CN101365812A - Method for producing a cold-rolled strip from stainless steel with a ferritic structure and a reduced susceptibility to ridging - Google Patents
Method for producing a cold-rolled strip from stainless steel with a ferritic structure and a reduced susceptibility to ridging Download PDFInfo
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- CN101365812A CN101365812A CNA2006800500453A CN200680050045A CN101365812A CN 101365812 A CN101365812 A CN 101365812A CN A2006800500453 A CNA2006800500453 A CN A2006800500453A CN 200680050045 A CN200680050045 A CN 200680050045A CN 101365812 A CN101365812 A CN 101365812A
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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
- C21D6/00—Heat treatment of ferrous alloys
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
- B22D11/0622—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/12—Accessories for subsequent treating or working cast stock in situ
- B22D11/124—Accessories for subsequent treating or working cast stock in situ for cooling
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
-
- 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
-
- 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
- C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
- C21D8/0215—Rapid solidification; Thin strip casting
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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
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
- C21D1/20—Isothermal quenching, e.g. bainitic hardening
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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
-
- 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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
-
- 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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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Heat Treatment Of Sheet Steel (AREA)
- Continuous Casting (AREA)
- Metal Rolling (AREA)
Abstract
The invention relates to a method for producing a cold-rolled strip with a ferritic structure. According to said method, molten steel that forms a ferritic structure on cooling is cast into a strip, if necessary the cast strip is hot-rolled in-line, the hot-rolled strip is wound and then in one or more steps is cold-rolled to form the cold-rolled strip. A method of this type permits the production of cold-rolled strips, in which the risk of a formation of an orange peel appearance or ridging is minimised during a cold forming process. To achieve this, the cast strip is cooled between the casting process and the winding process from a starting temperature above 1180 DEG C, at a cooling rate of at least 150 DEG C/s, to an intermediate maximum temperature of 1000 DEG C and is then held for at least 10 s at a maintenance temperature of between 900 and 1000 DEG C.
Description
The present invention relates to the method that a kind of preparation has the cold-rolled steel strip of ferritic structure, in the method the molten steel material is cast into the Cast Strip, this molten steel material forms ferritic structure when cooling, wherein if desired, can carry out online hot rolling to the Cast Strip, with the steel coil strip after the hot rolling around and in one or more steps, carry out cold rolling, thereby form cold-rolled steel strip.
Because the price height of nickel, therefore worldwide austenitic stainless steel is replaced by ferritic stainless steel just day by day, and the nickel that described ferritic stainless steel contains is usually only as production dependency associated element.For example, a kind of this paper of belonging to begins method described type, that can make the cold-rolled steel strip with ferritic structure and can learn from European patent EP 0 881 305 B1.According to the method for prior art, will contain in the casting gap between two rollers that (in weight %) the highest 0.12% C, Mn of the highest 1%, the highest 1% Si, the highest 0.04% P, the highest 0.030% S, 16% to 18% Cr, ferritic stainless steel that surplus is iron and unavoidable impurities cast in the double-roll type liquid filling machine and form the Cast Strip.Subsequently, with Cast Strip cooling, in this process, to avoid making steel band to be in cooling process in the austenite-ferrite phase transformation range.After the cooling, steel band is reeled under the temperature between 600 ℃ and the martensitic transformation temperature.
Subsequently, the steel band of reeling is cooled to 200 ℃ to the temperature between the envrionment temperature with the speed that is 300 ℃/hour to the maximum.At last, the steel band of reeling is carried out the known annealing at intermittence of script.
With regard to regard to the operation of continuous casting slab (it is generally used for preparing the ferrite steel plate) step, at first, then slab is reheated the steel slab surface typing, after this slab is made hot rolled strip in hot rolling mill, then with this steel band coiling.Immediately the hot rolled strip that is obtained by this mode is carried out annealing, the pickling and cold rolling of multi-pass.Finally, usually cold-rolled steel strip is carried out clean annealing and skin-pass rolling.
No matter adopt above-mentioned any method to make hot rolled strip, the problem of making cold-rolled steel strip by the ferritic stainless steel of Cr content in 17% scope is in cold working process subsequently, in the particularly deep-draw process may be wrinkling or form orange peel.At this, the wrinkling very significantly linear surface defective that under the ferritic chromium steel situation parallel, forms that is meant with rolling direction.On the other hand, the surface imperfection that is described as " orange peel " does not have directivity, and it has coarse appearance feature.
If will between separate cold rolling pass, carry out process annealing by the hot rolled strip that a kind of known preparation section makes, then can avoid wrinkling or the formation orange peel with extra cost.Yet the annealing steps of this costliness causes production cost to increase, and then causes the ferritic stainless steel steel band to have the market value higher than the equivalent material that is made by austenitic stainless steel.
