EP0473561B1 - A method of heat treatment of a steel product - Google Patents
A method of heat treatment of a steel product Download PDFInfo
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- EP0473561B1 EP0473561B1 EP91870119A EP91870119A EP0473561B1 EP 0473561 B1 EP0473561 B1 EP 0473561B1 EP 91870119 A EP91870119 A EP 91870119A EP 91870119 A EP91870119 A EP 91870119A EP 0473561 B1 EP0473561 B1 EP 0473561B1
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- cooling
- product
- temperature
- process according
- surface temperature
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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
- C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
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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
Definitions
- the present invention relates to a process for heat treatment of a steel product, preferably carried out immediately after the rolling of this product.
- the process of the invention is particularly applicable to long products, which generally undergo, after rolling, cooling on a cooler.
- These include beams, sheet piles, rails, bars and merchant bars of the most varied sections, but also tubes of any shape.
- a surface quenching treatment is applied to the profile, at its exit from the last stand of the rolling mill, when it is at a temperature above its point Ar3 and self-income.
- the profile is subjected to accelerated cooling with water, which causes the hardening of a surface layer of the product. This is then deposited on a cooler where it undergoes slow cooling with calm air, firstly comprising self-tempering of the hardened surface layer.
- Treatments of this kind make it possible above all to modify the microstructure of the steel and thus to improve in a manner often spectacular the physical properties of the treated product. However, they do not make it possible to reduce the total duration of the cooling cycle significantly compared with simple cooling in air.
- the object of the present invention is to propose a process for heat treatment of a steel product of the aforementioned type, which can be carried out in a significantly shorter time than the previous processes and which makes it possible to minimize deformation during cooling.
- the process of the invention allows the in-line cooling of the mother products leaving the rolling mill, as well as the dressing of these products, also in line, before their cutting to the desired length. It greatly reduces handling of the products and it leads to products having excellent mechanical properties, in particular high strength accompanied by high ductility and resilience.
- the method of heat treatment of a steel product at the outlet of the rolling mill in which during a first step the product is subjected to a rapid cooling with water from the end of rolling temperature to a surface temperature equal to or lower than the temperature at the start of the martensitic transformation, known as the Ms point, of said steel, with a cooling rate at least equal to the critical tempering speed of said steel and in a second step the product is subjected to a self-tempering phase during which, thanks to the heat given off by the unhardened part of the product, the heating of the surface layer quenched to a surface temperature, called self-tempering, between 550 ° C and 650 ° C, is characterized in that the product is then subjected to a secondary cooling phase comprising cooling to air to a surface temperature of about 550 ° C followed by cooling to a surface temperature below 450 ° C, and in that in a third step, the refr final oidification of the product up to a temperature below 120
- said cooling to a surface temperature below 450 ° C is carried out in air.
- said air cooling is carried out up to a surface temperature below 420 ° C.
- the product after the product has been cooled in air to a temperature of around 550 ° C., it is then cooled to a temperature substantially below 400 ° C, the product is allowed to warm up to a temperature between 400 ° C and 420 ° C, slow cooling in air is carried out and abrupt final cooling is carried out to a temperature below 120 ° C.
- the product is advantageously cooled to a temperature below 80 ° C during said final cooling, which preferably consists of cooling with strongly agitated water.
- the method of the invention is implemented continuously, with the product leaving the last rolling stand and then traversing the treatment device. After the final cooling according to one or the other embodiment, the product is drawn up continuously, then it is cut to the desired length.
- the reference numeral 1 in Figure 1 designates the rolled steel product, in this case a profile, which moves in the direction of arrow 2.
- This product circulates continuously in a series of devices where it is subjected to the stages of successive cooling, corresponding to the diagrams in Figures 2 and 3.
- Product 1 leaves the last stand of the rolling mill, symbolized by a pair of cylinders 3, and immediately enters a first cooling device 4.
- This first device known per se, consists of a tube of appropriate section, filled with circulating water.
- Product 1 undergoes abrupt surface cooling there, from the end of rolling temperature to a surface temperature below the point Ms of the steel considered; during this first cooling (of duration t1), a layer of martensite is formed on the surface of product 1.
- this surface layer of martensite depends on the speed and the intensity of the cooling, that is to say in fact on the duration t1 and on the surface temperature of the product to be the end of cooling.
- the product 1 is transferred to a cooler 5, where it is subjected to in-line cooling according to one or the other embodiment of the method of the present invention.
