RU2583536C1 - Method for production of hot-rolled sheets for construction of steel structures (versions) - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, mainly to production of hot-rolled sheets for construction of metal structures with welded and other compounds. Method for production of hot-rolled sheets for construction of steel structures involves obtaining workpiece of steel, wt. %: 0.12-0.15 C, 0.15-0.30 Si, 1.55-1.70 Μn, not more than 0.30 of Cr, not more than 0.30 of Ni, not more than 0.30 of Cu, not more than 0.003 of Ti, not more than 0.008 of Ν, not more than 0.05 of Al, not more than 0.005 of S, not more than 0.015 of Ρ, Fe and admixtures are rest, at that carbon equivalent C_e ≤ 0.45 %. Heating for rolling of continuously cast billet is performed to 1,180-1,200 °C for not more than 9 hours. At that, roughing of sheets with final thickness of up to 20 mm is carried out until reaching of 90-95 mm thickness by roll, finish rolling is started at 840-860 °C and is completed at 770±10 to final thickness of up to 20 mm, then sheets are subjected to accelerated cooling from temperature of not less than 750 °C to temperature 655±5 °C. For sheets with final thickness of more than 20 mm to 30 mm rough rolling is performed to achieving thickness 115-120 mm by roll, finish rolling is started at 810-830 °C and is completed at temperature of 780±10 °C to final thickness of more than 20 mm to 30 mm, then sheets are subjected to accelerated cooling from temperature of not less than 760 °C to temperature of 600±20 °C.

EFFECT: technical result consists in production of rolled stock with thickness of up to 30 mm with guaranteed yield point of not less than 345 MPa, as well as improved system of viscous and plastic properties.

2 cl, 3 tbl

Description

The invention relates to metallurgy, mainly to the production of hot rolled sheets for the construction of metal structures with welded and other joints.

A known method for the production of plate low alloy steel strip, including heating to a temperature of 1170-1200 ° C continuous casting containing 0.03-0.08% C, 1.6-2.2% Mn, 0.12-0.40% Si , 0.28-0.55% Ni, 0.20-0.45% Mo, 0.01-0.1% Cr, 0.1-0.4% Cu, 0.03-0.07% Nb , 0.01-0.04% Ti, 0.01-0.06% V, 0.01-0.05% Al, Fe and impurities with an impurity content of each element less than 0.05 - the rest, while the amount of sulfide non-metallic inclusions does not exceed 1.5 points, and the number of other non-metallic inclusions does not exceed 3 points, rough rolling, subsequent cooling of the intermediate workpiece to a temperature of 820-850 ° C, finish rolling with a temperature of the end of 770-820 ° C, accelerated cooling of the obtained strip to a predetermined temperature, determined depending on the thickness of the finished strip, its straightening on a roller straightening machine and subsequent slow cooling (RF patent 2463360, IPC C21D 8/02, C22C 38/58, 10/10/2012).

The closest in its technical essence and the achieved results to the proposed invention is a method for the production of low-plate thick-strip strip, including austenization of a continuously cast billet containing 0.03-0.10% C, 1.6-2.0% Mn, 0.15-0 , 35% Si, 0.30-0.60% Ni, 0.25-0.45% Ni, Cr≤0.15%, 0.1-0.4% Cu, 0.03-0.07% Nb, Ti≤0,03%, V≤0,035%, Fe and impurities with the content of each element of the impurity less than 0.05% - the rest, while the coefficient of crack resistance of the finished strip P _CM is less than 0.25%, and the size of the actual grain of ferrite does not exceed 15 microns, rough draft weaving at a temperature of at least 950 ° C with a reduction ratio of at least 10% per pass, with the exception of the last pass, to an intermediate billet thickness of 80-140 mm, subsequent cooling of the intermediate billet to a temperature of 820-850 ° C, finishing rolling, accelerated cooling of the obtained the strip to a predetermined temperature is completed at a temperature of 560-640 ° C., strip straightening at a temperature of at least 350 ° C. and delayed cooling of the strip (RF patent 2463359, IPC C21D 8/02, C22C 38/58, 10/10/2012).

