RU2247611C2 - Process for continuous rolling of metallic blank - Google Patents

Abstract

FIELD: continuous hot rolling processes and equipment.

SUBSTANCE: process for continuous rolling of metallic blank to ready round article comprises steps of rolling blank in successively arranged first and second roll grooved passes at temperature range 650 - 1000°C. First and second roll grooved passes are formed by means of two working rolls. Dimensions of said passes provide total reduction of surface area of cross section of blank at least by 20 - 55 % when according to distribution of effective deformation maximum effective deformation is concentrated in central zone of cross section. Then rolling of blank is going on at such distribution of effective deformation when maximum effective deformation is concentrated in central zone of cross section at least in third and fourth successively arranged roll grooved passes. Each of said passes is formed at least by means of three rolling rolls. Dimensions of said passes provide total reduction of surface area of cross section of blank no more than by 4 - 25 %.

EFFECT: highly uniform distribution of grain size of article from center of article to its surface.

4 cl, 3 dwg

Description

FIELD OF THE INVENTION

This invention relates to the continuous hot rolling of metal long products, including, inter alia, round, octagonal, square, and the like.

State of the art

In this case, in the rolling of round products, the term “calibration” means the final deformation during the last stage of rolling to obtain the final nominal diameter of the product within the specified standard tolerances, which are usually about ± 0.1 mm for a diameter and ovality of 0.1 mm or less . In this case, the term “free calibration” means adjusting the rolling gaps of the calibration mills to obtain final product diameters that are slightly larger or slightly smaller than the nominal diameter provided for the rolling gauges, but are diameters within the tolerances for the resulting diameter.

Various technologies have been developed for calibration and free calibration of long metal products. For example, US Pat. No. 4,907,438, issued March 13, 1990 to Sasaki et al., Discloses rolling round profiles through two successive calibration mills with a series of calibers arranged in a circle-circle system, while the rolling gauges are designed to provide a relatively small reduction about 8-15% per caliber.

A wide range of products can be calibrated by feeding round articles of various diameters from various stands to various intermediate stands or finishing sections of the mill, and by changing the diameters of the rolled products and the configuration of the streams, a wide range of products can be calibrated.

It is also possible some free calibration within a relatively narrow range due to the restrictions imposed by the broadening, which inevitably accompanies rolling in calibers of two rolls.

Another drawback of the circle-circle gauge sequence, according to the patent of Sasaki et al., Is the appearance of a duplex microstructure in some products, in which the grain in the cross section of the product changes by more than 2 ASTM grain size values (when measured in accordance with ASTM E112-84).

It is generally believed that changing the grain size in the product cross section by more than 2 ASTM numbers can cause surface cracks and tears when the product undergoes subsequent bending and cold drawing operations. In addition, such changes in grain size contribute to poor annealing quality, which, in turn, negatively affects the processes of cold deformation.

Subsequently, it was found that the appearance of duplex microstructures is caused by the inability of round gauges of easy compression to provide the corresponding deformation in the entire cross section of the product for a fairly short time. The technology described in US Pat. No. 5,325,697, issued July 5, 1994 to Shore et al., Is dedicated to this problem. In this case, two sequences of strong compression gauges according to the oval-circle system immediately precede two sequences of rolling easy-compression gauges in the circle-circle system. Strong compression performed in a sequence of calibers arranged in an oval-circle system creates a strain distribution that penetrates the center of the product with high deformations. Before the accompanying stresses are removed due to the recrystallization of the microstructure and return, rolling continues in the immediately following, two-roll, easy compression gauges.

Therefore, in fact, crimping performed in four successive calibers is an essentially continuous process, as a result of which the distribution of deformation in the cross section of the product prevents the occurrence of a duplex microstructure.

However, in this case, rolling with free calibration is also limited due to the broadening that occurs when rolling in calibers of two rolls.

It is also known to use calibers of three or four rolls in a sequence of calibers arranged in a circle-circle system. This provides a wider range of free calibration, since the products are more tightly covered in the rolling gauges and therefore do not experience the broadening available in calibers of two rolls.

However, compared to two-roll calibers, three or four-roll calibers are much less effective in providing sufficient penetration of deformation to the center of the product. Such penetration is necessary to obtain a uniform grain structure from the center to the surface of the product. This is especially important for products that get their properties by grinding grain.

