CN103834874B - Heavy wall height DWTT performance X65-70 subsea pipeline steel and manufacture method - Google Patents
Heavy wall height DWTT performance X65-70 subsea pipeline steel and manufacture method Download PDFInfo
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Abstract
The X65-70 subsea pipeline steel of heavy wall height DWTT performance and manufacture method, its composition by weight percent is: C0.03 ~ 0.050%, Si≤0.25%, Mn1.47 ~ 1.70%, P≤0.010%, S≤0.001%, Ti0.006 ~ 0.010%, Cr0.10 ~ 0.20%, Cu0.12 ~ 0.20%, Ni0.36 ~ 0.45%, Al0.025 ~ 0.045%, Ca0.0008 ~ 0.0025%, N≤0.0035%, O≤0.0025%, Nb0.040 ~ 0.050%, all the other are Fe and inevitable impurity; And, Ceq=0.34 ~ 0.4, Pcm=0.13 ~ 0.17.Adopt hot rolling TMCP mode to produce, alloying constituent is simple, with short production cycle, production method simple, and steel product cost is lower.Steel plate of the present invention has think gauge, high strength, excellent low-temperature impact toughness and weldability and good DWTT performance, can be used for additionally arranging of sea-bottom natural gas conveying longitudinal welded pipe.
Description
Technical field
The present invention relates to line pipe technology, in particular to a kind of heavy wall height DWTT performance X65-70 Submarine linepipe and manufacture method, heavy wall is greater than 25.4mm, yield strength 450 ~ 605MPa, tensile strength 570 ~ 760MPa, low-temperature impact toughness: at-20 DEG C, AKv>320J, FA% are greater than 90%; Total wall thickness DWTT performance: at-15 DEG C, SA% is greater than 85%.
Background technology
Cemented filling is the safest, economic, the efficient carrying method of oil and gas, and be therefore widely used for a long time, steel for pipe have also been obtained continuous development.Early stage in last century, steel for pipe adopts the general carbon steel of C, Mn, Si type always, comprises the pipe line steel of X52 and below X52 grade of steel.
From the sixties, along with the increase of transfer pressure and transfer lime caliber, oil transportation, tracheae material extensively adopt low-alloy high-strength steel, a kind of High Strength Structural Steel that this steel grade adds a small amount of alloying element and grows up on the basis of general carbon steel, mainly with hot rolling or the delivery of normalizing state, can obtain and there is some strength, toughness, formability, weldability and erosion-resisting good over-all properties.
Along with the requirements at the higher level that pipework proposes pipe line steel, at the end of the sixties, with the addition of X56, X60, X65 tri-kinds of grade of steels in API5LX and API5LS, these steel break through traditional Composition Design and technology controlling and process thinking, the alloying elements such as micro-Nb, V, Ti are added in steel, adopt controlled rolling technique, make steel comprehensive mechanical property be improved significantly, from then on pipe line steel enters microalloying and adds the new stage that controlled rolling produces.The beginning of the seventies is to the eighties, Mn-Nb system basis is developed Mn-Mo-Nb system microalloying pipe line steel, the type pipe line steel adopts TMCP technique, high strength and good low-temperature flexibility can be obtained, mainly for the manufacture of the pipe line steel of X70, X80 intensity rank, and complete the practical application to X80 pipe line steel in nineteen ninety.Subsequently, pipe line steel X100, X120 of higher category succeed in developing in succession, and have laid test section.
Pipe-line construction not only wants choose reasonable grade of steel, will consider the impact of the many factors such as pipe diameter, transfer pressure, delivery medium, Service Environment, weldability and economy simultaneously.From calculating, in gas transmission line, distribution pressure one timing, displacement increases with caliber and increases; Caliber one timing, displacement increases with transfer pressure and increases, and therefore adopts heavy caliber high pressure transport pipe more economically, is the trend of pipeline development, it is also proposed higher requirement thus to the intensity of pipeline, toughness and thickness specification.Meanwhile, along with the whole world is to the continuous expansion of energy demand, the exploitation of the energy progressively extends to the bad environments regions such as remote polar region, frozen soil, seabed, has higher requirement equally to the intensity of transport pipe, toughness and thickness.Therefore, develop the demand of X65-X70MO level Submarine linepipe positive adaptation marine so feed channel development of high strength, high tenacity, think gauge, have broad application prospects.
