CN102251170A - Ultrahigh-strength bainitic steel and manufacture method thereof - Google Patents
Ultrahigh-strength bainitic steel and manufacture method thereof Download PDFInfo
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Abstract
The invention discloses a low-carbon bainitic steel, comprising the following chemical compositions in percentage by weight: C 0.05-0.14%, Si 0.1%-0.5%, Mn 1.2%-2.0%, P <=0.015%, S <= 0.010%, Al 0.01%-0.05%, and N <=0.005%, and further comprising: at least one alloy element of Nb 0.015-0.070%, Ti 0.02-0.15%, and V 0.10-0.20%, and at least one alloy element of Cr 0.15-0.50%, and Mo 0.15-0.50%, and the balance of ferrum and unavoidable impurities; and the coiling temperature in the manufacture process is controlled between 430-630 DEG C. Therefore, the ultrahigh-strength bainitic steel plate with good cold bending property can be obtained and is applicable to manufacturing products such as automobile chassises, suspension parts, fender-guards and the like.
Description
Technical field
The present invention relates to bainitic steel, particularly relate to a kind of low-carbon bainite steel and hot-rolled steel sheet and steel band and manufacture method thereof of superstrength.Bainite steel plate of the present invention and steel band are mainly used in products such as making automobile chassis, suspender, collision bumper.
Background technology
Automobile " lightweight " can directly reduce discharging, reduces oil consumption, is the target of current automobile industry development.In the past ten years, because the raising that aspects such as comfortableness and safety performance require, the weight of automobile increases year by year.An important measures of automobile " lightweight " is exactly to adopt the steel plate of high-strength steel and superstrength to replace mild steel.Can realize 20～25% weight loss effect behind a large amount of employing high-strength steel.
At present, automobile mainly contains the dual phase steel that has intensity and unit elongation concurrently with super-high strength steel (tensile strength is not less than 700MPa), it is organized as ferrite (F) and martensite (M), the high TRIP steel of unit elongation, it is organized as ferrite (F), martensite (M) and residual austenite (A is residual) and the high martensitic steel of intensity, and it is organized as M and a small amount of F.Yet, because the moulding process of automobile steel is very complicated, although these steel grades have shown excellent performance in Elongation test, but do not have enough crystallized abilities in crooked and stretch flanging process, bainitic steel is because good clod wash and reaming performance are expected to become the complicated automobile structure such as the alternative steel grade of parts such as automobile chassis, suspender, B post and collision bumper, automotive seat.
Publication number is that the Chinese patent application of CN 1786245A discloses high tensile strength low carbon bainite thick steel plate and production method thereof.Publication number is that China's application of CN 1982491A discloses low-carbon tungsten-system bainite steel and production method thereof.Method in these two applications all adopts controlled rolling and cooling (TMCP)+tempering (T) technology, is used for the slab of 12 above～60mm of production tensile strength 800MPa.
Publication number is that the patent application of CN 1786247A discloses high toughness low carbon bainite thick steel plate and production method thereof, this method employing TMCP+ relaxation-separate out-control the technology of phase change technique (RPC)+T, production intensity is 600MPa and other slab of 700MPa level.
Publication number be the Chinese patent application of CN 1218115A to disclose a kind of copper boron be low-carbon (LC) and ULCB high-strength steel, it adopts the TMCP+T explained hereafter to be lower than the ultra-low-carbon bainite steel of 700MPa.
Publication number is the preparation method that the Chinese patent application of CN 1916195A discloses a kind of ultra high temperature bainitic steel in ultralow carbon, and it is by forging+cold pressing+thermal treatment process production 600MPa and other ultra-low-carbon bainite steel of 750MPa level.
Publication number is that the Chinese patent application of CN 1521285A discloses a kind of ultra-low-carbon bainite steel and production method thereof, and its explained hereafter 420MPa rank that adopts TMCP+RPC+T is to other ultra-low-carbon bainite steel of 690MPa level.
Publication number is that the Chinese patent application of CN1330166A discloses a kind of microalloyed low-carbon bainite ferrite steel and manufacture method thereof, and it adopts N and B is strengthening element, obtains the low-carbon microalloyed non-hardened and tempered steel of bainite ferrite tissue.
More than the related product of patent of each low-carbon bainite and ultra-low-carbon bainite steel be slab or large section workpiece, adopt RPC and/or tempering process to obtain finished product after the hot rolling, its described manufacturing process also is not suitable for the auto sheet production line.
