CN102286692A - Hardened and tempered low-temperature steel and manufacture method thereof - Google Patents
Hardened and tempered low-temperature steel and manufacture method thereof Download PDFInfo
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Abstract
The invention relates to hardened and tempered low-temperature steel, which comprises the following chemical ingredients by weight percentage: 0.040 percent to 0.080 percent of C, at most 0.15 percent of Si, 1.20 percent to 1.60 percent of Mn, at most 0.015 percent of P, at most 0.003 percent of S, at most 0.010 percent of Als, 0.05 percent to 0.35 percent of Cu, 0.10 to 0.40 percent of Ni, 0.10 percent to 0.30 percent of Mo, 0.007 percent to 0.012 percent of Ti, 0.020 percent to 0.050 percent of V, 0.0055 percent to 0.0085 percent of N, 0.0008 percent to 0.0020 percent of B and 0.001 percent to 0.004 percent of Ca. In addition, the element contents meet the following relationship that: Mn/C is greater than or equal to 15 but smaller than or equal to 30; the equivalent weight of Ni is greater than or equal to 0.25 percent; Ti/N is between 1.0 and 2.0; B is greater than 0.714(N-0.292Ti-0.518Als); Ni/Cu is greater than or equal to 1.0; Ca/S is between 1.0 and 3.0, and in addition, the Ca(percentage)*S(percentage)0.28 is greater than or equal to 1.0*10<-4> but smaller than or equal to 1.5*10<-3>; and the rest are iron and unavoidable impurities. The steel is manufactured through combining processes of recrystallization control milling, on-line direct quenching, tempering heat treatment, the excellent low-temperature performance can be obtained, and in addition, a steel plate can bear large-line energy welding and is particularly suitable for being used for making liquefied petroleum gas (LPG) low-temperature storage tanks.
Description
Technical field
The present invention relates to a kind of Cryogenic Steel, particularly relate to obtain in the low alloy steel composition system that a small amount of (Cu+Ni+Mo) alloying-ultra micro (Ti+B) of in the ultralow Als-of the high Mn-of a kind of low C-N-handles yield strength 〉=490MPa, tensile strength 〉=610MPa ,-50 ℃ Charpy transverse impact merit (single value) but 〉=the modified Cryogenic Steel of 100J large-line energy welding, be mainly used in the manufacturing material of low temperature storage tank, low-temperature pressure steel pipe, ice sea region ocean platform.
Background technology
During for the modified high-strength steel plate of low temperature transverse impact toughness (single the value) 〉=100J that adopts prior art manufacturing-50 related to the present invention ℃, generally in steel, add a certain amount of valuable alloying element Ni, to guarantee that the mother metal steel plate has excellent low-temperature flexibility, except that bringing the high enterprise of manufacturing cost, during the large-line energy welding, more serious deterioration takes place in welded heat affecting zone (HAZ) low-temperature flexibility, and the low-temperature flexibility of heat affected zone (HAZ) is difficult to reach the requirement [EP0288054A2 of Cryogenic Steel, US Patent 4851052, EP 0839921A1, EP0168038]; Nippon Steel Corporation adopts direct quenching to add tempering process technology (being DQT) production high strength in the eighties in last century, ductility steel plate, obtain certain effect [Japanese Laid-Open Patent PublicationNo.153730/1983, Japanese Laid-Open Patent Publication No.77527/1983, Japanese Post-Exam Patent Publication No.3011/1983], main technical schemes is more than Ar3, from answer/recrystallized structure, carry out direct quenching+tempering heat treatment, but the low-temperature flexibility of steel plate is relatively poor, show as steel plate low-temperature cracking-resistance deficiency, can not satisfy the requirement of Cryogenic Steel; A large amount of patent documentations just illustrate the low-temperature flexibility that how to realize the mother metal steel plate, for how under welding conditions, obtain good heat affected zone (HAZ) low-temperature flexibility and illustrate lessly, how to guarantee when especially adopting the large-line energy welding that the low-temperature flexibility of heat affected zone (HAZ) is few [clear 63-93845, clear 63-79921, clear 60-258410, special flat 4-285119, special flat open 4-308035, flat 3-264614, flat 2-250917, flat 4-143246, US Patent4855106, US Patent5183198, the US Patent4137104 of opening].
