EP1070148A1 - Method for making a hot-rolled steel strip for swaging - Google Patents

Method for making a hot-rolled steel strip for swaging

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Publication number
EP1070148A1
EP1070148A1 EP00900991A EP00900991A EP1070148A1 EP 1070148 A1 EP1070148 A1 EP 1070148A1 EP 00900991 A EP00900991 A EP 00900991A EP 00900991 A EP00900991 A EP 00900991A EP 1070148 A1 EP1070148 A1 EP 1070148A1
Authority
EP
European Patent Office
Prior art keywords
steel
rolling
temperature
ferritic
hot
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP00900991A
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German (de)
French (fr)
Other versions
EP1070148B1 (en
Inventor
Annick De Paepe
Jean-Claude Herman
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Centre de Recherches Metallurgiques CRM ASBL
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Centre de Recherches Metallurgiques CRM ASBL
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Classifications

    • 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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0426—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0431—Warm rolling

Definitions

  • the present invention relates to a method of manufacturing a hot rolled steel strip for stamping.
  • the steel strips intended for stamping operations are generally cold-rolled steel strips, which have very favorable properties in this respect.
  • the manufacture of these cold strips involves various thickness reduction operations and heat treatment which increase the cost.
  • the steels intended for stamping are mild steels, that is to say steels whose carbon content is less than 0.2% by weight, and preferably less than 0.1% in weight.
  • the roughing rolling is carried out in the austenitic field, while the Finishing rolling is carried out in the ferritic field, that is to say at a lower temperature.
  • ferritic rolling must be carried out at a sufficiently low temperature to avoid recrystallization in the finishing mill.
  • the higher rolling forces in a rolling mill operating at low temperature can therefore constitute a limiting factor for the rolling of thin strips hot.
  • the thin hot strips made of Ti + S-IF steel rolled in ferrite and recrystallized, which have increased titanium and sulfur contents, certainly have a high Lankford coefficient, with r ⁇ 1, 6-1, 7 , but their planar anisotropy remains too high ( ⁇ r ⁇ 1) to allow deep drawing.
  • the present invention provides a method of manufacturing a hot-rolled steel strip having a reduced titanium content and an improved drawing ability compared to the steel strips mentioned in the introduction.
  • a hot rolled steel strip produced by the the invention is distinguished by an anisotropy coefficient (r mean) and an improved planar anisotropy ( ⁇ r) substantially reduced relative to the prior art.
  • a method of manufacturing a hot rolled steel strip for stamping in which a steel slab is subjected at a temperature above Ac3 to a roughing rolling in the austenitic field and subsequently to a finishing rolling, is characterized in that the steel is a Ti-IF type steel containing less than 0.05% by weight of titanium and from 0.015% to 0.075% by weight of niobium, in that one performs said finish rolling at least partly in the ferritic field of steel, with a ferritic rolling start temperature of between 875 ° C and 800 ° C, with lubricated cylinders and with a thickness reduction rate d '' at least 80% during said finish rolling in the ferritic field, and in that the steel strip is wound at a temperature between 750 ° C and 500 ° C.
  • the winding in the temperature range between 680 ° C-750 ° C allows to produce a hot recrystallized strip and for direct application in stamping.
  • the winding between 500 ° C and 680 ° C leads to the formation of a non-recrystallized strip which requires a recrystallization treatment in a continuous annealing or galvanizing line.
