CN104131225A - Ultralow temperature nickel steel with low cost and manufacturing method thereof - Google Patents
Ultralow temperature nickel steel with low cost and manufacturing method thereof Download PDFInfo
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- CN104131225A CN104131225A CN201410369201.9A CN201410369201A CN104131225A CN 104131225 A CN104131225 A CN 104131225A CN 201410369201 A CN201410369201 A CN 201410369201A CN 104131225 A CN104131225 A CN 104131225A
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Abstract
An ultralow temperature nickel steel with low cost and a manufacturing method thereof. The steel comprises the following components by weight: 0.04-0.070% of C, no more than 0.15% of Si, 0.80-1.20% of Mn, no more than 0.010% of P, 0.0020% of S, 5.00-7.00% of Ni, 0.05-0.25% of Mo, 0.010-0.030% of Als, 0.008-0.018% of Ti, no more than 0.0040% of N, 0.001-0.004% of Ca, and the balance of Fe and the inevitable inclusion. The invention uses a component system containing ultra low C, ultra low Si, middle Mn, low N and ultramicro Ti for treatment of low alloy steel, and controls the value of (%Mn)*[7.33 (%Si) + 5.16 (%Al)] at no more than 1.0, and the value of austenite stabilization index Au / intercritical quenching temperature T at no less than 0.007 and no more than 0.009; an optimized recrystallization controlled rolling and subsequent special heat treatment process endows the ultralow temperature nickel steel with ultrahigh ultralow temperature toughness, excellent weldability and bearing of high heat input welding, and the ultralow temperature nickel steel gains excellent anti-high tempering parameter SR embrittlement characteristics, and can be manufactured at a low cost.
Description
Technical field
The present invention relates to low-carbon (LC) (high strength) low alloy steel, be particularly related to low cost very low temperature nickel steel and manufacture method thereof, this steel plate yield strength >=550MPa, tensile strength >=650MPa ,-196 DEG C of low-temperature impact work monodrome Akv >=100J, Z-direction performance >=35%, be mainly used in LNG tank, LNG tank peculiar to vessel.
Background technology
As everyone knows, low-carbon (LC) (high strength) low alloy steel is one of most important structural timber, is widely used among petroleum natural gas pipeline, ocean platform, shipbuilding, bridge structure, boiler vessel, building structure, automotive industry, transportation by railroad and machinofacture.Low-carbon (LC) (high strength) low alloy steel performance depends on the process system of its chemical composition, manufacturing processed, wherein intensity, toughness and weldability are the most important performances of low-carbon (LC) (high strength) low alloy steel, and its final decision is in the microstructure state of finished steel.Along with science and technology constantly advances, obdurability, weldability and the anti-processing deterioration of people to steel had higher requirement, in maintaining lower manufacturing cost, improve significantly comprehensive mechanical performance and the use properties of steel plate, cost-saving with the consumption of minimizing steel, subtract lightweight steel component own wt, stability and security.
In world wide, start the research climax that develops high-performance steel iron material of new generation at present, design, reform controlled rolling/TMCP (comprising DQ) technology and subsequent heat treatment technique by alloy combination and obtain better microstructure coupling, thereby make steel plate obtain better low-temperature flexibility, strong plasticity and toughness coupling and weldability.
When prior art is manufactured the Plate Steel of-196 DEG C of low temperature transverse impact toughness (single value) >=100J, generally in steel, add a large amount of precious alloy elemental nickel, nickel content general control is more than 9.0%, to guarantee that mother metal steel plate has excellent ultralow-temperature flexibility.As " the Japanese metal Chi of association " 30 (1966), P42; Ibid., 33 (1969), P856; " Kawasaki Steel skill report ", 18 (1986), P327; " NKK skill report ", 111 (1986), P1; " pressure techniques ", 31 (1993), P353; " CAMP-ISIJ ", 9 (1996), P437).But production cost is high, and product competitiveness in the market is low, as " pressure techniques ", 29 (1991), P341.
