RU2414972C1 - Method of steel strip hot rolling - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention aims at reducing rejects by increasing surface quality of hot-rolled stock (including etched stock) and cold-rolled stock (including coated stock) in rolling steel strips at continuous broad-strip mills. Proposed method comprises slab heating, slab multipass alternating gage and width reduction in mill roughing stands and subsequent multipass gage reduction to final thickness in finishing stands.

EFFECT: ruling out shelliness, optimum deformation over strip width.

1 tbl, 6 ex

Description

The invention relates to the field of metallurgy, specifically to the hot rolling of steel strips on continuous broadband mills, providing high-quality strips without surface defects, such as “rolling foam”. The “rolling captivity” defect is a peeling of a tongue-shaped metal, connected to the base metal by one side, formed as a result of rolling flaws or traces of deep cleaning on slabs. Flaws are open gaps located perpendicularly or at an angle to the direction of the largest metal drawing. Flaws form during hot deformation of the metal, and subsequent deformation leads to the expansion of initially thin flaws. The defect “rolling captivity” is located at a distance from the edge of up to 45 mm on the hot rolled strip and up to 30 mm on the cold rolled strip (taking into account the cut edges of 10-15 mm).

A known method of rolling a metal strip, including multi-pass alternating compression rolls in width in vertical rolls and in thickness in horizontal rolls of the roughing stand group, subsequent rolling in a continuous finishing group of stands with interstand tension to a final thickness. At the same time, in order to obtain a predetermined strip width in the final thickness using an automated control system, the roll compression is changed by the width of the vertical rolls of the roughing stand group [Application No. 19522494, Germany, MPK VVV 37/16, 1996].

The disadvantage of this method is that the method does not provide a high-quality surface of the strip, leads to the formation of defects "rolling captivity", and therefore to an increase in the expenditure coefficient.

A known method for the production of steel wide strips, including the rolling of slabs on a continuous broadband hot rolling mill with compression of the side edges in the vertical rolls of the rough group of the mill stands, determined from the ratio AB = 0.01 V _with ^ε , etching of the hot rolled strips, rolling in a cold rolling mill and cutting strips on the cutting unit with trimming of the side edges, where B _c is the width of the slab before rolling, ε is the relative lateral compression taken within ε = 6.2-7.1% [RF patent No. 2274504, IPC B21B 1/22, 17.08 .2004].

The disadvantage of this method is that the method does not provide a high-quality surface of the strip, leads to the formation of defects "rolling film".

The closest in technical essence to the present invention is a hot rolling method, including heating a slab, its multi-pass alternating compression in width and thickness in the roughing stand group and subsequent compression to a final thickness in the finishing stand group with regulated strip tension in the inter-gap spaces. Compression in width is completed when the ratio of strip thickness to width is reduced to a value of not less than 0.015, and in the finishing group of stands the specific tension of the strip is maintained equal to 0.05-0.45 of the value of its yield strength in the corresponding inter-span gap with a relative amount of compression per passage not more than 50% [RF patent No. 2273535, IPC B21B 1/22, 09/01/2004 - prototype].

The disadvantage of this method is that the method does not provide a high-quality surface of the strip, leads to a decrease in yield due to the presence of defects "rolling film", and therefore to an increase in the expenditure coefficient.

The technical problem solved by the invention is to improve the surface quality of the strip by eliminating surface defects "rolling film", and therefore, to reduce costs.

The stated technical problem is solved in that in the method of hot rolling of steel strips in the line of a continuous broadband mill, including heating the slab, its multi-pass alternating compression in width in vertical stands (VK) and thickness in horizontal stands in the roughing group of stands and subsequent multi-pass compression to the final thicknesses in a continuous finishing group, according to the invention, in the roughing group of stands, the width reduction is carried out in five vertical stands, the first of which is a descaling tool, while The term in the first two vertical stands is not more than 35%, in other vertical roll stands - 65-100% of the total reduction in width.

The invention consists in the following. During rolling in the roughing group of stands, the strip is successively crimped in horizontal and vertical rolls. In this case, a continuous decrease in the strip width occurs due to the strip calibration in width in vertical rolls. On the roll internal cracks and breaks from deformation are formed due to high stresses and low ductility of the metal, subsequent deformation leads to the formation of edge flaws, group defects, the so-called "rolling captivity". The main reason for the formation of defects "rolling captivity" is the non-optimal pattern of deformation along the width in the vertical rolls of the rough group. The objective of the invention is to optimize the deformation in width in order to prevent the formation of defects "rolling captivity".

It was experimentally established that during the compression of the slab in a vertical descaler and the second vertical stand with side compression of not more than 35% and the task of the main compression in the last vertical stands of the draft group - up to 65-100% defect “rolled captivity” was not found on hot-rolled and cold-rolled steel.

Method implementation examples

Slabs with a cross section of 250 × 1380-1540 mm were heated in a heating furnace and rolled on a continuous broadband mill 2000 to a width of 1305-1455 mm. In the roughing group of stands, the heated slab is crimped in vertical rolls. The table shows the data on lateral compression (in mm and%), sorting according to the defect "rolling captivity", the location of the defect from the edge.

The table shows that when implementing the proposed method (options No. 4-7), the defect "rolling captivity" is absent. In this case, the main reduction in width occurred in the last vertical stands (No. 3-5) - in the range from 65 to 100%, and in the vertical descaler (VOL) and the second vertical stand - in the range from 0 to 35%.

In the case of transcendental values of the declared parameters (options No. 1-3), the sorting by the “rolling captive” defect reaches 0.7-2.9% and the defects are located at a distance of 10 to 30 mm from the strip edge. In this case, the reduction in width attributable to the vertical descaler and the second vertical stand was 40-71% (which exceeds 35% according to the proposed method), and 29-60% in the last stands (No. 3-5).

Technical appraisal and economic advantages of the proposed method consist in the fact that when it is performed, edge defects are not formed on the strip “rolling captivity”. Due to this, a reduction in the expenditure coefficient of steel is achieved.

Table Lateral compression in the roughing group and sorting according to the defect "rolling captivity" Option No. Slab Width, mm The required width of the hot rolled strip, MM Lateral compression, mm /% Sorting by defect "rolling captivity" on cold-rolled steel,% The distance of the defect from the edge on the cold-rolled steel, mm VOL + 2VK (3 + 4 + 5) BK one 1540 1455 60 mm / 71% 25 mm / 29% 2.9 Up to 30 2 1380 1305 45 mm / 60% 30 mm / 40% 2.5 Up to 20 3 1450 1375 30 mm / 40% 45 mm / 60% 0.7 To 10 four 1540 1455 30 mm / 35% 55 mm / 65% 0 0 5 1380 1305 25 mm / 33% 50 mm / 67% 0 0 6 1450 1370 20 mm / 25% 60 mm / 75% 0 0 7 1380 1305 0 mm / 0% 75 mm / 100% 0 0 Note: the table does not contain data on the prototype, since the patent prototype No. 2273535 does not regulate the values of lateral compression in that embodiment, as specified in the proposed method

Claims (1)

A method of hot rolling steel strips in a continuous broadband mill line, including heating a slab, its multi-pass alternating compression in width in vertical stands and thickness in horizontal stands in the roughing stand group and subsequent multi-pass compression to a final thickness in a continuous finishing group, characterized in that the width of the draft group of stands is compressed in five vertical stands, the first of which is a scale breaker, while the reduction in the first two vertical stands is not more than 35%, in the remaining vertical stands ... 65-100% of the total reduction in width.