CN101649422B - Niobium microalloyed hot rolled steel band and manufacturing method thereof - Google Patents
Niobium microalloyed hot rolled steel band and manufacturing method thereof Download PDFInfo
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Abstract
The invention relates to a niobium microalloyed hot rolled steel band and a manufacturing method thereof. The niobium microalloyed hot rolled steel band contains the following ingredients in percentage by weight: C more than 0while less than or equal to 0.005, N more than 0 while less than or equal to 0.004, Si more than 0 while less than or equal to 0.03, Mn 0.10-0.20, P more than 0 while less than or equal to 0.018, S more than 0 while less than or equal to 0.015, Al 0.02-0.06, Nb more than 0 while less than or equal to 0.020, O more than 0 while less than or equal to 0.002, Cr more than 0 while less than or equal to 0.05, Ni more than 0 while less than or equal to 0.07, Cu more than 0 while less than or equal to 0.07 and Mo more than 0 while less than or equal to 0.020. The manufacturing method comprises the following steps: preparing a continuous casting blank by the ingredients as required, and processing the continuous casting blank into the hot rolled steel band; heating the continuous casting blank to more than 1200 DEG C during hot rolling with heat preservation time is longer than 2.5 hours by adopting a weak reducing atmosphere; keeping the finished rolling temperature of the hot rolled steel band 880-930 DEG C; rapidly water-cooling the hot rolled steel band to 680-750 DEG C after the finished rolling, rolling, controlling a steel coiled tower shape to be less than or equal to 50mm, and then cooling the hot rolled steel band to room temperature in air. The niobium microalloyed hot rolled steel band prepared by the manufacturing method has good surface quality.
Description
Technical field
A kind of niobium microalloyed hot rolled steel band and manufacture method thereof.
Background technology
Automotive industry is the mainstay industry of developed country's economy all the time, also is the important industry of some developing countries.Since calendar year 2001,, the demand of automobile steel has been risen significantly along with the fast development of Domestic Automotive Industry.Automobile steel is still based on steel plate at present, and wherein car accounts for 50% of car gross weight with steel plate weight.
Along with the development with the car manufacturing technology of improving constantly to the car service requirements, from the punching performance aspect, car with steel plate by the first-generation punching press steel that with the low-carbon (LC) rimming steel is representative, the s-generation punching press that with the carbon aluminium-killed steel is representative has developed into Ultra-low carbon with steel, nitrogen IF steel is the third generation punching press steel of representative, IF steel (Interstitial Free Steel) is a gapless atomic steel, be at ultralow C, add a certain amount of Nb or Ti or Nb in the N steel, the Ti alloying element, make C in the steel, the N atom is fixed to carbide, nitride, and the steel grade that gap-free atom exists in the steel, the IF steel has extremely good deep drawability.From condition of surface, car is just developed to surface treated steel plates such as hot-dip galvanizing sheet steel, alloyed hot-dip galvanized steel sheet, aludip, electrogalvanizing steel plate, electroplated zinc nickel alloy steel plate, electroplating zinc-iron alloy steel plate and organic coating-plating layer steel plates by cold-reduced sheet with steel plate, and the usage ratio on car strengthens gradually.The surface quality of steel plate not only influences the outward appearance of fabricated part, and also can produce obvious influence to the punching performance of steel plate.According to the finished surface quality grade, Deutsche Industry Norm DIN1623 is divided into O3, O4 and O5 plate with car with steel plate, wherein the O5 plate is called surperficial zero defect steel plate again, requires promptly in two of the products preferably that one side must not have any defective, can not influence the japanning back or electroplate after visual appearance.The O5 plate is one of kind of production difficulty maximum in the car usefulness steel plate as the car outside plate all the time, and enterprise classifies its production technique as the core technology secret, and its details can't be understood by the external world.
