CN110643897B - Steel for extra-wide thick-wall low-yield-ratio X80 straight welded pipe and production method thereof - Google Patents

Steel for extra-wide thick-wall low-yield-ratio X80 straight welded pipe and production method thereof Download PDF

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CN110643897B
CN110643897B CN201910944445.8A CN201910944445A CN110643897B CN 110643897 B CN110643897 B CN 110643897B CN 201910944445 A CN201910944445 A CN 201910944445A CN 110643897 B CN110643897 B CN 110643897B
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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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    • C22C38/00—Ferrous alloys, e.g. steel alloys
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    • 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
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • 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
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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    • 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
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • 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
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Abstract

The invention discloses steel for an extra-wide thick-wall low-yield-ratio X80 straight welded pipe and a production method thereof. The steel contains C: 0.045% -0.065%, Si: 0.26-0.40%, Mn: 1.60-1.80%, P is less than or equal to 0.010%, S is less than or equal to 0.0015%, Nb: 0.04-0.06%, Ti: 0.008% -0.020%, Ni: 0.10-0.24%, Cu: 0.16-0.25%, Mo is less than or equal to 0.12%, Cr is less than or equal to 0.30%, Ni + Cu + Mo + Cr: 0.45-0.75%, Al: 0.010% -0.030%, N: 0.0010 to 0.0040 percent, and the balance of Fe and inevitable impurities. The heating temperature of the casting blank is 1190-1220 ℃, and the soaking temperature is 1170-1200 ℃; 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 710-750 ℃. The thickness of the finished steel plate is more than or equal to 30mm, the width of the finished steel plate is more than or equal to 4320mm, and the low-temperature toughness and the strain resistance are good.

Description

Steel for extra-wide thick-wall low-yield-ratio 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 extra-wide, thick-walled, high-low-temperature-toughness and high-strain-resistance hot-rolled steel plate with the thickness of more than or equal to 30mm and the width of more than or equal to 4320mm and a production method thereof; the method is suitable for manufacturing the large-caliber oil and gas conveying straight welded pipe which is in service under complex environmental conditions such as a geological active area, a cold area, a cross-over area, a seabed suspended area and the like.
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, pipelines in service in environments such as cold regions, geological active regions, pipeline crossing regions, deep sea and the like are required to have good strain resistance and low-temperature toughness so as to meet the requirements of severe service environments; therefore, the development of the steel for the straight welded oil and gas conveying pipe, which has the comprehensive technical characteristics of extra-wide, thick-walled, high strength, high toughness, good strain resistance and the like, is an urgent need for the construction of oil and gas pipelines.
The complexity and diversity of technical characteristics and indexes remarkably increase the research and development difficulty of the steel for the ultra-wide thick-wall low-yield-ratio X80 straight welded pipe. 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-plasticity-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 Mo (0.15-0.20%) and 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 method for producing X80 pipeline steel wide and thick plates, and provides an X80 pipeline steel wide and thick plate and a method for producing the same, wherein low Si (0.10% -0.14%) and high-temperature rough rolling are adopted, and the method is 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, and provides a production process of a wide and thick pipeline steel, wherein the heating temperature of a casting blank is low (1120-1140 ℃), and the 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 published the research on the low temperature fracture behavior of thick X80 pipeline steel in "journal of materials research" volume 32, volume 1, 2018, which mainly introduced the relationship between the low temperature fracture toughness and microstructure of X80 with thickness of 27.2mm, emphasized 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 steel for X80 straight welded pipes having extremely wide, thick and low yield ratio.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, solve the problem of matching of technical indexes such as size specification, strength, uniform elongation, yield ratio, low-temperature toughness, strain resistance and the like of the steel for the X80 straight welded pipe with extra-wide thickness and low yield ratio, and provide a hot-rolled steel plate with X80 grade extra-wide thickness, thick wall, good low-temperature toughness and strain resistance and with the thickness of more than or equal to 30mm and the width of more than or equal to 4320mm for the oil-gas conveying straight welded pipe in a low-temperature environment and a production method thereof.
