RU2465079C1 - Method of rolling steel sectional bars - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: proposed method comprises heating the billets, their multipass reduction of rolls with opposite grooves making breakdown passes. Increased individual reductions over billet cross-section intensifying microstructure processing are ensured by performing reductions in, at least, one pair of adjacent passes, at extra total local deformation by 1-10 mm at total reduction ratio of 1.1-1.4 in every pass. Said extra reduction in first of two adjacent passes is performed by external ledges made on roll passes while in second pass, it is performed by rolling the billet with ledges and recesses in passes without external ledges. Besides, reduction with extra local deformation is performed at 1200 to 700°C.

EFFECT: expanded range of sectional bars.

3 cl, 1 tb, 6 ex

Description

The invention relates to rolling production and can be used to obtain long sections from continuously cast steel billets.

The known method of hot rolling of steel sections, including multi-pass hot deformation of the workpiece in the rolls, opposite streams on which form exhaust gauges of the oval - circle system (P.I. Polukhin and other rolling production. M .: Metallurgy, 1982, p. 284-285).

The disadvantages of this method are that its capabilities are limited by the minimum allowable drawing coefficients to obtain high-quality rolled products from continuously cast billets. This does not allow to obtain larger steel profiles with an increased cross-sectional area.

The closest analogue to the present invention is a method for producing high-quality profiles, including heating a continuously cast billet to austenitizing temperature and subsequent multi-pass hot rolling in rolls, opposite streams on which form exhaust gauges, with a temperature of rolling end of 860-1000ºC and a total exhaust hood of λ≥ 4.0 to λ≥15.0, determined by the steel grade (RF Patent No. 2243834, IPC B21B 1/46, 2005).

The disadvantages of this method are that it does not allow to obtain steel sections of large cross-sections. So, for example, with the minimum allowable drawing coefficient λ = 15 during the rolling of a continuously cast billet, a square of 100 mm with a cross-section S ₀ = 10000 mm ² from spring steel, you can get a high-quality high-quality profile with a cross-sectional area S _{max of} no more

The technical problem solved by the invention is to expand the range of profiles rolled from continuously cast billets, in the direction of increasing the cross-sectional area.

The stated technical problem is solved in that in the known method of rolling steel sections, including heating the workpieces, and their multi-pass compression in rolls, opposite streams on which form exhaust gauges, according to the invention, compression in at least one pair of two adjacent passes is carried out with an additional local deformation of the workpiece by 1-10 mm with a total drawing ratio of the workpiece in each pass 1.1-1.4.

Additional local deformation in the first of two adjacent passages is carried out using girdle protrusions made on roll streams, and in the second of them, by rolling the workpiece with protrusions and depressions on the surface in gauges with streams without girdle protrusions. In addition, the compression of the workpieces with additional local deformation is carried out at a temperature of from 1200 ° C to 700 ° C.

For intensive study of cast microstructure, grinding of microstructural components of cast steel and axial stitch non-metallic inclusions, it is proposed to increase the partial deformations along the workpiece cross section.

The figure shows the sequence of changes along the aisles of the transverse profile of the rolled billet of circular cross section.

In the process of crimping the initially round billet (profile 1 in the figure) in vertical rolls, on the streams of which the girdle protrusions are made, lateral depressions of depth δ separating the protrusions (profile 2) are formed on the profile due to local deformation. In this case, macroshift deformations of the metal arise in the longitudinal and transverse directions. In a subsequent adjacent passage, an oval transverse profile 2 with protrusions and depressions is crimped in horizontal rolls with a round gauge without encircling protrusions (profile 3). The presence of protrusions and depressions on the workpiece during compression in a round gauge leads to the reappearance of local macroshift deformations in the longitudinal and transverse directions. Thanks to local macroshift deformations in two adjacent passages, the study of the initial cast microstructure of steel is improved.

Thus, additional local deformation of the workpiece with a value of δ = 1-10 mm in a pair of exhaust gauges with an exhaust coefficient per pass λ _p = 1.1-1.4 provides the appearance of macro-shear deformations that intensify the plastic flow of metal in both longitudinal and transverse directions. This improves the development of the initially cast microstructure of the billet, thereby achieving high-quality high-quality profiles with an increased cross-sectional area.

Further rolling of the workpiece (profile 4, profile 5) is carried out using the well-known oval-circle calibration.

It was experimentally established that with local deformation of less than 1 mm and hoods of less than 1.1, improvement in the development of the microstructure does not occur. With local deformation of more than 10 mm and hoods of more than 1.4, the formation of defects in the form of “sunsets” in the subsequent pass, which cause delays, is not ruled out, which is unacceptable.