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, boilers and pressure vessel, building structure, automotive industry, transportation by railroad and the machinofacture.Low-carbon (LC) (high strength) low alloy steel performance depends on the process system of its chemical ingredients, 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 chemical ingredients and the microstructure state of finished steel.Along with science and technology constantly advances, people propose higher requirement to obdurability, the weldability of steel, promptly when keeping low manufacturing cost, improve the comprehensive mechanical performance and the use properties of steel plate significantly, save cost with the consumption that reduces steel, alleviate steel member own wt, stability and security.Started the research climax that develops high-performance steel iron material of new generation in the world wide at present, obtain better microstructure coupling by alloy combination design, innovation controlled rolling/TMCP (comprising DQ) technology and thermal treatment process, thereby make steel plate obtain higher strength and toughness coupling, better weldability; Steel plate of the present invention adopts above-mentioned technology just, develops the Steel Plates For Low Temperature Service of comprehensive mechanical property excellence at low cost.
Summary of the invention
The technical problem that the present invention will solve provides a kind of modified high strength Cryogenic Steel.
One of kind that modified high strength Steel Plates For Low Temperature Service is a difficulty maximum in the slab product, but its reason is such steel plate not only requires to have high strength, high low-temperature flexibility, good weldprocedure and day of one's doom energy welding, but also will have good anti-welding reheat crack(ing) performance and cold and hot working performance; Therefore, the present invention is in gordian technique route and composition technological design, combine the mutual relationship that influences between hardened and tempered steel plate microstructure and intensity, low-temperature flexibility, anti-welding reheat cracking susceptibility and the large-line energy weldability, successfully solved the contradiction between intensity, low-temperature flexibility and the day of one's doom energy weldability of quenching and tempering, high, but stable batch is produced the modified Steel Plates For Low Temperature Service of day of one's doom energy welding cheaply, is suitable for being used as manufacturing low temperature storage tank, low-temperature pressure steel pipe, ice sea region ocean platform etc. especially.
For solving the problems of the technologies described above, the chemical ingredients of modified Cryogenic Steel of the present invention (wt%) is C:0.040%～0.080%, Si≤0.15%, Mn:1.20%～1.60%, P≤0.015%, S≤0.003%, Als≤0.010%, Cu:0.05%～0.35%, Ni:0.10～0.40%, Mo:0.10%～0.30%, Ti:0.007%～0.012%, V:0.020%～0.050%, N:0.0055%～0.0085%, B:0.0008%～0.0020%, Ca:0.001%～0.004%;
And above-mentioned constituent content satisfies following relation:
15≤Mn/C≤30；
Ni equivalent 〉=0.25%;
Ti/N is between 1.0～2.0;
B≥0.714(N-0.292Ti-0.518Als)；
Ni/Cu≥1.0；
Ca/S is between 1.0～3.0 and 1.0 * 10
-4≤ (%Ca) * (%S)
0.28≤ 1.5 * 10
-3
All the other are iron and inevitably are mingled with.
Composition satisfies Pcm≤0.20% among the present invention.
Another technical problem that the present invention will solve provides the manufacture method of above-mentioned steel.
For this reason, the manufacture method of modified low-temperature steel of the present invention comprises:
TDS molten iron deep desulfuration, converter smelting, the LF refining, the RH refining is also fed the Si-Ca silk, and continuous casting is also gently depressed, and the basket pouring temperature is controlled at 1535～1555 ℃ in the continuous casting;
De-scaling after 1000～1100 ℃ of slab heating temperatures, slab are come out of the stove;
Fs adopts common rolling, rolling pass draft 〉=8%, accumulative total draft 〉=50%;
Subordinate phase adopts the recrystallize controlled rolling, and the controlled rolling start rolling temperature is 900～950 ℃, rolling pass draft 〉=7%, and accumulative total draft 〉=50%, finishing temperature is 850～900 ℃;
Online direct quenching, steel plate from finish to gauge finish to the timed interval beginning to cool down be 15～45 seconds, open cold temperature 〉=800 ℃, speed of cooling 〉=10 ℃ s stops cold temperature≤350 ℃;
Off-line tempering, steel plate tempering temperature are controlled at 600～650 ℃, and tempering time is 1.0～2.0min/t, and t is a steel plate thickness;
The steel plate tempering is come out of the stove the back air cooling to room temperature.
