EP1200647B1 - Method for producing improved cold rolled strip that is capable of being deep drawn or ironed, and cold rolled strip, preferably used for producing cylindrical containers and, in particular, battery containers - Google Patents

Abstract

The invention relates to a method for producing improved cold rolled strip which is capable of being deep drawn or ironed and which has a carbon content of less than 0.5 wt. %. The invention also relates to a cold rolled strip that can be produced by such a method, preferably used for producing cylindrical containers and, in particular, battery containers by deep drawing or ironing. The strip that is cold rolled with a cold rolling degree ranging from 30 to 95 % is subjected to a thermal treatment in the annealing furnace and to a preferably galvanic coating of at least one of both strip surfaces. In order to obtain an isotropic steel strip which has a low level of texturing and which has a low tendency toward earing, the coating produced with one or multiple layers contains the elements nickel/ cobalt/ iron/ bismuth/ indium/ palladium/ gold/ tin or alloys thereof, whereby the thermal treatment is effected by an annealing, which is carried out before or after the coating process, in the continuously running strip annealing furnace at a temperature greater than the limit temperature to the austenite range (η range).

Description

The invention relates to a method for producing deep-drawing or ironable, refined cold rolled strip with a carbon content of below 0.5% by weight, in which the cold rolled with a degree of cold rolling of 30 to 95% Band a heat treatment in the annealing furnace and one preferably galvanic coating of at least one of the two strip surfaces is subjected. The invention further relates to a cold strip, preferably for Manufacture of cylindrical containers and in particular battery containers Deep drawing or ironing, consisting of one with a cold rolling degree of 30 to 95% cold rolled, a carbon content of less than 0.5% by weight having band and a preferably electroplated Coating on at least one of the two belt surfaces. The invention finally relates to a battery sleeve made from such a cold strip.

From EP 0 809 307 A2 it is known to apply cold rolled strip with galvanically applied To provide layers of nickel or nickel alloys. Part of the procedure is also a multiple successive Annealing process in which the nickel-coated steel strip is initially at 640 ° C, d. H. the recrystallization temperature of the steel is annealed, then further annealing process with the same temperature before finally one further heat treatment with an oven temperature of 450 ° C is carried out. Follow the consecutive annealing of the strip is one Changing the arrangement and shape of the grains. The aim is with the method according to EP 0 809 307 A2, by appropriate selection of the to achieve nickel-containing galvanization that when using the tape for Deep drawing or ironing of battery sleeves is the harder of the two Band surfaces later form the inside of the battery case, whereas the Also with a nickel alloy finished belt surface of lower hardness later forms the outside of the battery sleeve.

DE 37 26 518 C2 describes a process for the production of nickel-plated and described cobalted cold strip, which is a thermal treatment in Temperature range between 580 and 710 ° C is subjected. That about this Cold strip used with a carbon content of up to 0.07 wt .-% pickled, cold-rolled, then electroplated and then at one Oven temperature between 580 and 710 ° C recrystallization annealed. It closes re-rolling or skin-dressing of the finished strip. proposed is further, an electrolytic on the electrolytic nickel layer Apply cobalt layer, which has a favorable effect on the corrosion behavior of the finished cold strip affects. Attention is also drawn to the increased Diffusion rate due to the crystallization annealing, the Penetration of the coating metals into the base material of the steel strip Diffusion shows a depth that is several times the depth of the nickel-cobalt coating is.

EP 0 629 009 B1 describes a method for producing low-tip nickel-plated cold rolled strip with a particularly low carbon content of less than 0.009% by weight. For the implementation of the procedure and the Sequence of the individual process steps are different alternatives specified. This is how the annealed steel strip is described after the nickel plating to glow a second time, but this is a complex process leads. Furthermore, it is also described that the cold strip is first annealed and only then to undergo the galvanic nickel plating without this would be followed by diffusion annealing. For the continuous Annealing process is a temperature range from 600 ° C to 900 ° C and specified Annealing time of 2 minutes.

A process for the production is also known from JP 53 039374 B. of steel sheets. The peculiarity of the method disclosed here is there in the fact that in a first step a nickel layer on a or galvanically deposited on both surfaces of a cold-rolled sheet and then the sheet at a temperature between 840 ° C and 900 ° C is annealed. A comparable process is also disclosed in JP 03 090592 A. A method for producing a is also disclosed here surface-treated steel sheet, with the surface of a cold-rolled steel sheet in a first process step, first a Nickel layer is electrodeposited. This will be in a subsequent Process step then annealed, and finally under the action of heat rolled. The temperature range for the tempering process is one Temperature from 600 ° C to 900 ° C proposed.