These methods are designed for the production of hot-rolled sheets with a thickness of not more than 20 mm, which is their main disadvantage. Also, with similar requirements for mechanical properties in known production methods, additional alloying is required, which increases the cost of the finished sheet.

EFFECT: production of rolled products with a thickness of up to 30.0 mm with a guaranteed yield strength of at least 345 MPa, as well as an improved complex of viscous and plastic properties.

The technical result is achieved by the fact that in the method for the production of hot rolled sheets for building steel structures up to 20 mm thick, which includes heating for rolling a continuously cast billet, rough rolling at a temperature of at least 950 ° C, reinforcing the roll, finishing rolling, accelerated cooling of the finished sheet to a predetermined temperature and subsequent delayed cooling in air, according to the invention, the preform is obtained from steel with the following ratio of elements, wt. %:

carbon 0.12-0.15 silicon 0.15-0.30 manganese 1.55-1.70 chrome no more 0.30 nickel no more 0.30 copper no more 0.30 titanium no more 0.003 nitrogen no more 0.008 aluminum no more 0.05 sulfur no more 0.005 phosphorus no more 0.015 iron and impurities rest

the carbon equivalent of C _e ≤0.45%, heating for rolling a continuously cast billet is carried out to a temperature of 1180-1200 ° C for no more than 9 hours, rough rolling is carried out until the roll thickness reaches 90-95 mm, finishing rolling is started at a temperature of 840-860 ° C and complete at a temperature of 770 ± 10 ° C, after which the sheets are subjected to accelerated cooling from a temperature of at least 750 ° C to a temperature of 655 ± 15 ° C.

The technical result is also achieved by the fact that in the method of manufacturing hot rolled sheets for building steel structures with a thickness of more than 20 mm to 30 mm, which includes heating for rolling a continuously cast billet, rough rolling at a temperature of at least 950 ° C, reinforcing the roll, finishing rolling, accelerated cooling of the finished sheet to a predetermined temperature and subsequent delayed cooling in air, according to the invention, the preform is obtained from steel with the following ratio of elements, wt. %:

carbon 0.12-0.15 silicon 0.15-0.30 manganese 1.55-1.70 chrome no more 0.30 nickel no more 0.30 copper no more 0.30 titanium no more 0.003 nitrogen no more 0.008 aluminum no more 0.05 sulfur no more 0.005 phosphorus no more 0.015 iron and impurities rest

the carbon equivalent of C _e ≤0.45%, heating for rolling a continuously cast billet is carried out to a temperature of 1180-1200 ° C for no more than 9 hours, rough rolling is carried out until the rolled thickness reaches 115-120 mm, finishing rolling is started at a temperature of 810-830 ° C and complete at a temperature of 780 ± 10 ° C, after which the sheets are subjected to accelerated cooling from a temperature of at least 760 ° C to a temperature of 600 ± 20 ° C.

The essence of the invention lies in the fact that the specified chemical composition of the steel provides the necessary phase composition, which determines the technical result when implementing the proposed technological modes.

Carbon in steel determines its strength properties. A decrease in carbon content of less than 0.12% leads to a drop in strength properties below an acceptable level, an increase in content of more than 0.15% leads to a decrease in ductility and toughness of steel.

When the silicon content is less than 0.15%, the contamination of the steel with oxide inclusions increases, an increase in the content of more than 0.30% leads to contamination by silicates - all this negatively affects the mechanical properties of steel.

Manganese, like carbon, increases the strength characteristics of steel. With an increase in the manganese content of more than 1.70%, a decrease in the toughness of steel and a decrease in weldability are observed. However, the introduction of manganese into steel is necessary for the deoxidation of steel and sulfur removal; therefore, a decrease in the manganese content of less than 1.55% is undesirable.

An increase in the content of chromium, nickel and copper of more than 0.30% for each is not economically feasible and leads to an increase in cost without improving properties.

The content of titanium (0.003%), aluminum (0.005%) and nitrogen (0.008%) is sufficient to provide the required level of mechanical properties. Their content above the specified maximum values is also not economically feasible and leads to an increase in cost without improving properties.

The declared limits of sulfur content (not more than 0.005%) and phosphorus (not more than 0.015%) provide high impact strength at low temperatures.

For the proposed chemical composition with values of carbon equivalent With _e more than 0.45%, a possible deterioration in weldability of steel.