Summary of the invention
The object of the present invention is to provide a kind of heavy wall height DWTT performance X65-70 subsea pipeline steel and manufacture method, adopt C-Mn-Nb-Cr component system, and adopt hot rolling TMCP mode to produce, alloying constituent is simple, with short production cycle, production method is simple, and steel product cost is lower.This steel plate has think gauge, high strength, excellent low-temperature impact toughness and weldability and good DWTT performance, its heavy wall is greater than 25.4mm, yield strength 450 ~ 605MPa, tensile strength 570 ~ 760MPa, low-temperature impact toughness: at-20 DEG C, AKv>320J, FA% are greater than 90%; Total wall thickness DWTT performance: at-15 DEG C, SA% is greater than 85%; Can be used for additionally arranging of sea-bottom natural gas conveying longitudinal welded pipe.
For achieving the above object, technical scheme of the present invention is:
Heavy wall height DWTT performance X65-70 Submarine linepipe, its composition by weight percent is:
C0.03～0.05％，
Si≤0.25％，
Mn1.47～1.70％，
P≤0.010％，
S≤0.001％，
Ti0.006～0.010％，
Cr0.10～0.20％，
Cu0.12～0.20％，
Ni0.36～0.45％，
Al0.025～0.045％，
Ca0.0008～0.0025％，
N≤0.0035％，
O≤0.0025％，
Nb0.040～0.050％，
All the other are Fe and inevitable impurity; And, Ceq=0.34 ~ 0.4, Pcm=0.13 ~ 0.17;
Wherein, Ceq=C+Mn/6+ (Cr+Mo+V)/5+ (Ni+Cu)/15;
Pcm＝C+Si/30+Cu/20+Ni/60+Cr/20+Mo/15+V/10。
In the Chemical Composition design of X65, X70 grade of steel heavy wall high-strength line-pipe steel of the present invention:
C: the most basic strengthening element, carbon dissolution forms interstitial solid solution in steel, plays solution strengthening, forms Carbide Precipitation with carbide, then play the effect of precipitation strength.But too high C is unfavorable to the ductility of steel, toughness and welding property, and is easy to segregation and reduces Properties of HIC resistance, affect solid solution and the strengthening effect degree of Nb simultaneously; The intensity of the too low reduction steel of C content, is conducive to the toughness improving pipe line steel, need realize good obdurability coupling in conjunction with other strengthening mechanism.So C controls 0.03% ~ 0.050%.
Mn: be the most basic alloying element of low-alloy high-strength steel grade, improved the intensity of steel by solution strengthening, causes loss of strength to compensate in steel because C content reduces.Mn still expands the element of γ phase region, can reduce γ → α transformation temperature of steel, contributes to obtaining tiny phase-change product, the toughness of steel can be improved, act on not obvious when content is less than 1.40, when content is greater than 1.8, greatly increase the microstructure segregation in steel, affect the homogeneity of hot rolling microstructure.Steel Mn content of the present invention is 1.47% ~ 1.70%.
S, P: inevitably detrimental impurity element in steel, the defect such as easily form segregation, be mingled with, worsens the welding property of pipe line steel, impelling strength and Properties of HIC resistance.Therefore, control P≤0.010, S≤0.001 in think gauge X65MO and X70MO pipe line steel in the present invention, and by Ca handle clip foreign material modification technology, inclusion morphology nodularization must be made and be evenly distributed, reducing it to toughness and corrupting influence.