Among the present invention, C is very big to intensity, low-temperature flexibility, unit elongation and the weldability influence of quenched and tempered steel, from improving hardened and tempered steel plate low-temperature flexibility and weldability angle (especially day of one's doom energy weldability), wishes that C content is controlled lowlyer in the steel; But microstructures Control and manufacturing cost angle from the hardening capacity of quenched and tempered steel, obdurability coupling, manufacturing process, C content should not be controlled lowly excessively, consider modified Steel Plates For Low Temperature Service microstructures Control, improve the tempering bainite splitting resistance, the content of C is controlled between 0.04%～0.08%.
Mn as most important alloying element in steel except that the intensity that improves steel plate, also have the austenite of expansion phase region, reduce Ar
3Point temperature, refinement hardened and tempered steel plate colony, increase between the lath the position to and improve the steel plate low-temperature flexibility effect, promote low temperature phase change tissue to form and the effect of raising armor plate strength; But segregation takes place in Mn easily in the molten steel solidification process, when especially Mn content is higher, not only can cause the pouring operation difficulty, and easily and element generation conjugation segregation phenomenas such as C, P, S, Mo, Cr, when especially C content is higher in the steel, the segregation that increases the weight of the strand centre is with loose, and serious strand central zone is segregated in follow-up rolling, thermal treatment and the welding process and easily forms abnormal structure, causes the low and welding joint of hardened and tempered steel plate low-temperature flexibility crackle to occur; Therefore according to the C content range, select suitable Mn content range extremely necessary with hardened and tempered steel plate for low temperature, composition of steel system and C content are 0.04%～0.08% according to the present invention, being fit to Mn content is 1.20%～1.60%, and when C content was high, Mn content suitably reduced, and vice versa; And when C content hanged down, Mn content suitably improved.
Si promotes deoxidation of molten steel and can improve armor plate strength, but adopt the molten steel of Al deoxidation, the desoxydatoin of Si is little, though Si can improve the intensity of steel plate, but the low-temperature flexibility of Si grievous injury steel plate (especially high-strength hardened and tempered steel plate), unit elongation and weldability, especially under the large-line energy welding conditions, Si not only promotes the M-A island to form, and the M-A island size that forms is comparatively thick, skewness, grievous injury welded heat affecting zone (HAZ) toughness and welding joint SR performance, therefore the Si content in the steel should be controlled lowly as far as possible, considers the economy and the operability of steelmaking process, and Si content is controlled at≤and 0.15%.
P is as harmful mechanical property that is mingled with steel plate in the steel, and especially low-temperature impact toughness, unit elongation, weldability and welding joint SR performance have huge detrimental effect, and it is low more good more to require in theory; But consider steel-making operability and steel-making cost, but for the low temperature hardened and tempered steel plate that requires superior weldability ,-50 ℃ of toughness and the energy welding of the excellent strength-toughness day of one's doom, P content need be controlled at≤0.013%.
S has very big detrimental effect as harmful low-temperature flexibility that is mingled with steel plate in the steel, the more important thing is that S combines with Mn in steel, form the MnS inclusion, in course of hot rolling, the plasticity-of MnS makes MnS along rolling to extension, forms along rolling to MnS inclusion band, and the low-temperature impact toughness of grievous injury steel plate, unit elongation, Z are to performance, weldability and welding joint SR performance, S produces hot short principal element in the course of hot rolling simultaneously, and it is low more good more to require in theory; But consider steel-making operability, steel-making cost and the smooth and easy principle of logistics, but for the low temperature hardened and tempered steel plate that requires superior weldability ,-50 ℃ of toughness and the energy welding of the excellent strength-toughness day of one's doom, S content need be controlled at≤0.0030%.
As austenite stabilizer element, add a spot of Cu and can improve armor plate strength simultaneously and improve low-temperature flexibility and do not damage its weldability; But when adding too much Cu, in hot rolling and temper process, with take place small and dispersed-the Cu precipitation, the low-temperature flexibility of infringement steel plate, the more important thing is that energy when welding day of one's doom easily produce thermal crack and cause copper brittleness, thus the Cu upper content limit be controlled at≤0.35%; If but add Cu content very few (＜0.05%), to improve intensity, the toughness effect is little, so Cu content is controlled between 0.05%～0.35%.
