RU2518039C2 - Control over continuous heat treatment - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to machine building and metallurgy. It aims at preventing the rejects of continuously annealed metal blank and allowing the maximum metal yield. Continuous thermal processing is continuously controlled by NDT testing of mechanical properties after thermal processing. Electric power intensity is used as a control record. Current power consumption is compared with power inputs derived from preset regression dependence of mechanical properties on power costs per unit for required mechanical properties. Blank heat treatment conditions are adjusted to make the magnitude of power inputs fall in the range of tolerable magnitudes.

EFFECT: sufficient mechanical properties.

6 cl, 1 tbl, 1 dwg

Description

The invention relates to the field of metallurgy and mechanical engineering, in particular, to continuous heat treatment of “endless” products (ribbons, wires, etc.).

A known method and device for continuous annealing of metal tapes [1], which allow you to set the temperature-time regime of each treatment of particles of annealed material. However, the resulting quality characteristics, for example, mechanical properties, depend not only on the annealing mode, but also on the specific chemical composition, thickness of the tape, which can vary significantly even within a single annealed roll. Thus, to control the quality characteristics obtained as a result of annealing, it is necessary to control the quality characteristics themselves or a parameter that is directly related to them. Moreover, the control should be non-destructive so as not to disrupt the continuity of the process.

Known methods and installations of non-destructive testing of physico-mechanical and other properties of this kind of "products" [2-5], but the accuracy of such control methods is usually small.

The closest in technical essence to the proposed method is a method for determining the mechanical properties [6], when a highly sensitive texture parameter is controlled. This texture parameter determines the degree of primary recrystallization and is closely related not only to the anisotropy parameters, but also to all mechanical properties [7]. The method provides extremely high accuracy of control of mechanical properties (and anisotropy of plastic properties [7]) at the stage of incomplete primary recrystallization (mid-stage annealing [8]), when a regular change in texture parameter occurs [7, 9]. At other stages of annealing, the texture does not change or its changes are of irregular insignificant nature, are at the level of fluctuations [10], as a result of which the method [6] is ineffective. For example, at the return stage (pre-crystallization annealing [8]), the crystallographic texture does not practically change, but, nevertheless, there is a change in quality characteristics, in particular, mechanical properties (as a rule, the material becomes softer) [8]. On the other hand, after the completion of primary recrystallization, the stages of collective and secondary recrystallization follow [9]. In this case, changes in the texture are illegal or insignificant in nature [8], but there is also a significant change in the properties of the material to a state that, as in the first case, can be claimed by the consumer. Indeed, regulatory requirements, for example, on the mechanical properties of non-ferrous rolled products (see GOST 2208-2007) cover a very wide range of conditions and the corresponding mechanical properties, almost each of which can be obtained according to the technological scheme, including the final continuous annealing. A significant part of the claimed range of properties can be obtained as a result of annealing to the state of partial occurrence of primary recrystallization (incomplete primary recrystallization). But it also extends to ribbons and sheets, the properties of which, during final annealing, can be obtained only by pre-crystallization or, conversely, only by complete annealing with secondary or collective recrystallization [8], when the texture control method (prototype [6]) is not applicable [ 7, 9].

In addition, the prototype [6] allows you to control the heat treatment of only flat products. Profiles of another type (round, that is, wire, rods, pipes, various shaped profiles) cannot be heat treated using the method [6] for two reasons: their texture is not controlled by known methods and (or) there is a fairly reliable relationship between their texture and quality characteristics not established [10].

The aim of the invention is to control the process of continuous heat treatment of "endless" metal products, for example, wires, strips, tapes, pipes, etc., to any degree of softening, that is, at different stages of the implementation of recrystallization or return processes by precise non-destructive continuous control of the value specific energy costs associated with standardized quality characteristics, and regulation of the quality characteristics of the products obtained on the basis of this connection.

The technical result of the invention is to prevent marriage and to expand the range of "endless" metal semi-finished products, annealed with this method of process control due to:

- expanding the controlled range of quality characteristics of the obtained semi-finished product, as it allows you to control and manage their production not only at the stage of primary recrystallization, but also during pre-crystallization and complete annealing, characterized by secondary or collective recrystallization;

- expanding the range of profiles, heat-treated using the proposed method for controlling continuous heat treatment, by annealing not only flat products, but also pipes, wire, any other profile.