Secondly, alloy steel plate is through too high tempering parameter TP>=18.5 × 10
3(TP=T (20+lgt) postweld heat treatment (being that SR processes), steel plate very low temperature impelling strength is seriously deteriorated, show as low-temperature impact work numerical value general all lower than 47J, seriously jeopardize the low temperature LNG storage tank safe reliability in process under arms, bury the hidden danger of Serious Accident.
In addition, while adopting large heat input welding, welded heat affecting zone (HAZ) low-temperature flexibility occurs more serious deteriorated, and the low temperature ductile-brittle transition temperature of heat affected zone (HAZ) is generally relatively difficult to reach-165 DEG C, says nothing of and reaches very low temperature-196 DEG C.
Existing a large amount of patent documentation just illustrates-40 DEG C～-60 DEG C low-temperature flexibilities that how to realize mother metal steel plate, for how under welding conditions, obtain good heat affected zone (HAZ) low-temperature flexibility and illustrate lessly, while especially adopting large heat input welding, how to ensure that-196 DEG C of low-temperature flexibilities of very low temperature nickel steel heat affected zone (HAZ) are less.(63-93845 as clear in Japanese Patent, clear 63-79921, clear 60-258410, special flat 4-285119, special flat open 4-308035, flat 3-264614, flat 2-250917, flat 4-143246 and US Patent No. Patent4855106, US Patent5183198, the US Patent4137104 of opening)
Summary of the invention
The object of the present invention is to provide a kind of low cost very low temperature nickel steel and manufacture method thereof, steel plate yield strength >=550MPa, tensile strength >=650MPa ,-196 DEG C of low-temperature impact work monodrome Akv >=100J, Z-direction performance >=35%, be particularly suitable for being used as and manufacture Large LNG very low temperature storage tank, LNG very low temperature storage tank peculiar to vessel, ice sea and region, polar region large-scale steel structure, and can realize the stable suitability for industrialized production in batches of low cost.
For achieving the above object, technical scheme of the present invention is:
The very low temperature nickel steel of anti-high tempering parameter SR embrittlement is one of steel grade that in slab kind, difficulty manufacture is larger, its reason is that such steel plate not only requires mother metal to have high ultralow-temperature flexibility, good weldability, but also require when after too high tempering parameter SR, steel plate still has above-mentioned performance, steel plate also has good weldability and can stand large heat input welding, therefore in gordian technique route and Composition And Process design, combine the low-temperature flexibility of-196 DEG C that affects very low temperature nickel steel, anti-welding reheat cracking susceptibility, can be larger heat input weldability and the softening factor with embrittlement of anti-high tempering parameter SR, creatively adopt the composition system of the low N-ultra micro of Mn-in the ultralow Si-of ultralow C-+Ti processing low alloy steel as basis, control (%Mn) × [7.33 (%Si)+5.16 (%Al)]≤1.0, quenching temperature T≤0.009,0.007≤stabilization of austenite Index A u/ two-phase region, Ca process and Ca/S ratio be controlled at 1.0～3.0 between and (%Ca) × (%S)
0.28≤ 1.0 × 10
-3optimize recrystallize controlled rolling and follow-up special combination thermal treatment process, make very low temperature nickel steel obtain high ultralow-temperature flexibility, good weldability, can bear larger heat input welding, the low temperature nickel steel of this invention of what is more important has excellent anti-high tempering parameter SR embrittlement characteristic, and can low cost fabrication (the very low temperature steel plate of the nickel content of relatively traditional 9.0% left and right).
