EP1253209A2 - Steel sheet with good forming properties and method for producing the same - Google Patents

Abstract

Deep drawing or drawing and ironing quality steel strip production involves subjecting hot rolled strip to pickling, one- or two-stage cold rolling, coil annealing and optionally re-rolling. Production of deep drawing or drawing and ironing quality steel strip comprises cold rolling hot rolled strip with ≥ 86% reduction and providing one or both strip sides with an electroplated coating of nickel (Ni), cobalt (Co), copper (Cu), iron (Fe), tin (Sn), indium (In), palladium (Pd), bismuth (Bi) and/or their alloys or a roll clad coating of Cu (alloy) and/or brass. The process steps after hot rolling comprise pickling, one- or two-stage cold rolling, coil annealing and optionally re-rolling. An Independent claim is also included for deep drawing or drawing and ironing quality steel strip produced by the above process. Preferred Features: The hot rolled strip contains (by wt.) 0.010-0.065% carbon (C), 0.100-0.275% manganese (Mn), NOTGREATER 0.050% phosphorus (P), NOTGREATER 0.050% sulfur (S), NOTGREATER 0.060% silicon (Si), NOTGREATER 0.0060% nitrogen (N) and 0.0013-0.0030 ppm boron (B).

Description

The invention relates to a method for producing steel strip for through Deep-drawn or ironing parts made using a hot strip multi-stage and cold formed with a cold rolling degree of at least 86% is, with at least one side of the strip material with a galvanic produced coating containing Ni, Co, Cu, Fe, Sn, In, Pd, Bi and / or their Alloys is provided.

Cold-rolled steel strip is used for the production of rotationally symmetrical cold formed parts such as B. battery sleeves used. The at the The processes used for cold forming are deep drawing and on the other hand, ironing, the latter also as a DI process (drawing and ironing).

Given the increasing demands on application and The properties of such steel strips are becoming increasingly better mechanical properties and in particular improved forming properties required. Good formability is characterized by the highest possible R-values characterizing deep-drawability for the anisotropy as well as high ones Stretchability characterizing n-values as well as high elongation values. Of It can also be advantageous that the forming properties in the different Directions, d. H. in the longitudinal, transverse and diagonal directions, if possible are the same and therefore largely isotropic. The advantages of isotropic properties Steel sheet expresses itself essentially in a uniformity of the Material flow from deep drawing or ironing, so that there is no or only a small tip formation occurs, which in turn leads to a reduction in the Metal waste leads.

A steel sheet is also used to achieve an almost isotropic forming with small thickness tolerances in a texture-free and homogeneous rolled strip or sheet needed.

The undesired tip formation and its causes are detailed in the Magazine "Sheet metal, tubes, profiles" 9/1977 on pages 341 to 346 explained. It is also described there that a tip-free material is usually only by normalizing annealing in a continuous annealing furnace at temperatures around can reach about 1000 ° C. Operation of a continuous furnace at these high However, temperatures are associated with high investment and operating costs.

From DE-38 03 064 C1 it is known to achieve low values for the anisotropy and thus a low tip tendency in the case of round-grain steels in that the steel has an increased titanium content of up to 0.04% by weight with a degree of salt rolling of over 80 % contains. With such high rolling degrees, however, limit values for the yield strength of the steel of well over 250 N / mm ^{2 are} reached. Furthermore, the steels stabilized by the addition of titanium are known to require high recrystallization temperatures, which, if such a steel strip was annealed in the wound state (coil annealing), would lead to a marked tendency of the individual strip layers to stick. The associated damage to the surface of the belt is, however, undesirable for high-quality products or would lead to a high failure rate.

The use of continuously operated strip annealing furnaces in the production of Sheet steel for parts made by drawing or ironing is also made the publications US-5,078,809, WO 98/06881 and EP 0 822 266 A1. In The latter publication is a steel with a low carbon content described, the steel analysis additionally shows boron, in one Proportion between 0.0005 and 0.0015% by weight. The aforementioned lower limit is based on the need to add boron to the molten steel To increase the resistance of the steel sheet to corrosion. The upper The limit of 0.0015% by weight is stated in EP 0 822 266 A1 justifies that with higher boron fractions with forming defects during manufacture cylindrical parts is to be expected.