  • said finishing rolling is carried out partly in the region at low temperature of the austenitic range of steel, without lubrication of the cylinders and with a thickness reduction rate greater than or equal to 30%, of preferably between 30% and 80%, and partly in the ferritic field of steel, with lubricated cylinders and with a ferritic rolling start temperature between 860 ° C and 800 ° C and an end of rolling temperature ferritic between 750 ° C and 600 ° C, said strip is wound at a temperature between 650 ° C and 500 ° C and annealed continuously at a temperature between 800 ° C and 850 ° C for a time between 30 seconds and 2 minutes.
  • An ester-based oil is preferably used for the lubrication of the cylinders during rolling in the ferritic field.
  • the process of the invention is intended for Ti-IF steels, in which the titanium is partially replaced by niobium. It has in fact been observed that the precipitation of niobium carbide (NbC) begins at increasing temperatures, in the austenitic domain, when the niobium content increases in the steel. As a result, the carbon in solution is almost entirely fixed before the beginning of the deformation in the ferritic domain. It is thus possible to obtain a final product, that is to say a hot rolled strip, which has a practically continuous tensile curve and which therefore lends itself remarkably to deep drawing.
  • NbC niobium carbide
  • niobium delays recrystallization between the rolling mill stands in the ferritic field.
  • the entry temperature into the finishing mill can therefore be higher than in prior practice and thus reach a value of 850 ° C to 875 ° C as indicated above.
  • the rolling forces can thus be lower in the finishing mill; similarly, the waiting time between the roughing rolling mill and the finishing rolling mill can be shortened, in favor of an increase in productivity. This waiting time can also be completely eliminated, by applying accelerated cooling of the product at the outlet of the roughing mill.
  • FIG. 1 represents the comparative evolution of the value of the coefficient r for a conventional Ti + S-IF steel and two Ti + Nb-IF steels according to the invention.
  • the products were reheated to 1050 ° C and then hot rolled in six passes to a final thickness of 1.3 mm. During this finish rolling, the first three passes were made in the region of low temperatures of the austenitic domain, that is to say at temperatures slightly above Ac3, with a thickness reduction rate of 73 % and without lubrication of the cylinders.
  • the other three passes were made in the ferritic field, with cylinders lubricated with an ester oil.
  • the temperature of the product at the inlet of the first pass of ferritic rolling was about 840 ° C and the outlet temperature of the last pass was around 620 ° C.
  • the strip was wound at 500 ° C and then annealed continuously at 820 ° C for 60 seconds.
  • FIG. 1 illustrates this development for the three steels of table 1, as a function of the angle relative to the rolling direction.
  • a steel slab Nb + Ti-IF1 was fabricated, which was reheated at high temperature, namely 1250 ° C., then the roughing rolling was carried out at high temperature in the austenitic domain.
  • the product 20 mm thick, was cooled from its end-of-roughing temperature from 1040 ° C to a temperature of 900 ° C, with a cooling rate of around 40 ° C / s.
  • the finishing rolling was carried out in four passes in the ferritic field, with an inlet temperature of 870 ° C, with lubricated cylinders and with a total thickness reduction, in ferrite, of 80%.
  • Curve 4 in Figure 1 shows the evolution of the anisotropy coefficient r; there is still a slight improvement in the average coefficient r as well as in the planar anisotropy ⁇ r, compared to curve 3.
  • the method of the invention makes it possible to manufacture hot-rolled steel strips for stamping, which present little risk of surface defects, due to a low content of titanium.
  • the presence of niobium substantially raises the non-recrystallization temperature in the austenite. This results in a finer grain structure after the allotropic austenite-ferrite transformation and, as a result, an improvement in planar anisotropy.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Steel (AREA)
  • Metal Rolling (AREA)