Concrete, low cost very low temperature nickel steel of the present invention, its composition weight percent is: C:0.040%～0.070%, Si :≤0.15%, Mn:0.80%～1.20%, P :≤0.010%, S :≤0.0020%, Ni:5.00%～7.00%, Mo:0.05%～0.25%, Als:0.010%～0.030%, Ti:0.008%～0.018%, N :≤0.0040%, Ca:0.001%～0.004%, all the other are Fe and being inevitably mingled with; And mentioned component must meet following relation simultaneously:
(％Mn)×[7.33(％Si)+5.16(％Al)]≤1.0；
Ti/N＝1.5～3.5；
Quenching temperature T≤0.009,0.007≤stabilization of austenite Index A u/ two-phase region,
Wherein, Au=2.54+40.53[(%C)+(%N)]+0.43[(%Cu)+(%Ni)+(%Mn)]-0.22 (%Al)-2.64[(%P)+(%S)]-1.26[(%Cr)+(%Mo)]-(%Si), the unit of T is K;
Ca/S is between 1.00～3.00, and (%Ca) × (%S)
0.28≤ 1.0 × 10
-3;
The low temperature nickel structure of steel obtaining is the complex phase microstructure on tiny uniform martensite/bainite+ferrite+austenite island.
In the Composition Design of steel plate of the present invention:
C, impelling strength on very low temperature nickel steel, high tempering parameter SR embrittlement and weldability impact are very large, from improving low-temperature impact toughness, anti-high tempering parameter SR embrittlement and the weldability angle of very low temperature nickel steel, wish in steel that C content is lower to be advisable; But from the intensity of steel plate, the prior microstructures Control angle from course of hot rolling and quenching process, C content is unsuitable too low, too low C content causes austenite grain boundary mobility high, this brings larger problem to the even thinning microstructure of hot rolling and quenching, easily form mixed grain structure, too low C content also causes Grain-boundary Junctions to make a concerted effort to reduce simultaneously, causes that steel plate low-temperature impact toughness is low, welded heat affecting zone low-temperature impact toughness is deteriorated; Comprehensive above factor, the content of C is controlled between 0.040%～0.070%.
Si promotes deoxidation of molten steel and can improve the intensity of very low temperature nickel steel, but adopt the molten steel of Al deoxidation, the desoxydatoin of Si is little, although Si can improve the intensity of very low temperature nickel steel, but Si alligatoring steel plate microstructure, the intrinsic toughness of grievous injury very low temperature nickel steel, anti-high tempering parameter SR embrittlement and weldability, especially under larger heat input welding conditions, Si not only promotes M-A island to form, and it is large to form M-A island size, skewness, low-temperature flexibility and the anti-fatigue performance of grievous injury welded heat affecting zone (HAZ), therefore the Si content in steel should be controlled lowly as far as possible, consider economy and the operability of steelmaking process, Si content is controlled at≤and 0.15%.
Mn as alloying element in very low temperature nickel steel except improving intensity and improving toughness, also there is the austenite of expansion phase region, reduce Ac
1, Ac
3, Ar
1, Ar
3point temperature, refinement steel plate grain-size, the position between increase bainite/martensite lath is to angle, the more important thing is under high Ni content condition, Mn can greatly improve the hardening capacity of steel plate, and refinement bainite/martensite colony size is improved the low-temperature flexibility of very low temperature nickel steel; But add too much Mn can increase the inner segregation degree of steel plate, reduce homogeneity and-196 DEG C of toughness of very low temperature nickel steel mechanical property, increase the especially anti-high tempering parameter SR embrittlement characteristic of very low temperature nickel steel temper brittleness, the larger heat input of deteriorated steel plate weldability.And when the welding of little heat input, welded heat affecting zone easily forms crisp sclerous tissues as martensite etc.; Therefore, Mn content range is controlled between 0.80%～1.20%.
P has huge detrimental effect as harmful being mingled with in steel to-196 of very low temperature nickel steel DEG C of impelling strength, anti-high tempering parameter SR embrittlement and weldabilities; It is more low better to require in theory, but considers that the logistics of steel-making condition, steel-making cost and steelworks is smooth and easy, require P content be controlled at≤0.010%.
