RU2529325C1 - Production method of cold-rolled mill products for baling band - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention can be used in the production of high-strength cold-rolled strip from cold-worked carbon steel with the thickness of 0.8-1.0 mm and weight of 17-26 t to manufacture a baling band. The method comprises hot rolling, reeling of the strip into rolls, etching and thermal processing. Temperature of hot rolling end and reeling is kept in the range of 830-870°C and 470-540°C, respectively. Thermal processing is carried out by heating of cold-rolled mill products up to the temperature of 370-440°C and holding under this temperature during the time τ=(m+h)/K, where m stands for weight of the maximal roll in a stack, t; h - strip thickness, mm; K=0.80-1.10 - empiric coefficient determined by experiments. The steel has the following chemical composition, wt %: 0.10-0.18 C; 0.30-0.80 Si; 1.1-1.8 Mn; maximum 0.020 P; maximum 0.015 S; maximum 0.06 Al; maximum 0.06 Cr; maximum 0.01 N; Fe, unavoidable impurities - the rest.

EFFECT: increased output of proper product due to improved mechanical properties.

2 cl, 3 tbl

Description

The invention relates to the field of ferrous metallurgy, and more particularly to the technology of rolling and heat treatment of metals, and can be used in the manufacture of high-strength cold-rolled strip of carbon steel in a cured state with a thickness of 0.8-1.0 mm and a mass of 17-26 tons to obtain a packing tape .

Packaging tape must meet the following set of properties (table 1):

Table 1 Mechanical properties of steel packaging tape σ _in, N / mm ² δ ₁₀₀ ,% Not less than 960 not less than 4

A known method of producing a cold rolled strip of carbon steel, including heating the slab, hot rolling, cooling and winding the strip into a roll, etching and cold rolling, according to which the slab is heated to a temperature of 1260-1320 ° C, hot rolling is completed at a temperature of 820-880 ° C , the strip is cooled to a temperature of 550-590 ° C, and cold rolling is carried out with a total compression of 60-73%. In addition, steel has the following chemical composition, wt.%:

Carbon 0.30-0.45 Silicon 0.01-0.05 Manganese 0.85-1.35 Aluminum 0.01-0.04 Chromium no more than 0.10 Nickel no more than 0,05 Copper no more than 0.10 Molybdenum no more than 0,05 Sulfur no more than 0,020 Phosphorus no more than 0,020 Iron the rest [1]

The disadvantage of this method is that it does not provide the required properties for the packaging tape in terms of elongation.

The closest analogue to the present invention is a method of processing a strip of low carbon steel, including hot rolling, strip winding, etching, cold rolling and annealing, according to which hot rolling is completed at a temperature of 840-860 ° C, strip winding is carried out at 550-650 ° C and cold rolling is performed with compression of 25-50% followed by annealing at 350-450 ° C [2].

The proposed method of processing the strip is used for low-carbon steel grades 08kp-3kp (ps).

The disadvantage of this method is that when it is used for the production of packaging tape, they have a low complex of mechanical properties, especially in terms of tensile strength, which reduces yield.

The technical problem solved by the invention is to increase the yield by increasing the complex of mechanical properties.

To solve the technical problem in the known method for the production of cold rolled products for packaging tape with a thickness of 0.8-1.0 mm and a mass of 17-26 tons, including hot rolling of steel strips, winding them into coils, pickling, cold rolling and heat treatment, according to According to the invention, the temperature of hot rolling and winding is maintained in the ranges of 830-870 ° C and 470-540 ° C, respectively, the heat treatment is carried out by heating the cold-rolled strips to a temperature of 370-440 ° C and holding at this temperature for a time τ = (m + h ) / K, where m is mass m ksimalnogo roll in the stack, that is, h - the thickness of the strip in mm, K = 0.80-1.10 - empirical coefficient obtained empirically.

