CN112899558A - 550 MPa-grade weather-resistant steel plate with excellent weldability and manufacturing method thereof - Google Patents
550 MPa-grade weather-resistant steel plate with excellent weldability and manufacturing method thereof Download PDFInfo
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- C21D2211/002—Bainite
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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Abstract
A550 MPa-grade weather-resistant steel plate with excellent weldability and a manufacturing method thereof adopt a low-C-low-Si-medium-Mn low alloy component system as a basis, improve the Al content in the steel as much as possible and ensure that Als/[ (% N) -0.292 (% Ti)]Not less than 39, ultra-low N content, Cu + Ni + Cr alloyAlloying, Ti + Nb microalloying, [ (% Mn) +21.17 (% Si)]X (% C) is not more than 0.475, Ca is treated, the Ca/S ratio is controlled to be 1.0 to 3.0, and (% Ca) × (% S)0.28≤1.0×10－3The equal alloy optimization combination design; the manufacturing method adopts an optimized TMCP process, so that the microstructure of the finished steel plate is a small amount of fine ferrite and bainite distributed in a dispersion way, the average grain size of the microstructure is below 15 mu m, the uniform and excellent low-temperature toughness of the base steel plate is obtained, and simultaneously, the low-temperature toughness of HAZ during high-heat input welding is also excellent, namely, the-40 ℃ impact toughness KV of the base steel plate is2Not less than 100J, and Akv not less than 100J at the temperature of-40 ℃ of a welding Heat Affected Zone (HAZ), and can realize stable batch industrial production with low cost.
Description
Technical Field
The invention relates to a 550 MPa-grade weather-proof steel plate with excellent weldability and a manufacturing method thereof, wherein the yield strength is more than or equal to 460MPa, the tensile strength is more than or equal to 570MPa, the Charpy impact energy (single value) at-40 ℃ is more than or equal to 120J, and the Charpy impact energy (single value) at-40 ℃ in a large heat input steel plate welding heat affected zone is more than or equal to 100J.
Background
As is well known, low carbon (high strength) low alloy steel is one of the most important engineering structural materials, and is widely used in petroleum and natural gas pipelines, offshore platforms, shipbuilding, hydroelectric engineering, bridge structures, boiler containers, building structures, the automotive industry, railway transportation and mechanical manufacturing. The properties of low carbon (high strength) low alloy steel depend on its chemical composition and manufacturing process, where strength, toughness, plasticity, weldability and the match between them are the most important properties of low carbon (high strength) low alloy steel, which ultimately depend on the microstructure and dislocation substructure of the finished steel.
With the continuous forward development of metallurgical technology, people put forward higher requirements on the toughness, plasticity and weldability of high-strength steel, namely that the steel plate has brittle fracture resistance and plasticity instability fracture resistance under the condition of low temperature (minus 40 ℃), the fracture elongation and uniform elongation reach the level of the steel plate with the yield strength of 355MPa, the weldability of the steel plate is excellent, and the high-heat input welding (the welding heat input is more than or equal to 100kJ/cm) can be borne; under the conditions of lower alloy content, particularly precious metal content and lower manufacturing cost, the comprehensive mechanical property and the service performance of the steel plate are greatly improved, the alloy consumption of steel is reduced, the cost is saved, the self weight, the stability and the safety of the steel member are reduced due to high strength and light weight, and more importantly, the cold/hot workability and the safety and the reliability in the service process of the steel member are further improved; at present, research booms for developing new generation high-performance steel materials are raised in the range of Japan and Korean, better microstructure matching is obtained through alloy combination design optimization design, control of a sub-microstructure fine structure and an innovative manufacturing process technology, and a high-strength steel is enabled to obtain better strong plasticity, plasticity and toughness matching and weldability through an ultra-fine metallographic microstructure and a sub-structure (dislocation configuration and packet) fine structure.