Abstract

The invention concerns a method for making a hot-rolled steel strip for swaging which consists in: subjecting a steel slab at temperature higher than Ac3 to a rough-rolling in the austenitic phase and subsequently to a finish-rolling, applied to steel of the Ti-IF type containing at least 0.05 wt. % of titanium and 0.015 wt. % of niobium; performing the finish-rolling partially in the low temperature region of the steel austenitic phase, without lubricating the rolls and at a thickness reduction rate ranging between 30 % and 80 %, and partially in the steel ferritic phase, with lubricated rolls and at an initial ferritic rolling temperature ranging between 860 DEG C and 800 DEG C and a final ferritic rolling temperature ranging between 750 DEG C and 600 DEG C; then winding the strip at a temperature ranging between 650 DEG C and 500 DEG C and continuously annealing it at a temperature ranging between 800 DEG C and 850 DEG C for a time interval between 30 seconds and 2 minutes. The lubricating of the rolls during the steel ferritic phase rolling is performed with an ester-based oil. The steel austenitic phase is rough-rolled and the steel is subjected to accelerated cooling down to a temperature not less than the initial finish-rolling temperature.

Description

Procédé de fabrication d'une bande d'acier laminée à chaud pour emboutissage.Method for manufacturing a hot rolled steel strip for stamping.
Domaine technique La présente invention concerne un procédé de fabrication d'une bande d'acier laminée à chaud pour emboutissage .Technical Field The present invention relates to a method of manufacturing a hot rolled steel strip for stamping.
Etat de la technique.State of the art.
A l'heure actuelle, les bandes d'acier destinées à des opérations d'emboutissage sont généralement des bandes d'acier laminées à froid, qui présentent des propriétés très favorables à cet égard. La fabrication de ces bandes à froid comporte cependant diverses opérations de réduction d'épaisseur et de traitement thermique qui en augmentent le coût.At the present time, the steel strips intended for stamping operations are generally cold-rolled steel strips, which have very favorable properties in this respect. The manufacture of these cold strips, however, involves various thickness reduction operations and heat treatment which increase the cost.
L'utilisation de bandes d'acier laminées à chaud pour des opérations d'emboutissage, en remplacement des bandes laminées à froid traditionnelles, suscite de ce fait un intérêt croissant, aussi bien au niveau de la fabrication que chez les utilisateurs.The use of hot-rolled steel strips for stamping operations, replacing the traditional cold-rolled strips, is therefore arousing growing interest, both in manufacturing and in users.
Il est bien connu que les aciers destinés à l'emboutissage sont des aciers doux, c'est-à- dire des aciers dont la teneur en carbone est inférieure à 0,2 % en poids, et de préférence inférieure à 0,1 % en poids.It is well known that the steels intended for stamping are mild steels, that is to say steels whose carbon content is less than 0.2% by weight, and preferably less than 0.1% in weight.
Selon la pratique habituelle, les aciers doux sont laminés à chaud dans le domaine austénitique et la température de fin de laminage est supérieure à la température de transformation Ar3. Les possibilités d'emploi de ces bandes à chaud conventionnelles sont cependant très limitées, en raison de leur texture aléatoire et de leur mauvaise aptitude à l'emboutissage. En outre, il est impossible en pratique de fabriquer des bandes minces laminées à chaud par cette méthode conventionnelle. En effet, la faible épaisseur des bandes entraîne un refroidissement rapide de celles-ci, même en cours de laminage à chaud, de sorte qu'il n'est pas possible d'effectuer le laminage de finition dans le domaine austénitique. Pour ces diverses raisons, il existe actuellement un intérêt croissant pour le laminage dit ferritique.According to the usual practice, mild steels are hot rolled in the austenitic range and the end of rolling temperature is higher than the transformation temperature Ar3. The possibilities of using these conventional hot strips are however very limited, because of their random texture and their poor drawing ability. In addition, it is impossible in practice to manufacture thin hot-rolled strips by this conventional method. Indeed, the small thickness of the strips results in rapid cooling thereof, even during hot rolling, so that it is not possible to carry out the finishing rolling in the austenitic field. For these various reasons, there is currently a growing interest in so-called ferritic rolling.
