E-grade weathering steel material capable of bearing large heat input welding and preparation method and application thereof

Abstract

The present application belongs to the technical field of weathering steel for welding, and particularly relates to E-grade weathering steel capable of bearing large heat input welding and a preparation method and application thereof. The E-grade weathering steel provided by the present application can avoid austenite grain growth and strength reduction caused by too low content of corresponding elements by optimizing alloying elements and limiting the content of Ti, V, B, C and N elements to satisfy 0.122 <= beta <= 0.230 without increasing the content of N, and can also avoid the generation of coarse (Nb, V, Ti)(C, N) and (Ti, Nb, V, B)(C, N) particles caused by exceeding the range, which can seriously reduce the strength and toughness of the steel plate. Under the condition, the E-grade weathering steel provided by the present application can satisfy large heat input welding of 150 KJ / cm, and the yield strength is not less than 370 MPa.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of weathering steel for welding, and particularly relates to an E-grade weathering steel material capable of bearing large heat input welding and a preparation method and application thereof. BACKGROUND

[0002] Under the background of the continuous development of high strength and large scale of structural construction in the fields of high-rise buildings, energy storage and transportation, ships and ocean engineering, the strength and thickness of the required steel material are greatly increased, and the construction of large steel structures gradually adopts high-efficiency large-line-energy welding process technologies such as multi-wire submerged-arc welding, gas-electric vertical welding and electroslag welding, so as to greatly improve the manufacturing efficiency and shorten the construction period. However, the large heat input welding process has the characteristics of high peak temperature and long high-temperature residence time. The coarse-grained heat-affected zone near the fusion line will have abnormal growth of austenite grains and serious coarsening of the structure, thereby seriously reducing the strength and toughness of the welded joint.

[0003] In order to solve the above problems, a large number of scholars have carried out a lot of research work. The patent for invention CN103343284A discloses a production method of large-line-energy welding Q345 grade steel plate, which is characterized by adding a large amount of Ti element 0.1-0.2% and controlling the Ti / N element content ratio to be 2.4-3.2 to form TiN precipitates which are relatively stable at high temperature, using the pinning effect of TiN on austenite grains in the welding thermal cycle to prevent the growth of austenite grains, and at the same time using V(C, N) to promote the nucleation of acicular ferrite in the grain to improve the internal structure of the grain. However, the control of the Ti / N element content ratio is difficult in industrial production, which increases the production cost and has a great influence on the production efficiency; the patent for invention CN104498827A discloses a 355MPa grade large-line-energy welding steel and its manufacturing method, which is characterized by adding Nb, Ti, V elements and controlling rolling and cooling process to form micro-alloyed carbonitride to inhibit the growth of austenite grains and increase the nucleation of acicular ferrite. However, this technology often increases the N content to more than 100ppm, and too high N content will produce a large amount of free N in the steel, which will seriously affect the large heat input welding performance. Too high N content will also affect the actual performance of the steel; the patent for invention CN102080189A discloses a large heat input welding structural steel and its manufacturing method, which is characterized by adding Si, Mn, Al in the converter, adjusting the oxygen content to 10-300ppm for LF furnace refining, and sequentially adding two or more elements such as Ti, Cr, Mo and Cu, and then performing continuous casting and rolling cooling after LF refining. However, the addition of multiple alloying elements in the refining and the strict control of the addition sequence and time make the production process complicated, reduce the production efficiency, increase the production cost, and are not conducive to the popularization and application of the technology.

[0004] Therefore, it is still a key technical problem in the field of low-carbon steel large heat input welding to ensure welding efficiency and joint toughness at the same time. SUMMARY

[0005] The application aims to provide an E-grade weathering steel material capable of bearing large heat input welding and a preparation method and application thereof.

[0006] To achieve the above-mentioned purpose, the application provides the following technical scheme.

[0007] The application provides an E-grade weathering steel material capable of bearing large heat input welding, which comprises the following elements in mass percentage: Mn 1.15-1.25%, Cr 0.35-0.50%, Ni 0.25-0.50%, Cu 0.25-0.45%, Si 0.20-0.35%, C 0.038-0.058%, Mo 0.02-0.10%, Al 0.015-0.034%, V 0.010-0.025%, Ti 0.005-0.012%, Sn 0.005-0.010%, N 0.004-0.008%, B 0.0008-0.0012%, P 0-0.015%, Nb 0-0.014%, S 0-0.005%, Ce 0-0.002%, and the balance being Fe and inevitable impurities.

[0008] The mass percentage of each element of the E-grade weathering steel material satisfies the following condition: 0.122≤β≤0.230, wherein the β=10.15Ti+5.24V+0.07B+0.14C+0.12N.

[0009] Preferably, the E-grade weathering steel material has an atmospheric corrosion resistance index I≥6.5, wherein the 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 .

[0010] Preferably, in the particles with a size of 20-80 nm of the E-grade weathering steel, the number percentage of (Nb, V, Ti)(C, N) composite precipitated particles is 57-68%, and the number density is 4.83×10 5 mm 3 -5.31×10 5 mm 3 .