- the product undergoes a first phase, self-income phase, during which there is an equalization of the temperature between the core and the surface of the product; the core cools and the surface heats up to a temperature between 550 ° C and 650 ° C, which causes self-tempering of the surface layer of martensite.
- the self-income phase has a duration t2. The differences between the forms of execution relate to the operations which follow the self-income phase.
- FIG. 2 represents the time evolution of the surface temperature of the product when the secondary phase of the second stage of the process consists only of air cooling.
- this secondary phase consists of air cooling of the product to a temperature below 450 ° C, and preferably below 420 ° C.
- the duration t3 of this cooling in still air naturally depends on the type of product, in particular on its thickness. It is essential to allow the product to cool in air to a temperature below 450 ° C, and preferably below 420 ° C, to guarantee good resilience of the final product. If the final cooling, that is to say the third stage of the process, is applied, from too high a temperature, the residual austenite which is not yet transformed and enriched in carbon can transform into martensite and give rise to a fragile structure.
- This final cooling, of duration t4 is carried out with water to limit the duration of the treatment; it should no longer have a metallurgical effect.
- the diagram in FIG. 3 represents the temporal evolution of the surface temperature of the product, when the second phase of the second stage of the process successively comprises air cooling (t31), intense cooling (t32), an auto -heating (t33) and air cooling (t34).
- An intense cooling (t32) is then carried out, generally with circulating water, from this temperature of approximately 550 ° C. to a surface temperature of 300 ° C.
- air cooling (t34) is carried out from 400 ° C to 300 ° C during which performs the ferrite overaging reaction; the final cooling is then carried out (t4) constituting the third step of the process. This final cooling is carried out with water up to the temperature of 80 ° C., temperature at which the product can be handled without alteration.
- the product 1 can still be dressed in a dressing device 7, then a shear 8 cuts it into sections of desired length, which are evacuated by an outlet conveyor 9.
- the dressing must be carried out at a temperature below 120 ° C and preferably below 80 ° C to avoid any subsequent deformation.
- the following two tables indicate typical cooling times for the different stages of the process of the invention, in the case of profiles of different thicknesses.
- the thicknesses e of the profiles are expressed in millimeters (mm) and the times (t i ) are expressed in seconds (s).
- Table 1 corresponds to the first embodiment described above and shown schematically in Figure 2.
- the duration of self-income (t3) increases rapidly with the thickness of the profile, and risks becoming prohibitive for products of very thick (> 40 mm); it is therefore interesting to insert intense cooling in the second phase of the second stage of the process, as shown in Figure 3.
- TABLE 2. e (mm) t1 (s) t2 (s) t31 (s) t32 (s) t33 (s) t34 (s) t4 (s) 28 5.5 20 120 3 12 180 25 40 8.85 40 160 49 22 180 45 125 55 360 570 31 180 180 320
- Table 2 illustrates this embodiment. We note that it brings in all cases a significant time saving (about 20 minutes for products of 125 mm thickness). This saving of time does not harm the quality of the products, because they have good straightness, high resistance, as well as excellent resilience at any point in their section.
- the method of the invention makes it possible to carry out the entire treatment, including dressing, on the parent products, that is to say as they come out of the rolling mill. We thus significantly reduce the number of manipulations required and therefore the risk of the appearance of faults linked to these manipulations. Finally, only one short cooler is used since the stay in air is short, which limits on the one hand the risk of confusion between the products and on the other hand the degree of oxidation of the product surface.
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- Crystallography & Structural Chemistry (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Heat Treatments In General, Especially Conveying And Cooling (AREA)
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Abstract
Description
La présente invention concerne un procédé de traitement thermique d'un produit en acier, effectué de préférence immédiatement après le laminage de ce produit.The present invention relates to a process for heat treatment of a steel product, preferably carried out immediately after the rolling of this product.
Le procédé de l'invention s'applique particulièrement aux produits longs, qui subissent généralement, après laminage, un refroidissement sur un refroidissoir. Il s'agit notamment des poutrelles, des palplanches, des rails, des barres et des fers marchands des sections les plus variées, mais aussi des tubes de forme quelconque.The process of the invention is particularly applicable to long products, which generally undergo, after rolling, cooling on a cooler. These include beams, sheet piles, rails, bars and merchant bars of the most varied sections, but also tubes of any shape.