The production process of existing micro-alloyed hot rolled steel strip relates to the hot continuous rolling operation.Surface imperfection on the hot rolled strip that the hot continuous rolling operation forms can be divided into two classes, one class is the iron scale defective, comprise that pit, bateau shape iron scale are pressed into, the strip iron scale is pressed into, the crude iron squama is pressed into and red iron scale etc., can't remove in wherein moderate iron scale defective or the serious pickling of iron scale defective before cold rolling, not only limit pickling speed, and caused cold rolling finished product degradation; Another kind of defective is various types of mechanical impression defectives, comprise that scuffing, scratch, foreign matter are pressed into, shaggy block etc., wherein moderate mechanical impression defective or serious mechanical impression defective also can produce detrimentally affect to surface quality, processability and the lumber recovery of finished product cold-rolled steel strip.(surface quality according to its severity be divided into zero defect, do not influence the minor defects of use, moderate defective and four kinds of surface quality grades of major defect.)
Though before the present invention, disclose the patent of invention of a plurality of relevant IF steel, do not found report as yet about great surface quality Nb microalloying IF hot rolled strip and manufacture method thereof.
On November 29th, 2007, the disclosed patent No. was " Method andInstallation for the Production of Steel Products Having an OptimumSurface Quality " patent of US2007272054 (A1), provide an employing electric furnace-CSP abbreviated system route to produce the technology of excellent surface quality IF steel, but be not provided at the detailed technology that the hot continuous rolling operation should be taked.
On June 6th, 2007, the disclosed patent No. was " a kind of CSP is produced the production technique of IF steel " patent of invention of CN1974824, a technology of producing Ti microalloying IF steel based on converter-CSP abbreviated system route is provided, does not also provide to make hot rolled strip have the technology of great surface quality.
Summary of the invention
In order to overcome the above-mentioned deficiency of existing micro-alloyed hot rolled steel strip, the invention provides the good niobium microalloyed hot rolled steel band of a kind of surface quality, a kind of manufacture method of this steel band is provided simultaneously.
In order to achieve the above object, and solve in moderate iron scale defective in hot rolled strip surface or the serious pickling of iron scale defective before cold rolling and can't remove, restriction pickling speed, cause the problem of cold rolling finished product degradation, mechanical impression defective that while is moderate for fear of the hot rolled strip surface or serious mechanical impression defective are to finished product cold-rolled steel strip surface quality, the detrimentally affect that processability and lumber recovery produce, the present invention produces a kind of great surface quality Nb microalloying IF hot rolled strip mainly by the rational Match of chemical ingredients and hot rolling technology system.
The mass percent proportioning of this niobium microalloyed hot rolled steel band is:
0＜C≤0.00 50＜P≤0.018 0＜S≤0.015 0＜N≤0.004
0＜Si≤0.03 Mn：0.10～0.20 Al：0.02～0.06 0＜Nb≤0.020
0＜Cr≤0.050＜ Ni≤0.07 0＜Cu≤0.070＜ Mo≤0.020
All the other are Fe and unavoidable impurities.
Its surface quality grade is zero defect or has the minor defects that do not influence use.
General width is 1000～2130mm, thickness 3.0-5.0mm.
This niobium microalloyed steel continuous casting base is heating in weak reducing atmosphere, insulation at first, so that austenite homogenizing, then remove the once oxidation iron sheet fully through roughing and by the roughing descaling device, last finish rolling becomes hot rolled strip, hot rolled strip through quick water-cooled, batch and in air cool to room temperature, obtain tiny and uniform ferrite crystal grain and thick sparse precipitate.
This niobium microalloyed hot rolled steel band is when finish rolling, and finishing train roll cooling water inflow is greater than 450m
3/ h, finishing train draft: F1:40-50%, F2:30-40%, F3:25-35%, F4:23-33%, F5:18.5-28.5%, F6:13.5-23.5%, F7:6-16%, 880-930 ℃ of hot rolled strip finishing temperature, to realize ausrolling, finished product hot rolled strip thickness 3.0-5.0mm.After the hot rolled strip finish to gauge fast water-cooled batch to 680-750 ℃, to obtain tiny and uniform ferrite crystal grain and thick sparse precipitate, control coil of strip turriform≤50mm, cool to room temperature then.
