CN110656288B - Steel for ultra-wide, ultra-thick and high-toughness X80 straight welded pipe and production method thereof - Google Patents

Steel for ultra-wide, ultra-thick and high-toughness X80 straight welded pipe and production method thereof Download PDF

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CN110656288B
CN110656288B CN201910942478.9A CN201910942478A CN110656288B CN 110656288 B CN110656288 B CN 110656288B CN 201910942478 A CN201910942478 A CN 201910942478A CN 110656288 B CN110656288 B CN 110656288B
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CN110656288A (en
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张帅
任毅
王爽
刘文月
高红
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Angang Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Abstract

The invention discloses ultra-wide, ultra-thick and high-toughness X80 straight welded pipe steel and a production method thereof. The steel contains C: 0.035-0.055%, Si: 0.12-0.22%, Mn: 1.60-1.75%, P is less than or equal to 0.010%, S is less than or equal to 0.0015%, Nb: 0.06% -0.10%, Ti: 0.008% -0.020%, Ni: 0.10% -0.24%, Mo: 0.15-0.24%, Cr is less than or equal to 0.25%, and (Ni + Mo + Cr): 0.40-0.65%, Al: 0.010% -0.030%, N: 0.0010-0.0040%, Ca: 0.0015 to 0.0045 percent, Ca/S is more than or equal to 1.8, and the balance is iron and inevitable impurities. The heating temperature of the casting blank is 1200-1230 ℃, and the soaking temperature is 1180-1210 ℃; the initial rolling temperature of rough rolling is 1100-1140 ℃, the initial rolling temperature of finish rolling is 810-840 ℃, and the initial cooling temperature is 730-760 ℃. The thickness of the finished steel plate is more than or equal to 31mm, the width of the finished steel plate is more than or equal to 4330mm, and the low-temperature toughness is good.

Description

Steel for ultra-wide, ultra-thick and high-toughness X80 straight welded pipe and production method thereof
Technical Field
The invention belongs to the technical field of low-carbon low-alloy steel, and particularly relates to an X80-grade ultra-wide, extra-thick and high-low-temperature-toughness hot-rolled steel plate with the thickness of more than or equal to 31mm and the width of more than or equal to 4330mm for a large-output oil and gas conveying straight welded pipe in a low-temperature environment and a production method thereof.
Background
For a long time, increasing the efficiency of oil and gas pipeline transportation has been the goal pursued in the pipeline transportation field. With the increasing consumption of oil and gas, the need for improving the efficiency of pipeline transportation is becoming more urgent. Increasing the caliber and the conveying pressure of the pipeline is an important measure for improving the oil and gas conveying efficiency; but must be premised on ensuring pipeline safety. The width of the steel for the longitudinal welded pipe must be increased in order to increase the caliber of the pipeline; steel plates must have higher strength, toughness and larger thickness in order to ensure safety and increase conveying pressure; in addition, the service pipeline in the low-temperature environment also needs to have good low-temperature toughness; therefore, the development of the steel for the oil gas transmission straight welded pipe, which has comprehensive technical characteristics of ultra-wide, ultra-thick, high strength, good low-temperature toughness and the like, becomes an urgent need for the construction of oil gas pipelines.
The complexity and diversity of technical characteristics and indexes remarkably increase the research and development difficulty of the ultra-wide, ultra-thick and high-toughness X80 straight welded pipe steel. Firstly, the width of the steel plate is increased, so that the rolling deformation resistance is increased, the pass deformation rate is limited, the grain refinement and control difficulty is multiplied, meanwhile, the width of the steel plate is increased, the shape control difficulty of the steel plate is increased, and higher requirements on the uniformity of rolling deformation and rapid cooling are provided; the increase of the thickness of the steel plate leads to the increase of the temperature gradient of the thickness section and the deterioration of the cooling and the structural uniformity in the thickness direction; secondly, the wide and thick specification characteristics of the steel plate can also excite the strength-toughness contradiction, and further increase the difficulty of performance control.
At present, there are some researches on wide and thick pipeline steel plates for oil and gas transmission at home and abroad, and partial patents and documents are found through search, but the content recorded in the steel plates is obviously different from the aspects of components, production methods, performances, product types, dimension specifications and the like in the technical scheme of the invention.
