E-grade weathering steel plate that can withstand welding heat input of 125kJ / cm and has a yield strength of not less than 420MPa

Abstract

The invention discloses an E-grade weathering steel plate which can withstand welding heat input of 125 kJ / cm and has a yield strength of not less than 420 MPa. The chemical composition is as follows by mass percentage: C 0.035-0.055, Si 0.20-0.40, Mn 1.35-1.45, Cu 0.30-0.50, Cr 0.40-0.55, Ni 0.30-0.45, Mo 0.13-0.16, Nb 0.032-0.058, V 0.020-0.035, Ti 0.013-0.017, B 0.0008-0.0012, Alt 0.015-0.034, N 0.0040-0.0080, Ca 0.004-0.006, O 0.0015~0.0025, Mg 0.008~0.013, P≤0.015, S≤0.005, and the rest are iron and unavoidable impurities. The present invention optimizes the alloy element ratio, on the basis of meeting the atmospheric corrosion resistance of the steel plate, constructs a double-peak toughness improvement system in the heat affected zone of the steel plate welding, which has nano-scale precipitated particles pinning austenite grain boundaries and micro-scale precipitated particles promoting needle-shaped / blocky ferrite heterogeneous nucleation to form a basket-shaped toughness structure, so that the weathering steel plate can withstand a welding heat input of 125kJ / cm and a yield strength of not less than 420MPa.

Description

Technical Field

[0001] The invention belongs to the field of weathering steel plate manufacturing and large heat input welding, and particularly relates to an E-grade weathering steel plate which can withstand a welding heat input of 125 kJ / cm and has a yield strength of not less than 420 MPa. Background Art

[0002] With the continuous development of the economy and society in various countries around the world, the contradiction between economic development and resources and environment has further intensified. It is an inevitable development direction to build a resource-saving and environmentally friendly society and promote the harmonious development of man and nature. Weathering steel is widely used in bridges, containers, railway vehicles, port buildings, offshore platforms, oil pipelines, oil storage tanks and other fields due to its significant advantages such as good corrosion resistance, low maintenance cost, less resource waste and environmental friendliness. At the same time, with the in-depth development of the economy, large-scale, high-parameter and safety of steel structures have become an inevitable trend, and the demand for high-performance and easy-to-weld medium and thick steel plates has continued to expand. High heat input welding technology (welding heat input is not less than 50 kJ / cm) represented by multi-wire submerged arc welding, narrow gap submerged arc welding, gas-electric vertical welding and electroslag welding can take into account both welding efficiency and production cost, and has been widely studied and applied in various industries.

[0003] In the prior art, the following related patent documents disclose technical solutions for weathering steel and manufacturing methods.

[0004] Patent CN 103451537 B discloses a low-temperature weathering steel plate with high welding performance and a production method thereof. The chemical composition (mass percentage) of the steel plate is C: 0.02~0.06%, Si: ≤0.15%, Mn: 0.40~0.80%, P: 0.001~0.01%, S: ≤0.004%, Cu: 0.20~0.60%, Ni: 1.2~5.0%, Ti: 0.01~0.02%, Al: <0.01%, Mo :0.10~0.50%, Zr: 0.003~0.008%, W: 0.02~0.2%, Sn: 0.001~0.004%, the balance is iron and inevitable impurities; the steel plate is prepared by smelting and TMCP production process, with tensile strength ≥550MPa, -60℃ impact toughness ≥240J; when the welding heat input is 150kJ / cm, the -40℃ impact toughness of the steel plate welding heat affected zone is ≥100J. The steel plate of this invention has excellent weldability and low temperature toughness, but a large amount of precious element Ni (1.2%~5.0%) needs to be added, which greatly increases the production cost, and the steel plate needs to regulate uncommon alloy elements such as Zr, W, Sn, etc., the alloy system is complex, and the smelting process is cumbersome, which greatly limits its wide application.

