An E-grade weathering steel, its preparation method and application

Abstract

This invention relates to the field of alloy steel technology, and provides an E-grade weathering steel, its preparation method, and its application. The E-grade weathering steel of this invention, by limiting the content of each chemical element and proposing innovative technical requirements, precisely controls the addition amount of some key elements to leverage the key regulatory role of element ratios on the comprehensive properties of the high heat input weathering steel, including its weldability, mechanical properties, and weather resistance. This results in a highly efficient, easily weldable E-grade weathering steel that meets the requirements of 100J / cm heat input welding, with a yield strength ≥420MPa, tensile strength ≥540MPa, elongation ≥19%, KV2 ≥120J at -40℃, and corrosion resistance index I ≥6.5.

Description

Technical Field

[0001] This invention belongs to the field of alloy steel technology, specifically relating to an E-grade weathering steel, its preparation method, and its application. Background Technology

[0002] In recent years, the construction of various steel structure buildings and bridges has driven the demand for steel and raised the bar for its performance. Steel is now required to possess not only high strength, toughness, a reasonable yield strength ratio, and excellent weldability, but also to minimize environmental pollution, meaning it must have a certain degree of corrosion resistance to resist rust from corrosive media in the air. The development of high-performance 420MPa grade weathering steel has, to some extent, met the requirements for mechanical and corrosion resistance in engineering projects. However, the assembly and combination of steel structures generally employs traditional single-wire gas shielded welding and submerged arc welding methods, with a welding heat input of 15–45 KJ / cm, resulting in low welding efficiency, high labor costs, and long project cycles. Using multi-wire gas shielded welding, double-wire submerged arc welding, or gas-electric vertical welding processes, with a heat input reaching 100 KJ / cm, can increase welding efficiency by 2–5 times or more, significantly reducing project budgets and timelines. However, due to the addition of alloying elements such as Si, Cu, and Cr, traditional weathering steels, when subjected to high heat input (≥50KJ / cm) welding, experience a decrease in cooling rate. Consequently, the weld heat-affected zone commonly exhibits side strip ferrite, coarse granular bainite, and hard and brittle M / A phases. This significantly reduces the joint strength and low-temperature toughness, failing to meet engineering standard requirements and making it difficult to achieve both high-efficiency welding and good mechanical properties of the steel.

[0003] To mitigate the impact of high heat input on the deterioration of strength and toughness in the heat-affected zone (HAZ) of low-alloy steel, extensive research has been conducted both domestically and internationally. Internationally, Japan, as a leading example, has achieved optimized control of micro / nano inclusions / precipitates in steel through precise regulation of metallurgical reactions, promoting IGF formation. Techniques such as Nippon Steel's HTUFF Mg / Ca oxysulfide technology and JFEEWEL's technology for controlling alloying elements like B, N, O, and Ca have been developed. However, steelmaking is complex and time-consuming, making it difficult to guarantee the quantity and size of inclusions. Large inclusions can also become crack initiation points, reducing low-temperature toughness and stability. Some experts have also proposed microalloying methods, which primarily focus on controlling "solid-phase reactions" rather than "liquid-phase reactions." By rationally controlling the addition of microalloying elements such as Nb, V, Ti, B, and N, the coarsening of the original austenitic structure is suppressed, and acicular ferrite nucleation is promoted, thereby improving the strength and toughness of the HAZ. For weathering steel, alloying elements such as Si, Cu, Cr, and Ni are required to ensure weather resistance. However, the addition of these alloys affects the phase transformation temperature, microstructure, particle precipitation behavior, and nucleation of the heat-affected zone after high heat input welding. When using microalloying to improve low-temperature toughness, the amount and ratio of microalloying elements added should be precisely controlled to achieve a balance between high heat input welding performance, corrosion resistance, good strength, and low-temperature toughness in weathering steel. To achieve these goals, many scholars have conducted the following beneficial explorations.

[0004] Chinese patent CN106574316 discloses a method for manufacturing a steel plate for high heat input welding. The steel plate of this invention has a yield strength ≥460MPa, a tensile strength ≥570MPa, an elongation ≥16%, and a heat-affected zone ductile-brittle transition temperature below -40℃ when welding with a heat input higher than 200KJ / cm. However, the Si content in this patent is only 0.01-0.1%, which may result in a high oxygen content in the steel plate. The addition of Ca may reduce the increase in oxygen content in the steel plate caused by low Si, but Ca is easy to combine with inclusions such as Mn and S. Especially during high heat input welding, Ca transitions to the weld through the melting base metal. The liquid molten pool stays for a long time, and the time for inclusions to combine and grow during the floating process is prolonged, which easily leads to the residue of large inclusions ≥3μm, increasing the crack sensitivity of the heat-affected zone and reducing low-temperature toughness. This patent uses Cu and Ni as the main alloys to improve corrosion resistance. During high heat input welding, the fusion ratio increases and the molten base metal transitions to the weld. The large amount of Cu and Ni reduces the fluidity of the weld pool, causing metallurgical quality problems in the weld and may also reduce the performance of the weld.

[0005] Chinese patent CN101845602 discloses a high-performance weather-resistant steel for building structures and its manufacturing method, which can meet the requirements of high heat input welding of thick plates ≥40mm. However, the Ti content in this patent is only 0.007-0.013%, while the Al and Ca contents are 0.035-0.065% and 0.001-0.005%, respectively. The increase in Al and Ca content can compensate for the deoxidation problem caused by the low Ti content, but Al and Ca can form high-melting-point composite inclusions, and the size is relatively large, resulting in high crack sensitivity of the steel plate. In addition, the nucleation ability of composite inclusions such as Al and Ca is limited, while the number of precipitated particles formed by Ti, N and Nb, V, etc. is limited, and the size may be difficult to reach the critical nucleation size (≥0.2μm). During high heat input welding, the number of nucleation sites is small, and the proportion of acicular ferrite in the microstructure is small, which is not conducive to the toughness of the heat-affected zone of high heat input welding.