[0011] Preferably, in the heterogeneous nucleation particles of the E-grade weathering steel, the percentage of (Ti,Nb,V,B)(C,N) composite precipitates is 61-71%, and the number density is 4.11 × 10⁻⁶. 4 pcs / mm 3 ~4.89×10 4 pcs / mm 3 .

[0012] This invention also provides a method for preparing the Grade E weathering steel described in the above technical solution, characterized by comprising the following steps:

[0013] According to the element ratio of the Grade E weathering steel described in the above technical solution, the steel is smelted and cast in sequence to obtain a cast alloy billet;

[0014] The cast alloy billet is subjected to heat treatment and rolling in sequence to obtain the E-grade weathering steel.

[0015] Preferably, the heat treatment temperature is 1120–1220°C, and the holding time is 2.5–3.5 h.

[0016] Preferably, the rolling process includes roughing and finishing rolling performed sequentially.

[0017] Preferably, the roughing temperature is ≥1050℃, the final rolling temperature is ≥950℃, the number of rolling passes is 4 to 6, the single-pass reduction rate is ≥10%, and the cumulative reduction is ≥60%.

[0018] The initial rolling temperature of the finishing mill is 800-850℃, the final rolling temperature is 760-810℃, the number of rolling passes is 5-7, the single-pass reduction rate is ≥8%, and the cumulative reduction is ≥55%.

[0019] Preferably, the rolling process further includes cooling;

[0020] The cooling start temperature is 750–800°C, and the cooling rate is 10–20°C / s.

[0021] 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.

[0022] The application provides an E-grade weather-resistant steel material which can withstand large heat input welding, and contains the following elements in percentage by mass: Mn 1.15-1.25%, Cr 0.35-0.50%, Ni 0.25-0.50%, Cu 0.25-0.45%, Si 0.20-0.35%, C 0.038-0.058%, Mo 0.02-0.10%, Al 0.015-0.034%, V 0.010-0.025%, Ti 0.005-0.012%, Sn 0.005-0.010%, N 0.004-0.008%, B 0.0008-0.0012%, P 0-0.015%, Nb 0-0.014%, S 0-0.005%, Ce 0-0.002%, and the balance of Fe and inevitable impurities; the percentage by mass of each element of the E-grade weather-resistant steel material satisfies the following condition: 0.122<=beta<=0.230, and the beta=10.15Ti+5.24V+0.07B+0.14C+0.12N. The E-grade weather-resistant steel material provided by the application optimizes the proportioning of alloy elements without increasing the content of N; when beta<0.122, the contents of Ti, V, B, C and N are low, the austenite grain grows, the strength is reduced, the content of acicular ferrite in the structure is reduced, the content of granular bainite is increased, the effective grain size is significantly increased, the density of large-angle grain boundaries is significantly reduced, and coarse M-A components are inevitably generated, which seriously damages the low-temperature toughness of the heat-affected zone; when beta>1.2, coarse (Nb, V, Ti)(C, N) and (Ti, Nb, V, B)(C, N) particles are generated, which seriously reduces the strength and toughness of the steel plate, so that the content of Ti, V, B, C and N is limited to the appropriate range, and under the condition, the E-grade weather-resistant steel material provided by the application can meet the large heat input welding of 150 KJ / cm, and the yield strength is not less than 370 MPa. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0024] Fig. 1 The schematic diagram of the microstructure of the base material of the E-grade weather-resistant steel material provided for the embodiment 1 is shown in the figure;

[0025] Fig. 2 The schematic diagram of the microstructure of the base material of the E-grade weather-resistant steel material provided for the embodiment 5 is shown in the figure;

[0026] Fig. 3A microstructure schematic diagram of a base material of the E-grade weather-resistant steel material provided for the example 7;

[0027] Fig. 4 A microstructure schematic diagram of a heat-affected zone of the E-grade weather-resistant steel material provided for the example 1 under the condition of a welding heat input of 150 kJ / cm;

[0028] Fig. 5 A microstructure schematic diagram of a heat-affected zone of the E-grade weather-resistant steel material provided for the example 5 under the condition of a welding heat input of 150 kJ / cm;

[0029] Fig. 6 A microstructure schematic diagram of a heat-affected zone of the E-grade weather-resistant steel material provided for the example 7 under the condition of a welding heat input of 150 kJ / cm. DETAILED DESCRIPTION

[0030] The present application provides an E-grade weather-resistant steel material capable of bearing large heat input welding, comprising the following elements in mass percentage: Mn 1.15-1.25%, Cr 0.35-0.50%, Ni 0.25-0.50%, Cu 0.25-0.45%, Si 0.20-0.35%, C 0.038-0.058%, Mo 0.02-0.10%, Al 0.015-0.034%, V 0.010-0.025%, Ti 0.005-0.012%, Sn 0.005-0.010%, N 0.004-0.008%, B 0.0008-0.0012%, P 0-0.015%, Nb 0-0.014%, S 0-0.005%, Ce 0-0.002%, and the balance being Fe and inevitable impurities.

[0031] The mass percentage of each element of the E-grade weather-resistant steel material satisfies the following condition: 0.122≤β≤0.230, wherein the β=10.15Ti+5.24V+0.07B+0.14C+0.12N.