The qualification of the chemical ingredients of this niobium microalloyed hot rolled steel band be the reasons are as follows:
C forms interstitial solid solution in steel, have significant solution strengthening effect, and along with the raising of C content, the yield strength of steel, tensile strength and hardness increase, but plasticity and processability obviously descend.Along with the raising of solid solution C content in the steel,＜111〉texture density reduce, and finished product timeliness tendency strengthens.Therefore, limit C content and must not be higher than 0.005%.
N is the same with C, and solid solution forms interstitial solid solution in Fe, and has significant solution strengthening effect equally, and yield strength, tensile strength and the hardness of steel are increased, and the plasticity of steel and processability are descended.Along with the reduction of temperature, the solubleness of N in ferrite sharply reduces, and how to separate out at crystal boundary with the AlN form, suppresses the ferrite crystal grain growth, improves yield strength, tensile strength and the hardness of steel, reduces its plasticity and processability.N also makes steel produce the strain aging phenomenon.Therefore, limit N content and must not be higher than 0.004%.
The Si solid solution forms substitutional solid solution in Fe, its solution strengthening ability is only second to P, can effectively improve the intensity of steel, but also reduces the plasticity and the toughness of steel simultaneously to a certain extent.When Si content is high, form the red iron scale that is difficult to remove on the hot rolled strip surface easily.Si is easier to be more oxidized than iron, can be in the recrystallization annealing process at surface of steel plate generation selective oxidation reaction, its oxidation products easily is enriched in surface of steel plate, this not only can influence the pot galvanize effect, and the alloying reaction sluggishness can make pot galvanize the time, cause making the anti-efflorescence ability drop of zinc layer of heat zinc coating plate because of high-temperature alloy.Therefore, limit Si content and must not be higher than 0.03%.
Mn in steel with the Fe formation sosoloid that dissolves each other, its solution strengthening ability is lower than P and Si, Mn and solid solution C coexistence can reduce the deep drawing quality of steel.Mn is good sweetening agent, can weaken or eliminate the red brittleness of the steel that causes because of S, improves the hot workability of steel.Mn content is crossed to hang down and not only can be made cost up, also easily increases the hot-short tendency of steel.Therefore, Mn content is limited to the 0.10%-0.20% scope.
Compare with other element, P is the strongest element of solution strengthening ferrite ability, and along with the raising of P content, the yield strength of steel, tensile strength and hardness significantly increase, but plasticity, processability and toughness, especially low-temperature flexibility but obviously descend.P is easily segregation in steel, and the homogeneity of infringement steel plate tissue causes formation of crack.P also can make the alloying reaction sluggishness in the hot galvanizing process at grain boundary segregation, thus the same problem that makes the anti-efflorescence ability drop of heat zinc coating plate zinc layer because of high-temperature alloy that produces.Therefore, limit P content and must not be higher than 0.018%.
S is little to the intensity and the plasticity influence of steel.The solubleness of S in ferrite is very low, and many forms with sulfide inclusion exist in steel, and these inclusiones can reduce the plasticity and the toughness of steel, make it produce tangible anisotropy, and cause finished surface and latent defect.S easily makes steel produce red brittleness, the hot workability of severe exacerbation steel.The easy segregation of S, the homogeneity of obvious damage steel plate tissue and quality is to make one of major reason that steel plate cracks.Therefore, limit S content and must not be higher than 0.015%.
Al and O have very strong avidity, generally Al are added in the steel as main reductor during smelting.Al and N also have stronger avidity, can play solid solution N in the fixing steel, eliminate the effect by the strain aging of its generation.But the alloying reaction speed when the too high meeting of Al content reduces pot galvanize in the steel also improves the alloying temperature.Therefore, Al content is limited to the 0.02%-0.06% scope.
Nb and O, C, N all have very strong avidity, can be respectively and the stable compound of its formation.Add Nb be in the IF steel in order to remove C in the steel, N atom, to obtain purified ferrite matrix, the characteristics of Nb microalloying IF steel are that the mechanical property anisotropy is less, and the anti-efflorescence ability of coating is stronger.If but the add-on of Nb is too high, also can cause cost to increase and the recrystallization temperature raising.Therefore, limit Nb content and must not be higher than 0.02%.