[0006] Chinese patent CN103451561 discloses a weathering steel plate capable of high heat input welding and its production method. During high heat input welding, it achieves an impact energy exceeding 47J at -20℃, but the low-temperature toughness at -40℃ is not explicitly stated. Low-temperature toughness is closely related to the microstructure. This patent mainly utilizes composite precipitates of Ti, B, and N to promote the formation of acicular ferrite to improve toughness. However, the lattice mismatch between Ti and B precipitates and ferrite is high, limiting their nucleation ability and resulting in a limited number of acicular ferrite in the weld. As the impact temperature decreases, crack sensitivity increases, and the impact energy at -40℃ may not meet the requirements. Furthermore, the Si and Mn contents in this composition are only below 0.1% and 0.40-0.80%, respectively. During high heat input welding, the microstructure of the heat-affected zone coarsens, the fine-grain strengthening effect weakens, and the solid solution strengthening effect of Si and Mn is limited, inevitably leading to a significant reduction in the strength of the heat-affected zone and posing a potential safety hazard to the entire component.

[0007] It is evident that the existing patents' summary of steel plate compositions that can meet the high heat input welding requirements of 420MPa grade weathering steel do not provide sufficient research on the design and control of multi-element alloying components. As a result, these steel plates still have many defects in terms of strength, low-temperature toughness, and corrosion resistance when welding with high heat input, making it difficult to achieve a balance of comprehensive performance. There is an urgent need to seek new alloying methods to meet the high heat input welding requirements of weathering steel. Summary of the Invention

[0008] The purpose of this invention is to provide an E-grade weathering steel, its preparation method, and its application. The E-grade weathering steel provided by this invention has a yield strength of not less than 420 MPa and can meet the requirements of high heat input welding of 100 KJ / cm.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] This invention provides a grade E weathering steel, comprising the following elements by mass percentage: Mn 1.3–1.4%, Cr 0.35–0.55%, Ni 0.3–0.4%, Cu 0.25–0.45%, Si 0.2–0.4%, Mo 0.09–0.12%, C 0.038–0.058%, V 0.020–0.035%, Alt 0.015–0.034%, Ti 0.013–0.017%, N 0.004–0.008%, Mg 0.003–0.007%, O 0.002–0.003%, La 0.001–0.003%, B 0.0004–0.0008%, Nb 0–0.014%, P 0–0.013%, S 0–0.008%, balance being Fe and unavoidable impurities;

[0011] The mass percentage content of each element in the E-grade weathering steel meets the following conditions: 1.0≤M≤1.50, where M=[27(%B)+(%Ni)+5(%Mo)+2(%Mn)] / [(%Cr)+3(%Cu)+5(%Si)]; 0.235≤T≤0.310, where T=7.80(%Ti)+4.94(%V)+0.06(%B)+0.14(%C)+0.08(%N);

[0012] The atmospheric corrosion resistance index (I) of the Grade E weathering steel is ≥6.5, where I = 26.01 (% Cu) + 3.88 (% Ni) + 1.20 (% Cr) + 1.49 (% Si) + 17.28 (% P) - 7.29 (% Cu)(% Ni) - 9.10 (% Ni)(% P) - 33.39 (% Cu) 2 .

[0013] Preferably, the yield strength R of the E-grade weathering steel is... eL ≥420MPa, tensile strength R m ≥540MPa.

[0014] Preferably, the E-grade weathering steel has a welding heat-affected zone impact energy of -40℃ KV2 ≥ 60J when the welding heat input is 100kJ / cm.

[0015] Preferably, in the heterogeneous nucleation particles of the weld heat-affected zone of the E-grade weathering steel at a welding heat input of 100 kJ / cm, the number density of (Ti,B,V)(C,N) composite precipitates is 6.14 × 10⁻⁶. 4 ~7.28×10 4 pcs / mm 3 The ratio of heterogeneous ferrite nucleation is ≥75%.

[0016] This invention also provides a method for preparing the Grade E weathering steel described in the above technical solution, comprising the following steps:

[0017] According to the element ratio of the Grade E weathering steel described in the above technical solution, the steel is smelted and cast sequentially to obtain a cast alloy billet;

[0018] The cast alloy billet is subjected to heat treatment and rolling in sequence to obtain the E-grade weathering steel.

[0019] Preferably, the heat treatment temperature is 1150–1280°C, and the holding time is ≥3 hours.

[0020] Preferably, the rolling process includes a first rolling and a second rolling, performed sequentially; the temperature of the first rolling is 1050–1150°C; and the temperature of the second rolling is 740–840°C.

[0021] Preferably, the heat treatment further includes phosphorus removal; the phosphorus removal method is high-pressure water phosphorus removal.

[0022] Preferably, the rolling process further includes cooling; the cooling includes sequential water cooling and air cooling.

[0023] The present invention also provides the application of the Grade E weathering steel described in the above technical solution or the Grade E weathering steel prepared by the preparation method described in the above technical solution in the preparation of welded structural components.