This result is achieved by comparing continuously monitored specific energy inputs with allowable energy inputs and adjusting the heat treatment parameters so that the actual values of specific energy inputs fall within the range of their allowable values. Moreover, the interval of permissible values of energy consumption is established according to predefined regression dependences of the quality characteristics on the indicators of specific energy consumption and the normalized interval of admissible values of the quality characteristics.

There are various methods of continuous heat treatment [11]. In particular, continuous heating methods based on electrical and electromagnetic energy can be divided into two categories:

- methods using a coolant (energy is used to heat, for example, the air surrounding the heated semi-finished product [12], or some “drum” [13] and only indirectly - to heat the "product"),

- methods in which energy enters directly into the heated "product", which is characterized by the highest efficiency. Of these methods, continuous induction heat treatment [14, 15] and continuous electric contact heating [16] are most known. The induced current or the current of the contact circuit heats the semi-finished product according to the Joule law, and energy transfer occurs most quickly, "without intermediaries." The bulk of the energy expended, regardless of the transverse profile of the annealed “product” [17] and its material (steel [18], aluminum and aluminum alloys [19], copper and brass [15, 20, 21]), is used to heat the “product” " In all cases, the efficiency of these heat treatment processes was very high [15-21]. Therefore, for example, during induction heating in the well-known formula for the balance of specific energy consumption (P`):

- потери в катушках, а $$P_{Fe}^{`}$$

- потери в стальном "сердечнике", доминирует "полезная" мощность, расходуемая на нагрев металла $$P_{П}^{`}$$

. (При электроконтактном отжиге в формуле баланса (1) взамен $$P_{Cu}^{`}$$

и $$P_{Fe}^{`}$$

присутствуют также относительно весьма незначительные потери мощности в местах контакта.) Это позволяет при анализе влияния энергозатрат на характеристики качества без существенной погрешности взамен $$P_{П}^{`}$$

использовать легко контролируемую величину активной мощности P и рассчитывать P` по формуле:Where: $$P_{Cu}^{`}$$

- losses in coils, and $$P_{Fe}^{`}$$

- losses in the steel "core", the "useful" power spent on heating the metal dominates $$P_P^{`}$$

. (In case of electric contact annealing in the balance formula (1) instead $$P_{Cu}^{`}$$

and $$P_{Fe}^{`}$$

relatively small power losses at the contact points are also present.) This allows us to analyze the effect of energy consumption on quality characteristics without a significant error in return $$P_P^{`}$$

use the easily controlled value of active power P and calculate P` according to the formula:

where: P is the active power; S is the cross-sectional area of the "product"; ρ is the density of the material; v is the speed of the product in the unit, C is the productivity of the heat treatment line.

Modern equipment allows you to register the value of P, as well as calculate and display in finished form on the display screen, chart tape, etc. the value of the specific energy consumption P`. Studies show that in these cases the slightest changes in the consumed electric energy are directly related to changes in the quality characteristics of the “product” after its annealing, and these relationships can be guaranteed to be described by reliable mathematical models. (The conclusions presented here do not exclude, on the one hand, the establishment of a sufficiently reliable dependence of the quality characteristics on energy consumption with other known methods of continuous heat treatment, and on the other, the development of new methods of continuous heat treatment, characterized by a no less close relationship of energy consumption and properties than in the example below .)

As can be seen from the available data, the proposed method for controlling the heat treatment mode, unlike the prototype [6], is universal:

- in relation to the state of the material to which the product is heat treated;

- regarding the profile shape of the annealed product (prototype [6] is based on the control of the rolling texture and recrystallization of only sheet materials).

Moreover, the proposed method for controlling the heat treatment mode is as versatile as the prototype [6] with respect to the annealed material, provided that specific texture parameters for all types of crystal lattices of the heat-treated metal will be developed for the prototype. But unlike the prototype [6], the proposed method is not universal with respect to the continuous heat treatment method, which should determine the degree of correlation between the specific energy consumption and the quality characteristic resulting from the heat treatment. Only a sufficiently high degree of correlation provides a reliable regression model of the dependence of the normalized quality characteristics on specific energy consumption.

