CN101490296A - Hot-rolled high-carbon steel sheets and process for production of the same - Google Patents
Hot-rolled high-carbon steel sheets and process for production of the same Download PDFInfo
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- CN101490296A CN101490296A CNA2007800269001A CN200780026900A CN101490296A CN 101490296 A CN101490296 A CN 101490296A CN A2007800269001 A CNA2007800269001 A CN A2007800269001A CN 200780026900 A CN200780026900 A CN 200780026900A CN 101490296 A CN101490296 A CN 101490296A
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/32—Soft annealing, e.g. spheroidising
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0273—Final recrystallisation annealing
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Sheet Steel (AREA)
- Metal Rolling (AREA)
Abstract
The invention provides a hot-rolled high-carbon steel sheet excellent in the homogeneity in the width direction. The steel sheet contains C: 0.2 to 0.7%, Si: 0.01 to 1.0%, Mn: 0.1 to 1.0%, P: 0.03% or below, S: 0.035% or below, Al: 0.08% or below and N: 0.01% or below with the balance consisting of Fe and unavoidable impurities. The texture of the sheet is characterized by a mean ferrite grain size in the sheet edge of less than 35[mu]m, a mean ferrite grain size in the central area of less than 20[mu]m, and a mean carbide grain size of 0.10mum to less than 2.0mum. The steel sheet of the invention is manufactured by rough rolling, finish rolling at a finishing temperature of (Ar3+40 DEG C) or above, cooling initiated within two seconds after the finish rolling at a cooling rate exceeding 120 DEG C/s until a cooling stop temperature exceeding 550 DEG C and below 650 DEG C, coiling at a temperature of 550 DEG C or below, pickling, and then spheroidizing at a temperature of 670 DEG C to Ac1 transformation point.
Description
Technical field
The present invention relates to high-carbon hot-rolled steel sheet and manufacture method thereof, particularly in the uniformity of width good high-carbon hot-rolled steel sheet and manufacture method thereof.
Background technology
The high carbon steel sheet that uses in instrument or the trolley part (gear, variator) etc. is implemented thermal treatments such as Q-tempering after stamping-out is shaped.In recent years, instrument, component manufacturers, be the user of high carbon steel sheet,, studying simplification from the component processing of utilizing cutting processing, forge hot of the cast material in past to the operation of the processing of the drawing that utilizes steel plate (comprising cold forging) in order to reduce cost.Meanwhile, for high carbon steel sheet, expect the stability that it has hardening capacity and is processed into complicated shape strongly as former material.And, from the viewpoint of keeping management of stamping machine and mould, the stability of the former material characteristic of strong request.
Based on as above present situation, homogenize for the material of high carbon steel sheet, studied several technology.
For example, proposed in the patent documentation 1, after hot rolling, be heated into the two phase region of ferritic-austenitic, carry out the manufacture method of the high-carbon steel band of anneal with the speed of cooling of regulation again with predetermined heating speed.In this technology, make in the two phase region of the ferritic-austenitic of high-carbon steel band more than the Ac1 point and anneal, form thick nodularization cementite thus and be uniformly distributed in tissue in the ferrite matrix.Particularly, make the high carbon steel that contains C:0.2～0.8%, Si:0.03～0.30%, Mn:0.20～1.50%, Sol.Al:0.01～0.10%, N:0.0020～0.0100% and Sol.Al/N:5～10, behind hot rolling, pickling, the deoxygenated skin, in the atmosphere steam stove that constitutes by hydrogen more than the 95 volume % and surplus nitrogen, with the temperature range more than 680 ℃, at rate of heating Tv (℃/hour): 500 * (0.01-N (%) asAlN)～2000 * (0.1-N (%) asAlN), soaking temperature TA (℃): Ac1 point～222 * C (%)
2Anneal under-411 * C (%)+912,1～20 hour the condition of soaking time, be cooled to room temperature with the speed of cooling below 100 ℃/hour.
