CN101880824B - Q345q-series super-thick bridge steel plate and production method thereof - Google Patents
Q345q-series super-thick bridge steel plate and production method thereof Download PDFInfo
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Abstract
The invention discloses a Q345q-series super-thick guaranteed performance and flaw detection bridge steel plate comprising the following chemical components in percentage by mass: 0.08-0.16 percent of C, 0.20-0.50 percent of Si, 1.15-1.60 percent of Mn, not more than 0.020 percent of P, not more than 0.010 percent of S, not more than 0.12 percent of microalloyed element (V+Nb+Ti+Ni), 0.010-0.050 percent of AlS and the balance of Fe and residual elements; and carbon equivalent is not more than 0.43. The invention also discloses a production method of the steel plate, comprising the steps of rolling, cooling, straightening, cooling in pile and thermal treatment. In the rolling, the cooling and the straightening, the 130 mm super-thick Q345qD(E) steel plate is successfully developed in the production line of a converter, die casting, mill rolling and normalization thermal treatment through carrying out reasonable composition design, die casting, TMCP (Thermal Mechanical Control Process) rolling and thermal treatment; the secondary flaw detection qualification rate reaches 90 percent, the performance initial test qualification rate reaches 100 percent, and the Z-direction performance of the entity of the steel plate can reach Z15 level. The development of the super-thick steel plate satisfies the higher requirements on bridge industry.
Description
Technical field
The present invention relates to steel, be specifically related to a kind of Q345q special thick bridge steel plate of series and working method thereof.
Background technology
Along with developing rapidly of Chinese national economy, the development of Bridge Steel is also thick towards the spy, extra wide, high-performance direction develop.Bridge structure is widely used in the main body of various Longspan Bridges with steel; Requirement can exempt to bear bigger quiet, moving load; Long active time is arranged; Therefore the Bridge Steel industry has proposed higher requirement to steel plate obdurability, welding property, yield tensile ratio, anti-lamellar tearing ability, HS, good low-temperature flexibility through and the demand of the Bridge Steel of good welds performance constantly increase.At present the above domestic fertile steel mill of bridge plate of thickness 100m is also few, but, tooling big with its production difficulty about thickness Q345q series (comprising: Q345qC steel, Q345qD steel and Q345qE steel) special thick bridge steel plate more than 100111m requires reason such as special to produce.
Summary of the invention
To the problems referred to above, the inventor has obtained the Q345q series special thick bridge steel plate of a kind of thickness more than 100m, thereby has accomplished the present invention through groping.
Therefore, the object of the present invention is to provide the Q345q series special thick bridge steel plate of a kind of thickness more than 100mm.Another object of the present invention is to provide the working method of this this steel plate.
For reaching above-mentioned first purpose; The technical scheme that the present invention takes be the special thick bridge steel plate of this Q345q series comprise following chemical components in mass percent (unit, wt%): C:0.08～0.16, Si:0.20～0.50, Mn:1.15～1.60, P :≤0.020, S :≤0.010, micro alloying element (V+Nb+Ti+Ni) :≤0.12, AlS:0.010～0.050, other is Fe and relict element;
Carbon equivalent [Ceq=C+Mn/5+ (Cr+Mo+V)/5+ (Ni+Cu)/15] :≤0.43.
More than the function analysis of each chemical ingredients following:
C: be most basic strengthening element in the steel, improve intensity, but C influences the welding property of steel and influences toughness.Take all factors into consideration, the content of carbon is hanging down of control as far as possible.
Si: be the solution strengthening element, favourable to the intensity that improves steel plate.
Mn: be the solution strengthening element, all favourable to intensity and the toughness that improves steel plate.
P: unfavorable to welding, and have certain cold shortness, and in this steel grade, belong to harmful element, that should control is low as far as possible.
S: be prone to form the MnS type impurity, have certain red brittleness, in this steel grade, belong to harmful element, that should control is low as far as possible.