The carbon equivalent C _e is determined by the results of the melting analysis according to the formula:

With _e = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15.

Rational parameters of the implementation of the method were determined empirically.

To achieve the specified technical result of obtaining rolled products with a thickness of up to 30.0 mm with a guaranteed yield strength of at least 345 MPa, as well as an improved complex of viscous and plastic properties, it is necessary to obtain a uniform and finely divided structure of hot-rolled sheets.

It was experimentally established that heating a continuously cast billet to a temperature below 1180 ° C is not sufficient to heat the billet over its cross section. An increase in the heating temperature above 1200 ° C is accompanied by an intensive growth of austenite grains and coarsening of the boundaries. Heating over 9 hours leads to excessive coarsening of the austenitic grain with subsequent formation of a crystalline fracture.

Rough rolling begins at a temperature not lower than 950 ° C. When the temperature of the start of rough rolling is less than 950 ° С, the metal enters the temperature region unfavorable for deformation, which can lead to increased loads on the equipment and the inability to provide the required amount of compression.

As a result of experimental rolling, the optimal thickness of the roll after rough rolling for various thicknesses of the finished sheet was determined.

It was found that an increase in the thickness of the roll after rough rolling is more than 90-95 mm for a sheet of final thickness up to 20 mm inclusive and more than 115-120 mm for a sheet of final thickness more than 20 mm, the elaboration of the structure along the thickness of the roll is significantly reduced.

It was experimentally determined that the start of finish rolling below 840 ° C for a sheet of final thickness up to 20 mm inclusive and below 810 ° C for a sheet of final thickness more than 20 mm does not allow austenite to be prepared for subsequent transformation, creating a high density of imperfections in the gamma-iron crystal lattice. At a temperature of rolling end above 860 ° C for a sheet of final thickness up to 20 mm inclusive and below 830 ° C for a sheet of final thickness more than 20 mm, the optimum ratio of structural components (ferrite, bainite, needle ferrite) is not ensured, which leads to a failure to provide a complex of mechanical properties .

Finishing rolling is completed for a sheet of final thickness up to 20.0 mm inclusive at a temperature of 770 ± 10 ° C, for a sheet of final thickness more than 20 mm at a temperature of 780 ± 10 ° C. If you violate the specified temperature ranges of the end of the finish rolling, there is a risk of non-provision of mechanical properties.

Accelerated cooling of the sheets after finishing rolling starts from a temperature of at least 750 ° C to a temperature of 655 ± 15 ° C for sheets of final thickness up to 20.0 mm inclusive and from a temperature of at least 760 ° C to a temperature of 600 ± 20 ° C for sheets of final thickness more than 20.0 mm. The accelerated cooling to a temperature below the indicated ranges is accompanied by the excessive development of the process of intermediate transformation of supercooled austenite with the release of the corresponding products that sharply worsen the viscosity properties of the material. Accelerated cooling of sheets to temperatures exceeding the declared ranges, provides a low cooling rate of the Central layers of the sheet with the release of adverse structural components.

From the above analysis it follows that the implementation of the proposed technical solution allows to obtain the required quality of hot-rolled sheets for the construction of metal structures with welded and other joints. This is achieved by choosing rational temperature-strain regimes for a given chemical composition of steel. However, in the event that the variable technological parameters go beyond the proposed boundaries, difficulties arise in obtaining stable and satisfactory mechanical properties. Thus, the data obtained confirm the correctness of the recommendations on the selection of acceptable values of the technological parameters of the proposed method for the production of hot-rolled sheets for building steel structures.

The application of the method is illustrated by an example of its implementation in the production of sheets C345 on a mill 5000.

Steel was smelted in an oxygen converter with a capacity of 370 t with a magnesium desulfurization process in a pouring ladle. Primary alloying, preliminary deoxidation and metal processing with solid slag mixtures with metal purging with argon in a steel pouring ladle were carried out at the issue. The final alloying, microalloying, metal processing with calcium and metal overheating for evacuation were carried out on the complex steel finishing unit. The metal was degassed by evacuation. The casting was carried out on a continuous casting machine with metal protection with argon from secondary oxidation into billets with a section of 315 × 1715-2003 mm.