Dans la pratique courante conventionnelle, les produits longs des types précités quittent le laminoir à une température supérieure à leur point Ar₃ et ils sont déposés sur un refroidissoir où ils subissent un refroidissement dans l'air jusqu'à la température ambiante. Cette pratique requiert de longues durées de refroidissement et elle n'offre aucune possibilité de réglage de l'intensité et de la durée de ce refroidissement.In conventional current practice, long products of the aforementioned types leave the rolling mill at a temperature above their point Ar₃ and they are deposited on a cooler where they are cooled in air to room temperature. This practice requires long cooling times and offers no possibility of adjusting the intensity and duration of this cooling.
Dans une technique, connue notamment par le brevet BE-A-834059, on applique au profilé, à sa sortie de la dernière cage du laminoir, alors qu'il se trouve à une température supérieure à son point Ar₃, un traitement de trempe superficielle et d'auto-revenu. Dans la pratique, on fait subir au profilé un refroidissement accéléré à l'eau, qui provoque la trempe d'une couche superficielle du produit. Celui-ci est déposé alors sur un refroidissoir où il subit un refroidissement lent à l'air calme comportant tout d'abord un auto-revenu de la couche superficielle trempée.In a technique, known in particular by patent BE-A-834059, a surface quenching treatment is applied to the profile, at its exit from the last stand of the rolling mill, when it is at a temperature above its point Ar₃ and self-income. In practice, the profile is subjected to accelerated cooling with water, which causes the hardening of a surface layer of the product. This is then deposited on a cooler where it undergoes slow cooling with calm air, firstly comprising self-tempering of the hardened surface layer.
On connaît également, par le brevet FR-A-2405998, un procédé de traitement de profilés tubulaires en acier, comportant un refroidissement primaire brusque et une deuxième étape comprenant une phase d'auto-revenu.Also known, from patent FR-A-2405998, is a process for treating tubular steel sections, comprising a sudden primary cooling and a second step comprising a self-tempering phase.
Les traitements de ce genre permettent surtout de modifier la microstructure de l'acier et d'améliorer ainsi de façon souvent spectaculaire les propriétés physiques du produit traité. Mais ils ne permettent pas de réduire la durée totale du cycle de refroidissement de façon notable par rapport à un simple refroidissement dans l'air.Treatments of this kind make it possible above all to modify the microstructure of the steel and thus to improve in a manner often spectacular the physical properties of the treated product. However, they do not make it possible to reduce the total duration of the cooling cycle significantly compared with simple cooling in air.
L'utilisation d'un refroidissoir, qui est nécessaire dans les méthodes précitées, entraîne les inconvénients les plus divers, qui s'ajoutent à la longue durée du refroidissement dans l'air calme. En effet, les produits subissent une oxydation superficielle assez importante pendant leur séjour de longue durée dans l'air. De plus, la conduite du refroidissoir impose de nombreuses manipulations des produits, qui sont coûteuses et qui risquent de provoquer des défauts. Enfin, les produits quittant le laminoir, dits produits-mères, sont souvent découpés à la longueur désirée, en produits-filles, avant d'être déposés sur le refroidissoir. Il est généralement nécessaire d'utiliser plusieurs refroidissoirs en parallèle pour le refroidissement simultané des divers produits-filles, ce qui entraîne des risques de confusion entre ces produits. De plus, le rendement de l'opération de dressage est réduit du fait que celle-ci est pratiquée sur les produits-filles, de longueur limitée.The use of a cooler, which is necessary in the aforementioned methods, involves the most diverse drawbacks, which are added to the long duration of cooling in still air. Indeed, the products undergo a fairly significant surface oxidation during their long-term stay in the air. In addition, the operation of the cooler requires numerous manipulations of the products, which are expensive and which risk causing defects. Finally, the products leaving the rolling mill, called parent products, are often cut to the desired length, into daughter products, before being placed on the cooler. It is generally necessary to use several chillers in parallel for the simultaneous cooling of the various daughter products, which entails risks of confusion between these products. In addition, the efficiency of the dressing operation is reduced because it is performed on the daughter products, of limited length.