V, Nb, Ti: in steel, can combine, form fine carbide or carbonitride, can play crystal grain thinning and dispersion-strengthened action, thereby reach the net effect of the obdurability of effective raising steel with C, N.
Ni: an amount of adding can effectively improve the low-temperature impact toughness of steel plate.
Al: can play the crystal grain thinning strengthening effect.
The thickness of the thick bridge steel plate of said spy is more than 100mm.
For achieving the above object, the working method that the present invention takes comprises: converter smelting, LF refining, vacuum refinement, cast, heating, control are cold, slow cooling, thermal treatment; It is characterized in that the fs start rolling temperature is controlled between 1000～1200 ℃, it is rolling to adopt high temperature low speed to depress greatly, and reduction in pass is not less than 40mm; When temperature is not less than 1000 ℃, stop rolling the steel that dries in the air, the steel thickness that dries in the air is 2-3 times of finished product thickness; When the rolled piece temperature was 860～920 ℃, the beginning subordinate phase was rolling, and reduction in pass is not less than 30mm, and last three percentage pass reductions >=15% increases progressively by the road; Finishing temperature is controlled at 800～860 ℃; The rolling back that finishes adopts the ACC control cold, and final cooling temperature is controlled between 650～750 ℃, is sent to the straightener aligning then.
The bridge structure steel is had relatively high expectations to intensity and welding property, makes the use of carbon equivalent be restricted, and for the thick bridge plate of spy, the composition design is more prudent and crucial.Maximum ga(u)ge in the GB/T714-2008 GB is merely 100mm; Expect the special thick bridge plate of 130mm; Should rationally select micro alloying element for use, utilize the compound adding of best proportioning of Nb, V, Ti, give full play to precipitation strength and refined crystalline strengthening double effects; Do not reducing under the flexible prerequisite, guaranteeing that each item performance index of bridge plate reach the requirement of GB 50-100mm.
For obtaining internal soundness preferably; Guarantee the requirement of detecting a flaw, the smelting of Clean Steel is the basis, mainly guarantees from two aspects; The one, total rank of non-metallic inclusion in the molten steel (A, B, C, D four big classes) is controlled in 4.0; The 2nd, the content of five big harmful elements in the strict molten steel, concrete measure is: desulfurization taked for two steps walked, and taked molten iron pre-desulfurization technology to guarantee the content into stove molten iron S on the one hand; Make white slag in the reinforcement of LF refining furnace on the other hand and carry out the secondary desulfurization.Deoxidation taked for two steps walked equally, and the deoxidation operation is strengthened in strict on the one hand control converter terminal C% content (preventing peroxo-), reinforcement pushing off the slag tapping, improves the molten steel purity; Make full use of the LF refining furnace on the other hand, adopt high temperature, high basicity, the abundant deoxidation of high quantity of slag suboxide iron slagging process; Moreover need prolongation dwell time under the VD vacuum condition fully outgases.In strict accordance with the Clean Steel production process route, guarantee that S, P, N, H, O five big harmful elements are controlled in the 160ppm.Adopt suitable burning steel temperature; Burning the steel time is 13min/cm+60min; Guarantee micro alloying element fully solid molten in the austenitic area, rough rolling step takes high temperature low speed to depress technology greatly, and the two-stage takes＞and the steel thickness that dries in the air of 2.5H is rolling; ACC adopts suitable roller speed and the cooling rate of 5～15 ℃/S, to guarantee the effect of controlled rolling crystal grain thinning.
Be further uniform formation, eliminate banded structure, crystal grain thinning improves the steel plate comprehensive mechanical property, adopts normalizing heat treatment technique to rolling the back steel plate, and normalizing temperature is chosen in Ar3+ (30-50 ℃) interval, adopts the soaking time of 2.2min/mm+30min.In order to guarantee obdurability and welding property requirement, the low-carbon high-manganese scheme is taked in the composition design, the steel grade [P] of keeping under strict control simultaneously, [S], [N], [H], [O] five big harmful constituent contents.