The invention has for its object to provide a process for the production of deep-drawn or ironable, refined cold strip with a carbon content of less than 0.5% by weight, which leads to a low-texture, isotropic steel strip with little tendency to tip formation.

To solve this problem, a process for the production of deep-drawn or ironable, refined cold strip with a carbon content of less than 0.5% by weight is proposed, in which the cold-rolled strip with a degree of cold rolling of 30 to 95% is subjected to heat treatment in an annealing furnace and one is preferably subjected to galvanic coating of at least one of the two strip surfaces, the one or more coating produced containing the elements nickel, cobalt, iron, bismuth, indium, palladium, gold or tin or their alloys, and wherein the heat treatment by means of a before or after annealing carried out in a continuous strip annealing furnace at a temperature above the limit temperature from the two-phase ferrite / austenite region (α / γ region in the iron / carbon system) to the austenite region (γ region in the iron / carbon system), with an additional one after the annealing Coating the tape in a galvanic bath Organic additives which increase the brittleness of the coating are used, degradation products of these organic substances which are part of the electrolyte bath and / or reaction products of organic substances which are constituents of the electrolyte bath being incorporated into the layer. As a result of the normalization annealing with crossing the boundary to the γ region twice, the steel is converted into a fine-grained, uniform structure. All structural and property changes caused by any previous processes such as hot and cold forming and any heat treatments are reversed by the normalization annealing above the limit temperature to the austenite area (γ area). Therefore, there is extensive graining of the structure with a relatively small grain structure, which, when the steel strip is used later for deep drawing or ironing z. B. of battery sleeves leads to a low lobedness, expressed by the planar anisotropy Δr. The grain size achieved with globular grain is also suitable for extreme degrees of drawing, the fine structure which results leads to a uniformly smooth surface of the finished drawn part. In addition, the fine-grained structure created by normalizing annealing in a continuous furnace improves the corrosion resistance of the drawn part made from refined cold strip. The reason for this is the significantly reduced tendency to crack in the galvanic layer during deep drawing or ironing due to the small grain size of the substrate.

The equalization of the associated two-time structural transformation mechanical properties and a complete change in texture Band length and width can also be compared to an increase in strength lead recrystallized material. This is especially with multi-stage drawing and Ironing operations advantageous, the z. B. in high-speed presses. The danger of constrictions and cracks, for which the tensile strength is decisive, are reduced.

Normalization annealing in a continuous annealing furnace also leads to the improved strength of the galvanized cold strip better dimensional accuracy and low-corneredness of the deep-drawn part, which is special in the manufacture of battery sleeves or similar rotationally symmetrical Products is important. The for the invention Normalization annealing in a continuous annealing furnace required temperature depends on the carbon content of the used Tape material. With a so-called decarburized steel of max. 0.01% by weight C is an annealing temperature of 950 ° C to 1000 ° C of the annealed object Aim for a maximum treatment time of 10 minutes. At higher Carbon content of, for example, 0.3% by weight, the annealing temperature is approx. 100 ° C less, but is still in the austenite area of the iron / carbon system.

The coating according to the invention is preferably galvanic, if necessary, however, vacuum evaporation is also possible. With both Processes are layers of the strip as well as multi-layer layers possible. Also, the coatings can be on either side of the tape be different to e.g. B. to improve the thermoforming behavior on both Different mechanical, tribological and / or electrical sides To achieve properties for the drawn part.

Will the coating proposed by the invention, which the elements Nickel / cobalt / iron / bismuth / indium / palladium / gold / tin or their Contains alloys, performed before annealing, then this results as a result of the heat treatment entering and far into the material of the steel strip sufficient diffusion for a very good adhesion of the coating on the Strip material. During later forming by deep drawing or ironing chipping of the layers is impossible. By the Normalization annealing to a temperature in the austenite area is carried out on the Coating material deposited from an amorphous deposition structure transformed into a globular structure that is characterized by a better Formability distinguishes.