Therefore, the objective of the invention is to disclose a kind of method, use this method to make cold-rolled steel strip by ferritic stainless steel, wherein risk wrinkling or the formation orange peel is dropped to minimum in the process of cold-forming.
According to the present invention, described purpose realizes in the following manner: begin in the method for described type at a kind of this paper of belonging to, between casting cycle and winding process, the Cast Strip is cooled to by the starting temperature that is not less than 1180 ℃ with at least 150 ℃/seconds speed of cooling is up to 1000 ℃ medium temperature, under the holding temperature between 900 ℃ to 1000 ℃, kept at least 10 seconds then.
The actual starting temperature of high strength cooling is generally 1180 ℃ to 1270 ℃, particularly 1200 ℃ to 1250 ℃.If do not reach 1180 ℃ minimum temperature, then may form a large amount of austenites at the edge of steel band, this will damage the effect of the inventive method.
What be particularly suitable for implementing the inventive method is a kind of steel that belongs to following other prior art of stainless steel-like, the stainless steel of described classification contains the Cr of the formation ferritic structure of 10 weight % to 18 weight %, and this stainless steel is in process of cooling, and the ferrite that forms during beginning can not change austenite fully into, change ferrite again into then.This steel also contains (in weight %) C of the highest 0.08%, 10% to 18% Cr, the highest 1% Si, the highest 1.5% Mn, the highest 1% Ni, the highest 0.04% P and the highest 0.015% S usually except containing iron and unavoidable impurities.Ni at this certain content that may exist does not add for metallurgical purpose, but the result who produces by manufacturing processed, nickel enters in the molten steel material via nickeliferous hot metal ladle, convertor or smelting furnace.Usually, the content of Ni is 0.7 weight % to 0.8 weight % in the steel of processing according to the present invention.
For the effect of the inventive method crucial part be with steel belt casting, fast cooling and with the Cast Strip 950 ± 50 ℃, particularly keep down time enough (minimum is 10 seconds) to combine at 950 ± 20 ℃.It is shocking, now show, in the cold-forming process of such cold-rolled steel strip, not only do not have wrinkling but also do not form orange peel, wherein said cold-rolled steel strip is to be made by a kind of Cast Strip of heat-treating according to the present invention, and it does not have experience to handle for the process annealing that reaches not only wrinkle resistant but also do not form the costliness that the purpose of orange peel must implement between the cold rolling stage.
The steel alloy that the present invention uses solidifies with the ferrite form in the process of steel belt casting at first.When the steel band that solidifies cooled off, ferrite partly changed austenite subsequently between 1200 ℃ to 800 ℃.Its thermodynamics former because: the solubleness of carbon in ferrite is very low, and this solubleness reduces along with the reduction of temperature.In addition, carbide that can combined carbon can only form below 900 ℃.On the other hand, the solubleness of carbon in austenite is significantly higher.
In normal process of cooling, austenite only forms at the crystal boundary place, and this is because the rapid diffusion once more of the carbon in the ferrite, and can migrate to edge by crystal grain inside.Therefore, ferritic crystal boundary is sign with the austenite.In case carbide forms being lower than under 900 ℃ the temperature, the austenite part at crystal boundary place reduces once more.Because the formation of carbide is relatively slow process, and this process can not thoroughly take place, so still residual have an austenite resistates, it is converted into martensite subsequently under 200 ℃ to 300 ℃ temperature.Therefore, use conventional treatment process, the residual austenite that remains in the crystal boundary place forms coarse as-cast structure.
At present, the present invention based on thinking comprise: be cooled to austenite very apace and partly form (950 ± 50 ℃, particularly 950 ± 20 ℃) near maximum temperature.The austenite that makes the crystal boundary place form like this is minimum, and this is that only the diffusion length of substitute element (Cr, Ni, Mn etc.) is just suitable because in described situation, the diffusion length of carbon is not enough in of short duration cooling time.
Simultaneously, under about 950 ℃ holding temperature, order about the motivating force maximum that austenite forms, and the temperature dependency spread coefficient is very little, makes the austenite particle form in crystal grain inside with nucleation mode.Because spread coefficient significantly reduces, make the distribution of the substitute element that contained in the various alloys not change or less degree change (quasi-equilibrium) only takes place.Simultaneously, reduced oversaturated carbon.
If the casting band kept under described temperature minimum 10 seconds, preferred 20 seconds in mode of the present invention, then the austenite particle will begin to separate out in the crystal grain inside at textural defect place.The new crystal grain that has destroyed initial as-cast structure forms in ferrite matrix.The time that keeps is long more, and pellet density is big more.This mechanism of separating out makes grain refining, thereby makes the cold-rolled steel strip that makes according to the present invention be not easy wrinkling and form orange peel.