Through carry out reasonable component design, die casting cast, TMCP is rolling and thermal treatment; Successfully developed special thick Q345qD (E) steel plate of 130mm at converter-die casting cast-rolling-normalizing heat-treatment production line; The secondary flaw detection qualification rate reaches 90%; Performance initial test qualification rate reaches 100%, and its ballistic work in kind can reach the E level, Z reaches the Z15 level to performance.The exploitation of the thick bridge plate of this spy has been satisfied bridge industry high requirement.
Description of drawings
Below in conjunction with accompanying drawing, the present invention is done further elaboration.
Fig. 1 is a process flow sheet of the present invention.
Fig. 2 is the metallographic structure figure of TMCP of the present invention after rolling.
Fig. 3 is the metallographic structure figure after the thermal treatment of the present invention.
Embodiment
The special thick bridge steel plate of Q345qD according to the invention comprises following chemical components in mass percent: C%:0.08～0.16, Si%:0.20～0.45, Mn%:1.15～1.60, P% :≤0.020, S :≤0.010, micro alloying element (V+Nb+Ti+Ni) % :≤0.12, AlS%:0.010～0.050, other is Fe and relict element; Carbon equivalent [Ceq=C+Mn/5+ (Cr+Mo+V)/5+ (Ni+Cu)/15] :≤0.43.
The working method that the present invention takes; Comprise rolling, cooling, aligning, cooling in heap, thermal treatment,, it is characterized in that the fs start rolling temperature is controlled between 1000～1200 ℃ at said rolling, cooling, aligning; It is rolling to adopt high temperature low speed to depress greatly, and reduction in pass is not less than 40mm; When temperature is not less than 1000 ℃, stop rolling the steel that dries in the air, the steel thickness that dries in the air is 2-3 times of finished product thickness; When the rolled piece temperature was 860～920 ℃, the beginning subordinate phase was rolling, and reduction in pass is not less than 30mm, and last three percentage pass reductions >=15% increases progressively by the road; Finishing temperature is controlled at 800～860 ℃; The rolling back that finishes adopts the ACC control cold, and final cooling temperature is controlled between 650～750 ℃, is sent to the straightener aligning then.
In said converter smelting, tapping carbon>=0.06%, tapping P≤0.012%, S≤0.012%; Point blows number of times and must not avoid slag under the tapping process greater than 2 times.
In said LF refining, take the big quantity of slag to carry out slag making, guarantee that the white slag hold-time is controlled at more than the 15min.
In said vacuum refinement, the dwell time under≤67Pa is controlled by>=10min.
Pine in said adding, the holding temperature of dead soaking pit is controlled at 1200 ℃～1300 ℃.
In said control is cold, return red temperature＜740 ℃, cooling rate is controlled at 5～15 ℃/s.
In said slow cooling, go into burial pit temperature >=300 ℃; Cooling in heap time >=24 hour.
In said thermal treatment, holding temperature: 910 ± 30 ℃; Heat-up time: 1.5-2.5min/mm; The type of cooling: air cooling or air-cooled.
In the said cooling in heap, the temperature before the steel plate stacking slow cooling should be higher than 300 ℃, the content of hydrogen, steel plate initial temperature and steel plate thickness in the stacking slow cooling basis of time steel plate and decide.
Embodiment 1
, slow cooling cold through converter smelting, LF refining, vacuum refinement, cast, heating, control, thermal treatment process obtain to be described in table 2 below the Q345qD Finished Steel of chemical ingredients, and wherein each processing parameter and mechanical property are seen like following table 4,5,6.
