Production method of seawater corrosion resistant steel Q345qNHY-I

Abstract

The invention discloses a production method of seawater corrosion resistant steel Q345qNHY-I. The technological process comprises the steps of converter smelting, refining, continuous casting, heating and rolling, cooling and checking and warehousing. The steel comprises the following chemical components in percentage by mass: 0.03 to 0.05 percent of C, 0.15 to 0.30 percent of Si, 0.8 to 0.9 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.0015 percent of S, 0.020 to 0.030 percent of Nb, 0.015 to 0.02 percent of Ti, 0.015 to 0.025 percent of Al, 1.32 to 1.45 percent of Ni, less than or equal to 0.06 percent of Cr, 0.23 to 0.27 percent of Mo, less than or equal to 0.01 percent of V, 0.45 to 0.50 percent of Cu, 0.9 to 2.0 percent of Ca / S, more than or equal to 1.29 percent of V and the balance of Fe and inevitable impurities. The steel produced by the method has moderate strength, good toughness, excellent low-temperature toughness, excellent processability and excellent welding performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy and relates to a production method of seawater corrosion resistant steel Q345qNHY-I. BACKGROUND

[0002] Bridge technology has developed from the initial cement arch bridge to the ordinary steel beam bridge. The steel beam bridge can be manufactured in sections, and can be scaled and factoryized, so that only assembly is needed on site, time is saved, the manufacturing period is shortened, and recycling and resource saving are achieved. Since the bridge is entirely built outdoors, the environmental conditions are relatively complex, and the ordinary steel beam needs to be coated with an anti-corrosion coating, and the bridge needs to serve for at least about 100 years, so the later service maintenance is also quite difficult. In recent years, more and more bridge projects have applied weather-resistant bridge steel, which requires a weathering index I≥6.0, and has been widely used in the southwest plateau region. Such weather-resistant bridge steel greatly reduces the application and maintenance cost and saves resources. However, China is vast in territory, and the climate differs greatly in different places. With the development of economy, there are more and more bridge construction projects in coastal areas, and the marine climate is highly corrosive. The Cl-concentration in groundwater is as high as 12000 ppm or more, which is a typical severe marine atmospheric environment, and the damage of solar ultraviolet radiation, high salt fog and high heat and humidity to the material is quite obvious, and the ordinary weather-resistant bridge steel cannot meet the service requirements.

[0003] The seawater corrosion resistant bridge steel is a new steel grade with high strength, strong corrosion resistance and high added value. In addition to strong corrosion resistance, it also has high strength, good elongation performance, cold bending performance, welding performance and low temperature crack stopping performance, and is mainly applied in marine environment climate to improve the service life of steel, increase the safety factor of engineering, reduce the service and maintenance cost, and save resources. SUMMARY

[0004] The application aims to provide a production method of seawater corrosion resistant steel Q345qNHY-I. The produced steel has high strength, good toughness, excellent low temperature toughness, excellent processing performance and excellent welding performance. The yield strength of the steel is 345-465 Mpa, the tensile strength is ≥490 Mpa, the yield strength ratio is ≤0.85, the low temperature impact toughness is-40℃, Akv≥300J. The inclusion A class coarse / fine is ≤0.5 level; the inclusion B class coarse / fine is ≤0.5 level; the inclusion C class coarse / fine is ≤0.5 level; and the inclusion D class coarse / fine is ≤1.0 level.

[0005] The application is implemented by the following technical scheme: The application discloses a production method of a seawater corrosion resistant steel Q345qNHY-I, and chemical compositions of the steel are as follows in percentage by mass: C=0.03-0.05, Si=0.20-0.30, Mn=0.8-0.9, P<=0.012, S<=0.0015, Nb=0.020-0.030, Ti=0.015-0.02, Al=0.015-0.025, Ni=1.32-1.45, Cr<=0.06, Mo=0.23-0.27, V<=0.01, Cu=0.45-0.50, Ca / S=0.9-2.0, V index>=1.29, and the rest is Fe and inevitable impurities; and key process steps include the following: (1) converter: a large oxygen flow spray gun is used for blowing oxygen in the converter, the converter controls oxygen>=600ppm, a slide plate device is used, lime and Al2O3 are added after the converter to perform slag treatment, no deoxidization alloying treatment is performed, and sufficient oxygen activity is maintained in the molten steel.