In the high strength cooling process according to Cast Strip of the present invention, speed of cooling is fast more, just can suppress austenitic formation reliably more, as purpose of the present invention.Therefore it is fast as far as possible to make every effort to speed of cooling in principle.Yet relevant therewith actual tests confirms, the effect that just can produce the present invention reliably when speed of cooling is 150 ℃ to 250 ℃/second and pursued.
On the basis of above-mentioned basic skills of the present invention, can obtain different variant of the present invention, these variants can be selected according to following factors, and described factor is: the requirement of the required property combination of the cold-rolled steel strip that makes in various situations, the thermoforming behavior of the Cast Strip that obtains in various situations, available equipment and technology or operation logic.Therefore, for example, can at first carry out the high strength cooling and handle, carry out hot rolling or breaking down then and handle (be higher than 1200 ℃, be ferritic form), carry out quick cooling process then.In addition, can also be apace by the two-phase region between 1200 ℃ and 800 ℃.Like this, do not have austenite to form at first, and the ferrite that contains oversaturated carbon solidify.If promptly by being heated to holding temperature below 800 ℃, then crystal grain inside forms austenite again.In this case, especially promptly reheating to holding temperature is that processing result brings active influence.If it is too slow that heating is carried out, then form unwanted austenite in the grain boundary, because the diffusion of carbon makes the supersaturation carbon of crystal grain inside reduce, finally cause the initial as-cast structure of fixed simultaneously.And, should avoid in 800 ℃ to 900 ℃ temperature range, keeping the oversize time, because actual test confirms that maintenance is after about 100 seconds, because the formation of carbide makes oversaturated carbon reduce in this temperature range.
If temperature reaches and is lower than 500 ℃ (for example envrionment temperatures) in process of cooling, then no longer form carbide.Distinct therewith is that oversaturated ferrite solidifies, and at the inner austenite particle that forms of crystal grain, can promptly reheat (off-line heating) subsequently to 950 ℃.
On basis of the present invention, the Cast Strip is cooled to 900 ℃ to 1000 ℃ medium temperature in the process of high strength according to the present invention cooling, make the temperature that is reached for key factor of the present invention in direct mode rapidly.
Actual test confirms, be quickly cooled to medium temperature according to the present invention, and remaining on the positive effect of meeting generation under the holding temperature between casting cycle and the winding process, in addition, make in this way, also make the cold-rolled steel strip of gained be not easy wrinkling and the formation orange peel, the hot rolling of having omitted in the described method between casting cycle and the winding process is handled.But, in described Cast Strip is in (for example) situation about preparing in a usual manner by the double-roll type liquid filling machine, for the homogeneity of its little tissue formation and its characteristic distribution, between steel band casting cycle and winding process, described Cast Strip is carried out the hot rolling of at least one passage usually.Because tissue defects is introduced in little tissue, therefore make austenite particulate density and speed of separating out increase with thermal distortion.Utilize the key of this grain refining mechanism to depend on texturizing condition and cooling and the rate of heating of selecting optimum.In principle, rapid heating or cooling are only to realize in thin steel band.Therefore, be particularly suitable for described thermodynamics and handle by the cast steel band that makes of mode according to the present invention.If using the method according to this invention to carry out hot rolling handles, then preferably, at first directly steel band is cast into the thickness of 1mm to 5mm, the thickness of preferred 2mm to 3mm, then the Cast Strip is carried out online hot rolling and handle, make that every time draft is 5% to 60%, particularly 10% to 40%.In this case, the function of method of the present invention is to handle the temperature control that (if desired) selects steel band at the hot rolling of being implemented, make that such temperature condition is preponderated in course of hot rolling, the required property combination of the extension behavior of described temperature condition and the steel processed in various situations or the steel band that is obtained reaches optimum matching.
Thus, the various variants (comprising hot rolling) of the method according to this invention are as follows:
Variant 1
-casting Cast Strip;
-be not less than 1180 ℃, be generally under 1180 ℃ to 1270 ℃ the hot-rolled temperature hot rolling (initial cooling takes place in the Cast Strip in course of hot rolling) is carried out in the Cast Strip;
-speed of cooling with at least 150 ℃/seconds is cooled to 900 ℃ to 1000 ℃ immediately after hot rolling, and medium temperature and holding temperature all equal this temperature;
-resulting steel band was kept 10 seconds under 900 ℃ to 1000 ℃, particularly 950 ℃ ± 20 ℃ relevant temperature at least.
About first variant of the inventive method, after hot rolling, only implement insulation according to cooling of the present invention and steel band.Simultaneously, in this case, should after hot rolling, begin to cool down as early as possible, thus in practice after leaving last hot rolling support less than 3 seconds in, particularly in 1 second, begin to cool off.Like this, the casting heat of Cast Strip can be directly transferred in the hot rolling stage, made not only can to obtain high hot-rolled temperature, and can also be reduced to the necessary energy expenditure of temperature that is used to control steel band minimum.