In The prior art, when a thick steel plate with yield strength of more than or equal to 420MPa and low-temperature impact toughness of more than or equal to 34J at-60 ℃ is manufactured, a certain amount of Ni or Cu + Ni element (more than or equal to 0.30%) is generally added into The steel [ The Firth (1986) international Symposium and inhibition on offset metals and arc Engineering, 1986, Tokyo, Japan, 354; "DEVELOPMENTS IN MATERIALS FOR ARCTIC OFFSHORE STRUCTURES"; "Structural Steel Plates for arrangement Use Produced by Multipurose accepted Cooling System" (Japanese), Tokawasaki iron technology, 1985, Nos. 168-72; "Application of accessed consistent For Producing 360MPa Yield Strength Steel plates of up to 150mm in Thickness with Low Carbon Equivalent", accessed consistent Rolled Steel, 1986, 209-219; "High Strength Steel Plates For Ice-Breaking Vessels Produced by Thermo-Mechanical Control Process", Accelerated Co-vibrating Rolled Steel, 1986, 249-260; "420 MPa Yield Strength Steel Plate with Superior frame Structure for extraction offset Structure", Kawasaki Steel technical report, 1999, No.40, 56; "420 MPa and 500MPa Yield Strength Steel Plate with High HAZ to microwave Process by TMCP for offset Structure", Kawasaki Steel technical report, 1993, No.29, 54; "Toughness Improvement in Bainite Structure by Thermo-Mechanical Control Process" (Japanese) Sumitomo Metal, Vol.50, No.1(1998), 26; "Steel plate for ocean platform Structure used in icy sea area" (Japanese), Steel research, 1984, No. 314, 19-43 ] to ensure excellent low temperature toughness of the base steel plate, and when welding with a linear energy of less than 50KJ/cm, the toughness of the HAZ in the heat affected zone can reach Akv ≥ 34J at-60 ℃; however, when welding with a large heat input (not less than 100KJ/cm), the low-temperature toughness of the weld Heat Affected Zone (HAZ) is generally difficult to achieve, and the low-temperature toughness of the Heat Affected Zone (HAZ) is severely degraded. A large number of Patent documents only describe how to achieve low-temperature toughness of a base steel plate, how to obtain excellent low-temperature toughness of a Heat Affected Zone (HAZ) under welding conditions is less, how to ensure less and less low-temperature toughness of the Heat Affected Zone (HAZ) particularly when welding with ultra-high heat input, and in order to ensure low-temperature toughness of the steel plate, a certain amount of Ni or Cu + Ni element is generally added to the steel, and the low-temperature toughness of the Heat Affected Zone (HAZ) of the steel plate with ultra-high heat input can rarely reach-60 ℃ (japanese Patent nos. sho 63-93845, sho 63-79921, sho 60-258410, japanese Patent publication No. 4-285119, japanese Patent publication No. 4-308035, hei 3-264614, hei 2-250917, hei 4-143246, US Patent nos. US 4855106, US Patent nos. 5183198 and US Patent No. 4137104).
At present, the main technology for improving the low-temperature toughness of the Heat Affected Zone (HAZ) of the welded steel plate with ultra-large heat input is the oxide metallurgy technology (U.S. Pat. No.4, 4629505, WO 01/59167A1) adopted by Nippon Nissian iron company, namely in the process of welding with large heat input, TiN particles are dissolved and lose effect due to the action of high temperature for a long time in the vicinity of a fusion line, and Ti2O3More stable than TiN and does not dissolve even when reaching the melting point of steel. Ti2O3The particles can become the needle ferrite nucleation positions in the austenite crystals, promote the needle ferrite (acicular ferrite-AF) nucleation in the austenite crystals, effectively divide the austenite crystals, refine the HAZ structure and form the needle ferrite structure with high strength and high toughness.
In order to ensure the low-temperature toughness of a large heat input welding heat affected zone, a certain amount of valuable alloy elements Cu and Ni are added into steel plates (especially super-thick steel plates) in order to ensure the low-temperature toughness of the large heat input welding heat affected zone, when the yield strength reaches 460MPa, a small amount of Mo is especially needed to be properly added, the large heat input welding manufacturability of the steel plates is good, but the toughness of the welding heat affected zone, especially the low-temperature toughness of the welding heat affected zone of the thick steel plates is not very stable (Mo promotes the formation of coarse upper bainite under the condition of large heat input welding, and the toughness of the welding coarse grain heat affected zone is degraded), the requirements of the impact toughness at minus 40 ℃ can not be stably met, and the manufacturing cost of the thick steel plates is also high; more importantly, none of the developed steel plates relate to atmospheric corrosion resistance.
Disclosure of Invention
The invention aims to provide a 550 MPa-grade weathering steel plate with excellent weldability and a manufacturing method thereof, wherein the weathering steel plate obtains uniform and excellent low-temperature toughness of a base steel plate, and simultaneously has excellent low-temperature toughness of HAZ during large heat input welding, namely the base steel plate has-40 ℃ impact toughness KV2Not less than 100J, and Akv not less than 100J at-40 ℃ of a welding Heat Affected Zone (HAZ); the method is particularly suitable for steel structures and equipment such as icebreaking ship shells, ocean platforms, cross-sea bridges, ocean wind power pile legs and wind tower structures, port machinery and the like in ice sea areas, and can realize stable and batch industrial production with low cost.