For example, proposed in the patent documentation 2, for containing C:0.1～0.8 quality %, the hot-rolled steel sheet that S:0.01 quality % is following, in Ac1-50 ℃～temperature range less than Ac1, keep after the heating in the 1st stage more than 0.5 hour, carry out in Ac1～Ac1+100 ℃ temperature range, keeping 0.5～20 hour heating in the 2nd stage and the heating that in the temperature range of Ac1-50 ℃～Ac1, keeps 2～20 hours the 3rd stage continuously, and making from the speed of cooling of the maintenance temperature in 3 stages of maintenance temperature to the in the 2nd stage is 5～30 ℃/hour manufacture method.That is, in patent documentation 2, by such enforcement 3 step annealings, wishing to obtain ferritic median size is the above high carbon steel sheets of 20 μ m.
For example, in patent documentation 3, proposed, the steel of the C that contains 0.2～0.7 quality % has been carried out hot rolling, be controlled to be and have volume fraction and surpass after the tissue of 70% bainite, anneal, make ferrite crystal grain thickization equably, thereby realize the method for dead-soft materialization.This technology is characterised in that, after carrying out hot rolling under the finishing temperature more than (Ar3 transformation temperature-20 ℃), to surpass 120 ℃/second speed of cooling and under the cooling end temp below 550 ℃, to cool off, then, under the coiling temperature below 500 ℃, batch, after the pickling, under the annealing temperature more than 640 ℃, below the Ac1 transformation temperature, anneal.
Patent documentation 1: Japanese kokai publication hei 9-157758 communique
Patent documentation 2: Japanese kokai publication hei 11-80884 communique
Patent documentation 3: TOHKEMY 2003-73742 communique
But, have following problem in the above-mentioned technology.
The technology that patent documentation 1 is put down in writing, though by annealing in the two phase region of the ferritic-austenitic of high-carbon steel band more than the Ac1 point is obtained thick nodularization cementite, so thick cementite is the tissue that is difficult to make hardening capacity, processibility stabilization.
In the technology that patent documentation 2 is put down in writing, because the annealing operation complexity, so when the imagination actually operating, the productivity variation, cost increases.
And, in the technology that patent documentation 3 is put down in writing, by containing the hot-rolled steel sheet Spheroidizing Annealing that volume fraction surpasses 70% bainite, make thickization of ferrite particle diameter, thereby make its dead-soft materialization, but after carrying out hot rolling under the finishing temperature more than (Ar3 transformation temperature-20 ℃), owing to surpassing chilling under 120 ℃/second the speed of cooling, therefore the cooling back produces the phase transformation heat release, and temperature raises, and has the problem of the poor stability of hot-rolled steel sheet tissue.And, for the hardness after the Spheroidizing Annealing, also can only be with the plate face of rockwell b scale chi hardness (HRB) assess sample, and since after the Spheroidizing Annealing coarse ferrite grains on the thickness of slab direction, be not formed uniformly, the inequality of material takes place easily, thereby can not obtain stable softening.
Summary of the invention
The present invention is in view of correlation circumstance, and purpose is to provide does not need complicated manufacturing process, hardening capacity, press formability to stablize high-carbon hot-rolled steel sheet that the uniformity of width is good and manufacture method thereof.Particularly with near the stable target that turns to of the tissue the steel plate edge.
The inventor to one-tenth be grouped into, microstructure and create conditions wholwe-hearted research has been carried out in the homogeneous influence of the width of high carbon steel sheet.It found that: in order to obtain the uniformity of good width, the ferrite median size and the carbide median size of the whole width of regulation steel plate are important.And, as can be known by with the ferrite median size of steel plate edge section, be controlled at respectively in the suitable scope than the ferrite median size and the carbide median size of the more close middle body in steel plate edge section, can guarantee that hardening capacity, press formability are stable, and obtain the good high-carbon hot-rolled steel sheet of uniformity of width.
And, among the present invention,, the manufacture method that is used to control above-mentioned tissue is studied based on above-mentioned opinion, established the manufacture method of the good high-carbon hot-rolled steel sheet of the uniformity of width.
The present invention is based on above opinion and carry out, its main points are as follows.
[1] a kind of high-carbon hot-rolled steel sheet, it is characterized in that, in quality %, contain that C:0.2～0.7%, Si:0.01～1.0%, Mn:0.1～1.0%, P:0.03% are following, S:0.035% is following, Al:0.08% is following, below the N:0.01%, surplus is made of iron and unavoidable impurities, and the ferrite median size with steel plate edge section is more than the 0.10 μ m and less than the tissue of 2.0 μ m less than 35 μ m, than the ferrite median size of the more close middle body in described steel plate edge section less than 20 μ m, carbide median size.On steel plate width direction when wherein, the steel plate edge section is meant hot rolling apart from the zone of both sides 25～75mm.
