EP0314667A1 - Process and apparatus for manufacturing thin wires, rods, pipes or sections made of steels or alloys with a low deformability, particularly of hardenable steels - Google Patents

Abstract

In the process and equipment for deformation of steels, metals and alloy of low deformability and/or deformation resistance at room temperature from raw material of small thickness, the raw material is heated, preferably by continuous rapid heating, to a temperature of at least 400 DEG C and at most up to the AC1 temperature of the alloy, and a two-stage or multi-stage deformation with an altogether large reduction in cross-section is carried out. <IMAGE>

Description

The invention relates to a method for deforming steels, metals and alloys with low deformability and / or high deformation resistance at room temperature, in particular hardenable steels, for example high-speed steels, with small primary material thicknesses, preferably less than 10 mm and with a large overall reduction in cross section, and a device for carrying them out of the method with a heating device, optionally a temperature compensation and guide device and a deformation device.

Wires, rods, tubes and profiles with a small diameter or wall thickness are produced by cold rolling or cold drawing after the hot forming of the primary material and, if necessary, after soft annealing. The primary material usually has a thickness of less than 10 mm.
During the cold forming process, the material solidifies, whereby with decreasing ductility or increasing resistance to deformation, higher degrees of hardening are given and the deformability of the material is exhausted at low degrees of deformation. Materials with high ductility at room temperature and thus high cold-forming properties can be highly deformed by cold rolling and cold drawing, and cross-sectional reductions of, for example, 10: 1 or 90% and higher are possible. The material solidifies in the course of the change in shape due to the low cold forming capacity so strongly that the Further processing to the desired final dimensions is not possible and cracks and breaks occur due to exhausted deformability, so softening by heating to higher temperatures or intermediate annealing must be activated. With this intermediate heat treatment, the solidifications in the material are broken down. For hardenable steels, in particular air hardeners, such as tool steels and high-speed steels, this intermediate heat treatment can be a soft annealing treatment. For economic reasons, however, long-term annealing is usually carried out for softening, possibly below the austenitizing temperature or below the AC 1 point of the alloy.

Pre-material with low cold forming ability and with a small thickness can usually not be deformed to the final dimension in the hot, ductile state because the energy loss due to radiation from the surface, which increases with the 4th power of the temperature, leads to low temperatures in the zone near the surface and In the case of hardenable steels and alloys, structural changes or hardening of the material also take place. The rapid cooling occurs because the heat content of the material is low due to the small cross section.
Furthermore, after a deformation of, for example, hardenable alloys in the forging-hot state, a low-temperature treatment must be carried out.

In order to avoid hardening or a heat treatment subsequent to the deformation, if necessary, and nevertheless to achieve an increase in the deformability and thus an increase in the cross-sectional decrease, it was proposed to deform at an elevated temperature temperature, but possibly below the austenitizing temperature or below the AC 1 point of the alloy. However, the deformation energy introduced must not lead to a temperature increase above the AC 1 point in any cross-sectional area.

Drawing has proven to be advantageous for the deformation process at elevated temperature, because the energy input is caused by the friction in the drawing cavity and by the main deformation in the zone near the surface and the radiation losses are thereby largely compensated for. The improved temperature distribution across the cross-section enables larger cross-sectional reductions to be used per deformation step and, with an overall high decrease in the initial cross-section, a reduction in the number of pulls and the intermediate softening treatments to be achieved by repeated pulling. However, the drawing speed at an elevated temperature of the material must be kept low, for example at 0.2 to 2 m / sec, because at higher values the drawing die wear becomes too great due to the tearing off of the lubricating film and the time for the preheating and softening of the material is long and therefore requires uneconomical warm-up sections.