CN107502836A discloses a thick-wall large-caliber high-steel grade pipeline steel for improving low-temperature toughness and a manufacturing method thereof, and provides a wide and thick plate for an X80 grade large-caliber straight welded pipe and a manufacturing method thereof, wherein the steel plate is designed by adopting more Ni (0.25-0.30%) in the components, so that the cost is high; the manufacturing process requires that the reduction rate of the final pass of rough rolling is more than 25 percent, has overhigh requirement on the equipment capacity and is not suitable for the production of high-strength wide-specification pipeline steel.
CN108396299A discloses a production method of X80 pipeline steel wide and thick plates, and provides an X80 pipeline steel wide and thick plate and a production method thereof, which adopt high-temperature rough rolling and are not beneficial to strengthening and grain refinement of steel plates.
CN107385326A discloses a production process of an ultra-fine grain wide and thick pipeline steel plate. The production process of the wide and thick pipeline steel is provided, the heating temperature of a casting blank is low (1120-1140 ℃), and solid solution of elements, particularly Nb, is not facilitated; the final pass reduction rate of rough rolling is too large (not less than 26 percent), and the requirement on the equipment capacity is too high.
RU2270873(C1) discloses a method for producing a high-performance steel plate for a welded submarine gas pipeline, and provides a submarine pipeline steel plate and a method for producing the same, in which more elements such as Ni, Cu, etc. are added to the components, resulting in high cost; the production method requires the cooling speed after rolling to be 35-55 ℃/s, and the process is difficult to realize.
Honghang, Zuoxirong, Jonglun et al, in the research on the low temperature fracture behavior of thick X80 pipeline steel published in journal 32, volume 1, 2018, mainly introduced the relation between the low temperature fracture toughness and microstructure of 27.2mm X80, emphasizing the effect of acicular ferrite on improving the low temperature toughness, and the product has small thickness, and the specific production process is not involved in the text.
In view of the above, the prior art has not been sufficiently studied on ultra-wide, ultra-thick, and high-toughness X80 straight welded pipe steel.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, solve the problem of matching of technical indexes such as dimension specification, strength, low-temperature toughness and the like of ultra-wide and ultra-thick pipeline steel, and provide an X80 grade ultra-wide, ultra-thick, high-strength and good low-temperature toughness hot-rolled steel plate for the oil-gas conveying straight welded pipe in the low-temperature environment, wherein the thickness of the hot-rolled steel plate is more than or equal to 31mm, and the width of the hot-rolled steel plate is more than or equal to 43.
The thickness of the steel for the ultra-wide, ultra-thick and high-toughness X80 straight welded pipe is more than or equal to 31mm, and the width of the steel is more than or equal to 4330 mm; the component design improves the toughness of the material through low C and low Mn, utilizes Nb and Ti elements to inhibit the growth of austenite grains and refine the grains by promoting nucleation in the austenite transformation process, controls the thickness core structure of the steel plate and improves the uniformity of the structure; meanwhile, aiming at the characteristics of ultra-wide high strength, the effect of Nb on inhibiting austenite recrystallization is utilized, the rolling temperature is increased, the rolling resistance is effectively reduced, and the increase of the rolling pass deformation rate is facilitated; the solid solution strengthening effect is increased by the Ni element, and the low-temperature toughness is improved by the Ni element; and the corresponding production processes of smelting, heating, rolling, cooling, straightening and the like are matched to obtain the ultra-wide, ultra-thick, high-strength, good low-temperature toughness and other comprehensive properties and ideal microstructures.
The specific technical scheme is as follows:
the steel for the ultra-wide, ultra-thick and high-toughness X80 straight welded pipe comprises the following chemical components in percentage by weight: 0.035-0.055%, Si: 0.12-0.22%, Mn: 1.60-1.75%, P is less than or equal to 0.010%, S is less than or equal to 0.0015%, Nb: 0.06% -0.10%, Ti: 0.008% -0.020%, Ni: 0.10% -0.24%, Mo: 0.15-0.24%, Cr is less than or equal to 0.25%, and (Ni + Mo + Cr): 0.40-0.65%, Al: 0.010% -0.030%, N: 0.0010-0.0040%, Ca: 0.0015 to 0.0045 percent, Ca/S is more than or equal to 1.8, and the balance is iron and inevitable impurities.