[2], wherein,, also contain one or more of Mo:0.005～0.5%, Ti:0.005～0.05%, Nb:0.005～0.1% in quality % as above-mentioned [1] described high-carbon hot-rolled steel sheet.
[3] a kind of method of making high-carbon hot-rolled steel sheet, it is characterized in that, to have after the steel roughing of each described composition in above-mentioned [1] or [2], under the finishing temperature that is higher than (Ar3+40 ℃), carry out finish to gauge, then, in after the finish to gauge 2 seconds, be cooled to the cooling end temp that is higher than 550 ℃, is lower than 650 ℃ with speed of cooling greater than 120 ℃/second, then, under the temperature below 550 ℃, batch, after the pickling, utilize the box annealing method, under the temperature more than 670 ℃, below the Ac1 transformation temperature, carry out Spheroidizing Annealing.
In addition, in this specification sheets, the % of the composition of expression steel is quality %.
According to the present invention, can guarantee that hardening capacity, press formability are stable, and obtain the good high-carbon hot-rolled steel sheet of uniformity of width.And, can not use special annealing conditions ground to make the good high-carbon hot-rolled steel sheet of uniformity of width of the present invention.Consequently can reach high rate of finished products, make cost degradation become possibility.
Embodiment
High-carbon hot-rolled steel sheet of the present invention is characterised in that, control becomes one-tenth as follows and is grouped into, and the ferrite median size with steel plate edge section is more than the 0.10 μ m and less than the tissue of 2.0 μ m less than 35 μ m, than the ferrite median size of the more close middle body in above-mentioned steel plate edge section less than 20 μ m and carbide median size.This is a most important characteristic of the present invention.Form and the shape (carbide median size) of metal structure (by the ferrite median size of width division), carbide by such predetermined component, to satisfy all conditions, can access and to guarantee comprising hardening capacity stable on the width of edge section, the high-carbon hot-rolled steel sheet of press formability.
In addition, here, in the present invention, on the steel plate width direction when the steel plate edge section is meant hot rolling apart from the zone of both sides 25～75mm.In general, apart from the easy undercooling of the scope of both sides 75mm, be difficult to carry out temperature control on the steel plate width direction.Therefore the inequality of tissue increases.On the other hand, generally be in the object of quality guarantee apart from the scope of both sides 25mm on the steel plate width direction beyond, or the part that abandons by shearings such as side deburrings.Therefore, among the present invention, the scope apart from both sides 25～75mm on the steel plate width direction is called " steel plate edge section ", purpose be to improve this scope tissue, make it near near the tissue the steel plate width direction central part.
And, to have after the steel roughing of aftermentioned composition, after carrying out finish to gauge under the finishing temperature that is higher than (Ar3+40 ℃), then in after the finish to gauge 2 seconds, be cooled to the cooling end temp that is higher than 550 ℃, is lower than 650 ℃ with speed of cooling greater than 120 ℃/second, then, under the temperature below 550 ℃, batch, after the pickling, utilize the box annealing method, under the temperature more than 670 ℃, below the Ac1 transformation temperature, carry out Spheroidizing Annealing, make the good high-carbon hot-rolled steel sheet of uniformity of above-mentioned width thus.
Like this, control cooling after hot finish to gauge, the finish to gauge, batch and create conditions, finish purpose of the present invention until annealed by integral body.
Below the present invention is at length described.
The qualification reason of the chemical ingredients of steel of the present invention at first, is described.
(1)C：0.2～0.7％
C is an alloying element the most basic in the carbon steel.According to its content difference, the carbide amount under quenching hardness and the as-annealed condition has bigger variation.C content when being applied to automobile with parts etc., can not obtain sufficient quenching hardness less than 0.2% steel.On the other hand, if C content greater than 0.7%, then the toughness after the hot rolling reduces, the manufacturing of steel band, the property handled variation can not be stablized manufacturing, and be difficult to cost degradation.Therefore, from the viewpoint of the steel plate that has appropriate quenching hardness and press formability concurrently is provided with low cost, making C content is more than 0.2%, below 0.7%, is preferably more than 0.2%, below 0.5%.