Nb: improve the most effective element of recrystallize final temperature in micro-alloyed steel, in conjunction with two-phase control rolling technique, effectively can reduce mill load, fairly obvious to the effect of grain refining.At recrystallize rolling sequence, the Nb of strain induced precipitate hinders the recovery and recrystallization of deformed austeaite, improves recrystallize final temperature, for non-recrystallize rolling provides wider deformation temperature range; In non-recrystallize rolling and controlled cooling model stage, when deformed austeaite is organized in phase transformation, change tiny phase-change product into, effective crystal grain thinning, to make steel plate, there is high strength and high tenacity; In the rapid cooling stage, the Nb of solid solution effectively can postpone ferrite transformation, promotes bainite transformation; In the slow cooling stage, the Nb of solid solution, with the form disperse educt of NbC, improves intensity and does not lose toughness.Too low Nb to recrystallize control and precipitation effect not obvious, the effect of crystal grain thinning, precipitation strength cannot be played, in addition owing to being subject to the restriction of C content and the impact of Heating temperature, too high Nb cannot solid solution completely, same performance not effect, and increase manufacturing cost, therefore in the present invention, Nb content controls 0.040% ~ 0.050%.
Ti: be strong solid N element, the stoichiometric ratio of Ti/N is not more than 3.5, utilizes the Ti of about 0.008% just can fix the N of below 30ppm in steel, can form the TiN precipitated phase of tiny high-temperature stable when sheet billet continuous casting.Austenite Grain Growth when this tiny TiN particle can hinder slab to reheat effectively, contributes to improving the solid solubility of Nb in austenite, has obvious effect simultaneously to the impelling strength improving welded heat affecting zone.
Cr: the important element improving the hardening capacity of steel, therefore need add the loss of strength that higher Cr raising hardening capacity is brought to make up thickness for the pipe line steel of think gauge, the homogeneity of performance on the improved strength thickness direction of raising steel; And Cr content more than 0.10% time, the corrosion resistance nature of steel can be improved; But too high chromium and manganese add in steel simultaneously, low melting point Cr-Mn composite oxides can be caused to be formed, in hot procedure, form surface crack, simultaneously can severe exacerbation welding property.Therefore Cr content of the present invention should be limited to 0.10% ~ 0.20%.
Cu, Ni: the intensity improving steel by solution strengthening effect, Cu also can improve the solidity to corrosion of steel simultaneously, and Ni adds the red brittleness mainly improved Cu and easily cause in steel, improves the hardening capacity of steel simultaneously, and effect is greater than Mn, therefore effectively can improve the strength of materials; Add a small amount of Ni in this external low alloy steel and can extend pearlitic incubation period, reduce transformation temperature, reduce the Critical cooling speed of bainite transformation, be conducive to the strength degradation caused because of the increase of thickness, bainite transformation is promoted under less cooling rate, effectively can improve the stability of armor plate strength performance, improve the stability of DWWTT; But Ni is too high, increase manufacturing cost.Ni content of the present invention controls within 0.30 ~ 0.40%.
Al: be the element added in order to deoxidation in steel, adds appropriate Al and is conducive to crystal grain thinning, improve the toughness and tenacity of steel.
Ca: the form that can be controlled sulfide by Ca process, improve the anisotropy of steel plate, improve low-temperature flexibility, its content does not have effect when being less than 0.001, then many CaO, CaS can be produced more than 0.006, and form Large Inclusions, the toughness of steel is caused damage, even affects the welding property of steel.So regulation Ca content range is 0.0008% ~ 0.0025%.