Summary of the invention
The object of the present invention is to provide a kind of low-carbon bainite steel of superstrength.
" superstrength " among the present invention is meant that tensile strength is not less than 700MPa.
For achieving the above object, technical scheme of the present invention is as follows.
The hot-rolled low carbon bainitic steel of superstrength of the present invention, its chemical component weight per-cent is: C:0.05%～0.14%, Si:0.1%～0.5%, Mn:1.2%～2.0%, P :≤0.015%, S :≤0.010%, Al:0.01%～0.05%, N :≤0.005%, also comprise Nb:0.015～0.07%, Ti:0.02～0.15%, at least a alloying element in V:0.10～0.20%, and Cr:0.15～0.50%, at least a alloying element in Mo:0.15～0.50%, and remainder is iron and unavoidable impurities.
The manufacturing of the hot-rolled low carbon bainitic steel of superstrength of the present invention is on the automobile steel production line basis of routine, and the control coiling temperature is 430～630 ℃.
Preferably, Nb:0.04～0.07%.
Preferably, Ti:0.025～0.110%.
Preferably, Mo:0.02～0.45%.
Preferably, Cr:0.21～0.45%.
Preferably, V:0.14～0.20%.
Another object of the present invention provides the hot-rolled low carbon bainitic steel hot-rolled steel sheet of superstrength or the manufacture method of steel band.
For realizing this purpose, preferably, the hot-rolled low carbon bainitic steel hot-rolled steel sheet of superstrength of the present invention or the manufacture method of steel band comprise:
A) smelting and continuous casting: with weight percent be: C:0.05%～0.14%, Si:0.1%～0.5%, Mn:1.2%～2.0%, P :≤0.015%, S :≤0.010%, Al:0.01%～0.05%, N :≤0.005%, also comprise Nb:0.015～0.07%, Ti:0.02～0.15%, at least a alloying element in V:0.10～0.20%, and Cr:0.15～0.50%, at least a alloying element in Mo:0.15～0.50%, and remainder is that the composition of iron and unavoidable impurities is smelted continuous casting;
B) rolling technology: to the continuous casting steel billet heating, Heating temperature is 1100～1250 ℃, carries out controlled rolling afterwards; The finish rolling start rolling temperature is 950～1000 ℃, and the finish rolling finishing temperature is 800～950 ℃; Hot-rolled sheet thickness is not more than 8mm;
C) roll postcooling technology: blank behind the rolling is carried out water cooling, and speed of cooling is not less than 30 ℃/s, and coiling temperature is 430～630 ℃.The cooling back obtains the hot-rolled sheet finished product;
Preferably, speed of cooling is 30～100 ℃.
Preferably, hot-rolled sheet can further obtain the acid-cleaning plate finished product through overpickling.
Preferably, hot-rolled sheet also can obtain hot rolling hot-galvanized steel board finished product through pot galvanize.
Another purpose of the present invention provides a kind of hot-rolled low carbon bainitic steel hot-rolled steel sheet or steel band of the superstrength of being made by above-mentioned manufacture method, and further will obtain acid-cleaning plate after the hot-rolled sheet pickling, or will obtain the hot rolling hot-dip galvanizing sheet steel after the pot galvanize of hot-rolled sheet process.
Bainite content 〉=95% of these hot-rolled sheets, steel band, acid-cleaning plate and hot rolling hot-dip galvanizing sheet steel, tensile strength 〉=700MPa.
In order to make hot-rolled sheet have superstrength (tensile strength is not less than 700MPa), and obtain bainite structure, the present invention selects the kind of above alloying element and the reasons are as follows of content:
C：0.05％～0.14％
Carbon is very big to intensity, forming property and the welding property influence of steel plate.The intensity that carbon is lower than 0.05% steel does not reach target call; Carbon is higher than 0.14%, and then the bainite structure that generates reduces, and easily generates martensitic stucture, unit elongation and hole expansibility are descended, so the present invention determines that the scope of carbon content is 0.05%～0.14%.
Si：0.1％～0.5％
Silicon is the bioelement of deoxidation in steel making, also has certain solution strengthening effect, when being lower than 0.1%, is difficult to obtain sufficient deoxidation effect; When silicone content is higher than 0.5%, be easy to generate the polygonal ferrite tissue, be unfavorable for the acquisition of bainite structure.So the present invention is limited to silicone content in 0.1%～0.5% the scope.