Variant 2
-casting Cast Strip;
-be cooled to 900 ℃ to 1000 ℃ medium temperature with at least 150 ℃/seconds speed of cooling;
-under medium temperature, hot rolling is carried out in the Cast Strip;
-resulting steel band was kept 10 seconds under holding temperature at least, this holding temperature can be similarly 900 ℃ to 1000 ℃, particularly is substantially equal to medium temperature or is 950 ℃ ± 20 ℃.
In this variant of the present invention, before hot rolling, be cooled to medium temperature, and after hot rolling is carried out in the Cast Strip, hold it under the holding temperature.By under 900 ℃ to 1000 ℃, carrying out hot rolling, in little tissue of hot rolled strip, produce additional dislocation, it plays the effect that is used to form austenitic nucleation site in the process under remaining in holding temperature subsequently.
Variant 3
-casting Cast Strip;
-be cooled to 900 ℃ to 1000 ℃ medium temperature with at least 150 ℃/seconds speed of cooling;
-Cast Strip was kept 10 seconds under holding temperature at least, this holding temperature can be similarly 900 ℃ to 1000 ℃, particularly is substantially equal to medium temperature or is 950 ℃ ± 20 ℃;
-under medium temperature, hot rolling is carried out in the Cast Strip;
According to the 3rd variant, before hot rolling is carried out in the Cast Strip, it is cooled to medium temperature and remains under the holding temperature.The little tissue of highdensity austenite crystal in ferrite matrix (it is by forming in the operation of implementing before that remains under the holding temperature) is carried out the hot rolling meeting cause highdensity dislocation, it can cause forming fine grain structure in recrystallization subsequently.This recrystallization is normally handled and to be produced owing to suitable full annealed, and described processing is as being undertaken by standard in the manufacturing processed of such cold-rolled steel strip of being discussed.
Variant 4
-casting Cast Strip;
-be cooled to at least 150 ℃/seconds speed of cooling and be lower than 900 ℃, the medium temperature in 800 ℃ of scopes particularly;
-under medium temperature, hot rolling is carried out in the Cast Strip;
-resulting steel band quickly heated up to 950 ℃ ± 50 ℃, particularly 950 ℃ ± 20 ℃ holding temperature;
-steel band is remained under the holding temperature.
In this variant, be lower than 900 ℃, particularly under the temperature in about 800 ℃ of scopes, the pure ferritic phase with yielding stress carried out hot rolling (yielding stress of described pure ferritic phase is lower than the yielding stress when mixed phase is rolled).Therefore, if this situation be need and ideal, then can under the condition of energy expenditure that reduces and lower roller wearing and tearing, obtain higher degree of deformation.
According to the present invention Cast Strip high strength cooling is rolled the Cast Strip or is being lower than 500 ℃, particularly is lower than under 400 ℃ the temperature and carries out further heat treated possibility to being lower than to provide in 900 ℃ the temperature range being lower than basically under 800 ℃ the temperature.
Can on the liquid filling machine of described Cast Strip, implement the method for the present invention described in the above-mentioned variant especially economically, wherein cast continuously successively, hot rolling (if desired), reel and of the present inventionly be cooled to medium temperature and remain on step under the holding temperature what implement between casting cycle and the winding process according to the order of step.
Yet the effect that the present invention pursued also provides the possibility of discontinuous enforcement according to each treatment step of the inventive method.For example, if the corresponding apparatus technology is available or is preferably in different time in logic reason and carries out described treatment step that then discrete mode can prove favourable.The 5th variant of the present invention below having obtained thus.
Variant 5
-casting Cast Strip;
-be cooled to at least 150 ℃/seconds speed and be lower than 900 ℃, particularly be lower than 800 ℃ medium temperature;
-be cooled to and be lower than 500 ℃, envrionment temperature particularly;
-quickly heat up to final hot-rolled temperature;
-under hot-rolled temperature, hot rolling is carried out in the Cast Strip;
-resulting steel band quickly heated up to 950 ℃ holding temperature;
-steel band is remained under the holding temperature.
According to the 4th variant of the present invention, will be defined as according to Cast Strip of the present invention process of cooling: the Cast Strip is cooled to is lower than 900 ℃, particularly is lower than 800 ℃ medium temperature, this process of cooling can be reduced to envrionment temperature low temperature like that.Subsequently the Cast Strip is reheated to holding temperature.Be meant subsequently in this article can and keep at cooling step carrying out other treatment steps between the step, for example under specified temp, carry out hot rolling, deposit, be divided into plate etc.
In addition, can after casting, the Cast Strip be cooled to envrionment temperature, and and then at first the Cast Strip be heated to and be used for the hot rolled optimum temps, make it be under the holding temperature then and keep the required time at following a moment.
