A method for producing atmospheric corrosion resistant steel plate

Abstract

A method for producing an atmospheric corrosion resistant steel plate, wherein the weight percentage of the steel is C=0.03%~0.08%, Si≤0.60%, Mn=0.50%~1.50%, P≤0.025%, S≤0.005%, Al=0.01%~0.06%, Cu=0.30%~0.60%, Ni=0.30%~1.0%, Cr=0.30%~0.60%, Mo≤0.50%, and one or more of Ti≤0.03%, Nb≤0.10%, and V≤0.10% can be added, and the balance is Fe and inevitable impurity elements. A layer of dense and uniform iron oxide scale with extremely strong adhesion can be obtained by adopting heating, rolling, cooling and finishing processes, which can play the role of "stopping rust with rust" and improve the atmospheric corrosion resistance of the steel plate. At the same time, due to the simple process, no need for heat treatment and rust layer stabilization treatment, etc., the delivery time of steel plates is greatly shortened, the production cost is reduced, and it is a green production method.

Description

Technical Field

[0001] The invention belongs to the technical field of low alloy steel production and relates to a method for producing an atmospheric corrosion resistant steel plate. Background Art

[0002] The corrosion of steel is one of the main reasons for the damage of steel structures. The use of coating can extend the life of steel structures, but there are problems such as high maintenance costs, environmental pollution, difficulty in the application of large components, and difficulty in welding. Atmospheric corrosion-resistant steel is referred to as weathering steel. Phosphorus, copper, chromium, nickel and other elements are often added to form a dense and highly adhesive protective film on the surface of the steel, which can prevent oxygen and water in the atmosphere from penetrating into the steel matrix, slowing down the further diffusion and in-depth development of rust, thereby slowing down the corrosion rate of steel and playing the role of "rusting with rust". Its corrosion resistance is 2 to 8 times that of ordinary carbon steel. Therefore, weathering steel is widely used in bridges, containers, railway carriages, oil derricks, port buildings, oil production platforms and other fields.

[0003] There have been a lot of studies on the effect of alloying elements on atmospheric corrosion resistance. For example, the United States proposed the atmospheric corrosion resistance index I ≥6.0( I =26.01Cu+3.88Ni+1.2Cr+1.49Si+17.28P-7.29CuNi-9.1NiP-33.39CuCu); Japan proposed the weather resistant alloy index V >1.0( V =1 / [(1.0-0.16C)×(1.05-0.05Si)×(1.04-0.016Mn)×(1.0-0.5P)×(1.0+ 1.9S)×(1.0-0.1Cu)×(1.0-0.12Ni)×(1.0-0.3Mo)×(1.0-1.7Ti)]). I and V The larger the value, the higher the atmospheric corrosion resistance. However, in addition to the influence of alloying elements on weather resistance, the structure of steel, especially the surface structure, is also crucial to its atmospheric corrosion resistance.

[0004] In order to obtain a good "rust-stopping" ability, many scholars have studied the formation and stability of iron oxide scale on the surface of steel and proposed some control measures. Chinese patent CN113621873B proposes a weather-resistant structural steel with a stabilized rust layer and a preparation method thereof. Through the quick rust treatment of periodic water sprinkling and the stabilization treatment of spraying 5% to 10% potassium phosphate solution, a stable rust layer is quickly formed on the surface. However, this method not only increases the cost and prolongs the delivery time, but also requires a site for spraying operations, and the stabilizer often pollutes the environment to a certain extent. Chinese patent CN108570601B proposes a low-carbon bainitic weathering steel, which adopts a heat treatment process of normalizing + accelerated cooling + isothermal aging to form an inner layer with a higher FeO ratio and better adhesion, and a layer of red Fe with a relatively dense structure is covered on the surface. 2 O 3 The iron oxide scale structure is used to slow down the further development of rust, but it requires an additional heat treatment process, which also increases production costs and reduces production efficiency. Chinese patent CN105568208A discloses a method for surface treatment of weathering steel. After shot peening, the steel plate is oxidized at 250℃~350℃ for 1h~4h to obtain a dense reddish-brown oxide layer, thereby promoting the stability of the rust layer and hindering further corrosion of the substrate under the rust layer. Although low-temperature heating reduces energy consumption, long-term heating at this temperature is prone to "blue brittleness" and reduces the plastic toughness of the steel plate. Summary of the invention

[0005] In view of the above-mentioned deficiencies of the prior art, the object of the present invention is to provide a method for efficiently producing atmospheric corrosion resistant steel plates, so that a layer of dense and uniform iron oxide scale with extremely strong adhesion is generated on the surface of the steel plate to improve the stability of the rust layer.