In order to achieve the purpose, the technical scheme of the invention is as follows:
the invention starts from alloy combination design, adopts low-C-low-Si-medium Mn series low alloy body as a base, improves the content of Al in steel as much as possible, and has Als/[ (% N) -0.292 (% Ti)]Not less than 39, ultra-low N content, Cu + Ni + Cr alloying, Ti + Nb microalloying, [ (% Mn) +21.17 (% Si)]X (% C) is not more than 0.475, Ca is treated and the Ca/S ratio is controlled to be 1.0 to 3.0 and (% Ca) × (% S)0.28≤1.0×10－3The equal alloy optimization combination design; the manufacturing process adopts an optimized TMCP (Thermo-mechanical control process) process.
Specifically, the 550 MPa-grade weather-resistant steel plate with excellent weldability comprises the following components in percentage by weight:
C：0.050％～0.090％，
Si：≤0.20％，
Mn：1.00％～1.40％，
P：≤0.013％，
S：≤0.003％，
Cu：0.20％～0.50％，
Ni：0.15％～0.45％，
Cr：0.40％～0.80％，
Nb：0.010％～0.030％，
Ti：0.008％～0.016％，
Als：0.040％～0.070％，
N：≤0.005％，
Ca：0.0010％～0.0035％，
the balance of Fe and inevitable impurities; and the content of the elements must satisfy the following relation at the same time:
als/[ (% N) -0.292 (% Ti) ] > 39; the content of free [ N ] in a large heat input welding heat affected zone is eliminated, and the microstructure (high-density fine AlN particles are formed, the pinning austenite grains grow large, the microstructure of HAZ is refined) and the low-temperature toughness and crack arrest characteristics (the free [ N ] of HAZ is eliminated, and the embrittlement effect of the free [ N ] is eliminated) of the welding heat affected zone are improved.
[ (% Mn) +21.17 (% Si) ] × (% C) ≦ 0.475; the method has the advantages that the occurrence degree of conjugate segregation in the molten steel solidification process is reduced, the internal segregation of a plate blank is reduced, the three properties of the steel plate are improved, namely soundness, purity and homogeneity, the low-temperature toughness, crack resistance and crack arrest characteristics, the Z-direction performance and weldability of the steel plate are improved, carbide precipitation in the large heat input welding process is promoted, the formation of an M-A island is inhibited, and the low-temperature toughness and crack resistance and crack arrest characteristics of a welding heat affected zone are improved; this is one of the key core technologies of the present invention.
Ca treatment, and the ratio of Ca/S is between 1.00 and 3.00,% Ca) x (% S)0.28≤1.0×10-3；
The influence of the inclusions on low-temperature toughness and weldability is reduced to the minimum while the spheroidization of the sulfide is ensured, and meanwhile, Ca (O, S) particles are uniformly and finely distributed in the steel, so that the growth of austenite grains in a large heat input welding heat affected zone is inhibited, and the low-temperature toughness of the welding heat affected zone is improved.
0.0038≤[(TStopping cooling)×H]/[(DIOL)×ξ×(TOpen cold)]Less than or equal to 0.0159, ensuring that the steel plate has low C and lower carbon equivalent CEVThe high-heat-input weldability steel plate has high strength, excellent low-temperature toughness, fatigue resistance and weather resistance, and successfully eliminates the mutual opposition between the high strength, excellent low-temperature toughness, fatigue resistance and corrosion resistance of the steel plate and the excellent weldability, especially the high-heat-input weldability of the steel plate. Wherein the content of the first and second substances,
Tstopping coolingThe quenching end temperature for on-line quenching of DQ, i.e., the stop temperature for accelerated cooling, is expressed in degrees c.
H is the thickness of the steel plate and is in mm;
DIOLthe index is the online hardenability index of the steel plate, and the unit is mm;
DIOL＝0.514C0.5(1+0.7Si)(1+3.33Mn)(1+0.35Cu)(1+0.36Ni)(1+2.16Cr)(1+3Mo)(1+1.75V)(1+1.77Al)×25.4；
xi is the rolling control accumulated reduction rate, and the unit is percent;
Topen coldThe cooling temperature was started for accelerated cooling in units of ℃.
The microstructure of the steel plate is a small amount of fine ferrite and bainite distributed in a dispersion way, and the average grain size of the microstructure is below 15 mu m.