When implementing method of the present invention, if medium temperature reaches 800 ℃ to 900 ℃, then when reheating, in principle owing to the reason of having mentioned should be passed through this temperature range fast to holding temperature.Therefore, an advantageous embodiment of the present invention provides in 1 to 5 second, has particularly reheated to holding temperature from each medium temperature in 2 to 3 seconds.
If in process of cooling, the medium temperature that is reached is lower than 800 ℃ basically, particularly medium temperature is envrionment temperature or a little higher than this envrionment temperature, then owing to mention, steel band must be reheated fast enough to carry out hot rolling.Therefore, in 200 seconds, particularly reheated to specific hot-rolled temperature from low medium temperature in 100 seconds, this temperature is generally 700 ℃ to 800 ℃ to regulation of the present invention with steel band.If the speed that is heated to 800 ℃ is too slow, then may separate out unwanted carbide.This causes hypersaturated state to disappear too early, and causes the austenite pellet density significantly to reduce thus, and the result can't reach the effect of the grain refining that the present invention makes every effort to.
Therefore, the invention provides such method, this method provides in the production stage of avoiding costliness, prepares all possibilities of competitive product of performance and price.The special benefits of the inventive method is: the cold-rolled steel strip that can make the surface that it is characterized by uniform outward appearance and non-oxidation layer.Realize in the following manner on the surface of non-oxidation layer: removed any attached to the zone of oxidation on the Cast Strip in high strength cooling process according to the present invention as much as possible, make in the process of carrying out hot rolling (if desired), in the worst case, reach minimum by the degree that still is present in the caused surface damage of zone of oxidation on the steel band.
Therefore, use method of the present invention, omitted the deoxidation layer process (it often causes successive production order to be interrupted) of the costliness of prior art.In addition, can save prior art by method of the present invention is used for cold rolling material is carried out the necessary cost that intermittence, annealing was still needed.In the process of the inventive method, can be cooled to the temperature that is lower than 800 ℃ and further allow under such as 600 ℃ temperature, (for example) Cast Strip or hot rolling band to be repaired the common like this planarization problem of avoiding.At last, the method according to this invention makes the thermal distortion degree on the casting steel strip line increase, this be since by means of the support of (for example) second roller or more the working roll of minor diameter realize that substantially alternating temperature control freely causes, the result, by the cold-rolled steel strip of conventional production technique manufacturing, cold-rolled steel strip constructed in accordance can have better deep-draw/tension ability relatively.Implementing the necessary temperature variation fast of method of the present invention can be only by using the steel band casting technique to realize, because have only the Cast Strip of thickness minimum that temperature is changed on the entire cross section of steel band fully fast in situation of the present invention.Exemplary: in various situations, the ferritic steel that contains (in weight %) C of 0.043%, 0.25% Si, 0.36% Mn, 0.021% P, 0.002% S, 16.23% Cr, 0.49% Ni is the basis of exemplary what follows, implements described embodiment and is used to confirm effect of the present invention (test I to IV).
In the casting rolling equipment of conventional design, make the Cast Strip of each scheme by suitable molten steel material, thereby being carried out hot rolling, the Cast Strip makes hot rolled strip, at last hot rolled strip is reeled.The wind2 of arranging along described transmission direction that steel band casting equipment used herein comprises the double-roll type liquid filling machine, is arranged in the hot rolling support behind the liquid filling machine with online mode and is positioned at hot rolling support rear along the delivery direction of Cast Strip.According to specific testing sequence, also can use high strength water cooling equipment, induction furnace and electronic heat-insulating stove.
After thermal treatment according to the present invention, the hot rolled strip of gained has fine grain structure, with little the organizing that is described as " carefully " usually distinctly be, in fine grain structure of the present invention, the many particles of discovery in many relatively ferrite crystal grains (matrix) (martensite, residual austenite and carbide).Therefore, this little organize thinner generally, and itself also than the close grain of routine little organize more inhomogeneous.Being characterized as of little tissue of the steel band that therefore, makes: in each crystal grain, have a lot of particles according to the present invention.
Subsequently, in a conventional manner, each hot rolled strip that makes according to the present invention in the test I to IV that uses the casting rolling equipment is handled, comprised intermittently annealing, pickling, under the condition of not carrying out process annealing, carry out cold rolling, clean annealing and skin-pass rolling.
Prepare sample by the cold-rolled steel strip (the total deformation degree is 70%) that adopts this mode to obtain.Orange peel or wrinkling appears in none in these tests.
Test I
In first variant according to the inventive method, the thickness of Cast Strip is 3mm.When reaching 1180 ℃ Cast Strip temperature in the Cast Strip in the casting gap of leaving the double-roll type liquid filling machine, carry out the high strength water cooling and handle.The Cast Strip is in the medium temperature of 2 seconds internal cooling to 950 ℃.
Then, the refrigerative Cast Strip kept 10 seconds down in holding temperature (holding temperature equals medium temperature in this case) in the induction type process furnace incessantly with successive production order in this manner.