La présente invention a pour objet de proposer un procédé de traitement thermique d'un produit en acier du type précité, réalisable en un temps nettement plus court que les procédés antérieurs et permettant de minimiser les déformations pendant le refroidissement. Le procédé de l'invention permet le refroidissement en ligne des produits-mères quittant le laminoir, ainsi que le dressage de ces produits, également en ligne, avant leur découpage à la longueur désirée. Il réduit fortement les manipulations des produits et il conduit à des produits présentant d'excellentes propriétés mécaniques, en particulier une haute résistance accompagnée d'une ductilité et d'une résilience élevées.The object of the present invention is to propose a process for heat treatment of a steel product of the aforementioned type, which can be carried out in a significantly shorter time than the previous processes and which makes it possible to minimize deformation during cooling. The process of the invention allows the in-line cooling of the mother products leaving the rolling mill, as well as the dressing of these products, also in line, before their cutting to the desired length. It greatly reduces handling of the products and it leads to products having excellent mechanical properties, in particular high strength accompanied by high ductility and resilience.
Conformément à la présente invention, le procédé de traitement thermique d'un produit en acier à la sortie du laminoir, dans lequel au cours d'une première étape on soumet le produit à un refroidissement rapide à l'eau depuis la température de fin de laminage jusqu'à une température de surface égale ou inférieure à la température du début de la transformation martensitique, dite point Ms, dudit acier, avec une vitesse de refroidissement au moins égale à la vitesse critique de trempe dudit acier et au cours d'une deuxième étape on soumet le produit à une phase d'auto-revenu au cours de laquelle, grâce à la chaleur dégagée par la partie non trempée du produit, on réalise le réchauffage de la couche superficielle trempée jusqu'à une température de surface, dite d'auto-revenu, comprise entre 550°C et 650°C, est caractérisé en ce que l'on soumet ensuite le produit à une phase de refroidissement secondaire comprenant un refroidissement à l'air jusqu'à une température de surface d'environ 550°C suivi d'un refroidissement jusqu'à une température de surface inférieure à 450°C, et en ce qu'au cours d'une troisième étape, on effectue le refroidissement final du produit jusqu'à une température inférieure à 120°C.According to the present invention, the method of heat treatment of a steel product at the outlet of the rolling mill, in which during a first step the product is subjected to a rapid cooling with water from the end of rolling temperature to a surface temperature equal to or lower than the temperature at the start of the martensitic transformation, known as the Ms point, of said steel, with a cooling rate at least equal to the critical tempering speed of said steel and in a second step the product is subjected to a self-tempering phase during which, thanks to the heat given off by the unhardened part of the product, the heating of the surface layer quenched to a surface temperature, called self-tempering, between 550 ° C and 650 ° C, is characterized in that the product is then subjected to a secondary cooling phase comprising cooling to air to a surface temperature of about 550 ° C followed by cooling to a surface temperature below 450 ° C, and in that in a third step, the refr final oidification of the product up to a temperature below 120 ° C.
Selon une première forme d'exécution du procédé de l'invention, ledit refroidissement jusqu'à une température de surface inférieure à 450°C est effectué à l'air.According to a first embodiment of the method of the invention, said cooling to a surface temperature below 450 ° C is carried out in air.
Suivant une caractéristique supplémentaire de ce procédé, on effectue ledit refroidissement à l'air jusqu'à une température de surface inférieure à 420°C.According to an additional characteristic of this process, said air cooling is carried out up to a surface temperature below 420 ° C.
Suivant une forme d'exécution particulièrement intéressante du procédé de l'invention, après le refroidissement du produit à l'air jusqu'à une température d'environ 550°C, on le refroidit ensuite jusqu'à une température substantiellement inférieure à 400°C, on laisse réchauffer le produit jusqu'à une température comprise entre 400°C et 420°C, on effectue un refroidissement lent dans l'air et on procède à un refroidissement final abrupt jusqu'à une température inférieure à 120°C.According to a particularly advantageous embodiment of the process of the invention, after the product has been cooled in air to a temperature of around 550 ° C., it is then cooled to a temperature substantially below 400 ° C, the product is allowed to warm up to a temperature between 400 ° C and 420 ° C, slow cooling in air is carried out and abrupt final cooling is carried out to a temperature below 120 ° C.
On refroidit le produit avantageusement jusqu'à une température inférieure à 80°C lors dudit refroidissement final, qui consiste de préférence en un refroidissement à l'eau fortement agitée.The product is advantageously cooled to a temperature below 80 ° C during said final cooling, which preferably consists of cooling with strongly agitated water.