For example, a soft annealed high-speed steel wire (material DIN No. 1.3343) with a diameter of 5.5 mm can be continuously drawn off a reel in a lead bath with a length of 10 m and a lead bath temperature of 700 ° C for a throughput time of 20 seconds be, whereupon a deformation in the die to a diameter of 4.7 mm at a speed of 0.5 m / sec, after which the wire is rewound. The deformation in this case is approx. 27%. In seven further steps carried out in the same way, possibly with four intermediate softening anneals with oxidation protection at a temperature of approx. 800 ° C and a glow duration of approx. 1 hour, the wire is brought to a diameter of 1.6 mm, the heating up to temperature and the further degradation of the hardening in the lead baths takes place before the respective deformation.
The disadvantages of deformation due to drawing at elevated temperatures of steels and alloys, in particular hardenable steels, with small starting material thicknesses are the complex processing required in several steps with intermediate softening annealing, the low drawing speed and the problems with the high-temperature drawing agents and the wear of the drawing block.

Starting from this prior art, the object of the invention was to avoid the above disadvantages and to create a method and a device with which overall large cross-sectional reductions can be carried out in one work step and the desired final cross-section can be achieved with largely any dimensions.

This object is achieved according to the invention in a process of the type mentioned at the outset in that the starting material is heated to a temperature of at least 400 ° C. and at most 1100 ° C., preferably at most 950 ° C., if necessary at most up to the AC 1 temperature or transition temperature into the Gamma structure of the alloy is heated and that a two- or multi-stage deformation is carried out with an overall large reduction in cross section becomes. It is preferred if the heating of the primary material is carried out by means of continuous rapid heating, the heating with direct current passage with a variable heating distance bringing additional process advantages if the electrical power, which is influenced by the cross-sectional area of the mean specific heat and the density of the material, is proportional to that Quotients, formed from the speed of the material to be heated and the heating section, is regulated. It is particularly advantageous and of economic importance if the primary material is deformed by rolling and a total cross-sectional decrease of at least 40%, preferably at least 60%, is carried out. The rolling deformation in the individual passes should be carried out in such a way that a reduction in cross-section of at least 10%, preferably at least 15%, or a decrease in height of at least 20%, preferably at least 30%, is carried out on the rolling stock. The cooling of the rolling stock which is possibly to be used advantageously is to be regulated in the order of magnitude in accordance with the deformation performance of the preceding pass or passages converted into heat. Furthermore, the method can be used particularly well and economically if the feed speed of the primary material into the first roller caliber is at least 0.2 m / sec, preferably at least 0.5 m / sec. If necessary, the deformation of the primary material can advantageously also take place in a multi-roller mill. Furthermore, the invention consists in a device for carrying out the method, whereby after a preferably electrical heating device by induction or with direct current passage through the heating material with a variable heating distance and optionally a temperature compensation device with protection gas atmosphere to prevent oxidation, a deformation unit, in particular a two-stand or multi-stand continuous rolling mill, preferably designed as a cassette rolling mill, and optionally adjustable cooling devices are arranged between the rolling stands. The device has proven to be advantageous if the device for temperature compensation and for guiding raw materials can be heated and in which a protective gas atmosphere can be set. In order to achieve particularly good rolling results, it is advantageous for flat products and profiles to use an alternately open and closed caliber sequence, the last caliber being a closed caliber for dimensional calibration. When manufacturing products with a round cross section, for example wires, a closed caliber shape is advantageously used in all rolling stands. Particularly good results combined with high cost-effectiveness can be achieved if cooling devices are arranged between the roll stands, by means of which cooling medium can be regulated in a controllable manner on the roll surfaces and / or the rolling stock. A particularly high level of economy is also provided if the rolls are made of hard metal or tempered high-speed steel and optionally have a hard material layer which is formed from oxide and / or nitride and / or carbide and / or their compound, for example oxycarbonitride. For certain cross-sectional shapes of the products, the device advantageously has a multi-roller mill as a deformation unit.