O is an indispensable one of the chief elements in the smelting process, especially in converter steelmaking.Be solid-solubilized in the steel O seldom, most of O exists with the form of various oxide inclusion in the steel, and these inclusiones are separated out at intracrystalline or crystal boundary, reduces plasticity, processability and the surface quality of steel, may cause the red brittleness of steel when serious, generally O be treated as the harmful element in the steel.Therefore, limit O content and must not be higher than 0.002%.
Cr, Ni, Cu, Mo all can play solution strengthening effect to a certain degree, improve the yield strength of steel, reduce its plasticity and processability, and Mo can also improve the recrystallization temperature of steel.Therefore, limit Cr content and must not be higher than 0.05%, Ni content must not be higher than 0.07%, and Cu content must not be higher than 0.07%, and Mo content must not be higher than 0.02%.
The manufacture method of this niobium microalloyed hot rolled steel band comprises following sequential steps:
A prepares continuously cast bloom:
By molten iron pretreatment desulfurizing, top bottom blowing converter smelting, RH refining and heavy slab continuous casting, the quality per distribution ratio of the chemical ingredients of the continuously cast bloom of acquisition is:
0＜C≤0.005 0＜P≤0.018 0＜S≤0.015 0＜N≤0.004
0＜Si≤0.03 Mn：0.10～0.20 Al：0.02～0.06 0＜Nb≤0.020
0＜Cr≤0.05 0＜Ni≤0.07 0＜Cu≤0.070＜ Mo≤0.020
All the other are Fe and unavoidable impurities.
Require continuously cast bloom not have the inside and outside defective that influences hot rolled strip, cold-rolled steel strip processability and surface quality.
B adopts the traditional hot continuous rolling process that continuously cast bloom is processed into hot rolled strip
Rolling unit must not be greater than 2500 tons, and general 1800-2400 ton is checked hot continuous mill roller-way completely comprehensively, changes the roller that does not rotate or be out of shape.Carry out cleaning works between the finishing train frame, prevent that milling train from bringing foreign matter into.Guarantee that the nozzle de-scaling is unimpeded, prevent that descaling sprays from lagging behind de-scaling water pressure＞18MPa.
Continuously cast bloom heats in walking beam furnace, and Heating temperature is not less than 1200 ℃, and soaking time is not shorter than 2.5 hours, makes the austenite homogenizing, adopts the weak reducing atmosphere heating.The continuously cast bloom that heats is removed the once oxidation iron sheet through the roughing and the hot-work in two stages of finish rolling fully by the roughing descaling device.Finishing train roll cooling water inflow is not less than 450m
3/ h, finishing train draft: F1:40-50%, F2:30-40%, F3:25-35%, F4:23-33%, F5:18.5-28.5%, F6:13.5-23.5%, F7:6-16%, 880-930 ℃ of hot rolled strip finishing temperature, to realize ausrolling, finished product hot rolled strip thickness 3.0-5.0mm.After the hot rolled strip finish to gauge fast water-cooled batch to 680-750 ℃, obtaining tiny and uniform ferrite crystal grain and thick sparse precipitate, control coil of strip turriform≤50mm, and then in air cool to room temperature.
Beneficial effect of the present invention is, rational Match by chemical ingredients and hot rolling technology system, produce a kind of great surface quality Nb microalloying IF hot rolled strip, its surface quality grade is zero defect or has the minor defects that do not influence use, avoided on hot rolled strip, forming pit, bateau shape iron scale is pressed into, the strip iron scale is pressed into, the crude iron squama is pressed into and moderate iron scale defective such as red iron scale or serious iron scale defective, has avoided scuffing simultaneously, scratch, foreign matter is pressed into, mechanical impression defective that shaggy block etc. are moderate or serious mechanical impression defective.With this hot rolled strip is the raw material production cold-rolled steel strip, pickling efficient and lumber recovery height, and the finished product cold-rolled steel strip has favorable surface quality, and surface roughness value Ra is 0.6-1.6 μ m, is applied to industries such as automobile, household electrical appliances manufacturing.