To diffuse the coating into the base material of the steel strip To achieve the appropriate depth of penetration, the coating of the tape must before glowing. In a further embodiment of the process proposed that the strip be coated for the first time before annealing, and that after the annealing another coating which the elements Nickel / cobalt / iron / bismuth / indium / palladium / gold / tin or their Contains alloys on which tape is applied.

To further improve the thermoforming behavior, the tape should be removed after the Normalization annealing first go through a skin pass rolling stage.

The subsequent one after the annealing treatment and the rolling Coating takes place using a galvanic bath, which in order to increase the hardness and brittleness of the layer obtained organic additives are added. This results in later dragging or Ironing a sleeve produced from the cold strip according to the invention to tear open the very brittle coating. The one with the coating shows the provided side, if it is the one during deep drawing or ironing prevailing strong forming forces is exposed to a particularly low electrical contact resistance, which is particularly important in the manufacture of batteries with alkaline electrolyte is an advantage. On the inside of such a thing manufactured battery sleeve compared to the prior art low values for the electrical contact resistance between the Cathode substance of the battery and the inner surface of the battery sleeve.

The addition of the organic additives mentioned to the electrolyte bath is particularly advantageous if the further coating with cobalt or a Cobalt alloy is made.

It is also possible to add to the layer containing organic additives Improvement of the conductivity to include additional electrically conductive particles.

In the first, that is applied before the annealing, electrically conductive or conductive particles of z. As carbon, carbon black, graphite, TaS ₂ , TiS ₂ and / or MoSi _{2 can be} stored. Such inclusions can reduce the electrical contact resistance when the cold strip is later used to produce battery sleeves. For this purpose, it is also possible to coat the coating with a conductive particle such. B. carbon, carbon black, graphite, TaS ₂ , TiS ₂ and / or MoSi ₂ containing galvanic dispersion coating. The carbon content of the electroplating should be 0.7 to 15% by weight. As carbon suspended in the electroplating bath, primarily finely divided particles of carbon (graphite or soot) come into consideration. The particle size is preferably 0.5 to 15 μm.

To achieve an even distribution of carbon in the electroplating should be in the electroplating bath during the Galvanization process a uniform flow can be generated. The galvanic is preferably used to achieve the uniform flow Bath circulated evenly. A forced one has proven particularly suitable Flow rate of the electrolyte from 6 to 10 m / s highlighted. Further can the galvanic bath suspension stabilizing and / or contain coagulation-reducing substances so as to ensure a uniform Distribution of carbon particles with no local or temporal To achieve concentrations.

Regarding the Cold strip is proposed a cold strip, preferably for the production of cylindrical containers and in particular battery containers by deep drawing or Ironing, consisting of one with a cold rolling degree of 30 to 95% cold-rolled strip with a carbon content of less than 0.5% by weight and a preferably electroplated coating on at least one of the two belt surfaces, the coating comprising the elements nickel, Cobalt, iron, bismuth, indium, palladium, gold or tin or their alloys contains and wherein the strip in a continuous strip annealing furnace is heat treated at an annealing material temperature above the limit temperature from the two-phase ferrite / austenite region to the austenite region.

Finally, it is suggested that the cold strip over the first coating another coating of the elements nickel, cobalt, iron, bismuth, Contains indium, palladium, gold or tin or their alloys. As galvanic or layers applied by vacuum evaporation are particularly useful consideration:

Cobalt, nickel / iron, nickel / cobalt, nickel / cobalt / iron, cobalt / iron, Nickel / indium, iron / indium, nickel / bismuth, palladium, palladium / nickel, Palladium / iron, palladium / cobalt, palladium / indium and palladium / bismuth.

Those for the normalization annealing of the cold strip according to the invention in one Continuous strip annealing furnace temperature depends on Carbon content of the strip material used. In a so-called decarburized steel of max. 0.01 wt .-% C is an annealing temperature of 950 ° C to 1000 ° C of the annealing material / object with a maximum treatment time of 10 Aim for minutes. With higher carbon proportions of, for example, 0.3 % By weight, the annealing temperature is approx. 100 ° C less, but is still in the Austenite area of the Fe / C system.

A further coating is carried out after the normalization annealing a galvanically applied layer of preferably cobalt or one Cobalt alloy Organic substances become the electrolyte bath added. As a result of the during the galvanic coating in the The organic additives break down into electrolytes of flowing electricity Degradation products. These can then be combined with other ingredients of the Electrolyte bath, especially metal ions, react. The so won Reaction products are, if necessary, together with others Degradation products together with the cobalt or the cobalt alloy on the Cold strip deposited and cause a significant embrittlement of the layer. in the Traps containing sulfur or carbon-containing organic substances can these reaction products are, for example, cobalt sulfides or cobalt carbides.