(2)Si：0.01～1.0％
Si is the element that hardening capacity is improved.If Si content is less than 0.01%, the hardness deficiency when then quenching.On the other hand, if Si content greater than 1.0%, then because solution strengthening, ferrite sclerosis, press formability variation.And there is the tendency that hinders hardening capacity in the carbide greying.Therefore, from the viewpoint of the steel plate that has appropriate quenching hardness and press formability concurrently is provided, making Si content is more than 0.01%, below 1.0%, is preferably more than 0.01%, below 0.8%.
(3)Mn：0.1～1.0％
Mn is the same with Si, is the element that hardening capacity is improved.And S fixes with the form of MnS, is the important element that prevents the steel billet hot tearing.If Mn content less than 0.1%, then can not fully obtain above-mentioned effect, and hardening capacity reduces significantly.On the other hand, if Mn content greater than 1.0%, then because solution strengthening, the ferrite sclerosis causes the press formability variation.Therefore, from the viewpoint of the steel plate that has appropriate quenching hardness and press formability concurrently is provided, making Mn content is more than 0.1%, below 1.0%, is preferably more than 0.1%, below 0.8%.
(4) below the P:0.03%
Owing to P segregation in crystal boundary makes ductility and toughness variation, therefore making P content is below 0.03%, to be preferably below 0.02%.
(5) below the S:0.035%
Owing to S and Mn form MnS make press formability and quench after the toughness variation, therefore be the element that must reduce, preferably its content is few.But because S content can allow to reach 0.035%, therefore making S content is below 0.035%, to be preferably below 0.030%.
(6) below the Al:0.08%
If add excessive Al, then AlN separates out in a large number, and hardening capacity is reduced, and therefore making Al content is below 0.08%, to be preferably below 0.06%.
(7) below the N:0.01%
Because when containing excessive N, cause ductility to reduce, therefore making N content is below 0.01%.
Though must add element by above, steel of the present invention can obtain target property, but except above-mentioned must adding the element, the proeutectoid ferrite when cooling off in order to suppress hot rolling generates, improves hardening capacity, also can add more than a kind or 2 kinds of Mo, Ti, Nb as required.At this moment, if addition separately be Mo less than 0.005%, Ti less than 0.005%, Nb is less than 0.005%, then has the situation that can not fully obtain additive effect.On the other hand, if Mo greater than 0.5%, Ti greater than 0.05%, Nb is greater than 0.1%, then effect is saturated, cost increases, and because solution strengthening, precipitation strength etc., intensity rises and increases, and therefore has the situation of processibility variation.Therefore, during interpolation, making Mo is more than 0.005%, below 0.5%, and making Ti is more than 0.005%, below 0.05%, and Nb is more than 0.005%, below 0.1%.
In addition, above-mentioned surplus in addition is made up of Fe and unavoidable impurities.As unavoidable impurities, for example,, bring detrimentally affect to quality because O forms non-metallic inclusion, therefore preferably be reduced to below 0.003%.And, among the present invention,, also can contain Cu, Ni, W, V, Zr, Sn, the Sb of 0.1% following scope as the trace element that does not hinder action effect of the present invention.
Below, the tissue of the good high-carbon hot-rolled steel sheet of the uniformity of width of the present invention is described.
(1) the ferrite median size of steel plate edge section: less than 35 μ m
In order to make the homogeneous microstructureization of width, particularly importantly suppress the generation of easy overcooled edge part office coarse grain.Produce the uniform grainization that reaches tissue by suppressing edge part office coarse grain, can obtain good press formability.That is,, then, therefore can not obtain stable press formability owing to become the mixed grain structure that comprises coarse grain if the ferrite median size is more than the 35 μ m.Therefore, in order to reach stable press formability, make the ferrite median size less than 35 μ m.And, in order to obtain stable press formability, expectation makes as far as possible with particle diameter difference than the more close middle body in steel plate edge section (below, be called the steel plate middle body) and does not exist, and the difference of therefore preferred steel plate middle body and steel plate edge section is below the 15 μ m.