Selon ce procédé de laminage, connu notamment par le brevet EP-A-0 524 162, le laminage de dégrossissage est effectué dans le domaine austénitique, tandis que le laminage de finition est effectué dans le domaine ferritique, c'est-à-dire à plus basse température.According to this rolling process, known in particular from patent EP-A-0 524 162, the roughing rolling is carried out in the austenitic field, while the Finishing rolling is carried out in the ferritic field, that is to say at a lower temperature.
Dans les lignes de fabrication à chaud avec enfournement froid des brames de coulée continue, cette technique s'avère particulièrement intéressante parce qu'elle permet de réaliser de substantielles économies d'énergie. En effet, la température de réchauffage est moins élevée que dans les procédés conventionnels. Le laminage de finition à plus basses températures permet ainsi de fabriquer des bandes laminées à chaud de faible épaisseur, ayant une bonne aptitude à l'emboutissage.In hot production lines with cold charging of continuous casting slabs, this technique is particularly interesting because it allows substantial energy savings. In fact, the reheating temperature is lower than in conventional methods. Finishing rolling at lower temperatures thus makes it possible to manufacture hot-rolled strips of small thickness, having good drawing ability.
La mise en œuvre de cette technique est cependant soumise à diverses conditions et présente de ce fait quelques inconvénients.The implementation of this technique is however subject to various conditions and therefore has some drawbacks.
En particulier, la quantité de carbone se trouvant en solution pendant le laminage ferritique doit être minimisée. Il en résulte qu'il n'est possible de fabriquer des tôles pour emboutissage profond qu'à partir d'aciers ne contenant pas d'atomes interstitiels, dits aciers IF (Interstitial Free). Il a été proposé d'améliorer la situation par des additions de titane et de soufre, mais une telle solution peut entraîner des défauts de surface et ne s'avère pas toujours intéressante au point de vue économique.In particular, the amount of carbon in solution during ferritic rolling must be minimized. As a result, it is possible to manufacture sheets for deep drawing only from steels not containing interstitial atoms, called IF steels (Interstitial Free). It has been proposed to improve the situation by adding titanium and sulfur, but such a solution can cause surface defects and is not always advantageous from the economic point of view.
En outre, le laminage ferritique doit être effectué à une température suffisamment basse pour éviter toute recristallisation dans le laminoir de finition. Les forces de laminage plus élevées dans un laminoir opérant à basse température peuvent dès lors constituer un facteur de limitation pour le laminage de bandes minces à chaud.In addition, ferritic rolling must be carried out at a sufficiently low temperature to avoid recrystallization in the finishing mill. The higher rolling forces in a rolling mill operating at low temperature can therefore constitute a limiting factor for the rolling of thin strips hot.
Les bandes minces à chaud, fabriquées en acier Ti + S-IF laminé dans la ferrite et recristallisé, qui comportent des teneurs accrues en titane et en soufre, présentent certes un coefficient de Lankford élevé, avec r ≈ 1 ,6-1 ,7, mais leur anisotropie planaire reste trop importante (Δ r ≈ 1 ) pour permettre l'emboutissage profond.The thin hot strips, made of Ti + S-IF steel rolled in ferrite and recrystallized, which have increased titanium and sulfur contents, certainly have a high Lankford coefficient, with r ≈ 1, 6-1, 7 , but their planar anisotropy remains too high (Δ r ≈ 1) to allow deep drawing.
Présentation de l'inventionPresentation of the invention