[0024] This invention provides a grade E weathering steel, comprising the following elements by mass percentage: Mn 1.3–1.4%, Cr 0.35–0.55%, Ni 0.3–0.4%, Cu 0.25–0.45%, Si 0.2–0.4%, Mo 0.09–0.12%, C 0.038–0.058%, V 0.020–0.035%, Alt 0.015–0.034%, Ti 0.013–0.017%, N 0.004–0.008%, Mg 0.003–0.007%, O 0.002–0.003%, La 0.001–0.003%, B 0.0004–0.0008%, Nb 0–0.014%, P 0~0.013%, S 0~0.008%, balance being Fe and unavoidable impurities; the mass percentage content of each element in the E-grade weathering steel meets the following conditions: 1.0≤M≤1.50, where M=[27(%B)+(%Ni)+5(%Mo)+2(%Mn)] / [(%Cr)+3(%Cu)+5(%Si)]; 0.235≤T≤0.310, where T=7.80(%Ti)+4.94( %V)+0.06(%B)+0.14(%C)+0.08(%N); The atmospheric corrosion resistance index I of the E-grade weathering steel is ≥6.5, where I = 26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.10(%Ni)(%P)-33.39(%Cu) 2 This invention, by limiting the content of each chemical element and proposing innovative technical requirements, precisely controls the addition amount of some key elements to leverage the crucial regulatory role of element ratios in the comprehensive performance of the high heat input weathering steel, including its weldability, mechanical properties, and weather resistance. This results in a high-efficiency, easily weldable, Grade E weathering steel that meets the requirements of 100J / cm heat input welding, exhibiting a yield strength ≥420MPa, tensile strength ≥540MPa, elongation ≥19%, KV2 ≥120J at -40℃, and a corrosion resistance index I ≥6.5. Meanwhile, the E-grade weathering steel described in this invention can meet the welding requirements of various high-efficiency welding methods such as double-wire submerged arc welding, multi-wire gas shielded welding, and gas-electric vertical welding. When the heat input is 100kJ / cm, its heat-affected zone KV2 at -40℃ is ≥60J, and the welding efficiency is 2 to 5 times higher than that of traditional welding methods. Furthermore, due to the addition of weathering elements, the E-grade weathering steel provided by this invention can be used for unpainted high-rise building structures and bridge structures, and can achieve low-cost, stable, and mass industrial production, reducing manufacturing costs, shortening the construction period, and meeting the requirements of environmental protection and high efficiency. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A schematic diagram of a high-heat-input twin-wire submerged arc welding process;

[0027] Figure 2 Comparative microstructures of the parent material of the E-grade weathering steel provided by the present invention and the comparative alloy steel provided by the comparative example are shown in the following figures: (a) is the parent material microstructure of the E-grade weathering steel described in Example 1; (b) is the parent material microstructure of the E-grade weathering steel described in Example 5; (c) is the parent material microstructure of the comparative alloy steel described in Comparative Example 1; and (d) is the parent material microstructure of the comparative alloy steel described in Comparative Example 4.

[0028] Figure 3 Comparative microstructures of the heat-affected zone of the E-grade weathering steel provided by the present invention and the comparative alloy steel provided by the comparative examples under a welding heat input of 100 kJ / cm are shown in (a) to (c), respectively. The heat-affected zone microstructures of the E-grade weathering steel described in Examples 2, 4 and 10 are shown in (d) to (h), respectively.

[0029] Figure 4 Comparative images and energy dispersive spectroscopy (EDS) of precipitated particles in the heat-affected zone of the E-grade weathering steel provided in Example 2 and the comparative alloy steel provided in Comparative Example 2, under a welding heat input of 100 kJ / cm. Detailed Implementation

[0030] This invention provides a grade E weathering steel, comprising the following elements by mass percentage: Mn 1.3–1.4%, Cr 0.35–0.55%, Ni 0.3–0.4%, Cu 0.25–0.45%, Si 0.2–0.4%, Mo 0.09–0.12%, C 0.038–0.058%, V 0.020–0.035%, Alt 0.015–0.034%, Ti 0.013–0.017%, N 0.004–0.008%, Mg 0.003–0.007%, O 0.002–0.003%, La 0.001–0.003%, B 0.0004–0.0008%, Nb 0–0.014%, P 0–0.013%, S 0–0.008%, balance being Fe and unavoidable impurities;

[0031] The mass percentage content of each element in the E-grade weathering steel meets the following conditions: 1.0≤M≤1.50, where M=[27(%B)+(%Ni)+5(%Mo)+2(%Mn)] / [(%Cr)+3(%Cu)+5(%Si)]; 0.235≤T≤0.310, where T=7.80(%Ti)+4.94(%V)+0.06(%B)+0.14(%C)+0.08(%N); 1.0≤M≤1.50;

[0032] The atmospheric corrosion resistance index (I) of the Grade E weathering steel is ≥6.5, where I = 26.01 (% Cu) + 3.88 (% Ni) + 1.20 (% Cr) + 1.49 (% Si) + 17.28 (% P) - 7.29 (% Cu)(% Ni) - 9.10 (% Ni)(% P) - 33.39 (% Cu) 2 .

[0033] The Grade E weathering steel of this invention comprises 1.3-1.4% Mn, preferably 1.32-1.48% by mass percentage. In this invention, Mn, as an alloying element, enhances strength and toughness in the steel plate, while also expanding the austenite phase region, lowering the Ac1, Ac3, Ar1, and Ar3 point temperatures, and refining ferrite grains. By controlling the Mn content within the aforementioned range, this invention prevents excessive Mn from increasing segregation within the steel plate, reducing the uniformity of its mechanical properties and low-temperature toughness, and also prevents excessive Mn from increasing hardenability, affecting high-heat welding, and leading to an increased yield strength ratio.