The thickness of the steel for the ultra-wide thick-wall low-yield-ratio X80 straight welded pipe is more than or equal to 30mm, and the width of the steel is more than or equal to 4320 mm; the composition design improves the toughness of the material through low C and low Mn, utilizes Si to improve the strength and strain strengthening effect, increases the solid solution strengthening effect through Ni and Cu elements and utilizes Ni elements to improve the low-temperature toughness; nb and Ti elements are used for inhibiting the growth of austenite grains and promoting nucleation in the austenite transformation process to refine the grains, the thickness core structure of the steel plate is controlled, the uniformity of the structure is improved, and proper phase transformation temperature and phase transformation dynamic conditions are obtained by controlling the contents of Mn, Mo and other elements, so that the formation of polygonal ferrite and the control of the grain size are facilitated; and the corresponding production processes of smelting, heating, rolling, cooling, straightening and the like are matched to obtain the ultra-wide, thick-walled, high-strength, high-uniform elongation, low yield ratio, good low-temperature toughness, strain resistance and other comprehensive properties and ideal microstructures.
The specific technical scheme is as follows:
the steel for the ultra-wide thick-wall low-yield-ratio X80 straight welded pipe comprises the following chemical components in percentage by mass: 0.045% -0.065%, Si: 0.26-0.40%, Mn: 1.60-1.80%, P is less than or equal to 0.010%, S is less than or equal to 0.0015%, Nb: 0.04-0.06%, Ti: 0.008% -0.020%, Ni: 0.10-0.24%, Cu: 0.16-0.25%, Mo is less than or equal to 0.12%, Cr is less than or equal to 0.30%, and (Ni + Cu + Mo + Cr): 0.45-0.75%, Al: 0.010% -0.030%, N: 0.0010 to 0.0040 percent, and the balance of iron and inevitable impurities.
The invention relates to a CE steel for X80 straight welded pipe with extra wide, thick wall and low yield ratioIIWControlled at 0.39% -0.44%, wherein, CEIIW＝C+Mn/6+(Cr+Mo)/5+(Ni+Cu)/15；CEPcmControlled at 0.17% -0.19%, wherein, 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 large influence on the plasticity and toughness, particularly on the 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 0.045-0.065%.
Si: in the invention, the silicon can effectively improve the tensile strength and the strain hardening effect, and is also beneficial to improving the hardenability; however, the content of the Si is too high, so that the M/A in the structure is increased, the size of bainite crystal grains is increased, the toughness and the plasticity are reduced, cold brittleness is easily caused, and the control range of the Si is 0.26-0.40%.
Mn: mn can effectively improve the strength and the hardenability; the austenite phase transition temperature and the phase transition dynamic condition are changed, the formation of polygonal ferrite is facilitated, meanwhile, the growth of phase transition grains before the steel plate is accelerated to be cooled is inhibited, and the grain refining effect 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 the manganese content is preferably controlled to be 1.60% to 1.80%.
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 extra-wide thick-wall pipeline steel plate is obvious; however, too high niobium content 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 niobium content to 0.04% to 0.06%.
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, the grain refinement and the homogenization of the thick-wall pipeline steel plate; however, the price of nickel is higher, so the content of nickel is controlled to be 0.10-0.24 percent.
Cu: cu can improve the strength and make up for the strength loss caused by the reduction of the carbon content; copper improves hardenability, increases austenite stability, is beneficial to improving the cooling effect of the thick-wall steel plate, and can also improve corrosion resistance; however, the excessively high copper content is disadvantageous in toughness and impairs weldability, and it is considered that the present invention is preferable to control the copper content to 0.16% to 0.25%.
Mo: mo can improve hardenability, promote medium and low temperature structure transformation and has a certain fine-grain effect, but the over-high content of the molybdenum can inhibit ferrite transformation on one hand and is not beneficial to improving plastic deformation performance, and the molybdenum can deteriorate strain aging performance; on the other hand, the high price of molybdenum increases the cost, so the content of the molybdenum is controlled not to exceed 0.12 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 terms of plasticity and weldability, the present invention controls the chromium content to not more than 0.30%.
Ni + Cu + Mo + Cr: the total amount of the four elements is too low to be beneficial to the control of performance and microstructure, and the content is too high to influence the weldability and the economy, so the invention controls the (Ni + Cu + Mo + Cr) to be 0.45-0.75%.
Al: al is a deoxidizing element, the welding performance is not good due to the excessively high content of Al, and the content of Al is preferably controlled to be 0.010-0.030%.
N: n can form fine precipitates with niobium and titanium at high temperature to play a role of fine grains and precipitation strengthening so as to improve the toughness, but the toughness is deteriorated due to overhigh content, so the content of the N is controlled to be 0.0010-0.0040 percent.