Pour éviter les inconvénients précités, la présente invention propose un procédé de fabrication d'une bande d'acier laminée à chaud présentant une teneur en titane réduite et une aptitude à l'emboutissage améliorée par rapport aux bandes d'acier évoquées dans l'introduction. Une bande d'acier laminée à chaud produite par le procédé de l'invention se distingue notamment par un coefficient d'anisotropie (rmoyen) amélioré et une anisotropie planaire (Δ r) sensiblement réduite par rapport à l'état de la technique.To avoid the abovementioned drawbacks, the present invention provides a method of manufacturing a hot-rolled steel strip having a reduced titanium content and an improved drawing ability compared to the steel strips mentioned in the introduction. . A hot rolled steel strip produced by the the invention is distinguished by an anisotropy coefficient (r mean) and an improved planar anisotropy (Δ r) substantially reduced relative to the prior art.
Conformément à l'invention, un procédé de fabrication d'une bande d'acier laminée à chaud pour emboutissage, dans lequel on soumet une brame d'acier à une température supérieure à Ac3 à un laminage de dégrossissage dans le domaine austénitique et ultérieurement à un laminage de finition, est caractérisé en ce que l'acier est un acier de type Ti-IF contenant moins de 0,05 % en poids de titane et de 0,015 % à 0,075 % en poids de niobium, en ce que l'on effectue ledit laminage de finition au moins en partie dans le domaine ferritique de l'acier, avec une température de début de laminage ferritique comprise entre 875 °C et 800°C, avec des cylindres lubrifiés et avec un taux de réduction d'épaisseur d'au moins 80 % au cours dudit laminage de finition dans le domaine ferritique, et en ce que l'on bobine la bande d'acier à une température comprise entre 750°C et 500°C.According to the invention, a method of manufacturing a hot rolled steel strip for stamping, in which a steel slab is subjected at a temperature above Ac3 to a roughing rolling in the austenitic field and subsequently to a finishing rolling, is characterized in that the steel is a Ti-IF type steel containing less than 0.05% by weight of titanium and from 0.015% to 0.075% by weight of niobium, in that one performs said finish rolling at least partly in the ferritic field of steel, with a ferritic rolling start temperature of between 875 ° C and 800 ° C, with lubricated cylinders and with a thickness reduction rate d '' at least 80% during said finish rolling in the ferritic field, and in that the steel strip is wound at a temperature between 750 ° C and 500 ° C.
Le bobinage dans l'intervalle de température compris entre 680°C-750°C permet de produire une bande à chaud recristallisée et pour application directe en emboutissage. Le bobinage entre 500°C et 680°C conduit à la formation d'une bande non recristallisée qui nécessite un traitement de recristallisation dans une ligne de recuit continu ou de galvanisation.The winding in the temperature range between 680 ° C-750 ° C allows to produce a hot recrystallized strip and for direct application in stamping. The winding between 500 ° C and 680 ° C leads to the formation of a non-recrystallized strip which requires a recrystallization treatment in a continuous annealing or galvanizing line.
Selon une mise en œuvre particulière, on effectue ledit laminage de finition en partie dans la région à basse température du domaine austénitique de l'acier, sans lubrification des cylindres et avec un taux de réduction d'épaisseur supérieur ou égal à 30 %, de préférence compris entre 30 % et 80 %, et en partie dans le domaine ferritique de l'acier, avec des cylindres lubrifiés et avec une température de début de laminage ferritique comprise entre 860°C et 800°C et une température de fin de laminage ferritique comprise entre 750°C et 600°C, on bobine ladite bande à une température comprise entre 650°C et 500°C et on la recuit en continu à une température comprise entre 800°C et 850°C pendant un temps compris entre 30 secondes et 2 minutes.According to a particular implementation, said finishing rolling is carried out partly in the region at low temperature of the austenitic range of steel, without lubrication of the cylinders and with a thickness reduction rate greater than or equal to 30%, of preferably between 30% and 80%, and partly in the ferritic field of steel, with lubricated cylinders and with a ferritic rolling start temperature between 860 ° C and 800 ° C and an end of rolling temperature ferritic between 750 ° C and 600 ° C, said strip is wound at a temperature between 650 ° C and 500 ° C and annealed continuously at a temperature between 800 ° C and 850 ° C for a time between 30 seconds and 2 minutes.
