RU2796664C1 - METHOD FOR PRODUCTION OF COILED HOT-ROLLED STRIP STEEL WITH A THICKNESS OF 2-16 mm - Google Patents

Abstract

FIELD: rolling production.

SUBSTANCE: invention can be used in production of hot-rolled coiled steel for manufacturing of welded metal structures and building products. Method for production of rolled hot-rolled strip steel with a thickness of 2-16 mm includes steel smelting in a steel-smelting unit, steel tapping into a steel ladle, out-of-furnace processing, casting, hot rolling by rough and finish rolling to produce hot-rolled strips and their winding into rolls. Steel is smelted containing, wt.%: carbon 0.1-0.2, manganese 1.1-1.9, silicon not more than 0.05, sulfur not more than 0.01, phosphorus not more than 0.015, chromium 0.05-0.3, nickel 0.05-0.3, copper 0.05-0.3, aluminum 0.02-0.1, niobium 0.005-0.05, titanium 0.005-0.05, nitrogen no more than 0 .01, while the carbon equivalent is not more than 0.45%. Finish rolling starts at a temperature of 950-1050°C and ends at temperatures up to 915°C. Winding of hot-rolled strips into coils is carried out at temperatures up to 700°C.

EFFECT: rolled products with a given set of physical and mechanical properties are obtained: yield strength - not less than 355 MPa, tensile strength - not less than 470 MPa, relative elongation - not less than 20%.

4 cl, 2 tbl, 1 ex

Description

The invention relates to rolling production and can be used in the production of hot-rolled coiled steel for the manufacture of welded metal structures and building products.

A known method for the production of hot-rolled wide-strip rolled products from steel grade S355MC, including rolling, accelerated cooling and coiling of strips into coils, where the steel contains components in specified ratios, while the temperature of the end of rolling is maintained in the range Ar ₃ ÷ (Ar ₃ -30) ° C , the coiling temperature is lower than Ar ₁ by 100÷150°C, and Ar ₃ and Ar ₁ are determined from the equations, depending on the content of carbon, silicon, manganese, chromium and nickel in the steel, wt.%. [Patent RU No. 2516212, IPC C21D 8/02, C22C 38/38, B21B 1/26, 2014].

The disadvantage of this method is the low carbon content, which does not provide sufficient strength properties and the required level of physical and mechanical properties of rolled products.

The closest analogue to the claimed object is a method for the production of coils of strips of hot-rolled steel with a thickness of 8-16 mm with a carbon content of 0.14-0.20%, including heating the slab for hot rolling, rolling it in roughing and finishing continuous groups of stands of a broad-strip mill with a temperature the end of rolling is 780-840°C, the strip is cooled with water on a discharge roller table, followed by winding into a roll, while the temperature of the end of rolling in the roughing group of stands, depending on the final thickness of the strip, is set equal to 1030-1100°C [Patent RU No. 2351413, IPC B21B 1/26, 2009].

The disadvantage of this method is the difficulty of providing the required level of physical and mechanical properties of hot-rolled strips.

The technical problem solved by the claimed invention is the development of a technology for the production of well-welded, hot-rolled steel with a thickness of 2-16 mm with a given set of physical and mechanical properties (yield strength of at least 355 MPa, tensile strength of at least 470 MPa, relative elongation of at least 20%) .

The task is achieved by the fact that in the method for the production of hot-rolled strip steel with a thickness of 2-16 mm, including steel smelting in a steel-smelting unit, steel tapping into a steel ladle, out-of-furnace processing, pouring, hot rolling by rough and finish rolling to obtain hot-rolled strips and winding them into rolls, according to the invention, steel is smelted containing the following components, wt. %:

Carbon 0.1-0.2

Manganese 1.1-1.9

Silicon not more than 0.05

Sulfur not more than 0.01

Phosphorus not more than 0.015

Chrome 0.05-0.3

Nickel 0.05-0.3

Copper 0.05-0.3

Aluminum 0.02-0.1

Niobium 0.005-0.05

Titanium 0.005-0.05

Nitrogen no more than 0.01,

while the carbon equivalent is not more than 0.45%,

finishing rolling starts at a temperature of 950-1050°C and ends at a temperature of up to 915°C, and the winding of hot-rolled strips into coils is carried out at a temperature of up to 700°C.

The average score of non-metallic inclusions in the structure of hot-rolled strip steel for each type of inclusion does not exceed 2.5.

The steel has a yield strength of at least 355 MPa, tensile strength of 470-630 MPa, relative elongation of at least 20%, impact strength of at least 27 J/cm ² .

Smelted steel may additionally contain REM in an amount of not more than 0.001 wt.%.

The essence of the proposed technical solution is as follows.

The essence of the proposed technical solution is to optimize the chemical composition of the steel and the parameters of the temperature regime of rolling and winding for strip steel, which makes it possible to obtain hot-rolled steel with desired physical and mechanical properties.