Embodiment
Describe the concrete of this niobium microalloyed hot rolled steel band and manufacture method thereof in detail below in conjunction with embodiment
Embodiment, but the embodiment of this niobium microalloyed hot rolled steel band and manufacture method thereof is not limited to
In following embodiment.
The working condition of following embodiment is the hot metal pretreatment facility, 180 tons of top bottom blowing converters, RH a refining unit, heavy slab continuous caster, semi continuous tradition hot rolled strip production line.
Nb microalloying IF hot rolled strip chemical analysis method is GB/T 223, sampling method GB/T 222.
With the online surface quality tester of Parsytec, according to GB/T 14977 " general requirement of hot-rolled steel sheet surface quality ", detect the surface quality of Nb microalloying IF hot rolled strip, and determine its surface quality grade.
Steel band embodiment one
The thick 3.0mm of the niobium microalloyed hot rolled steel band of present embodiment, the quality per distribution ratio of chemical ingredients is:
C：0.0015 N：0.0019 Si：0.009 Mn：0.13 P：0.006
S：0.004 Al：0.05 Nb：0.016 Cr：0.01 Ni：0.01
Cu:0.01 Mo:0.001, all the other are Fe and unavoidable impurities.
Its surface quality grade is zero defect or has the minor defects that do not influence use.
Steel band embodiment two
The thick 4.0mm of the niobium microalloyed hot rolled steel band of present embodiment, the quality per distribution ratio of chemical ingredients is:
C：0.0013 N：0.0018 Si：0.01 Mn：0.145 P：0.007
S：0.0035 Al：0.043 Nb：0.014 Cr：0.01 Ni：0.01
Cu:0.01 Mo:0.0023, all the other are Fe and unavoidable impurities.
Its surface quality grade is zero defect or has the minor defects that do not influence use.
Steel band embodiment three
The thick 5.0mm of the niobium-titanium composite micro-alloyed hot rolled steel strip of present embodiment, the quality per distribution ratio of chemical ingredients is:
C：0.0012 N：0.0015 Si：0.005 Mn：0.149 P：0.0063
S：0.0045 Al：0.051 Nb：0.0146 Cr：0.015 Ni：0.013
Cu:0.01 Mo:0.0022, all the other are Fe and unavoidable impurities.
Its surface quality grade is zero defect or has the minor defects that do not influence use.
Steel band preparation method embodiment one
The present embodiment manufacturing be steel band embodiment one, the manufacture method of present embodiment comprises following sequential steps:
A prepares continuously cast bloom:
By molten iron pretreatment desulfurizing, 180 tons of top bottom blowing converter smeltings, RH refining and heavy slab continuous castings, the quality per distribution ratio of the chemical ingredients of the continuously cast bloom of acquisition is:
C：0.0015 N：0.0019 Si：0.009 Mn：0.13 P：0.006
S：0.004 Al：0.05N b：0.016 Cr：0.01 Ni：0.01
Cu:0.01 Mo:0.001, all the other are Fe and unavoidable impurities.
Require continuously cast bloom not have the inside and outside defective that influences hot rolled strip, cold-rolled steel strip processability and surface quality.
B adopts the traditional hot continuous rolling process that continuously cast bloom is processed into hot rolled strip
2150 tons of rolling units are checked hot continuous mill roller-way completely comprehensively, change the roller that does not rotate or be out of shape.Carry out cleaning works between the finishing train frame, prevent that milling train from bringing foreign matter into.Guarantee that the nozzle de-scaling is unimpeded, prevent that descaling sprays from lagging behind de-scaling water pressure＞18MPa.Continuously cast bloom is heated to 1220 ℃ in walking beam furnace, soaking time 3 hours makes the austenite homogenizing, adopts the weak reducing atmosphere heating.The continuously cast bloom that heats is removed the once oxidation iron sheet through the roughing and the hot-work in two stages of finish rolling fully by the roughing descaling device.Finishing train roll cooling water inflow 510m
3/ h, finishing train draft: F1:44.8%, F2:35.8%, F3:31.6%, F4:28.3%, F5:23.3%, F6:18.2%, F7:11.1%, 900 ℃ of hot rolled strip finishing temperatures, finished product hot rolled strip thickness 3.0mm.After the hot rolled strip finish to gauge fast water-cooled to 690 ℃ batch, coil of strip turriform 45mm, and then in air cool to room temperature.