The manufacture method of heavy wall height DWTT performance X65-70 subsea pipeline steel of the present invention, comprises the steps:
1) smelt, cast
Smelt by mentioned component, be cast as slab; Superheating temperature 15 ~ 25 DEG C, pulling rate 0.6 ± 0.05m/min;
2) heating of plate blank
Tapping temperature 1110 ± 20 DEG C;
3) hot rolling
Roughing finish to gauge surface temperature >=950 DEG C; Finish rolling start rolling temperature 800 ± 20 DEG C, finish rolling finishing temperature 790 ± 15 DEG C, finish rolling adds up draught > 60%; Period, slab needs to carry out the cooling of middle continuous coo1ing Water spray after roughing finish to gauge, and intermediate blank carries out finish rolling according to finish rolling start rolling temperature after fully returning temperature;
4) cool
After hot rolling, slab can cool fast, cooling rate 20 ± 2 DEG C/s, final cooling temperature 520 ± 30 DEG C; Final acquisition microstructure is acicular ferrite structure, yield strength 450 ~ 605MPa, tensile strength 570 ~ 760MPa, low-temperature impact toughness: at-20 DEG C, AKv>320J, FA% are greater than 90%; Total wall thickness DWTT performance: the pipe line steel that at-15 DEG C, SA% is greater than 85%.
Preferably, slab heating time: every centimetre of slab thickness heat-up time is 8-12 minute, for this reason, 300mm slab its be 240-360 minute in stove heat-up time, ensure the dissolving of carbonitride and uniform austenite grain size with this.
In manufacture method of the present invention:
Need in Rolling Production first by heating of plate blank to austenitizing temperature.From the viewpoint of advantageous deformation, wish that Heating temperature is more high better, this is conducive to rolling; But Heating temperature is high causes initial austenite coarse grains, the critical strain amount of occurrence dynamics recrystallize increases, and the work range of dynamic recrystallization is diminished, and considers from the angle of controlled rolling crystal grain thinning simultaneously, original austenite grains is less, and the ferrite crystal grain after transformation is also less.Therefore, original austenite grains size is produced very important to pipe line steel.
Rising austenite crystal along with Heating temperature becomes large, but the trend of growing up at different heating temperature is different.Heating temperature grain growth not obvious before 1150 DEG C, between 1150-1200 DEG C, grain coarsening phenomenon is the most serious, when 1200 DEG C of trend of growing up become again mild later, consider Heating temperature to the impact on pipeline steel strength and toughness of the impact of austenite grain size and austenite grain size, it is suitable that billet heating temperature does not exceed 1150 DEG C.
Controlled rolling technique refers to that steel billet is at stable austenite region (A
r3) or at meta region (A
r3-A
r1) in be rolled, the theory of the austenitic recrystallize of abundant application and non-recrystallization two aspect, by reducing the Heating temperature of slab, controlling distortion amount and finishing temperature, make full use of the molten strengthening of solid solution, the strengthening mechanism of precipitation strength, dislocations strengthening and grain refining, makes steel internal grain reach maximum refinement thus improves the low-temperature flexibility of steel, increase intensity, improve the over-all properties of steel.
Pipe line steel adopts two-stage rolling usually, and the first stage is rolling in spontaneous recrystallize region, is the stage that deformation and recrystallize carry out simultaneously, by repeated deformation and recrystallize, makes the remarkable refinement of austenite crystal, in order to the temperature of rough rolling step sets; Subordinate phase is rolling in non-recrystallization region, be the stage that deformation and phase transformation are carried out simultaneously, in this stage, austenite crystal is stretched, and produces slip band simultaneously, the increase of austenite grain boundary and slip band appear as ferrite forming core and provide favourable condition, and then obtain close grain ferrite.
According to dynamic recrystallization temperature experiment result, when texturing temperature is below 950 DEG C, after strain rate brings up to 5/s by 0.1/s, dynamic recrystallization no longer occurs.In order at roughing section steel billet repeated deformation and recrystallize, make the continuous refinement of austenite crystal, for this reason, guarantee that rough rolling step must ensure that finish to gauge terminates before the rolling pass temperature having dynamic recrystallization, i.e. roughing finishing temperature is more than 950 DEG C.In addition, under the texturing temperature of 850 DEG C, after strain rate is brought up to 5/s by 0.1/s, dynamic recovery weakens, and show that finish rolling start rolling temperature is lower, austenite crystal dynamic recovery weakens, be conducive to crystal grain thinning, in order to austenite crystal swell during hindering intermediate blank isothermal processed, the cooling of middle continuous coo1ing Water spray need be carried out, shorten intermediate blank isothermal time.