The yield strength of the steel plate is more than or equal to 460MPa, the tensile strength is more than or equal to 570MPa, the Charpy impact energy (single value) at the temperature of minus 40 ℃ is more than or equal to 120J, and the impact toughness KV at the temperature of minus 40 ℃ is more than or equal to KV2Not less than 100J, and Akv not less than 100J at-40 ℃ of a welding Heat Affected Zone (HAZ).
In the composition design of the steel of the invention:
c has great influence on the strength, low-temperature toughness, elongation and weldability of the TMCP steel plate, particularly on the large heat input weldability, and the C content in the steel is expected to be controlled to be lower from the aspects of improving the low-temperature toughness, weather resistance (when the C content is too high, Cr carbide is easily precipitated at the grain boundary of the weather-resistant steel to cause grain boundary corrosion) and the large heat input weldability of the TMCP steel plate; however, from the viewpoints of strength, low-temperature toughness and microstructure control and manufacturing cost in the production and manufacturing process of steel plate steel, the content of C is not too low, too high grain boundary mobility is easily caused by too low content of C, grains of the base metal steel plate and the welded HAZ microstructure are coarse and easily generate mixed crystals, and the grain boundary is weakened due to too low content of C in the steel, so that the low-temperature toughness of the base metal steel plate and the welded HAZ is seriously degraded; therefore, the reasonable range of the C content is 0.050 to 0.090 percent.
Si promotes molten steel deoxidation and can improve the strength of a steel plate, but Si deoxidizes little by adopting Al deoxidized molten steel, Si can improve the strength of the steel plate, but Si seriously damages the low-temperature toughness, elongation, weather resistance (Si promotes electrochemical corrosion) and weldability of the steel plate, particularly for weather-resistant steel with high Cr content, Si not only promotes the formation of M-A islands, but also forms large-sized and unevenly distributed M-A islands which seriously damages the low-temperature toughness of a welding Heat Affected Zone (HAZ) and also causes the weather resistance of a welding joint to be reduced during high heat input welding, so that the Si content in the steel is controlled to be as low as possible, and the Si content is controlled to be less than 0.20% in consideration of the economy and operability of a steel making process.
Mn, the most important alloying element, improves the strength of the steel sheet, expands the austenite phase region, and reduces Ar in the steel3Point temperature, refining TMCP steel plate grains to improve the strength of the steel plate (fine grain strengthening effect), improve the low-temperature toughness of the steel plate (fine grain toughening), improve the fatigue resistance of the steel plate, promote the formation of low-temperature phase transformation structure (phase transformation strength effect) and improve the strength of the steel plate; however, Mn is easily segregated in the molten steel solidification process, especially when the Mn content is high (especially when the C content in the steel is high), not only casting operation is difficult, but also conjugate segregation with elements such as C, P, S is easily generated, so that segregation and porosity of the central part of a casting blank are increased, abnormal structures are easily formed in the subsequent TMCP and welding processes due to the region segregation at the center of the casting blank, and low-temperature toughness of a steel plate is low and cracks occur in a welded joint, and in addition, for weather-resistant steel, a large amount of weather-resistant elements such as Cu and Cr are contained in the steel, and when the Mn content is too high, low-temperature toughness, elongation and weldability of the steel plate are rapidly deteriorated; therefore, the reasonable range of the Mn content is 1.00-1.40%.
P as harmful impurities in steel has great harm effect on the mechanical properties of the steel, particularly low-temperature impact toughness, elongation and weldability (particularly high-heat-input welding high-Cr weathering steel), the lower the requirement is better theoretically, but in consideration of steelmaking operability and steelmaking cost, the content of P needs to be controlled to be less than or equal to 0.013 percent for the weathering TMCP steel plate which can be welded by large heat input and has-40 ℃ toughness, high strength and high heat input.
S has great damage effect on low-temperature toughness, weldability and fatigue resistance of steel as harmful inclusions in the steel, more importantly, the S is combined with Mn in the steel to form MnS inclusions, MnS plasticity enables MnS to extend along the rolling direction in the hot rolling process to form MnS inclusion bands along the rolling direction, the low-temperature impact toughness, the elongation, the Z-direction performance, the fatigue resistance and the weldability (particularly the high heat input weldability) of the steel plate are seriously damaged, meanwhile, the S is a main element generating hot brittleness in the hot rolling process, the lower the requirement is theoretically better, but the better the steel-making operability, the steel-making cost and the logistics smoothness principle are considered, and the S content needs to be controlled to be less than or equal to 0.003 percent for the weather-resistant TMCP steel plate which requires high linear energy welding, toughness at-40 ℃, high strength and high heat input welding.