Online surface quality tester check result shows that this hot rolled strip surface quality grade is zero defect or has the minor defects that do not influence use.
Steel band preparation method embodiment two
The present embodiment manufacturing be steel band embodiment two, the manufacture method of present embodiment comprises following sequential steps:
A prepares continuously cast bloom:
By molten iron pretreatment desulfurizing, 180 tons of top bottom blowing converter smeltings, RH refining and heavy slab continuous castings, the quality per distribution ratio of the chemical ingredients of the continuously cast bloom of acquisition is:
C：0.0013 N：0.0018 Si：0.01 Mn：0.145 P：0.007
S：0.0035 Al：0.043 Nb：0.014 Cr：0.01 Ni：0.01
Cu:0.01 Mo:0.0023, all the other are Fe and unavoidable impurities.
Require continuously cast bloom not have the inside and outside defective that influences hot rolled strip, cold-rolled steel strip processability and surface quality.
B adopts the traditional hot continuous rolling process that continuously cast bloom is processed into hot rolled strip
2380 tons of rolling units are checked hot continuous mill roller-way completely comprehensively, change the roller that does not rotate or be out of shape.Carry out cleaning works between the finishing train frame, prevent that milling train from bringing foreign matter into.Guarantee that the nozzle de-scaling is unimpeded, prevent that descaling sprays from lagging behind de-scaling water pressure＞18MPa.Continuously cast bloom is heated to 1230 ℃ in walking beam furnace, soaking time 3 hours makes the austenite homogenizing, adopts the weak reducing atmosphere heating.The continuously cast bloom that heats is removed the once oxidation iron sheet through the roughing and the hot-work in two stages of finish rolling fully by the roughing descaling device.Finishing train roll cooling water inflow 500m
3/ h, finishing train draft: F1:45.1%, F2:35.1%, F3:29.3%, F4:26.6%, F5:21.3%, F6:16.3%, F7:10.3%, 905 ℃ of hot rolled strip finishing temperatures, finished product hot rolled strip thickness 4.0mm.After the hot rolled strip finish to gauge fast water-cooled to 700 ℃ batch, coil of strip turriform 40mm, and then in air cool to room temperature.
Online surface quality tester check result shows that this hot rolled strip surface quality grade is zero defect or has the minor defects that do not influence use.
Steel band preparation method embodiment three
The present embodiment manufacturing be steel band embodiment three, the manufacture method of present embodiment comprises following sequential steps:
A prepares continuously cast bloom:
By molten iron pretreatment desulfurizing, 180 tons of top bottom blowing converter smeltings, RH refining and heavy slab continuous castings, the quality per distribution ratio of the chemical ingredients of the continuously cast bloom of acquisition is:
C：0.0012 N：0.0015 Si：0.005 Mn：0.149 P：0.0063
S：0.0045 Al：0.051 Nb：0.0146 Cr：0.015 Ni：0.013
Cu:0.01 Mo:0.0022, all the other are Fe and unavoidable impurities.
Require continuously cast bloom not have the inside and outside defective that influences hot rolled strip, cold-rolled steel strip processability and surface quality.
B adopts the traditional hot continuous rolling process that continuously cast bloom is processed into hot rolled strip
1950 tons of rolling units are checked hot continuous mill roller-way completely comprehensively, change the roller that does not rotate or be out of shape.Carry out cleaning works between the finishing train frame, prevent that milling train from bringing foreign matter into.Guarantee that the nozzle de-scaling is unimpeded, prevent that descaling sprays from lagging behind de-scaling water pressure＞18MPa.Continuously cast bloom is heated to 1210 ℃ in walking beam furnace, soaking time 3 hours makes the austenite homogenizing, adopts the weak reducing atmosphere heating.The continuously cast bloom that heats is removed the once oxidation iron sheet through the roughing and the hot-work in two stages of finish rolling fully by the roughing descaling device.Finishing train roll cooling water inflow 490m
3/ h, finishing train draft: F1:43.9%, F2:33.6%, F3:31.6%, F4:26.1%, F5:21.3%, F6:17.1%, F7:10.8%, 910 ℃ of hot rolled strip finishing temperatures, finished product hot rolled strip thickness 5.0mm.After the hot rolled strip finish to gauge fast water-cooled to 710 ℃ batch, coil of strip turriform 35mm, and then in air cool to room temperature.