The chemical ingredients of table 1 embodiment 1 steel
| C(％) | Si(％) | Mn(％) | P(％) | S(％) | Ni+V+Nb+Ti(％) | AlS(％) | N(％) |
| 0.12 | 0.30 | 1.50 | 0.013 | 0.002 | 0.09-0.10 | 0.030 | 0.004 |
Embodiment 2
, slow cooling cold through converter smelting, LF refining, vacuum refinement, cast, heating, control, thermal treatment process obtain to be described in table 2 below the Q345qD Finished Steel of chemical ingredients, and wherein each processing parameter and mechanical property are seen like following table 4,5,6.
The chemical ingredients of table 2 embodiment 2 steel
| C(％) | Si(％) | Mn(％) | P(％) | S(％) | Ni+V+Nb+Ti(％) | AlS(％) | N(％) |
| 0.11 | 0.28 | 1.50 | 0.011 | 0.001 | 0.09 | 0.020 | ≤0.006 |
Embodiment 3
, slow cooling cold through converter smelting, LF refining, vacuum refinement, cast, heating, control, thermal treatment process obtain to be described in table 2 below the Q345qD Finished Steel of chemical ingredients, and wherein each processing parameter and mechanical property are seen like following table 4,5,6.
The chemical ingredients of table 3 embodiment 3 steel
| C(％) | Si(％) | Mn(％) | P(％) | S(％) | Ni+V+Nb+Ti(％) | AlS(％) | N(％) |
| 0.13 | 0.35 | 1.45 | 0.012 | 0.002 | 0.10 | 0.032 | ≤0.008 |
Operational path of the present invention
Molten iron KR desulfurization-converter smelting-LF is concise-VD vacuum outgas-die casting cast-steel ingot demoulding slow cooling-heating-dephosphorization-mill milling-ACC cooling-aligning-steel plate cooling in heap-surface inspection-finishing-normalizing thermal treatment-flaw detection-Performance Detection one warehouse-in.
1.1 steel-making part
1.1.1 composition design
The bridge structure steel is had relatively high expectations to intensity and welding property, makes the use of carbon equivalent be restricted, and for the thick bridge plate of spy, the composition design is more prudent and crucial.Maximum ga(u)ge in the GB/T714-2008 GB is merely 100mm; Expect the special thick bridge plate of 130mm; Should rationally select micro alloying element for use, utilize the compound adding of best proportioning of Nb, V, Ti, Ni, give full play to precipitation strength and refined crystalline strengthening double effects; Do not reducing under the flexible prerequisite, guaranteeing that each item performance index of bridge plate reach the requirement of GB 50-100mm.In order to guarantee obdurability and welding property requirement, the low-carbon high-manganese scheme is taked in the composition design, the steel grade [P] of keeping under strict control simultaneously, [S], [N], [H], [O] five big harmful constituent contents.
1.1.2 compression ratio design
Owing to require to protect flaw detection, strict to performance index simultaneously, in conjunction with practical experience in the past; This compression ratio in conjunction with the steel ingot characteristics, selects the 33t ingot shape more reasonable at least >=4; The thick 820mm of this steel ingot microcephaly, the thick 960mm of major part, mean thickness 890mm; Average compression ratio 6.85 reaches design requirements fully.
1.1.3 molten steel cleanliness factor
For obtaining internal soundness preferably; Guarantee secondary flaw detection requirement, the smelting of Clean Steel is the basis, mainly guarantees from two aspects; The one, total rank of non-metallic inclusion in the molten steel (A, B, C, D four big classes) is controlled in 4.0; The 2nd, the content of five big harmful elements in the strict molten steel, concrete measure is: desulfurization taked for two steps walked, and taked molten iron pre-desulfurization technology to guarantee into stove molten iron S content≤0.005% on the one hand; Make white slag in the reinforcement of LF refining furnace on the other hand and carry out the secondary desulfurization.Deoxidation taked for two steps walked equally, and the deoxidation operation is strengthened in strict on the one hand control converter terminal C% content (preventing peroxo-), reinforcement pushing off the slag tapping, improves the molten steel purity; Make full use of the LF refining furnace on the other hand, adopt high temperature, high basicity, the abundant deoxidation of high quantity of slag suboxide iron slagging process; Moreover need prolongation dwell time under the VD vacuum condition fully outgases.In strict accordance with the Clean Steel production process route, guarantee that S, P, N, H, O five big harmful elements are controlled in the 160ppm.