Pour la lubrification des cylindres pendant le laminage dans le domaine ferritique, on utilise de préférence une huile à base d'esters. Comme on l'a indiqué plus haut, le procédé de l'invention s'adresse à des aciers Ti-IF, dans lesquels le titane est partiellement remplacé par du niobium. On a en effet constaté que la précipitation du carbure de niobium (NbC) commençait à des températures croissantes, dans le domaine austénitique, lorsque la teneur en niobium augmente dans l'acier. Il en résulte que le carbone en solution est presqu'entièrement fixé avant le début de la déformation dans le domaine ferritique. On peut ainsi obtenir un produit final, c'est-à-dire une bande laminée à chaud, qui présente une courbe de traction pratiquement continue et qui se prête dès lors remarquablement à l'emboutissage profond.An ester-based oil is preferably used for the lubrication of the cylinders during rolling in the ferritic field. As indicated above, the process of the invention is intended for Ti-IF steels, in which the titanium is partially replaced by niobium. It has in fact been observed that the precipitation of niobium carbide (NbC) begins at increasing temperatures, in the austenitic domain, when the niobium content increases in the steel. As a result, the carbon in solution is almost entirely fixed before the beginning of the deformation in the ferritic domain. It is thus possible to obtain a final product, that is to say a hot rolled strip, which has a practically continuous tensile curve and which therefore lends itself remarkably to deep drawing.
En outre, une telle addition de niobium retarde la recristallisation entre les cages de laminoir dans le domaine ferritique. La température d'entrée dans le laminoir de finition peut donc être plus élevée que dans la pratique antérieure et atteindre ainsi une valeur de 850°C à 875°C comme on l'a indiqué plus haut .In addition, such an addition of niobium delays recrystallization between the rolling mill stands in the ferritic field. The entry temperature into the finishing mill can therefore be higher than in prior practice and thus reach a value of 850 ° C to 875 ° C as indicated above.
Les efforts de laminage peuvent ainsi être moins élevés dans le laminoir finisseur ; de même, le temps d'attente entre le laminoir dégrossisseur et le laminoir finisseur peut être raccourci, au profit d'un accroissement de la productivité. Ce temps d'attente peut d'ailleurs être complètement supprimé, en appliquant un refroidissement accéléré du produit à la sortie du laminoir dégrossisseur.The rolling forces can thus be lower in the finishing mill; similarly, the waiting time between the roughing rolling mill and the finishing rolling mill can be shortened, in favor of an increase in productivity. This waiting time can also be completely eliminated, by applying accelerated cooling of the product at the outlet of the roughing mill.
Brève description de la figure 1Brief description of Figure 1
La figure 1 unique représente l'évolution comparée de la valeur du coefficient r pour un acier Ti + S-IF conventionnel et deux aciers Ti + Nb-IF suivant l'invention.The single FIG. 1 represents the comparative evolution of the value of the coefficient r for a conventional Ti + S-IF steel and two Ti + Nb-IF steels according to the invention.
Modes de mise en œuvre de l'inventionModes of implementing the invention
On a fabriqué des brames d'aciers présentant les compositions indiquées dans le tableau 1 ci-dessous.Slabs of steel having the compositions indicated in Table 1 below were produced.
TABLEAU 1 - Composition chimique des aciers (% poids)TABLE 1 - Chemical composition of steels (% by weight)
. 5 . . 5.
Les produits ont été réchauffés à 1050°C puis laminés à chaud en six passes jusqu'à une épaisseur finale de 1 ,3 mm. Au cours de ce laminage de finition, les trois premières passes ont été effectuées dans la région des basses températures du domaine austénitique, c'est-à-dire à des températures légèrement supérieures à Ac3, avec un taux de réduction d'épaisseur de 73 % et sans lubrification des cylindres.The products were reheated to 1050 ° C and then hot rolled in six passes to a final thickness of 1.3 mm. During this finish rolling, the first three passes were made in the region of low temperatures of the austenitic domain, that is to say at temperatures slightly above Ac3, with a thickness reduction rate of 73 % and without lubrication of the cylinders.
Les trois autres passes ont été effectuées dans le domaine ferritique, avec des cylindres lubrifiés au moyen d'une huile à base d'esters. La température du produit à l'entrée de la première passe de laminage ferritique était d'environ 840°C et la température de sortie de la dernière passe était d'environ 620°C.The other three passes were made in the ferritic field, with cylinders lubricated with an ester oil. The temperature of the product at the inlet of the first pass of ferritic rolling was about 840 ° C and the outlet temperature of the last pass was around 620 ° C.