Mn：1.2％～2.0％
Manganese be the effective element that improves intensity and obtain bainite structure, bainite transformation is had builds big promoter action, and with low cost, thus the present invention with manganese as main adding elements.Manganese content is limited to 1.51%～2.0%.
Al：0.01％～0.05％
Aluminium has the effect of deoxidation in steelmaking process, be the element that adds in order to improve the molten steel purity.The aluminium fixedly nitrogen in the steel makes it to form stable compound, effective crystal grain thinning, and its content was less than 0.01% o'clock, and effect is less, surpasses at 0.05% o'clock, and desoxydatoin reaches capacity, and high more then have negative impact to mother metal and welded heat affecting zone.So aluminium content is limited to 0.01%～0.05%.
Nb：0.015～0.07％；
Niobium is the important interpolation element among the present invention, and it is the austenitic recrystallize of delayed deformation effectively, stops growing up of austenite crystal, improves austenite recrystallization temperature, and crystal grain thinning improves intensity and unit elongation simultaneously; It can promote bainite transformation with the boron compound action of trace.But content of niobium is higher than at 0.07% o'clock, cost is increased, and effect is no longer remarkable, so content of niobium is limited to below 0.07% among the present invention.Preferably, Nb:0.04～0.07%.
Ti：0.02～0.15％
Titanium forms tiny double carbide, stops austenite crystal to be grown up, and crystal grain thinning also can play the effect of precipitation strength.Do not reduce unit elongation and hole expansibility when improving the intensity of steel, but titanium content is greater than after 0.15%, it is not remarkable to increase its content effect again, so titanium content is limited to below 0.15% among the present invention.Ti content is less than not having crystal grain thinning and precipitation strength effect at 0.02% o'clock.Preferably, Ti:0.025～0.110%.
V：0.10～0.20％
The effect of vanadium is to form carbide, improves the intensity of steel, but content of vanadium is greater than after 0.20%, and it is not remarkable to increase its content effect again, so content of vanadium is limited to below 0.20% among the present invention.V content is not remarkable less than 0.10% o'clock precipitation strength effect.Preferably, V:0.14～0.20%.
Cr：0.15～0.50％；Mo：0.15～0.50％
Chromium and molybdenum increase CCT curve Medium pearlite and ferritic incubation period, suppress perlite and ferritic formation, are easy to obtain bainite structure when making cooling.Simultaneously, chromium and molybdenum help the refinement of austenite crystal when rolling and the generation of tiny bainite, improve the intensity of steel, but addition surpass at 0.5% o'clock, and cost improves, and weldability obviously reduces.Thereby in the present invention chromium and molybdenum content all are limited to below 0.5%.Cr and Mo content are not remarkable to the influence of CCT curve less than 0.15% o'clock.Preferably, Cr:0.21～0.45%, Mo:0.20～0.45%.
The upper limit of the impurity element in the steel is controlled at P :≤0.015%, and S :≤0.010%, N :≤0.005%, the pure more effect of steel is better.
Manufacturing process of the present invention is to produce in conjunction with hot rolling postcooling technology on traditional automotive sheet hot rolling technology basis.
Slab heating temperature: slab heating temperature influences austenite grain size.When making the low-carbon bainite steel plate of superstrength, adding for alloying element such as Ti and Nb can form carbide or nitride, to improve the intensity of steel plate.During the slab heating, these form sosoloid completely in austenite for alloying element must dissolve in, in the process of cooling of postorder, could form tiny carbide or nitride, play the effect of reinforcement, and help the generation of bainite, so slab heating temperature preferably is limited to 1100～1250 ℃.
Finishing temperature: when finishing temperature is not less than 800 ℃, can obtain tiny and uniform tissue, when finishing temperature is lower than 800 ℃, the banded structure that forms during hot-work will keep, and the probability of failure in the forming process is increased, therefore, preferably, finishing temperature is defined as and is not less than 800 ℃.Generally the upper limit of finishing temperature does not need special stipulation, but considers slab heating temperature, and finishing temperature generally is no more than 950 ℃.
In order to stop supercooled austenite to change polygonal ferrite or perlite into, rate of cooling is defined as and is not less than 30 ℃/s and is.Preferably, rate of cooling is 30～100 ℃ of s.