Add the hardening capacity of Mo raising steel plate, promote martensite/bainite to form, but Mo is as the strong carbide forming element, when promoting that martensite/bainite forms, the position is very little to difference between the increase martensite/size of bainite colony and the martensite/lath of bainite of formation, reduces the resistance that crackle passes martensite/bainite colony; Therefore Mo has reduced low-temperature flexibility, the unit elongation of hardened and tempered steel plate when increasing substantially hardened and tempered steel plate intensity; And when Mo adds when too much, the not only unit elongation of grievous injury steel plate, day of one's doom energy weldability and welding joint SR performance, and increase steel plate SR fragility and production cost; But for low-carbon (LC) 60 kg class hardened and tempered steel plate, certain Mo content must be arranged, have enough hardening capacity and anti-temper softening to guarantee steel plate.Therefore take all factors into consideration the phase transformation strengthening effect of Mo and to the influence of mother metal steel plate low-temperature flexibility, unit elongation and day of one's doom energy weldability, Mo content is controlled between 0.10%～0.30%.
Ni is that steel plate obtains the indispensable alloying element of good ultralow-temperature flexibility; Add Ni simultaneously in the steel and can also reduce the copper brittleness generation, alleviate the cracking of course of hot rolling; Therefore theoretically, Ni content is high more within the specific limits good more in the steel, but Ni is a kind of very expensive alloying element, produce angle in batches from low cost, suitable add-on is 0.10%～0.40%, far below the Ni content of traditional low temperature quenched and tempered steel, and lower Ni content helps to improve anti-SCC of steel plate and temper embrittlement, and this also is that the present invention adopts low Ni content to produce the technical characteristic of Cryogenic Steel.
The span of control of N is corresponding with the span of control of Ti, B, and for the large-line energy welding steel, Ti/N is best between 1.0～2.0.N content is low excessively, generates TiN, the BN number of particles is few, can not play the effect of the weldability of improving steel, and is harmful to weldability on the contrary; But during the N too high levels, free [N] increases in the steel, and especially heat affected zone (HAZ) free [N] content sharply increases under the large-line energy welding conditions, grievous injury HAZ low-temperature flexibility, the weldability of deterioration steel; Therefore N content is controlled at 0.0055%～0.0085%.
The Ti purpose that adds trace in the steel is to combine with N in the steel, generates the very high TiN particle of stability, and inhibition welded H AZ district austenite crystal is grown up and changed the second-order phase transition product, improves the low-temperature flexibility of large-line energy welded H AZ.The Ti content that adds in the steel will contain flux matched with the N in the steel, and the principle of coupling is that TiN can not separate out in liquid molten steel and must separate out in solid phase; Therefore the separating out temperature and must guarantee to be lower than 1400 ℃ of TiN is according to log[Ti] [N]=-16192/T+4.72 can determine the add-on of Ti.When adding Ti content very few (＜0.007%), form TiN number of particles deficiency, the austenite crystal that is not enough to suppress HAZ is grown up and is changed the second-order phase transition product and improve the low-temperature flexibility of large-line energy welded H AZ; When adding Ti content too much (＞0.012%), part TiN particle is separated out large-sized TiN particle in the solidification of molten steel process, and this large size TiN particle not only can not suppress the austenite crystal of HAZ grows up, and becomes the starting point of crack initiation on the contrary; Therefore the optimum controling range of Ti content is 0.007%～0.012%.
Form in the Thermal Cycle process of cooling in order to ensure BN in the steel, suppress AlN and form, in the steel sour molten aluminium Als be controlled at≤0.010%.