Après le laminage à chaud, la bande a été bobinée à 500°C puis a été recuite en continu à 820°C pendant 60 secondes.After hot rolling, the strip was wound at 500 ° C and then annealed continuously at 820 ° C for 60 seconds.
On a mesuré les propriétés mécaniques de ces échantillons, on a déterminé leur texture à mi-épaisseur, puis on a calculé l'évolution du coefficient d'anisotropie r.The mechanical properties of these samples were measured, their texture was determined at mid-thickness, then the evolution of the anisotropy coefficient r was calculated.
La figure 1 unique illustre cette évolution pour les trois aciers du tableau 1 , en fonction de l'angle par rapport à la direction de laminage.The single FIG. 1 illustrates this development for the three steels of table 1, as a function of the angle relative to the rolling direction.
Les courbes 1 et 2, correspondant respectivement aux aciers Nb + Ti-IF 1 et Nb + Ti-IF2, montrent une nette amélioration du coefficient d'anisotropie rmoyen ainsi que de l'aniso- tropie planaire (Δ r = rmax - rmin) par rapport à l'acier Ti + S-IF conventionnel (courbe 3).Curves 1 and 2, corresponding respectively to Nb + Ti-IF 1 and Nb + Ti-IF2 steels, show a clear improvement in the average anisotropy coefficient r as well as in planar anisotropy (Δ r = r max - r min ) compared to conventional Ti + S-IF steel (curve 3).
Dans un autre exemple (courbe 4), on a fabriqué une brame d'acier Nb + Ti-IF1 , qui a été réchauffée à haute température, à savoir 1250°C, puis le laminage de dégrossissage a été effectué à haute température dans le domaine austénitique. Le produit, d'une épaisseur de 20 mm, a subi un refroidissement depuis sa température de fin de laminage de dégrossissage de 1040°C jusqu'à une température de 900°C, avec une vitesse de refroidissement de l'ordre de 40°C/s. Le laminage de finition a été effectué en quatre passes dans le domaine ferritique, avec une température d'entrée de 870°C, avec des cylindres lubrifiés et avec une réduction totale d'épaisseur, dans la ferrite, de 80 %.In another example (curve 4), a steel slab Nb + Ti-IF1 was fabricated, which was reheated at high temperature, namely 1250 ° C., then the roughing rolling was carried out at high temperature in the austenitic domain. The product, 20 mm thick, was cooled from its end-of-roughing temperature from 1040 ° C to a temperature of 900 ° C, with a cooling rate of around 40 ° C / s. The finishing rolling was carried out in four passes in the ferritic field, with an inlet temperature of 870 ° C, with lubricated cylinders and with a total thickness reduction, in ferrite, of 80%.
La bande a été refroidie dans l'air calme, puis bobinée à 730°C. La courbe 4 de la figure 1 montre l'évolution du coefficient d'anisotropie r ; il apparaît encore une légère amélioration du coefficient rmoyen ainsi que de l'anisotropie planaire Δ r, par rapport à la courbe 3.The strip was cooled in still air and then wound up to 730 ° C. Curve 4 in Figure 1 shows the evolution of the anisotropy coefficient r; there is still a slight improvement in the average coefficient r as well as in the planar anisotropy Δ r, compared to curve 3.
Le procédé de l'invention permet de fabriquer des bandes d'acier laminées à chaud pour emboutissage, qui présentent peu de risques de défauts de surface, en raison d'une faible teneur en titane. De plus la présence de niobium relève sensiblement la température de non recristallisation dans l'austénite. Il en résulte une structure de grain plus fine après la transformation allotropique austénite-ferrite et, de ce fait, une amélioration de l'anisotropie planaire.The method of the invention makes it possible to manufacture hot-rolled steel strips for stamping, which present little risk of surface defects, due to a low content of titanium. In addition, the presence of niobium substantially raises the non-recrystallization temperature in the austenite. This results in a finer grain structure after the allotropic austenite-ferrite transformation and, as a result, an improvement in planar anisotropy.
Enfin, les températures de laminage plus élevées dans le laminoir de finition réduisent les efforts de laminage . Finally, the higher rolling temperatures in the finishing mill reduce the rolling efforts.

