SU1303623A1 - Method for producing thin high-strength steel strip with iron-zinc alloy coating - Google Patents

Abstract

The invention relates to the field of metallurgy, and more specifically to the rolling production of high-strength iron-zinc coated steel strip. The purpose of the invention is to increase the productivity of the process while maintaining the level of properties. The method includes strip stripping, zinc coating on a hot rolled rolled steel, cold deformation of 65-90%, heat treatment, in which a iron-zinc coating is formed. The use of the proposed method allows an increase in labor productivity due to the use of hot rolled strip and the absence of secondary cold rolling. At the same time, a high level of strength properties of galvanized steel strip is maintained. 2 hp f-ly. S (l

Description

one

The invention relates to ferrous metallurgy, in particular to rolling production, and can be used in the manufacture of a thin high-strength steel strip coated with a zinc-iron alloy.

The purpose of the invention is to increase the productivity of the process while maintaining the level of properties.

The proposed production method — a thin, high-strength steel strip coated with an iron-zinc alloy is as follows. The hot rolled steel strip is subjected to cleaning (chemical cleaning or thermochemical degreasing in a non-oxidizing atmosphere at 350-500 ° C) on a continuous galvanizing unit, in which thin and other contaminants are removed from the surface of the steel, thin oxide films. Thereafter, a zinc coating is applied to the steel strip on a continuous hot or electrolytic galvanizing unit. Then the hot rolled galvanized strip is cold rolled with a total reduction of 65-90%.

Applying a zinc coating to a hot rolled pickled strip with a thickness of 1.5-2.0 mm on a continuous unit and subsequent cold rolling of a hot rolled galvanized steel strip to the required thickness (for example, up to 0.25-0.6 mm) increases the productivity of the process 3-4 times due to the use of hot rolled strip before galvanizing, since the surface area of one ton of hot rolled strip 1.5 mm thick (85 m) is much less than 1 ton of cold

0.5 mm (255 m) thick strip, as well as due to the absence of such additional processing as secondary cold rolling, repeated heat treatment of galvanized strip.

As a result of heat treatment of galvanized steel strip in batch units at A50-.

530 ° C

within 5-10 hours and also in

Continuous units at 550-580 ° C for 1-3 min. Structural changes occur not only in the zinc coating and in the steel base.

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In the steel base, a partial recrystallized structure is formed and the hardening obtained by cold rolling is maintained, which provides a high level of yield strength, temporary resistance of the gap, a steel strip with a sufficient ductility life and the resulting mechanical CBOPicTBa meets all the requirements imposed on high-strength steel. m coated with iron-zinc alloy.

In the zinc coating (during the heat treatment of the galvanized strip), the iron content increases from 12 to 30% as a result of the interdiffusion of iron from the steel base and zinc from the outer α-phase layer and the iron-zinc compound Fe-Zn is formed. After heat treatment, a thin coating of an iron-zinc alloy, due to the absence of zinc crystallization patterns, a highly developed surface (some roughness), as well as high hardness and increased melting temperature, is characterized by better dyeability and weldability. When the temperature of the heat treatment of a galvanized strip is less than 450 ° C with a shutter speed of less than 5 hours (in batch units) or less with a shutter speed of less than 1 min (in units of continuous action), the required level of iron content in the coating is not achieved (at least 12%), also the homogeneity of the structure of iron-zinc coatings, providing high quality coatings (better dyeability, weldability, high corrosion resistance). In addition, the residual stresses of the steel strip are not removed and the plasticity resource is very low (the maximum value of the relative elongation is no more than 3%).

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When the temperature of heat treatment of a galvanized strip is more than 530 ° C with an exposure of more than 10 hours (in batch units) or more than 580 s with an exposure of more than 3 minutes (in units of continuous action), more zinc iron-zinc alloy compounds are formed in the zinc coating and the adhesive strength of the coating with the substrate decreases . In addition, at a temperature of more than 10 hours exposure (in pe1 units) of iodic action) or more than 580 ° C with a exposure time of more than 3 minutes (in units of continuous action), the structure of the steel base is fully recrystallized and thus a high yield strength and The hardness of the galvanized steel strip obtained during cold rolling is not maintained.

In the proposed method for the production of thin high-strength steel strip coated with an iron-zinc alloy, low-carbon steels of grades 08kp, 08ps and others according to GOST 9045-80, as well as carbon steel of ordinary quality according to GOST 380-71, can be used.

Example 1. Hot rolling of a steel strip of mark 08kp was performed under the following conditions: the temperature of the end of hot rolling is 860-880 ° C; coiling temperature in roll 560 С; The thickness of the laminated strip is 1.5 mm. Etching was performed in a continuous etching unit in a sulfuric acid plant. A hot-rolled pickled strip with a thickness of 1.5 mm was subjected to chemical cleaning in hot alkaline solutions, followed by jet washing in hot water, drying and galvanizing on a continuous hot-dip galvanizing unit. Chemical cleaning of the strip surface:

Washing solutions of NaPO NaOH in the bath of the lock, g / l 15.2 14.7 in the brush-washing machine 4.0 3.0, g / l

Solution temperature, C

89

in the bath lock

in a brush-washer 88 After chemical cleaning, a zinc coating was applied with a thickness of 8 ..

Hot-rolled galvanized steel strip was cold rolled with a total reduction of 65%.