V content is between 0.020%～0.050%, and along with the increase of steel plate thickness, V content is the capping value suitably.Adding the V purpose is that (C N) separates out in ferrite/bainite, improves the intensity of steel plate by V; V adds very few, is lower than 0.020%, and (C N) very little, can not effectively improve the intensity of steel plate to the V that separates out; The V addition is too much, is higher than 0.050%, infringement steel plate low-temperature flexibility, unit elongation, day of one's doom energy weldability
B is strong hardenability element, the solid solution B atom of several ppm gathers partially at austenite grain boundary, the strongly inhibited proeutectoid ferrite forms, promote the formation of low temperature phase change tissues such as bainite, thus in the direct quenching process solid solution B intensity of raising steel plate is most important for obtaining low temperature phase change tissue such as bainite.B can also improve the low-temperature flexibility of the heat affected zone HAZ of large-line energy welding: I) Ti and B all are the strong forming elements of nitride, but in the Thermal Cycle process, TiN and BN effect fundamental difference, TiN (≤1250 ℃) under higher relatively temperature has higher stability, can effectively suppress the HAZ grain growth far away apart from welded bonds, but in the time of near welded bonds (FL), the Thermal Cycle peak temperature becomes very high (＞1350 ℃), the TiN particle is partly dissolved, and can not effectively suppress the HAZ grain growth.Though at high temperature the BN particle does not have the particle-stabilised and whole solid solutions of TiN in steel, but because the high diffusibility of B in steel, BN separates out fast again in the Thermal Cycle process of cooling that (diffustivity of Ti, Als is very low, TiN, AlN can't separate out in the Thermal Cycle process of cooling again, it is very slow to be that TiN, AlN separate out kinetics speed), the BN particle is because the singularity of crystalline structure, has the low energy orientation relationship with ferrite, the BN particle can become the active position of ferrite forming core, promote ferrite crystal grain forming core in austenite crystal, refinement HAZ tissue; For making the BN particle promote form tiny ferrite crystal grain, at first to promote the formation of BN, and reach certain quantity, adopt Ca to handle that (O, S) inclusion promote separating out of BN, i.e. be everlasting Ca (O, S) heterogeneous nucleation on the inclusion of BN to form superfine Ca.II) uses B and Ti alloying together, make the Fe that forms small and dispersed in the steel
23(CB)
6+ TiN+MnS composite particles and since the matrix around this composite particles mutually in, form the microcell of poor C, poor Mn, improve ferrite transformation temperature (Ac
3), increase ferrite forming core motivating force (Ac
3-Ar
3), promoting the ferrite crystal grain forming core, tiny ferrite is at Fe
23(CB)
6Forming core on the+TiN+MnS composite particles, refinement HAZ tissue improves the HAZ low-temperature flexibility; Simultaneously, gather several ppm B freely on austenite grain boundary partially, improve the hardenability of steel, suppress the thick ferrite of crystal boundary and form, also promote ferrite forming core in the austenite crystal.To achieve these goals, in the steel B content between 0.0008%～0.0020%.
Steel is carried out Ca to be handled, on the one hand can pure molten steel, on the other hand sulfide in the steel is carried out denaturing treatment, make it to become non deformable, stablize tiny spherical sulfide, suppress S red brittleness, improve steel plate impelling strength and Z to performance, improve the anisotropy of steel plate impelling strength.What of Ca add-on are depended on the height of S content in the steel, and the Ca add-on is low excessively, and treatment effect is little; The Ca add-on is too high, and formation Ca (O, S) oversize, fragility also increases, and can become the 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 a sulfide inclusion shape control index, be advisable between the span 1.0～3.0, so the span of control of Ca content is 0.001%～0.004%.
Among the present invention, for a kind of Plate Steel that is used to make the LPG low temperature storage tank is provided, component comprises: Fe, C, Si, Mn, P, S, Als, Cu, Ni, Mo, V, Ti, N, B, Ca, the weight percent of component is: C:0.040%～0.080%, Si :≤0.15%, Mn:1.20%～1.60%, P :≤0.015%, S :≤0.003%, Als :≤0.010%, Cu:0.05%～0.35%, Ni:0.10～0.40%, Mo:0.10%～0.30%, Ti:0.007%～0.012%, V:0.020%～0.050%, N:0.0055%～0.0085%, B:0.0008%～0.0020%, Ca:0.001%～0.004%, and also above-mentioned constituent content must satisfy following relation simultaneously:
15≤Mn/C≤30, evenly tiny and to guarantee hardened and tempered steel plate bainite colony at-50 ℃ of following Charpy bar fracture fiber rate 〉=50%;
Ni equivalent 〉=0.25%, reduce ferrite dislocation 1/2＜111 under the low temperature〉the P-N power of (110) motion, to guarantee-50 ℃ of following ferrites 1/2＜111〉(110) dislocation has higher mobility, promote dislocation to hand over slippage, improve the low-temperature flexibility of hardened and tempered steel plate intrinsic, draw Ni equivalent=Ni+0.28Mn+0.13Cu-1.33Si-0.89Al-3.36P according to experimental study;
Ti/N is between 1.0～2.0, when guaranteeing that the even small and dispersed of TiN particle is distributed in the steel, what is more important guarantees that the Ostward slaking be difficult to take place the TiN particle (is the macroparticle small-particle of eating, cause number of particles to reduce significantly, it is big that size of particles becomes, lose pinning effect to crystal boundary), guarantee that TiN particle granularity, distribution in the Thermal Cycle process keep stable, and alligatoring does not take place;
B 〉=0.714 (N-0.292Ti-0.518Als) and Pcm≤0.20%, to guarantee that steel plate is under the ultra-large linear energy input condition, BN in the Thermal Cycle process of cooling fast at Ca (O, S) separate out on the particle, bring out the ferrite forming core, suppress upper bainite and form, cut apart near the thick austenite crystal of welded bonds (FL), obtain good HAZ low-temperature flexibility;
Ni/Cu 〉=1.0 guarantee in Cu, the Ni composite toughening, to prevent that thermal crack from appearring in the day of one's doom energy welding joint when direct quenching;
Ca/S is between 1.0～3.0 and 1.0 * 10
-4≤ (%Ca) * (%S)
0.28≤ 1.5 * 10
-3, when guaranteeing in the steel plate sulfide nodularization, the inclusion small and dispersed, quantity is suitable, guarantees BN amount of separating out [BN Ca (O S) goes up forming core] in the Thermal Cycle process of cooling, improves the low-temperature flexibility and the day of one's doom energy welded H AZ low-temperature flexibility of steel plate;
All the other are iron and inevitably are mingled with.