[0006] (2) refining: during the heating process, large argon stirring is used, when the carbon content reaches <=0.03%, lime and refining slag are added to perform deoxidization and sulfur removal, the refining slag basicity CaO / SiO2<=4.5-6.0; under the condition of 0.5tor vacuum degree, the vacuum time is kept for more than 18 minutes; the molten steel is treated to remove nitrogen, hydrogen and oxygen, and H<=1.5, O<=13ppm are controlled.

[0007] (3) continuous casting: full-process low-heat superheat protection casting is performed, the casting temperature is <=1534 DEG C, the superheat is controlled to be 8-12 DEG C, the dynamic proportioning water method is used for secondary cooling, the water amount is 0.25-0.45 L / kg, the dynamic soft reduction technology is used, and the casting blank reduction amount is 6-8 mm; after the casting blank is flame cut, the casting blank quenching device is used to rapidly cool to <=600 DEG C, the casting blank is cooled to <=350 DEG C in a heat preservation device, and is then put into a furnace for rolling.

[0008] (4) rolling: the heating temperature is 1150-1180 DEG C, the heating time is 280-320 min, and the warm blank thickness is kept for more than 3 h; the opening rolling temperature is 840-930 DEG C, the final rolling temperature is 770-810 DEG C, the starting cooling temperature is 780-820 DEG C, the final cooling temperature is 580-620 DEG C, and the cooling rate is 8-15 DEG C / s; the weather resistant bridge steel with the yield strength of 360-460 MPa, the tensile strength of 490-610 MPa, the yield strength ratio of <=0.85 and the low-temperature impact toughness of Akv>=300 J at-40 DEG C is obtained.

[0009] The technical creative principle of the application is explained as follows: About step (1) converter: using large oxygen jet to stir the molten pool, high basicity slag is made, so that the oxygen content of the tapping is ≥400ppm, carbon oxygen product = 0.0023%, P ≤ 0.010%, using slide plate slag stopping, reducing the mixed out of high oxidized slag, adding lime 300~400kg, slag treatment, locking P in the slag not to spread to the molten steel, without deoxidation and alloying, avoiding the production of Al2O3 deoxidation product, maintaining the high oxygen content of the molten steel, laying the foundation for the subsequent LF pre-decarburization.

[0010] About step (2) refining: in the early stage of power transmission, large argon is used to stir the molten pool, the oxygen content of the molten steel is further reacted with carbon to generate CO, CO2 gas, when the carbon content is reduced to below 0.03%, deoxidation and alloying are carried out, using lime and refining slag to deoxidize and sulfur, high basicity and fluidity slag is made, the refining slag basicity CaO / SiO2: 4.5~6.0, which is beneficial to the transformation of CaO-AL2O3-SiO2-MgO complex inclusions, and is beneficial to the floating and removal of inclusions, the inclusion stable control A class coarse / fine ≤0.5 level; B class coarse / fine ≤0.5 level; C class coarse / fine ≤0.5 level; D class coarse / fine ≤1.0 level.

[0011] About step (3) continuous casting: automatic pouring in tundish, long nozzle argon blowing protection, argon flow (20~60) L / min, avoiding secondary oxidation of molten steel, controlling the tundish temperature ≤1534℃ during casting, which can effectively reduce the generation of secondary oxides, controlling the superheat 8~12℃, continuous casting two cooling dynamic water distribution technology, solidification end three segment dynamic soft reduction technology, reduction amount 6~8mm, reducing the formation of center bridge, reducing center segregation and porosity, center segregation C ≤0.5 level; after flame cutting, the casting blank is quenched to ≤600℃ by casting blank quenching device, the uniform casting blank organization, after slow cooling to ≤350℃ in the offline protective cover, the furnace is loaded for rolling, which is beneficial to the diffusion and precipitation of hydrogen, the segregation of casting blank state organization is further stabilized, and fine equiaxed crystal organization is obtained.