Thickness of the rolled galvanized strip of 0.5 mm; zinc coating thickness 2.8 µm.

After. cold rolling galvanized strip was subjected to heat treatment: the temperature of the strip during heat treatment 550 C; heating rate

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50 degrees / s; holding time 3 min; cooling rate 30 degrees / s.

After heat treatment, the zinc coating is converted into an iron – zinc compound. The iron content in the coating is 13%.

Mechanical properties of steel strip coated with iron-zinc alloy: G 470 MPa; GTg, 560 Sha; 0 20%; The bond strength of the coating (180 ° bend) is good.

Example 2. Hot rolling of a 1kp steel strip was performed under the following conditions: the temperature of the end of hot rolling is 860-880 ° C; coiling temperature in roll 580 С; The thickness of the laminated strip is 1.8 mm.

The etching was carried out as in Example 1. A 1.8 mm thick pickled strip was subjected to chemical cleaning in hot alkaline solutions as in Example 1 and then a 16 µm thick zinc coating was applied to the strip on a continuous unit. The hot-rolled galvanized steel strip was cold rolled with a total reduction of 90%; thickness of rolled galvanized strip 0.18 mm; tolcin zinc coating 2 µm.

After cold rolling, the galvanized strip was subjected to heat treatment: the strip temperature was heat-treated at 580 ° C; heating rate of 50 degrees / s; lash time 1 min; cooling rate 60 degrees / s.

After heat treatment, the zinc coating is converted to an iron-zinc compound. The iron content in the coating - 14%.

Mechanical properties of steel strip coated with iron-zinc alloy:

GT 440 MPa; G 550 MPa; 5 24%; adhesion strength of the coating (180 bend) is good.

PRI me R 3. A hot-rolled etched strip 2.0 mm thick from 08kp steel was chemically cleaned in hot alkaline solutions as in Example 1 and then a 10 μm thick zinc coating was applied to the strip on a continuous aggregate action

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1p galvanized galvanized steel strip was cold rolled with total compression. 80%; only

thickness of rolled galvanized strips 0.35 mm; zinc coating thickness 2 µm.

After the cold rolling, the galvanized strip was heat treated in two modes in bell-type furnaces,

The first mode “Temperature of the strip during heat treatment is 450 ° С; heating rate of 100 degrees / h; holding time 10 h; cooling rate - cooled under the muffle to 120 ° C, then in air.

Second mode. The temperature of the strip during heat treatment is 530 ° C; heating rate of 150 degrees / h; vyderlski time 5 h; cooling rate — cooled under finely felled to 120 ° C, then in air.

After heat treatment, the zinc coating turns into a zinc-rich compound. Mechanical properties of steel strip coated with iron-zinc alloy after heat treatment.

First Mode G. 680 Sha; Ots 740 MPa; S 6%; leselose content in the coating was 20%; The adhesion strength of the coating to the base is good (180 ° C).

Second mode. G 650 Mna; (Jg 700 ffla; J 7%; the iron content in the coating was 28%; the adhesion strength of the coating to the substrate is good (180 ° bend).

An example of steel processing according to the prototype method, Low carbon, distal steel of 1kp grade is 1.8 mm thick and 1050 I-IM wide in rolls with chemical composition,%: С 0.08; Si 0.01; Mp 0.32; S 0.017; P 0.011; Cr 0.03; Ni 0.07; Cu 0.07 was cold rolled on a continuous four-stand mill to thickness O ,, 6 Mt-io. After cold rolling, the metal was galvanized on an aggregate of continuous hot-dip galvanizing. After zinc docking, the metal has mechanical properties with a-1S-1e; Sha; 3,350 Sha; 5 28%; hardness, zinc coating thickness 15 µm.

The cold rolling of the galvanized strip was carried out by a total reduction of 40%; laminated strip thickness 0.36 mm; zinc coating thickness 8 µm.

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Mechanical properties of the hot-dip galvanized strip; G, 700 Mlla; , 0%; HRB% 100 units The repeated annealing of the heated galvanized strip is carried out at 360 ° C in a bell furnace.

Physical and mechanical properties of galvanized strip after re-annealing: G 530 MPa.br 630 MPa; 8 6%; , coating thickness 10 µm, iron content in the coating 11%, surface roughness, 0 µm.

The use of the proposed method for a thin high-strength steel strip coated with an iron-zinc alloy compared to existing methods has the following advantages: the productivity of the process is increased due to the use of a hot rolled strip before applying the zinc coating, as well as the productivity of the process due to the absence of such a zinc coating; additional processing (operations) as secondary cold rolling, repeated heat treatment of galvanized strip. In addition, a high level of strength properties of galvanized steel strip is maintained.

Claims (3)

1. A method of producing a thin high-strength steel strip coated with an iron-zinc alloy, including hot rolling, pickling, cold rolling, cleaning the surface of the strip, applying a zinc coating, strip annealing at a temperature below the temperature of recrystallization of the steel base, increasing the productivity of the process while maintaining the level of properties, cleaning the surface of the strip and applying a zinc coating is carried out after hot rolling and pickling the strip, then cold rolling with a total reduction of 65-90%. 2. A method according to claim 1, characterized in that the galvanized strip is annealed in batch units at 450530 ° C for 5-10 hours. 3. The method of claim 1, about tl and - h and y and the fact that the galvanized strip is annealed in continuous units at 550-580 ° C for 1-3 min.