The invention relates to a CE steel for ultra-wide, ultra-thick and high-toughness X80 straight welded pipesIIWControlled at 0.39% -0.43%, CEIIW＝C+Mn/6+(Cr+Mo)/5+(Ni+Cu)/15；CEPcmControlled at 0.15% -0.18%, CEPcm＝C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B。
The invention has the following design reasons:
c: c can play a strengthening role through interstitial solid solution, can also form fine carbide precipitation through the action of alloy elements such as niobium and the like, and is precipitated before rolling deformation or austenite phase transformation, so that the crystal grain growth is hindered, the nucleation rate is improved, and the structure is refined; meanwhile, dislocation movement can be hindered, and strength is effectively improved, so that the carbon content is not low; however, the increase in carbon has a bad influence on toughness, particularly low-temperature toughness; moreover, the increase of carbon increases the solid solution temperature of carbide when the casting blank is reheated, promotes the growth of crystal grains, so the carbon content cannot be too high, and the invention considers that the carbon is preferably controlled to be 0.035 to 0.055 percent.
Si: si plays a strengthening role and is also beneficial to improving hardenability; however, when the content is too high, the M/A in the structure is increased, the bainite crystal grain size is increased, the toughness is reduced, cold brittleness is easily caused, and the suitable range is 0.12-0.22%.
Mn: mn can effectively improve the strength and the hardenability; the austenite phase transition temperature is reduced, the growth of phase transition crystal grains before the steel plate is accelerated to be cooled is inhibited, and the effect of refining the crystal grains is exerted; however, when the manganese content is too high, segregation is easily induced, the structural uniformity and the thickness center toughness of the thick-walled steel plate are deteriorated, and welding is not facilitated, and it is considered that the manganese content is preferably controlled to be 1.60% to 1.75%.
P, S: p, S are harmful impurity elements in the invention, the lower the content, the better; wherein, P has obvious adverse effect on low-temperature toughness, P is controlled to be less than or equal to 0.010 percent, and the increase of S content can promote the generation, growth and deterioration of inclusions, so that S is less than or equal to 0.0015 percent.
Nb: the effects of niobium in the present invention include (1) solid solution strengthening; (2) in the rolling process and before accelerated cooling, the precipitation is carried out, the grain boundary is pinned, the nucleation is promoted, and the crystal grains are effectively refined, so that the strength is improved and the toughness is improved; (3) the austenite phase transition temperature is reduced, and grains can be refined; (4) the recrystallization rolling temperature is increased, the rolling force is reduced, and the effect of improving the rolling pass deformation rate and the fine grain effect of the ultra-wide and ultra-thick pipeline steel plate is obvious; however, too high a content of niobium deteriorates the toughness of the weld and the heat affected zone and increases the cost, and it is considered that the present invention is preferable to control the content of niobium to 0.06% to 0.10%.
Ti: ti can exert nitrogen fixation effect, form a precipitation phase mainly comprising TiN, inhibit the growth of austenite grains under high temperature condition and improve the toughness of a heat affected zone after welding, and the invention considers that the control of the titanium content to be 0.008-0.020% is more appropriate.
Ni: ni can improve the strength and the low-temperature toughness, and is beneficial to good matching of the toughness and the toughness; the nickel can reduce the critical cooling speed and delay the pearlite transformation, and is beneficial to the structure control, grain refinement and homogenization of the extra-thick pipeline steel plate; however, the price of nickel is higher, so the content of nickel is controlled to be 0.10-0.24 percent.
Mo: mo is an effective strengthening element, can improve hardenability and is beneficial to improving the cooling effect of the thick-wall pipeline steel plate; but also can promote the transformation of medium and low temperature tissues and has a certain fine grain effect, but the molybdenum has higher price and can increase the cost, so the content of the molybdenum is controlled to be 0.15 to 0.24 percent.
Cr: cr has a solid solution strengthening effect, improves the stability of austenite, reduces the austenite phase transition temperature and can improve the uniformity of the structure in the thickness direction; however, since too high a chromium content is disadvantageous in plasticity and weldability, the chromium content is controlled to 0.25% or less.
The Ni + Mo + Cr content is too low to be beneficial to performance and microstructure control, and the content is too high to be beneficial to weldability and economy, so that the invention controls the (Ni + Mo + Cr) content to be as follows: 0.40 to 0.65 percent.
Al: al is a deoxidizing element, the welding performance is not good when the content of Al is too high, and the content of Al is preferably controlled to be 0.010-0.030 percent in the invention.
N: n can form fine precipitates with niobium and titanium at high temperature to play a role in fine grains and precipitation strengthening, so that the toughness is improved, but the toughness is deteriorated due to overhigh content, and the content of the N is controlled to be 0.0010-0.0040%.
Ca: ca mainly promotes the denaturation of inclusions and reduces the damage of the inclusions to the performance, and the invention considers that the Ca: 0.0015 to 0.0045 percent and Ca/S more than or equal to 1.8 can achieve the ideal inclusion control effect.
