Steel strip with good deformability characteristics, and method of its manufacture

 

The invention relates to the manufacture of steel strip for parts made deep hood or hood with thinning. Hot-rolled strip is subjected to pickling, cold rolling in one or more of the techniques and the degree of compression, at least 86%. Then, at least one side of the material strip covered galvanic coating containing Ni, Co, Cu, Fe, Sn, In, Pd, Bi and/or their alloys, or lakirovannym roll coating containing Cu and/or brass, and/or their alloys, annealing the strip in the wound state in the roll and, if necessary, the training band. Hot rolled strip preferably contains boron in an amount 0,0013-0,0060 weight. %, and the weight ratio of boron and nitrogen is 0.5 to 2.5. The invention reduces manufacturing costs by reducing the number of operations. 2 s and 5 C. p. F.-ly, 2 tab.

The invention relates primarily to a method of manufacturing a steel strip for parts made deep hood or hood with thinning, in which the hot rolled strip is treated in a cold state, the pressure in one or several stages, and with a degree of compression during cold rolling, component, at least 86%, at the n, In, Pd, Bi and/or their alloys, or by coating a cladding containing si and/or brass, and/or their alloys.

Cold rolled steel strip is often used for manufacturing rotationally symmetrical processed in a cold state, pressure parts, such as housings for batteries. Used in cold working pressure methods is, on the one hand, a deep hood and, on the other hand, the hood with thinning, the latter method is also known as DI (drawing and ironing - drawing and thinning).

Due to increased demands for consumer properties such strip steels increases the demand for the improvement of the mechanical characteristics and, in particular, to improve the characteristics of the strain. Good deformability different high distinguishing ability of metal for deep drawing coefficients (r-Werte) anisotropy, and high ratios indicate the ability to be pulling the hood (n-Werte), and high elongation. The advantage may be that the characteristics of deformability in different directions, i.e. in the longitudinal, transverse and diagonal directions, possible the same and is ravnomernost yield strength of the material by deep drawing or drawing with thinning, so education festoons or not, or the formation of small scallops, which leads to the reduction of waste sheet.

To achieve approximately isotropic plastic forming is required steel sheet with small tolerances on the thickness in textured and uniformly rolled strip or sheet.

Undesirable formation of festoons and his reasons explained in detail in the journal "Blech, Rohre, Profile 9/1977 (Sheet, pipe, profiles") on pages 341-346. It is also described that the material without festoons usually can only be obtained by normalization in reheating furnaces for annealing at temperatures around 1000oC. However, the operation of passing the furnace for annealing at such high temperatures associated with high capital and operating costs.

From DE-3803064 C1 it is known to obtain steel with round grains of low anisotropy and thus low tendency to form festoons by the fact that the steel contains a high proportion of titanium component to 0.04 weight. % when the degree of compression during cold rolling over 80%. However, with such high values of the degree of compression during cold rolling limit value of steel yield strength testing what they require high temperatures, recrystallization, what if such steel strip was subjected to annealing in a wound state (annealing roll), would have led to a clear trend of bonding of the individual layers of the strip. However, arising thereby damage on the surface of the strip in such high quality products are undesirable and would lead to a high percentage of rejection.

The use of furnaces for annealing strip of continuous operation in the manufacture of sheet steel parts produced by the extraction or extraction with thinning, it is also known from the publication US-5078809, WO 98/06881 and EP 0822266 A1. In the last mentioned publication describes a steel with low carbon content, the analysis of which shows the presence of boron, namely 0,0005-0,0015 weight. %. The above-mentioned lower limit is based on the requirement to improve the corrosion resistance of the steel sheet by adding boron to the molten steel. The upper limit 0,0015% wt. justified in EP 0822266 A1, provided that at higher boron content should take into account the defects forming in the manufacture of cylindrical parts.

DE 2019494 AND discloses a method of making steel with corrosion-resistant coating. On the pickled hot-rolled steel strip is coated, at least one meta is cold rolled to the desired final size. In the process of cold rolling in one or more of the techniques you can get a degree rolling about 90% or more. Cold rolled steel strip is annealed for recrystallization and annealing is carried out preferably in a continuous way. If you want only one annealing operation, the application can find a way annealing roll, and the annealing temperature must be maintained within 566-621oC for 1-5 hours. This is necessary to prevent too strong fusion of the coating applied by spraying on a hot streak with hot metal strip. As an example of the composition of the steel sheets used in the above method of manufacture, specified 0.035% of S; 0,49% MP; 0,10% P; 0,11% S and 0.035% Si. On the proportion of boron in the steel in this publication is not mentioned.