Online surface quality tester check result shows, this hot rolled strip surface quality grade is zero defect or has the minor defects that do not influence use, surface quality with its cold rolling finished product that is processed into has reached Deutsche Industry Norm DIN 1623 cars O5 plate, is called the requirement of surperficial zero defect steel plate again.
Claims (3)
1. niobium microalloyed hot rolled steel band, its mass percent proportioning is:
0＜C≤0.005 0＜N≤0.004 0＜Si≤0.03 Mn：0.10～0.20
0＜P≤0.018 0＜S≤0.015 Al：0.02～0.06 0＜Nb≤0.020
0＜O≤0.002 0＜Cr≤0.05 0＜Ni≤0.07 0＜Cu≤0.07
0＜Mo≤0.020, all the other are Fe and unavoidable impurities;
Its surface quality grade is zero defect or has the minor defects that do not influence use;
Used continuously cast bloom is heating in weak reducing atmosphere, insulation at first, so that austenite homogenizing, then remove the once oxidation iron sheet fully through roughing and by the roughing descaling device, last finish rolling becomes hot rolled strip, hot rolled strip through quick water-cooled, batch and in air cool to room temperature, obtain tiny and uniform ferrite crystal grain and thick sparse precipitate.
2. the manufacture method of niobium microalloyed hot rolled steel band according to claim 1, it comprises following sequential steps:
A prepares continuously cast bloom:
By molten iron pretreatment desulfurizing, top bottom blowing converter smelting, RH refining and heavy slab continuous casting, the quality per distribution ratio of the chemical ingredients of the continuously cast bloom of acquisition is:
0＜C≤0.005 0＜N≤0.004 0＜Si≤0.03 Mn：0.10～0.20
0＜P≤0.018 0＜S≤0.015 Al：0.02～0.06 0＜Nb≤0.020
0＜O≤0.002 0＜Cr≤0.05 0＜Ni≤0.07 0＜Cu≤0.07
0＜Mo≤0.020, all the other are Fe and unavoidable impurities;
Require continuously cast bloom not have the inside and outside defective that influences hot rolled strip, cold-rolled steel strip processability and surface quality;
B is processed into hot rolled strip with continuously cast bloom;
Continuously cast bloom heats in walking beam furnace, and Heating temperature is not less than 1200 ℃, and soaking time is not shorter than 2.5 hours, makes the austenite homogenizing, adopts the weak reducing atmosphere heating; The continuously cast bloom that heats is through the roughing and the hot-work in two stages of finish rolling, and 880-930 ℃ of hot rolled strip finishing temperature is to realize ausrolling; After the hot rolled strip finish to gauge fast water-cooled batch to 680-750 ℃, obtaining tiny and uniform ferrite crystal grain and thick sparse precipitate, control coil of strip turriform≤50mm, and then in air cool to room temperature;
Remove the once oxidation iron sheet fully by the roughing descaling device, finishing train roll cooling water inflow is greater than 450m
3/ h;
Finishing train draft: F1:40-50%, F2:30-40%, F3:25-35%, F4:23-33%, F5:18.5-28.5%, F6:13.5-23.5%, F7:6-16%.
3. the manufacture method of niobium microalloyed hot rolled steel band according to claim 2 is characterized in that:
A prepares continuously cast bloom:
By molten iron pretreatment desulfurizing, top bottom blowing converter smelting, RH refining and heavy slab continuous casting, the quality per distribution ratio of the chemical ingredients of the continuously cast bloom of acquisition is:
C：0.0015 N：0.0019 Si：0.009 Mn：0.13 P：0.006
S：0.004 Al：0.05 Nb：0.016 Cr：0.01 Ni：0.01
Cu:0.01 Mo:0.001, all the other are Fe and unavoidable impurities.
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