Selon une caractéristique supplémentaire, le procédé de l'invention est mis en oeuvre en continu, avec le produit quittant la dernière cage de laminoir et parcourant ensuite le dispositif de traitement. Après le refroidissement final suivant l'une ou l'autre forme d'exécution, on dresse le produit en continu, puis on le découpe à la longueur désirée.According to an additional characteristic, the method of the invention is implemented continuously, with the product leaving the last rolling stand and then traversing the treatment device. After the final cooling according to one or the other embodiment, the product is drawn up continuously, then it is cut to the desired length.
Le procédé de l'invention sera maintenant exposé de manière plus détaillée, en faisant référence aux dessins annexés, dans lesquels la
- Fig. 1
- illustre schématiquement une installation permettant la mise en oeuvre des différentes formes d'exécution du procédé de l'invention; la
- Fig. 2
- représente le diagramme de l'évolution de la température de la surface du produit au cours du traitement thermique objet de l'invention, lorsque ce traitement thermique comporte durant la deuxième étape, un refroidissement secondaire effectué sans discontinuité à la suite de la phase d'auto-revenu; et la
- Fig. 3
- représente le diagramme de l'évolution de la température de la surface d'un produit lorsque le refroidissement secondaire comprend un refroidissement rapide et un revenu intermédiaire.
- Fig. 1
- schematically illustrates an installation allowing the implementation of the various embodiments of the method of the invention; the
- Fig. 2
- represents the diagram of the evolution of the temperature of the surface of the product during the heat treatment object of the invention, when this heat treatment comprises during the second stage, a secondary cooling carried out without discontinuity following the phase of self-income; and the
- Fig. 3
- represents the diagram of the evolution of the temperature of the surface of a product when the secondary cooling comprises a rapid cooling and an intermediate tempering.
Les figures ne comportent pas d'échelle particulière; on n'y a représenté que les éléments nécessaires à la bonne compréhension de l'invention.The figures do not include a particular scale; there are shown only the elements necessary for a good understanding of the invention.
La description donnée ci-après se réfère au refroidissement de profilés de différentes épaisseurs. Elle n'a bien entendu aucun caractère limitatif, notamment en ce qui concerne les durées des différentes étapes de refroidissement et l'intensité du refroidissement. Ces paramètres sont adaptés de manière connue par l'homme de l'art en fonction du type et de l'analyse du produit.The description given below refers to the cooling of profiles of different thicknesses. It is of course in no way limiting, in particular as regards the durations of the various cooling stages and the intensity of the cooling. These parameters are adapted in a manner known to those skilled in the art depending on the type and analysis of the product.
Le repère numérique 1 de la Figure 1 désigne le produit laminé en acier, en l'occurrence un profilé, qui se déplace dans le sens de la flèche 2. Ce produit circule en continu dans une série de dispositifs où il est soumis aux étapes de refroidissement successives, correspondant aux diagrammes des Figures 2 et 3.The
Le produit 1 quitte la dernière cage du laminoir, symbolisée par une paire de cylindres 3, et pénètre immédiatement dans un premier dispositif de refroidissement 4. Ce premier dispositif, connu en soi, se compose d'un tube de section appropriée, rempli d'eau en circulation. Le produit 1 y subit un refroidissement superficiel brusque, depuis la température de fin de laminage jusqu'à une température de surface inférieure au point Ms de l'acier considéré; au cours de ce premier refroidissement (de durée t1), il se forme une couche de martensite à la surface du produit 1.
De façon également connue en soi, l'épaisseur de cette couche superficielle de martensite dépend de la vitesse et de l'intensité du refroidissement, c'est-à-dire en fait de la durée t1 et de la température de surface du produit à la fin du refroidissement.In a manner also known per se, the thickness of this surface layer of martensite depends on the speed and the intensity of the cooling, that is to say in fact on the duration t1 and on the surface temperature of the product to be the end of cooling.
Après cette première étape du traitement thermique, le produit 1 est transféré sur un refroidissoir 5, où il est soumis à un refroidissement en ligne suivant l'une ou l'autre forme d'exécution du procédé de la présente invention. Dans tous les cas, le produit subit une première phase, phase d'auto-revenu, au cours de laquelle il se produit une égalisation de la température entre le coeur et la surface du produit; le coeur se refroidit et la surface se réchauffe, jusqu'à une température comprise entre 550°C et 650°C, ce qui provoque un auto-revenu de la couche superficielle de martensite. La phase d'auto-revenu a une durée t2. Les différences entre les formes d'exécution portent sur les opérations qui suivent la phase d'auto-revenu.After this first stage of the heat treatment, the
Une première forme d'exécution est illustrée par la Figure 2, qui représente l'évolution temporelle de la température de surface du produit lorsque la phase secondaire de la deuxième étape du procédé consiste uniquement en un refroidissement à l'air.A first embodiment is illustrated in FIG. 2, which represents the time evolution of the surface temperature of the product when the secondary phase of the second stage of the process consists only of air cooling.
