Adding copper to steel helps form a dense, well-adhesive amorphous oxide (hydrocarbon oxide) protective layer on the steel surface, resulting in significant corrosion resistance. Furthermore, copper reacts with sulfur to form insoluble sulfides, thus offsetting the harmful effects of copper on the steel's corrosion resistance. However, when the copper content is too high, due to copper's low melting point (below the billet heating temperature), the precipitated copper accumulates in a liquid state at the austenite grain boundaries. When the precipitated copper content reaches a certain level, cracks are easily generated during heating or hot rolling.

[0032] Ni (Ni): Adding nickel to steel significantly improves its corrosion resistance. Simultaneously, nickel forms a nickel-rich copper phase with copper, which remains solid in the outer oxide layer, reducing the copper enrichment in the matrix and decreasing the chance of liquid copper-rich phase formation. This prevents hot brittleness defects and reduces the susceptibility to hot cracking during casting, hot rolling, and welding. Furthermore, nickel is an indispensable alloying element for achieving excellent low-temperature toughness in steel plates; therefore, the Ni / Cu ratio in steel is generally controlled to be ≥1 / 2. However, excessive nickel content increases the adhesion of oxide scale, which, when pressed into the steel, can form hot-rolling defects on the surface. Moreover, nickel is a precious metal, and excessively high nickel content significantly increases the cost of steel alloys.

[0033] Ti: Titanium produces strong precipitation strengthening and moderate grain refinement. Adding trace amounts of titanium to steel aims to combine with nitrogen in the steel to form highly stable titanium nitride particles. This inhibits austenite grain growth in the weld hard zone (HAZ) and alters secondary phase transformation products, improving the low-temperature toughness of high heat input welding. The titanium content added to the steel must match the nitrogen content. If too little titanium is added, the number of titanium nitride particles formed will be insufficient to inhibit austenite grain growth in the HAZ and alter secondary phase transformation products, thus failing to improve the low-temperature toughness of the HAZ in high heat input welding. If too much titanium is added, large-sized titanium nitride particles precipitate during the solidification process of the molten steel. These large particles not only fail to inhibit austenite grain growth in the HAZ but also become the initiation point for crack initiation.

[0034] The beneficial effects of this invention are as follows:

[0035] This invention employs a low-cost microalloying design with a simple composition. By combining low carbon with trace amounts of P, Cu, Cr, Ni, and other elements, it improves weather resistance and overall mechanical properties while reducing the amount of precious elements used. The low carbon equivalent design enhances the material's weldability. It does not rely on a large reduction rate in rough rolling and is produced through controlled rolling, resulting in a short production cycle, low cost, and ease of widespread application.

[0036] The steel plate of this invention has excellent strength-plasticity matching, weldability, low yield strength ratio (≤0.65), weather resistance improved by more than 1.5 times, fatigue resistance, and improves the service life and safety of structural components. It is suitable for unpainted buildings and bridges, outdoor tower structures, and engineering machinery manufacturing. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1Metallographic image of the 10mm ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel prepared in Example 3. Detailed Implementation

[0039] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0040] In the following embodiments, the marine atmospheric corrosion resistance index ξ is calculated according to the following formula:

[0041] ξ=(1.0-0.14[%C])×(1.005[%Si])×(1.0-0.056[%Mn])×(1.0+0.6[%P])×(1.0-0.36[%S])×(1 .0+0.30[%Cu])×(1.0+0.32[%Ni])×(1.0+0.70[%Ti])+21.28[%P]-3.5[%Ni][%P]+0.5[%Cr].

[0042] The hardenability index ф is calculated according to the following formula:

[0043] ф=2.4×[%C] 1 / 2 +1.4×[%Cr]+0.4×[%Ni]+2.1×[%Mo]+0.56×[%Mn]-1.68×[%Cu] 1 / 2 +1.386×[%Cu].

[0044] During the second stage of rolling, the surface temperature T2 of the rolled piece is calculated according to the following formula:

[0045] T2 = (T + 1600 / H - 1.8H)℃

[0046] In the formula, T = 870 + 11.2[%C] - 1.8[%Si] + 18[%Mn] + 1.6[%Al] - 1.2[%Cr].

[0047] H represents the thickness of the steel plate, in mm.