[0034] The E-grade weathering steel of this invention comprises 0.35-0.55% Cr, preferably 0.4-0.5%, by mass percentage. In this invention, Cr can form a dense oxide layer on the steel plate surface, which improves the steel's resistance to atmospheric corrosion and weathering performance. This invention controls the Cr content within the above-mentioned range to prevent excessive Cr content from forming side-laminated ferrite in the steel microstructure, thus reducing the steel's weldability.

[0035] The E-grade weathering steel of this invention comprises 0.3-0.4% Ni, preferably 0.32-0.38%, by mass percentage. In this invention, the addition of Ni promotes the formation of a stable rust layer, improves the low-temperature toughness of the steel, significantly enhances the low-temperature toughness of the matrix and the weld heat-affected zone, effectively prevents network cracking caused by Cu hot brittleness, and also improves the weather resistance of the steel. By controlling the Ni content within the above range, this invention reduces the manufacturing cost of the steel.

[0036] The E-grade weathering steel of this invention comprises 0.25-0.45% Cu, preferably 0.3-0.4%, by mass percentage. In this invention, Cu improves the weather resistance of the steel, while the combined addition of Cr and Cu further enhances its resistance to atmospheric corrosion and its resistance to corrosion from industrial or marine atmospheres. This invention controls the Cu content within the above-mentioned range to prevent excessive Cu content from causing brittle cracks in the continuously cast billet, affecting the quality of the steel plate; and to prevent excessive Cu content from increasing the sensitivity to cold cracking during welding, thus reducing the weldability of the steel plate.

[0037] The E-grade weathering steel of this invention comprises 0.2-0.4% Si, preferably 0.25-0.35%, by mass percentage. In this invention, Si promotes deoxidation of molten steel and improves the strength of the steel plate. Controlling the Si content within the above range is based on the economic efficiency and operability of the steelmaking process, while also preventing excessive Si content from impairing the low-temperature toughness and weldability of the steel plate. Especially under high heat input welding conditions, Si not only promotes the formation of weathering islands (MA islands), but also results in large, unevenly distributed MA islands. Excessive Si content severely damages the low-temperature toughness of the weld heat-affected zone.

[0038] The E-grade weathering steel of this invention comprises 0.09-0.12% Mo, preferably 0.1-0.11%, by mass percentage. In this invention, Mo plays a role in refining grains during steel plate preparation and high heat input welding, thereby improving the strength and toughness of the steel plate and the weld heat-affected zone. On the other hand, the addition of a small amount of Mo to the weathering steel can also form molybdates during corrosion, improving the corrosion resistance of the weathering steel.

[0039] The E-grade weathering steel of this invention comprises 0.038–0.058% C, preferably 0.04–0.05%, by mass percentage. In this invention, C is an indispensable element in alloy steel, directly affecting the steel's strength, low-temperature toughness, and weldability. By controlling the C content within the above-mentioned range, this invention prevents excessively high C content from deteriorating weldability and increasing the tendency for cold cracking, while also preventing excessively low C content (<0.02%) from reducing steel strength and hindering steel rolling.

[0040] The E-grade weathering steel of this invention, by mass percentage, comprises 0.020–0.035% V, preferably 0.03–0.034%. In this invention, the addition of V can form V(C,N) and composite (V,Ti)(C,N) in the steel. V(C,N) precipitates in ferrite / bainite, increasing the strength of the steel. Simultaneously, the V(C,N) and (V,Ti)(C,N) precipitated during high-heat welding can act as nucleation sites for acicular ferrite, promoting nucleation and refining grains. This invention controls the V content within the above range to prevent insufficient V addition (below 0.01%), resulting in too little precipitated V(C,N) and insufficient improvement in the strength of the steel plate; and to prevent excessive V addition (above 0.10%), which would impair the low-temperature toughness, elongation, and weldability of the steel plate. In this invention, as the steel thickness increases, the V content can be appropriately taken closer to the upper limit.

[0041] The E-grade weathering steel of this invention comprises 0.015–0.034% Alt, preferably 0.02–0.03%, by mass percentage. In this invention, the Alt in the steel can fix free nitrogen ([N]) in the steel, reduce free nitrogen ([N]) in the weld heat-affected zone (HAZ), promote the precipitation of ferrite during the welding cooling cycle (the pre-precipitated AlN can serve as a nucleation site for ferrite, refining the microstructure of the HAZ), and improve the low-temperature impact toughness of the HAZ in high heat input welding. This invention controls the Alt content within the above range to prevent the addition of excessive Alt from forming a large number of dispersed needle-like Al2O3 inclusions in the steel, which would impair the low-temperature impact toughness and weldability of the steel plate.

[0042] The E-grade weathering steel of this invention comprises 0.013–0.017% Ti, preferably 0.014–0.016%, by mass percentage. In this invention, Ti combines with N to form TiN particles with high high-temperature stability, which can inhibit austenite growth (temperature ≤1350℃), refine grains, and improve the low-temperature toughness of the steel plate and its HAZ region, thereby improving weldability. This invention controls the Ti content within the above range to prevent excessive Ti content from forming large Ti composite particles, which would reduce the toughness of the HAZ region.

[0043] Based on mass percentage, the E-grade weathering steel of this invention comprises 0.004–0.008% N, preferably 0.005–0.007%. In this invention, the added V and Ti form TiN and VN particles with N. TiN can prevent the growth of austenite during the heating and holding process of the steel billet, thereby refining the ferrite grain size and improving the strength and plasticity of the steel. VN can act as nucleation sites for ferrite during high heat input welding, promoting the formation of acicular ferrite, refining the grains, and improving the toughness of the weld heat-affected zone.