In addition, the ferrite median size of steel plate edge section obtains less than the steel plate of 35 μ m temperature and the cooling conditions can be as described later by control finish to gauge the time.Particularly, the ferrite median size of steel plate edge section can followingly obtain less than the steel plate of 35 μ m: after roughing, after under the finishing temperature that is higher than (Ar3+40 ℃), carrying out finish to gauge, then in after the finish to gauge 2 seconds, be cooled to the cooling end temp that is higher than 550 ℃, is lower than 650 ℃ with speed of cooling greater than 120 ℃/second.
Like this, avoided the low temperature finish to gauge after the roughing, implement suitable cooling conditions (in 2 seconds, be cooled to the cold but end temp that is higher than 550 ℃, is lower than 650 ℃ with speed of cooling) greater than 120 ℃/second, thus, particularly can avoid the generation of the thick ferrite crystal grain that the edge part office takes place frequently.
(2) than the ferrite median size of the more close middle body in steel plate edge section (steel plate middle body): less than 20 μ m
The ferrite median size is the important factor of the stability of control drawing.That is, become less than the few uniform grain of the coarse grain of 20 μ m, can obtain good processibility by making the ferrite median size.Therefore, make the ferrite median size of steel plate middle body less than 20 μ m.On the other hand, if become excessively thin crystal grain, then hardness increases, the possibility of existence generation reduction die life etc., thereby preferable particle size is greater than 5 μ m.
In addition, the ferrite median size of steel plate middle body obtains less than the steel plate of 20 μ m temperature and the cooling conditions can be as described later by control finish to gauge the time.Particularly, following the obtaining of above-mentioned steel plate energy: after roughing, after under the finishing temperature that is higher than (Ar3+40 ℃), carrying out finish to gauge, then in after the finish to gauge 2 seconds, be cooled to the cooling end temp that is higher than 550 ℃, is lower than 650 ℃ with speed of cooling greater than 120 ℃/second.
(3) carbide median size: more than the 0.10 μ m and less than 2.0 μ m
Because the quenching intensity of the heat treatment stages of carbide median size after to press formability, stamping-out processibility and drawing has a significant impact, and is important feature therefore.If it is fine that carbide becomes, the heat treatment stages after processing then, carbide are easy to dissolving, can guarantee stable quenching hardness, if but the carbide median size less than 0.10 μ m, then along with the rising of hardness, the press formability variation.On the other hand, though press formability improve along with the increase of carbide median size,, if become more than the 2.0 μ m, the heat treatment stages after processing then, carbide become and are difficult to dissolving, quenching hardness reduces.Thus, making the carbide median size is more than the 0.10 μ m and less than 2.0 μ m.In addition, the carbide median size can by described laterly create conditions, particularly cooling conditions, coiling temperature and the annealing conditions after the hot rolling controlled.
Below, the manufacture method of high-carbon hot-rolled steel sheet of the present invention is described.
The high-carbon hot-rolled steel sheet that the uniformity of width of the present invention is good can followingly obtain: will be adjusted to the steel roughing in the above-mentioned chemical ingredients scope, under desirable finishing temperature, carry out finish to gauge, then, under desirable cooling conditions, cool off, batch, after the pickling, carry out desirable Spheroidizing Annealing by the box annealing method.Below these are at length described.
(1) finishing temperature of finish to gauge (rolling temperature)
If the finishing temperature the during hot-rolled steel rolling temperature of passage (final) be below (Ar3+40) ℃, the nucleation site increase of phase transformation the part of a plurality of shear zones then appears being imported in the original austenite grain, in the steel plate edge section.Therefore, it is fine that ferrite crystal grain becomes, and during Spheroidizing Annealing, is motivating force with high crystal boundary energy, and particularly in the steel plate edge section, the situation that thick ferrite crystal grain produces increases.Therefore, make finishing temperature be higher than (Ar3+40) ℃.And, in order more stably to prevent the generation of thick ferrite crystal grain, obtaining the uniformity of better width, preferred finishing temperature is higher than (Ar3+80) ℃.Though there is not the upper limit of special stipulation finishing temperature, because when the high temperature that is higher than 1000 ℃, the oxide skin defective takes place easily, therefore preferably below 1000 ℃.
Finishing temperature when thus, the making hot-rolled steel rolling temperature of passage (final) is higher than (Ar3+40) ℃.
In addition, the Ar3 transformation temperature (℃) can calculate by following formula (1).