S as in steel harmful be mingled with-196 of very low temperature nickel steel DEG C of impelling strength (especially laterally low-temperature flexibility), anti-high tempering parameter SR embrittlement detrimental effect very large; In addition, S is combined with Mn in steel, form MnS inclusion, in course of hot rolling, the plasticity-of MnS makes MnS along rolling to extension, form along rolling to MnS inclusion band, the horizontal low-temperature impact toughness of grievous injury steel plate, Z-direction performance, anti-high tempering parameter SR embrittlement and weldability produce hot short principal element in S or course of hot rolling simultaneously; It is more low better to require in theory, but considers the smooth and easy principle of logistics of steel-making condition, steel-making cost and steelworks, require S content be controlled at≤0.0020%.
Ni is that steel plate obtains good ultralow-temperature flexibility, the indispensable alloying element of anti-high tempering parameter SR embrittlement, Ni has the P-N power that reduces ferrite dislocation motion under condition of ultralow temperature, improve ferrite dislocation mobility under condition of ultralow temperature, promote that ferrite dislocation occurs to hand over slippage, improve the intrinsic plasticity and toughness of ferritic steel for low temperature service plate; Therefore theoretically, in steel, Ni content is more high better within the specific limits, but Ni is a kind of very expensive alloying element, and from low cost batch production angle, suitable add-on is 5.00%～7.00%.
Mo is as ferrite grain-boundary strengthening element, have and suppress the high tempering parameter SR of low temperature nickel steel embrittlement and intensity softening, that improve very low temperature nickel steel, in steel, the appropriate Mo of interpolation can further reduce C content, reduce the bainite/martensite substructure form in very low temperature nickel steel, when improving very low temperature nickel steel-196 DEG C toughness and weldability, improve the anti-high tempering parameter SR of very low temperature nickel steel embrittlement, therefore for the very low temperature nickel steel of anti-high tempering parameter, Mo alloying is indispensable; But as excessive interpolation, the weldability of infringement steel plate, the weldability under especially large hot initial conditions; Therefore Mo broiler diets is 0.05%～0.25%.
Als in steel plate can fix the freedom [N] in steel, reduce freely [N] of welded heat affecting zone (HAZ), there is refinement steel plate microstructure (effect of AlN anchoring) and the effect of eliminating (comprising welded heat affecting zone) solid solution N in steel; But in steel, add excessive Als not only can in steel, form the needle-like Al of a large amount of disperses
2o
3inclusion, infringement steel plate low-temperature impact toughness and cracking resistance, crack arrest; And promote temper embrittlement, the large heat input weldability of infringement and welding joint abnormal structure to occur, according to the system anlysis of steel plate composition, optimum Al s content is controlled between 0.010%～0.030%.
In steel, adding micro-Ti object is that N is combined in steel, generates the very high TiN particle of stability, and refinement mother metal steel plate microstructure, improves impelling strength and the anti-high tempering parameter SR embrittlement of steel used at ultra-low temperature; In addition, suppress welded H AZ district Austenite Grain Growth and change second-order phase transition product, improving the low-temperature flexibility of Large Heat Input Welding HAZ.The Ti content adding in steel will with steel in N containing flux matched, the principle of coupling is that TiN can not separate out and must in solid phase, separate out in liquid molten steel; Therefore the Precipitation Temperature of TiN must be guaranteed lower than 1400 DEG C, according to log[Ti] [N]=-16192/T+4.72 can determine the add-on of Ti.When adding, Ti content is very few, forms TiN number of particles deficiency, is not enough to suppress the Austenite Grain Growth of HAZ and changes second-order phase transition product and improve the low-temperature flexibility of Large Heat Input Welding HAZ; While adding Ti content too much, TiN Precipitation Temperature exceedes 1400 DEG C, part TiN particle is separated out large-sized TiN particle in solidification of molten steel process, and this large size TiN particle not only can not suppress the Austenite Grain Growth of HAZ, becomes on the contrary the starting point of crack initiation; Therefore the optimum controling range of Ti content is 0.008%～0.018%.