[0044] Based on mass percentage, the E-grade weathering steel of the present invention comprises 0.003 to 0.007% Mg, preferably 0.004 to 0.006%.

[0045] Based on mass percentage, the E-grade weathering steel of the present invention comprises 0.002 to 0.003%, preferably 0.0022 to 0.0028%.

[0046] Based on mass percentage, the E-grade weathering steel of this invention comprises 0.001 to 0.003% La, preferably 0.0015 to 0.0025%.

[0047] In this invention, by adding Mg, La and O elements, fine inclusions containing Mg oxide and La oxide are formed during the steelmaking process. Before the phase transformation, the nanoscale inclusions can pin the original austenitic grain boundaries, while the submicron-scale inclusions can also significantly promote the heterogeneous nucleation of ferrite, which has the effect of further increasing the content of acicular ferrite in the microstructure.

[0048] Based on mass percentage, the E-grade weathering steel of this invention comprises 0.0004–0.0008% B, preferably 0.0005–0.0007%. In this invention, B plays two roles: a certain amount of dissolved B improves the hardenability of the steel, preventing excessive softening of the heat-affected zone during high heat input welding; dissolved B can also segregate at grain boundaries, inhibiting the growth of original austenitic grain boundaries; on the other hand, precipitated B and N can form BN particles, which act as heterogeneous nucleation sites for ferrite.

[0049] The E-grade weathering steel of this invention comprises 0-0.014% Nb, preferably 0-0.01%, by mass percentage. In this invention, Nb mainly plays a role in improving the strength of the steel plate. During the rolling process of the steel plate, Nb precipitates in the form of Nb(C,N) particles, playing a precipitation strengthening role.

[0050] The E-grade weathering steel of this invention comprises 0-0.013% P by mass percentage, preferably 0-0.01%. In this invention, P can improve the atmospheric corrosion resistance of steel. Controlling the P content within the above range can prevent the weather resistance from being difficult to guarantee due to excessively low phosphorus content, while avoiding the deterioration of the low-temperature toughness of the base metal and weld joint due to excessively high phosphorus content. In particular, it can prevent the phosphorus in the base metal from excessively entering the weld during the welding process, forming a eutectic, which would reduce the impact energy of the weld joint.

[0051] The E-grade weathering steel of this invention, by mass percentage, comprises 0-0.008% sulfur (S), preferably 0-0.005%. In this invention, sulfur (S), as a harmful inclusion in steel, significantly impairs the low-temperature toughness (especially transverse low-temperature toughness) and weather resistance of the steel plate. More importantly, S combines with manganese (M) in the steel to form MnS inclusions. During hot rolling, the plasticity of MnS causes it to extend along the rolling direction, forming MnS inclusion bands along the rolling direction, severely damaging the transverse low-temperature impact toughness, Z-axis properties, and weldability of the steel plate. Furthermore, S is a major element causing hot brittleness during hot rolling. Considering steelmaking conditions and costs, the S content is controlled within the aforementioned range.

[0052] In this invention, the mass percentage content of each element in the E-grade weathering steel satisfies the following conditions: 1.0≤M≤1.50; M=[27(%B)+(%Ni)+5(%Mo)+2(%Mn)] / [(%Cr)+3(%Cu)+5(%Si)]; 0.235≤T≤0.310; T=7.80(%Ti)+4.94(%V)+0.06(%B)+0.14(%C)+0.08(%N).

[0053] In this invention, during welding with a high heat input of 100 KJ / cm, the hard phases such as M / A become coarser due to the significant increase in the amount of Cr, Cu, and Si elements added, leading to higher crack sensitivity in the heat-affected zone and reduced low-temperature toughness. By setting M within the aforementioned range and adjusting the amounts of B, Ni, Mi, Mn, Cr, Cu, and Si elements added, the hard phase M / A in the heat-affected zone is made more dispersed and refined, reducing crack sensitivity and thus improving impact toughness.

[0054] In this invention, T is set within the aforementioned range. During welding with a high heat input of 100 KJ / cm, the precipitation of (Ti,B,V) and (C,N) particles is regulated, and the precipitated particles of 0.1–1.6 μm that have a nucleation effect are satisfied within 6.14 × 10⁻⁶. 4 ~7.28×10 4 pcs / mm 3 Between these conditions, the nucleation of acicular ferrite in the heat-affected zone was improved, with its number reaching over 75%, which increased the number of large-angle grain boundaries and improved low-temperature toughness.

[0055] In this invention, the atmospheric corrosion resistance index (I) of the Grade E weathering steel is ≥ 6.5; I = 26.01 (% Cu) + 3.88 (% Ni) + 1.20 (% Cr) + 1.49 (% Si) + 17.28 (% P) - 7.29 (% Cu)(% Ni) - 9.10 (% Ni)(% P) - 33.39 (% Cu) 2 .

[0056] In this invention, by adjusting the four main components Cu, Ni, Cr and Si (excluding the brittle element P), the I is set within the above range to ensure that the weathering steel of this invention does not exceed 1 mm in thickness due to corrosion over a 100-year lifespan under typical atmospheric conditions.

[0057] In this invention, the yield strength R of the E-grade weathering steel is... eL Preferably ≥420MPa, more preferably 450~550MPa; tensile strength R m Preferably ≥540MPa, more preferably 570~650MPa.

[0058] In this invention, the impact energy of the weld heat-affected zone of the E-grade weathering steel at a welding heat input of 100 kJ / cm at -40℃ KV2 is preferably ≥60J, more preferably 60~180J, and most preferably 65~160J.