The invention relates to CEIIWControlled at 0.39% -0.44%, CEPcmThe control is between 0.17 and 0.19 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 thick-wall low-yield-ratio X80 straight welded pipe comprises the steps of molten iron pretreatment, converter smelting, external refining, continuous casting, 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 8.5; 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 1190-1220 ℃, the temperature of a soaking section is 1170-1200 ℃, the time of the soaking section is not less than 50min, the heating process can ensure the solid solution of the alloy, particularly niobium, and simultaneously, the excessive growth of austenite grains is prevented, and the temperature uniformity of the blank can be ensured by the heating time.
The initial rough rolling temperature is 1100-1140 ℃, the final rough rolling temperature is 1000-1030 ℃, 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 1060 ℃, 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 ensured to be larger than 15% and the pass interval is not more than 15s in the longitudinal rolling stage; 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 thick-wall 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, so that the grain refinement target is achieved, and the method is suitable for producing the ultra-wide thick-wall pipeline steel plate.
The thickness of the intermediate temperature-waiting blank is 2.6 t-3.5 t, wherein t is the thickness of a finished steel plate, the finish rolling initial rolling temperature is 810-840 ℃, the finish rolling final rolling temperature is 750-770 ℃, and the accumulated deformation rate below 790 ℃ is not lower than 15%; 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 is reduced, the toughness and plasticity are improved, and the yield ratio is reduced.
Carrying out accelerated water cooling on the rolled steel plate, wherein the interval time from the rolling completion to the water cooling starting is 25-50 s, the water cooling starting cooling temperature is 710-750 ℃, the final cooling temperature is 320-400 ℃, 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 proportion and the size of ferrite in the structure can be controlled by the starting water cooling temperature and the interval time of the steel plate, and the plasticity and the toughness are improved; the final cooling temperature can promote the formation of bainite, refine M/A and obtain a good structure with combined soft and hard phases; 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 proper 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 extra-wide thick-wall steel plate.
The final microstructure of the steel plate is mainly a composite structure of bainite and polygonal ferrite, wherein the volume percentage of the polygonal ferrite is 20-45%, the grain size reaches 11 grades or thinner, and the steel plate has extra-wide, thick-walled, high strength, low yield ratio, high uniform elongation, high stress ratio, high strain resistance and good low-temperature toughness, and meets the requirement of manufacturing phi 1422mm large-caliber thick-walled X80 oil and gas transmission pipelines for complex service environments such as geological active areas, cold regions, cross-over areas, seabed suspension areas and the like.
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 Si to improve the strength and strain strengthening effect, increase the solid solution strengthening effect through Ni and Cu elements and utilize Ni elements to improve the low-temperature toughness; nb and Ti elements are used for inhibiting the growth of austenite grains and promoting nucleation in the austenite transformation process to refine the grains, the core structure of the thickness is controlled, the uniformity of the structure is improved, and proper phase transformation temperature and phase transformation dynamic conditions are obtained by controlling the contents of Mn, Mo and other elements, so that the formation of polygonal ferrite and the control of the grain size are facilitated; matched with a corresponding unique production process, the matching problem of technical indexes such as size specification, strength, uniform elongation, yield ratio, low-temperature toughness, strain resistance and the like of the extra-wide thick-wall pipeline steel is solved.
(2) Carbon equivalent CE of the inventionIIWAnd CEPcmAnd the material is ensured to have 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 an ideal structure, plays the roles of strengthening and fine-crystallizing fine precipitated phases, effectively improves the product performance, increases the cooling uniformity and effectively controls the plate shape of the ultra-wide steel plate.
(5) The steel for the extra-wide thick-wall low-yield-ratio X80 straight welded pipe has the thickness of more than or equal to 30mm, the width of more than or equal to 4320mm, the transverse yield strength of 510-570 MPa, the transverse tensile strength of 685-740 MPa, the transverse uniform elongation UEL of more than or equal to 7%, the transverse yield ratio of not more than 0.80, the stress ratio Rt1.5/Rt0.5 of more than or equal to 1.1, the transverse impact mean value of more than or equal to 300J at-60 ℃, the transverse DWTT shearing area of more than or equal to 85% at-20 ℃, and the microstructure mainly adopts a bainite and polygonal ferrite composite structure, wherein the polygonal ferrite volume percentage is 20-45%, the grain size reaches 11 grades or thinner, and the requirement of manufacturing phi 1422mm large-caliber X80 oil and gas conveying pipelines for complex service environments such as geological active areas, thick-wall cold areas, cross-zones, seabed.