Coiling temperature: coiling temperature is to obtain one of the most key processing parameter of bainite structure.Coiling temperature can form pearlitic structure during greater than 630 ℃, and the performance of steel plate is had negative effect, on the other hand, when coiling temperature can form martensitic stucture during less than 430 ℃, unfavorable to the forming property of steel plate, therefore, preferably, coiling temperature of the present invention is defined as 430～630 ℃.
The present invention is on the basis of carbon manganese steel, rationally control composition range and add microalloy element, on the automobile steel production line basis of routine, control certain coiling temperature scope, the strong low-carbon bainite steel of superelevation that production tensile strength 700MPa is above, it is characterized by bainite content is 0a greater than 95%, 180 ° of cold-bending property, promptly can obtain the good superstrength low-carbon bainite steel of cold-bending property, be suitable for making products such as automobile chassis, suspender, collision bumper.
Embodiment
Below the present invention is described in detail by specific embodiment.
The present invention rationally controls composition range and adds microalloy element on the basis of carbon manganese steel, on the automobile steel production line basis of routine, controls certain coiling temperature scope, produces the good superstrength low-carbon bainite steel of cold-bending property.
Wherein, cold-bending property is meant that metallic substance can bear bending and the performance of not breaking at normal temperatures.Degree of crook is generally used bent angle alpha (exterior angle) and the flexual center diameter d ratio value representation to material thickness a, and a is bigger or d/a is littler, and then the clod wash of material better.Cold-bending property is the flexual center diameter of 180 ° of bendings in the table 2.
Embodiment A-1
With the steel of composition A in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the A-1, carry out finish rolling at 830 ℃, batch at 530 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 715MPa, and the A50 unit elongation is 20.5%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and the flexual center diameter of 180 ° of bendings of cold-bending property is 0a.
The bainite steel plate of this embodiment has reached that ultrahigh-strength steel plates requires and cold-bending property is fine.
Comparative example A-2
With the steel of composition A in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the A-2, carry out finish rolling at 880 ℃, batch at 640 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 653MPa, and the A50 unit elongation is 25.0%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
Because the coiling temperature of this comparative example surpasses 630 ℃, so its tensile strength is lower than 700MPa, do not reach the requirement of ultrahigh-strength steel plates.
Embodiment B
With the steel of composition B in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the B, carry out finish rolling at 830 ℃, batch at 560 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 870MPa, and the A50 unit elongation is 20.1%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
The bainite steel plate of this embodiment has reached that the super-high strength steel plate requires and cold-bending property is fine.
Embodiment C
With the steel of composition C in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the C, carry out finish rolling at 880 ℃, batch at 470 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 783MPa, and the A50 unit elongation is 15.0%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
The bainite steel plate of this embodiment has reached that ultrahigh-strength steel plates requires and cold-bending property is fine.
Embodiment D
With the steel of components D in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the D, carry out finish rolling at 840 ℃, batch at 510 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 835MPa, and the A50 unit elongation is 15.2%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
The bainite steel plate of this embodiment has reached that ultrahigh-strength steel plates requires and cold-bending property is fine.
Comparative Examples E-1
With the steel of composition E in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the E-1, carry out finish rolling at 880 ℃, batch at 640 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 666MPa, and the A50 unit elongation is 21.5%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
Because the coiling temperature of this comparative example surpasses 630 ℃ of the upper limits of the present invention, so its tensile strength is lower than 700MPa, do not reach the requirement of ultrahigh-strength steel plates.
Embodiment E-2
With the steel of composition E in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the E-2, carry out finish rolling at 830 ℃, batch at 580 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 838MPa, and the A50 unit elongation is 16.8%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
The bainite steel plate of this embodiment has reached that ultrahigh-strength steel plates requires and cold-bending property is fine.
Embodiment E-3
With the steel of composition E in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the E-3, carry out finish rolling at 830 ℃, batch at 550 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 810MPa, and the A50 unit elongation is 19.0%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
The bainite steel plate of this embodiment has reached that ultrahigh-strength steel plates requires and cold-bending property is fine.
Embodiment E-4
With the steel of composition E in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the E-4, carry out finish rolling at 880 ℃, batch at 540 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 793MPa, and the A50 unit elongation is 17.0%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
The bainite steel plate of this embodiment has reached that ultrahigh-strength steel plates requires and cold-bending property is fine.