[0059] In this invention, the preferred number density of (Ti,B,V)(C,N) composite precipitates in the heterogeneous nucleation particles of the E-grade weathering steel in the weld heat-affected zone at a welding heat input of 100 kJ / cm is 6.14 × 10⁻⁶. 4 ~7.28×10 4 pcs / mm 3 More preferably 6.85×10 4 ~7.28×10 4 pcs / mm 3 The ratio of heterogeneous ferrite nucleation is preferably ≥75%, more preferably ≥80%.

[0060] This invention, by limiting the content of each chemical element and proposing innovative technical requirements, precisely controls the addition amount of some key elements to give full play to the key regulatory role of element ratio on the comprehensive performance of the high heat input weathering steel of this invention, such as high heat input welding performance, mechanical properties, and weather resistance. It has yielded a high-efficiency easy-to-weld E-grade weathering steel that can meet the requirements of 100J / cm heat input welding, with a yield strength ≥420MPa, tensile strength ≥540MPa, elongation ≥19%, KV2 ≥120J at -40℃, and corrosion resistance index I ≥6.5. Meanwhile, the E-grade weathering steel described in this invention can meet the welding requirements of various high-efficiency welding methods such as double-wire submerged arc welding, multi-wire gas shielded welding, and gas-electric vertical welding. When the heat input is 100kJ / cm, its heat-affected zone KV2 at -40℃ is ≥60J, and the welding efficiency is 2 to 5 times higher than that of traditional welding methods. Furthermore, due to the addition of weathering elements, the E-grade weathering steel provided by this invention can be used for unpainted high-rise building structures and bridge structures, and can achieve low-cost, stable, and mass industrial production, reducing manufacturing costs, shortening the construction period, and meeting the requirements of environmental protection and high efficiency.

[0061] This invention also provides a method for preparing the Grade E weathering steel described in the above technical solution, comprising the following steps:

[0062] According to the element ratio of the Grade E weathering steel described in the above technical solution, the steel is smelted and cast sequentially to obtain a cast alloy billet;

[0063] The cast alloy billet is subjected to heat treatment and rolling in sequence to obtain the E-grade weathering steel.

[0064] According to the above technical solution, the element ratio of Grade E weathering steel is sequentially smelted and cast to obtain a cast alloy billet.

[0065] The present invention does not impose any particular limitation on the smelting and casting methods, and any method known to those skilled in the art can be used.

[0066] After obtaining the cast alloy billet, the present invention performs heat treatment and rolling on the cast alloy billet in sequence to obtain the E-grade weathering steel.

[0067] In this invention, the heat treatment temperature is preferably 1150-1280℃, more preferably 1180-1250℃; the heat treatment time is preferably ≥3h, more preferably 3-6h.

[0068] In this invention, the purpose of setting the above-mentioned heat treatment temperature range is to heat the steel billet to the temperature of complete austenitization.

[0069] In this invention, the heat treatment preferably includes phosphorus removal; the phosphorus removal method is preferably high-pressure water phosphorus removal; this invention does not have a special limitation on the process of high-pressure water phosphorus removal, and any method known to those skilled in the art can be used.

[0070] In this invention, the rolling process preferably includes a first rolling and a second rolling process performed sequentially; the temperature of the first rolling is preferably 1050-1150°C, more preferably 1080-1130°C; the temperature of the second rolling is preferably 740-840°C, more preferably 760-820°C.

[0071] In this invention, the first rolling temperature is the rolling temperature of the austenite recrystallization region, and the second rolling temperature is the rolling temperature of the austenite non-recrystallization region. The purpose of the first stage rolling is to refine the austenite grains, and the purpose of the second stage rolling is to provide high-density ferrite nucleation sites.

[0072] In this invention, the rolling process preferably includes cooling; the cooling preferably includes water cooling and air cooling performed sequentially; the water cooling rate is preferably 10-20℃ / s, more preferably 10-15℃ / s; the temperature of the steel after water cooling is 480-630℃, more preferably 480-600℃; this invention does not have any special limitations on the air cooling process, and any method known to those skilled in the art can be used.

[0073] The preparation method provided by this invention defines the process parameters of thermomechanical rolling, including heat treatment temperature, two-step rolling temperature, cooling rate and stopping cooling temperature. Its purpose is to form a moderately refined multiphase composite structure in the weathering steel base material to meet the mechanical property requirements of 420MPa grade weathering steel.

[0074] The present invention also provides the application of the Grade E weathering steel described in the above technical solution or the Grade E weathering steel prepared by the preparation method described in the above technical solution in the preparation of welded structural components.

[0075] In this invention, the welding method of the welded component preferably includes double-wire submerged arc welding, multi-wire gas shielded welding, or gas-electric vertical welding.

[0076] To further illustrate the present invention, the following detailed description, in conjunction with the accompanying drawings and embodiments, describes the Grade E weathering steel, its preparation method, and its applications, but these descriptions should not be construed as limiting the scope of protection of the present invention.