[0005] Patent CN 103695801 B discloses a high-toughness, high-weathering steel and its manufacturing method, the weight percentage of which is: C: 0.035-0.075%, Si: ≤0.30%, Mn: 0.40-0.80%, P: 0.07-0.11%, S: ≤0.004%, Cu: 0.20-0.50%, Ni: 0.10-0.40%, Cr: 0.40-0.70%, Ti: 0.008-0.016%, Nb: 0.010-0.030%, N: ≤0.0050%, Ca: 0.001%-0.004%, the rest is Fe and unavoidable inclusions. The yield strength of the invented steel is ≥355MPa, the tensile strength is ≥490MPa, and the -40℃ Charpy V-type impact energy is ≥47J. Although the steel plate of this invention has good atmospheric corrosion resistance, its strength is relatively low, and the contents of Ti, Nb, C, and N cannot guarantee the necessary resistance to high heat input welding.

[0006] Although there have been many studies on weathering steel and steel for high heat input welding, there are few studies on steel plates that have both atmospheric corrosion resistance and high heat input welding resistance, and the performance cannot meet the needs of social development. In order to ensure the atmospheric corrosion resistance of steel plates, it is often necessary to add alloying elements such as Si, Cr, Ni, Cu, and Mo, but the above elements will promote the transformation or growth of bainite, form more hard phase M / A components, and inhibit the nucleation of acicular / blocky ferrite in the tough phase, increase the effective grain size, and lead to deterioration of impact toughness; in order to ensure the high heat input welding resistance of steel plates, it is generally necessary to reduce the content of alloying elements in steel, reduce or eliminate the content or size of Widmanstatten structure, side plate ferrite, coarse granular bainite, and hard and brittle phase M / A components in the welding heat affected zone, and inhibit the coarsening of austenite grains to improve the low-temperature impact toughness of steel plates. Therefore, it is often difficult to take into account both atmospheric corrosion resistance and high heat input welding resistance, the contradiction between the proportion of alloying elements is prominent, and the research and development is difficult. Summary of the invention

[0007] The problem to be solved by the present invention is to provide an E-grade weathering steel plate that can withstand welding heat input of 125 kJ / cm and has a yield strength of not less than 420 MPa. By optimizing the alloy element ratio and cooperating with the TMCP process, on the basis of meeting the atmospheric corrosion resistance of the steel plate (I≥6.5), a double-peak toughness improvement system is constructed in the heat affected zone of the steel plate welding, which has nano-scale precipitated particles pinning the austenite grain boundaries and micron-scale precipitated particles promoting the heterogeneous nucleation of needle-shaped / blocky ferrite to form a basket-shaped toughness structure, thereby achieving the weathering steel plate that can withstand welding heat input of 125 kJ / cm and has a yield strength of not less than 420 MPa.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is: an E-grade weathering steel plate that can withstand welding heat input of 125 kJ / cm and has a yield strength of not less than 420 MPa, and the chemical composition of the E-grade weathering steel plate is as follows by mass percentage: C 0.035-0.055, Si 0.20-0.40, Mn 1.35-1.45, Cu 0.30-0.50, Cr0.40-0.55, Ni 0.30-0.45, Mo 0.13-0.16, Nb 0.032-0.058, V 0.020-0.035, Ti 0.013-0.017, B 0.0008-0.0012, Alt 0.015-0.034, N0.0040-0.0080, Ca 0.004~0.006, O 0.0015~0.0025, Mg 0.008~0.013, P ≤0.015, S ≤0.005, and the rest are iron and inevitable impurities; the contents of Ti, Nb, V, B, C, and N meet the following conditions: 0.28≤H* ≤0.45, wherein H*=9.75Ti+3.27Nb+2.44V+0.03B+0.15C+0.10N; the atmospheric corrosion resistance index of the E-grade weathering steel plate is I≥6.5, wherein I=26.01Cu+3.88Ni+1.20Cr+1.49Si+17.28P-7.29CuNi-9.10NiP-33.39Cu 2 .

[0009] Furthermore, when the heat input reaches 125KJ / cm by double-wire submerged arc welding, multi-wire gas shielded welding or gas-electric vertical welding, the welding heat affected zone of the E-grade weathering steel plate has KV2≥47J at -40°C.

[0010] Furthermore, among the nanoparticles with a size of 20-80 nm that can inhibit the growth of austenite grains in the heat affected zone of welding, the number of (Nb, Ti, V) (C, N) composite precipitated particles accounts for 72-85% of the total number of particles of the same size, with a number density of 6.51×10 5 Pieces / mm 3 ~7.56×10 5 Pieces / mm 3 .