Compression of workpieces with additional local deformation at temperatures above 1200ºC reduces the grinding efficiency of microstructural components of continuously cast steel. At temperatures below 700ºC, a predetermined profile cannot be ruled out with additional plastic deformation due to insufficient plasticity of the steel.

Method implementation examples

A continuously cast round billet (profile 1 in the figure) with a diameter of 200 mm and a cross-sectional area S ₀ = 31,400 mm ² of 60C2 alloy steel spring is heated to an austenitizing temperature T _a = 1180ºC and delivered to the furnace rolling table of a section-rolling mill. The heated billet (profile 1) at a temperature of T _d = 1150ºC is set in the roughing stand of the varietal mill 550 and squeezed in vertical rolls with an oval caliber with a drawing coefficient λ _p = 1.2. On the middle parts of the creeks of the rolls, girdles with a rounded shape 6.0 mm high are made. After crimping in vertical rolls, the workpiece acquires an oval cross-sectional profile with rounded troughs with a depth of δ = 6.0 mm, located on both sides of the oval (profile 2). Additional local deformation of the workpiece by the girdle protrusions contributes to the intensification of the development of the cast steel structure due to macroshifts in the longitudinal and transverse directions.

After exiting the oval gauge, an adjacent pass is carried out at a temperature T _d = 1150ºC, setting the workpiece in horizontal rolls with a round gauge, the streams of which have no protrusions. Compression in this passage is also carried out with a drawing coefficient λ _p = 1.2. The presence of rounded protrusions and depressions on the workpiece when it is crimped in an adjacent round gauge into profile 3 at the indicated temperature also leads to the generation of additional macro-shear deformations in the longitudinal and transverse directions and to an improvement in the development of the microstructure.

Further rolling of the workpiece is carried out using a conventional oval-circle calibration system (profile 4, profile 5) into a round bar with a maximum area S _max = 2461.8 mm ² and with a maximum final diameter D _max = 56.0 mm. The finished varietal profile is of high quality in terms of mechanical properties and microstructure.

When applying the known method, a high-quality bar from the same billet would have the maximum possible cross-sectional area

which corresponds to a bar of circular cross section with the largest possible diameter D _max = 5.6 mm.

Implementation options of the proposed method and indicators of their effectiveness are shown in the table.

Table Modes of rolling bars of steel grade 60C2 and their effectiveness No. p / p δ, mm λ _p T _d , ºС Maksim. area S _max , mm ² Maksim. diameter D _max , mm Quality control one. 0.9 1.09 690 2122.6 52.0 Axial bandedness 2. 1,0 1,1 700 2374.6 55.0 Satisfying 3. 6.0 1,2 1150 2461.8 56.0 Satisfying four. 10.0 1.4 1200 2374.6 55.0 Satisfying 5. 11.0 1,5 1210 2106.3 51.8 Defects "sunset" 6. 0 1.3 1100 2093.3 51.6 Axial bandedness

From the data presented in the table, it follows that when implementing the proposed method (options No. 2-4), the assortment of profiles rolled from continuously cast billets is expanded to increase the cross-sectional area. With exorbitant values of the declared parameters (options No. 1 and No. 5), as well as the implementation of the prototype method (option No. 6), there is a narrowing of the range of rolled profiles for the maximum allowable cross-sectional area.

The technical and economic advantages of the proposed method consist in the fact that the crimping is performed in at least one pair of two adjacent passages with additional local deformation of the workpiece at the beginning with the help of girdling protrusions on the grooves of the rolls by 1-10 mm, and then in caliber without protrusions with a drawing coefficient in each pass 1.1-1.4 and a temperature from 1200ºC to 700ºC, additional macro-shear deformations of the continuously cast billet appear in the longitudinal and transverse directions. This leads to a more intensive study of the cast structure of steel, crushing of crystallites, and the destruction of line non-metallic inclusions. Thanks to this, it is possible to obtain high-quality high-quality profiles with a larger cross-sectional area in comparison with the known rolling methods. A side effect is improving the quality of profiles.

Implementation of the proposed method will increase the profitability of the production of steel sections by 10-20%.

Claims (3)

1. The method of rolling steel sections, including heating the workpieces and their multi-pass compression in rolls, opposite streams on which form exhaust gauges, characterized in that the compression in at least one pair of two adjacent passes is performed with additional local deformation of the workpiece by 1 -10 mm with a total drawing ratio of the workpiece in each pass 1.1-1.4. 2. The method according to claim 1, characterized in that the additional local deformation in the first of two adjacent passages is carried out using girdling protrusions made on the streams of the rolls, and in the second of them by rolling the workpiece obtained in the previous pass with protrusions and depressions on the surface in calibers with streams without girdles. 3. The method according to claim 1, characterized in that the compression of the workpieces with additional local deformation is carried out at a temperature of from 1200 ° C to 700 ° C.