RU2661297C1 - Method of continuous heat treatment of l63 brass plane rolling in the transverse magnetic field - Google Patents

Abstract

FIELD: metallurgy; machine building.

SUBSTANCE: invention relates to the field of metallurgy and machine building, in particular to the processes of continuous heat treatment of metal flat products, in particular tapes and strips. Method of the continuous heat treatment of L63 brass flat products in a transverse magnetic field includes heating the strip in the inductor while moving from the unwinder to the coiler with the subsequent look into the roll according to the regime providing heating at the output from the inductor to a temperature sufficient for the recrystallization of the metal, in this case, the tape roll is produced at metal temperature of at least 540 °C at a mass of rolled up tape of at least 300 kg, followed by cooling the roll at temperature of 10÷30 °C for at least two hours.

EFFECT: invention is aimed at preventing the occurrence of rejects and the stable production of annealed rolled products in a soft state.

1 cl, 2 dwg, 2 tbl, 1 ex

Description

The invention relates to the field of metallurgy and mechanical engineering, in particular to the processes of continuous heat treatment of metal flat products (tapes, strips) and to ensure the quality of these products.

It is known that heat treatment of a metal tape is carried out in order to increase ductility during subsequent deformation, as well as as a final operation to obtain the desired properties [Technology of metal forming processes / P.I. Polukhin, A. Hensel, V.P. Polukhin [et al.] - M .: Metallurgy, 1988. - 408 p.]. (Soft rolled products from brass L63, in particular, must in accordance with GOST 2208-2007 meet the following requirements: tensile strength σ _of 290 ÷ 400 MPa, elongation δ of at least 38%).

A known traditional method of annealing rolls of rolled metal in a cage [Krucher G.N. Comprehensive newsletter on heat treatment of non-ferrous metals No. 2/14 / G.N. Krucher. - JSC Institute Giprotsvetmetobrabotka. - M., 1994. - 274 p.]. The method is characterized by significant energy and time costs: it takes time to heat, soak at a given temperature and cooling. In addition, the method can lead to heterogeneity of properties, since the temperature heterogeneity over the cross section of a large mass roll, and even more so in the volume of the entire cage, especially in a furnace not specially equipped, can reach hundreds of degrees Celsius [Luzhbin, A.S. Regulation of transverse heterogeneity of properties and thickness variation of continuously heat-treated strips / A.S. Luzhbin, M.Z. Pevzner // Production of rental. - 1998. - No. 9. - S. 14-18).

Known methods for continuous heat treatment of a metal strip, which reduce the processing time and increase the uniformity of heating compared with batch annealing [Vertlib I.L. A review of the current state and development prospects of broaching furnaces and lines for annealing copper and brass tapes / I.L. Wertlieb. - M.: Giprotsvetmetobrabotka, 1969. - 28 p.]. Indeed, the heterogeneity of the temperature over the cross section of the tape uniformly moving through the heating device is incomparably less than its inhomogeneity in the volume of the annealed roll. But with continuous heat treatment, it is required for a very short period of time the tape moves through the heating device to heat it to a temperature not less than the recrystallization temperature [S. Gorelik Recrystallization of metals and alloys / S.S. Gorelik, S.V. Dobatkin, L.M. Kaputkina: 3rd ed. - M .: MISIS, 2005. - 432 p.]. Meanwhile, the heat transfer rate from certain elements heated by electrical resistance to the hire itself, moving at a certain distance from these elements, on which these methods are based, is even limited even with the most intense “jet” heating [Vertlib I.L. Heat transfer in broaching jet heating furnaces during heat treatment of tapes / I.L. Wertlieb, N.N. Buravchenko, Yu.V. Piguzov // Non-ferrous metals. - 1977. - No. 5. - S. 61-64]. Therefore, such methods are used to heat a relatively thin strip of materials having a sufficiently low recrystallization temperature [Vertlib I.L. A review of the current state and development prospects of broaching furnaces and lines for annealing copper and brass tapes / I.L. Wertlieb. - M.: Giprotsvetmetobrabotka, 1969. - 28 p.]. The heat transfer features also explain the large losses during heat transfer, which means significant specific energy consumption (low efficiency) during heat treatment in this way.

The closest in technical essence to the proposed method is a method of continuous heat treatment of flat products in a transverse magnetic field (transverse flux induction heating, TFIH), in which the magnetic flux is perpendicular to the surface of the rolled products moving between two halves (magnetic circuits) of the inductor (Fig. 1) [ Baker, R. Transverse Flux Induction Heating / R. Baker // Transactions of the American Institute of Electrical Engineers. - 1950 .-- V. 65, Part II. - P. 711-719; Pevzner M.Z. Continuous induction heat treatment of tapes and strips / M.Z. Pevzner, N.M. Shirokov, S.G. Khayutin. - M.: Metallurgy, 1994. - 128 p.].