According to the present invention, the steel plate tissue with extremely good very low temperature impelling strength (50 ℃ and following) is the evenly tiny ferrite that bainite+a small amount of disperse distributes.
The manufacturing process of steel of the present invention is as follows:
TDS molten iron deep desulfuration → converter smelting → LF → RH (feed Si-Ca silk) → continuous casting (adopt and gently depress technology) → slab finishing → slab scale fire that rolls off the production line is cut → heat → recrystallize controlled rolling → direct quenching (DQ) → steel plate slow cooling → AUT/MUT → swarf, crop end → tempering heat treatment (T) → sampling and performance test → cut scale steel plate → surface quality and apparent size, sign and detection → dispatch from the factory.
Casting technique of the present invention recommends to adopt continuous casting process, and adopts and gently depress technology, and preferably the light draft of continuous casting is controlled between 3%～7%, continuous casting process emphasis control trough casting temperature, and the basket pouring temperature is between 1535 ℃～1555 ℃.
Adopt high-pressure water descaling after 1000 ℃～1100 ℃ of slab heating temperatures, slab are come out of the stove, de-scaling is de-scaling not to the utmost repeatedly;
Fs is common rolling, rolling pass draft 〉=8%, accumulative total draft 〉=50%, guarantee that the deformation metal takes place dynamically/static recrystallize, refine austenite crystal grain, preferably, the rolling pass draft is 8～20%, and preferably adding up draft is 50～80%.
Subordinate phase adopts the recrystallize controlled rolling, 900～950 ℃ of controlled rolling start rolling temperatures, and rolling pass draft 〉=7%, accumulative total draft 〉=50% is considered the rolling power of milling train and the problem of template, 850 ℃～900 ℃ of finishing temperatures.Preferably, the rolling pass draft is 8～20%; Preferably, the accumulative total draft is 50～80%, more preferably 50～75%.
Quench and adopt online direct quenching, steel plate finishes to the time interval controls beginning to cool down between 15s～45s from finish to gauge, and when guaranteeing that the rolling deformation tissue is finished recrystallize, solid solution B gathers again partially on newly-generated austenite grain boundary; Open cold temperature 〉=800 ℃, be preferably 800～900 ℃, cold temperature≤350 ℃ are stopped in speed of cooling 〉=10 ℃/s.Preferably, speed of cooling is 10～30 ℃/s; Preferably, stopping cold temperature is 250～350 ℃.
Off-line tempering process emphasis control steel plate tempering temperature, tempering time and tempering postcooling speed.The steel plate tempering temperature is controlled between 600～650 ℃; Tempering time is pressed the furnace charge amount and is decided, and general tempering time is got 1.0～2.0min/mm * t (steel plate thickness), and after the steel plate tempering was come out of the stove, natural air cooling was to room temperature.
Beneficial effect
In gordian technique route and composition technological design, combine the mutual relationship that influences between hardened and tempered steel plate microstructure and intensity, low-temperature flexibility, anti-welding reheat cracking susceptibility and the large-line energy weldability, successfully solved the contradiction between intensity, low-temperature flexibility and the day of one's doom energy weldability of quenching and tempering, high, but stable batch is produced the modified Steel Plates For Low Temperature Service of day of one's doom energy welding cheaply, is suitable for being used as manufacturing low temperature storage tank, low-temperature pressure steel pipe, ice sea region ocean platform etc. especially.