Ar3＝910-310C-80Mn-15Cr-80Mo (1)
Here, the symbol of element in the formula is represented the content (quality %) of each element.
(2) cooling: after the finish to gauge 2 seconds with interior speed of cooling greater than 120 ℃/second
If the method for cooling after the hot rolling is slow cooling, then austenitic condensate depression is little, and proeutectoid ferrite generates in a large number.If speed of cooling is below 120 ℃/second, then the generation of proeutectoid ferrite becomes significantly, and annealing back carbide disperses unevenly, can not obtain stable uniform grain tissue.Therefore, make speed of cooling after the hot rolling greater than 120 ℃/second.Be preferably more than 200 ℃/second.In addition, though be not particularly limited the upper limit of speed of cooling, for example, if the hypothesis thickness of slab is when being 3.0mm, the ability from existing installation is considered, is limited to 700 ℃/second on it.
And, then same as described above if surpass 2 seconds from finish to gauge to the time that cooling begins, generate proeutectoid ferrite, carbide disperses unevenly after annealing equally, can not obtain stable uniform grain tissue.Therefore, make from finish to gauge to the time of cooling off beginning in 2 seconds.In addition, for the stabilization of organizing, preferably the time from finish to gauge to the cooling beginning is in 1.5 seconds, more preferably in 1.0 seconds.
(3) cooling end temp: greater than 550 ℃, less than 650 ℃
It is below 550 ℃ the time that once cooling after the hot rolling stops temperature, particularly in the hot-rolled sheet stage, the phenomenon that exists trickle bainite structure to produce in the steel plate edge part office that temperature reduces, it is behind final annealing, become thick ferrite crystal grain tissue, can not on width, obtain the tissue of homogeneous.And, if be more than 650 ℃, then becoming thick ferrite-pearlite tissue in the hot-rolled sheet stage, annealing back carbide disperses unevenly, can not obtain stable uniform grain tissue.Therefore, make the cooling end temp for greater than 550 ℃, less than 650 ℃.
(4) coiling temperature: below 550 ℃
Cooled coiling temperature is during greater than 550 ℃, and the miniaturization of ferrite-pearlite tissue is insufficient, and behind the final annealing, carbide disperses unevenly, can not obtain stable uniform grain tissue.Therefore, making coiling temperature is below 550 ℃.In addition, though there is not the lower limit of special stipulation coiling temperature,, therefore be preferably more than 200 ℃ because the shape of the low more steel plate of temperature is poor more.
(5) pickling: implement
Hot-rolled steel sheet after batching carries out before the Spheroidizing Annealing, implements to be used for removing the pickling of descaling.Pickling can be carried out according to usual method.
(6) Spheroidizing Annealing: more than 670 ℃～temperature below the Ac1 transformation temperature under box annealing
Behind the pickling hot-rolled steel sheet, for ferrite crystal grain being grown up fully and making carbide spheroidization and anneal.Spheroidizing Annealing roughly is divided into: (1) is heated to firm method above slow cooling after the temperature of Ac1; (2) method that under the temperature that just is lower than Ac1, keeps for a long time; (3) just surpassing and just be lower than under the temperature of Ac1, repeatedly heating/refrigerative method.Wherein, among the present invention,, be purpose with the grain growth of ferrite crystal grain and the nodularization of carbide simultaneously according to the method for above-mentioned (2).Therefore, because the Spheroidizing Annealing time is long, thereby select box annealing.If annealing temperature is less than 670 ℃, then the nodularization of the homogenizing of ferrite crystal grain and carbide all becomes insufficient, can't become sufficient uniform grain tissue, so poor in processability.On the other hand, when annealing temperature surpasses the Ac1 transformation temperature,, become the state that coarse grain is easy to generate in the steel plate edge section.Thus, the annealing temperature of Spheroidizing Annealing is more than 670 ℃, below the Ac1 transformation temperature, is preferably more than 670 ℃, below 710 ℃.In addition, the Ac1 transformation temperature (℃) can calculate by following formula (2).
Ac1＝754.83-32.25C+23.32Si-17.76Mn+4.51Mo (2)
Here, the symbol of element in the formula is represented the content (quality %) of each element.