The Cu element only contributes to the weather resistance of the steel plate second to the P element, and a certain amount of Cu is necessary to be added into the weather-resistant steel; in addition, Cu is used as an austenite stabilizing element, can improve the strength of the steel plate and has certain positive contribution to the low-temperature toughness of the steel plate; however, when excessive Cu (not less than 0.50 percent) is added, particularly under the condition of high P content, a low-melting-point CuxPy intermetallic compound is formed in a crystal boundary, so that serious copper brittleness and crystal fracture are caused; however, if the Cu content is too low (< 0.20%), the steel sheet does not meet the requirement of improving weather resistance, and therefore, the reasonable range of Cu content is 0.20% to 0.50%.
The addition of Ni in the weathering steel has the following effects:
1) ni is an excellent weather-resistant element, and the weather resistance of the steel plate can be improved by adding a certain amount of Ni into the steel;
2) the addition of Ni in the steel can prevent the occurrence of crystal cracks (copper brittleness) of a high-copper-content steel plate, and reduce the hot crack sensitivity in the processes of casting, hot rolling and welding;
3) the addition of Ni not only can improve the mobility of ferrite low-temperature dislocation, promote dislocation cross slip and improve the ferrite intrinsic toughness, but also can reduce Ar by taking Ni as an austenite stabilizing element3Point temperature and steel plate microstructure refinement, so that Ni has the function of improving the strength and low-temperature toughness of the TMCP steel plate (fine grain strengthening and fine grain toughening) at the same time; therefore, theoretically, the higher the Ni content in the steel is, the better the steel is, but Ni is a very expensive alloy element, and the reasonable range of the Ni content is 0.15-0.45% from the viewpoint of low cost and mass production.
The Cr element has a large effect of promoting a compact amorphous oxide layer, and a certain amount of Cr is necessary to be added into the weathering steel; a certain amount of Cr (less than or equal to 0.80 percent) is added to improve the weather resistance of the steel plate under the conditions of not damaging the low-temperature toughness and bending cold processing of the steel plate; however, if the content of Cr added is too small (< 0.40%), Cr has small contribution to the weather resistance of the steel plate and cannot meet the requirement of high weather resistance; if the amount of Cr is too large (> 0.70%), the low-temperature toughness and bending cold workability of the steel sheet, particularly the weldability of the steel sheet, cannot withstand large heat input welding, and the low-temperature toughness of the welding heat-affected zone deteriorates (the welding heat-affected zone forms a coarse feather-like upper bainite structure), and therefore, the reasonable range of the Cr content is 0.40% to 0.80%.
The purpose of adding trace Nb element into the steel is to control rolling without recrystallization, refine the grain size of the steel plate and improve the strength and toughness of the TMCP steel plate, and when the addition amount of Nb is less than 0.010 percent, the strengthening capability of the steel plate is insufficient except the rolling control function which can not be effectively exerted; when the addition amount of Nb exceeds 0.030 percent (particularly, the weathering steel with high Cr content), the formation of upper bainite (Bu) and the secondary precipitation embrittlement of Nb (C, N) are induced under the condition of high heat input welding, and the low-temperature toughness of a heat-affected zone (HAZ) of the high heat input welding is seriously damaged, so that the Nb content is controlled between 0.010 percent and 0.030 percent, the optimal rolling control effect is obtained, and the toughness/strength-plasticity matching of the TMCP steel plate is realized without damaging the toughness of the HAZ of the high heat input welding.
Adding a trace amount of Ti into the steel for combining with N in the steel to generate TiN particles with high stability, and inhibiting the growth of steel plate grains and grains in a welding HAZ area; the Ti content added in the steel is matched with the N content in the steel according to the principle that TiN cannot be precipitated in liquid molten steel and must be precipitated in a solid phase, so that the precipitation temperature of TiN must be ensured to be lower than 1400 ℃; when the addition amount of Ti in the steel is too small (less than 0.008 percent), the formed TiN particles are insufficient, and the growth of austenite grains in TMCP and welding heat circulation processes is not inhibited enough to improve the low-temperature toughness and weldability of the steel plate; when the Ti content is excessive (more than 0.016 percent), the TiN precipitation temperature exceeds 1400 ℃, and large-size TiN particles are precipitated from partial TiN particles in the molten steel solidification process, so that the large-size TiN particles can not inhibit the growth of crystal grains and become the starting point of crack initiation; therefore, the optimal control range of the Ti content is 0.008 to 0.016 percent.