[0048] Example 1

[0049] A 60mm ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel has the following chemical composition:

[0050] C: 0.06%, Si: 0.16%, Mn: 1.32%, P: 0.068%, S: 0.001%, Als: 0.028%, Ni: 0.41%, Ti: 0.016%, with the remainder being Fe and unavoidable impurities. The calculated marine atmospheric corrosion resistance index ξ = 1.53 and hardenability index ф = 1.49.

[0051] Its preparation method is as follows:

[0052] 1) The smelting converter adopts top and bottom blowing to fully decarburize and dephosphorize, with the final carbon content being 0.03% and the phosphorus content being 0.08%; LF is used for microalloying, with the final carbon content being 0.040% and the phosphorus content being 0.063%, and the microalloying content is added to the target value; RH vacuum reaches below 133pa, the pressure holding time is 13min, the pure degassing time is 11min, the soft blowing time is 12min, and the RH treatment and subsequent calming time is 33min.

[0053] 2) The casting end adopts heavy pressure reduction technology with a reduction ratio of 12.6%.

[0054] 3) Slow cooling: After the billet is cut, it is placed in a slow cooling pit. The initial slow cooling temperature of the billet is 668℃, and the temperature of the billet when it leaves the pit is 332℃.

[0055] 4) Heating: The billet loading temperature is 310℃, the billet unloading temperature is 1160℃, the time coefficient in the furnace is 10.2min / cm, and the temperature difference between the inside and outside of the billet is ≤10℃.

[0056] 5) Rolling: Two-stage rolling is adopted. After descaling, the billet is rolled in the first stage. The surface temperature of the billet in the first stage is 1067℃. The surface temperature of the rolled piece in the second stage is T2=812℃. The rolled steel plate is not water-cooled.

[0057] 6) Stacking cooling: After rolling, the steel plate is quickly placed between steel plates at 586℃ for stacking cooling for 60 hours.

[0058] Example 2

[0059] A 30mm ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel has the following chemical composition:

[0060] C: 0.05%, Si: 0.18%, Mn: 1.30%, P: 0.064%, S: 0.001%, Als: 0.026%, Cr: 0.62%, Ni: 0.4%, with the remainder being Fe and unavoidable impurities. The calculated marine atmospheric corrosion resistance index ξ = 1.77 and hardenability index ф = 2.29.

[0061] Its preparation method is as follows:

[0062] 1) The smelting converter adopts top and bottom blowing to fully decarburize and dephosphorize, with the final carbon content being 0.03% and the phosphorus content being 0.085%; LF is used for microalloying, with the final carbon content being 0.040% and the phosphorus content being 0.062%, and the microalloying content is added to the target value; RH vacuum reaches below 133pa, the holding time is 14min, the pure degassing time is 10min, the soft blowing time is 12min, and the RH treatment and subsequent calming time is 35min.

[0063] 2) The casting end adopts heavy pressure reduction technology with a reduction ratio of 12.8%.

[0064] 3) Slow cooling: After the billet is cut, it is placed in a slow cooling pit. The initial slow cooling temperature of the billet is 670℃, and the temperature of the billet when it leaves the pit is 326℃.

[0065] 4) Heating: The billet loading temperature is 308℃, the billet unloading temperature is 1162℃, the time coefficient in the furnace is 10.3min / cm, and the temperature difference between the inside and outside of the billet is ≤10℃.

[0066] 5) Rolling: Two-stage rolling is adopted. After descaling the billet, the first stage of rolling is carried out. The surface temperature of the billet in the first stage is 1063℃. The surface temperature of the rolled piece in the second stage is T2=892℃. The rolled steel plate is not water-cooled.

[0067] 6) Stacking cooling: After rolling, the steel plate is quickly placed between steel plates at 576℃ for stacking cooling for 53 hours.

[0068] Example 3

[0069] A 10mm ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel has the following chemical composition:

[0070] C: 0.06%, Si: 0.17%, Mn: 1.28%, P: 0.066%, S: 0.001%, Als: 0.023%, Cr: 0.68%, Cu: 0.39%, with the remainder being Fe and unavoidable impurities. The calculated marine atmospheric corrosion resistance index ξ = 1.93 and hardenability index ф = 1.75.