Quite surprisingly, it has been shown that the deep deformation occurring during the rolling process only results in a slight increase in temperature in the core of the material calls, so that, for example, hardenable steels do not exceed the AC 1 temperature, especially in the center. This effect is also given at rolling temperatures just below the alloy's AC 1 temperature, whereby the material's throughput speed through the rolls can be significantly higher than that through the drawing die. It could also not be assumed that multi-stand rolling in one operation and / or at a higher rate of deformation, possibly with surface cooling, between the rolling steps allows the temperature distribution in the rolling stock to be set such that the desired temperature, for example the AC 1, is not exceeded in any area -Temperature, entering. Also other prejudices of the professional world, namely that material hardening occurs several times in succession in one work step and the deformation capacity is exhausted and that the time between the individual roll deformations is insufficient due to the increasing rolling speed with decreasing cross-section to allow softening processes to take place in the material , could not find any confirmation.

Preferred embodiments of the invention can be found in the following description, the subclaims and the drawings.

• Fig. 1 bis 3 eine Vorrichtung zur Herstellung eines Flachprofiles aus Rundmaterial, wobei in der
• Fig. 1 schematisch ein zweigerüstiges Walzwerk mit vorgeschalteter Erwärmungs- und Temperaturausgleichseinrichtung dargestellt ist und in
• Fig. 2 der erste Stich mit freier Breitung, in
• Fig. 3 der zweite Stich im geschlossenen Kaliber, in
• Fig. 4 eine Walzstraße für Rundprofile mit Kassettenwalzwerk, in
• Fig. 5 ein Dreiwalzen-Dreikantkaliber, in
• Fig. 6 ein Dreiwalzen-Rundkaliber, in
• Fig. 7 Querschnittsformen des Walzgutes in einer zwölfgerüstigen Walzenstraße und in
• Fig. 8 eine Kühlvorrichtung für Walzen und Walzgut schematisch dargestellt sind.

The invention is explained in more detail below with reference to the drawings. Show it:

• 1 to 3 a device for producing a flat profile from round material, in which
• Fig. 1 shows schematically a two-stand rolling mill is shown with upstream heating and temperature compensation device and in
• Fig. 2 the first stitch with free width, in
• Fig. 3 the second stitch in the closed caliber, in
• Fig. 4 is a rolling mill for round profiles with cassette rolling mill, in
• Fig. 5 is a three-roll triangular caliber, in
• Fig. 6 is a three-roll round caliber, in
• Fig. 7 cross-sectional shapes of the rolling stock in a twelve-stand mill and in
• Fig. 8 schematically shows a cooling device for rolls and rolling stock.

In Fig. 1, a rolling mill mounted on a foundation A for producing a wide flat profile with the dimensions of 8 mm x 1 mm from round wire primary material with a diameter of 3.8 mm is shown schematically. Here, from a supply reel 2 from a drum 21, which is rotatably fastened in a support device 22 by means of bolts 23, primary material 1 is drawn off, heated in a rapid heating device 3, fed by a temperature compensation and guide device 4 to a two-stand deformation device 5 and thus rolled, whereupon in a final reel 7, the dimensionally accurate flat profile tape is wound on a drum 71, which is driven by a shaft 73 and is rotatably mounted in a support 72.
At the start of rolling, the contact roller stand 31, which is slidably connected to a support 33, is in a position 31 'and near a contact roller stand 32 brought, which shortens the heating distance. The wire-shaped primary material 1 with a diameter of 3.8 mm is, for example, a high-speed steel, material no. 1.3343, in a soft-annealed condition and is carried out through the gap of contact rollers 311 and 311 'in position 31' until it has an electrically conductive connection a pair of contact rollers 322 or 322 'produces, whereupon the power supply of terminals 34 takes place. The passage of current through the primary material heats it up and, when a temperature of 800 ° C. is reached, the wire is moved into a guide and temperature compensation tunnel 41, which is preheated via a connecting pipe 42 and supplied with inert gas can, inserted. The wire feed can be carried out by a separate pair of rollers, not shown, or by the contact rollers of the contact roller frame (s). After emerging from the tunnel or from the tunnel guide, the primary material, which has a temperature of 500 ° C. and a diameter of 3.8 mm, is deformed in a first roll stand 51 to a thickness of 2 mm and an average width of 5.3 mm . The deformation takes place, as shown in FIG. 2, with free spreading between rollers 511 and 512, a decrease in height of approx. 47%, a spreading of approx. 40% with a degree of deformation or a reduction in the cross-sectional area of approx. 6% given are. 2, the number 1 represents the initial cross section of the primary material and 1 'the rolled cross section. Immediately after this first pass, the material deformed in the caliber of the first stand 51 is in a second closed caliber of a rolling stand 52, which in FIG is shown on the desired cross cutting dimension of 1 x 8 mm deformed. An upper roller 521 and a lower roller 522 leave the roll gap of 1 mm free, side rollers 523 and 524 being placed on the sides of the upper and lower rollers and thereby preventing the rolling stock from spreading beyond the desired dimension of 8 mm. With this finish stitch or calibration stitch, the height decrease is approx. 50%, the width approx. 51% and the area decrease approx. 25%. The inlet speed of the primary material, which has a temperature of 800 ° C, is 0.8 m / sec, the outlet speed from the roll stand 52, with which the high-speed steel strip is subsequently wound up, is approximately 1.13 m / sec, whereby a rolling stock temperature of 810 ° C is present immediately after the last rolls.
The degree of deformation achieved in one operation with two-stage rolling is approximately 30% in total. The tests carried out on the product, which was produced continuously or without interruption by the above process, showed that the required dimensions with the corresponding tolerances were present over the entire length of the wide flat strip and sharp edges were present without any edge breaks.