[0032] The E-grade weather-resistant steel material according to the present application comprises Mn 1.15-1.25% in mass percentage, preferably 1.18-1.22%. In the present application, the atomic radius of Mn is similar to that of Fe, and Mn is easy to form a substitutional solid solution, which can significantly improve the strength of the steel plate. The solid-solved Mn element will reduce the phase transition temperature of the steel, increase the supercooling degree, refine the grains and further improve the low-temperature toughness of the steel. When the content of Mn is lower than 1.10%, the strength is reduced, and the harmful effect of sulfides is enhanced; Mn has a weak effect on the formation of M-A, and can be appropriately added more. However, when the content of Mn is higher than 1.80%, the content of M-A components is increased, and the toughness of the heat-affected zone is deteriorated. Therefore, the content of Mn in the present application is controlled to be 1.15-1.25%.

[0033] The E-grade weathering steel material according to the present application contains Cr 0.35-0.50%, preferably 0.40-0.48% by mass. In the present application, the secondary distribution of Cr during corrosion process forms iron-chromium multi-element alloy oxides in the rust layer, which enriches at the grain boundaries and the texture of the rust layer, on the one hand making the rust layer denser, and on the other hand increasing the electrochemical potential of the matrix, improving the corrosion resistance of the matrix. Higher Cr content promotes initial corrosion and accelerates the formation of a dense protective rust layer during long-term corrosion. High chromium content increases the content of amorphous phase in the rust layer, reduces the content of α-FeOOH in the rust layer, makes the rust layer dense, and reduces the electrochemical activity in acidic conditions. Cr-doped rust layer inhibits the transformation of amorphous phase to a-FeOOH and inhibits the growth process of FeOOH particles, thereby improving the density of the rust layer during long-term corrosion and improving the corrosion resistance. However, with the increase of Cr content, the grain size of the coarse grain heat affected zone increases significantly, and the hardening structure is easy to produce, which makes the low temperature impact toughness decrease significantly. Therefore, the Cr content is controlled to be 0.40-0.48%.

[0034] The E-grade weathering steel material according to the present application contains Ni 0.25-0.50%, preferably 0.30-0.45% by mass. In the present application, the addition of Ni can significantly improve the atmospheric corrosion resistance of the steel. The Ni element in the steel plate is easy to enrich in the internal rust layer, and at the same time, the Ni element can refine the structure of the rust layer, make γ-FeOOH more easily transform into stable α-FeOOH, improve the protection ability of the rust layer, make it difficult for chloride ions to contact with the steel matrix, and reduce the corrosion rate of the steel plate. Ni element can improve the intrinsic low temperature toughness of the steel, reduce the ductile-brittle transition temperature, in the process of continuous cooling after welding thermal cycle, Ni can reduce the phase transition point, increase the supercooling degree, refine the bainite structure, and enhance the low temperature toughness of the heat affected zone. At the same time, the large supercooling degree will cause the increase of Gibbs free energy and nucleation efficiency of acicular ferrite, and the increase of martensite-austenite content, and acicular ferrite is beneficial to the improvement of low temperature toughness of welding heat affected zone. However, due to the high cost of Ni element, in order to reduce the cost, it is not appropriate to add too much, and the content is controlled to be 0.25-0.50%.

[0035] The E-grade weathering steel material according to the present application contains Cu 0.25-0.45% (preferably 0.3-0.4%) by mass. In the present application, Cu is an important weathering element, which can inhibit the growth of α-FeOOH particles in the rust layer to refine the particle size, thereby improving the compactness of the rust layer. It can also hinder the entry of O2, slow down the corrosion process, reduce the electrical conductivity of the rust layer, and Cu can form a negative molecular structure in the rust layer, thereby increasing the cation selectivity of the rust layer and hindering the invasion of corrosive ions. An appropriate amount of Cu will promote the nucleation of acicular ferrite, but too high Cu content will produce hot cracks during rolling and is not conducive to the welding performance. Therefore, the Cu content is controlled to be 0.25-0.45%.

[0036] The E-grade weathering steel material according to the present application contains Si 0.20-0.35% (preferably 0.2-0.3%) by mass. In the present application, Si is a deoxidizing element and also a strengthening element. When Si is less than 0.05%, the deoxidizing effect is poor, and the steel plate surface is prone to pitting and red rust; but when Si is greater than 0.35%, the microstructure is coarsened, M-A constituents are increased, and the welding cold and hot crack sensitivity is increased. At the same time, Si can promote the formation of a mixture of α-FeOOH and nanoscale silicon oxide in the rust layer, which can not only refine the rust layer, but also effectively prevent Cl ions from penetrating the rust layer to reach the steel substrate, thereby improving its corrosion resistance. Therefore, the Si content is controlled to be 0.20-0.35%.