In addition, steel has the following chemical composition, wt.%:

Carbon 0.10-0.18 Silicon 0.30-0.80 Manganese 1.10-1.80 Aluminum no more than 0,06 Chromium no more than 0,06 Phosphorus no more than 0,020 Sulfur no more than 0.015 Nitrogen no more than 0,01 Iron and inevitable impurities rest

The invention consists in the following.

With the regulated parameters of hot rolling (temperatures of the end of rolling T _kn = 830-870 ° C and winding T _cm = 470-540 ° C), the formation of optimal structural components of the phases is achieved to obtain high strength and plastic properties. As a result, strip steel has a high uniformity of structure, the grain is characterized by small size. The end of the hot rolling of strips at a temperature below 830 ° C, in the two-phase region, leads to a significant heterogeneity of the structure, which entails instability of the mechanical properties in the hot rolled and then in the cold rolled state. An increase in the temperature of the end of hot rolling above 870 ° C leads to enlargement of the grain and a decrease in the strength properties of hot-rolled steel. Winding strips below 470 ° C greatly increases the strength of steel, but significantly reduces ductility. At a winding temperature above 540 ° C, the ductility of the steel increases, however, this leads to a decrease in its strength below an acceptable level.

Heat treatment of steel at temperatures of 370-440 ° C, performed after cold rolling, allows to increase the plastic properties of steel, while maintaining strength properties at the required level. At temperatures above 440 ° C, there is a sharp decrease in strength properties. At temperatures below 370 ° C, to obtain optimal ductility, a longer exposure of the metal is required, which entails a greater energy consumption.

To achieve a satisfactory level of ductility of steel, optimal metal exposure at 370-440 ° C is required.

It was experimentally established that if the exposure time during heat treatment is less than calculated by the formula τ = (m + h) / K, then the plasticity does not increase to the required level, there is no leveling of properties. The increase in exposure time over calculated by the formula τ = (m + h) / K leads to a decrease in the strength properties of the finished tape and yield, increase in production costs. It was also found that the value of the coefficient K depends on the mass of the roll.

Carbon in the proposed steel is the main reinforcing element. When the carbon content is less than 0.10%, the strength properties of cold rolled steel are below the permissible level. An increase in carbon concentration in excess of 0.18% leads to an increase in the strength characteristics of the cured tape, but the ductility of the metal is greatly reduced.

Silicon deoxidizes and hardens steel. A decrease in the silicon content of less than 0.3% leads to a decrease in the strength properties of the strip. An increase in the content of this element of more than 0.80% leads to a loss of ductility and viscosity.

Manganese has a strengthening effect. With a manganese content of less than 1.1%, the strength properties and hardness are below the permissible level, and an increase in its content of more than 1.8% sharply reduces the ductility index.

Phosphorus and sulfur are harmful impurities, and their content should be minimized. When the phosphorus content is more than 0.02%, the strength increases and steel embrittlement is caused. Along with this, elongation is greatly reduced. Sulfur has virtually no effect on strength, but with a sulfur content of more than 0.015% it reduces ductility. General ductility is reduced by MnS particles. The decrease in general ductility exponentially occurs with an increase in the volume fraction of particles of the second phase of MnS.

Aluminum is introduced to deoxidize steel and bind nitrogen to nitrides. Aluminum nitrides reinforce cold rolled steel. An increase in aluminum content of more than 0.06% contributes to graphitization of steel, a decrease in its strength properties and hardness.

Chrome strengthens the steel, but at a concentration of more than 0.06%, the ductility of the fretted strip falls below an acceptable level.

Nitrogen strengthens the steel, but if its amount exceeds 0.01%, the steel becomes prone to destruction, the yield of the strip decreases.

An example implementation of the method. Production of cold rolled coils weighing from 18 to 20 tons, 1.0 mm thick, 1000 mm wide.