Then, the Cast Strip hot rolling after will heat-treating according to mode of the present invention is the thick steel band of 2.5mm.
It is preceding to arrive wind2 (steel band is wound into volume herein) at steel band, and it is cooled to about 550 ℃ coiling temperature on the runoff table behind the hot rolling support.
The hot rolled strip of Huo Deing has columnar grain tissue (about 100 μ m are wide, and 500 μ m are long) and center equiax crystal district (gleichachsigen Bandmittenbereich) (grain-size is 150 μ m) in this manner.Crystal boundary is occupied by the thin layer of martensite and carbide.In the inner discovery of crystal grain grain-size is the zone of the recrystallization of 20 μ m.In addition, the isolating particle of the fine distribution that is made of carbide, martensite and retained austenite is present in little tissue.Pellet density is generally 15 to 25 particle/crystal grain.
Test II
In second test, at first prepare the Cast Strip of thickness as 2.8mm by the molten steel material that uses alloy mentioned above.This Cast Strip remained in the induction type process furnace under 1200 ℃ the temperature, under this temperature, be rolled into the steel band that thickness is 2.1mm then.
After hot rolling, carry out the high strength water cooling immediately.In this case, the steel band that will carry with about 1 meter per second is in the medium temperature of 1 second internal cooling to 950 ℃.Then, steel band arrives on the runoff table, and the first part of this runoff table links to each other with the hot rolling support, and to be equipped with length be 15 meters plate cover, and it is used for guaranteeing steel band was kept 15 seconds under substantially invariable temperature in first part.Subsequently, still on runoff table steel band is cooled to about 500 ℃ coiling temperature, steel band finally is wound into volume under this temperature.
Little tissue of the hot rolled strip that obtains in second test has with the hot rolled strip that obtains in first test little organizes identical columnar grain tissue (about 100 μ m are wide, and 500 μ m grow) and center equiax crystal district (grain-size is 150 μ m).In addition, in this case, crystal boundary shows as the thin layer that is occupied by martensite and carbide.Equally, be the zone of the recrystallization of 20 μ m in the inner discovery of crystal grain grain-size.In addition, the isolating particle of fine distribution (it is also identical with the steel band that obtains in first test, is made of carbide, martensite and retained austenite) is present in little tissue.Pellet density is generally 20 to 30 particle/crystal grain.
Test III
In the 3rd test, at first casting thickness is the Cast Strip of 3mm.Reach 1180 ℃ temperature in the Cast Strip after, begin to carry out the high strength water cooling and handle, the Cast Strip is in the medium temperature of 3 seconds internal cooling to 780 ℃.Then, will be in this manner the refrigerative Cast Strip in the induction type process furnace, be incubated, be heated to 800 ℃ hot-rolled temperature, and under this hot-rolled temperature, the Cast Strip be rolled into the steel band that thickness is 2.5mm.Then steel band is cooled to about 550 ℃ coiling temperature on runoff table, and under this temperature, reels.
At ambient temperature, from the steel band that obtains in this manner, be partitioned into the sample steel plate.Then, at first the sample steel plate is heated to 800 ℃ with induction heating mode, then at 15 seconds internal heating to 950 ℃.Continue 2 seconds the heat-up time between 800 ℃ and 950 ℃.
Use holding furnace, steel band was kept 20 seconds under 950 ℃ holding temperature.Subsequently, carry out air cooling.
Little the organizing of heat treated like this hot rolled strip sample panel shows columnar grain tissue (about 100 μ m are wide, and 500 μ m are long) and center equiax crystal district (grain-size is 150 μ m) equally.At the crystal boundary place, thin layer is also occupied by martensite and carbide.Found also that in crystal grain inside grain-size is the zone of the recrystallization of 20 μ m, and the isolating particle of the fine distribution that is made of carbide, martensite and retained austenite is present in little tissue.Pellet density is generally 40 to 60 particle/crystal grain.
Test IV
III is similar with test, and preparation thickness is the Cast Strip of 3mm, when the Cast Strip temperature reaches 1180 ℃, carries out high strength cooling and handles, till reaching 780 ℃ medium temperature.Yet different with test III is be not only the step that keeps holding temperature, and hot-rolled step all to be that off-line carries out.
In order to reach described purpose, after the Cast Strip is cooled to envrionment temperature, be partitioned into steel plate by this Cast Strip, and these steel plates were heated to 800 ℃ hot-rolled temperature by envrionment temperature with induction heating mode in 30 seconds, wherein said steel plate is the thick steel band of 2.4mm by hot rolling.After hot-rolled steel sheet is cooled off repeatedly, in 3 seconds, these steel plates are reheated to 950 ℃ holding temperature.
Use holding furnace, the steel band that reheats was kept 20 seconds under holding temperature.Subsequently, this steel band being carried out air cooling handles.