[0071] Its preparation method is as follows:

[0072] 1) The smelting converter adopts top and bottom blowing to fully decarburize and dephosphorize, with the final carbon content being 0.03% and the phosphorus content being 0.083%; LF is used for microalloying, with the final carbon content being 0.040% and the phosphorus content being 0.063%, and the microalloying content is added to the target value; RH vacuum reaches below 133pa, the holding time is 13min, the pure degassing time is 9min, the soft blowing time is 12min, and the RH treatment and subsequent calming time is 33min.

[0073] 2) The casting end adopts heavy pressure reduction technology with a reduction ratio of 12.5%.

[0074] 3) Slow cooling: After the billet is cut, it is placed in a slow cooling pit. The initial slow cooling temperature of the billet is 676℃, and the temperature of the billet when it leaves the pit is 328℃.

[0075] 4) Heating: The billet loading temperature is 311℃, the billet unloading temperature is 1168℃, the time coefficient in the furnace is 10.7min / cm, and the temperature difference between the inside and outside of the billet is ≤10℃.

[0076] 5) Rolling: Two-stage rolling is adopted. After descaling the billet, the first stage of rolling is carried out. The surface temperature of the billet at the start of the first stage of rolling is 1078℃. The surface temperature of the rolled piece at the start of the second stage of rolling is T2=1035℃. The rolled steel plate is not water-cooled.

[0077] 6) Stacking cooling: After rolling, the steel plate is quickly placed between steel plates at 596℃ for stacking cooling for 55 hours.

[0078] The steel plates of Examples 1-3 were observed to have fine and uniform metallographic structures, mainly consisting of ferrite and pearlite, with the grain size of the ferrite reaching level >10.

[0079] The comprehensive performance of the steel plates in Examples 1-3 was tested, and the results are shown in Table 1 below.

[0080] Table 1 Tensile properties and low-temperature toughness of the steel plates in the embodiments of the present invention

[0081]

[0082] As shown in Table 1, the steel plate prepared by the method of the present invention has a low yield strength ratio, combined with Figure 1 It can be seen that the steel plate prepared by the method of the present invention has fine grains and a uniform microstructure. It can be concluded that the method of the present invention can significantly enhance the safety and seismic and fatigue resistance of structural components. Although the phosphorus content is high, the excellent microstructure allows the steel plate to still possess good toughness at -40℃.

[0083] The electrochemical corrosion potential of the steel plates in Examples 1-3 was determined using a three-electrode system: the working electrodes were 10 × 10 mm² and 10 × ... 2 The study included bare electrode plates and rusted electrodes prepared after 30 cycles of alternating wet and dry etching. The reference electrode was a saturated calomel electrode (SCE), and the auxiliary electrode was a 9 cm² electrode. 2A platinum sheet was used, with a salt bridge connecting the working electrode and the reference electrode. The operating temperature was room temperature (25°C), and all potential values ​​are relative to a saturated calomel electrode. Polarization curves were obtained using a Solartron 1287 potentiodynamic scanning instrument with a scanning potential range of ±0.2V vs. Ecorr (relative to self-corrosion potential) and a scan rate of 0.1667 mV / s. The experiment was conducted at room temperature. The self-corrosion potentials after electrochemical measurements are shown in Table 2 below.

[0084] Table 2 Self-corrosion potential of steel plates in embodiments of the present invention

[0085]

[0086] As can be seen from the data in Table 2, the self-corrosion potential of the steel plate produced by the method of the present invention is lower than that of the American standard weathering steel Corten-A, indicating that the corrosion resistance of the ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel provided by the present invention is higher than that of the American standard weathering steel Corten-A.

[0087] The steel plates from Examples 1 to 3 were processed into standard specimens according to the "TB / T 2375-1993 Test Method for Cyclic Immersion Corrosion of Weathering Steel for Railways" and compared with Corten-A steel. A 72-hour cyclic immersion test was conducted, and the test results are shown in Table 3.

[0088] Table 3. Results of periodic immersion test on steel plates according to embodiments of the present invention.