1.1.4TMCP it is rolling
Adopt suitable burning steel temperature; Burning the steel time is 13min/cm+60min; Guarantee micro alloying element fully solid molten in the austenitic area, rough rolling step takes high temperature low speed to depress technology greatly, and the two-stage takes＞and the steel thickness that dries in the air of 2.5H is rolling; ACC adopts suitable roller speed and the cooling rate of 5～15 ℃/S, to guarantee the effect of controlled rolling crystal grain thinning.
1.1.5 thermal treatment
Be further uniform formation, eliminate banded structure, crystal grain thinning improves the steel plate comprehensive mechanical property, adopts normalizing heat treatment technique to rolling the back steel plate, and normalizing temperature is chosen in Ar3+ (30-50 ℃) interval, adopts the soaking time of 2.2min/mm+30min.
2.2 ingot shape is selected
Conventional ingot casting has 24T, 26T, 32T, 33T, 43T and 48T, and the water cooled mo(u)ld ingot has 50T and 60T, selects the conventional die casting ingot shape of comparatively suitable 33T.
2.3 heating
Different heating cycles influences austenite original grain degree, and austenite original grain degree influences the grain size behind the recrystallize.Contain the higher Nb of content in Q345qD (E) steel; The carboritride that this type of steel temperature reaches niobium more than 900 ℃ just begins to decompose solid solution; Make austenite crystal begin to grow up; More even to 1150 ℃ of grain growths, crystal grain was further grown up when temperature was brought up to 1200 ℃, and promptly so-called secondary recrystallization takes place.Therefore, for the steel after rolling have evenly tiny crystal grain, Heating temperature generally is advisable with about 1150 ℃.If be heated to 1050 ℃, then austenite grain size is uneven, makes to roll the easy mixed crystal that produces of back steel; If be heated to 1200 ℃ or higher, then crystal grain is excessively grown up, and makes to roll back steel crystal grain and be difficult to refinement; Therefore, Heating temperature is set at 1100～1200 ℃, and soaking time is 13cm/min+60min.
2.4 controlled rolling and controlled cooling
Adopt (austenite recrystallization district, the austenite non-recrystallization district) controlled rolling of II stage.In fs rolling; Mainly be static recrystallize, this stage makes the critical draft (simultaneously total deformation greater than 50%) of percentage pass reduction greater than static recrystallize as far as possible, and this specification steel plate is rolled with steel ingot in addition; For improving subsurface defect, adopt high temperature low speed to depress technology greatly.For avoiding rolling in part austenite recrystallization district; The two-stage start rolling temperature should be given bigger accumulative total draft (total deformation 60%～80%) simultaneously less than 950 ℃, and a suitable temperature thickness of treating is promptly arranged; Austenite fully is out of shape; Form many deformation bands, increase deformed nucleus, reach the purpose of refinement ferritic and pearlitic grain.By above-mentioned distortion distribution principle, rolling back its intensity of steel improves, and brittle transition temperature reduces, low-temperature flexibility be improved significantly.
Be the austenite structure before the abundant refinement phase transformation, stop or postpone carbide and in process of cooling, separate out too early, its disperse in ferritic is separated out; Improve intensity, reduce the size of pearlite colony simultaneously, the refine pearlite sheet interlayer spacing; Improve the comprehensive mechanical property that steel comprise plasticity, toughness etc., after controlled rolling is accomplished, according to finished product thickness; Rationally control ACC technology is carried out controlled chilling, guarantees that steel plate returns red temperature and is lower than Ar1.