Dans cette forme d'exécution, cette phase secondaire, de durée t3, consiste en un refroidissement à l'air du produit jusqu'à une température inférieure à 450°C, et de préférence inférieure à 420°C. La durée t3 de ce refroidissement dans l'air calme dépend bien entendu du type de produit, en particulier de son épaisseur. Il est fondamental de laisser le produit se refroidir à l'air jusqu'à une température inférieure à 450°C, et de préférence inférieure à 420°C, pour garantir une bonne résilience du produit final. Si on applique le refroidissement final, c'est-à-dire la troisième étape du procédé, à partir d'une température trop élevée, l'austénite résiduelle non encore transformée et enrichie en carbone peut se transformer en martensite et donner lieu à une structure fragile. Ce refroidissement final, de durée t4, est réalisé à l'eau pour limiter la durée du traitement; il ne doit plus avoir d'effet métallurgique.In this embodiment, this secondary phase, of duration t3, consists of air cooling of the product to a temperature below 450 ° C, and preferably below 420 ° C. The duration t3 of this cooling in still air naturally depends on the type of product, in particular on its thickness. It is essential to allow the product to cool in air to a temperature below 450 ° C, and preferably below 420 ° C, to guarantee good resilience of the final product. If the final cooling, that is to say the third stage of the process, is applied, from too high a temperature, the residual austenite which is not yet transformed and enriched in carbon can transform into martensite and give rise to a fragile structure. This final cooling, of duration t4, is carried out with water to limit the duration of the treatment; it should no longer have a metallurgical effect.
Le diagramme de la Figure 3 représente l'évolution temporelle de la température de surface du produit, lorsque la seconde phase de la deuxième étape du procédé comprend successivement un refroidissement à l'air (t31), un refroidissement intense (t32), un auto-réchauffage (t33) et un refroidissement à l'air (t34).The diagram in FIG. 3 represents the temporal evolution of the surface temperature of the product, when the second phase of the second stage of the process successively comprises air cooling (t31), intense cooling (t32), an auto -heating (t33) and air cooling (t34).
Dans cette forme d'exécution, le refroidissement à l'air (t31), immédiatement après l'auto-revenu de la couche superficielle martensitique, ramène la température de surface du produit à environ 550°C. On effectue ensuite un refroidissement intense (t32), généralement avec de l'eau en circulation, depuis cette température d'environ 550°C jusqu'à une température de surface de 300°C. Après un temps de séjour (t33) assurant l'égalisation de la température sur la section du produit jusqu'à 400°C, on effectue un refroidissement à l'air (t34) de 400°C à 300°C pendant lequel s'accomplit la réaction de survieillissement de la ferrite; on opère ensuite le refroidissement final (t4) constituant la troisième étape du procédé. Ce refroidissement final est effectué à l'eau jusqu'à la température de 80°C, température à laquelle le produit peut être manipulé sans subir d'altérations.In this embodiment, the air cooling (t31), immediately after the self-tempering of the martensitic surface layer, reduces the surface temperature of the product to around 550 ° C. An intense cooling (t32) is then carried out, generally with circulating water, from this temperature of approximately 550 ° C. to a surface temperature of 300 ° C. After a residence time (t33) ensuring the equalization of the temperature on the product section up to 400 ° C, air cooling (t34) is carried out from 400 ° C to 300 ° C during which performs the ferrite overaging reaction; the final cooling is then carried out (t4) constituting the third step of the process. This final cooling is carried out with water up to the temperature of 80 ° C., temperature at which the product can be handled without alteration.