Show that ferrite starts formation temperature A along with finishing temperature reduces by test result
r3point also declines, and consider to utilize and roll rear waste heat and carry out controlled cooling model, finishing temperature suitably improves, and the effect of favourable performance ACC (accelerating cooling), finishing temperature is set as that 790 ± 15 DEG C are advisable for this reason.
In actual industrial production, workpiece thickness is set as the finished product thickness of 5 times, namely requires that the total deformation of rough rolling step is more than or equal to 46% for (300-5T)/300, and every time adopts the maximum depression rate of milling train, guarantee causes repeated deformation and recrystallization process, thus crystal grain thinning; The total deformation in finish rolling stage is (5T-T)/5T is 80%, along with the increase of deflection, austenite is constantly stretched, produce slip band simultaneously, the increase of austenite grain boundary and the ferrite forming core that appears as of slip band provide favourable condition, promote the refinement of ferrite compact grained to greatest extent.Heavy wall sea pipe X65-X70 should take larger speed of cooling, and final cooling temperature is unsuitable too low, occurs to prevent island-like martensite.Rear quick cooling is rolled in setting for this reason, and cooling rate is chilled to 500 DEG C eventually with 20 DEG C/s; Proeutectoid ferrite and pearlitic precipitation can be reduced like this, enable austenite structure have sufficient space to separate out acicular ferrite structure.
The technology of the present invention tool compared with existing patent has the following advantages:
Japanese Patent JP2006307324 proposes a kind of method adopting hot rolling+thermal treatment process to manufacture think gauge high-intensity high-tenacity Pipeline Steel Plate, and the present invention adopts TMCP technique, and processing route is different; In addition, on Composition Design, this patent with the addition of B element raising hardening capacity to improve the intensity of material, and the present invention then adopts Cr, Ni etc. to improve hardening capacity alloying element to improve the obdurability of steel plate.
Japanese Patent JP2003003229 proposes a kind of manufacture method with good fatigue property, manufacturability, high-strength steel plate, and the steel plate of manufacture can be used for line pipe, pressurized vessel and deck of boat structure.This patent adopts the composition design method of higher C content, and adopts controlled rolling air cooling+heat treated manufacturing process, different with TMCP manufacturing process from low-carbon microalloyed Composition Design of the present invention.
Japanese Patent JP53118221 proposes the manufacture method of a kind of high strength, evenly the natural gas transmission pipeline steel of toughness, it mainly adopts the composition design method of C and alloying, and with the addition of higher Mo element (0.60% ~ 2.00%), cost of alloy is higher; And the present invention's employing take C-Mn as the Nb microalloying ingredient method of design of base, do not have a mind to add Mo content, remnants are limited within 0.03%, have larger difference with this Japanese Patent.
Chinese patent CN101082108 proposes a kind of method manufacturing Submarine pipeline steel plate, and with the addition of Mo element (0.07 ~ 0.20%).With contrast patent unlike, present invention employs the loss of strength that higher Mn content makes up low-carbon (LC); With the addition of higher Ni to improve the hardening capacity of slab simultaneously, improve the homogeneity of the performance in steel plate thickness direction; Not with the addition of Mo element and obtain refining grain size with lower micro-Tiization process and play precipitation strength effect, improving the obdurability of steel; Do not add the low temperature precipitation strength elements such as V, to ensure that steel plate has good low-temperature flexibility.
Chinese patent CN1978695 proposes a kind of manufacture method of the high strength X 100 pipeline steel hot rolled slab containing Cr.Same intensity rank is not belonged to the manufacture of X65MO, X70MO pipe line steel of the present invention.On this external Composition Design, this patent have employed higher Mo and Ni content, and cost of alloy is higher, and Ni content of the present invention is limited within 0.45%, Composition Design less expensive; In technology controlling and process, it is lower that this patent stops cold temperature, to obtain lower bainite+martensitic microstructure, and the present invention's design to stop cold temperature higher, design organization is acicular ferrite is main microstructure.