[0037] The E-grade weathering steel material according to the present application contains C 0.038-0.058% (preferably 0.04-0.055%) by mass. In the present application, C is the main element that determines the strength of the steel material. When C is too low, it is difficult to obtain the required strength. When the C content is too high, the hardening structure appearing in the welding heat-affected zone will severely deteriorate the welding performance and low-temperature toughness of the steel plate, and a large amount of carbides will be produced, leading to galvanic corrosion between different phases and deteriorating the weathering performance of the steel. Therefore, the C content is controlled to be 0.038-0.058%.

[0038] The E-grade weathering steel material according to the present application contains Mo 0.02-0.10% (preferably 0.04-0.08%) by mass.

[0039] The E-grade weathering steel material according to the present application contains Al 0.015-0.034% (preferably 1.32-1.48%) by mass. In the present application, Al is used as a main deoxidizer and mainly plays a role in deoxidation during steelmaking. When appropriately added, Al in the steel can form a precipitated phase with N, refine grains, and improve the strength and toughness of the steel. However, if excessively added, a large amount of large-sized alumina inclusions will remain in the steel after the deoxidation process, which will seriously damage the low-temperature toughness of the steel. Therefore, the content of Al is controlled to be 0.015-0.034%.

[0040] The E-grade weathering steel material according to the present application contains V 0.010-0.025% (preferably 0.015-0.020%) by mass. In the present application, V has a strong precipitation strengthening effect and contributes greatly to the improvement of strength. When the content of V is lower than 0.005%, the precipitation strengthening cannot be prominently played. When the content of V is higher than 0.07%, the hardenability of the steel plate is enhanced, and the toughness of the steel plate and the heat-affected zone is decreased. Therefore, the content of V is controlled to be 0.01-0.025%.

[0041] The E-grade weathering steel material according to the present application contains Ti 0.005-0.012% (preferably 0.006-0.010%) by mass. In the present application, Ti is a main element in the steel for large heat input. Ti combines with N to form TiN, which prevents the growth of austenite grains and can effectively improve the toughness of the heat-affected zone. The addition of Ti can also reduce the solid solution content of N and improve the aging performance of the steel. When the content of Ti is lower than 0.005%, the amount of beneficial nitrides formed is small, and the effect of inhibiting the growth of grains is weak. When the content of Ti exceeds 0.025%, large-sized TiN particles are easily produced during steelmaking, which are extremely easy to become crack sources when remaining in the steel plate. Therefore, the content of Ti is controlled to be 0.005-0.012%.

[0042] The E-grade weathering steel material according to the present application contains Sn 0.005-0.010% (preferably 0.006-0.009%) by mass.

[0043] The E-grade weathering steel material according to the present application contains N 0.004-0.008% (preferably 0.004-0.006%) by mass. In the present application, N is another important element. N has two existing modes, one of which is solid solution, which is not conducive to the properties of the base material, and the other of which is the formation of fine-grained nitrides, which can improve the toughness of the heat-affected zone. A high amount of N will increase the solid solution N, which will not be good for the toughness and aging performance of the base material, and the continuous casting billet is prone to cracking. The content of N is controlled to be 0.004-0.008% in the present application.

[0044] The E-grade weathering steel material according to the present application includes B 0.0008-0.0012%, preferably 0.0009-0.0011% by mass. In the present application, the main role of B in the steel is to increase the hardenability of the steel, thereby saving other more expensive metals, and thus the content is added to 0.0008-0.0012%.

[0045] The E-grade weathering steel material according to the present application includes P 0-0.015%, preferably 0.005-0.013% by mass. In the present application, P can improve the weather resistance of the weathering steel, but can significantly affect the plasticity of the steel plate, and can seriously damage the welding performance of the steel plate. And the cost of metallurgical P removal is very high, so the content of P is limited to below 0.015%.

[0046] The E-grade weathering steel material according to the present application includes Nb 0-0.014%, preferably 0.005-0.010% by mass. In the present application, a small amount of Nb can improve the strength of the steel without affecting the plasticity or toughness of the steel. Due to the effect of refining the grain, the impact toughness of the steel can be improved and the brittle transition temperature can be reduced. However, excessive Nb can be transferred to the weld during welding, resulting in hot cracking and seriously damaging the low-temperature toughness of the joint, so the content of Nb is controlled to be below 0.014%.

[0047] The E-grade weathering steel material according to the present application includes S 0-0.005%, preferably 0.001-0.004% by mass. In the present application, when the sulfur content in the steel is high, S exists in the form of FeS-Fe eutectic around the grain of the steel, and the plasticity and toughness are extremely easy to crack during TMCP, and the sulfide can reduce the atmospheric corrosion resistance of the weathering steel, so the content of S is controlled to be below 0.005%.

[0048] The E-grade weathering steel material according to the present application includes Ce 0-0.002%, preferably 0.0005-0.0015% by mass. In the present application, the addition of Ce element can refine the grain and improve the distribution of alloying elements in the steel, but excessive addition of Ce will make the cost too high, so the content of Ce is controlled to be ≤0.002%.

[0049] In the present application, the mass percentage of each element of the E-grade weathering steel material satisfies the following condition: 0.122≤β≤0.230, wherein β=10.15Ti+5.24V+0.07B+0.14C+0.12N. Wherein, the element symbol represents the mass percentage value of the element.

