RU2334567C1 - Method of hot rolling of thick-sheet steel - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: method involves steel rolling at rated impact elasticity value with a given passage number in given rolling and cooling modes depending on the sheet thickness. Thick sheet quality is improved due to setting rolling end temperature Tre=780°...830°C for rolling steels 3 and 09G2S with thickness h=30...49 mm, Tre=780°...830°C for h=50...89 mm thick sheets, and Tre=800°...850°C for h=90...160 mm Tre=830°...880°C thick sheets, applying accelerated roll cooling with water descaling. 5...10 passes for h=30...49 mm thick sheets are made with 2h double-thick strip plates and for h>49 mm thick sheets with h+50 mm thick strip plate.

EFFECT: increased mill production rate.

2 ex

Description

The invention relates to the processing of metals by pressure and can be used in the production of hot-rolled plate.

The main operation of this production is rolling in a specialized mill for several passes of the initial heated slabs to the roll of a given thickness. The features of the technology for hot rolling of plate steel are described in sufficient detail, for example, in the reference manual, ed. V.I. Zyuzina and A.V. Tretyakov "Technology of rolling production", book 2, M., "Metallurgy", 1991, S. 498-512. An important parameter for obtaining sheets with the required properties is the temperature of the end of rolling (TKP). Often, to intensify the process, accelerated cooling of the rolled metal, usually water, is used.

A known method of hot rolling of sheets, in which the deformation along the edges of the roll is carried out with variable compression, creating a deliberately longitudinal longitudinal thickness, which is then removed in the form of trim, which improves the quality of the sheets by reducing their transverse thickness variation (see. AS USSR No. 1419745, CL B21B 1/38, BI No. 32, 1988). The disadvantage of this technology is the increased consumption of metal due to an increase in trimmings, as well as the uncertainty in the temperature of the end of rolling.

The closest analogue to the claimed method is the technology of hot rolling of thick sheets on the mill 2800, described in the book of VB Bakhtinov "Rolling production", M., "Metallurgy", 1987, S. 317-320.

This rolling technology for the regulated number of passes for the given rolling modes with subsequent cooling of the roll is characterized by the fact that the compression values are taken from the calculation of the dross continuity, which is removed by hydraulic breakdown, and the rolling temperature in the last passes varies depending on the thickness of the finished sheet. A disadvantage of the known technology is the impossibility of producing high-quality sheets with thickness h = 30 ... 160 mm from steel grades st.3 and st.09G2S with a normalized impact strength (the maximum thickness of sheets obtained by this technology is h = 16 mm).

An object of the present invention is to increase the performance of a plate mill hot rolling and the quality level of sheet steel.

To solve this problem, in a method for rolling plate steel with a standardized value of impact strength for a regulated number of passes according to the specified rolling and cooling regimes of a sheet depending on the sheet thickness, for st.3 and st.09G2S with thickness h = 30 ... 49 mm, the end temperature rolling take Tkp = 780 ... 830 ° C; for h = 50 ... 89 mm - Tkp = 800 ... 850 ° C and for h = 90 ... 160 mm - Tkp = 830 ... 880 ° C, using accelerated cooling of the roll under the hydraulic sintering scale, while 5 ... 10 passes for sheets with h = 30 ... 49 mm are made of double-rolled tackle of 2h thickness and of tacked thickness of h + 50 mm for sheets with h> 49 mm.

The essence of the proposed technical solution lies in differentiating the rolling temperatures for different sheet thicknesses, as well as in choosing a method for cooling the roll and optimizing the thickness of the initial tack and the number of passes made for this tack depending on the range of thicknesses of the finished sheets. As a result of this, the productivity of the mill increases and the quality level of plate steel of the indicated grades with a given value of impact strength increases.

The inventive method is implemented as follows.

Before rolling the above-mentioned steels by the thickness of the finished sheets (it is determined by order), the temperature range of the end of rolling Tkp is set. If the thickness of the sheets h = 30 ... 49 mm, then 5 ... 10 passes are carried out on the mill from double-rolled tackle - 2h = 60 ... 78 mm, and with a final sheet thickness h> 49 mm - the same number of passes They are made of rolled material with a thickness of h + 50 mm, i.e. H = (50 ... 160) + 50 = 100 ... 210 mm. The cooling of any rumble from the indicated steels is made accelerated using a device for descaling on this mill.

An experimental verification of the proposed method was carried out on a plate mill 4500 OJSC "Magnitogorsk Iron and Steel Works". For this purpose, during the hot rolling of sheets with a thickness of 30 ... 160 mm from steel grades st.3 and 09G2S, the above rolling parameters were varied, evaluating the results by the hourly productivity of the mill and by the output of high-quality thick sheets with a given value of impact strength.

The best results (maximum productivity of the mill and the output of high-quality sheets within 98.2 ... 99.5%) were obtained using the inventive rolling technology. Deviations from its recommended parameters worsened the achieved indicators.

Thus, an increase in TKP by 10 ° ... 40 ° above the indicated maximum values, as well as its decrease by 10 ° ... 50 ° below the minimum recommended values, gave the yield of finished products with the required characteristics of not more than 93%. A decrease in the intensity of cooling of the reel led to a decrease in the hourly productivity of the mill with a simultaneous decrease in the yield of high-quality sheets. The number of passes (5 ... 10) made from tackle with a thickness of 2h or h + 50 mm, as well as the thickness of the tackle, turned out to be optimal: reducing the number of passes to 3 ... 4, increasing them to 11 ... 12 and changing the thickness of the roll (H <2h, H <h + 50 mm, H> 2h and H> h + 50 mm) negatively affected either the hourly productivity of the mill or the quality level of the finished product.

The technology of hot rolling of sheet steel, selected as the closest analogue, was not tested in the experiments due to its apparent unsuitability for solving the task (see above). Thus, an experimental verification confirmed the acceptability of the technical solution found to achieve the goal and its advantage over a known object.

According to technical and economic studies carried out at OJSC MMK, the use of the proposed method of hot rolling in the production of thick sheets from st.3 and 09G2S with a normalized impact strength will increase the productivity of the 4500 mill in this range by approximately 7% with a simultaneous increase in output quality sheets with a thickness of 30 ... 160 mm by at least 5%.

Case Studies

1. At the hot rolling mill 4500, sheets with a thickness of h = 40 mm from station 3 are rolled. the temperature of the end of rolling Tkp = 805 ° C; 7 passes are carried out from the rolling stock with Н = 2h = 2 · 40 = 80 mm, using accelerated cooling of the roll under the hydraulic breakdown of the mill scale.

2. At the same mill, sheets with h = 120 mm are rolled from st.09G2S with Tkp = 850 ° C. Eight passes are made from tackle with H = h + 50 mm = 120 + 50 = 170 mm, also using accelerated cooling of the roll under hydraulic breakdown.

In both cases, the impact strength meets the requirements of the order.

Claims (1)

The method of hot rolling of plate steel grades st.3 and st.09G2S with a normalized value of impact strength, including rolling with predetermined modes and a regulated number of passes and cooling the roll with intensity depending on the thickness of the sheet, in which at a sheet thickness h = 30 ... 49 mm the temperature of the end of rolling take Tkp = 780 ° ... 830 ° C, sheet thickness h = 50 ... 89 mm - Tkp = 800 ° ... 850 ° C, and the thickness of the sheet h = 90 ... 160 mm - Tkp = 830 ° ... 880 ° C, use accelerated cooling of the roll with hydroscale of scale, with 5 ... 10 passes for sheets with h = 30 ... 49 mm r of rolled double thickness 2h, and for sheets with h> 49 mm - the thickness of the rolled h + 50 mm.