Method description

The proposed method includes:

- preliminary determination of the dependence of the quality characteristics on the specific energy consumption by regression analysis [22] of the relationship of the experimental values of the specific energy costs and the corresponding values of the quality characteristics (according to the expression used in the prototype [6], "calibration" of the quality characteristics according to the value of specific energy costs);

- establishing the interval of permissible energy consumption based on a joint analysis of the interval of acceptable values of the quality characteristic and the resulting regression dependence of the quality characteristic on the specific energy consumption ("calibration");

- continuous monitoring during heat treatment of the actual values of specific energy consumption and comparing them with the values of the boundaries of the pre-set interval of allowable energy consumption;

- regulation of the heat treatment mode so that the actual values of the specific energy consumption "fall" into the range of acceptable energy costs, thus ensuring that the quality characteristics "fall" into the range of its acceptable values.

The parameters that determine the specific energy consumption by which it is possible to control the heating modes can be: the speed of the annealed semi-finished product, electric current, voltage, heating temperature.

Based on the proposed method, it is possible to organize automatic statistical control by the heat treatment process. For this, the specific energy consumption P`, automatically determined by formula (2), enters the comparison unit, where it is compared with the boundaries or with the middle of the interval of permissible energy inputs. Depending on the result of the comparison, the size of the control action on the adjustable technological parameter is determined, which determines the value of the specific energy consumption. Based on the results of monitoring the actual values and the limits of permissible energy consumption, it is possible to automatically build a control map [23], which is continuously updated as new values P` arrive [24]. The size of the control action on the adjustable technological parameter can also be set according to the results calculated and determined by GOST P 50779.44-2001 and continuously updated indicator of the process tuning accuracy.

Execution example

Brass ingots of the L68 grade according to GOST 15527 measuring 180 × 600 × 1,500 mm were heated using natural gas in a continuous method furnace for 3.5 hours at a temperature that decreased in the furnace zones from 980 to 920 ° C. As a result, the temperature of the ingot at the furnace exit was 800 ± 20 ° C. The ingots were rolled on a reversible 2-roll mill up to 5.5 mm with a roll roll. Cold rolling was carried out on a tandem mill Tandem-1000 to a workpiece thickness of 2.7, 2.5, 2.05 mm in 1 pass and up to 1.5 mm in 2 passes. After intermediate annealing, the billet on a four-roll mill was rolled with various compression into a strip with a thickness of h≈0.6 mm, h≈0.8 mm and h≈1.0 mm. Thus, the obtained tape differed in thickness and degree of last deformation (ε). Inductive heating of the tape was carried out in the line of induction annealing in a transverse magnetic field and etching LOT [20] when connecting the windings of both modules of the inductor into a triangle. The air gap between the upper and lower modules of the inductor was ~ 30 mm. We changed the speed of the tape in the inductor (v), controlling the value of the active power of the three-phase network (P) and calculating the specific energy consumption P` by the formula (2). (The heating temperature of the tape is not controlled here, because, unlike speed, it continuously changes when the tape moves in the inductor). The annealed tape was tested for breaking, determining, in particular, the tensile strength σ _B (MPa), yield strength (σ _T = σ ₀₂ , MPa), and elongation (δ,%). Table 1 presents, as an example, the values of the speed of movement in the inductor of the tape, pre-processed according to one of the options presented here (h≈0.8 mm, ε≈62%), the obtained values of the specific energy consumption and temporary resistance (ultimate strength).

Figure 1 presents built in the framework of MS Excel (tool "Chart Wizard"):

- experimental points of temporary resistance and the corresponding specific energy consumption, taken from table 1,

- a trend line connecting these points,

- a regression equation reflecting the trend line, describing the logarithmic relationship of the specific energy consumption (x) with the value of temporary resistance (y),

- coefficient of determination of R ² .

In order to determine, in accordance with the formula of the present invention, the intervals of permissible energy consumption, which ensure that “temporary resistance” falls into the intervals regulated for various conditions, we give an excerpt from table 14 “Mechanical properties of tapes and sheets” GOST 2208-2007 “FOIL, TAPES, SHEETS AND PLATES BRASS Specifications "for brass grade L68 (Table 2).

