RU2260062C1 - Method for making zinc-plated flat bars of low-carbon hot-rolled steel - Google Patents

Abstract

FIELD: black metallurgy.

SUBSTANCE: method includes hot rolling, cooling down to winding temperature, winding of bar in a roll, heating bar up to zinc-plating temperature and applying of zinc plating, cooling of bar is performed after black group of cages with speed 0,3-0,6°C/c, and after white - with speed 20-30°C/c with point of start of process in 2,5-3,0 after exit of bar from last cage of white group.

EFFECT: higher efficiency.

1 tbl, 5 ex

Description

The invention relates to the field of ferrous metallurgy and can be used to obtain a galvanized sheet of mild steel.

A known method for the production of low-carbon steel, which consists in the fact that the steel after smelting is heated and hot rolled, then the strip is cooled to a winding temperature of 640-700 ° C at a speed of 4-50 ° C / h, wound into a roll, coil cooling to a temperature of 550 -510 ° С are conducted at a speed of 16-50 ° С / h, to the etching temperature, cooled to a temperature of 30-40 ° С and trained with small compression to 1.0 ± 0.2%. Patent No. 2185450.

The disadvantage of this method is the increased output sorting by surface defects (for example, the defect "break").

A known method for the production of galvanized steel strips, which consists in the fact that after hot rolling the strip is cooled to a temperature of 800-820 ° C at a speed of 3-5 ° C / s, then to a coil temperature at a speed of 40-45 ° C / s reducing the cooling rate in the initial and final sections of the strip with a length of 50-100 m to 4-8 ° C / s in the range from 730 ° C to the winding temperature, after which the strip is wound onto a roll, then heated to a galvanizing temperature and a zinc coating is applied. A.S. No. 1344794.

The disadvantage of this method is the difficult temperature control along the length of the strip, which leads to a lengthening of the rolling cycle and, therefore, to reduce production.

The mechanical properties of finished steel are also inferior to the mechanical properties of rolled products obtained with intermediate cold rolling.

An object of the invention is to increase production by reducing the rolling cycle, as well as reducing production costs while maintaining high quality galvanized sheet.

The technical problem is solved in that the method for the production of galvanized strips from mild hot rolled steel, including hot rolling, cooling to a winding temperature, winding a strip into a roll, heating to a galvanizing temperature and applying a zinc coating, is characterized in that the cooling is carried out after the roughing group with stands at a speed 0.3-0.6 ° C / s, and after finishing - at a speed of 20-30 ° C / s at the start point of scenting 2.5-3.0 s after the strip leaves the last stand of the finishing group.

When cooling the roll after the roughing group of stands at a rate of less than 0.3 or more than 0.6% C / s, partial recrystallization of the grain, the appearance of perlite and, as a consequence, insufficient ductility occur.

When cooling the roll after the finishing group of stands at a speed of less than 20 and more than 30 ° C / s, there is also a decrease in ductility in the finished product and leads to the formation of scale on the surface.

When the start point of choking is less than 2.5 s after the strip leaves the last stand of the finishing group, partial recrystallization, the formation of perlite sections, as well as different grades of grain occur, which worsens the ductility of the finished product, and for more than 3 seconds after the strip leaves, the rolling cycle is extended, leading to lower production.

Case Studies

Steel grade 08Yu was smelted in an oxygen converter, poured into slabs in a continuous casting machine. Hot rolling of the slabs was carried out on a hot rolling mill 2000 to a thickness of 1.5 mm; during rolling, the roll was cooled according to the modes produced in the table. Then etched, trained and galvanized strips.

As can be seen from the table in examples No. 1 and 2, the cooling of the roll after the roughing group of stands was carried out at a speed of 0.3 and 0.5 ° C / s at temperatures of 1100 and 1080 ° C, the cooling of the bands after the finishing group was carried out at a speed of 25 and 30 ° C / s at the start point of scenting 2.5 and 3 s, respectively, i.e. all modes covered by the claims.

In examples No. 3 and 4, the cooling of the roll after the roughing group of stands was carried out at a speed of 0.2 and 0.6 ° C / s at temperatures of 1200 and 1040 ° C, and the cooling after the finishing group at a speed of 18 and 32 ° C / s at start of showering 1.5 and 2 s.

Example No. 5 shows the mechanical properties of rolled products obtained by the method in accordance with the prototype.

From the data of the table it follows that the proposed method allows to obtain a finished galvanized strip according to mechanical properties at the level of requirements of GOST 9045-80 for the hood categories - a very particularly difficult hood (WWS) and a particularly difficult hood (WWS) without the use of intermediate cold rolling, and also reduce energy intensity of the process.

Claims (1)

A method for the production of galvanized strips from mild hot-rolled steel, including hot rolling, cooling to a winding temperature, winding a strip into a roll, heating the strip to a galvanizing temperature and applying a zinc coating, characterized in that the rolling is cooled after the roughing group by stands at a speed of 0.3- 0.6 ° C / s, and after finishing - at a speed of 20-30 ° C / s at the start point of scenting 2.5-3.0 s after the strip leaves the last stand of the finishing group.