In FIG. 1 is a cross-sectional view of an inductor (2), consisting of two halves, representing magnetic circuits of width B _AND , located above and below the annealed strip (1) of width B, moving continuously in a direction perpendicular to the plane of FIG. one.

The induced currents are heated due to the Joule heat release in the entire volume of the rolling stock, and an almost unlimited energy transfer intensity is achieved. This makes it possible to anneal continuously thick strips and obtain an exceptionally high heating rate and, accordingly, the rolling speed of the rolled products in the inductor, for example, an order of magnitude higher than with the previous method [Gibson, R.C. High efficiency induction heating as a production tool for heat treatment of continuous strip metal / R.C. Gibson, R.H. Jonson // Sheet metal industries. - 1982. - V. 59. - No. 12. - P. 889-892]. Due to this (minimum heating and water cooling time), as well as due to the lack of exposure at maximum temperature, the minimum processing cycle time is noted [Experience of using induction annealing in the practice of processing non-ferrous metals / N.M. Shirokov, V.A. Krutilin, M.Z. Pevzner, V.M. Yutkin // Non-ferrous metals. - 1989. - No. 1. - S. 101-103]. Actually, the heat transfer itself, in the generally accepted sense, is not observed here, and, therefore, there is no loss in its implementation, as a result of which it is noted for its exceptional energy efficiency, which allows obtaining efficiency up to 95% [Gibson, R.C. High efficiency induction heating as a production tool for heat treatment of continuous strip metal / R.C. Gibson, R.H. Jonson // Sheet metal industries. - 1982. - V. 59. - No. 12. - P. 889-892. Kozhin, V.D. Energy consumption during induction heating of the tape / B.D. Kozhin, M.Z. Pevzner, A.M. Podolyak // Non-ferrous metals. - 1994. - No. 2. - C. 55-57]. In the process of mastering and operating the equipment, the exceptional efficiency of the method was established during annealing of single-phase materials [Experience of using induction annealing in the practice of processing non-ferrous metals / N.M. Shirokov, V.A. Krutilin, M.Z. Pevzner, V.M. Yutkin // Non-ferrous metals. - 1989. - No. 1. - S. 101-103].

. - М.: Машиностроение, 2004. - 336 с., ил.]. Наиболее распространенная в промышленности двойная (состоящая из двух основных компонентов меди и цинка) латунь Л63 по своему составу расположена на границе фазового перехода. Поэтому преобладание α-, α+β- или β-фазового состояния и свойства сплава очень сильно зависят как от условий обработки, так и от ограничиваемого ГОСТ 15527-2004 содержания в конкретной партии проката каждого составляющего элемента, включая примеси [Ефремов, Б.Н. Роль фазового перехода в формировании структуры и свойств (α+β)-латуней / Б.Н. Ефремов // Оптимизация свойств и рациональное применение латуней и алюминиевых бронз. - М., 1988. - С. 19-26]. (Известно, что содержание каждого элемента в зависимости от коэффициента Гийе влияет по-разному [Осинцев О.Е. Медь и медные сплавы. Отечественные и зарубежные марки: Справочник / О.Е. Осинцев, В.Н.

. - М.: Машиностроение, 2004. - 336 с., ил.]).But at the same time, the strip and strip of brass L63, even under the most intense TFIH annealing modes (the lowest possible speeds and maximum heating temperatures for rolled products), showed a higher β-phase content compared to the equilibrium state [Structural Features of Heat Treatment of Brass L63 in Induction Annealing Lines / O.A. Avdyushkin, B.N. Efremov, M.Z. Pevzner, A.A. Filippov // Abstracts of the All-Union Conference “Production, Application and Properties of Copper Alloys of General and Special Purpose”. - M., 1990 .-- S. 49; Experience of using induction annealing in the practice of processing non-ferrous metals / N.M. Shirokov, V.A. Krutilin, M.Z. Pevzner, V.M. Yutkin // Non-ferrous metals. - 1989. - No. 1. - S. 101-103]. Correspondingly, too high values of strength characteristics were observed and low - ductility characteristics, often beyond acceptable values (σ _in more than 400 MPa, δ less than 38%). This phenomenon is explained by the features of both TFIH and brass L63 [Osintsev, O.E. Copper and copper alloys. Domestic and foreign brands: Reference book / O.E. Osintsev, V.N.

. - M.: Mechanical Engineering, 2004. - 336 p., Ill.]. The most common in industry double (consisting of two main components of copper and zinc) brass L63 in its composition is located at the boundary of the phase transition. Therefore, the predominance of the α-, α + β- or β-phase state and the properties of the alloy very much depend both on the processing conditions and on the content of each component element, including impurities, limited by GOST 15527-2004 [Efremov, B.N . The role of the phase transition in the formation of the structure and properties of (α + β) brass / B.N. Efremov // Optimization of properties and rational use of brass and aluminum bronzes. - M., 1988. - S. 19-26]. (It is known that the content of each element depending on the Guilllet coefficient affects differently [Osintsev O.E. Copper and copper alloys. Domestic and foreign brands: Reference book / O.E. Osintsev, V.N.