DE 20 19 494 A discloses a process for the production of corrosion-resistant coated steels. On a pickled, hot-rolled Steel strip is a coating of at least one metal, which is made of Co, Cu, Ni and Ti composing group applied, and the hot rolled Steel strip is then with the coating on it on the desired Gauge block cold reduced. You can do this in one or more stages Cold reduction process Reduction levels of around 90% and more can be achieved. The cold reduced steel strip is annealed for recrystallization, the annealing is preferably carried out in a continuous annealing process. is A box annealing process can be required just a single annealing step Find use, the annealing temperature in a range between 566 and 621 ° C for a period of between 1 and 5 hours. This happens to an alloying of the by vapor deposition on the hot strip applied coating with the metal of the hot strip in an excessive prevent strong measure. As an exemplary composition of the beginning of the Steel plate manufacturing process uses 0.035% C; 0.49% Mn; 0.10% P; 0.11% S and 0.035% Si indicated. A proportion of boron in the steel is found in no mention of this document.

GB 2 101 156 A describes a method for producing a steel strip for deep drawing. The method described in this document includes conventional hot rolling and cold rolling steps, which are based on an aluminum alloy Steel can be applied. The steel used according to this document contains nitrogen with a share of not more than 0.007% and boron in one Amount of a given boron to nitrogen ratio in the range of 0.5 to 2.5 corresponds. The amounts of boron given in the examples are between 0.0025 and 0.0040%. The steel strip is annealed in accordance with this Print only using the continuous annealing process.

JP-A-2 267 242 describes a method for producing a cold rolled one Steel strip made of aluminum-soothed steel with low carbon content. to chemical bonding of the nitrogen contained in the steel is the Starting steel added aluminum, which in the following Hot rolling process the nitrogen contained in the steel in the form of Aluminum nitride binds after pickling and subsequent to the hot rolling Cold rolling steps are used to anneal the steel strip in a box annealing process. On According to this publication, the steel band does not have a coating, just as little contains the steel boron.

Finally, in DE-195 47 181 C1 is a steel with proportions of titanium, vanadium or niobium, due to certain hot rolling conditions below the gamma range of the iron-carbon diagram and due to a kind of mixed grain is achieved at a high coiling temperature in the hot strip. at Rolling degrees between 50 and 85% lead to a reduced grain size Tip inclination, but also for the formation of coarse, line cementit, which in the Deep drawing of thin parts with high surface requirements to undesirable Structures on the surface of the belt and thus in practice one Committee leads.

The object of the invention is therefore to develop a method of the generic type which, with regard to the anisotropy, comes very close to the material properties achieved by normalizing, but at the same time can be operated at relatively lower production costs and manages with as few process steps as possible. After annealing, a globular grain is to be achieved, and the steel strip produced by the process according to the invention should not have any disadvantages due to aging or higher mechanical-technological values at high rolling degrees.

• das Beizen
• das ein- oder zweistufige Kaltwalzen
• das Glühen des Bandes in aufgewickeltem Zustand (Coil-Glühen)
• ggf. das Nachwalzen des Bandes,

wobei der Überzug nach einem Kaltwalzschritt jedoch vor dem Glühen auf das Band aufgebracht wird, wobei das Warmband Bor mit einem Anteil zwischen 0,0013 und 0,0060 Gew.-% enthält, wobei das Gewichtsverhältnis des Bor zum Stickstoff 0,5 bis 2,5 beträgt. Insbesondere bevorzugt angestrebt ist ein Bor-Anteil zwischen 0,0013 und 0,0030 Gew.-%.According to the invention, it is proposed in a method of the type mentioned at the outset that the method steps carried out after hot rolling include

• pickling
• the one- or two-stage cold rolling
• the annealing of the strip in the wound state (coil annealing)
• if necessary, re-rolling the strip,

the coating being applied to the strip after a cold rolling step before the annealing, the hot strip containing boron in a proportion between 0.0013 and 0.0060% by weight, the weight ratio of boron to nitrogen being 0.5 to 2, 5 is. A boron fraction between 0.0013 and 0.0030% by weight is particularly preferred.

This is done to achieve a uniform structure of the strip material Hot rolling preferably with a roll temperature of over 870 ° C and one Reel temperature below 710 ° C.

To achieve a low tip height when deep drawing or ironing and in particular a relative peak height of at most 2.5%, the value of the Anisotropy Δ r of the strip after coil annealing not more than +/- 0.12 be.

With the method according to the invention, finally, a deep-drawing or receive steel strip capable of being ironed.

The method according to the invention and a deep-drawing or ironing-capable Steel strip according to the method of the invention are described below an example explained.