Experiments with raw material temperatures of below 400 ° C or at room temperature have shown that during the rolling of, for example, hardenable steels, in particular high-speed steels, the alloy solidifies to such an extent in this temperature range that the formability is exhausted at least in places, which in addition leads to increased roller wear Fractures or material separations occur, particularly in the area of the edges of the strip. Further tests have also shown that the temperature of the raw material is slightly below the AC-1 temperature of the alloy Temperature compensation device can be shortened, if necessary also omitted, with only one guide ensuring the desired wire entry into the first rolling stand.

Fig. 4 shows schematically a device mounted on a foundation A for producing a round wire with a diameter of 1.8 mm from a round, with a diameter of 5.5 mm, raw material, wherein a twelve-stand mill or a cassette mill is used.
From the reel 2 with the drum 21 rotatably mounted in a support 22 by means of a bolt 23, the primary material 1 is drawn off, brought to a temperature of 780 ° C. in a rapid heating system 3, conveyed through the temperature compensation and control device 4 and in a cassette rolling mill 5 deformed, whereupon in the end reel 7 the winding of the wire deformed to the final dimension on the drum 71, which rests on the support 72 and is driven by the shaft 73, takes place. The roll stand 51 of the shaping device 5 can, for example, have a three-roll triangular caliber, as is shown schematically in FIG. 5. The working surfaces of the rollers 511, 512, 513 result in a roller cross section 11 which has a convexly convex triangular shape. In an associated follower mill stand 51 'three rolls can also be used, as shown in Fig. 6, the shape of the working surfaces of the rolls 511', 512 ', 513' provides a circular rolling cross section 12. The roll stands 52 and 52 ', 53 and 53', 54 and 54 ', 55 and 55', 56 and 56 'can have rolls with the same caliber sequences and decreasing caliber cross section. The triangular caliber does not have to be rolled be completely filled, however, with the round caliber due to the required product dimensions or
Dimensional tolerances require complete caliber filling.

Pre-material, for example made of material no. 1.3247, in the soft-annealed condition with a diameter of 5.5 mm, is rolled to a diameter of 1.8 mm in a device described in principle above. In this case, at a speed of 0.5 m / min in the rapid heating device 3 with direct current passage, heating to a temperature of 780 ° C. takes place, a power of approximately 45 kW being taken from the power supply 34 for this purpose. The electrical power required to achieve different primary material temperatures is proportional to the quotient, formed from the speed of the material to be heated and the heating section, so that readjustment can easily be carried out when parameters change.