[0012] The beneficial effects of the present application: the produced steel has high strength, good toughness, excellent low temperature toughness, excellent processing performance and excellent welding performance, the yield strength of the steel is 345~465Mpa, the tensile strength is ≥490Mpa, the yield strength ratio is ≤0.85, the low temperature impact toughness is -40℃, Akv is ≥300J. Inclusion A class coarse / fine ≤0.5 level; B class coarse / fine ≤0.5 level; C class coarse / fine ≤0.5 level; D class coarse / fine ≤1.0 level. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The organization chart of the steel produced in example 1. DETAILED DESCRIPTION

[0014] The present application will be further described in conjunction with examples.

[0015] Example 1: Production of 20mm Q345qNHY-I Corrosion Resistant Steel The chemical composition of the alloying elements is C=0.04, Si=0.23, Mn=0.88, P=0.010, S≤0.0012, Nb=0.023, Ti=0.016, Ni=1.34, Cr=0.04, Mo=0.25, V=0.002, Cu=0.48, Ca / S=1.2, V=1.3, and the balance is iron and unavoidable impurities. The key process steps are as follows: (1) Converter smelting: the oxygen content of the converter tapping is 640ppm, the carbon content is 0.046%, 350kg of lime is added, and the steel is not deoxidized and alloyed, and the oxygen content in the molten steel is maintained.

[0016] (2) LF furnace refining: refine the electrode heating, large argon flow stirring, argon flow 10L / min, make C oxygen fully react, exclude excess C of the steel grade, when the carbon content is below 0.03%, deoxidize and alloy; the refining temperature is 1500~1650℃; it is beneficial to the transformation of CaO-AL2O3-SiO2-MgO complex inclusions, and it is beneficial to the floating and removal of inclusions; A class coarse and fine / fine system 0 level; B class coarse / fine system 0.5 level; C class coarse / fine system 0 level; D class coarse / fine system 0.5 level; under 0.5torr vacuum, maintain the vacuum time for 18 minutes; the molten steel is treated for denitrification, hydrogen, and oxygen, and the oxygen content is ≤13ppm, which greatly improves the purity of the molten steel.

[0017] (3) Continuous casting: control the superheat 10℃, long nozzle argon protection flow 40L / min, continuous casting secondary cooling water distribution ratio water quantity 0.25L / kg, solidification end three section dynamic soft reduction technology, reduction amount 7mm, reduce the formation of center bridge, reduce center segregation and porosity, center segregation 0.5 level; after flame cutting, the cast blank is quenched by the cast blank quenching device at 580℃, and after cooling to 320℃ in the offline protection cover, it is charged into the furnace for rolling, the hydrogen of the cast blank is diffused and precipitated, the cast blank state organization is further stabilized, and fine equiaxed crystal organization is obtained.

[0018] (4) Rolling: heating temperature 1150~1180℃, heating time 280~320min, waiting for temperature blank thickness >3h, opening rolling temperature 840~930℃, final rolling temperature 770~810℃, starting cooling temperature 780~820℃, final cooling temperature 580~620℃, cooling rate 8~15℃ / s, to obtain a yield strength of 360~460Mpa, a tensile strength of 490~610Mpa, a yield strength ratio of ≤0.85, a low temperature impact toughness of -40℃, and an Akv of ≥300J of the weathering bridge steel.

[0019] Example 2: Production of 44mm Q345qNHY-I Corrosion Resistant Steel The chemical composition of the alloying elements is C = 0.038, Si = 0.25, Mn = 1.12, P = 0.009, S ≤ 0.0008, Nb = 0.021, Ti = 0.017, Al = residual, Ni = 1.36, Cr = 0.04, Mo = 0.26, V = 0.002, Cu = 0.48, Ca / S = 1.1, V index = 1.3. Key process steps: (1) Converter smelting: the oxygen content of the converter tapping is 650 ppm, the carbon content is 0.044%, 330 kg of lime is added, no deoxidizing alloying is performed, and the oxygen content in the molten steel is maintained.

[0020] (2) LF furnace refining: the refining electrode is heated, the argon flow is large, the argon flow is 10 L / min, the C oxygen is fully reacted, the excess C of the steel grade is removed, when the carbon content reaches below 0.03%, deoxidizing alloying is performed, the refining temperature is 1500~1650℃; it is convenient for CaO-AL2O3-SiO2-MgO complex inclusions to transform, it is beneficial for the inclusions to float and be removed, the A class coarse and fine / fine system is 0 level; the B class coarse and fine / fine system is 0.5 level; the C class coarse and fine / fine system is 0 level; the D class coarse and fine / fine system is 0.5 level, under 0.5 torr vacuum, the vacuum time is maintained for 18 minutes; the molten steel is treated for denitrification, hydrogen, and oxygen, the oxygen content is ≤13 ppm, the purity of the molten steel is greatly improved.