The invention relates to CEIIWControlled at 0.39% -0.43%, CEPcmThe control is 0.15 to 0.18 percent, which not only can ensure the obdurability of the steel plate, but also can ensure the steel plate to have proper weldability.
The production method of the steel for the ultra-wide, ultra-thick and high-toughness X80 straight welded pipe comprises the steps of molten iron pretreatment, converter smelting, external refining, continuous casting, slab heating, rolling, cooling and straightening; wherein the smelting tapping temperature of the converter is less than or equal to 1640 ℃, the C is less than or equal to 0.035%, the phosphorus control effect of the converter can be ensured by adopting lower tapping temperature, and the carbon content of the final product can be effectively controlled by adopting lower tapping carbon content. The casting superheat degree of the continuous casting billet is 10-25 ℃, and the thickness of the continuous casting billet/the thickness of a finished steel plate is more than or equal to 8; the control of the pouring superheat degree can effectively reduce the quality defect of the casting blank; the grain size can be effectively controlled by increasing the compression ratio from the continuous casting billet to the finished steel plate.
The temperature of a heating section of the continuous casting billet is 1200-1230 ℃, the temperature of a soaking section is 1180-1210 ℃, and the time of the soaking section is not less than 50 min; the heating process can meet the solid solution of the alloy, particularly niobium, and simultaneously prevent austenite grains from excessively growing; the heating time can ensure the temperature uniformity of the blank.
The initial rough rolling temperature is 1100-1140 ℃, the final rough rolling temperature is 1020-1050 ℃, a transverse and longitudinal rolling mode is adopted, after the transverse rolling of the casting blank is finished, the casting blank can be cooled to a longitudinal rolling starting temperature in a spraying and air cooling mode, the longitudinal rolling starting temperature is lower than 1070 ℃, the rolling speed is 1.0-2.0 m/s, and the longitudinal rolling stage ensures that the deformation rate of each pass of at least the last 2 passes is more than 15% and the time interval of the passes is not more than 15 s; the rolling temperature and the deformation process in the rough rolling stage ensure that austenite grains are recrystallized and the grains are inhibited from growing, the accelerated cooling and the air cooling after the rough rolling and the transverse rolling are favorable for inhibiting the grains from growing, and the lower rolling speed is matched to promote the rolling deformation to permeate to the thickness center of a casting blank and refine the structure near the thickness center, so that the improvement on the performance of the extra-thick pipeline steel is favorable; the equipment load of the ultra-wide pipeline steel can be reduced by adopting a large reduction and short interval process at the end of longitudinal rolling, and the recrystallization of austenite is promoted by utilizing the multi-pass deformation superposition effect to achieve the grain refinement target, so that the method is suitable for producing the ultra-wide and ultra-thick pipeline steel plate.
The thickness of the intermediate temperature-waiting blank is 2.5 t-3.4 t, wherein t is the thickness of a finished steel plate, the start rolling temperature of finish rolling is 810-840 ℃, the finish rolling temperature is 740-770 ℃, and the accumulated deformation rate below 790 ℃ is not lower than 20%; the thickness of the intermediate blank to be heated can meet the requirement of accumulation of austenite deformation and deformation energy in a non-recrystallization region, and can ensure that enough deformation rate is obtained in the rough rolling stage under the condition of certain thickness of the original casting blank, so that the purpose of grain refinement is achieved; the low finish rolling temperature promotes the accumulation of austenite transformation energy and the induced precipitation of fine precipitated phases of Nb and Ti, and increases nucleation positions; sufficient deformation near the transformation point temperature at the final stage of finish rolling is beneficial to the generation of fine ferrite, the effective grain size can be reduced, and the low-temperature toughness is obviously improved.
Carrying out accelerated water cooling on the rolled steel plate, wherein the time interval from the rolling completion to the water cooling start does not exceed 25s, the water cooling start temperature is 730-760 ℃, the final cooling temperature is 380-460 ℃, and the water cooling time is not less than 15 s; and then, carrying out thermal straightening and air cooling, then carrying out secondary straightening at 100-250 ℃, and then carrying out air cooling to room temperature. The growth of proeutectoid ferrite can be inhibited by controlling the starting water cooling temperature and the interval time of the steel plate, the effective grain size is reduced, and the low-temperature toughness is improved; the final cooling temperature can promote the formation of bainite and refine M/A; the longer water cooling time can improve the cooling uniformity and improve the plate shape under the condition of ensuring the water cooling effect; the internal stress of the steel plate is effectively released at the appropriate secondary straightening temperature, the steel plate is not deformed after being straightened, and the method plays an important role in ensuring the shape of the ultra-wide and ultra-thick steel plate.