Patent GB 2101156 And describes a method of manufacturing a steel strip for deep drawing. Described in this publication, the method includes the usual operation of hot and cold rolling, used for soothing aluminum steel. Applied in accordance with this publication, the steel contains nitrogen in a proportion of not more than 0,007% and boron in an amount that corresponds to the specified ratio of boron to nitrogen in the range of 0.5 to 2.5. Specified in primaziale continuous way.

Patent JP-A-2267242 describes a method of manufacturing a cold-rolled steel strip from soothing aluminum steel with a low content of carbon. For chemical binding is contained in the steel of the nitrogen in the original steel type aluminum, which in the following way hot rolling links contained in the steel nitrogen in the form of aluminum nitride, in accordance with the following after hot rolling operations pickling and cold-rolling the steel strip is annealed by the method of annealing in a roll. In accordance with this publication, the steel tape has no coating, the steel also contains little boron.

Finally, in the patent DE-19547181 C1 described steel with a content of titanium, vanadium or niobium, and due to certain conditions of hot rolling is below the field of gamma radiation state diagrams of the system iron - carbon and due to the high winding temperature in the hot-rolled strip get mixed grains. When the degree of compression 50-85% of this mixed grains leads to a decrease in the tendency to form festoons, however, and to the formation of coarse-grained banded cementite, which when deep drawing parts of small thickness with high requirements to the surface leads to regulatel is carried out in to develop a way in which parts of the anisotropy is very close to the obtained normalization properties of the material, but at the same time can be used with low operating costs and costs fewer process operations. After annealing must be received globular grain structure, and then manufactured by the method in accordance with the invention the steel strip should not have any deficiencies due to aging or high mechanical and technological values at high degrees of compression.

According to the invention for this purpose, the method of the aforementioned type is proposed to be conducted after hot rolling operation included: - pickling, cold rolling in one or two installments, the annealing of the strip in the wound state (annealing roll), - if necessary, training of the strip and hot rolled strip contains boron in an amount 0,0013-0,0060 wt.%, and the weight ratio of boron and nitrogen is 0.5 to 2.5.

In particular, preferably the boron content 0,0013-0,0030 wt.%.

To produce a uniform structure of the material strip hot rolling to produce preferably at temperatures above 870oWith temperature and with the winding below 710or strip after annealing in the roll must be no more than0,12.

Finally, the invention provides a steel strip, which can be processed by a deep hood or hood with thinning, and which in accordance with the method produces at least one of the claims relating to the way.

The method according to the invention, as well as steel strip, which can be processed by a deep hood or hood with thinning according to the method in accordance with the invention, explained below using examples.

The source material is hot rolled strip original width of 1.2-8 mm, preferably 2.0 to 2.5 mm Analysis were applied to hot rolled strip in the first embodiment is shown below in table. 1 at the end of the description.

According to the second variant of implementation especially following preferred composition of the steel (see table. 2 at the end of the description).

Hot rolling strip is produced at temperatures above 870oWith temperature and with the winding below 710oIn order to ensure a particularly uniform structure of the steel strip. When testing was ustanovleni>2
.

At higher boron content than the configured efforts are needed hot rolling noticeably increase. But when the boron content is less 0,0060 weight. % parts per million can work with less effort hot rolling. This also leads to reduced tolerance on thickness across the width of the strip due to the significantly smaller deflection of the rolls.

Then hot rolled strip is treated with pickling and cold rolling in one or two installments. The degree of compression when cold rolling is 86% or more. Thus it is possible to perform the cold rolling of the source material with the thickness of 1.2-8 mm to a final thickness of 0.1 to 1.0 mm After cold rolling should recrystallization annealing in the container, that is, the annealing of the strip in the wound position. Such recrystallization annealing, which is usually carried out in continuous furnaces with laminated strip, very close on the effects of normalization. After annealing roll produce extra training band to improve its surface and the stabilization of mechanical and technological parameters.