Embodiment F-1
With the steel of composition F in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the F-1, carry out finish rolling at 880 ℃, batch at 600 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 810MPa, and the A50 unit elongation is 15.0%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
The bainite steel plate of this embodiment has reached that ultrahigh-strength steel plates requires and cold-bending property is fine.
Comparative Examples F-2
With the steel of composition F in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the F-2, carry out finish rolling at 870 ℃, batch at 420 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 880MPa, and the A50 unit elongation is 11.0%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 1a.
Because the coiling temperature of this comparative example is lower than 430 ℃ of lower limits of the present invention, therefore,, reach the requirement of ultrahigh-strength steel plates though tensile strength surpasses 700MPa, cold-bending property is undesirable.
Embodiment G-1
With the steel of composition G in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the G-1, carry out finish rolling at 830 ℃, batch at 530 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 755MPa, and the A50 unit elongation is 23.5%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
The bainite steel plate of this embodiment has reached that ultrahigh-strength steel plates requires and cold-bending property is fine.
Embodiment G-2
With the steel of composition G in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the G-2, carry out finish rolling at 830 ℃, batch at 610 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 729MPa, and the A50 unit elongation is 22.8%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
The bainite steel plate of this embodiment has reached that ultrahigh-strength steel plates requires and cold-bending property is fine.
Comparative Examples G-3
With the steel of composition G in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the G-3, carry out finish rolling at 880 ℃, batch at 650 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 663MPa, and the A50 unit elongation is 21.0%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
Because the coiling temperature of this comparative example exceeds 630 ℃ of the upper limits of the present invention, therefore, its tensile strength does not reach the requirement of ultrahigh-strength steel plates.
Comparative Examples H
With the steel of composition H in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the H, carry out finish rolling at 880 ℃, batch at 620 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 670MPa, and the A50 unit elongation is 20.5%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
Because the carbon content of this comparative example is not in scope of the present invention (greater than the upper limit of the present invention), therefore, its tensile strength does not reach the requirement of ultrahigh-strength steel plates.
Comparative Examples
With the steel of composition in the table 1 after smelting at 1250 ℃ of reheat, press shown in the table 2, carry out finish rolling at 810 ℃, batch at 450 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 695MPa, and the A50 unit elongation is 17.5%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
Because the carbon content of this comparative example is not at scope of the present invention (less than lower limit of the present invention), therefore, its tensile strength does not reach the requirement of ultrahigh-strength steel plates.
Comparative Examples J
With the steel of composition J in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the J, carry out finish rolling at 880 ℃, batch at 510 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 655MPa, and the A50 unit elongation is 18.5%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 0a, and cold-bending property is fine.
Because the Mn content of this comparative example is not at scope of the present invention (less than lower limit of the present invention), therefore, its tensile strength does not reach the requirement of ultrahigh-strength steel plates.
Comparative Examples K
With the steel of composition K in the table 1 after smelting at 1250 ℃ of reheat, press in the table 2 shown in the K, carry out finish rolling at 880 ℃, batch at 600 ℃ and obtain the steel plate of thickness less than 8mm.
Get along rolling the tension specimen to JIS 5#, testing data is as shown in table 2, and tensile strength is 785MPa, and the A50 unit elongation is 10.0%.
Carry out material can bear bending at normal temperatures and not disruptive cold-bending property test, its result is as shown in table 2, and cold-bending property is that the flexual center diameter of 180 ° of bendings is 1a.
Because the Mn content of this comparative example is not in scope of the present invention (greater than the upper limit of the present invention), therefore, though tensile strength reaches more than the 700MPa, cold-bending property is undesirable.
In the table 1, embodiment A～G is a steel of the present invention, and carbon and manganese content exceed the scope of composition of the present invention among Comparative Examples H～K, do not belong to the scope of the invention.
As seen, when composition departed from the scope of the invention, the tensile strength of Comparative Examples H, Comparative Examples I and Comparative Examples J steel was less than 700MPa; Though the tensile strength of Comparative Examples K steel is greater than 700MPa, unit elongation is lower, and this is owing to Mn content in the steel is high, contain a large amount of martensite in the hot rolling attitude tissue, this will have a negative impact to the forming property of steel, and the cold-bending property variation does not meet purpose of the present invention.