The span of control of N is corresponding with the span of control of Ti, and for compared with Large Heat Input Welding steel plate, Ti/N is best between 1.5～3.5.When too low the and Ti too high levels of N content, generate that TiN number of particles is few, size is large, can not play the effect of the weldability of improving steel, harmful to weldability on the contrary; But when N too high levels, freely [N] increases in steel, especially sharply increase grievous injury HAZ low-temperature flexibility, the weldability of deterioration steel compared with heat affected zone (HAZ) under Large Heat Input Welding condition free [N] content; In addition,, when N content is higher, steel slab surface severe crack, causes slab to scrap when serious.Therefore N content be controlled at≤0.0040%.
Steel is carried out to Ca processing, on the one hand can pure molten steel, on the other hand steel medium sulphide content is carried out to denaturing treatment, make it to become non deformable, stablize tiny spherical sulfide, suppress S red brittleness, improve steel plate impelling strength and Z-direction performance, improve the anisotropy of steel plate impelling strength.The number of Ca add-on, depends on the height of S content in steel, and Ca add-on is too low, and treatment effect is little; Ca add-on is too high, forms Ca (O, S) oversize, and fragility also increases, and can become fracture crack starting point, reduces the low-temperature flexibility of steel, also reduces purity of steel simultaneously, pollutes molten steel.General control Ca content is pressed ACR=(wt%Ca) [1-1.24 (wt%O)]/1.25 (wt%S), and wherein ACR is sulfide inclusion shape control index, and therefore the span of control of Ca content is 0.001%～0.004%.
Particularly, in Composition Design of the present invention, (%Mn) × [7.33 (%Si)+5.16 (%Al)]≤1.0, this is one of gordian technique point of the present invention.
Si and Al promote the conjugation segregation between Mn, C, P, S, cause the inner segregation of steel plate serious, damage steel plate endoplasm viability and homogeneity, cause Plate Welding, temper embrittlement and low-temperature flexibility significantly to reduce.
The present invention is by controlling (%Mn) × [7.33 (%Si)+5.16 (%Al)]≤1.0, suppress the segregation of very low temperature nickel steel intralamellar part, improve the anti-temper brittleness of very low temperature nickel steel plate, especially improve the characteristic of anti-high tempering parameter SR embrittlement, refinement mother metal steel plate and welded heat affecting zone bainite/martensite colony size, position between increase bainite/martensite lath increases the resistance of crack propagation to angle, improve cracking resistance, the crack arrest characteristic (being low-temperature flexibility) of very low temperature nickel steel plate.
In addition, in Composition Design of the present invention,
Quenching temperature T≤0.009,0.007≤stabilization of austenite Index A u/ two-phase region, wherein Au=2.54+40.53[(%C)+(%N)]+0.43[(%Cu)+(%Ni)+(%Mn)]-0.22 (%Al)-2.64[(%P)+(%S)]-1.26[(%Cr)+(%Mo)]-(%Si), the unit of T is K, this is one of gordian technique point of the present invention, by mating between stabilization of austenite index and ferrite+austenite two-phase region tempering temperature, obtain reasonable quantity, be evenly distributed, the high stability austenite island that geomery is suitable, this austenite island has conclusive effect for very low temperature steel plate:
A) under-196 DEG C of conditions, austenite has good chemistry, mechanical stability, under the effect of various chemistry and power, martensitic transformation does not occur, and as face-centered cubic plasticity and toughness phase, disperse is distributed in steel;
B) this austenite island is as crack blunting device, in the time that crack propagation arrives austenite island, austenite generation plastic deformation, absorb crack tip stress field energy, passivation crack tip, prevention crackle further expands, improve very low temperature nickel steel plate cracking resistance, crack arrest characteristic (being low-temperature flexibility);
C) austenite island has the effect of the bainite/martensite of cutting apart lath, and refinement bainite/martensite slat dimension is improved the ultralow-temperature flexibility of steel plate;
D) austenite island has the ferritic phase effect of purification (bainite/martensite lath is ferritic phase), eliminates embrittlement interstitial element C, N etc. in ferritic phase, improves bainite/martensite lath very low temperature intrinsic plasticity and toughness.