[0050] The present application limits β in the above range, because when β < 0.122, Ti, V, B, C, N elements are low, austenite grain grows, the strength is reduced; and the content of acicular ferrite in the structure is reduced, the granular bainite is increased, the effective grain size is significantly increased, the large-angle grain boundary density is significantly reduced, and the coarse M-A component inevitably occurs, which seriously damages the low-temperature toughness of the heat-affected zone. When β > 1.2, coarse (Nb, V, Ti) (C, N) and (Ti, Nb, V, B) (C, N) particles are produced, which seriously reduces the strength and toughness of the steel plate.

[0051] In the present application, the impact energy of the welding heat-affected zone of the E-grade weathering steel material when the welding heat input is 150 kJ / cm is preferably -40℃ KV2≥100 J, more preferably 110-250 J, and most preferably 130-200 J.

[0052] In the present application, the microstructure of the welding heat-affected zone of the E-grade weathering steel material when the welding heat input is 150 kJ / cm preferably includes granular bainite, acicular ferrite and blocky ferrite.

[0053] In the present application, the welding heat-affected zone is the area close to the weld with a peak temperature of 1250-1400℃ and a temperature retention time above 500℃ of 100-200 s.

[0054] In the present application, the welding method for providing the welding heat input is preferably multi-wire submerged arc welding.

[0055] In the present application, the yield strength R eL of the E-grade weathering steel material is preferably ≥370 MPa, more preferably 400-500 MPa, and most preferably 400-450 MPa; and the tensile strength R m of the E-grade weathering steel material is preferably ≥500 MPa, more preferably 500-600 MPa, and most preferably 500-550 MPa.

[0056] In the present application, the atmospheric corrosion resistance index I of the E-grade weathering steel material is ≥6.5, and 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 . Wherein, the "% element symbol" represents the mass percentage value of the element.

[0057] In the present application, in the particles of the E-grade weathering steel with a size of 20-80 nm, the number percentage of (Nb, V, Ti) (C, N) complex precipitated particles is preferably 57-68%, more preferably 60-68%; the number density is preferably 4.83 x 105 individual / mm 3 ~5.31x10 5 individual / mm 3 , more preferably 4.85x10 5 individual / mm 3 ~5.25x10 5 individual / mm 3 ;

[0058] In the present application, the percentage of the number of (Ti, Nb, V, B)(C, N) complex precipitated particles in the heterogeneous nucleation particles of the E-grade weathering steel is preferably 61-71%, more preferably 62-70%; the number density is preferably 4.11x10 4 individual / mm 3 ~4.89x10 4 individual / mm 3 , more preferably 4.15x10 4 individual / mm 3 ~4.85x10 4 individual / mm 3 .

[0059] In the present application, the nanoscale (Nb, V, Ti)(C, N) particles and the micrometer and submicron (Ti, Nb, V, B)(C, N) particles are most obvious in ensuring the strength and toughness of the steel plate joint. The nanoscale (Nb, V, Ti)(C, N) particles can pin the original austenite grain boundary, inhibit the growth of austenite grains, the micrometer and submicron (Ti, Nb, V, B)(C, N) particles can promote the nucleation of intragranular acicular ferrite, refine the grains and improve the strength and toughness. At the same time, the two kinds of second phase particles form a bimodal size distribution state, which can fully play the role of the two kinds of particles in the solid phase reaction to regulate the steel under the condition of large heat input welding, avoiding the complicated liquid phase reaction control, and can stably produce in large quantities.

[0060] The present application also provides a preparation method of the E-grade weathering steel material according to the above technical solution, characterized in that it comprises the following steps:

[0061] According to the element ratio of the E-grade weathering steel material according to the above technical solution, smelting and casting are sequentially carried out to obtain a cast alloy billet;

[0062] The cast alloy billet is sequentially subjected to heat treatment and rolling to obtain the E-grade weathering steel material.

[0063] According to the element ratio of the E-grade weathering steel material according to the above technical solution, smelting and casting are sequentially carried out to obtain a cast alloy billet.

[0064] The present application does not have special limitations on the smelting and casting method, and the method well known to those skilled in the art can be used.

[0065] After obtaining the as-cast alloy blank, the as-cast alloy blank is sequentially subjected to heat treatment and rolling to obtain the E-grade weather-resistant steel material.

[0066] In the present application, the temperature of the heat treatment is preferably 1120-1220℃, more preferably 1140-1200℃; and the holding time is preferably 2.5-3.5h, more preferably 3-3.5h.

[0067] In the present application, the rolling comprises rough rolling and finish rolling which are sequentially performed.

[0068] In the present application, the rough rolling has an opening rolling temperature of preferably ≥1050℃, more preferably 1050-1150℃; a final rolling temperature of preferably ≥950℃, more preferably 950-1000℃; a rolling pass of preferably 4-6 passes, more preferably 5-6 passes; a single pass reduction of preferably ≥10%, more preferably 10-15%; and a cumulative reduction of preferably ≥60%, more preferably 60-80%.