[0006] The technical solution of the present invention:

[0007] A method for producing an atmospheric corrosion resistant steel plate, wherein the weight percentage of the steel is C=0.03%~0.08%, Si≤0.60%, Mn=0.50%~1.50%, P≤0.025%, S≤0.005%, Al=0.01%~0.06%, Cu=0.30%~0.60%, Ni=0.30%~1.0%, Cr=0.30%~0.60%, Mo≤0.50%, Ti≤0.03%, Nb≤0.10%, V≤0.10% or more may be added, and the balance is Fe and unavoidable impurity elements; the key process steps include:

[0008] (1) Heating: Before heating, use flame cleaning to remove the primary iron oxide scale on the surface of the continuous casting billet, and the removal depth is not less than 2mm; then use a walking beam heating furnace for heating, control the residual oxygen content in the furnace to ≤2.5%, control the furnace temperature to ≤1250℃, and control the furnace time to ≤300min;

[0009] (2) Rolling: After the ingot is removed from the heating furnace, it is initially descaled. The descaling high-pressure water pressure is ≥22MPa and the descaling speed is ≤1.0m / s. After the initial descaling, the surface temperature of the slab is above 1100℃. Then the slab is swung and air-cooled for 60~180s before rolling. During the rolling process, high-pressure water descaling is performed. The first pass is not descaling, and the second pass is descaling. When the slab surface temperature is higher than 1000℃ or lower than 900℃, descaling is performed every 30~60s. When the slab surface temperature is between 900~1000℃ or the descaling interval is ≥60s, high-pressure water descaling is performed before each rolling pass.

[0010] (3) Cooling: After rolling, the steel plate is cooled until the surface temperature is lower than A r1 Air cooling is performed before ±5℃. A r1 It is the starting temperature of the transformation of supercooled austenite to pearlite; the steel plate continues to cool and the surface temperature is controlled within the range of 570~250℃ for no more than 600s; no bending straightening is used during the entire cooling process;

[0011] (4) Finishing: Use flame cutting to trim and cut to size.

[0012] Preferably, in step (2), when the surface temperature of the slab after initial descaling is between 1150 and 1200°C, the slab is swung in the air to cool to a temperature for 1 to 2 minutes; when the surface temperature of the slab after initial descaling is between 1100 and 1150°C, the slab is swung in the air to cool to a temperature for 2 to 3 minutes.

[0013] Preferably, in step (2), the reduction ratio of the final rolling pass is controlled to be less than 5%.

[0014] Preferably, in step (3), the rolled steel plate is air-cooled and then accelerated to a temperature of 5°C / s. B s The following, among which, B s is the starting temperature of bainite transformation.

[0015] Preferably, in step (4), if the plate shape is poor, a flattening machine is preferably used for flattening.