Le refroidissement intermédiaire (t32) peut être effectué dans un dispositif 5', représenté en trait mixte dans la Figure 1 parce qu'il n'est pas utilisé dans toutes les formes d'exécution du procédé de l'invention. Ce dispositif 5', ainsi que le dispositif 6 où s'effectue le refroidissement final (t4) se compose essentiellement d'un tube de section appropriée parcouru par de l'eau. Dans la Figure 1 annexée, il faut comprendre que le dispositif 6 est disposé à la suite du refroidissoir 5; le trait mixte qui les relie exprime cette disposition tout en permettant de limiter l'encombrement du dessin.Intermediate cooling (t32) can be carried out in a 5 'device, shown in phantom in Figure 1 because it is not used in all embodiments of the method of the invention. This
A ce stade, c'est-à-dire après le refroidissement final (t4), le produit 1 se trouve toujours sous forme continue, tel qu'il est sorti du laminoir 3. Les interventions de refroidissement sont réalisées de manière à assurer au produit une bonne rectitude.At this stage, that is to say after the final cooling (t4), the
Après le refroidissement final à l'eau, le produit 1 peut encore être dressé dans un dispositif de dressage 7, puis une cisaille 8 le découpe en tronçons de longueur désirée, qui sont évacués par un convoyeur de sortie 9. Le dressage doit être réalisé à une température inférieure à 120°C et de préférence inférieure à 80°C pour éviter toute déformation ultérieure.After the final cooling with water, the
A titre d'exemple les deux tableaux suivants indiquent des durées de refroidissement typiques pour les différentes étapes du procédé de l'invention, dans le cas de profilés d'épaisseurs différentes. Les épaisseurs e des profilés sont exprimées en millimètres (mm) et les temps (ti) sont exprimés en secondes (s).
Le tableau 1 correspond à la première forme d'exécution décrite plus haut et schématisée à la Figure 2. La durée de l'auto-revenu (t3) croît rapidement avec l'épaisseur du profil, et risque de devenir prohibitive pour des produits de fortes épaisseur (> 40 mm); il est dès lors intéressant d'insérer un refroidissement intense dans la seconde phase de la deuxième étape du procédé, comme représenté à la Figure 3.
Le tableau 2 illustre cette forme d'exécution. On constate qu'elle apporte dans tous les cas un gain de temps important (environ 20 minutes pour les produits de 125 mm d'épaisseur). Ce gain de temps ne nuit pas à la qualité des produits, car ceux-ci présentent une bonne rectitude, une résistance élevée, ainsi qu'une excellente résilience en tout point de leur section.Table 2 illustrates this embodiment. We note that it brings in all cases a significant time saving (about 20 minutes for products of 125 mm thickness). This saving of time does not harm the quality of the products, because they have good straightness, high resistance, as well as excellent resilience at any point in their section.
Le procédé de l'invention permet d'effectuer la totalité du traitement, y compris le dressage, sur les produits-mères, c'est-à-dire tels qu'ils sortent du laminoir. On réduit ainsi nettement le nombre des manipulations nécessaires et dès lors le risque d'apparition de défauts liés à ces manipulations. Enfin, on n'utilise qu'un seul refroidissoir de faible longueur étant donné que le séjour à l'air est de courte durée, ce qui limite d'une part le risque de confusion entre les produits et d'autre part le degré d'oxydation de la surface des produits.The method of the invention makes it possible to carry out the entire treatment, including dressing, on the parent products, that is to say as they come out of the rolling mill. We thus significantly reduce the number of manipulations required and therefore the risk of the appearance of faults linked to these manipulations. Finally, only one short cooler is used since the stay in air is short, which limits on the one hand the risk of confusion between the products and on the other hand the degree of oxidation of the product surface.
Claims (8)
- Process for the heat treatment of a steel product at the exit of the rolling mill, according to which, in the course of a first stage, one submits the product to a rapid cooling by water, from the temperature at the end of the rolling to a surface temperature equal to or below the temperature of the beginning of the martensitic transformation, called MS point, of the said steel, with a cooling rate which is at least equal to the critical quenching speed of the said steel, and according to which, in the course of a second stage, one submits the product to a phase of self-tempering in the course of which, thanks to the heat released by the non quenched part of the product, one realizes the reheating of the quenched surface layer up to a surface temperature, called self-tempering temperature, comprised between 550°C and 650°C, characterized in that thereafter one submits the product to a secondary cooling phase comprising an air cooling to a surface temperature of approximately 550°C followed by a cooling to a surface temperature below 450°C, and in that in the course of a third stage one executes the final cooling of the product to a temperature below 120 °C.
- Process according to the claim 1, characterized in that the said cooling down to a surface temperature below 450°C is executed in the air.