When coiling temperature was too high, as the compared steel A-2 in the table 2, E-1, G-3, coiling temperature can produce a large amount of pearlitic structures greater than 630 ℃ when batching, and its tensile strength is also less than 700MPa.The coiling temperature of compared steel F-2 is 420 ℃, less than lower limit of the present invention, can produce a large amount of martensitic stuctures when batching, and tensile strength is high, but unit elongation is lower, and also the cold-bending property to steel has disadvantageous effect.
In sum, the present invention is on the basis of carbon manganese steel, control reasonable component scope, and interpolation microalloy element, on the automobile steel production line basis of routine, further control coiling temperature, the strong low-carbon bainite steel of superelevation that production tensile strength 700MPa is above, it is characterized by bainite content is 0a greater than 95%, 180 ° of cold-bending property.Be suitable for making products such as automobile chassis, suspender, collision bumper.
Though abovely describe the present invention by specific embodiment; but be not limited only to these embodiment; break away from protection under the prerequisite of design of the present invention, more changeableization and improved other embodiment can also be arranged, and these changes and improvements all should belong to the claimed scope of claim.
Claims (14)
1. ultra-high strength bainite, its chemical component weight per-cent is: C:0.05%～0.14%, Si:0.1%～0.5%, Mn:1.2%～2.0%, P :≤0.015%, S :≤0.010%, Al:0.01%～0.05%, N :≤0.005%, also comprise Nb:0.015～0.07%, Ti:0.02～0.15%, at least a alloying element in V:0.10～0.20%, and Cr:0.15～0.50%, at least a alloying element in Mo:0.15～0.50%, and remainder is iron and unavoidable impurities, and the control coiling temperature is 430～630 ℃ in manufacturing processed.
2. ultra-high strength bainite as claimed in claim 1 is characterized in that, Nb:0.04～0.07%.
3. ultra-high strength bainite as claimed in claim 1 or 2 is characterized in that, Ti:0.025～0.110%.
4. as the arbitrary described ultra-high strength bainite of claim 1～3, it is characterized in that V:0.14～0.20%.
5. as the arbitrary described ultra-high strength bainite of claim 1～4, it is characterized in that Cr:0.21～0.45%.
6. as the arbitrary described ultra-high strength bainite of claim 1～5, it is characterized in that Mo:0.20～0.45%.
7. the manufacture method of a low-carbon bainite hot-rolled steel sheet comprises
The chemical component weight per-cent of steel plate is: C:0.05%～0.14%, Si:0.1%～0.5%, Mn:1.2%～2.0%, P :≤0.015%, S :≤0.010%, Al:0.01%～0.05%, N :≤0.005%, also comprise Nb:0.015～0.07%, Ti:0.02～0.15%, at least a alloying element in V:0.10～0.20%, and Cr:0.15～0.50%, at least a alloying element in Mo:0.15～0.50%, and remainder is iron and unavoidable impurities;
To the continuous casting steel billet heating that mentioned component is smelted and continuous casting obtains, Heating temperature is 1100～1250 ℃, carries out controlled rolling afterwards; The finish rolling start rolling temperature is 950～1000 ℃, and the finish rolling finishing temperature is 800～950 ℃;
Blank behind the rolling is carried out water cooling, and speed of cooling is not less than 30 ℃/s, and coiling temperature is 430～630 ℃.
8. method as claimed in claim 7 is characterized in that, described speed of cooling is 30～100 ℃/s.
9. as claim 7 or 8 described methods, it is characterized in that hot-rolled sheet thickness is not more than 8mm.
10. as the arbitrary described method of claim 7～9, it is characterized in that, also comprise: will obtain acid-cleaning plate after the hot-rolled sheet pickling.
11. as the arbitrary described method of claim 7～10, it is characterized in that, also comprise: will obtain the hot rolling hot-dip galvanizing sheet steel after the pot galvanize of hot-rolled sheet process.
12. as the bainite hot-rolled steel sheet that the arbitrary described method of claim 7～9 is made, its bainite content 〉=95%, tensile strength 〉=700MPa.
13. the acid-cleaning plate that method as claimed in claim 10 is made, its bainite content 〉=95%, tensile strength is for drawing intensity 〉=700MPa.
14. the hot-dip galvanizing sheet steel that method as claimed in claim 11 is made, its bainite content 〉=95%, tensile strength is for drawing intensity 〉=700MPa.
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