In sum, by mating between stabilization of austenite Index A and ferrite+austenite two-phase region tempering temperature T, realize the key of steel plate ultralow-temperature flexibility under-196 DEG C of conditions; Also be to realize relative low nickel content (5.00%～7.00%) to substitute high nickel content (more than 9.0%), significantly reduce the gordian technique of manufacturing cost.
Ca/S between 1.00～3.00 and (%Ca) × (%S)
0.28≤ 1.0 × 10
-3, inclusion content of steel is few and evenly slightly disperse is in steel, and refinement steel plate and large heat are inputted welded heat affecting zone microstructure; Improve very low temperature nickel steel plate and welded heat affecting zone cracking resistance, crack arrest characteristic.
Low cost very low temperature nickel steel of the present invention and manufacture method thereof, it comprises the steps:
1) smelt, cast
Smelt, cast employing continuous casting process by above-mentioned composition, Continuous Casting Soft Reduction rate is controlled between 3%～7%, and basket pouring temperature is between 1520 DEG C～1550 DEG C, to improve continuously cast bloom center segregation with loose; Two cold employings are weak cold, be controlled at≤0.60L/ of specific water (ton × min);
2) 1050 DEG C～1150 DEG C of slab heating temperatures, slab adopts high-pressure water descaling after coming out of the stove, and de-scaling is de-scaling not to the utmost repeatedly;
3) rolling, steel plate overall compression ratio is slab thickness/finished steel plate thickness >=4.00
First stage is common rolling, adopts rolling uninterruptedly, guarantees that dynamically/Static Recrystallization occurs deformation metal, first stage accumulative total draft >=50%, refine austenite crystal grain;
Subordinate phase adopts recrystallize controlled rolling RCR, 780 DEG C～840 DEG C of controlled rolling start rolling temperatures, rolling pass draft >=8%, recrystallization zone accumulative total draft >=50%, 740 DEG C～800 DEG C of finishing temperatures;
4) normalizing+quenching
Normalizing temperature is 780 DEG C～820 DEG C, and the normalizing hold-time is 10～20min, and after normalizing, steel plate natural air cooling is to room temperature; Quenching temperature is 650 DEG C～700 DEG C, and the quenching hold-time is 15～25min, and steel plate quenching is to room temperature;
5) tempering
Tempering temperature is 600～650 DEG C, and the tempering hold-time is 30～60min, and tempering finishes rear steel plate natural air cooling to room temperature.
The composition system according to the present invention, High Nickel Steel steel slab surface easily cracks, and steel making working procedure emphasis technique is continuous casting process, continuous casting process priority control trough casting temperature, light draft and two cold cooling modes; Continuous Casting Soft Reduction rate is controlled between 3%～7%, and basket pouring temperature is between 1520 DEG C～1550 DEG C, to improve continuously cast bloom center segregation with loose; Two cold employings are weak cold, and be controlled at≤0.60L/ of specific water (ton × min), to improve High Nickel Steel continuously cast bloom surface crack.
1050 DEG C～1150 DEG C of slab heating temperatures, slab adopts high-pressure water descaling after coming out of the stove, and de-scaling is de-scaling not to the utmost repeatedly;
Evenly tiny for guaranteeing very low temperature nickel steel microstructure, steel plate overall compression ratio (slab thickness/finished steel plate thickness) >=4.00.
First stage is common rolling, adopts large rolling pass draft to carry out rolling uninterruptedly, guarantees that dynamically/Static Recrystallization occurs deformation metal, first stage accumulative total draft >=50%, refine austenite crystal grain.