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
Examples C Si Mn P S Nb Ti Ni
1 0.048 0.28 1.73 0.006 0.0013 0.052 0.015 0.14
2 0.062 0.36 1.69 0.008 0.0010 0.041 0.018 0.16
3 0.055 0.26 1.64 0.006 0.0011 0.053 0.014 0.21
4 0.064 0.31 1.78 0.007 0.0014 0.049 0.018 0.23
5 0.049 0.32 1.74 0.008 0.0014 0.041 0.009 0.22
6 0.059 0.38 1.68 0.005 0.0013 0.048 0.014 0.17
Examples Cu Mo Cr Ni+Cu+Mo+Cr Al N CEIIW CEPcm
1 0.18 0.05 0.24 0.61 0.024 0.0030 0.416 0.171
2 0.21 0.11 0.19 0.67 0.018 0.0021 0.428 0.189
3 0.23 0 0.26 0.70 0.014 0.0023 0.410 0.174
4 0.23 0 0 0.46 0.026 0.0015 0.391 0.179
5 0.24 0 0.18 0.64 0.020 0.0037 0.406 0.171
6 0.19 0.08 0.23 0.67 0.026 0.0036 0.425 0.185
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 1638 0.031 24 9.3
2 1629 0.033 15 9.7
3 1630 0.030 12 9.3
4 1632 0.031 18 9.7
5 1626 0.034 11 9.7
6 1630 0.033 22 9.7
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 1214 1175 91
2 1198 1192 66
3 1193 1184 93
4 1203 1189 80
5 1197 1179 83
6 1216 1195 59
Table 4 rough rolling process of the present invention example
Figure BDA0002223775670000111
TABLE 5 finish rolling process of examples of the present invention
Figure BDA0002223775670000112
TABLE 6 Cooling and straightening process of an embodiment of the invention
Figure BDA0002223775670000113
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 32.1 4335 31 11.5
2 30.8 4340 23 11.5
3 32.1 4335 38 11
4 30.8 4340 27 12
5 30.8 4340 32 11.5
6 30.8 4340 34 11.5
TABLE 8 Performance of examples of the invention
Figure BDA0002223775670000121
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 thick-wall low-yield-ratio X80 straight welded pipe is characterized by comprising the following chemical components in percentage by mass: c: 0.045% -0.065%, Si: 0.31-0.40%, Mn: 1.60-1.80%, P is less than or equal to 0.010%, S is less than or equal to 0.0015%, Nb: 0.04-0.06%, Ti: 0.008% -0.020%, Ni: 0.10-0.24%, Cu: 0.16-0.25%, Mo is less than or equal to 0.12%, Cr is less than or equal to 0.30%, Ni + Cu + Mo + Cr: 0.45-0.75%, Al: 0.010% -0.030%, N: 0.0010 to 0.0040 percent of the total weight of the alloy, and the balance of Fe and inevitable impurities, CEIIWControl at 0.406% -0.44%, CEPcmControlled at 0.171% -0.19%, 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 is controlled to be 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 8.5;
the temperature of the heating section of the continuous casting billet is 1190-1220 ℃, the temperature of the soaking section is 1170-1200 ℃, 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 1000-1030 ℃, 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 1060 ℃, 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 passes is less than or equal to 15s in the longitudinal rolling stage; the thickness of the intermediate temperature-waiting blank is 2.6 t-3.5 t, wherein t is the thickness of a finished steel plate;
the initial rolling temperature of finish rolling is 810-840 ℃, the final rolling temperature of finish rolling is 750-770 ℃, and the accumulated deformation rate below 790 ℃ is more than or equal to 15 percent; carrying out accelerated water cooling on the rolled steel plate, wherein the interval time from the rolling completion to the beginning of water cooling is 25-50 s, the beginning temperature of water cooling is 710-750 ℃, the final cooling temperature is 320-400 ℃, 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 extra-wide thick-wall low-yield-ratio X80 straight welded pipe according to claim 1, wherein the steel plate has a thickness of 30mm or more and a width of 4320mm or more.
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