Thus, can access the good high-carbon hot-rolled steel sheet of uniformity of width of the present invention.In addition, during the composition of high carbon steel of the present invention is adjusted, can use in converter or the electric furnace any one.To carry out the adjusted high carbon steel of composition like this by making base-split rolling method or continuous casting, be made as the steel billet of the former material of steel.This steel billet is carried out hot rolling, at this moment,, preferably make billet heating temperature below 1300 ℃ for fear of owing to producing the condition of surface variation that oxide skin causes.And, continuous casting steel billet directly or to suppress temperature can be reduced to purpose and carry out directly rolling while being incubated rollingly.And, can when hot rolling, omit roughing, carry out finish to gauge.In order to ensure the finishing temperature of steel plate edge section, also can utilize heating units such as strip well heater, edge heater to be rolled material heating in the hot rolling.And, in order to promote nodularization or to reduce hardness, also can use device such as slow cooling cover that coiled material is incubated after batching.
After the annealing, carry out temper rolling as required.Because therefore this temper rolling is not particularly limited its condition not influence of hardening capacity.
The high-carbon hot-rolled steel sheet that obtains like this when keeping hardening capacity, has good press formability, thinks that its reason is as follows.As the uniformity of the material of press formability index, it is bigger influenced by the ferrite median size, and tissue is by uniform grainization, and, by controlling sneaking into of thick ferrite particle diameter, improve press formability.And about hardening capacity, the carbide median size has considerable influence.When carbide was thick, during solution treatment before quenching, the solid solution carbide was not residual easily, and quenching hardness reduces.From above aspect, form and the shape (carbide median size) of metal structure (ferrite median size), carbide by predetermined component, to satisfy all conditions, can when guaranteeing hardening capacity and press formability, obtain the good high-carbon hot-rolled steel sheet of uniformity of width.
Embodiment
Steel with chemical ingredients shown in the table 1 is carried out continuous casting, the steel billet that obtains is heated to 1250 ℃, carry out hot rolling under the conditions shown in Table 2 after, pickling, then, utilize the box annealing method to carry out Spheroidizing Annealing under the conditions shown in Table 2, make the hot-rolled steel sheet of thickness of slab 4.0mm.
Then,, measure the ferrite median size of steel plate edge section, the ferrite median size and the carbide median size of steel plate middle body, and measure the former material hardness of these tissues of reflection from the hot-rolled steel sheet collected specimens that obtains by aforesaid operations.Each measuring method and condition are as described below.
＜ferrite median size 〉
By the opticmicroscope tissue on the rolling direction thickness of slab cross section of sample, measure according to JIS G0552 (1998) " the ferrite grain size number test method of steel ".That is, obtain granularity numbering G according to its cutting-off method of putting down in writing, by m=2
(G+3)Calculate every 1mm
2The quantity m of the crystal grain of section area tries to achieve average crystallite particle diameter d by following formula (1) again.In addition, the mensuration of median size is that ferrite crystal grain is cut to more than 3000, enough visual field numbers is measured, and got the mean value of the particle diameter in each visual field.
D (μ m)=1000/ √ m ... formula (1)
＜carbide median size 〉
Grind, corrode after the rolling direction thickness of slab cross section of sample, use scanning electronic microscope that microstructure is taken pictures, carry out the mensuration of carbide particle diameter.In addition, median size is the mean value of carbide sum more than 500.
＜former material hardness 〉
Use Rockwell Hardness (HRB) that 3 of the width position of sample (central authorities, apart from edge 25mm) surface are in addition measured, try to achieve average hardness.And, use these average hardness of trying to achieve, obtain the difference of hardness (Δ HRB=(hardness of steel plate edge section)-(hardness of steel plate middle body)) of steel plate middle body and edge section.
The result who obtains by above mensuration is shown in the table 3.
In the table 3, steel plate No.1～10,19～25 create conditions within the scope of the present invention, be ferrite median size with steel plate edge section less than the ferrite median size of 25 μ m, steel plate middle body less than 20 μ m, the carbide median size is that 0.10 μ m is above and less than the example of the present invention of the tissue of 2.0 μ m.As can be known in example of the present invention, coarse grain does not produce in steel plate edge part office, the former material difference of hardness (Δ HRB) of steel plate middle body and steel plate edge section is also stable 10 hardness on width when following, particularly to surpass the Δ HRB of example of the present invention (steel plate No.1～10 and steel plate No.23～25) of (Ar3+80 ℃) more stable 5 hardness on width when following for finishing temperature, and can obtain having the high-carbon hot-rolled steel sheet of trickle carbide.Consequently can obtain the stable high-carbon hot-rolled steel sheet of hardening capacity and press formability.