[0069] In the present application, the finish rolling has an opening rolling temperature of preferably 800-850℃, more preferably 820-840℃; a final rolling temperature of preferably 760-810℃, more preferably 770-800℃; a rolling pass of preferably 5-7 passes, more preferably 6-7 passes; a single pass reduction of preferably ≥8%, more preferably 8-12%; and a cumulative reduction of preferably ≥55%, more preferably 55-65%.

[0070] In the present application, the rolling preferably further comprises cooling; the cooling has an opening cooling temperature of preferably 750-800℃, more preferably 760-790℃; a re-red temperature of preferably 450-550℃, more preferably 480-530℃; and a cooling speed of preferably 10-20℃ / s, more preferably 12-18℃ / s.

[0071] In the present application, two-stage rolling treatment is adopted, and a large number of nanoscale (Nb, V, Ti)(C, N) particles are precipitated during the process, which pin the original austenite grain boundaries and inhibit the growth of austenite grains. Meanwhile, a large number of micron and submicron (Ti, Nb, V, B)(C, N) particles are precipitated, which promote the nucleation of intracrystalline acicular ferrite, refine the grains and improve the strength and toughness. Meanwhile, during the welding thermal cycle, part of the undissolved second phase particles pin the original austenite grain boundaries and inhibit the growth of the original austenite. In addition, due to the change of cold and heat during the welding thermal cycle, thermal stress is generated, which accelerates the precipitation of (Nb, V, Ti)(C, N) particles and further inhibits the growth of the original austenite. During the cooling process of the welding thermal cycle, these second phase particles will further promote the nucleation of acicular ferrite, refine the structure and improve the strength and toughness.

[0072] In the present application, the cooling is preferably followed by tempering; the temperature of the tempering is preferably 500-600 DEG C, more preferably 520-580 DEG C; and the holding time is preferably the thickness of the steel material + (10-50) min, with the thickness of the steel material being in mm.

[0073] The preparation method provided by the present application limits the element composition and heat treatment process, controls the size and distribution of the second phase particles in the steel, and makes enough nanoscale particles and micrometer scale particles in the steel which can inhibit the growth of austenite grains and can be intracrystalline nucleated, so that the austenite grain size and intracrystalline structure are controlled, the strength of the steel material is ensured, and the welding performance of the steel material to large heat input is improved.

[0074] The present application also provides the application of the E-grade weathering steel material or the E-grade weathering steel material prepared by the preparation method in the preparation of a welded structural member.

[0075] The present application does not have any special limitation on the application process of the E-grade weathering steel material in the preparation of a welded structural member, and the method well known to those skilled in the art can be used.

[0076] In order to further illustrate the present application, the E-grade weathering steel material capable of withstanding large heat input welding, the preparation method and the application thereof provided by the present application are described in detail below with reference to the accompanying drawings and examples, but they should not be understood as limiting the scope of protection of the present application.

[0077] Examples 1-6 and Comparative Examples 1-3

[0078] Six furnaces of the example steel and three furnaces of the comparative example steel were prepared in a 50 kg vacuum induction furnace, wherein the element ratio of the example steel conforms to the limited requirements of the present application. The example steel and the comparative example steel were sequentially subjected to melting and casting to obtain a cast alloy blank; the blank was heated to 1200 DEG C and held for 3 h to completely austenitize. The rolling process adopted two-stage rolling, the rough rolling stage was controlled at a rolling temperature of 1080 DEG C and a final rolling temperature of 970 DEG C, 6 passes were rolled, and the cumulative reduction was 70%; the finish rolling stage was controlled at a rolling temperature of 820 DEG C and a final rolling temperature of 790 DEG C, 7 passes were rolled, and the cumulative reduction was 60%. In the cooling process, the open cooling temperature was 770 DEG C, the red temperature was 500 DEG C, and the cooling speed was 15 DEG C / s. In order to eliminate the influence of stress, the steel was tempered after the cooling process, the tempering temperature was 550 DEG C, and the holding time was 1 h, and finally the steel was rolled into a 30 mm plate.

[0079] The steel provided in Examples 1-6 and Comparative Examples 1-3 was subjected to composition detection according to GB / T 4336 "Carbon and Low-alloy Steel Analysis Method of Spark Source Atomic Emission Spectrometry (Routine Method)", and the detection results are shown in Table 1. Other elements not shown in the table, such as S, Sn, etc., the content of the examples and the comparative examples is within the range required by the present application.

[0080] Table 1 provides chemical composition data (wt.%) of the steels used in Examples 1-6 and Comparative Examples 1-3.

[0081]

[0082]

[0083] Test Example 1

[0084] Samples were taken from the steels used in the examples, and their metallographic structure was observed using an Axiovert-200MAT optical microscope. Schematic diagrams of the base metal microstructure of the Grade E weathering steels provided in Examples 1, 5, and 7 are shown below. Figs. 1-3 .

[0085] Depend on Figs. 1-3 As can be seen, the microstructure of the E-grade weathering steel provided by this invention is mainly a mixture of granular bainite, acicular ferrite and blocky ferrite, which ensures the strength and toughness of the steel plate.