The chemical composition of the steels is given in table 1.

Steel is obtained with the following composition of chemical elements: C = 0.15%; Si = 0.22%; Mn = 1.62%; Cr = 0.03%; Ni = 0.02%; Cu = 0.10%; Ti = 0.002%; N = 0.005%; Al = 0.05%; S = 0.005%; P = 0.012%; iron and impurities - the rest. The carbon equivalent was 0.44%.

Continuously cast billets were heated to a temperature of 1186 ° C for 8 h 20 min and rolled in the rough stage at a temperature of rolling onset of 1011 ° C to a roll thickness of 95.0 mm, cooled in air to a temperature of 860 ° C, rolled at the finishing stage to a final thickness 20.0 mm with the end of the deformation process at 780 ° C. after that, the sheets are accelerated cooled from a temperature of 760 ° C to 670 ° C.

Tensile tests were carried out on cylindrical specimens according to GOST 1497. Impact strength tests were performed according to GOST 9454, impact tests after mechanical aging were carried out according to GOST 7268.

Implementation options of the proposed method and indicators of their effectiveness are shown in tables 2 and 3, respectively.

From tables 2 and 3 it follows that when implementing the claimed production method (modes No. 2-5), hot-rolled sheets are obtained for the construction of metal structures with welded and other joints with a level of mechanical properties corresponding to strength category 345.

With the transcendental values of the proposed modes (modes No. 1 and No. 6), it is not possible to obtain a finished sheet with the required yield strength, while the elongation and impact strength are significantly reduced.

Technical appraisal and economic advantages of the considered invention consist in the fact that the use of the proposed method provides the production of thick sheets of low alloy steel with a thickness of up to 30 mm for the construction of metal structures with welded and other joints.

Claims (2)

1. A method of manufacturing hot rolled sheets for building steel structures, including heating for rolling continuously cast billets, rough rolling at a temperature not lower than 950 ° C, stiffening rolling, finish rolling, accelerated cooling of finished sheets to a predetermined temperature and subsequent delayed cooling in air, characterized in that the preform is obtained from steel having the following element content, wt. %:
carbon 0.12-0.15 silicon 0.15-0.30 manganese 1.55-1.70 chromium no more than 0.30 nickel no more than 0.30 copper no more than 0.30 titanium no more than 0,003 nitrogen no more than 0,008 aluminum no more than 0,05 sulfur no more than 0,005 phosphorus no more than 0.015 iron and impurities rest
wherein the carbon equivalent C _e ≤0,45%, heating for rolling continuous casting to produce a temperature 1180-1200 ° C is not more than 9 hours, the roughing rolling is performed until the peal of 90-95 mm thickness, finish rolling the sheet started at a temperature 840- 860 ° C and complete at a temperature of 770 ± 10 ° C with a final sheet thickness of up to 20 mm, after which the sheets are subjected to accelerated cooling from a temperature of at least 750 ° C to a temperature of 655 ± 5 ° C. 2. A method of manufacturing hot rolled sheets for building steel structures, including heating for rolling continuously cast billets, rough rolling at a temperature not lower than 950 ° C, stiffening rolling, finish rolling, accelerated cooling of finished sheets to a predetermined temperature and subsequent slow cooling in air, characterized in that the preform is obtained from steel having the following element content, wt. %:
carbon 0.12-0.15 silicon 0.15-0.30 manganese 1.55-1.70 chromium no more than 0.30 copper no more than 0.30 nickel no more than 0.30 titanium no more than 0,003 nitrogen no more than 0,008 aluminum no more than 0,05 sulfur no more than 0,005 phosphorus no more than 0.015 iron and impurities rest
the carbon equivalent of C _e ≤0.45%, heating for rolling a continuously cast billet is carried out to a temperature of 1180-1200 ° C for no more than 9 hours, rough rolling is carried out until the rolled thickness reaches 115-120 mm, finishing rolling of sheets begins at a temperature of 810- 830 ° C and complete at a temperature of 780 ± 10 ° C to a final sheet thickness of more than 20 mm to 30 mm, after which the sheets are subjected to accelerated cooling from a temperature of at least 760 ° C to a temperature of 600 ± 20 ° C.