- Process according to the claim 2, characterized in that one executes the said air cooling down to a surface temperature below 420°C.
- Process according to the claim 1, characterized in that, after the air cooling of the product down to a temperature of approximately 550°C, one cools it thereafter down to a temperature substantially below 400°C, in that one allows the product to get warmed up again to a temperature comprised between 400°C and 420°C, in that one executes a slow air cooling and in that one proceeds to an abrupt final cooling down to a temperature below 120°C.
- Process according to the one or the other of the claims 1 to 4, characterized in that one cools the product down to a temperature below 80°C during the said final cooling.
- Process according to the one or the other of the claims 1 to 5, characterized in that the said final cooling is a water cooling with strongly agitated water.
- Process according to the one or the other of the claims 1 to 6, characterized in that it is carried out immediately after the exit of the last stand of the rolling mill.
- Process according to the one or the other of the claims 1 to 7, characterized in that it is carried out in a continuous manner.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| BE9000787 | 1990-08-14 | ||
| BE9000787A BE1004526A6 (en) | 1990-08-14 | 1990-08-14 | Heat treatment method of steel product. |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0473561A1 EP0473561A1 (en) | 1992-03-04 |
| EP0473561B1 true EP0473561B1 (en) | 1996-02-07 |
Family
ID=3884898
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP91870119A Revoked EP0473561B1 (en) | 1990-08-14 | 1991-08-06 | A method of heat treatment of a steel product |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0473561B1 (en) |
| JP (1) | JPH04232206A (en) |
| AT (1) | ATE133996T1 (en) |
| BE (1) | BE1004526A6 (en) |
| DE (1) | DE69116958D1 (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6264767B1 (en) | 1995-06-07 | 2001-07-24 | Ipsco Enterprises Inc. | Method of producing martensite-or bainite-rich steel using steckel mill and controlled cooling |
| IT1295566B1 (en) * | 1997-06-05 | 1999-05-13 | Danieli Off Mecc | THERMAL TREATMENT PROCESS FOR LAMINATES |
| KR100505730B1 (en) * | 2002-12-13 | 2005-08-03 | 두산중공업 주식회사 | Heat treatment of high strength and high toughness roll shell |
| JP4817898B2 (en) * | 2006-03-14 | 2011-11-16 | トピー工業株式会社 | Heat treatment apparatus and heat treatment method |
| CZ201786A3 (en) * | 2017-02-15 | 2019-01-30 | Západočeská Univerzita V Plzni | Method of manufacturing steel parts |
| CN108285950B (en) * | 2018-02-11 | 2019-08-20 | 中冶陕压重工设备有限公司 | A kind of heat treatment method controlling the quenching distortion of sendzimir mill working roll |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1090143B (en) * | 1975-01-29 | 1985-06-18 | Centre Rech Metallurgique | PROCESS FOR MANUFACTURING LAMINATED STEEL PRODUCTS |
| BE834059A (en) * | 1975-09-30 | 1976-01-16 | PROCESS FOR TREATING LAMINATED STEEL PRODUCTS | |
| BE854647A (en) * | 1977-05-13 | 1977-09-01 | Centre Rech Metallurgique | PROCESS FOR THE PRODUCTION OF IMPROVED QUALITY STEEL PROFILES |
| DE2844331A1 (en) * | 1977-10-14 | 1979-04-19 | Centre Rech Metallurgique | METHOD FOR TREATMENT OF TUBULAR STEEL PROFILES |
| BE896347A (en) * | 1983-03-31 | 1983-09-30 | Ct De Recheches Metallurg Ct V | PROCESS FOR IMPROVING THE QUALITY OF STEEL PROFILES |
-
1990
- 1990-08-14 BE BE9000787A patent/BE1004526A6/en not_active IP Right Cessation
-
1991
- 1991-08-06 AT AT91870119T patent/ATE133996T1/en active
- 1991-08-06 EP EP91870119A patent/EP0473561B1/en not_active Revoked
- 1991-08-06 DE DE69116958T patent/DE69116958D1/en not_active Expired - Lifetime
- 1991-08-14 JP JP3204443A patent/JPH04232206A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| BE1004526A6 (en) | 1992-12-08 |
| JPH04232206A (en) | 1992-08-20 |
| ATE133996T1 (en) | 1996-02-15 |
| DE69116958D1 (en) | 1996-03-21 |
| EP0473561A1 (en) | 1992-03-04 |
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