Chinese patent CN101855378 proposes the manufacture method of a kind of steel for pipe of resistance to HIC plate and steel pipe.Different from the purposes of X65MO, X70MO pipe line steel of the present invention.On this external Composition Design, this patent have employed higher Mo and Ni content, and cost of alloy is higher, and Ni content of the present invention be limited in 0.45% within and containing Mo, and Nb content also exceedes this patent, Composition Design less expensive; In technology controlling and process, it is lower that this patent stops cold temperature, and mainly solve HIC-resistance energy to obtain Bainite Phases of Some (preferably more than 75%), the length of hardness and Nb carbonitride that portion is analysed by control center solves; The present invention's design to stop cold temperature higher, design organization is the microstructure based on acicular ferrite, mainly by the performance of composition and technique solution total wall thickness DWTT accurately.
By finding with the contrast of external and domestic patent, steel of the present invention adopts economic Composition Design method and heavy plate rolling manufacturing process, and without thermal treatment, heavy wall X65, X70 level pipe line steel Wide and Thick Slab with high intensity, good low-temperature impact toughness and good welding property (low Pcm index) can be produced, on Composition Design or technological design, there is bigger difference with existing patent.
The present invention is directed to micro-alloying low-carbon acicular ferrite structure and there is high-intensity high-tenacity and good welds performance, and the feature such as low Bauschinger effect, based on the material reinforcement theories such as grain refining, phase transformation strengthening, precipitation strength and dislocations strengthening, the Composition Design with acicular ferrite X65 and X70 pipe line steel be have employed to the Composition Design of lower carbon content, super low sulfur, Nb, Ni, Ti microalloying.Process for making adopts the smelting Technology for Clean Steel of inclusion morphology control, hot rolling technology have employed the thermo-mechanical processi technology of controlled rolling and controlled cooling, the organizational controls of the finished product is carried out, to obtain the low-carbon (LC) acicular ferrite structure with high-intensity high-tenacity by reasonable component and technique.
(1) main based on C, Mn, Nb alloy, add a small amount of Cu, Ni to improve toughness and solidity to corrosion, can reach the obdurability requirement of heavy wall (being greater than 25.4MM) X65, X70 subsea pipeline steel, production cost is lower.
(2) the present invention produce heavy wall (being greater than 25.4MM) X65, X70 steel plate and UOE welded tube there is excellent mechanical property:
Yield strength: 450-605MPa;
Tensile strength: 570-760MPa;
Low-temperature impact toughness: at-20 DEG C, AKv>320J, FA% are greater than 90%;
Total wall thickness DWTT performance: at-15 DEG C, SA% is greater than 85%.
(3) the present invention can produce thicker X65 X70 steel plate, thickness reaches more than 28mm, can be used for manufacture Longitudinal SAW Pipe, be mainly used in three, four classes area.
(4) steel of the present invention has lower Pcm index, and welding property is very excellent, is conducive to the enforcement of tubulation straight weld and site girth welding.
Embodiment
Below in conjunction with embodiment, the present invention will be further described.
According to steel Chemical Composition of the present invention requirement, above-mentioned technique is adopted to be rolled, and tabular stretching (38.5mm) is carried out to finished product, the service check such as full thickness of slab Drop-Weight Tear Test (DWTT) at full-scale Charpy impact (10 × 10 × 55mm) and-15 DEG C at-20 DEG C, manufactured different thickness specification X65, X70 pipe line steel slab, concrete Chemical Composition is in table 1.
Table 2 is the manufacturing process of the embodiment of the present invention.Table 3 is the performance of embodiment of the present invention steel.