[0016] The control principle of the iron scale on the surface of the steel plate of the present invention is as follows: firstly, the primary iron scale after continuous casting of the slab and the primary iron scale after heating are removed, and then the slab is air-cooled at a relatively high temperature for a period of time before rolling to obtain a uniform and complete secondary iron scale, and the secondary iron scale is pressed into the surface by rolling, while the descaling interval is controlled, the purpose of which is to gradually thicken the pressed secondary iron scale on the one hand, and to prevent the secondary iron scale from peeling and then being pressed in again, resulting in pits, stress concentration and other defects that are not conducive to atmospheric corrosion resistance. Finally, a layer of dense and uniform secondary iron scale with extremely strong adhesion is formed on the surface of the steel plate after rolling. In order to protect the integrity and stability of this layer of iron oxide, the technical means adopted include: air cooling in the two-phase region to cause ferrite phase transformation on the surface, and carbon will diffuse into the untransformed austenite inside, so that the surface austenite is almost completely transformed into ferrite, greatly reducing the surface convexity caused by shear phase transformation; the surface temperature is controlled in the range of 570~250℃ for a period of time to avoid the pre-eutectoid transformation and eutectoid transformation of FeO in the surface iron oxide scale, while retaining more FeO with better adhesion; ensure that stretch and bending straightening, which has a greater destructive force on the surface iron oxide scale, is not used during the entire cooling process, and create conditions for this. The final rolling preferably uses a small pass reduction rate to obtain a good rolled plate shape. At the same time, if the plate shape is poor after cooling, it is preferred to use a flattening machine for flattening; and offline flame trimming and sizing are used to prevent mechanical cutting from damaging the iron oxide scale on the edge.

[0017] The beneficial effects of the present invention are as follows: (1) The process adopted by the present invention is simple, and no heat treatment and rust layer stabilization treatment are required. A layer of dense and uniform iron oxide scale with extremely strong adhesion can be obtained through the controlled rolling and controlled cooling process, which can play the role of "stopping rust with rust", improve the atmospheric corrosion resistance of the steel plate, and greatly shorten the delivery time of the steel plate, thereby reducing the production cost; (2) The atmospheric corrosion resistant steel described in the present invention has a wide composition range, and has few restrictions on the range of key process parameters affecting mechanical properties such as rolling temperature, cooling rate, and red-returning temperature. Therefore, the production method of the present invention is suitable for the production of low-strength atmospheric corrosion resistant steel plates and high-strength atmospheric corrosion resistant steel plates. At the same time, the heating, rolling, cooling and finishing processes used can adapt to a wide range of steel plate thicknesses; (3) The production method of atmospheric corrosion resistant steel plates proposed by the present invention is a green production method, which is easy to implement, simple to operate, and can be widely promoted. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a scanning electron microscope micrograph of the iron oxide scale on the surface of the atmospheric corrosion resistant steel plate according to Example 1 of the present invention. DETAILED DESCRIPTION

[0019] The present invention is further described below with reference to the embodiments and drawings.

[0020] Embodiment 1:

[0021] The production of atmospheric corrosion resistant steel plates has a yield strength level of Q345MPa and a thickness of 30mm. The chemical composition of the steel is C=0.06%, Si=0.20%, Mn=0.92%, P=0.012%, S=0.002%, Al=0.036%, Cu=0.32%, Ni=0.33%, Cr=0.35%, Mo=0.02%, Ti=0.016%, and the balance is Fe and unavoidable impurity elements; the key process steps include:

[0022] (1) Heating: Before heating, flame cleaning is used to remove the primary iron oxide scale on the surface of the continuous casting billet, and the removal depth is 2~3mm; then a walking beam heating furnace is used for heating. During the heating process, the residual oxygen content in the furnace is 1.5%~2.5%, the maximum furnace temperature is 1225℃, and the furnace time is 240min;

[0023] (2) Rolling: After the ingot is removed from the heating furnace, it is initially descaled. The descaling high-pressure water pressure is 22 MPa and the descaling speed is 1.0 m / s. The surface temperature of the slab after initial descaling is 1165 °C. The slab is then swung and air-cooled for 120 seconds before rolling. The surface temperature of each rolling pass and rolled steel plate, the interval time from the last descaling, and whether descaling is performed are shown in Table 1. The reduction rate of the final rolling pass is 3.3%;

[0024] (3) Cooling: After rolling, the steel plate is cooled in air until the surface temperature reaches 720℃, which is lower than the A r1 Temperature (thermal simulation test to obtain the cooling rate under A r1 The temperature is about 720℃); then the steel plate is cooled to 600℃ at a cooling rate of 6℃ / s (the thermal simulation test shows that the B s Temperature is about 650℃), then air-cooled, and the time from the time the surface temperature of the steel plate is measured to the time it takes to cool to 250℃ is 560s, and even with the accelerated cooling time it is no more than 600s; no bending straightening is used during the entire cooling process;

[0025] (4) Finishing: Use flame cutting to trim and cut to size.