Subordinate phase adopts recrystallize controlled rolling RCR, 780 DEG C≤controlled rolling start rolling temperature≤840 DEG C, rolling pass draft >=8%, recrystallization zone accumulative total draft >=50%, 740 DEG C≤finishing temperature≤800 DEG C, further state steel plate microstructure is rolled in refinement, for uniform quenching super-refinement microstructure lays the foundation.
Adopt combination thermal treatment process as follows: normalizing temperature is 780 DEG C～820 DEG C, and the normalizing hold-time is 10～20min, and after normalizing, steel plate natural air cooling is to room temperature; Quenching temperature is 650 DEG C～700 DEG C, and the quenching hold-time is 15～25min (steel plate quenching is to room temperature); Tempering temperature is 600～650 DEG C, and the tempering hold-time is 30～60min, and tempering finishes rear steel plate natural air cooling to room temperature.
Beneficial effect of the present invention:
The present invention is in gordian technique route and Composition And Process design, combine the low-temperature flexibility of-196 DEG C that affects very low temperature nickel steel, anti-welding reheat cracking susceptibility, can be larger heat input weldability and the softening factor with embrittlement of anti-high tempering parameter SR, creatively adopt the composition system of the low N-ultra micro of Mn-in the ultralow Si-of ultralow C-+Ti processing low alloy steel as basis, control (%Mn) × [7.33 (%Si)+5.16 (%Al)]≤1.0, quenching temperature T≤0.009,0.007≤stabilization of austenite Index A u/ two-phase region, Ca process and Ca/S ratio be controlled at 1.0～3.0 between and (%Ca) × (%S)
0.28≤ 1.0 × 10
-3, optimize recrystallize controlled rolling and follow-up special combination thermal treatment process, make very low temperature nickel steel obtain high ultralow-temperature flexibility, good weldability, can bear larger heat input welding, what is more important, low temperature nickel steel of the present invention has excellent anti-high tempering parameter SR embrittlement characteristic, and can low cost fabrication (steel plate of relatively traditional very low temperature 9.0% nickel content), be particularly suitable for being used as manufacture Large LNG very low temperature storage tank, LNG very low temperature storage tank peculiar to vessel, ice sea and region, polar region large-scale steel structure, and can realize the stable suitability for industrialized production in batches of low cost.
The present invention realizes part substitute nickel with manganese, adopts compared with low nickel content and produces very low temperature steel plate, reduces by 2%～4% than conventional very low temperature steel plate nickel content, significantly reduces manufacturing cost, and product has very strong competitive power.
Brief description of the drawings
Fig. 1 is the steel plate microstructure of embodiment of the present invention E.
Embodiment
Below in conjunction with embodiment and accompanying drawing, the present invention will be further described.
Table 1 is the composition of embodiment of the present invention steel, and table 2, table 3 are the manufacturing process of embodiment of the present invention steel, and table 4, table 5 are the performance of embodiment of the present invention steel.
Embodiment of the present invention manufacturing process is as follows:
TDS molten iron deep desulfuration → converter smelting → LF → RH (feed Si-Ca silk) → continuous casting (adopting light soft reduction process) → slab roll off the production line finishing → slab scale fire cut → heat → recrystallize controlled rolling (RCR) → steel plate piles slow cooling/hole slow cooling → AUT/MUT → swarf, crop end → rough polishing ball removes surface of steel plate oxide skin → austenite one phase district's quenching+austenite and ferrite two-phase region quenching+tempering thermal treatment (Q+Q'+T) → sampling and performance test → cut scale steel plate → surface quality and apparent size, identify and detect → dispatch from the factory.
As seen from Figure 1, the complex phase microstructure that is organized as tiny uniform martensite/bainite+ferrite+austenite island of embodiment of the present invention steel, thus ensure that very low temperature nickel steel has high ultralow-temperature flexibility, good weldability, can bear larger heat input welding and excellent anti-high tempering parameter SR embrittlement characteristic.