[0077] Examples 1-10 and Comparative Examples 1-5

[0078] Ten heats of the steel from the embodiments of the present invention and five heats of the steel from the comparative examples were produced in a 125kg vacuum induction furnace, wherein the elemental composition of the steel from the embodiments of the present invention conforms to the requirements defined in the present invention. The steel from the embodiments and the steel from the comparative examples were melted and cast sequentially according to a specific elemental composition ratio to obtain as-cast alloy billets. These billets were held at 1150-1280℃ for at least 3 hours to ensure complete austenitization. After exiting the furnace, they were descaled using high-pressure water. A two-stage rolling process was adopted: the first stage rolling temperature was controlled between 1050-1150℃, with 4-7 passes and a cumulative reduction of ≥60%; the second stage rolling temperature was 740-840℃, with 4-8 passes and a cumulative reduction of ≥75%. In the cooling process, after rolling, the billets were directly fed into a rapid cooling water device and cooled at a rate of 10-20℃ / s to between 480-630℃ before being air-cooled to room temperature, finally producing 24mm thick plates. The specific rolling processes of the embodiments and comparative examples are shown in Table 1 below.

[0079] Table 1 Rolling parameters of Examples 1-10 and Comparative Examples 1-5

[0080]

[0081]

[0082] The composition of the steels provided in Examples 1-10 and Comparative Examples 1-5 was analyzed according to GB / T 4336 "Spark Source Atomic Emission Spectroscopy Analysis Method for Carbon Steel and Medium-Low Alloy Steel (Conventional Method)". The results are shown in Table 2.

[0083] Table 2 provides chemical composition data (wt.%) of the steels used in Examples 1-10 and Comparative Examples 1-5.

[0084]

[0085]

[0086] Samples were taken from the steels provided in Examples 1-10 and Comparative Examples 1-5. Tensile specimens were taken transversely and longitudinally at 1 / 2 of the plate thickness according to GB / T 13239 standard, and strength tests were performed. Impact specimens were taken along the rolling direction at 1 / 2 of the plate thickness according to GB / T 229 standard. A total of three specimens were tested, and the average value was taken. The results of the basic mechanical property tests are shown in Table 3.

[0087] Table 3 provides mechanical property data for steel from Examples 1-10 and Comparative Examples 1-5.

[0088]

[0089]

[0090] As shown in Tables 2 and 3, Examples 1-10 and Comparative Examples 11-15 produced according to the technical requirements of this invention all exhibit excellent strength and toughness, meeting the requirements of yield strength ≥420MPa, tensile strength ≥540MPa, yield-to-tensile ratio below 0.84, elongation ≥20%, and low-temperature impact energy of the base material at -40℃ all exceeding 120J, fully meeting the mechanical property requirements of Grade E steel. Furthermore, the weather resistance index I calculated based on the chemical composition is all not less than 6.5.

[0091] The microstructure of the steel provided in the examples and comparative examples was observed. Figure 2 As can be seen, compared with the steel in the comparative example, the E-grade weathering steel provided by the present invention has a mixed structure of granular bainite, acicular ferrite and blocky ferrite, which can ensure that the steel plate has excellent strength, toughness and plasticity, and is more conducive to controlling the yield strength ratio of the steel plate.

[0092] Using the steels provided in Examples 1-10 and Comparative Examples 1-5, a 100 KJ / cm double-wire submerged arc welding test was conducted according to the bevel type, welding process parameters, and welding sampling plan in Tables 4 and 5. The welding schematic diagram is shown below. Figure 1Mechanical properties were tested at 1 mm and 2 mm outside the fusion line. The welding test results are shown in Table 6.

[0093] Table 4. Welding test parameters with a heat input of 100 KJ / cm.

[0094]

[0095] Table 5. Simplified diagram of welding deposition, welding process parameters, and welding sampling plan.

[0096]

[0097] Table 6 shows the heat-affected zone (-40℃) low-temperature toughness of steel under high heat input welding in Examples 1-10 and Comparative Examples 1-5.

[0098]

[0099]

[0100] As shown in Table 6, the impact performance of the heat-affected zones (HAZs) at -40°C in Examples 1-10, 1 mm and 2 mm outside the fusion line, all reached over 60 J. However, the impact performance of the HAZs in the comparative examples 11-15 was generally lower. This difference is attributed to the composition ratio and the microstructure of the HAZ. Figure 3 The following analysis is made on the differences in low-temperature toughness in the heat-affected zone.

[0101] The chemical compositions of Examples 1-10 meet the requirements of this invention and satisfy 1.0≤M≤1.50 and 0.235≤T≤0.31. These two regulatory relationships limit the proportions of alloying elements, restricting the quantity and size of the M / A hard and brittle phase generated during high heat input welding, and limiting the size and quantity of submicron-sized precipitates with heterogeneous nucleation effects. These two limitations ensure that, under a heat input of 100 KJ / cm, the M / A size in the heat-affected zone is small, and the proportion of acicular ferrite in the microstructure reaches over 75%, enabling the impact performance of Examples 1-10 to reach -40℃ KV2≥60J.

[0102] Comparative Examples 1, 3, 4, and 5 all satisfy the chemical regulation relationship 1.0 ≤ M ≤ 1.50, but the regulation relationship T is only 0.19, 0.13, 0.09, and 0.13, respectively. Although the base material of this composition reaches the strength level of 420 MPa weathering steel and has excellent low-temperature toughness through the regulation of alloying elements such as Si, Mn, and Ni. However, after welding with a high heat input of 100 KJ / cm, the low-temperature impact toughness of the heat-affected zone decreased significantly. Its microstructure was dominated by a large amount of granular bainite. It is generally believed that the formation temperature of granular bainite and acicular ferrite is in the intermediate temperature transformation range of 400-600℃. Granular bainite nucleates at grain boundaries, while acicular ferrite heterogeneously nucleates on intragranular inclusions or precipitates. Numerous studies have confirmed that acicular ferrite can provide a good combination of strength and toughness. The main reason for the poor toughness of the above four comparative examples is that the proportion of toughness-beneficial elements such as acicular ferrite in the microstructure is relatively small. This is mainly due to the unreasonable alloy element ratio, which results in a small number of precipitated particles or the precipitated particles failing to meet the nucleation size requirements during the slow cooling process after high heat input welding. This leads to the formation of a large amount of granular bainite in the intermediate temperature transformation range, resulting in a significant decrease in low-temperature toughness.