In addition, in this exemplary embodiment, after under remaining in holding temperature, little organization table of hot-rolled steel sheet reveals the columnar grain tissue, and (about 100 μ m are wide, 500 μ m are long) and center equiax crystal district (grain-size is 150 μ m), wherein have the thin layer that is occupied by martensite and carbide equally, and find also that in crystal grain inside grain-size is the zone of the recrystallization of 20 μ m at the crystal boundary place.Just the same with other test, the isolating particle of the fine distribution that is made of carbide, martensite and retained austenite is present in little tissue equally.Pellet density is generally 40 to 60 particle/crystal grain.
Claims (21)
1. method for preparing cold-rolled steel strip with ferritic structure, wherein the molten steel material is cast into the Cast Strip, described molten steel material forms ferritic structure when cooling, wherein if desired, then online hot rolling is carried out in described Cast Strip, with the steel coil strip after the hot rolling around and carry out one the step or multistep cold rolling, thereby form described cold-rolled steel strip, described method is characterised in that, between described casting cycle and described winding process, described Cast Strip is cooled to by the starting temperature that is not less than 1180 ℃ with at least 150 ℃/seconds speed of cooling and is up to 1000 ℃ medium temperature, under the holding temperature between 900 ℃ to 1000 ℃, kept at least 10 seconds then.
2. method according to claim 1 is characterized in that, the starting temperature of described high strength cooling is 1180 ℃ to 1270 ℃, particularly 1200 ℃ to 1250 ℃.
3. according to any described method in the aforementioned claim, it is characterized in that described molten steel material is made of the following ingredients in weight %:
Cr:10.5% to 18%,
C：≤0.08％，
Si：≤1％，
Mn：≤1.5％，
Ni：≤1.00％，
P：≤0.04％，
S：≤0.015％，
All the other are iron and unavoidable impurities.
4. according to any described method in the aforementioned claim, it is characterized in that described speed of cooling is 150 ℃/second to 250 ℃/second.
5. according to any described method in the aforementioned claim, it is characterized in that described medium temperature is 900 ℃ to 1000 ℃.
6. method according to claim 5 is characterized in that described medium temperature equals described holding temperature.
7. according to any described method in the aforementioned claim, it is characterized in that, hot rolling is carried out in described Cast Strip.
8. method according to claim 7 is characterized in that, described cooling step and described maintenance step are carried out after described hot rolling.
9. method according to claim 8 is characterized in that, after described hot rolled strip leaves final hot rolling support, less than 3 seconds, begin described hot rolled strip is cooled off in particularly less than 1 second time.
10. method according to claim 7 is characterized in that, before hot rolling is carried out in described Cast Strip, this Cast Strip is cooled to described medium temperature, and remains under the described holding temperature.
11. method according to claim 7 is characterized in that, before hot rolling is carried out in described Cast Strip, it is cooled to described medium temperature, and after described Cast Strip is by hot rolling, holds it under the described holding temperature.
12., it is characterized in that described Cast Strip the time reaches in cooling and is lower than 900 ℃, particularly is lower than 800 ℃ medium temperature according to any described method in the aforementioned claim, described subsequently Cast Strip is reheated to described holding temperature.
13. according to claim 7 and 12 described methods, it is characterized in that, carry out hot rolling being lower than under 800 ℃ the medium temperature.
14. according to any described method in claim 12 and 13, it is characterized in that, in 1 to 5 second, reheat.
15. according to any described method in the claim 12 to 14, it is characterized in that, according to discrete production implement in proper order casting step, depending on the circumstances or the needs of the situation and the hot-rolled step that carries out, coiling step and between described casting step and described coiling step, carry out be cooled to medium temperature and remain on step under the holding temperature.
16. method according to claim 15 is characterized in that, in when cooling, described steel band reaches and is lower than 500 ℃, particularly is lower than 400 ℃ temperature.
17. method according to claim 16 is characterized in that, after casting, described steel band is cooled to envrionment temperature.
18. according to any described method in claim 16 and 17, it is characterized in that, in 200 seconds, particularly in 100 seconds, described steel band is heated to each described hot-rolled temperature to carry out hot rolling.
19. according to any described method in the claim 1 to 14, it is characterized in that, according to successive production implement in proper order casting step, depending on the circumstances or the needs of the situation and the hot-rolled step that carries out, coiling step and between described casting step and described coiling step, carry out be cooled to medium temperature and remain on step under the holding temperature.
20., it is characterized in that described steel band is to use the double-roll type liquid filling machine to cast according to any described method in the aforementioned claim.