6 experimental steel melts were smelted in an oxygen converter, the chemical composition of which is given in table 2:

table 2 Chemical composition of steels (ladle test) Composition number The content of chemical elements, wt.% FROM Si Mn Al R S Cr N Fe and inevitable impurities one 0,080 0.23 1.10 0,030 0.014 0.005 0.55 0.006 Rest 2 0,120 0.35 1.18 0,034 0.010 0.004 0,03 0.006 -: - 3 0.150 0.55 1.43 0,040 0.015 0.008 0.04 0.007 -: - four 0.165 0.65 1,67 0,055 0.017 0.013 0.05 0.008 -: - 5 0.148 0.45 1.39 0,030 0,020 0.004 0,045 0.007 -: - 6 0.150 0.12 0.50 not regl. 0.010 0,020 0.10 0.006 -: -

The smelted steel was cast on a continuous casting machine into 250 mm thick slabs. The slabs were heated in a walking beam heating furnace and rolled on a continuous broadband mill 2000 into 2.9 mm thick strips. Hot rolled strips on the discharge roller table were cooled with water and wound onto a roll. Chilled rolls were subjected to hydrochloric acid etching in a continuous pickling unit. Then, the etched strips were rolled on a 5 stand mill to a final thickness of 1 mm. Cold rolled coils were heat treated in bell furnaces. After all operations, samples were taken and tests were performed to determine the mechanical properties of the car. Cold rolled strips in the form of rolls, the mechanical properties of which satisfy the requirements given in Table 1, were shipped to consumers for further processing (cutting, passivation, coating, etc.). Thanks to the use of this technology, an increase in yield is achieved up to Q = 100%.

Implementation options of the proposed method and indicators of their effectiveness are shown in table 3.

Table 3 Production Modes and Their Efficiency Production Modes Mechanical properties Composition number m, t TO T _kp , ° C T _cm , ° C T _otzh , ° C τ, hour σ _in , H / mm ² δ ₁₀₀ ,% Q% one eighteen 0.83 830 470 420 23 877 5 - 2 eighteen 0.83 830 470 370 23 1011 7 one hundred 3 twenty 0.91 850 500 400 23 1000 8 one hundred four twenty 0.91 870 540 430 23 1000 6 one hundred 5 eighteen 0.61 850 500 387 31 890 9 - 6 (prototype) twenty 845 555 390 23 650 17 -

From the data given in table 3, it follows that when implementing the proposed method (options No. 2-No. 4), an increase in yield is achieved by increasing the complex of mechanical properties.

In the case of transcendental values of the declared parameters (options No. 1 and No. 5), as well as in the implementation of the known method [2] (option No. 6), it was not possible to obtain cold rolled steel for the production of finished packaging tape due to the low complex of mechanical properties.

The technical and economic advantages of the proposed method are that due to the simultaneous optimization of the hot rolling and heat treatment, an increase in the complex of mechanical properties of steel in the cold-rolled annealed state is achieved.

Information sources

1. Patent of the Russian Federation No. 2203965, IPC C21D 8/02, C22C 38/04, 2003

2. USSR author's certificate No. 995925, IPC B21B 3/00, 1981

Claims (2)

1. Method for the production of cold rolled products for packaging tape with a thickness of 0.8-1.0 mm and a coil weight of 17-26 tons, including hot rolling, strip winding into rolls, pickling, cold rolling and heat treatment, characterized in that the hot rolling is completed at a temperature of 830-870 ° C, strip winding is carried out at a temperature of 470-540 ° C, heat treatment is carried out by heating cold-rolled steel to a temperature of 370-440 ° C and holding at this temperature for a time τ = (m + h) / K ,
where m is the mass of the maximum roll in the foot, t;
h is the strip thickness, mm;
K = 0.80-1.10 - empirical coefficient obtained experimentally. 2. The method according to claim 1, characterized in that the steel is melted, containing, wt.%:
Carbon 0.10-0.18 Silicon 0.30-0.80 Manganese 1.10-1.80 Aluminum no more than 0,06 Chromium no more than 0,06 Phosphorus no more than 0,020 Sulfur no more than 0.015 Nitrogen no more than 0,01 Iron and inevitable impurities rest