[0011] Furthermore, among the micron-sized particles with heterogeneous nucleation size of 0.5-1.5 μm in the weld heat affected zone, the number of composite precipitated particles of (Ti, V, B)(C, N) accounts for 70-81% of the total number of particles of the same size, with a number density of 6.86×10 4 Pieces / mm 3 ~7.51×10 4 Pieces / mm 3 .

[0012] Furthermore, the welding heat affected zone is an area where the peak temperature near the weld is between 1250 and 1400° C. and the temperature is maintained above 500° C. for between 100 and 200 seconds.

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

[0014] The scope of each alloying element of the present invention is limited based on the following reasons:

[0015] C: C is the main element that determines the strength of steel. When C is low, it is difficult to obtain the required strength; when C is high, the hardened structure MA component and degenerate pearlite in the welding heat affected zone increase significantly, which deteriorates the toughness and easily generates welding cracks. In the present invention, C is controlled at 0.035-0.055%.

[0016] Si: Si promotes the formation of a mixture of α-FeOOH and nano-scale silicon oxide in the rust layer, which can not only refine the rust layer, but also prevent Cl ions from penetrating the rust layer to reach the steel matrix, thereby improving its corrosion resistance. In addition, Si can improve the strength of the steel plate due to solid solution strengthening. However, the addition of Si will lead to a significant increase in the content of granular bainite, a significant increase in grain size, and a significant decrease in toughness. In the present invention, Si is controlled at 0.20-0.40%.

[0017] Mn: Mn is a solid solution strengthening element. It can refine ferrite grains by expanding the austenite phase region and reducing the phase transformation point, thereby improving strength and toughness. It can replace part of C. Appropriate reduction of C can reduce the carbon equivalent CEV of the steel plate and improve welding performance. However, an increase in Mn content can easily cause central segregation of the steel plate and increase the sensitivity of welding cracks. In the present invention, Mn is controlled at 1.35~1.45%.

[0018] P: P is an inevitable impurity element in steel, which increases the brittleness of steel, but has a certain beneficial effect on weather resistance. In the present invention, P is controlled at 0.015% or less.

[0019] S: S is an inevitable impurity element in steel and should be reduced as much as possible. In the present invention, S is controlled at 0.005% or less.

[0020] Cu: Cu is an important weather-resistant element, which can inhibit the growth of α-FeOOH particles in the rust layer to refine its particle size, thereby improving the density of the rust layer. An appropriate amount of Cu can also promote the nucleation of needle-shaped / blocky ferrite, but too high a Cu content will cause hot cracks during rolling, which will have an adverse effect on welding performance. In the present invention, the Cu content is controlled at 0.30-0.50%.

[0021] Cr: Cr is conducive to the formation of a dense protective rust layer on the steel surface, and enrichment in the rust layer improves the selective permeability of the rust layer to corrosive media, thereby improving the weather resistance of the steel. At the same time, it can play a certain role in solid solution strengthening and improve the strength of the steel plate. A small amount of Cr can reduce the phase transition temperature, increase the degree of supercooling, and have a certain beneficial effect on grain refinement; but too high Cr will significantly promote the growth of bainite, and the coarse granular bainite will cause the toughness to deteriorate. The Cr content of the present invention is controlled at 0.40~0.55%.

[0022] Ni: Ni can significantly improve the atmospheric corrosion resistance of steel, making it easier for γ-FeOOH to transform into stable α-FeOOH, and reducing the corrosion rate of steel plates. At the same time, the Ni element can significantly improve the toughness of the matrix and the heat-affected zone of welding, and improve the resistance of steel plates to high heat input welding. However, Ni is expensive, and adding too much will lead to a sharp increase in costs. In the present invention, Ni is controlled at 0.30-0.45%.

[0023] Mo: During the corrosion process, adding Mo can promote the formation of molybdates. At the same time, Mo is enriched in the rust layer in the form of FeMo3O4 and MoO3, which improves the compactness of the rust layer and thus improves the atmospheric corrosion resistance. A small amount of Mo can promote the precipitation of nano-scale precipitated phases NbC and TiC, pin the austenite grain boundaries to refine the phase transformation structure, and improve toughness; but too much Mo will form coarse granular bainite, which deteriorates the low-temperature impact toughness. The Mo content of the present invention is controlled at 0.13~0.16%.