Claims

R E V E N D I C A T I O N S
1. Procédé de fabrication d'une bande d'acier laminée à chaud pour emboutissage, dans lequel on soumet une brame d'acier à une température supérieure à Ac3 à un laminage de dégrossissage dans le domaine austénitique et ultérieurement à un laminage de finition, caractérisé en ce que l'acier est un acier de type Ti-IF contenant moins de 0,05 % en poids de titane et de 0,015 % à 0,075 % en poids de niobium, en ce que l'on effectue ledit laminage de finition au moins en partie dans le domaine ferritique dudit acier, avec une température de début de laminage ferritique comprise entre 875 °C et 800°C, avec des cylindres lubrifiés et avec un taux de réduction d'épaisseur total d'au moins 80 %, et en ce que l'on bobine la bande d'acier à une température comprise entre 750°C et 500°C.1. Method for manufacturing a hot-rolled steel strip for stamping, in which a steel slab is subjected at a temperature higher than Ac3 to a roughing rolling in the austenitic field and subsequently to a finishing rolling, characterized in that the steel is a Ti-IF type steel containing less than 0.05% by weight of titanium and from 0.015% to 0.075% by weight of niobium, in that said finish rolling is carried out with less partially in the ferritic range of said steel, with a ferritic rolling start temperature of between 875 ° C and 800 ° C, with lubricated cylinders and with a total thickness reduction rate of at least 80%, and in that the steel strip is wound at a temperature between 750 ° C and 500 ° C.
2. Procédé suivant la revendication 1 , caractérisé en ce que l'on effectue ledit laminage de finition en partie dans la région à basse température du domaine austénitique de l'acier, sans lubrification des cylindres et avec un taux de réduction d'épaisseur compris entre 30 % et 80 %, et en partie dans le domaine ferritique de l'acier, avec des cylindres lubrifiés et avec une température de début de laminage ferritique comprise entre 860°C et 800°C et une température de fin de laminage ferritique comprise entre 750°C et 600°C, en ce que l'on bobine ensuite ladite bande à une température comprise entre 650°C et 500°C, et en ce qu'on la recuit en continu à une température comprise entre 800°C et 850°C pendant un temps compris entre 30 secondes et 2 minutes.2. Method according to claim 1, characterized in that said finishing rolling is carried out partly in the low temperature region of the austenitic range of steel, without lubrication of the cylinders and with a reduction rate of thickness included between 30% and 80%, and partly in the ferritic field of steel, with lubricated cylinders and with a ferritic rolling start temperature between 860 ° C and 800 ° C and a ferritic rolling end temperature included between 750 ° C and 600 ° C, in that the said strip is then wound at a temperature between 650 ° C and 500 ° C, and in that it is continuously annealed at a temperature between 800 ° C and 850 ° C for a time between 30 seconds and 2 minutes.
3. Procédé suivant l'une ou l'autre des revendications 1 et 2, caractérisé en ce que la lubrification des cylindres pendant le laminage dans le domaine ferritique de l'acier est effectuée au moyen d'une huile à base d'esters.3. Method according to either of claims 1 and 2, characterized in that the lubrication of the cylinders during rolling in the ferritic field of steel is carried out by means of an oil based on esters.
4. Procédé suivant l'une ou l'autre des revendications 1 à 3, caractérisé en ce que l'on effectue ledit laminage de dégrossissage dans le domaine austénitique de l'acier et en ce que l'on soumet l'acier à un refroidissement accéléré jusqu'à une température qui n'est pas inférieure à la température de début du laminage de finition . 4. Method according to either of claims 1 to 3, characterized in that said roughing rolling is carried out in the austenitic field of steel and in that the steel is subjected to a accelerated cooling to a temperature which is not lower than the temperature at the start of the finish rolling.
EP00900991A 1999-02-05 2000-01-24 Method for making a hot-rolled steel strip for swaging Expired - Lifetime EP1070148B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
BE9900078A BE1012462A3 (en) 1999-02-05 1999-02-05 Process for producing a steel strip for stamping hot rolled.
BE9900078 1999-02-05
PCT/BE2000/000007 WO2000046411A1 (en) 1999-02-05 2000-01-24 Method for making a hot-rolled steel strip for swaging

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EP1070148A1 true EP1070148A1 (en) 2001-01-24
EP1070148B1 EP1070148B1 (en) 2006-06-21

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AT509707B1 (en) * 2010-05-04 2011-11-15 Siemens Vai Metals Tech Gmbh METHOD FOR HOT ROLLING OF STEEL STRIPS AND HOT ROLLING STRIP
CN106834906B (en) * 2017-01-10 2019-04-12 首钢京唐钢铁联合有限责任公司 The production method of ultra-low-carbon steel

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LU86509A1 (en) * 1986-07-10 1988-02-02 Centre Rech Metallurgique STEELS FOR LAMINATION OF LOW TEMPERATURE BELTS
BE1002093A6 (en) * 1988-07-11 1990-06-26 Centre Rech Metallurgique Method for manufacturing a thin steel band for hot rolling
US4973367A (en) * 1988-12-28 1990-11-27 Kawasaki Steel Corporation Method of manufacturing steel sheet having excellent deep-drawability
US5200005A (en) * 1991-02-08 1993-04-06 Mcgill University Interstitial free steels and method thereof
DE19600990C2 (en) * 1996-01-14 1997-12-18 Thyssen Stahl Ag Process for hot rolling steel strips
BE1010164A6 (en) * 1996-05-13 1998-02-03 Centre Rech Metallurgique Process for manufacturing a thin stamped strip of hot rolled mild steel

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ES2265908T3 (en) 2007-03-01
BE1012462A3 (en) 2000-11-07
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DE60028875T2 (en) 2006-11-30
DE60028875D1 (en) 2006-08-03
AU2086900A (en) 2000-08-25

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