Execution technology is following: the fs start rolling temperature is controlled between 1000～1200 ℃, and it is rolling to adopt high temperature low speed to depress greatly, and reduction in pass is not less than 40mm; When temperature is not less than 1000 ℃, stop rolling the steel that dries in the air, the steel thickness that dries in the air is 2-3 times of finished product thickness; When the rolled piece temperature was 860～920 ℃, the beginning subordinate phase was rolling, and reduction in pass is not less than 30mm, and last three percentage pass reductions >=15% increases progressively by the road; Finishing temperature is controlled at 800～860 ℃; The rolling back that finishes adopts the ACC control cold, and final cooling temperature is controlled between 650～750 ℃, is sent to the straightener aligning then.
2.5 cooling in heap technology
Adopt high temperature cooling in heap technology can effectively avoid to reduce the content of hydrogen in the steel plate simultaneously greatly, improve the steel plate inspection defective because of cooling off the unrelieved stress that produces fast.Temperature before the steel plate stacking slow cooling should be higher than 300 ℃, the content of hydrogen, steel plate initial temperature and steel plate thickness etc. in the stacking slow cooling basis of time steel plate and decide.
2.6 thermal treatment process
Execution technology is holding temperature: holding temperature: 910 ± 30 ℃; Heat-up time: 1.5-2.5min/mm; The type of cooling: air cooling or air-cooled.
Trial result is analyzed
3.1 Composition Control analysis
For guaranteeing good welding property, should control carbon equivalent Ceq about 0.38, carbon is as one of strengthening element, and limit control in composition design internal control scope, adopting in the time of the proof strength performance, does not cause deterioration to welding property; Mn is one of crystal grain thinning element, in order to improve intensity, reduces the steel brittle transition temperature, improves low-temperature impact toughness, but that Mn content is difficult for is too high, otherwise unfavorable to toughness and welding property, so Mn content is controlled at about 1.5%.The Nb element has significant crystal grain thinning effect, and the over-all properties of improving steel is apparent in view, but Nb content makes easily in the strand process of cooling and produce surface crack when high, preferably helps controlling the surface quality of continuously cast bloom with V, the compound adding of Ti alloy.So control of Nb, V, Ti.P, S content are controlled in the lower scope.In a word, whole Composition Control is stable, satisfies the design requirements of Q345qD (E) composition.
3.2 mechanical mechanics property analysis
This produces 20 crowdes of the thick Q345Qd of 130mm (E) altogether as a trial; Because Q345qD (E) has adopted Ni+V+Nb+Ti combined microalloying composition system, in the operation of rolling, micro-alloying technology and TMCP technology is effectively combined, and gives full play to the refined crystalline strengthening effect of microalloy element; Improved steel plate obdurability index effectively; Wherein: ys is controlled at 315～350MPa, has on average reached 335MPa, than the rich 40MPa of standard; Tensile strength is controlled at 490～515MPa, has on average reached 500MPa, than the rich 30MPa of standard; Elongation is controlled at 29%-32%, on average reaches 28%, than standard rich 8%;-20 ℃ of impact of collision power controls have on average reached 178J built in 144～256J, and performance index have satisfied Q345Qd (E) development requires, and table 4 is Q345qD (E) performance level in kind.Simultaneously in order further to understand the in kind real performance level of this time experiment, to the steel plate of this time experiment carried out thickness Z to stretch ,-40 ℃ of indexs such as impact detect, detected result is seen table 5.The result shows, the special thick Q345qD bridge plate of this exploitation has reached the level of E level, Z15.