[0024] Nb: Nb can be dissolved into the matrix, and improve strength, refine structure, and improve toughness by solute dragging; and Nb can be precipitated from the matrix in the form of nano-scale NbC, NbN precipitates or nano-scale composite precipitates formed with Ti and V, pinning the original austenite grain boundaries, inhibiting the coarsening of the structure, and thus improving the high heat input welding performance. In the present invention, Nb is controlled at 0.032-0.058%.

[0025] V: A proper amount of V combines with C and N elements in steel, precipitates from the matrix to form dispersed micron-sized V (C, N) particles, which as heterogeneous nucleation particles can effectively promote the intracrystalline nucleation of needle-shaped / blocky ferrite in the welding heat affected zone, refine the structure, and greatly improve the steel plate's resistance to high heat input welding. However, excessive V will lead to increased production costs, and the formation of excessively large V-rich precipitated particles as crack sources will deteriorate impact toughness. In the present invention, V is controlled at 0.020~0.035%.

[0026] Ti: Ti is the main element in high heat input welding steel. Ti can be combined with N to form TiN precipitated particles with strong high temperature thermal stability. Nano-sized TiN particles pin the original austenite grain boundary, hindering the growth of grains, and effectively improving the welding performance of steel plates. When the Ti content is high, oversized micron-sized TiN liquid particles will be formed. Under the impact load, TiN liquid particles act as microcrack sources to promote the nucleation and expansion of microcracks, but worsen the impact toughness of the steel plate and the heat-affected zone of the weld. The Ti content of the present invention is controlled at 0.013~0.017%.

[0027] B: B can greatly improve the hardenability of the steel plate. At high temperatures, the solid solution B segregates at the original austenite grain boundary to hinder grain growth. At the same time, BN particles can serve as heterogeneous nucleation cores to promote the nucleation of needle-shaped / blocky ferrite in the crystal, forming a precisely interlocked basket-like structure to hinder the expansion of microcracks, greatly improving the steel plate's resistance to high heat input welding. However, excessive B will lead to the formation of "boron phase", resulting in deterioration of low-temperature impact toughness. In the present invention, B is controlled at 0.0008~0.0012%.

[0028] Al: Al is the main deoxidizer and plays a deoxidation role in the steelmaking process. Therefore, the Al content is controlled at 0.015~0.034%.

[0029] N: Appropriate addition of N can promote the precipitation of TiN and V (C, N) particles. Nano-sized TiN particles can pin the original austenite grain boundary, inhibit the growth of original austenite grains, refine the grains, and improve the toughness of the welding heat affected zone; at the same time, the submicron-sized (V, Ti) (C, N) particles formed by the composite of V (C, N) on TiN can serve as heterogeneous nucleation cores, promote the intracrystalline nucleation of needle-shaped / blocky ferrite, refine the structure, and significantly improve the low-temperature toughness. However, too much N can cause strain aging embrittlement. In the present invention, N is controlled at 0.0040~0.0080%.

[0030] Ca: Ca is the main deoxidizing and desulfurizing element in steel, but too much Ca easily forms large-sized inclusions, which has an adverse effect on impact toughness. In the present invention, Ca is controlled at 0.004-0.006%.

[0031] O: O is an inevitable impurity element in the steelmaking process. In the present invention, O is controlled within 0.0015-0.0025%.

[0032] Mg: Appropriate Mg combined with O through oxide metallurgy can improve the high heat input welding resistance of the steel plate. The Mg content of the present invention is controlled at 0.008-0.013%.

