RU2379140C1 - Method of producing cold-rolled steel for zinc-plating - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes etching of hot-rolled strips in hydrochloric acid and its following cold rolling in rollers with specified treatment and profiling of its barrels. Removing of geometry defect of manufactured steel is provided ensured by that rolling in the last mill of continuous rolling mill is implemented with counter-bending of grooved or grinded rollers, herewith grooved rollers are implemented with microgeometry Ra=3.0…3.5 mcm and grinned with Ra=0.5…1.5 mcm, and concavity of barrels generatrix of grinned rollers for 0.05…0.10 mm is more than analogous concavity of grooved rollers, and at passing of front and back ends of strips through the latter mill effort conterbending of its rollers is reduced for 10…15% relative to effort at passing of middle part of strips.

EFFECT: increasing of consumer properties of zinc-coated sheet steel ensured by improvement of its geometry.

1 ex

Description

The invention relates to rolling production and can be used in the manufacturing technology of cold-rolled strip steel for galvanizing.

The galvanized billet goes through all stages of the technological process characteristic for the production of cold-rolled thin-sheet steel: pickling of hot-rolled strips in a solution of hydrochloric (or sulfuric) acid, cold rolling on a continuous mill and (if necessary) recrystallization annealing followed by tempering. The production technology of cold-rolled sheet steel is described in sufficient detail, for example, in the book of VB Bakhtinov. "Rolling production." M .: "Metallurgy", 1987, p.337-346.

Of great importance for the surface quality and geometry of the finished cold-rolled strips are the nature of the processing (notched or ground) of the surfaces of the work rolls of the cold rolling mill, the microgeometry of this surface, as well as the profiling of the roll barrels (with a convex or concave generatrix). The geometry of the cross section of the rolled strips is regulated by anti-bending of the rolls.

A known method for the production of cold rolled steel, including etching of hot rolled strips, their cold rolling and longitudinal dissolution, in which the strip is straightened by stretching with an elongation of metal in the range of 1.0 ... 1.2% (see US Pat. RF No. 2314885, class B21B 1/28, published in BI No. 2, 2008). However, this method is of little use for producing high-quality galvanized steel, since it does not stipulate the nature of processing and microgeometry of work rolls.

The closest analogue to the claimed method is the technology for the production of cold rolled steel, described in the book by P. I. Polukhin and others. “Rolling production”. M.: Metallurgy, 1982, p. 487-491 and 511-519.

This technology includes the etching of hot-rolled strips in hydrochloric acid and their subsequent cold rolling in rolls with the specified processing and profiling of their barrels and is characterized by the fact that rolling is carried out with a significant tension of the strip from the front and rear sides of the stand, and the specific tension is 50 ... 60% from the yield strength of the rolled metal. A disadvantage of the known technology is also the uncertainty of the nature of the processing and microgeometry of the rolls, which does not guarantee high consumer properties of galvanized sheet steel.

The technical task of the present invention is to increase the consumer properties of galvanized steel by improving the geometry.

To solve this problem, the proposed method includes etching hot rolled strips in hydrochloric acid and their subsequent cold rolling in rolls with a given processing and profiling of their barrels, and rolling in the last stand of a continuous mill is carried out with anti-bending of grooved or polished rolls, while notched rolls with Ra microgeometry = 3.0 ... 3.5 microns and polished - with Ra = 0.5 ... 1.5 microns, and the concavity of the barrel forming polished rolls is 0.05 ... 0.10 mm greater than the similar concavity of the notched rolls when passing the front and rear it ends of the strips through the last stand effort protivoizgiba its roll is reduced by 10 ... 15% in comparison with the force of the passage of the middle part of the strip.

The above process parameters are obtained empirically and are empirical.

The essence of the proposed technical solution is to optimize microgeometry (average height Ra microroughness) of the surface of the barrels of the work rolls of the last (finishing) stand of the continuous cold rolling mill, as well as the profile of these barrels and the ratio of the anti-bending of the rolls of the finishing stand. The concavity of the barrels of the notched rolls is chosen less than that of the polished ones, since when rolling in the first of them, large rolling forces (pressure) arise, i.e. notched rolls receive greater deflection. The force of the anti-bending of the rolls when passing the ends of the strips decreases to reduce the non-flatness (warping) of the ends, i.e. in order to reduce the stretching of medium-wide strip sections.

Experimental verification of the proposed method was carried out on a continuous cold rolling mill 2500 OJSC "Magnitogorsk Iron and Steel Works".

For this purpose, when rolling strips of various assortments, the microgeometry of the incised and polished rolls of the last (finishing) mill stand, their profiling (the size of the deflection arrow forming the roll barrels), and the anti-bending force of the rolls of this stand when passing the ends of the strips, were varied. The experimental results were evaluated by the yield of galvanized steel of the first grade.

The best results (yield of such steel within 99.1 ... 99.8%) were obtained using the proposed technology. Deviations from its recommended parameters worsened the achieved indicators. Thus, an increase in Ra of grooved and polished rolls (more than 3.5 and 1.5 μm, respectively) not only worsened the surface quality of the strips, but also forced to reduce the anti-bending of the rolls, which increased the lenticularity of the rolled cross section, leading, in some cases, to an unacceptable difference thicknesses of edges and middle sections of strips.

A decrease in the values of Ra of the rolls (less than 3.0 and 0.5 μm) worsened the adhesion of the rolled metal to the surface of the rolls, leading to the appearance of scratches and scratches on the strips and to the transfer of up to 3% of the finished rolled to the 2nd grade. An increase in the concavity of the barrels of polished rolls necessitated an increase in their anti-bending, which led to the sorting of part of the hire by unacceptable warping. A decrease in concavity also led to a decrease in the transverse convexity (lenticularity) of the finished strips, which worsened their lateral stability during the passage of a continuous galvanizing unit. An increase in the anti-bending of the rolls of the last stand led to an inevitable increase in the metal pressure on them and to an increase in the warping of the end sections of the strips, and a decrease in the force of the anti-bending reduced the transverse convexity of the strips with the above-mentioned negative consequences.

When using technology taken as the closest analogue (see above), the yield of first-class rolled products did not exceed 83%. Thus, an experimental verification confirmed the acceptability of the technical solution found to achieve the goal and its advantage over a known object.

Concrete example

After hot rolling, the tackle for galvanized steel is etched in hydrochloric acid and then cold rolled to a thickness of 1.5 mm on a 2500 mill.

The rolls of the finishing stand of the mill are polished with Ra = 1.0 μm, and their concavity is 0.70 mm. When using notched rolls, their Ra = 3.3 μm, and the concavity of the barrel is 0.50 mm.

When the front and rear ends of the strips pass through the last rolling stand, the roll bending force is reduced by 12%.

Claims (1)

A method of manufacturing cold rolled steel for galvanizing, including etching of hot rolled strips in hydrochloric acid and their subsequent cold rolling in rolls of a continuous mill with the specified processing and profiling of their barrels, characterized in that the rolling in the last stand of the continuous mill is carried out with anti-bending of the notched rolls with microgeometry of their surface barrels Ra = 3.0 ... 3.5 microns or polished rolls with Ra = 0.5 ... 1.5 microns, with a concavity forming the barrels of polished rolls 0.05 ... 0.10 mm more than the concavity of the notched rolls, and when the front and rear ends of the strips pass through the last stand, the anti-bending force of its rolls is reduced by 10 ... 15%.