Suitable organic additives in the electrolyte are those from the galvanic Coating known primary and secondary gloss agents. galvanic Precipitation from such additives lead to a very hard and at the same time brittle coating, which causes the material to later form through Deep drawing or ironing tends to crack. Draw the cracks is characterized by a relatively uniform structure with a diamond-shaped shape individual crack plates.

Suitable gloss additives have z. B. 1,4 butynediol, o-benzoic acid sulfimide (saccharin), paratoluenesulfonamide and mixtures of these substances were found. The electrolyte thus provided with gloss additives is guided when a predominantly cobalt-containing electrolyte bath is prepared at an electrolyte bath temperature of 50-70 ° C. and a current density of 6-15 A / dm ² . The pH value of the electrolyte bath should preferably be set to 4.0.

Five examples which are suitable within the scope of the invention are given below Steel analyzes for the base material used with a thickness of 0.1 to 1 mm stated:

1. Unalloyed, low carbon steel

carbon 0.010 - 0.100% manganese 0.140 - 0.345% silicon Max. 0.06% phosphorus Max. 0.025% sulfur Max. 0.030% aluminum 0.02 - 0.08% nitrogen Max. 0.0080% copper Max. 0.10% chrome Max. 0.10% nickel Max. 0.10% boron Max. 0.006% titanium Max. 0.015% Rest: iron

2. Decarburized steel (IF steel)

carbon Max. 0.010% manganese 0.10 - 0.25% silicon Max. 0.15% phosphorus Max. 0.020% sulfur Max. 0.020% aluminum 0.015 - 0.060% nitrogen Max. 0.004% copper Max. 0.08% chrome Max. 0.06% nickel Max. 0.10% titanium 0.02 - 0.10% niobium Max. 0.10% Rest: iron

3. Low carbon steel

carbon 0.010 - 0.020% manganese 0.50 - 0.70% silicon Max. 0.06% phosphorus Max. 0.025% sulfur Max. 0.020% aluminum 0.02 - 0.08% nitrogen Max. 0.009% copper Max. 0.12% chrome Max. 0.06% nickel Max. 0.10% Rest: iron

4. Micro alloy steel

carbon Max. 0.10% manganese Max. 1.65% silicon Max. 0.50% phosphorus Max. 0.12% sulfur Max. 0.030% aluminum at least 0.015 niobium Max. 0.09% titanium Max. 0.22% vanadium Max. 0.25% Rest: iron

5. High-strength, micro-alloyed steel

carbon Max. 0.25% manganese Max. 1.65% silicon Max. 0.60% aluminum minute 0.02% phosphorus Max. 0.025% sulfur Max. 0.035% vanadium minute 0.03% niobium minute 0.03% molybdenum minute 0.20% Rest: iron (the% values each refer to% by weight)

Claims (2)

1. A method of producing refined cold rolled strip, which is capable of being deep drawn or quench drawn, with a carbon content of less that 0.5% by wt. in which the strip, which is cold rolled with a degree of cold rolling of 30% to 95%, is subjected to a heat treatment in an annealing furnace and a preferably galvanic coating of at least one of the two strip surfaces, whereby the coating, which is produced once or a number of times, contains the elements nickel/cobalt/iron/bismuth/indium/palladium/gold/tin or alloys thereof and the heat treatment is effected by annealing conducted before or after the coating in a continuously running strip annealing furnace at a temperature above the threshold temperature of the two-phase region of ferrite/austenite (α/γ region in the iron/carbon system) to the austenite region (γ-region in the iron/carbon system) characterised in that after the annealing process, an additional coating of the strip is effected in a galvanic bath using organic additives which increase the brittleness of the coating, whereby decomposition products of these organic substances, which are a component of the electrolyte bath, and/or reaction products of organic substances, which are a component of the electrolyte bath, are incorporated into the layer.
2. Method as claimed in claim 1, characterised in that the organic electrolyte bath additives, whose decomposition and or reaction products from reaction of these decomposition products with other components of the bath, which are incorporated into the coating, are brightness additives (so called primary or secondary brightness agents).