Als in the steel sheet can fix the free [ N ] in the steel]Reduction of weld Heat Affected Zone (HAZ) free [ N ]]Improving the low-temperature impact toughness of the large heat input welding HAZ; however, excessive addition of Als to steel not only forms a large amount of dispersed acicular Al in the steel2O3Inclusions damage the low-temperature impact toughness and weldability of the steel plate, and the optimal Als content is controlled to be between 0.040 and 0.070 percent according to the analysis of a steel plate component system.
The control range of N corresponds to the control range of Ti, and Ti/N is optimal between 1.5 and 3.5 for controlling steel plate grains and improving the low-temperature toughness and weldability of the steel plate. The content of N is too low, the generated TiN particles are small in quantity and large in size, the effect of controlling steel plate grains cannot be achieved, the low-temperature toughness and weldability of the steel plate are improved, and the low-temperature toughness and weldability of the steel plate are harmful; however, if the N content is too high, the free [ N ] in the steel increases, and particularly, the free [ N ] content in the Heat Affected Zone (HAZ) sharply increases under high heat input welding conditions, so that the HAZ low-temperature toughness and the bending cold workability are seriously impaired, and the workability of the steel is deteriorated. Therefore, the content of N is controlled to be less than or equal to 0.0050 percent.
Performing Ca treatment on steel, namely further purifying the molten steel on one hand, and performing denaturation treatment on sulfides in the steel on the other hand to ensure that the sulfides are changed into non-deformable, stable and fine spherical sulfides, inhibit the hot brittleness of S, improve the low-temperature toughness, the elongation and the Z-direction performance of the steel plate, and improve the anisotropy and the weldability of the toughness of the steel plate; the addition amount of Ca depends on the content of S in steel, the addition amount of Ca is too low, and the treatment effect is not great; the Ca addition is too high, the formed Ca (O, S) has too large size and increased brittleness, and can be used as a starting point of fracture crack, reduce the low-temperature toughness and elongation of steel and the weldability of a steel plate, and simultaneously reduce the purity of steel and pollute molten steel; the Ca content is generally controlled in terms of ESSP (wt% Ca) [1-1.24 (wt% O) ]/1.25 (wt% S), where ESSP is a sulfide inclusion shape control index, and is preferably in the range of 0.80 to 4.00, and therefore, a suitable range of the Ca content is 0.0010% to 0.0035%.
The invention relates to a method for manufacturing a 550 MPa-grade weather-resistant steel plate with excellent weldability, which comprises the following steps:
1) smelting and casting
Smelting and continuously casting the components into a plate blank; the pouring temperature of the tundish is 1530-1560 ℃, the wire drawing speed is 0.6-1.0 m/min, and the fluctuation of the liquid level of the crystallizer is less than or equal to 5 mm;
2) heating the plate blank, wherein the heating temperature is controlled between 1070 ℃ and 1150 ℃;
3) rolling of
The first stage is common rolling, the rolling average pass reduction rate is more than or equal to 8 percent, and the accumulated reduction rate is more than or equal to 45 percent;
rolling is controlled in the second stage by adopting non-recrystallization, the rolling start temperature is controlled to be 760-820 ℃, the rolling pass reduction rate is more than or equal to 7%, the accumulated reduction rate is more than or equal to 45%, and the final rolling temperature is 750-790 ℃;
4) cooling down
After rolling control is finished, the steel plate is conveyed to cooling equipment, and then accelerated cooling is carried out on the steel plate, the starting cooling temperature of the steel plate is 740-780 ℃, the cooling speed is more than or equal to 5 ℃/s, the stopping cooling temperature is 400-600 ℃, and then the steel plate is naturally air-cooled to the room temperature.
Preferably, when the thickness of the finished steel plate is more than or equal to 50mm, the steel plate is slowly cooled after cooling and stopping cooling in the step 4), and the slow cooling process is that the surface temperature of the steel plate is kept at more than or equal to 250 ℃ for more than 24 hours, and then the steel plate is naturally cooled to the room temperature.
According to the components of the steel plate, the heating temperature of the plate blank is controlled between 1070 ℃ and 1150 ℃, so that the austenite grains of the plate blank are not abnormally grown while the steel plate Nb is completely dissolved into austenite in the heating process of the plate blank.