The selected limits of carbon content (0.1÷0.2%) in combination with manganese (1.1÷1.9%), nickel and copper (0.05÷0.3% each) provide a ferrite-pearlite structure, allow to achieve high values of yield strength, tensile strength, relative elongation, as well as improve weldability. The carbon content of more than 0.2% impairs weldability, promotes the formation of hot and cold cracks. When the carbon content is less than 0.1% and manganese is less than 1.1%, the steel is not strong enough. With a manganese content of more than 1.9%, the ductility of steel and its resistance to impact loads are noticeably reduced, the ratio of yield strength to tensile strength increases, and the resistance of the metal in the heat-affected zone of the weld deteriorates due to the formation of segregation defects.

The declared content of silicon (not more than 0.05%) and aluminum (0.02÷0.1%) provide the necessary cleanliness of steel for non-metallic inclusions. Silicon deoxidizes steel, increases its strength and elasticity, silicon content of not more than 0.05% provides sufficient strength characteristics of steel.

Sulfur and phosphorus are harmful impurities that reduce the entire range of steel properties. Phosphorus gives steel cold brittleness - brittleness at normal and low temperatures, and sulfur - hot brittleness (red brittleness) - brittleness at hot working temperatures. Phosphorus helps to reduce the level of impact strength of steel at low temperatures, increasing the cold brittleness threshold. The content of sulfur is not more than 0.01% and phosphorus is not more than 0.015% is necessary to obtain high values of impact strength and resistance of the metal to brittle fracture at low temperatures.

When the content of chromium and nickel is more than 0.3%, the steel has excessive hardness, the ductility of steel and its resistance to shock loads decrease, and the cost of steel also rises.

The stated copper content (0.05÷0.3%) increases strength without compromising the toughness of steel, helping to prevent the formation of hot cracks in rolled products. With a copper content of more than 0.3%, the ductility of steel and its resistance to shock loads decrease.

For effective deoxidation of steel, improvement of steel toughness, aluminum content of 0.02÷0.10% is required. When the aluminum content is more than 0.10%, the number of non-metallic inclusions in the steel increases, which leads to a decrease in its ductility and impact resistance.

With a niobium content of more than 0.05%, the tendency of steel to become brittle increases.

Titanium contributes to the refinement of the structure, and is also a steel deoxidizer. When the titanium content is less than 0.005%, the steel is insufficiently deoxidized, its strength decreases, and the sensitivity to overheating increases. The upper limit of its content is limited to 0.05%, since the addition of large amounts of titanium leads to a significant deterioration in toughness and resistance to brittle fracture due to the formation of titanium carbides.

The upper limit of nitrogen content in steel is limited to 0.01%, since a larger value has a negative effect on the impact strength and cold resistance of the metal.

The limitation of the carbon equivalent With _eq ≤0.45 wt.% improves the weldability of hot-rolled metal. At C _eq >0.45%, the weldability of steel decreases, and as a result, the weld metal becomes less ductile and more prone to brittle fracture.

The declared temperatures of the beginning, end of hot rolling and coiling temperature are determined experimentally and allow to increase the yield strength and strength while maintaining a stable elongation value.

The finish rolling start temperature of 950-1050°C is necessary to suppress recrystallization and provide conditions for grain refinement. When the temperature drops below 950°C, there is a significant increase in the load on the mill equipment, when the temperature rises above 1050°C, the efficiency of finishing rolling decreases significantly due to the intensity of diffusion processes.

A decrease in the temperature of the end of finishing rolling below 915 °C and an increase in the coiling temperature above 700 °C leads to a significant decrease in the cooling rate and an increase in the ferrite grain, which in turn leads to a decrease in strength characteristics and unsatisfactory quality of rolled metal.

Providing an average score of non-metallic inclusions in steel of no more than 2.5 makes it possible to achieve an improvement in the complex of mechanical properties of steel: tensile strength, yield strength and elongation.

Rare earth metals (REM) have an effective deoxidizing and desulfurizing ability, improve the quality of steel. An increase in the content of REM over 0.001% does not lead to a further improvement in the mechanical properties of steel.

The invention is illustrated by the results of experiments (table 1, table 2).

Table 1 shows the chemical compositions of steels with different content of alloying elements. Table 2 presents the rolling parameters and controlled parameters of steels. The score of non-metallic inclusions in the experiments was 2.0. REM, in the amount of 0.0008%, were present in steel in 4 and 5 experiments.

An example of the implementation of the method.

On a broadband hot rolling mill 2000, steel was rolled with a content of 0.1-0.2 wt.% carbon, 0.05% silicon, 1.1-1.9% manganese, 0.05-0.3% chromium, 0. 05-03% nickel, 0.01% sulfur, 0.015% phosphorus, 0.02-0.1% aluminum, 0.05-0.3% copper, 0.005-0.05% titanium, 0.01 nitrogen, niobium 0.005-0.05%.