Table 4 the present invention test-manufactures the thick bridge structure of 130mm and uses the rigidity ability
Table 5 the present invention test-manufactures the thick bridge structure of 130mm with steel additional properties level detection
3.3 mirco structure analysis
Fig. 2 is the thickness of slab 1/4 place high power metallographic structure figure of the rolling back of TMCP steel plate, and display organization is ferritic and perlite as a result, 1.5 grades of banded structures, grain fineness number 6-7 level.Fig. 3 shows that for the thickness of slab 1/4 place high power metallographic structure figure of steel plate after the thermal treatment, result banded structure disappears, 9 grades of grain fineness numbers.Show according to data; Continuous reduction along with the Bridge Steel carbon content; Standard weave is also developed to acicular ferrite and bainite and full bainite direction by ferritic and perlite; This low-carbon micro steel-alloy can obtain a series of tissues usually when cooling off continuously: polygonal ferrite, quasi-polygonal ferrite, acicular ferrite, granular bainite, ferrite bainite and M/A tissue etc.; The carbon content of this test is basically more than 0.10%, and what obtain after TMCP is rolling is conventional ferritic and pearlitic structure.
Claims (9)
1. the special thick bridge steel plate of Q345q series; The thickness that it is characterized in that the special thick bridge steel plate of said Q345q series is more than 100mm, and above-mentioned steel plate comprises following chemical components in mass percent: C:0.08～0.16, Si:0.20～0.50, Mn:1.15～1.60, P :≤0.020, S :≤0.010, micro alloying element (V+Nb+Ti+Ni) :≤0.12, Al
S: 0.010～0.050, other is Fe and relict element; Carbon equivalent :≤0.43.
2. the working method of the special thick bridge steel plate of Q345q series as claimed in claim 1; Comprise converter smelting, LF refining, vacuum refinement, cast, heating, controlled rolling and controlled cooling, slow cooling, thermal treatment; In the controlled rolling and controlled cooling step; Execution technology is following: the fs start rolling temperature is controlled between 1000～1200 ℃, and it is rolling to adopt high temperature low speed to depress greatly, and reduction in pass is not less than 40mm; When temperature is not less than 1000 ℃, stop rolling the steel that dries in the air, the steel thickness that dries in the air is 2-3 times of finished product thickness; When the rolled piece temperature was 860～920 ℃, the beginning subordinate phase was rolling, and reduction in pass is not less than 30mm, and last three percentage pass reductions >=15% increases progressively by the road; Finishing temperature is controlled at 800～860 ℃; The rolling back that finishes adopts the ACC control cold, and final cooling temperature is controlled between 650～750 ℃, is sent to the straightener aligning then.
3. the working method of the special thick bridge plate steel plate of Q345q series as claimed in claim 2, in said converter smelting, tapping carbon>=0.06%, tapping P≤0.012%, S≤0.012%; Point blows number of times and must not avoid slag under the tapping process greater than 2 times.
4. the working method of the special thick bridge steel plate of Q345q series as claimed in claim 2 is characterized in that in said LF refining, taking the big quantity of slag to carry out slag making, guarantees that the white slag hold-time is controlled at more than the 15min.
5. the working method of the special thick bridge steel plate of Q345q as claimed in claim 2 series is characterized in that in said vacuum refinement, and the dwell time under≤67Pa is controlled by>=10min.
6. the working method of the special thick bridge steel plate of Q345q series as claimed in claim 2 is characterized in that pining in said adding, and the holding temperature of dead soaking pit is controlled at 1200 ℃～1300 ℃.
7. the working method of the special thick bridge steel plate of Q345q as claimed in claim 3 series is characterized in that in said control is cold, returns red temperature＜740 ℃, and cooling rate is controlled at 5～15 ℃/s.
8. the working method of the special thick bridge steel plate of Q345q as claimed in claim 3 series is characterized in that in said slow cooling, goes into burial pit temperature >=300 ℃; Cooling in heap time >=24 hour.
9. the working method of the special thick bridge steel plate of Q345q series as claimed in claim 3 is characterized in that in said thermal treatment holding temperature: 910 ± 30 ℃; Heat-up time: 1.5-2.5min/mm; The type of cooling: air cooling or air-cooled.
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