The technology of the present invention adopts low Ni content by the modified Cryogenic Steel of online direct quenching production high strength, this not only reduces precious resource consumption, reduce manufacturing cost, shortened the manufacturing cycle, also reduced the organization of production difficulty (steel plate that the Ni constituent content is higher, surface quality of continuously cast slab is relatively poor, generally all needing rolls off the production line carries out surface-conditioning, sometimes also needing to carry out the surface colour penetration inspection is that so-called PT checks), also eliminated the difficulty of the steel scrap recovery that contains Ni in a large number simultaneously, realize the environmental protection of manufacturing processed, promoted the market competitiveness of Baosteel slab manufacturing technology ability and Cryogenic Steel.
Description of drawings
Fig. 1 is the microstructure (magnification is 500) of embodiments of the invention C.
Embodiment
By the following examples the present invention is carried out comparatively detailed explanation.
The present invention starts with from the alloy combination design, creatively adopted low alloy steel composition system that a small amount of (Cu+Ni+Mo) alloying-ultra micro (Ti+B) of N-among the ultralow Als-of the high Mn-of low C-handles as the basis, reduce sour molten Als content≤0.01% in the steel, control Ni equivalent 〉=0.25%, B 〉=0.714 (N-0.292Ti-0.518Als) and 15≤Mn/C≤30, a spot of (Cu+Ni+Mo) alloying, Ca handles and the Ca/S ratio be controlled at 1.0～3.0 between and 1.0 * 10
-4≤ (%Ca) * (%S)
0.28≤ 1.5 * 10
-3Optimize recrystallize controlled rolling, online direct quenching and follow-up tempering heat treatment process, when obtaining high strength, good low-temperature flexibility, steel plate can bear the large-line energy welding, be suitable for especially being used as and make low temperature storage tank, low-temperature pressure steel pipe, ice sea region ocean platform, and can realize low-cost stable suitability for industrialized production in batches.
Be the chemical ingredients of embodiments of the invention shown in the table 1, satisfy simultaneously
15≤Mn/C≤30；
Ni equivalent 〉=0.25%;
Ti/N is between 1.0～2.0;
B≥0.714(N-0.292Ti-0.518Als)；
Ni/Cu≥1.0；
Ca/S is between 1.0～3.0 and 1.0 * 10
-4≤ (%Ca) * (%S)
0.28≤ 1.5 * 10
-3
All the other are iron and inevitably are mingled with.
Shown in table 2 and the table 3 processing condition of embodiments of the invention.
It shown in the table 4 performance of modified high strength Steel Plates For Low Temperature Service of the present invention.
Table 4 is the result show, modified high strength Steel Plates For Low Temperature Service of the present invention has yield strength 〉=490MPa, tensile strength 〉=610MPa, Charpy transverse impact merit (single value) 〉=100J of-50 ℃, Charpy transverse impact merit (single value) 〉=75J of-50 ℃ of large-line energy welding analog heat affected zone, can satisfy the requirement of Cryogenic Steel, particularly can be used for making the LPG low temperature storage tank.
The steel plate technical characterstic according to the present invention, the new invention steel plate combines with recrystallize controlled rolling, online direct quenching, tempering heat treatment process by the unitized design of rational alloying element, steel plate can obtain excellent low-temperature flexibility, and steel plate can bear the large-line energy welding, thereby saved the cost that the user member is made, shortened the time that user's member is made, for the user has created very big value, thereby this type of steel plate is the product of high added value, green environmental protection; Owing to do not need to add any equipment in the steel plate production process of the present invention, manufacturing process is succinct, production process control is easy, therefore cheap for manufacturing cost, has the very high performance-price ratio and the market competitiveness; And technological adaptability is strong, can promote to all Heavy Plate Production producers with Equipment for Heating Processing, has very strong business promotion, has higher technology trade and is worth.
Along with China's sustained economic development, increasing to the oil and gas demand, the transfering natural gas from the west to the east two wires 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 that will occur building low temperature gas storage, storage tank for the Deposits in Eastern Coastal China area that lacks hydrocarbon resources, crucial tank body material--low-temperature high-strength hardened and tempered steel plate as low temperature gas storage, storage tank will have vast market prospect.At present Baogang Stocks Trading Co. (our department) but Thick Plate Plant successfully adopts this patented technology to produce excellent property and large-line energy welding low temperature quenched and tempered high tensile strength plate at low cost, and possess the volume shipment ability.