. - M.: Engineering, 2004. - 336 p., Ill.]).

As a result of the discrepancy between the properties and their regulated values, the resulting hire is classified as final defect or, if possible, redistribution (availability of orders for the corresponding products) is rolled to thin sizes, but a small margin of plasticity of the material leads to the need for additional intermediate heat treatment. Thus, unlike single-phase alloys, heat treatment of L63 brass by the TFIH method, due to, as a rule, the large mass of each annealed coil, leads to significant material losses or, in the best case, to a significant rise in production cost [Experience using induction annealing in the practice of processing non-ferrous metals / N.M. Shirokov, V.A. Krutilin, M.Z. Pevzner, V.M. Yutkin // Non-ferrous metals. - 1989. - No. 1. - S. 101-103]. On the other hand, the rejection of induction heat treatment, in particular, in the production of soft strips and rather thick L63 tapes, leads to an uncontested need to return to energy-intensive and long-term cage annealing.

The aim of the invention is the guaranteed receipt as a result of continuous induction heat treatment of rolled brass L63 with properties in the intervals regulated for the mild state of GOST 2208-2004, with all possible changes in the composition of this alloy within the limits regulated by GOST 15527-70.

The technical result of the proposed invention is to achieve the required (regulated for a mild state) property values and, as a result, to prevent the occurrence of defects and, due to this, to reduce the cost of production while maintaining all the advantages of the prototype (minimum energy consumption and maximum productivity).

This result is achieved by optimizing the cooling mode of the rolled steel heated in the inductor, which ensures that the material is kept in equilibrium and, as a result, its complete softening. To prevent any non-equilibrium phase transformations, the slow cooling of the rolled products in a preformed roll of a sufficiently large mass (at least 300 kg) begins with a sufficiently high temperature (at least 540 ° C) and is carried out at the temperature of the production room (10 ÷ 30 ° C) in for a period of not less than 2 hours. As a result, it is guaranteed to obtain rolled products in a soft state, when the characteristics of its structure and properties approach the characteristics formed as a result of cage annealing. At the same time, the duration of the production cycle due to the slow cooling of the coil practically does not increase (productivity does not decrease), since after the convolution the coil is removed (removed from the winder) and the line is again ready for heat treatment of the next batch of rolled products.

Method description

The proposed method includes:

- continuous heating of rolled steel L63 by the TFIH method;

- broaching (rewinding) of the rolled product from the inductor to the winder (device winding into a roll) so that the temperature of the rolled metal is at least 540 ° C, and the mass of rolled into a roll is not less than 300 kg;

- slow (in air) cooling of the rolled metal coil for at least two hours at a temperature of the production room 10 ÷ 30 ° C.

Execution example

To compare the efficiency of using the proposed method, prototype and analogue on the same equipment and material obtained by the semi-continuous method of L63 brass ingots in accordance with GOST 15527-70, some of which were specially cast with a copper (Cu) content of 62.5 ± 0.2%, 63 ± 0 , 2% and 64 ± 0.2%, were milled, cut to a measured length and rolled on a hot rolling mill to a thickness of 5.0 mm. Cold rolling was carried out to a thickness of 2.0 mm and 2.4 mm, and after trimming the edges to a width B of 618 mm, the strips were annealed in two ways:

- rolls in a resistance furnace according to a regime of 620 ° C for 3 hours;

- by the TFIH method in an induction annealing line with an inductor consisting of four modules, each of which is, in fact, a separate inductor, see FIG. 1 [The experience of using induction annealing in the practice of processing non-ferrous metals / N.M. Shirokov, V.A. Krutilin, M.Z. Pevzner, V.M. Yutkin // Non-ferrous metals. - 1989. - No. 1. - S. 101-103]. Used two schemes for switching on the windings of the inductor:

1 - total Δ for modules No. 1 and No. 2 (the first two modules along the strip);

2 - total Δ for modules No. 1 and No. 2; star for modules No. 3 and No. 4 (all four modules).

A flexible chromel-alumel cable thermocouple was minted to observe the kinetics of temperature changes (Т, ° С) during the tape movement in the LIO before annealing into its central part in width. When winding the annealed coil between its middle turns, another cable thermocouple was installed to control the pattern of metal cooling in the coil. In addition, the temperature of the strip at the outlet of the 2nd or 4th module (depending on the inductor switching circuit) was continuously monitored by an IT-1 stationary pyrometer, and the temperature of the strip winding into a roll using a Hanna contact device. Due to the fact that the annealing modes for each of the two switching circuits of the inductor and for each of the two cooling options were different, in FIG. 2 changes in the temperature of the strip as it moves to the coiler and when cooling in a roll (see dotted lines 1b, 2b on the left side of the diagram) are shown only schematically.