[0033] The weathering steel of the present invention controls the morphology of the second phase particles in the steel by microalloying elements (Ti, Nb, V, B), which is specifically embodied in the regulation relationship 0.28≤H*≤0.45, wherein H*=9.75Ti+3.27Nb+2.44V+0.03B+0.15C+0.10N, so as to ensure that there are mainly two different types of particles in the steel, forming a bimodal size distribution state, namely, nano-scale particles with a size of 20-80 nm that can inhibit the growth of austenite grains and submicron-scale particles with a size of 0.5-1.5 μm for heterogeneous nucleation. When the chemical composition of the steel plate satisfies the relationship 0.28≤H*≤0.45, among the nano-scale particles with a size of 20-80 nm that can inhibit the growth of austenite grains in the welding heat affected zone, the number of (Nb,Ti,V)(C,N) composite precipitated particles accounts for 72-85% of the total number of particles of the same size, and the amount density is 6.51×10 5 Pieces / mm 3 ~7.56×10 5 Pieces / mm 3 Among the micron-sized particles with a size of 0.5-1.5 μm that can be heterogeneously nucleated, the number of composite precipitated particles of (Ti, V, B) (C, N) accounts for 70-81% of the total number of particles of the same size, and the number density is 6.86×10 4 Pieces / mm 3 ~7.51×10 4 Pieces / mm 3 . At this time, the growth of austenite grains can be effectively suppressed during high heat input welding, and a large amount of heterogeneous nucleation needle-shaped / blocky ferrite can be generated inside the grains, which can refine the structure and improve toughness. If H* is too low, precipitated particles with sufficient size and heterogeneous nucleation ability cannot be formed, resulting in a reduction in needle-shaped / blocky ferrite structure, thereby deteriorating low-temperature toughness; if H* is too high, a large number of particles with sizes exceeding nanometers and below submicrometers are formed. Such precipitated particles cannot effectively pin the original austenite grain boundaries, causing serious growth of austenite grains, thereby causing coarse-grain embrittlement problems and poor impact toughness.

[0034] The atmospheric corrosion resistance index of weathering steel calculated by the mass percentage of chemical composition is I≥6.5, where I=26.01Cu+3.88Ni+1.20Cr+1.49Si+17.28P-7.29CuNi-9.10NiP-33.39Cu 2 The steel of the present invention controls the relationship I≥6.5 to ensure that the corrosion thinning of the steel of the present invention does not exceed 1 mm in a hundred-year life cycle under typical industrial atmospheric conditions with a mild climate. Too low I value will cause insufficient weather resistance, while too high I value will damage welding performance and increase production costs.

[0035] The beneficial effects of the present invention are:

[0036] (1) Ensure that the weathering index of the steel plate is ≥ 6.5 by optimizing the proportion of alloy elements;

[0037] (2) By controlling the proportion of microalloying elements, it is ensured that although particles with a size of 20-80 nm are dissolved during the welding thermal cycle, the overall number is still sufficient to inhibit the growth of austenite grains and effectively control the austenite grain size in the heat-affected zone;

[0038] (3) By controlling the proportion of microalloying elements, a large number of particles with a size of 0.5-1.5 μm are ensured to promote the nucleation of intragranular needle-shaped / blocky ferrite and optimize the microstructure and distribution of the welding heat affected zone;

[0039] (4) By controlling the proportion of microalloying elements, the two types of second phase particles are made to form a bimodal size distribution state, giving full play to the characteristics of the two types of particles in the solid phase reaction to regulate the high heat input welding performance of the steel, avoiding the complicated liquid phase reaction control, and enabling stable mass production;

[0040] (5) Yield strength R eL ≥420MPa, tensile strength R m ≥540MPa, when the heat input reaches 125KJ / cm2 by double-wire submerged arc welding, multi-wire gas shielded welding, gas-electric vertical welding and other welding methods, the welding heat affected zone can still meet -40℃ KV2≥47J.

[0041] The present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The microstructure diagram of the heat affected zone of the steel in Example 1 under the condition of welding heat input of 125 kJ / cm;

[0043] Figure 2 The heat-affected zone microstructure diagram of the comparative example 1 steel under the condition of heat input of 125 kJ / cm;

[0044] Figure 3 The grain boundary orientation difference distribution of the heat-affected zone of the steel in Example 1 and Comparative Example 1 under the condition of heat input of 125 kJ / cm;

[0045] Figure 4 The distribution of precipitated phase particles and EDS characterization of the heat affected zone of the steel in Example 1 under the condition of heat input of 125 kJ / cm;