The slab, heated to the required temperature of 1200-1250 °C (temperature of the beginning of rough rolling), enters the broadband hot rolling mill. After rolling in the roughing group of stands of the wide-strip mill with a temperature of 950-1050°C, the roll is sent along the intermediate roller table to the finishing continuous group of stands. In this case, depending on the required final thickness of the strip, individual relative reductions in each stand of the finishing group of the mill were maintained in the range from 9% to 15%. The temperature of the end of the strip rolling in the last finishing pass of the group was set to 915°C. After that, the hot-rolled strip is directed to the coilers of the second group, where it is wound into a roll at a temperature of 700°C. If the temperature of the beginning, end of rolling and coiling exceeds the declared values, the tensile strength will exceed the allowable values (630 MPa), and the elongation will be below the minimum value (20%).

The claimed technology for the production of hot-rolled steel coils makes it possible to obtain the following physical and mechanical properties in a hot-rolled strip 2-16 mm thick after normalization: yield strength σ _t - not less than 355 MPa, tensile strength σ _in - 470-630 MPa, relative elongation δ not less than 20%, impact strength: KCV-20°C not less than 27 J/cm ² .

Thus, the proposed production method makes it possible to produce hot-rolled coils with desired physical and mechanical properties. It has been experimentally confirmed that the obtained physical and mechanical properties of steel increase the durability and resistance of parts made from them. The steel has satisfactory weldability, the metal in the weld zone meets the necessary requirements for steel building structures in accordance with GOST 23118-99.

Table 1
Chemical compositions of steels Example No. Content of chemical elements, % C Si Mn P S Cr Ni Cu Al N2 Ti Nb 1 0.143 0.024 1.52 0.01 0.0035 0.161 0.119 0.119 0.03 0.0068 0.011 0.027 2 1.117 0.024 1.51 0.09 0.0053 0.085 0.067 0.067 0.031 0.0068 0.023 0.026 3 0.136 0.019 1.53 0.01 0.0062 0.158 0.122 0.136 0.027 0.007 0.012 0.025 4 0.144 0.023 1.45 0.01 0.0082 0.145 0.112 0.121 0.037 0.0066 0.015 0.025 5 0.141 0.013 1.47 0.01 0.011 0.145 0.121 0.129 0.034 0.006 0.015 0.025

table 2
Technological parameters of rolling hot-rolled steel strip S355JR and S355J2 Example No. Thickness, mm Controlled parameters Yield strength, MPa Tensile strength, MPa Relative extension, % Impact strength, J / cm ² Rolling start temperature, °C Temperature at the end of rolling, °C Winding temperature, °С H/c after N H/c after N H/c after N H/c after N 1 16 415 389 547 515 25 28 1066 905 651 Prototype 16 n/a 305 n/a 450 n/a 19 n/a 21 1040 1080 n/a 2 12 413 370 521 481 26 31 1103 914 659 Prototype 12 n/a 320 n/a 480 n/a 23 n/a 27 1050 1090 n/a 3 10 432 387 544 506 27 31 1087 907 651 Prototype 10 n/a 320 n/a 470 n/a 23 n/a 26 1060 1100 n/a 4 8 442 400 547 504 27 thirty 1101 903 648 Prototype 8 n/a 360 n/a 500 n/a 28 n/a 29 1000 1050 n/a 5 5 469 424 555 525 26 28 1114 906 648

Claims (7)

1. A method for the production of hot-rolled strip steel with a thickness of 2-16 mm, including steel smelting in a steel-smelting unit, steel tapping into a steel ladle, out-of-furnace processing, casting, hot rolling by rough and finish rolling to obtain hot-rolled strips and winding them into rolls , characterized in that steel is smelted containing the following components, wt.%: Carbon 0.1-0.2 Manganese 1.1-1.9 Silicon no more than 0.05 Sulfur no more than 0.01 Phosphorus no more than 0.015 Chromium 0.05-0.3 Nickel 0.05-0.3 Copper 0.05-0.3 Aluminum 0.02-0.1 Niobium 0.005-0.05 Titanium 0.005-0.05 Nitrogen no more than 0.01, while the carbon equivalent is not more than 0.45 wt.%, finishing rolling starts at a temperature of 950-1050°C and ends at a temperature of up to 915°C, and the winding of hot-rolled strips into coils is carried out at a temperature of up to 700°C. 2. The method according to claim 1, characterized in that the average score of non-metallic inclusions in the structure of the rolled hot-rolled steel strip for each type of inclusion does not exceed 2.5. 3. The method according to claim 1, characterized in that the steel has a yield strength of at least 355 MPa, tensile strength of 470-630 MPa, elongation of at least 20%, impact strength of at least 27 J/cm ² . 4. The method according to p. 1, characterized in that steel is smelted, additionally containing REM in an amount of not more than 0.001 wt.%.