The annealing mode was varied by changing the speed of the strip (V), and reached its minimum possible values when the superheated strip was stretched under the action of a tension force; in order to prevent a break, its width was continuously measured. Annealed strips moving from the inductor to the coiler, rolling them into coils, were quickly cooled with water (a special “choking” device) to a temperature of less than 100 ° C, V ~ 10 m / min (heat treatment options 1a and 2a) or relatively slowly in air ( heat treatment options 1b and 2b), see FIG. 2. It can be seen that, in addition to the cooling option and the annealing mode (the speed of the strip determining the time of its cooling in air), the temperature of the strips at the time of their convolution into a roll depended on the inductor switching circuit, otherwise, the distance from the last switched on module to the winder, also determining lane movements to the coiler. As a result, the temperature of the winding into a roll during annealing in two muffles (a large distance to the winder) without subsequent cooling with water (option 1b) was 460 ÷ 500 ° C, that is, it did not meet the conditions of the proposed method. On the contrary, with the same cooling, but during annealing in four muffles (option 2b, a relatively small distance to the winder), the temperature of the winding into a roll in accordance with the conditions of the proposed method was 540 ÷ 580 ° C. Moreover, in both cases, the temperature of the rolled products at the outlet of the last included module in the direction of rolling ranged from 620 ÷ 680 ° C, V ~ 8 m / min. Samples of annealed rolled products were tensile, determining the values of temporary resistance (σ _V , MPa) and elongation (δ,%), and also controlled the structure characteristics: β-phase content (β,%) and grain size (μ, μm).

From the table. Figure 1 shows that the most “soft” properties, guaranteed to satisfy regulated values, were observed in the workpiece annealed by rolls in resistance furnaces. At the same time, the copper content had a rather insignificant effect on the structure and properties, which made it possible to combine both variants of the copper content in one line. The tape obtained according to the scheme: hot rolling, cold rolling, annealing by the TFIH method according to option 1a in the entire possible range of Cu content, is characterized by rather “tough” properties that do not guarantee obtaining regulated properties. But nevertheless it is seen that a relatively insignificant difference in chemical composition led to significant differences in structure and properties (see table. 1).

The properties and structure of the tape annealed by the TFIH method without water cooling (Table 2) significantly differ depending on the inductor switching circuit, which is quite explainable based on our results. When annealing in the first 2 modules (option 1b), the hire reaches the coiler is relatively cold. Changes in the phase composition in it no longer occur. On the contrary, when heating in 4 modules (option 2b corresponding to the proposed method is indicated in bold), the temperature of the tape being rolled up is high enough so that the processes occurring in it are similar to those occurring during batch annealing, as a result of which the phase composition approaching equilibrium.

Comparison of the table. 1 and 2 shows that the properties and structure of the tape annealed in 4 modules of the inductor, only after exclusion of water cooling, are close to the characteristics of the tape obtained in the furnace. Thus, the efficiency of introducing the 3rd and 4th module is guaranteed to be revealed when the main condition of the proposed method is fulfilled, in which the temperature of the winding into a roll should be at least 540 ° C. In this case, the transition to the second circuit for switching on the inductor reduced the length of the cooling zone and cooling time, which ensured a sufficiently high temperature of the coil winding (the temperature of the onset of slow cooling).

The proposed method will allow, in contrast to the prototype, to guarantee the quality of rolled products from L63 brass in a mild condition with minimal energy consumption and processing time in comparison with its batch annealing and, thus, by eliminating the occurrence of marriage, reduce the total cost of production at the highest achievable labor productivity .

Table 1 - structural characteristics and properties of rolled brass L63 2.0 mm thick after final annealing: batch (analog) or continuous by the TFIH method according to the traditionally used option 1a, see Fig. 2 (prototype).

Table 2 - mechanical properties and structure of rolled products with a copper content of ~ 63% after the IE at a speed of V ~ 11 m / min to T ~ 620 ° C, rolled up without cooling (technology options 1b and 2b).

Claims (1)

The method of continuous heat treatment of flat products made of brass L63 in a transverse magnetic field, including heating the tape in the inductor in the process of moving from the uncoiler to the coiler, followed by winding into a roll according to a mode that ensures at the outlet of the inductor heating to a temperature sufficient to recrystallize the metal, characterized in that winding into a roll of tape is carried out at a metal temperature of at least 540 ° C with a mass of tape wound into a roll of at least 300 kg, followed by cooling of the roll at a temperature of 10 ÷ 30 ° C for at least two hours ov.

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