The final microstructure of the steel plate is mainly a composite structure of bainite and fine polygonal ferrite, wherein the volume percentage of the polygonal ferrite is 5-25%, the grain size reaches 11 grades or finer, and the average grain size of the polygonal ferrite is lower than 7 mu m; the steel plate has super-wide, super-thick, high strength and good low-temperature toughness, and meets the requirement of manufacturing a phi 1422mm large-caliber thick-wall X80 oil and gas transmission pipeline for a low-temperature environment.
Has the advantages that:
compared with the prior art, the invention has the following beneficial effects:
(1) the components of the invention improve the toughness of the material through low C and low Mn design, utilize Nb and Ti elements to inhibit the growth of austenite grains and refine the grains by promoting nucleation in the austenite transformation process, control the thickness core structure of the steel plate and improve the uniformity of the structure; meanwhile, aiming at the characteristics of ultra-wide high strength, the effect of Nb on inhibiting austenite recrystallization is utilized, the rolling temperature is increased, the rolling resistance is effectively reduced, and the increase of the rolling pass deformation rate is facilitated; the solid solution strengthening effect is increased by the Ni element, and the low-temperature toughness is improved by the Ni element; matched with a corresponding unique production process, the matching problem of technical indexes such as size specification, strength, low-temperature toughness and the like of the ultra-wide and ultra-thick pipeline steel is solved.
(2) Carbon equivalent CE of the inventionIIWAnd CEPcmProper, ensures that the material has good strength and weldability。
(3) The smelting and continuous casting process scheme of the invention realizes low-phosphorus and low-carbon control, improves the quality of casting blanks and further improves the performance of final products.
(4) The invention adopts a unique production process, fully refines crystal grains, obtains a tissue structure of bainite and fine polygonal ferrite, plays the reinforcing and fine-grained effects of fine precipitated phases, effectively improves the product performance, particularly the low-temperature toughness, simultaneously increases the cooling uniformity and the temperature straightening, and effectively controls the plate shape of the ultra-wide steel plate.
(5) The steel for the ultra-wide, ultra-thick and high-toughness X80 straight welded pipe has the thickness of more than or equal to 31mm, the width of more than or equal to 4330mm, the transverse yield strength of 530-590 MPa, the transverse tensile strength of 650-710 MPa, the transverse yield ratio of not more than 0.88, the transverse impact mean value of minus 60 ℃ of not less than 360J, the transverse DWTT shearing area of 20 ℃ of not less than 85 percent, and the microstructure mainly comprises a composite structure of bainite and fine polygonal ferrite, wherein the volume percentage of the polygonal ferrite is 5-25 percent, the grain size reaches 11 grades or finer, the average size of the polygonal ferrite grains is less than 7 mu m, and the requirement of manufacturing a phi 1422mm large-caliber thick-wall X80 oil and gas conveying pipeline for a low-temperature environment is.
Drawings
FIG. 1 shows a metallographic structure of a steel plate according to example 2 of the present invention.
Detailed Description
The following examples are intended to illustrate the invention in detail, and are intended to be a general description of the invention, and not to limit the invention.
The chemical compositions of the examples of the invention are shown in table 1; the smelting continuous casting process of the corresponding embodiment is shown in a table 2; the slab heating process of the corresponding example is shown in table 3; the rough rolling process of the corresponding example is shown in table 4; the finish rolling process of the corresponding example is shown in Table 5; the cooling and straightening processes of the corresponding examples are shown in Table 6; the microstructure of the corresponding examples is shown in Table 7. The properties of the corresponding examples are shown in Table 8.