Therefore, there is a need for an improved method for hot rolling of long products that is able to provide calibration tolerances and a substantially uniform grain structure from center to surface and which also has an extended free calibration range. This task is the basis of this invention.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, the machined round iron profile is first rolled in the first and second rolling gauges at an elevated temperature in the range of 650 to 1000 ° C. to provide a total strong reduction of the cross-sectional area by at least 20-55% during distribution effective strain with a predominance of the concentration of maximum effective strain in the central zone of the specified cross-sectional area. Before changes in the microstructure occur, due to recrystallization and recovery, and while maintaining the prevailing concentration of the maximum effective strain in the distribution of effective deformation, the product is rolled in at least the third and fourth rolling calibers, each of which is formed according to at least three rolls to provide additional total relatively easy compression of the cross-sectional area of not more than 4-25%.

When rolling a round profile in the above manner into a final round product, such as a bar or bar, the first rolling gauge creates an oval cross-section, and the second rolling gauge creates a circular cross-section profile.

The third and fourth rolling gauges complete formation of circular cross-sectional profile of circular shape in end, having a tolerance of not more than ± 0,1 mm diameter and 0.1 mm or ovality tolerance of the bars and rods, equal to ^{a _1/4} ASTM, whichever which is smaller. After cooling to a temperature equilibrium, the resulting product has a grain size change in cross section of not more than 2 ASTM grain size numbers.

List of drawings

A detailed description of these and other features and advantages of the present invention is presented with reference to the drawings, which depict:

figure 1 - diagram of two alternative sequences of calibers according to this invention;

figa-2D - based on the final element of the model of effective plastic deformation due to deformation of the product in the sequence of rolling calibers P ₁ , P ₂ , P ₃ , P ₄ shown in figure 1; and

figa-3B - based on the final element of the model of effective plastic deformation due to deformation of the product in rolling gauges P _{3 '} and P _4' after the initial rolling of the product in calibers P ₁ and P ₂ .

Information confirming the possibility of carrying out the invention

As shown in figure 1, the sequence of calibers according to this invention includes four rolling calibers P ₁ -P ₄ made with the possibility of rolling a circular profile 10A in the finished round product 10e. The rolling gauge P _{1 is} formed by two work rolls 12 having streams 14 configured to roll a circular profile 10c into an oval 10b.

The rolling gauge P _{2 is} formed by two work rolls 16 having streams 18 configured to roll the oval 10b into a circular profile 10e. Depending on the rolling mode used, the rolling gauges P ₁ , P ₂ are sized to provide a total reduction in the range of about 20 to 55%, with about 11-28% of the rolling gauge P ₁ and about 10-23% the proportion of rolling caliber P ₂ .

The rolling gauge P _{3 is} formed by three work rolls 20 having streams 22 configured to roll the round profile 10c into another round profile 10d. The rolling gauge P _{4 is} also formed by three work rolls 24 having streams 26 configured to roll the round profile 10d into the finished round profile 10e.

In this case, also depending on the rolling mode used, the rolling gauges P ₃ , P ₄ have dimensions that provide a total reduction in the range from about 3 to 25%, with about 1.8-17% of the rolling gauge P ₃ and about 1.2-10% - for the share of the rolling caliber P ₄ .

With this sequence of gauges, for example, if profile 10a has a diameter of 14.032 mm, and the finished round profile should have a diameter of 10.0 mm, then the consistent decrease in area in rolling calibers P ₁ -P ₄ is, respectively, 22, 18, 10, 8 %

Usually rolling in rolling calibrations P ₁ -P _{4 is} carried out at elevated temperatures in the range from about 650 to 1000 ° C.

On figa-2D shows the distribution of the effective deformation of the product when you exit the sequentially located rolling gauges shown in figure 1. As shown in FIG. 2A, the oval profile 10b emerging from the double rolling gauge P _{1 of} high compression has an effective strain distribution in which the concentration of maximum effective strain in the central zone a ₁ prevails. From a central zone ₁ zone extend outwardly b _1, c _1, d ₁ and e _1, having a progressively decreasing effective strain levels, the lowest level of effective strain available in areas f ₁ adjacent to the outer boundaries of the cross sectional area of the product.