The first stage is common rolling, continuous rolling is carried out by adopting the maximum rolling capacity of a rolling mill, the recrystallization of the deformed billet is ensured while the productivity of a rolling line is improved to the maximum extent, austenite grains are refined, the cumulative rolling reduction rate is more than or equal to 50 percent, and the rolling average pass reduction rate is more than or equal to 8 percent.
And the second stage adopts non-recrystallization controlled rolling, and according to the Nb content range in the steel, in order to ensure the non-recrystallization controlled rolling effect, the controlled rolling initial rolling temperature is controlled to be 760-820 ℃, the rolling pass reduction rate is more than or equal to 7 percent, the cumulative reduction rate is more than or equal to 45 percent, and the final rolling temperature is 750-790 ℃.
The invention has the beneficial effects that:
the steel plate of the invention is combined with TMCP manufacturing process through simple component combination design, not only can produce TMCP type weather-proof steel plate with excellent comprehensive performance at low cost, but also greatly shortens the manufacturing period of the steel plate, creates great value for enterprises and realizes green and environment-friendly manufacturing process.
The high performance and high added value of the steel plate are collectively shown in that the steel plate has high strength, excellent low-temperature toughness, fatigue resistance and corrosion resistance, the weldability of the steel plate is also excellent, the steel plate can bear high heat input weldability, the opposition between the high strength, excellent low-temperature toughness, fatigue resistance and corrosion resistance of the steel plate and the excellent weldability of the steel plate, particularly the high heat input weldability is successfully solved, and the safety stability and the durability of a large heavy steel structure are greatly improved; the good weldability (especially the high heat input weldability) saves the manufacturing cost of the user steel component, shortens the manufacturing time of the user steel component and creates great value for users.
Drawings
FIG. 1 is a photograph of the microstructure (1/4 thickness) of the steel of example 3 of the present invention.
Detailed Description
The invention is further illustrated with reference to the following figures and examples.
The steel plate components of the embodiments of the invention are shown in table 1, tables 2 to 3 are process parameters of the embodiments of the invention, and table 4 is performance parameters of the embodiments of the invention.
As is clear from FIG. 1, the microstructure of the steel sheet is a small amount of fine ferrite + bainite dispersed therein, and the average grain size of the microstructure is 15 μm or less.
The invention obtains the uniform and excellent low-temperature toughness of the base steel plate by optimally designing the components and combining the TMCP process, and simultaneously, the low-temperature toughness of the HAZ during large heat input welding is also excellent, namely the-40 ℃ impact toughness KV of the base steel plate2Not less than 100J, and Akv not less than 100J at the temperature of-40 ℃ of a welding Heat Affected Zone (HAZ), and can realize stable batch industrial production with low cost.
The steel plate of the invention is combined with TMCP manufacturing process through simple component combination design, not only can produce TMCP type weather-proof steel plate with excellent comprehensive performance at low cost, but also greatly shortens the manufacturing period of the steel plate, creates great value for enterprises and realizes green and environment-friendly manufacturing process. The high performance and high added value of the steel plate are collectively shown in that the steel plate has high strength, excellent low-temperature toughness, fatigue resistance and corrosion resistance, the weldability of the steel plate is also excellent, the steel plate can bear larger heat input weldability, the opposition between the high strength, excellent low-temperature toughness, fatigue resistance and corrosion resistance of the steel plate and the excellent weldability of the steel plate, particularly the large heat input weldability is successfully solved, and the safety stability and the durability of a large heavy steel structure are greatly improved; the good weldability (especially the high heat input welding) saves the manufacturing cost of the user steel member, shortens the manufacturing time of the user steel member, and creates great value for users, so the steel plate is not only a product with high added value and environmental protection.
The steel plate is mainly used for icebreaking ship shells, ocean platforms, cross-sea bridges, ocean wind power pile legs and wind tower structures, port machinery and the like in ice sea areas, can realize low-cost stable batch industrial production, and breaks technical monopoly and technical barriers of foreign low-temperature structural steel.
With the development of national economy and the requirement of building a conservation-oriented harmonious society in China, the key materials in the industries of infrastructure construction, ocean engineering development and major equipment manufacturing, namely 550 MPa-level weather-resistant steel plates with excellent weldability, in China are emerging at present, and the market prospect is wide.