[0046] Figure 5 The distribution of precipitated phase particles and EDS characterization of heat-affected zone of comparative example 1 steel under the condition of heat input of 125 kJ / cm;

[0047] Figure 6The heterogeneous nucleation of acicular ferrite in the heat-affected zone of the steel in Example 1 under the condition of heat input of 125 kJ / cm;

[0048] Figure 7 The curves of the relationship between the corrosion weight loss and time of the industrial atmospheric environment periodic accelerated corrosion test of the steel plates in Example 1 and Comparative Example 1 are shown;

[0049] Figure 8 This is a curve showing the relationship between the corrosion weight loss rate and time of the steel plates in Example 1 and Comparative Example 1 in the industrial atmospheric environment periodic accelerated corrosion experiment. DETAILED DESCRIPTION

[0050] The invention provides an E-grade weathering steel plate which can withstand a welding heat input of 125 kJ / cm and has a yield strength of not less than 420 MPa. The chemical composition of the E-grade weathering steel plate is as follows in percentage by mass: C 0.035-0.055, Si 0.20-0.40, Mn 1.35-1.45, Cu 0.30-0.50, Cr 0.40-0.55, Ni 0.30-0.45, Mo 0.13-0.16, Nb 0.032-0.058, V 0.020-0.035, Ti 0.013-0.017, B 0.0008-0.0012, Alt 0.015-0.034, N 0.0040-0.0080, Ca 0.004-0.006, O 0.0015-0.0025, Mg 0.008~0.013, P ≤0.015, S ≤0.005, the rest are iron and unavoidable impurities.

[0051] The contents of Ti, Nb, V, B, C and N in the above chemical composition meet the requirement of 0.28≤ H* ≤0.45, wherein H*=9.75Ti+3.27Nb+2.44V+0.03B+0.15C+0.10N.

[0052] The atmospheric corrosion resistance index of E-grade weathering steel plate is I≥6.5, where I=26.01Cu+3.88Ni+1.20Cr+1.49Si+17.28P-7.29CuNi-9.10NiP-33.39Cu 2 .

[0053] The solution of the present invention is described in detail below in conjunction with specific embodiments.

[0054] The compositions of the embodiments and comparative examples of the present invention are shown in Table 1. According to the chemical composition ratios of the embodiments and comparative examples, the steel was refined in a 75kg vacuum induction furnace, and the chemical composition was detected according to GB / T 4336 "Spark Source Atomic Emission Spectrometric Analysis Method for Carbon Steel and Medium and Low Alloy Steel (Conventional Method)".

[0055] Table 1 Chemical composition of the embodiments and comparative examples (wt / %)

[0056] .

[0057] The steel plates of the embodiment and the comparative example are rolled by the same TMCP process, kept in the heating furnace for 2 hours, and the heating temperature is controlled to be 1250~1300℃; the rolling temperature of the recrystallization zone is 1050~1200℃, and the rolling temperature of the non-recrystallization zone is 730~810℃; in the cooling process, after rolling, it directly enters the rapid cooling water device, cools to 450~590℃ at a rate of 15~25℃ / s, and then air-cools to room temperature. The mechanical properties of the steel plates that have completed the rolling process are tested, and the results are shown in Table 2. It can be seen that the yield strength of the steel plates of the embodiment and the comparative example is greater than 420MPa, the tensile strength is greater than 510MPa, the elongation is ≥20%, the bending performance is all qualified, and the -40℃ longitudinal impact absorption energy KV2 is greater than 250J.

[0058] Table 2 Steel plate performance test results

[0059] .

[0060] Welding test plate under the condition of welding heat input of 125kJ / cm: Cut the sample with the size of 10.5*10.5*80mm along the longitudinal direction of the rolled steel plate, and process the sample into a 10*10*55mm standard impact specimen in the welding heat cycle process of multi-wire submerged arc welding with a large heat input of 125kJ / cm in the Gleeble thermal simulation test machine; at the same time, set the welding heat input to 125kJ / cm, use self-developed welding wire and flux to weld the butt test plate, after 48 hours of non-destructive testing, take the position of the fusion line +1mm of the butt weld as the heat affected zone detection position, take samples from the butt test plate, and process them into a 10*10*55mm standard impact specimen. The impact absorption energy KV2 of the simulated sample and the actual welded sample under -40℃ is tested with the help of a pendulum impact tester, and the test results are shown in Table 3.