Steel strip is provided at least on one of its surfaces plated. Pok is acetone electrolytic coating on the first or second stage of cold rolling, and then, on further stages produce the annealing roll and training band. It is also possible additional step of annealing between the two stages of cold rolling.

Coating at least on one side of the steel strip can be produced alternative described ways of galvanization by cladding by rolling a metal foil. In this case, after hot rolling and pickling of steel strip first produce cladding by rolling and then annealing in a roll. Also after annealing in a roll can be repeated cold rolling and the second annealing in a roll, after which the band finally put the training to improve the surface.

For cladding by rolling suitable layers consisting of copper and/or brass, and/or their alloys. Then the improved electrolytic or cladding by rolling a strip, you can additionally apply a non-metallic or plating in order to achieve special effects and properties.

When applying the electroplating process, the thickness of electroplated coatings on one or both sides of the steel strip must be 0.1-8 μm. For cladding by rolling the sum of unilateral or bilateral layer is festoons in the steel strip parameters during cold rolling establish such so after a simple annealing roll was anisotropyr maximumof 0.12, which corresponds to the relative height of the festoon maximum of 2.5%. This creates a preferred structure of globular grains for subsequent deep drawing and drawing with thinning.

Claims

1. A method of manufacturing a steel strip for deep drawing or drawing with thinning, including pickling hot-rolled steel strip, causing galvanic coating on at least one side of the strip, consisting of one metal belonging to the group of Ni, Co, cu, Fe, Sn, In, Pd, Bi, and/or their alloys or clad by rolling coatings containing si and/or brass, and/or their alloys, cold rolling in one or two installments, with the degree of compression, at least 86%, annealing in a roll, wherein the hot-rolled steel strip contains boron in an amount 0,0013-0,0060 wt. %, the weight ratio of boron and nitrogen is 0.5 to 2.5, coating is carried out after the cold rolling before annealing and after annealing are training.

2. The method according to p. 1, characterized in that the strip contains boron in an amount 0,0013-0,0030 wt. %.

3. The method according to p. 1 ilure below 710oC.

4. The method according to any of paragraphs. 1-3, characterized in that the value of the anisotropyr strip after annealing roll is not more than0,12.

5. The method according to any of paragraphs. 1-4, characterized in that the hot-rolled strip made of steel containing components in the following ratio, wt. %: carbon 0,010-0,065, manganese 0,100-0,275, phosphorus 0,050, sulfur 0,050, to 0.060 silicon, nitrogen 0,0060 and boron 0,0013-0,0030.

6. The method according to any of paragraphs. 1-5, characterized in that the hot-rolled strip prior to cold rolling has a thickness of 1.2-8 mm

7. Steel strip for deep drawing or drawing with thinning, characterized in that it is manufactured according to the method, at least one of PP. 1-6.

 

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FIELD: metallurgy, production of rolled steel.

SUBSTANCE: the invention is pertaining to the field of metallurgy, production of rolled steel, in particular, to methods of production of cold rolled steel sheets with the high drawing properties for a cold forming of details of cars bodies. The technical problem being solved by the invention consists in improvement of the quality of a cold rolled sheet steel. The method provides for hot rolling of continuously-cast low-carbon steel slabs, etching treatment, multirun cold rolling with total relative reduction of no less than 75 %, a recrystallization annealing in the following mode: a heating at an average speed of 70-80°C/h up to temperature of 490-510°C, a repeated heating at an average speed of 3-4 °C/h up to the intermediate temperatures of 540-560 °C/h and the final heating at an average speed of 50 - 55°C/h up to the annealing temperature of 700-720 °C, at which the steel rolls are kept for 12-18 h. Upon termination of keeping the rolls at the annealing temperature they are cooled at the rate of 19-21 °C/h up to the temperatures not exceeding 690 °C. At that the continuously cast low-carbon steel slabs have the following chemical composition (in mass %): 0.025-0.050 - carbon, 0.003-0.010 - silicon, 0.12-0.19 - manganese, 0.02-0.05 - aluminum, no more than 0,011 - nitrogen, the rest - iron and impurities.

EFFECT: the invention ensures improvement of the quality of a cold rolled sheet steel.

3 cl, 5 ex, 3 tbl

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