The starting material is a hot strip with an initial thickness of 1.2 to 8 mm, preferably 2.0 to 2.5 mm. In a first embodiment, the steel analysis of the hot strip used is as follows: % By weight minimal % By weight maximum C 0,010 0,065 Mn 0,100 0,275 P 0,040 S 0,040 Si 0,050 N 0.0040 Al (acid soluble) 0,070 B ppm 0.0013 0.0060 Cu 0,100 sn 0,100 Cr 0,100 Ni 0,100 Mo 0,030 Fe rest B / N (ratio) 0.5 2.5

According to a second variant, which is particularly preferred, the steel composition is as follows: % By weight minimal % By weight maximum C 0,010 0,040 Mn 0.140 0,200 P 0,020 S 0,020 Si 0,030 N 0.0025 Al (acid soluble) 0,035 B ppm 0.0013 0.0030 Cu 0,040 sn 0,010 Cr 0,040 Ni 0,040 Mo 0,010 Fe rest B / N (ratio) 0.8

The strip is hot-rolled with a final roll temperature of over 870 ° C and a coiling temperature of below 710 ° C, in order to ensure a particularly even structure of the steel strip. Experiments have shown that the limit values for the yield strength between the edge and the center of the strip vary by less than 15 N / mm ² .

If the boron content is higher than the specified one, the required hot rolling forces increase clearly. In contrast, with boron contents below 0.0060% by weight ppm be worked with moderate hot rolling forces. This also leads this means that the thickness tolerance across the width of the belt is then clear due to the lower roll deflection is reduced.

The hot-rolled strip is then pickled and then one or two subjected to two-stage cold rolling. The degree of cold rolling is 86% or more. The starting material with a thickness of 1.2 to 8 mm can be in this way cold roll to a final thickness of 0.1 to 1.0 mm. Cold rolling there is a recrystallization annealing in the coil, i.e. an annealing of the strip in the wound state. Such recrystallization annealing comes to you Normal annealing, as is usually the case in continuous furnaces with stretched strip is carried out in the effects very close. Closes after coil annealing re-rolling the strip to improve its surface and adjust the mechanical-technological values.

The steel strip is galvanized with at least one of its two surfaces manufactured cover provided. This can be Ni, Co, Cu, Fe, Sn, In, Pd, Bi and / or their alloys contain. As part of the whole Process flow can be the electrolytic finishing on the first or on connect the second stage of cold rolling, followed by another Steps, the annealing in the coil and the rolling of the strip are carried out. A an additional annealing stage between the two cold rolling stages is also possible.

Finally, the electrolytically finished strip can also be used non-metallic or galvanic coatings, so to achieve special effects and properties.

The thickness of the entire electroplating on one or both sides of the Steel strip should be 0.1 µm to 8 µm.

The parameters are used to achieve a low lobedness of the steel strip set during the cold rolling so that following the simple Annealing in the coil an ansiotropy Δ r of max. +/- 0.12 gives what a relative Tip height of max. Corresponds to 2.5%. This also arises for the later Deep drawing or ironing advantageous round grain structure made of globular Grain a.

Claims (6)

Process for the production of steel strip for parts produced by deep drawing or ironing, in which a hot strip is cold-formed in one or more stages and with a degree of cold rolling of at least 86%, at least one side of the strip material having an electroplated coating containing Ni, Co, Cu , Fe, Sn, In, Pd, Bi and / or their alloys is provided,
characterized in that the process steps after hot rolling include pickling, one- or two-stage cold rolling, annealing of the strip in the wound state (coil annealing) and possibly re-rolling the strip, the coating after a cold rolling step, however, before the annealing is applied to the strip that the hot strip contains boron in a proportion between 0.0013 and 0.0060% by weight and that the weight ratio of boron to nitrogen is 0.5 to 2.5. A method according to claim 1, characterized in that the boron content is between 0.0013 and 0.0030% by weight. Method according to one of claims 1 or 2, characterized in that the hot rolling is carried out with a final rolling temperature of above 870 ° C and a coiling temperature of below 710 ° C. Method according to one of claims 1 to 3, characterized in that the value of the anisotropy Δ r of the strip after the coil annealing is not more than +/- 0.12. Method according to one of the preceding claims, characterized by the following weight fractions in the hot strip: % By weight minimal % By weight maximum C 0,010 0,065 Mn 0,100 0,275 P 0,050 S 0,050 Si 0,060 N 0.0060 B ppm 0.0030 Method according to one of the preceding claims, characterized in that the hot strip has a thickness of 1.2 mm to 8 mm before cold rolling.