Claims (7)
1. A550 MPa-grade weather-resistant steel plate with excellent weldability comprises the following components in percentage by weight:
C：0.050％～0.090％，
Si：≤0.20％，
Mn：1.00％～1.40％，
P：≤0.013％，
S：≤0.003％，
Cu：0.20％～0.50％，
Ni：0.15％～0.45％，
Cr：0.40％～0.80％，
Nb：0.010％～0.030％，
Ti：0.008％～0.016％，
Als：0.040％～0.070％，
N：≤0.005％，
Ca：0.0010％～0.0035％，
the balance of Fe and other inevitable impurities;
and the content of the elements must satisfy the following relation at the same time:
Als/[(％N)-0.292(％Ti)]≥39；
[(％Mn)+21.17(％Si)]×(％C)≤0.475；
ca treatment, the Ca/S ratio is 1.00-3.00, and, (% Ca) × (% broken)S)0.28)≤1.0×10-3；
0.0038≤[(TStopping cooling)×H]/[(DIOL)×ξ×(TOpen cold)]Less than or equal to 0.0159, wherein,
Tstopping coolingThe quenching end temperature of on-line quenching DQ, namely the stop temperature of accelerated cooling, is the unit of;
h is the thickness of the steel plate and is in mm;
DIOLthe index is the online hardenability index of the steel plate, and the unit is mm;
DIOL＝0.514C0.5(1+0.7Si)(1+3.33Mn)(1+0.35Cu)(1+0.36Ni)(1+2.16Cr)(1+3Mo)(1+1.75V)(1+1.77Al)×25.4；
xi is the accumulated rolling reduction rate of non-recrystallization controlled rolling, and the unit is percent;
Topen coldThe cooling start temperature is in units of ℃ to accelerate cooling.
2. The 550 MPa-grade weathering steel plate with excellent weldability according to claim 1, characterized in that the microstructure of the steel plate is a small amount of fine ferrite + bainite dispersed therein, and the average grain size of the microstructure is 15 μm or less.
3. The 550MPa class weathering steel plate with excellent weldability according to claim 1 or 2, characterized in that the steel plate has a yield strength of 460MPa or more, a tensile strength of 570MPa or more, a Charpy impact energy (single value) of-40 ℃ or more of 120J or more, and an impact toughness KV of-40 ℃ or more2Not less than 100J, and Akv not less than 100J at-40 ℃ of a welding Heat Affected Zone (HAZ).
4. The method for manufacturing a 550 MPa-grade weathering steel plate with excellent weldability according to claim 1, 2 or 3, characterized by comprising the steps of:
1) smelting and casting
Smelting and continuously casting the components according to the claim 1 into a slab; the pouring temperature of the tundish is 1530-1560 ℃, the wire drawing speed is 0.6-1.0 m/min, and the fluctuation of the liquid level of the crystallizer is less than or equal to 5 mm;
2) heating the plate blank, wherein the heating temperature is controlled between 1070 ℃ and 1150 ℃;
3) rolling of
The first stage is common rolling, the rolling average pass reduction rate is more than or equal to 8 percent, and the accumulated reduction rate is more than or equal to 45 percent;
rolling is controlled in the second stage by adopting non-recrystallization, the rolling start temperature is controlled to be 760-820 ℃, the rolling pass reduction rate is more than or equal to 7%, the accumulated reduction rate is more than or equal to 45%, and the final rolling temperature is 750-790 ℃;
4) cooling down
And after rolling control is finished, immediately conveying the steel plate to cooling equipment, immediately carrying out accelerated cooling on the steel plate, wherein the starting cooling temperature of the steel plate is 740-780 ℃, the cooling speed is more than or equal to 5 ℃/s, the stopping cooling temperature is 400-600 ℃, and then naturally air-cooling the steel plate to the room temperature.
5. The method of manufacturing a 550 MPa-grade weathering steel plate with excellent weldability according to claim 4, wherein when the thickness of the finished steel plate is greater than or equal to 50mm, the steel plate is slowly cooled after cooling stop in step 4), and the slow cooling process is performed by keeping the surface temperature of the steel plate at 250 ℃ or higher for 24 hours or more, and then the steel plate is naturally air-cooled to room temperature.
6. The method of producing a 550 MPa-grade weathering steel plate with excellent weldability according to claim 4, characterized in that the microstructure of the steel plate is a small amount of fine ferrite + bainite dispersed therein, and the average grain size of the microstructure is 15 μm or less.
7. The method of manufacturing a 550 MPa-grade weathering steel plate with excellent weldability according to claim 4, wherein the steel plate has a yield strength of 460MPa or more, a tensile strength of 570MPa or more, a Charpy impact energy (single value) of-40 ℃ or more of 120J or more, and an impact toughness KV of-40 ℃ or more2Not less than 100J, and Akv not less than 100J at-40 ℃ of a welding Heat Affected Zone (HAZ).
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