FIG. 2B shows that the round profile 10c emerging from the double rolling gauge P _{2 of} high compression retains the distribution of effective deformation, in which the concentration of maximum effective deformation in the central zone a ₂ prevails, with gradually decreasing levels of effective deformation in the surrounding zones b ₂ -f ₂ .

On figs shows the distribution of effective deformation in a circular profile 10d, emerging from the triple rolling gauge P ₃ weak reduction. The maximum level of effective deformation is maintained in the central zone a ₃ , which is again surrounded by zones b ₃ -f ₃ with gradually decreasing levels of effective deformation.

In the final triple rolling gauge P _{4 of} low compression, as shown in FIG. 2D, the round profile 10e maintains the distribution of effective deformation, in which the concentration of maximum effective deformation in the central zone a ₄ prevails with gradually decreasing levels of effective deformation in the surrounding zones b ₄ -f ₄ .

Thus, the smallest grain size will be in zone a ₄ with a gradually increasing grain size in the surrounding zones b ₄ -f ₄ . With the subsequent cooling of the finished circular profile 10e, the cooling rate in its cross section will decrease from the maximum in the outermost zone f ₄ , where the grains are larger, to the minimum in the innermost zone a4, where the grains are smaller. When cooling, the grains in each zone increase by an amount proportional to the time required for cooling each zone, which reduces the difference in grain size in the innermost and outermost zones, as a result of which the change in grain size in the cross section of the product does not exceed about 2 ASTM size numbers grains.

As shown in FIG. 1, the round profile 10c emerging from the rolling gauge P ₂ can, as an alternative solution, be calibrated in the four-roll gauges P _{3 '} and P _4' . The rolling gauge P _{3 ′ is} formed by four work rolls 20 ′ having streams 22 ′ configured to roll the circular profile 10c into another circular profile 10d ′. The rolling gauge P _{4 'is} also formed by four work rolls 24' having streams 26 'configured to roll the round profile 10d' into the finished round profile 10e '.

The distribution of the effective deformation of the product at the exit from the rolling gauges P ₁ and P ₂ described above and shown in figa and 2B. The distribution of the effective deformation of the product at the exit from the rolling gauges P _{3 ′} and P _{4 ′ is} shown, respectively, in FIGS. 3A and 3B. Again, it can be seen that profile 10d 'has an effective strain distribution with a predominance of maximum effective strain in zone a _3' surrounded by zones b _{3 '} -f _3' with gradually decreasing levels of effective strain.

FIG. 3B shows that the same distribution remains in the finished product 10e ′ exiting the rolling gauge P _{4 ′} .

Claims (4)

1. A method for continuous rolling a metal blank into a round finished product comprising rolling a circular cross-section blank into successive first and second roll calibers at an elevated temperature in the range 650-1000 ^{° C,} wherein the first and second rolling gauges are formed by two work rolls and are sized providing a total decrease in the cross-sectional area of the specified workpiece by at least 20 - 55% when distributing effective deformation with a predominance of the concentration of max total effective deformation in the central zone of the indicated cross-sectional area; subsequent rolling, provided that the effective strain distribution is maintained with a concentration of the maximum effective strain prevailing in the central zone of the specified cross-sectional area, in at least the third and fourth successive rolling calibers, each of which is formed by at least three work rolls and has dimensions providing a total decrease in the cross-sectional area of the specified workpiece by no more than 4 - 25%, while the rolls of the first caliber have streams, made nnye with the possibility of giving the blank of oval cross-section, second, third and fourth gauges - with the possibility of giving the blank of circular cross-section. 2. The method according to claim 1, characterized in that the rolling is continued in the specified third and fourth rolling gauges before changes in the microstructure due to recrystallization and return. 3. The method according to claim 1, characterized in that the finished round profile emerging from the last of these third and fourth rolling calibers is performed with a tolerance of not more than

0.1 mm in diameter and 0.1 mm ovality. 4. The method according to claim 1, characterized in that after cooling to a state of temperature equilibrium receive the specified workpiece with a change in grain size in its cross section of not more than about 2 ASTM numbers of grain size.

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