When passing through the temperature equalization and control tunnel 41, which is charged with inert combustion gas and has a length of 2 mm, no noticeable change in the temperature is found.
In the deformation device 5 or in the twelve-stand cassette rolling mill, for example, the deformation is carried out with a calibration and a respective degree of deformation according to Table 1. Mill stand Initial diameter ⌀ 5.5 mm Degree of deformation (round-round) 51 1st caliber = 3 kt 5.3 51 ′ 2nd caliber = ⌀ 4.9 21% 52 3rd caliber = 3 kt 4.5 52 ′ 4.caliber = ⌀ 4 34% 53 5th caliber = 3 kt 3.7 53 ′ 6.caliber = ⌀ 3.25 34% 54 7. Caliber = 3 kt 3.0 54 ′ 8. Caliber = ⌀ 2.7 31% 55 9. Caliber = 3kt 2.6 55 ′ 10. Caliber = ⌀ 2.2 33% 56 11. Caliber = 3 kt 2.0 56 ′ 12. Caliber = ⌀ 1.8 33% Final diameter ⌀ 1.8 89%

The round wire emerges from the last caliber at a speed of approx. 4.7 m / sec, the total cross-sectional deformation being approx. 89%.
The respective cross-sections, which are available due to the calibration after the individual passes, can be seen by means of cross-sections of the rolling stock from FIG. 7, with the initial cross-section of 5.5 mm in diameter at the top right and the final cross-section of 1.8 mm in diameter at the bottom left are shown.
Examinations of the rolled material showed perfect dimensional accuracy and good surface quality of the round wires over the entire length of the roll, which is due to the preservation of the formability of the material at temperatures of min at least 400 ° C and at most 1100 ° C, preferably at most 950 ° C, possibly at most up to the AC 1 temperature, indicates in the roll forming also with high cross-sectional decreases.
Cooling devices 5 can be arranged between the roll stands. Such cooling devices are shown in principle in FIG. 8, a cooling element 61 being positioned between the rollers 511 or 512 and 521. The cooling elements, as shown on the upper cooling element, consist, for example, of a connection 611, a cooling medium supply line 612 and a nozzle head 613. By means of the nozzles 615 and 614, the rollers 511 and 512 can be exposed to cooling medium, the rays of the nozzle 614 being directed onto the Rolled material are directed. The individual flows of the cooling media can be designed to be separately controllable, the regulations not being shown in the sketch.

The use of hard metal or tempered high-speed steel as the roller material has proven to be advantageous for economic and technical reasons. The application of hard material layers on roller work surfaces to reduce roller wear was regarded by the experts as not expedient or as an obstacle to the rolling process, because hard material layers reduce the friction between the roller work surface and the surface of the rolling material and therefore the rolling stock cannot be drawn into the caliber. Surprisingly, however, it has been shown that in a device with at least two roll stands arranged one behind the other in the rolling direction and with two or more work rolls in each case, a hard material coating of the roll work surfaces does not impair the rolling process that however, there is a substantial extension of the roll service life with improved rolling stock quality.

Claims (22)