[0061] Table 3 Performance test results of welding heat affected zone (simulation, actual welding)

[0062] .

[0063] It can be seen from Table 3 that the impact absorption energy -40°C KV2 of the simulated welding heat affected zone and the actual welding heat affected zone of the steels in various embodiments of the present invention under the condition of a heat input of 125 kJ / cm is much greater than 47 J, and the low-temperature toughness is excellent; while the impact absorption energy -40°C KV2 of the welding heat affected zone and the actual welding heat affected zone of the steels in comparative examples 1-2 is lower than 47 J, and the low-temperature toughness is poor.

[0064] Under the condition of welding heat input of 125 kJ / cm, the microstructures of the heat affected zones of the steels in Example 1 and Comparative Example 1 are shown in the attached figures. Figure 1 , 2 The heat affected zone of the steel in Example 1 is mainly composed of a multiphase composite structure consisting of acicular ferrite (AF), blocky ferrite (PF), granular bainitic ferrite (GBF), M / A components and degenerate pearlite (DP) (see Appendix). Figure 1 ), among which the proportion of acicular ferrite (AF) is about 37%, and that of blocky ferrite (PF) is about 18%, and the overall structure is relatively fine, which corresponds well to the low-temperature impact toughness result; the microstructure of the heat-affected zone of comparative example 1 steel is coarse M / A components, degenerate pearlite (DP), granular bainitic ferrite (GBF), blocky ferrite (PF) and acicular ferrite (AF), among which the content of acicular ferrite (AF) is extremely low, and the structure is rich in coarse hard phase M / A components and degenerate pearlite (DP), which act as crack sources under impact loads and contribute to the initiation of microcracks. The microcracks extend in the coarse bainitic ferrite (GBF) matrix, thereby inducing brittle fracture and causing deterioration of low-temperature impact toughness.

[0065] The distribution of grain boundary misorientation angles in the heat affected zone of the steel in Example 1 and the steel in Comparative Example 1 was measured using an electron backscatter diffraction device (EBSD) mounted on a scanning electron microscope. Figure 3 It can be seen that under the condition of welding heat input of 125 kJ / cm, the proportion of high-angle grain boundaries in the heat-affected zone of the steel in Example 1 is significantly higher than the proportion of high-angle grain boundaries in the heat-affected zone of the steel in Comparative Example 1. This is related to the large amount of acicular ferrite (AF) and blocky ferrite (PF) in the heat-affected zone of the steel in Example 1. The grain boundaries between them and other grains are high-angle grain boundaries. During the expansion of microcracks, a large amount of crack expansion work can be consumed, causing the microcracks to bend or stop expanding at the high-angle grain boundaries, thereby improving the impact toughness.

[0066] The precipitated phase particles in the heat affected zone of the steel of Example 1 and the steel of Comparative Example 1 were observed by transmission electron microscopy. Figure 4 , 5 As shown. Under the condition of welding heat input of 125 kJ / cm, the precipitation phase in the heat affected zone of the steel in Example 1 is nano-scale fine dispersed (Ti, V) (C, N), (Ti, Nb) (C, N) composite precipitation particles, which can effectively pin the original austenite grain boundary, hinder the growth of austenite grains, and refine the organization; while the precipitation phase in the heat affected zone of the steel in Comparative Example 1 is coarse (Ti, Nb) (C, N) composite precipitation particles, and the number is small. The excessive size does not have the effect of hindering grain growth, and the coarse organization deteriorates the impact toughness.

[0067] The heterogeneous nucleation of acicular ferrite in the heat affected zone of the steel in Example 1 was observed by scanning electron microscopy. Figure 6 It can be found that under the condition of welding heat input of 125 kJ / cm, the submicron-sized (Ti, V, B) (C, N) composite precipitated particles in the heat affected zone of the steel in Example 1 can serve as nucleation points for acicular ferrite (AF), promote the nucleation of acicular ferrite, form more acicular ferrite structures in the organization, and several acicular ferrites are interlaced to form a basket-like precise interlocking result, which greatly improves the low-temperature toughness of the heat affected zone of the steel plate.