21., it is characterized in that the maximum ga(u)ge of described Cast Strip is 6mm according to any described method in the aforementioned claim.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE102005063058A DE102005063058B3 (en) | 2005-12-29 | 2005-12-29 | Producing cold rolled strip of ferritic stainless steel comprises controlled cooling before cold rolling |
| DE102005063058.8 | 2005-12-29 | ||
| PCT/EP2006/070223 WO2007074157A2 (en) | 2005-12-29 | 2006-12-27 | Method for producing a cold-rolled strip from stainless steel with a ferritic structure and a reduced susceptibility to ridging |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN101365812A true CN101365812A (en) | 2009-02-11 |
| CN101365812B CN101365812B (en) | 2012-10-10 |
Family
ID=37989777
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN2006800500453A Expired - Fee Related CN101365812B (en) | 2005-12-29 | 2006-12-27 | Method for producing a cold-rolled steel strip with a ferritic structure |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US20090065104A1 (en) |
| EP (1) | EP1966399B1 (en) |
| JP (1) | JP2009522106A (en) |
| KR (1) | KR101362388B1 (en) |
| CN (1) | CN101365812B (en) |
| BR (1) | BRPI0620748A2 (en) |
| DE (1) | DE102005063058B3 (en) |
| WO (1) | WO2007074157A2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105177255A (en) * | 2015-10-15 | 2015-12-23 | 东北大学 | Heat treatment technological method for ferrite-austenite duplex stainless steel |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101563606B1 (en) * | 2009-03-11 | 2015-10-27 | 잘쯔기터 플래시슈탈 게엠베하 | Method for producing a hot rolled strip and hot rolled strip produced from ferritic steel |
| DE102011000089A1 (en) * | 2011-01-11 | 2012-07-12 | Thyssenkrupp Steel Europe Ag | Method for producing a hot rolled flat steel product |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19930519C1 (en) * | 1999-07-05 | 2000-09-14 | Thyssenkrupp Stahl Ag | Non-textured electrical steel sheet, useful for cores in rotary electrical machines such as motors and generators, is produced by multi-pass hot rolling mainly in the two-phase austenite-ferrite region |
| JPS59576B2 (en) * | 1980-08-09 | 1984-01-07 | 新日本製鐵株式会社 | Manufacturing method of ferritic stainless thin steel sheet with excellent workability |
| JPS6256529A (en) * | 1985-09-06 | 1987-03-12 | Nippon Steel Corp | Manufacture of ferritic stainless steel sheet having satisfactory ridging characteristic |
| JPS62176649A (en) * | 1986-01-28 | 1987-08-03 | Nippon Yakin Kogyo Co Ltd | Production for ferite stainless steel thin hoop having no roping |
| BR9606325A (en) * | 1995-04-14 | 1997-09-16 | Nippon Steel Corp | Apparatus for the production of a stainless steel strip |
| FR2763960B1 (en) * | 1997-05-29 | 1999-07-16 | Usinor | PROCESS FOR PRODUCING FERRITIC STAINLESS STEEL THIN STRIPS AND THIN STRIPS THUS OBTAINED |
| ITRM20010678A1 (en) * | 2001-11-15 | 2003-05-15 | Acciai Speciali Terni Spa | PROCEDURE FOR THE ONLINE RECRYSTALLIZATION OF RAW SOLIDIFICATION TAPES IN CARBON STEEL AND IN ALLOY AND BONDED STEEL |
-
2005
- 2005-12-29 DE DE102005063058A patent/DE102005063058B3/en not_active Expired - Fee Related
-
2006
- 2006-12-27 CN CN2006800500453A patent/CN101365812B/en not_active Expired - Fee Related
- 2006-12-27 JP JP2008547960A patent/JP2009522106A/en active Pending
- 2006-12-27 EP EP06847041A patent/EP1966399B1/en not_active Expired - Fee Related
- 2006-12-27 WO PCT/EP2006/070223 patent/WO2007074157A2/en active Application Filing
- 2006-12-27 US US12/159,343 patent/US20090065104A1/en not_active Abandoned
- 2006-12-27 BR BRPI0620748-0A patent/BRPI0620748A2/en not_active Application Discontinuation
- 2006-12-27 KR KR1020087015484A patent/KR101362388B1/en active IP Right Grant
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105177255A (en) * | 2015-10-15 | 2015-12-23 | 东北大学 | Heat treatment technological method for ferrite-austenite duplex stainless steel |
Also Published As
| Publication number | Publication date |
|---|---|
| DE102005063058B3 (en) | 2007-05-24 |
| US20090065104A1 (en) | 2009-03-12 |
| JP2009522106A (en) | 2009-06-11 |
| EP1966399B1 (en) | 2012-07-11 |
| WO2007074157A3 (en) | 2007-10-04 |
| WO2007074157A2 (en) | 2007-07-05 |
| EP1966399A2 (en) | 2008-09-10 |
| KR101362388B1 (en) | 2014-02-12 |
| BRPI0620748A2 (en) | 2011-11-22 |
| CN101365812B (en) | 2012-10-10 |
| KR20080089362A (en) | 2008-10-06 |
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