TABLE 1 chemical composition wt% of steel sheet of inventive example
Figure BDA0002223300090000091
In the table: CEIIW＝C+Mn/6+(Cr+Mo)/5+(Ni+Cu)/15；
CEPcm＝C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B
TABLE 2 smelting and continuous casting process of the present invention
Examples temperature/DEG C of smelting tapping Content of C in the smelted steel Degree of superheat of casting/deg.C Slab thickness/finished product thickness
1 1627 0.030 16 8.3
2 1639 0.032 22 9.3
3 1633 0.032 20 8.3
4 1628 0.034 20 9.3
5 1630 0.030 17 9.3
6 1631 0.031 19 9.3
Table 3 slab heating process of the embodiment of the present invention
Examples Heating temperature/. degree.C Soaking temperature/. degree.C Soaking period time/min
1 1211 1184 69
2 1205 1191 73
3 1227 1202 68
4 1223 1194 62
5 1216 1182 70
6 1228 1206 60
Table 4 rough rolling process of the present invention example
Figure BDA0002223300090000101
TABLE 5 finish rolling process of examples of the present invention
Figure BDA0002223300090000111
TABLE 6 Cooling and straightening process of an embodiment of the invention
Figure BDA0002223300090000112
TABLE 7 microstructures of examples of the invention
Examples Thickness/mm of steel plate Width of steel plate/mm Volume percent of ferrite/%) Grain size grade
1 35 4330 17 11.5
2 32.1 4335 19 11.5
3 35 4330 11 11.5
4 32.1 4335 13 12
5 32.1 4335 15 11.5
6 32.1 4335 7 12
TABLE 8 Performance of examples of the invention
Figure BDA0002223300090000121
Note: the tensile sample is a full-thickness rectangular sample, and the plate width of a parallel test section is 38.1 mm; the DWTT test sample is a full-thickness test sample; the impact specimen size was 10 x 55 mm.

Claims (2)

1. The steel for the ultra-wide, ultra-thick and high-toughness X80 straight welded pipe is characterized by comprising the following chemical components in percentage by mass: c: 0.035-0.055%, Si: 0.12-0.22%, Mn: 1.60-1.75%, P is less than or equal to 0.010%, S is less than or equal to 0.0015%, Nb: 0.071-0.10% of Ti: 0.008% -0.020%, Ni: 0.10% -0.24%, Mo: 0.15-0.24%, Cr is less than or equal to 0.18%, and (Ni + Mo + Cr): 0.40-0.65%, Al: 0.010% -0.030%, N: 0.0010-0.0040%, Ca: 0.0015-0.0045 percent and Ca/S is not less than1.8, and the balance of Fe and inevitable impurities; CE of SteelIIWControl at 0.402% -0.43%, CEPcmControlled at 0.15% -0.18%, wherein, CEIIW＝C+Mn/6+(Cr+Mo)/5+(Ni+Cu)/15；CEPcm＝C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B；
The production process of the steel plate comprises the following steps: the method comprises the steps of molten iron pretreatment, converter smelting, external refining, continuous casting, slab heating, rolling, cooling and straightening, wherein,
the tapping temperature of the converter smelting is less than or equal to 1640 ℃, and the content of C in the molten steel is less than or equal to 0.035% during tapping; the casting superheat degree of the continuous casting billet is 10-25 ℃, and the thickness of the continuous casting billet/the thickness of a finished steel plate is more than or equal to 8;
the temperature of a heating section of the continuous casting billet is 1200-1230 ℃, the temperature of a soaking section is 1180-1210 ℃, and the time of the soaking section is more than or equal to 50 min;
the initial rough rolling temperature is 1100-1140 ℃, the final rough rolling temperature is 1020-1050 ℃, a transverse and longitudinal rolling mode is adopted, after the transverse rolling of the casting blank is finished, the casting blank is cooled to a longitudinal rolling starting temperature in a spraying and air cooling mode, the longitudinal rolling starting temperature is less than 1070 ℃, the rolling speed is 1.0-2.0 m/s, and the deformation rate of each pass of at least the last 2 passes is more than 15% and the time interval of the pass is less than or equal to 15s in the longitudinal rolling stage;
the thickness of the intermediate temperature-waiting blank is 2.5 t-3.4 t, wherein t is the thickness of a finished steel plate, the start rolling temperature of finish rolling is 810-840 ℃, the finish rolling temperature is 740-770 ℃, and the accumulated deformation rate below 790 ℃ is not lower than 20%;
carrying out accelerated water cooling on the rolled steel plate, wherein the time interval from the rolling completion to the beginning of water cooling is less than or equal to 25s, the beginning temperature of water cooling is 730-760 ℃, the final cooling temperature is 380-460 ℃, and the water cooling time is more than or equal to 15 s; and then, carrying out thermal straightening and air cooling, then carrying out secondary straightening at 100-250 ℃, and then carrying out air cooling to room temperature.
2. The steel for the ultra-wide ultra-thick high-toughness X80 straight welded pipe according to claim 1, wherein the steel plate has a thickness of 31mm or more and a width of 4330mm or more.
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