[0068] It can be seen from Table 1 that the atmospheric corrosion resistance index I of the steels in Examples 1 to 8 of the present invention and the steels in Comparative Examples 1 to 2 is greater than 6.5. 50*50*4mm corrosion samples were cut from the steel plates in Example 1 and Comparative Example 1, and 6 cycles (240 hours in total) of industrial atmospheric environment periodic immersion accelerated corrosion test were carried out. Samples were taken for each cycle and weighed, and the weight loss was measured. The corrosion weight loss-time relationship curve was plotted. See the attached figure. Figure 7 , Corrosion weight loss rate-time relationship see attached Figure 8 It can be seen that the corrosion weight loss and corrosion weight loss rate of the steel in Example 1 are higher than those of the steel in Comparative Example 1, indicating that the steel in Example 1 has better atmospheric corrosion resistance.

[0069] In summary, the E-grade weathering steel plate of the present invention can withstand a welding heat input of 125 kJ / cm and has a yield strength of not less than 420 MPa. When welded with a typical heat input of 125 kJ / cm, the steel plate has excellent low-temperature impact toughness in the welding heat-affected zone, and its -40°C impact absorption energy KV2 is much greater than 47 J. Moreover, the steel plate of the present invention has good atmospheric corrosion resistance, achieving an excellent match between atmospheric corrosion resistance and high heat input resistance welding performance.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. An E-grade weathering steel plate capable of withstanding welding heat input of 125 kJ / cm and having a yield strength of not less than 420 MPa, characterized in that: The chemical composition of the E-grade weathering steel plate is as follows in mass percentage: C 0.035-0.055, Si 0.20-0.40, Mn 1.35-1.45, Cu 0.30-0.50, Cr 0.40-0.55, Ni 0.30-0.45, Mo 0.13-0.16, Nb 0.032-0.058, V 0.020-0.035, Ti 0.013-0.017, B 0.0008-0.0012, Alt 0.015-0.034, N 0.0040-0.0080, Ca 0.004-0.006, O 0.0015-0.0025, Mg 0.008-0.013, P ≤0.015, S ≤0.005, the rest is iron and unavoidable impurities; The contents of Ti, Nb, V, B, C and N meet the following requirements: 0.28 ≤ H* ≤ 0.45, where H*=9.75Ti+3.27Nb+2.44V+0.03B+0.15C+0.10N; The atmospheric corrosion resistance index of the E-grade weathering steel plate is I≥6.5, wherein I=26.01Cu+3.88Ni+1.20Cr+1.49Si+17.28P-7.29CuNi-9.10NiP-33.39Cu 2 .

2. The E-grade weathering steel plate according to claim 1, characterized in that: When the heat input reaches 125KJ / cm2 by double-wire submerged arc welding, multi-wire gas shielded welding or gas-electric vertical welding, the welding heat affected zone of the E-grade weathering steel plate is KV2≥47J at -40°C, and the welding heat affected zone is an area where the peak temperature near the weld is between 1250 and 1400°C and the temperature is maintained above 500°C for 100 to 200s.

3. The E-grade weathering steel plate according to claim 2, characterized in that: Among the nanoparticles with a size of 20-80 nm that can inhibit the growth of austenite grains in the heat affected zone of welding, the number of (Nb, Ti, V) (C, N) composite precipitated particles accounts for 72-85% of the total number of particles of the same size, with a number density of 6.51×10 5 Pieces / mm 3 ~7.56×10 5 Pieces / mm 3 .

4. The E-grade weathering steel plate according to claim 2, characterized in that: Among the micron-sized particles with heterogeneous nucleation size of 0.5-1.5 μm in the heat affected zone of welding, the number of composite precipitated particles of (Ti, V, B) (C, N) accounts for 70-81% of the total number of particles of the same size, and the number density is 6.86×10 4 Pieces / mm 3 ~7.51×10 4 Pieces / mm 3 .

5. The E-grade weathering steel plate according to any one of claims 1 to 4, characterized in that: The yield strength R of the E-grade weathering steel plate eL ≥420MPa, tensile strength R m ≥540MPa.

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