[0089]

[0090] As can be seen from the data in Table 3, the steel plate produced by this method has a much lower weight loss than the American standard weathering steel Corten-A under the same corrosion conditions, indicating that the corrosion resistance of the ultra-low yield strength ratio high phosphorus atmospheric corrosion resistant steel provided by this invention is higher than that of the American standard weathering steel Corten-A.

[0091] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for producing an ultra-low yield ratio high phosphorus atmospheric corrosion resistant steel, characterized by, The chemical composition and weight percentage of the ultra-low yield ratio and high-phosphorus atmospheric corrosion-resistant steel are as follows: C: 0.05% - 0.07%, Si: 0.10% - 0.20%, Mn: 1.20% - 1.35%, 0.060% ≤ P ≤ 0.080%, S ≤ 0.003%, Als: 0.010% - 0.040%, 0 < Cr ≤ 0.80%, Cu ≤ 0.50%, Ni ≤ 0.50%, Ti ≤ 0.020%, and the balance is Fe and unavoidable impurities; the thickness of the ultra-low yield ratio and high-phosphorus atmospheric corrosion-resistant steel ≤ 60 mm, and the yield ratio ≤ 0.65; the metallographic structure of the ultra-low yield ratio and high-phosphorus atmospheric corrosion-resistant steel is mainly ferrite + pearlite, and the ferrite grain size is greater than 10 grades; The preparation method at least includes the following steps: Put the cut billet into a slow cooling pit, the starting slow cooling temperature of the billet ≥ 500 °C, and the ending slow cooling temperature is not lower than 300 °C; Heat the billet after slow cooling, control the billet out-of-furnace temperature to be 1140 - 1170 °C, and the in-furnace time coefficient is 10 - 11 min / cm; Adopt two-stage rolling. After descaling the billet, carry out the first-stage rolling. When starting the second-stage rolling, the surface temperature T2 of the rolled piece = (T + 1600 / H - 1.8H) °C, where T = 870 + 11.2[%C] - 1.8[%Si] + 18[%Mn] + 1.6[%Al] - 1.2[%Cr], H is the thickness of the steel plate in mm, and the rolled steel plate is not water-cooled; After rolling, place the steel plate between steel plates at 500 - 600 °C for stacking and cooling, and the stacking and cooling time is not less than 48 hours; The chemical composition of the ultra-low yield ratio and high-phosphorus atmospheric corrosion-resistant steel satisfies the marine atmospheric corrosion resistance index 1.50 ≤ ξ ≤ 2.0; ξ = (1.0 - 0.14[%C]) × (1.005[%Si]) × (1.0 - 0.056[%Mn]) × (1.0 + 0.6[%P]) × (1.0 - 0.36[%S]) × (1.0 + 0.30[%Cu]) × (1.0 + 0.32[%Ni]) × (1.0 + 0.70[%Ti]) + 21.28[%P] - 3.5[%Ni] × [%P] + 0.5[%Cr]; The chemical composition of the ultra-low yield ratio and high-phosphorus atmospheric corrosion-resistant steel satisfies the hardenability index 1.40 ≤ ф ≤ 2.4; f = 2.4 x [%C] 1 / 2 + 1.4 x [%Cr] + 0.4 x [%Ni] + 2.1 x [%Mo] + 0.56 x [%Mn] - 1.68 x [%Cu] 1 / 2 + 1.386 x [%Cu].

2. The production method according to claim 1, wherein It also includes the following steps: adopt converter smelting, top-bottom combined blowing, fully decarburize and dephosphorize to make the end carbon content 0.045% - 0.065% and the phosphorus content 0.060% ≤ P ≤ 0.080%; Through LF-RH refining, reduce the content of harmful elements / impurities and carry out microalloying; Protect the casting throughout the process, and use the heavy reduction technology at the end of casting, with the reduction ratio of 12% - 13%.

3. An ultra-low yield ratio and high-phosphorus atmospheric corrosion-resistant steel produced by using the preparation method described in any one of claims 1 - 2.

4. The ultra-low yield ratio high phosphorus atmospheric corrosion resistant steel according to claim 3, characterized in that, The yield strength of the ultra-low yield ratio and high-phosphorus atmospheric corrosion-resistant steel ≥ 350 MPa, the tensile strength ≥ 630 MPa, the elongation after fracture ≥ 20%, and -40 °C KV2 ≥ 47 J.

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