From the composition of table 1 ~ table 3, technique and performance actual achievement, when reduction Ni content, adopt higher C, Mn content and add appropriate Mo, V when adopting higher rolling temperature simultaneously, the performances such as intensity meet standard-required, but can not meet the requirement of DWTT performance.And effectively can improve DWTT performance when adopting suitable C, Mn, Ni content in the present invention and accurately control open rolling and finishing temperature, and meet the requirement of DNVF101 and APISPEC5L-2007 standard to DWTT.
In sum, it is basic that the present invention adopts at Composition Design with C-Mn-Nb-Cr, is aided with a small amount of Cu, Ni alloying and micro-Ti treatment technology, cost of alloy reduces greatly; Secondly in technique, adopt lower reheating temperature, the reasonably control of finish rolling compression ratio, lower finishing temperature and cool control accurately, while guarantee plate property stability, produce the think gauge Submarine linepipe of thickness range 28.6-32mm, intensity rank reaches X65MO, X70MO grade of steel, and there is excellent low-temperature flexibility and weldability, this steel plate can be used for producing heavy caliber high pressure conveying longitudinal welded pipe.
Table 2
Table 3
Remarks: B is steel plate tail, and T is steel plate head, and C is that steel plate is horizontal, and L is that steel plate is longitudinal.
Claims (3)
1. heavy wall height DWTT performance X65-70 subsea pipeline steel, its composition by weight percent is:
C0.03～0.050％，
Si≤0.25％，
Mn1.47～1.70％，
P≤0.010％，
S≤0.001％，
Ti0.006～0.010％，
Cr0.10～0.20％，
Cu0.12～0.20％，
Ni0.36～0.45％，
Al0.025～0.045％，
Ca0.0008～0.0025％，
N≤0.0035％，
O≤0.0025％，
Nb0.040～0.050％，
All the other are Fe and inevitable impurity; And, Ceq=0.34 ~ 0.40, Pcm=0.13 ~ 0.17;
Wherein, Ceq=C+Mn/6+ (Cr+Mo+V)/5+ (Ni+Cu)/15;
Pcm＝C+Si/30+Cu/20+Ni/60+Cr/20+Mo/15+V/10；
Pipe line steel microstructure is acicular ferrite structure, yield strength 450 ~ 605MPa, tensile strength 570 ~ 760MPa, low-temperature impact toughness: at-20 DEG C, AKv>320J, FA% are greater than 90%; Total wall thickness DWTT performance: at-15 DEG C, SA% is greater than 85%.
2. the manufacture method of heavy wall height DWTT performance X65-70 subsea pipeline steel as claimed in claim 1, comprises the steps:
1) smelt, cast
Smelt by mentioned component, be cast as slab; Superheating temperature 15 ~ 25 DEG C, pulling rate 0.6 ± 0.05m/min;
2) heating of plate blank
Tapping temperature 1110 ± 20 DEG C;
3) hot rolling
Roughing finishing temperature >=1000 DEG C; Finish rolling start rolling temperature 800 ± 20 DEG C, finish rolling finishing temperature 790 ± 15 DEG C, finish rolling adds up draught > 60%; Period, slab needs to carry out the cooling of middle continuous coo1ing Water spray after roughing finish to gauge, and intermediate blank carries out finish rolling according to finish rolling start rolling temperature after fully returning temperature;
4) cool
After hot rolling, slab can cool fast, cooling rate 20 ± 2 DEG C/s, final cooling temperature 520 ± 30 DEG C; Final acquisition microstructure is acicular ferrite structure, yield strength 450 ~ 605MPa, tensile strength 570 ~ 760MPa, low-temperature impact toughness: at-20 DEG C, AKv>320J, FA% are greater than 90%; Total wall thickness DWTT performance: the pipe line steel that at-15 DEG C, SA% is greater than 85%.
3. the manufacture method of heavy wall height DWTT performance X65-70 subsea pipeline steel as claimed in claim 2, is characterized in that, step 2) slab heating time: the heat-up time of every centimetre of slab thickness is 8 ~ 12 minutes.
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