[0021] (3) Continuous casting: the superheat is controlled to be 10℃, the long nozzle argon blowing protection flow is 40 L / min, the water distribution ratio of the secondary cooling of the continuous casting is 0.25 L / kg, the three-section dynamic soft reduction technology at the solidification end, the reduction amount is 8 mm, the formation of the center bridge is reduced, the center segregation and porosity are reduced, the center segregation is 0.5 level; after the casting blank is cut by the flame, the casting blank is quenched by the quenching device at 580℃, after being cooled to 310℃ in the down-line protection cover, it is charged into the furnace for rolling, the casting blank state organization is further stabilized, and fine equiaxed crystal organization is obtained.

[0022] (4) Rolling: the heating temperature is 1150~1180℃, the heating time is 280~320 min, the warm blank thickness is >3 h, the starting rolling temperature is 840~930℃, the final rolling temperature is 770~810℃, the on-line quenching is adopted, the starting cooling temperature is 780~820℃, the final cooling temperature is 240~320℃, the cooling rate is 8~15℃ / s, and the weather-resistant bridge steel with the yield strength of 360~460 Mpa, the tensile strength of 490~610 Mpa, the yield strength ratio of ≤0.85, and the low-temperature impact toughness of -40℃, Akv≥300 J is obtained.

[0023] The material detection performance of the steel produced in Example 1 and Example 2 is shown in Table 1.

[0024] Table 1 Material performance of the steel produced in the examples .

Claims

1. A method for producing seawater corrosion resistant steel Q345qNHY-Ⅰ, characterized in that: The chemical composition of the steel (by mass percentage) is C=0.03~0.05, Si=0.20~0.30, Mn=0.8~0.9, P≤0.012, S≤0.0015, Nb=0.020~0.030, Ti=0.015~0.02, Al=0.015~0.025, Ni=1.32~1.45, Cr≤0.06, Mo=0.23~0.27, V≤0.01, Cu=0.45~0.50, Ca / S=0.9~2.0, V index ≥1.29, with the remainder being Fe and unavoidable impurities. Key process steps include: (1) Converter: The converter uses a high oxygen flow rate lance for oxygen blowing. The oxygen level in the converter is controlled at ≥600ppm. A sliding plate device is used. Lime and Al2O3 are added after the furnace for slag treatment. No deoxidation and alloying treatment is performed to maintain sufficient oxygen activity in the molten steel. (2) Refining: During the heating process, a large amount of argon gas is used for stirring. When the carbon content reaches ≤0.03%, lime is added to the refining slag for deoxidation and desulfurization. The basicity of the refining slag CaO / SiO2 is ≤4.5~6.

0. The vacuum time is maintained for more than 18 minutes under a vacuum degree of 0.5tor. The molten steel is denitrified, dehydrogenated and deoxygenated, and the H is controlled to be ≤1.5 and O to be ≤13ppm. (3) Continuous casting: casting is carried out under low superheat protection throughout the process. The casting temperature is ≤1534℃ and the superheat is controlled at 8~12℃. The secondary cooling adopts the dynamic water ratio method with a water ratio of 0.25~0.45L / kg. The billet reduction is 6~8mm using dynamic light reduction technology. After the billet is flame-cut, it is rapidly cooled to ≤600℃ using a billet quenching device. The billet is then slowly cooled to ≤350℃ by a heat preservation device after leaving the line and then loaded into the furnace for rolling. (4) Rolling: Heating temperature 1150~1180℃, heating time 280~320min, billet thickness after heating >3h; initial rolling temperature 840~930℃, final rolling temperature 770~810℃, initial cooling temperature 780~820℃, final cooling temperature 580~620℃, cooling rate 8~15℃ / s; Weathering bridge steel with yield strength of 360~460Mpa, tensile strength of 490~610Mpa, yield strength ratio ≤0.85, low temperature impact toughness of -40℃, and Akv≥300J was obtained.

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