On the other hand, steel plate No.11～18,26～29th, creating conditions does not meet the comparative example of the scope of the invention.Steel plate No.14,18,16～29, more coarse grain produces in steel plate edge part office, and the ferrite median size is more than the 35 μ m, beyond scope of the present invention.Consequently the former material difference of hardness of steel plate middle body and steel plate edge section surpasses 10 points, can not obtain uniform material on the width, and the press formability instability.And, because steel plate No.11～13,15～17 steel plate not only the ferrite median size uniform grainization big, tissue of middle body are insufficient, and the carbide median size is also big, so the ferrite median size of steel plate middle body and carbide median size are beyond scope of the present invention.Consequently hardening capacity, press formability are all unstable.
Utilize possibility on the industry
The high-carbon hot-rolled steel sheet that the homogenieity of the width of the application of the invention is good can Under underload, process simply the section of the complicated shapes such as transmission components take gear as representative Part, therefore, can be at the multiple use centered by instrument or automobile component (gear, speed changer) The aspect is used.
Claims (3)
1. high-carbon hot-rolled steel sheet, it is characterized in that, in quality %, contain C:0.2～0.7%, Si:0.01～1.0%, Mn:0.1～1.0%, below the P:0.03%, below the S:0.035%, below the Al:0.08%, below the N:0.01%, surplus is made of iron and unavoidable impurities, and the ferrite median size with steel plate edge section is less than 35 μ m, than the ferrite median size of the more close middle body in described steel plate edge section less than 20 μ m, the carbide median size is that 0.10 μ m is above and less than the tissue of 2.0 μ m, on steel plate width direction when wherein, the steel plate edge section is meant hot rolling apart from the zone of both sides 25～75mm.
2. high-carbon hot-rolled steel sheet as claimed in claim 1 wherein, in quality %, also contains one or more of Mo:0.005～0.5%, Ti:0.005～0.05%, Nb:0.005～0.1%.
3. method of making high-carbon hot-rolled steel sheet, it is characterized in that, to have after the steel roughing of each described composition in claim 1 or 2, under the finishing temperature that is higher than (Ar3+40 ℃), carry out finish to gauge, then, in after the finish to gauge 2 seconds, be cooled to the cooling end temp that is higher than 550 ℃, is lower than 650 ℃ with speed of cooling greater than 120 ℃/second, then, under the temperature below 550 ℃, batch, after the pickling, utilize the box annealing method, under the temperature more than 670 ℃, below the Acl transformation temperature, carry out Spheroidizing Annealing.
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| JP221885/2006 | 2006-08-16 | ||
| JP2006221885 | 2006-08-16 | ||
| JP2007200672A JP5262012B2 (en) | 2006-08-16 | 2007-08-01 | High carbon hot rolled steel sheet and manufacturing method thereof |
| JP200672/2007 | 2007-08-01 | ||
| PCT/JP2007/065788 WO2008020580A1 (en) | 2006-08-16 | 2007-08-06 | Hot-rolled high-carbon steel sheets and process for production of the same |
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| CN101490296A true CN101490296A (en) | 2009-07-22 |
| CN101490296B CN101490296B (en) | 2011-09-28 |
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| US (1) | US20090260729A1 (en) |
| JP (1) | JP5262012B2 (en) |
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- 2007-08-06 KR KR1020087030308A patent/KR101084874B1/en active IP Right Grant
- 2007-08-06 US US12/373,903 patent/US20090260729A1/en not_active Abandoned
- 2007-08-06 WO PCT/JP2007/065788 patent/WO2008020580A1/en active Application Filing
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Also Published As
| Publication number | Publication date |
|---|---|
| KR20090007798A (en) | 2009-01-20 |
| KR101084874B1 (en) | 2011-11-21 |
| JP2008069452A (en) | 2008-03-27 |
| JP5262012B2 (en) | 2013-08-14 |
| WO2008020580A1 (en) | 2008-02-21 |
| CN101490296B (en) | 2011-09-28 |
| US20090260729A1 (en) | 2009-10-22 |
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