1. A process for the deformation of steels, metals and alloys with low deformation capacity and / or high deformation resistance at room temperature, in particular of hardenable steels and high-speed steels made of primary material of small thickness, preferably less than 10 mm, characterized in that the primary material is at a temperature of at least 400 ° C and at most 1100 ° C, preferably at most 950 ° C, optionally at most up to the AC 1 temperature or the transition temperature into the gamma structure of the alloy, and that a two-stage or multi-stage deformation is carried out with an overall large reduction in cross section. 2. The method according to claim 1, characterized in that the heating of the primary material is carried out as continuous rapid heating. 3. The method according to claim 1 or 2, characterized in that the heating of the primary material, as is known per se, takes place by means of direct current passage through the heating material and the heating path or the distance between the electrical contact elements is varied, the for increasing the temperature at least 400 ° C, but at most 1100 ° C, preferably at most 950 ° C, possibly at most the electrical power required by the AC 1 temperature, which is influenced by the cross-sectional area, the mean specific heat and the density of the material, proportional to the quotient is regulated from the heating material speed and the heating section and the end preheating of the Material for the start of the deformation process is carried out with a short heating section. 4. The method according to claim 2 or 3, characterized in that after the continuous rapid heating of the primary material and before the first deformation step, a time period of at least 0.5 sec, preferably at least 1.5 sec is provided, in which a temperature compensation takes place. 5. The method according to any one of claims 1 to 4, characterized in that the deformation of the primary material is carried out by rolling and a cross-sectional decrease of at least 40%, preferably at least 60%, is carried out. 6. The method according to claim 5, characterized in that the rolling deformation in several steps or several passes, each with a cross-sectional decrease of at least 10%, preferably at least 15%, and / or a decrease in height of at least 20%, preferably at least 30% becomes. 7. The method according to claim 5 or 6, characterized in that after each or after several roll deformations, cooling of the roll surface and / or the rolling stock is carried out, the cooling capacity of the rolling stock being of the order of magnitude corresponding to the deformation performance of the preceding pass (s) converted into heat is regulated. 8. The method according to any one of claims 5 to 7, characterized in that the rolling of the primary material in first stitch at an entry speed of at least 0.2 m / sec, preferably at least 0.5 m / sec. 9. The method according to any one of claims 1 or 5 to 8, characterized in that the two- or multi-stage deformation is carried out with a large reduction in cross section in a multi-roller mill. 10. The device with a heating device, optionally a temperature and guide device and a deformation device for performing the method according to one of claims 1 to 9, characterized in that after the heating device (3) for setting the temperature of at least 400 ° C and at most 1100 ° C, preferably at most 950 ° C, possibly at most up to the AC 1 temperature or the transition temperature into the gamma structure of the alloy of the rolling stock (1) at least one deformation device (5) is arranged for at least two-stage deformation. 11. The device according to claim 10, characterized in that the heating device (3) is designed as an electrical rapid heating device with an energy input into the heating material (1) by induction or by direct current passage. 12. The apparatus according to claim 11, characterized in that the rapid heating device (3) with a direct current passage has a variable heating path. 13. Device according to one of claims 10 to 12, characterized in that after the heating device (3) a temperature compensation in the heating material and the guidance of the primary material serving device (4), e.g. a compensation tunnel (41) is arranged, which can be heated if necessary and in which a protective gas atmosphere can preferably be set. 14. Device according to one of claims 10 to 13, characterized in that for the deformation at least two roll stands (51) or (51 ') to (56) or (56'), each with two or more work rolls arranged one behind the other in the rolling direction are. 15. The apparatus according to claim 14, characterized in that the rollers alternately have an open and a closed caliber shape, the last caliber being a closed caliber, possibly a dimensional caliber. 16. The apparatus according to claim 14, characterized in that the work rolls in preferably all roll stands, in particular in the last roll stand, have a closed caliber shape. 17. The device according to one of claims 14 to 16, characterized in that the rollers in the roll stands are driven individually with appropriate speed control or together with corresponding speed ratios and caliber shape sequences. 18. Device according to one of claims 14 to 17, characterized in that the roll stands are independent gig fixed from each other and connected to the drive device, wherein the multi-stand rolling mill is preferably designed as a cassette rolling mill. 19. Device according to one of claims 14 to 18, characterized in that an adjustable cooling device (61, 62) is arranged between the roll stands, with which cooling medium can be applied to the roll surfaces and / or to the rolling stock. 20. Device according to one of claims 14 to 19, characterized in that the rollers are made of hard metal or tempered high-speed steel and optionally have a hard material coating. 21. Device according to one of claims 10 to 20, characterized in that a multi-roll mill is arranged after the heating device (3) for adjusting the temperature of the rolling stock. 22. Use of a device according to claims 10 to 21, for carrying out the method according to claims 1 to 9.

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