Using the trend line or regression equation shown in Fig. 1, we can graphically or analytically determine for a given tape obtained by a specific technology and heat-treated in a particular device, the allowable intervals of specific energy consumption required to obtain various states, which are given in Table 3. (Of course, in order to guarantee the necessary properties under conditions of substantial dispersion of the experimental data presented here, it is desirable to adhere to the middle of the specific energy consumption interval determined in this way).

To obtain the required state of the material, for example, solid, it is necessary to select the middle of the interval of specific energy consumption (41 kWh / t) according to Table 3. As applied to the heating method used in this example, to select the initial belt speed for this energy consumption value, one can use Table 1 and obtain ~ 59 m / min. In the process of annealing, it is necessary to continuously monitor and adjust the true value of specific energy consumption, achieving its location near the middle of the allowable interval for a given state (27-55 kWh / t).

As can be seen from figure 1 in magnitude of R ² there is a very "close" logarithmic relationship of the specific energy consumption with temporary resistance. Table 4 summarizes the data: the values of the determination coefficient R ² for various functions approximating the relationship of specific energy consumption with different controlled properties, averaged for a L68 brass strip, rolled before induction annealing to various thicknesses with different degrees of deformation. It can be seen that not only the logarithmic, but also other approximating functions provide a good relationship between energy consumption and properties, especially with σ _B and σ _T , which is not surprising, since the control accuracy of the latter is higher than the relative elongation δ when testing, in particular, non-ferrous rolled products [ 25].

The proposed control method for continuous heat treatment will guarantee quality, reduce costs and expand the range of semi-finished products obtained by final annealing.

Table 1 Parameters (values of the tape speed in the inductor and specific energy consumption) and results (temporary tensile strength) of induction annealing of L68 brass tape with a thickness of 0.77 mm, pre-rolled after intermediate annealing in the amount of 2.05 mm The speed of the tape, m / min Specific energy consumption, kW · h / t Temporary resistance, MPa 26 84.9 330 thirty 76.3 378 34 62.6 418 42 56.6 433 46 52.7 436 52 48.3 456 60 40.6 503 70 32,3 515

table 2 Technical conditions (permissible temporary resistance values) for brass grade L68 from "GOST 2208-2007" FOIL, TAPES, SHEETS AND PLATES BRASS TECHNICAL CONDITIONS " Material condition Temporary resistance MPa minimum permissible maximum Soft 280 370 Semi-solid 340 470 Solid 430 540 Extra hard 520 -

Table 3 The allowable intervals of specific energy consumption obtained from the permissible values of temporary resistance (Table 2) and the regression dependence of the specific energy consumption on the properties (figure 1) Material condition Specific energy consumption, kW · h / t min Max. Soft 77 - Semi-solid 45 88 Solid 27 55 Extra hard - 33

Table 4. The values of the determination coefficient R ² for various functions that approximate the relationship of specific energy consumption with different controlled properties, averaged for all variants of combinations of h and ε Characterization of mechanical properties Approximation function Power Logarithmic Exponential σ _B , MPa 0.894 0.922 0.926 σ _T , MPa 0.916 0.9 0.914 δ,% 0.864 0.87 0.86

Information sources

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Claims (6)

1. A method for controlling the heat treatment of a continuous metal semi-finished product, including non-destructive continuous monitoring of the mechanical properties obtained as a result of heat treatment, using the specific energy consumption as a control characteristic, comparing the current energy consumption values with the energy consumption values obtained from previously established regression dependences of the mechanical properties on specific energy costs, providing the necessary mechanical properties, taking into account which regulate the heat treatment of the semi-finished product, providing specific energy consumption in the range of permissible values. 2. The method according to claim 1, characterized in that the heat treatment is carried out in the form of annealing with induction heating. 3. The method according to claim 1, characterized in that the heat treatment is carried out in the form of annealing with electric contact heating. 4. The method according to claim 1, characterized in that as a characteristic of the heat treatment of heat treatment, which determines the magnitude of the specific energy consumption, use the speed of movement of the workpiece. 5. The method according to claim 1, characterized in that as a characteristic of the heat treatment heating mode, which determines the value of specific energy consumption, the value of the electric current of the supply network is used. 6. The method according to claim 1, characterized in that as a characteristic of the heating mode of heat treatment, which determines the magnitude of the specific energy consumption, use the value of the electric voltage of the supply network.

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