The steel plate technical characterstic according to the present invention, the present invention combines with recrystallize controlled rolling, specific combination thermal treatment process by the unitized design of rational alloying element, very low temperature nickel steel can obtain excellent ultralow-temperature flexibility, anti-high tempering parameter SR embrittlement with softening, and steel plate can bear compared with Large Heat Input Welding, thereby saved the cost that user's member is manufactured, shorten the time that user's member is manufactured; Owing to not needing to add any equipment in very low temperature nickel steel production process of the present invention, manufacturing process is succinct, production process control is easy, therefore (especially cost of alloy, compared with traditional very low temperature nickel steel, reduces more than approximately 1500 yuan/ton) cheap for manufacturing cost.
Along with China's sustained economic development, increasing to oil and gas demand, the second west to east gas pipeline project that is about to recently to go into operation, to go out river pipeline, Sino-Russian pipeline, Sino-Kazakhstan pipeline construction be exactly best illustration, the climax of very low temperature LNG storage tank will be there is building for the Deposits in Eastern Coastal China area that lacks hydrocarbon resources, as the crucial tank body material of very low temperature LNG storage tank--the very low temperature nickel steel of anti-high tempering parameter SR, has wide market outlook.
Claims (2)
1. low cost very low temperature nickel steel, its composition weight percent is:
C：0.040％～0.070％
Si：≤0.15％
Mn：0.80％～1.20％
P：≤0.010％
S：≤0.0020％
Ni：5.00％～7.00％
Mo：0.05％～0.25％
Als：0.010％～0.030％
Ti：0.008％～0.018％
N：≤0.0040％
Ca：0.001％～0.004％
All the other are Fe and are inevitably mingled with; And mentioned component must meet following relation simultaneously:
(％Mn)×[7.33(％Si)+5.16(％Al)]≤1.0；
Ti/N＝1.5～3.5；
Quenching temperature T≤0.009,0.007≤stabilization of austenite Index A u/ two-phase region,
Wherein, Au=2.54+40.53[(%C)+(%N)]+0.43[(%Cu)+(%Ni)+(%Mn)]-0.22 (%Al)-2.64[(%P)+(%S)]-1.26[(%Cr)+(%Mo)]-(%Si), the unit of T is K;
Ca/S is between 1.00～3.00, and (%Ca) × (%S)
0.28≤ 1.0 × 10
-3;
The low temperature nickel structure of steel obtaining is the complex phase microstructure on tiny uniform martensite/bainite+ferrite+austenite island.
2. the manufacture method of low cost very low temperature nickel steel as claimed in claim 1, is characterized in that, comprises the steps:
1) smelt, cast
Smelt, cast employing continuous casting process by composition claimed in claim 1, Continuous Casting Soft Reduction rate is controlled between 3%～7%, and basket pouring temperature is between 1520 DEG C～1550 DEG C; Two cold employings are weak cold, be controlled at≤0.60L/ of specific water (ton × min);
2) 1050 DEG C～1150 DEG C of slab heating temperatures, slab adopts high-pressure water descaling after coming out of the stove, and de-scaling is de-scaling not to the utmost repeatedly;
3) rolling, steel plate overall compression ratio is slab thickness/finished steel plate thickness >=4.00
First stage is common rolling, adopts rolling uninterruptedly, first stage accumulative total draft >=50%;
Subordinate phase adopts recrystallize controlled rolling, 780 DEG C～840 DEG C of controlled rolling start rolling temperatures, rolling pass draft >=8%, recrystallization zone accumulative total draft >=50%, 740 DEG C～800 DEG C of finishing temperatures;
4) normalizing+quenching
Normalizing temperature is 780 DEG C～820 DEG C, and the normalizing hold-time is 10～20min, and after normalizing, steel plate natural air cooling is to room temperature; Quenching temperature is 650 DEG C～700 DEG C, and the quenching hold-time is 15～25min, and steel plate quenching is to room temperature;
5) tempering
Tempering temperature is 600～650 DEG C, and the tempering hold-time is 30～60min, and tempering finishes rear steel plate natural air cooling to room temperature.
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