[0086] Test Example 2

[0087] The size distribution of the precipitated particles was observed using a ZEISS ULTRA55 field emission scanning electron microscope, and the proportion was statistically analyzed. The proportion and density of the second phase particles in the steels provided in Examples 1-6 and Comparative Examples 1-3 are shown in Table 2.

[0088] Table 2 shows the percentage and density of (Ti,Nb,V,B) and (C,N) composite precipitates in the second phase particles of the steels provided in Examples 1-6 and Comparative Examples 1-3.

[0089]

[0090]

[0091] As shown in Table 2, the E-grade weathering steel provided by this invention can suppress the growth of austenite grains with a size of 20-80 nm. The number of (Nb,V,Ti) and (C,N) composite precipitates accounts for 57-68% of these particles, and the number density is 4.83 × 10⁻⁶. 5 pcs / mm 3 Up to 5.31×10 5 pcs / mm 3 Between these particles, the original austenite grain boundaries can be pinned, inhibiting austenite grain growth; among the heterogeneous nucleation particles with a size of 0.5–1.5 μm, the number of (Ti,Nb,V,B) and (C,N) composite precipitates is 61–71%, with a number density of 4.11 × 10⁻⁶. 4 pcs / mm 3 Up to 4.89×10 4 pcs / mm3 between, promote intracrystalline acicular ferrite nucleation, refine grain to improve strength and toughness.

[0092] Test Example 3

[0093] The steel provided by Examples 1-6 and Comparative Examples 1-3 was sampled, and according to GB / T 13239 standard, a transverse and longitudinal tensile sample was taken at 1 / 2 of the plate thickness, and a total of two samples were tested, and the average value was taken. According to GB / T 229 standard, an impact sample was taken along the rolling direction at 1 / 2 of the plate thickness, and a total of three samples were tested, and the average value was taken. The basic mechanical property test results are shown in Table 3.

[0094] Table 3 Mechanical property and welding performance data of the steel provided by Examples 1-10 and Comparative Examples 1-5

[0095]

[0096]

[0097] As can be seen from Table 3, the E-grade weathering steel provided by the present application all has excellent strength and toughness, the yield strength reaches 400Mpa grade, the yield strength ratio is below 0.85, and the base metal low temperature impact energy at-40℃ is higher than 100J. The basic mechanical properties of the base metal of Comparative Examples 1-3 also meet the use requirements, but are relatively lower than the examples.

[0098] Test Example 4

[0099] The steel provided by Examples 1-6 and Comparative Examples 1-3 was sampled, and a multi-wire submerged arc welding method was used to perform a welding process with a heat input of 150KJ / cm, the near-weld heat affected zone was a region close to the weld with a peak temperature of 1250-1400℃, and a temperature above 500℃ maintained for 100-200s. The microstructure schematic diagram of the heat affected zone of the E-grade weathering steel provided by Examples 1, 5 and 7 under the condition of welding heat input of 150kJ / cm is shown in Figs. 4-6 The sample was taken from the welding heat affected zone position, and a standard impact sample of 10x10x55mm was processed, and according to GB / T 229 standard, the-40℃ impact energy was tested, and the experimental results were taken as the average value of three samples, and the results are shown in Table 3.

[0100] As can be seen from Table 3, the E-grade weathering steel provided by the present application all has excellent strength and toughness, the yield strength reaches 400Mpa grade, the yield strength ratio is below 0.85, and the base metal low temperature impact energy at-40℃ is higher than 100J. The basic mechanical properties of the base metal of Comparative Examples 1-3 also meet the use requirements, but are relatively lower than the examples. Figs. 4-6 It can be seen that the microstructure is mainly a mixed structure of granular bainite, acicular ferrite and blocky ferrite, fine and dispersed precipitated phase and high-density dislocation acicular ferrite characteristics, which plays an important role in improving the strength and toughness of the material.

[0101] As shown in Table 3, the E-grade weathering steel provided by the application has excellent low-temperature impact toughness of the coarse-grained heat-affected zone at -40 DEG C. When the heat input is 150 KJ / cm, the low-temperature impact energy of the coarse-grained heat-affected zone at -40 DEG C is higher than 100 J, which fully meets the use requirements in cold regions.

[0102] As shown in the above examples and test examples, it can be seen that:

[0103] The steel provided by Comparative Example 1 meets the content limit of each element, but β = 0.236, which exceeds the limit of β ≤ 0.230. Mainly because the Ti, V, and N contents are relatively high, the grain boundary nanometer precipitated particles and the intracrystalline micron and submicron particles grow up, which leads to the growth of bainite during welding, and the nucleation of the ductile phase acicular ferrite is inhibited, and the effective grain size is greatly increased, and a large amount of bulk martensite-austenite components are generated, which leads to a significant decrease in the low-temperature toughness of the coarse-grained heat-affected zone. The low-temperature impact energy of the coarse-grained heat-affected zone at -40 DEG C is only 40 J when the heat input is 150 KJ / cm, which cannot meet the use requirements in cold regions.