[0103] The chemical regulation relationships in Comparative Example 2 satisfy 1.0≤M≤1.50 and 0.235≤T≤0.310, respectively. Compared with other comparative examples, its low-temperature toughness at -40℃ is somewhat improved, but its V content is only 0.015% and N content is only 0.0038%. During the high heat input welding cooling process, due to the high solubility of V, the preferentially precipitated particles are Ti(C,N) particles. As the cooling temperature drops to about 900℃, V(C,N) begins to precipitate and is enriched in Ti, indicating the formation of Ti,V(C,N) composite precipitates. Compared with Ti(C,N) alone, V-rich Ti,V(C,N) has a lower mismatch with ferrite, which can reduce the interfacial energy for ferrite nucleation and is more conducive to nucleation. However, for Example 2, the V and N contents are relatively low. During the cooling process, some Ti,V(C,N) composite precipitates are formed, which serve as ferrite nucleation sites. The majority of the precipitates in the microstructure are still Ti(C,N) precipitates, which have a weak nucleation ability. This results in a low number of acicular ferrite particles in Comparative Example 2. Although the low-temperature toughness is improved, it still cannot meet the low-temperature toughness requirements of the heat-affected zone for high heat input welding.

[0104] Depend on Figure 3 As can be seen, compared with the weld heat-affected zone of the steel described in the comparative example, the weld heat-affected zone of the E-grade weathering steel of the present invention has a large amount of acicular ferrite and blocky ferrite, which can significantly increase the proportion of large-angle grain boundaries in the microstructure, increase the resistance to crack propagation, and improve the toughness of the heat-affected zone.

[0105] Depend on Figure 4As can be seen, compared with the submicron-sized precipitates of Ti(C,N) in the heat-affected zone of the steel welded in the comparative example, the precipitates in the heat-affected zone of the E-grade weathering steel welded in this invention are submicron-sized V-rich (Ti,V)(C,N) particles. The V-rich precipitates can reduce the mismatch with ferrite, improve the heterogeneous nucleation ability of ferrite, and increase the content of heterogeneous nucleation of ferrite in the heat-affected zone.

[0106] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A type of E-grade weathering steel, characterized in that, The composition includes the following elements in mass percentage: Mn 1.3~1.4%, Cr 0.35~0.55%, Ni 0.3~0.4%, Cu 0.25~0.45%, Si 0.2~0.4%, Mo 0.09~0.12%, C 0.038~0.058%, V 0.020~0.035%, Alt 0.015~0.034%, Ti 0.013~0.017%, N 0.004~0.008%, Mg 0.003~0.007%, O 0.002~0.003%, La 0.001~0.003%, B 0.0004~0.0008%, Nb 0~0.014%, P 0~0.013%, S 0~0.008%, with the balance being Fe and unavoidable impurities. The mass percentage content of each element in the E-grade weathering steel meets the following conditions: 1.0≤M≤1.50, where M=[27(%B)+(%Ni)+5(%Mo)+2(%Mn)] / [(%Cr)+3(%Cu)+5(%Si)]; 0.235≤T≤0.310, where T=7.80(%Ti)+4.94(%V)+0.06(%B)+0.14(%C)+0.08(%N); The atmospheric corrosion resistance index (I) of the Grade E weathering steel is ≥ 6.5, where I = 26.01(%Cu) + 3.88(%Ni) + 1.20(%Cr) + 1.49(%Si) + 17.28(%P) - 7.29(%Cu)(%Ni) - 9.10(%Ni)(%P) - 33.39(%Cu) 2 ; The yield strength R of the E-grade weathering steel eL ≥420MPa, tensile strength R m ≥540MPa; The E-grade weathering steel has an impact energy of -40℃ KV2 ≥ 60J in the weld heat-affected zone when the welding heat input is 100kJ / cm. In the heterogeneous nucleation particles of the weld heat-affected zone of the E-grade weathering steel at a welding heat input of 100 kJ / cm, the number density of (Ti,B,V)(C,N) composite precipitates is 6.14 × 10⁻⁶. 4 ~7.28×10 4 pcs / mm 3 The ratio of heterogeneous ferrite nucleation is ≥75%.

2. The method for preparing the Grade E weathering steel according to claim 1, characterized in that, Includes the following steps: The elements of the Grade E weathering steel are smelted and cast sequentially to obtain a cast alloy billet. The cast alloy billet is subjected to heat treatment and rolling in sequence to obtain the E-grade weathering steel.

3. The preparation method according to claim 2, characterized in that, The heat treatment temperature is 1150~1280℃, and the holding time is ≥3h.

4. The preparation method according to claim 2, characterized in that, The rolling process includes a first rolling and a second rolling, performed sequentially; the temperature of the first rolling is 1050~1150℃; and the temperature of the second rolling is 740~840℃.

5. The preparation method according to claim 2 or 3, characterized in that, The heat treatment process also includes phosphorus removal; the phosphorus removal method is high-pressure water phosphorus removal.

6. The preparation method according to claim 2 or 4, characterized in that, The rolling process also includes cooling; the cooling includes sequential water cooling and air cooling.

7. The application of the Grade E weathering steel according to claim 1 or the Grade E weathering steel prepared by the preparation method according to any one of claims 2 to 6 in the preparation of welded structural components.

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