Claims (13)
1. modified Cryogenic Steel, its chemical ingredients by weight percentage is:
C：0.040％～0.080％，Si≤0.15％，Mn：1.20％～1.60％，P≤0.015％，S≤0.003％，Als≤0.010％，Cu：0.05％～0.35％，Ni：0.10～0.40％，Mo：0.10％～0.30％，Ti：0.007％～0.012％，V：0.020％～0.050％，N：0.0055％～0.0085％，B：0.0008％～0.0020％，Ca：0.001％～0.004％
And above-mentioned constituent content satisfies following relation:
15≤Mn/C≤30；
Ni equivalent 〉=0.25%;
Ti/N is between 1.0～2.0;
B≥0.714(N-0.292Ti-0.518Als)；
Ni/Cu≥1.0；
Ca/S is between 1.0～3.0 and 1.0 * 10
-4≤ (%Ca) * (%S)
0.28≤ 1.5 * 10
-3
All the other are iron and inevitably are mingled with.
2. modified Cryogenic Steel as claimed in claim 1 is characterized in that, Pcm≤0.20%.
3. the manufacture method of modified Cryogenic Steel as claimed in claim 1 or 2 comprises the steps:
TDS molten iron deep desulfuration, converter smelting, the LF refining, the RH refining is also fed the Si-Ca silk, and continuous casting is also gently depressed, and the basket pouring temperature is controlled at 1535～1555 ℃ in the continuous casting;
De-scaling after 1000～1100 ℃ of slab heating temperatures, slab are come out of the stove;
Fs adopts common rolling, rolling pass draft 〉=8%, accumulative total draft 〉=50%;
Subordinate phase adopts the recrystallize controlled rolling, and the controlled rolling start rolling temperature is 900～950 ℃, rolling pass draft 〉=7%, and accumulative total draft 〉=50%, finishing temperature is 850～900 ℃;
Online direct quenching, steel plate from finish to gauge finish to the timed interval beginning to cool down be 15～45 seconds, open cold temperature 〉=800 ℃, speed of cooling 〉=10 ℃ s stops cold temperature≤350 ℃;
Off-line tempering, steel plate tempering temperature are controlled at 600～650 ℃, and tempering time is 1.0～2.0min/t, and t is a steel plate thickness;
The steel plate tempering is come out of the stove the back air cooling to room temperature.
4. method as claimed in claim 3 is characterized in that, in the fs rolling in, percentage pass reduction is 8～20%, accumulative total draft be 50～80%.
5. as claim 3 or 4 described methods, it is characterized in that in subordinate phase was rolling, the rolling pass draft was 8～20%, the accumulative total draft is 50～80%.
6. method as claimed in claim 5 is characterized in that, the accumulative total draft is 50～75%.
7. as the arbitrary described method of claim 3～6, it is characterized in that in the described quenching, opening cold temperature is 800～900 ℃.
8. as the arbitrary described method of claim 3～7, it is characterized in that in the described quenching, speed of cooling is 10～30 ℃ of s.
9. as the arbitrary described method of claim 3～8, it is characterized in that in the described quenching, stopping cold temperature is 250～350 ℃.
10. as the arbitrary described method of claim 3～9, it is characterized in that, after slab heating is come out of the stove, use high-pressure water descaling, de-scaling is not to the utmost the time, de-scaling repeatedly.
11., it is characterized in that in the described continuous casting, the draft of gently depressing is 3～7% as the arbitrary described method of claim 3～10.
12. as the modified Steel Plates For Low Temperature Service that the arbitrary described method of claim 3～11 is made, yield strength 〉=490MPa, tensile strength 〉=610MPa ,-50 ℃ the single value 〉=100J of Charpy transverse impact merit.
13. the modified Steel Plates For Low Temperature Service that method as claimed in claim 12 is made is characterized in that-50 ℃ the single value 〉=75J of Charpy transverse impact merit of large-line energy welding analog heat affected zone.
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| CN103014281A (en) * | 2012-12-21 | 2013-04-03 | 鞍钢股份有限公司 | Online treatment method for low-alloy high-strength steel plate |
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| CN109423572A (en) * | 2017-08-31 | 2019-03-05 | 宝山钢铁股份有限公司 | High crack arrest, strain resistant initial aging stage characteristic Seawater corrosion-resistant steel plate and its manufacturing method |
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