[0104] The steel provided by Comparative Example 2 meets the content limit of each element, but β = 0.109, which is lower than the limit of 0.122 ≤ β. Mainly because the Ti, V, N, Nb, and C contents are relatively low, and the grain boundary nanometer precipitated particles and the intracrystalline micron and submicron particles cannot be precipitated in sufficient amount, the pinning ability of austenite and the intracrystalline nucleation ability are greatly reduced, which inhibits the nucleation of the ductile phase acicular ferrite, and the low-temperature toughness of the coarse-grained heat-affected zone is significantly reduced. The low-temperature impact energy of the coarse-grained heat-affected zone at -40 DEG C is only 35 J when the heat input is 150 KJ / cm, which cannot meet the use requirements in cold regions.

[0105] The steel provided by Comparative Example 3 meets the ratio of V, B, C, and N between 0.122 ≤ β ≤ 0.230, but the element content does not meet the composition requirement limit, and only a small amount of beneficial size particles can be precipitated. The low-temperature impact energy of the coarse-grained heat-affected zone at -40 DEG C is only 22 J when the heat input is 150 KJ / cm, which cannot meet the use requirements in cold regions.

[0106] In summary, the E-grade weathering steel material provided by the application pins the original austenite grain boundary with nanoscale (Nb, V, Ti)(C, N) particles precipitated in a two-stage rolling process, inhibits the growth of austenite grains, and promotes the nucleation of intragranular acicular ferrite, refines the grains and improves the strength and toughness through micrometer and submicron (Ti, Nb, V, B)(C, N) particles precipitated in a large amount. Meanwhile, when experiencing a welding thermal cycle, some undissolved second-phase particles pin the original austenite grain boundary, inhibit the growth of the original austenite, and the thermal stress generated due to the cold and hot changes in the welding thermal cycle process will accelerate the precipitation of (Nb, V, Ti)(C, N) particles to further inhibit the growth of the original austenite. In the cooling process of the welding thermal cycle, these second-phase particles will further promote the nucleation of acicular ferrite, refine the structure and improve the strength and toughness. Meanwhile, the nanoscale (Nb, V, Ti)(C, N) particles and the micrometer and submicron (Ti, Nb, V, B)(C, N) particles form a bimodal size distribution state, fully play the characteristics of the two types of particles in the solid-phase reaction, and regulate the large heat input welding performance of the steel, avoiding the complicated liquid-phase reaction control, and enabling stable mass production.

[0107] Although the above embodiments have made a detailed description of the application, it is only a part of the embodiments of the application, not all the embodiments, and other embodiments can be obtained according to the embodiments without creativity, which belong to the protection scope of the application.

Claims

1. A type of E-grade weathering steel capable of withstanding high heat input during welding, characterized in that, It includes the following elements in mass percentage: Mn 1.15~1.25%, Cr 0.35~0.50%, Ni 0.25~0.50%, Cu 0.25~0.45%, Si 0.20~0.35%, C 0.038~0.058%, Mo 0.04~0.08%, Al 0.015~0.034%, V 0.010~0.025%, Ti 0.005~0.012%, Sn 0.005~0.010%, N 0.004~0.008%, B 0.0008~0.0012%, P 0.005~0.013%, Nb 0~0.014%, S 0.001~0.004%, Ce 0~0.002%, with the balance being Fe and unavoidable impurities; The mass percentage content of each element in the E-grade weathering steel meets the following condition: 0.122≤β≤0.230, where β=10.15Ti+5.24V+0.07B+0.14C+0.12N; In the E-grade weathering steel, the number percentage of (Nb,V,Ti)(C,N) composite precipitated particles in particles with a size of 20~80nm is 57~68%, and the number density is 4.83×105 particles / mm3~5.31×105 particles / mm3; In the heterogeneous nucleation particles of the E-grade weathering steel with a size of 0.5~1.5μm, the percentage of (Ti,Nb,V,B)(C,N) composite precipitates is 61~71%, and the number density is 4.11×104 particles / mm3~4.89×104 particles / mm3.

2. The E-grade weathering steel according to claim 1, characterized in that, 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.

3. The method for preparing the Grade E weathering steel according to claim 1 or 2, 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.

4. The preparation method according to claim 3, characterized in that, The heat treatment temperature is 1120~1220℃, and the holding time is 2.5~3.5h.

5. The preparation method according to claim 3, characterized in that, The rolling process includes roughing and finishing rolling performed sequentially.

6. The preparation method according to claim 5, characterized in that, The roughing temperature is ≥1050℃, the final rolling temperature is ≥950℃, the number of rolling passes is 4~6, the single-pass reduction rate is ≥10%, and the cumulative reduction is ≥60%. The initial rolling temperature of the finishing mill is 800~850℃, the final rolling temperature is 760~810℃, the number of rolling passes is 5~7, the single pass reduction rate is ≥8%, and the cumulative reduction amount is ≥55%.

7. The preparation method according to claim 3, 5 or 6, characterized in that, The rolling process also includes cooling. The cooling start temperature is 750~800℃, and the cooling rate is 10~20℃ / s.

8. The application of the Grade E weathering steel according to any one of claims 1 to 2 or the Grade E weathering steel prepared by the preparation method according to any one of claims 3 to 7 in the preparation of welded structural components.

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