[0026] The surface oxide scale of the atmospheric corrosion resistant steel plate of Example 1 was observed by scanning electron microscope. Figure 1 It can be seen that the iron oxide scale on the surface of the steel plate of Example 1 is dense and uniform, closely combined with the steel matrix, with a thickness of about 20 um and a single phase composition.

[0027] Embodiment 2:

[0028] The production of atmospheric corrosion resistant steel plates has a yield strength level of Q420MPa and a thickness of 80mm. The chemical composition of the steel is C=0.05%, Si=0.18%, Mn=1.23%, P=0.015%, S=0.003%, Al=0.038%, Cu=0.36%, Ni=0.50%, Cr=0.48%, Mo=0.10%, Ti=0.012%, Nb=0.027% by weight, and the balance is Fe and unavoidable impurity elements; the key process steps include:

[0029] (1) Heating: Before heating, flame cleaning is used to remove the primary iron oxide scale on the surface of the continuous casting billet, and the removal depth is 2~3mm; then a walking beam heating furnace is used for heating. During the heating process, the residual oxygen content in the furnace is 1.4%~2.2%, the maximum furnace temperature is 1240℃, and the furnace time is 285min;

[0030] (2) Rolling: After the ingot is removed from the heating furnace, it is initially descaled. The descaling high-pressure water pressure is 22 MPa and the descaling speed is 0.5 m / s. The surface temperature of the slab after initial descaling is 1180°C. The slab is then swung and air-cooled for 90 seconds before rolling. The surface temperature of each rolling pass and rolled steel plate, the interval time from the last descaling, and whether descaling is performed are shown in Table 2. Water cooling is used between the 7th and 8th passes. The reduction rate of the final rolling pass is 2.5%.

[0031] (3) Cooling: After rolling, the steel plate is cooled in air until the surface temperature reaches 710℃, which is lower than the A r1 Temperature (thermal simulation test to obtain the cooling rate under A r1 The temperature is about 708℃); then the steel plate is cooled to 420℃ at a cooling rate of 13.6℃ / s (the thermal simulation test shows that the B s Temperature is about 615℃), then air cooling is adopted, and the time from the time when the surface temperature of the steel plate is measured to the time when it cools down to 250℃ is 550s, and even with the accelerated cooling time, it is no more than 600s; no bending straightening is used in the whole cooling process;

[0032] (4) Finishing: Use flame cutting to trim and cut to size.

[0033] Example 3: The strength level is a yield strength of 500 MPa, and the thickness of the steel plate is 12 mm.

[0034] The chemical composition of the steel is C=0.06%, Si=0.22%, Mn=1.41%, P=0.013%, S=0.002%, Al=0.032%, Cu=0.40%, Ni=0.62%, Cr=0.55%, Mo=0.12%, Ti=0.018%, Nb=0.025%, V=0.035% by weight, and the remainder is Fe and unavoidable impurity elements; the key process steps include:

[0035] (1) Heating: Before heating, flame cleaning is used to remove the primary iron oxide scale on the surface of the continuous casting billet, and the removal depth is 2~3mm; then a walking beam heating furnace is used for heating. During the heating process, the residual oxygen content in the furnace is 1.5%~2.1%, the maximum furnace temperature is 1245℃, and the furnace time is 210min;

[0036] (2) Rolling: After the ingot is removed from the heating furnace, it is initially descaled. The descaling high-pressure water pressure is 22 MPa and the descaling speed is 0.8 m / s. The surface temperature of the slab after initial descaling is 1140 °C. The slab is then swung and air-cooled for 150 s before rolling. The surface temperature of each rolling pass and rolled steel plate, the interval time from the last descaling, and whether descaling is performed are shown in Table 3. The reduction rate of the final rolling pass is 4.2%;

[0037] (3) Cooling: After rolling, the steel plate is cooled in air until the surface temperature reaches 700℃, which is lower than the A r1 Temperature (thermal simulation test to obtain the cooling rate under A r1 The temperature is about 703℃); then the steel plate is cooled to 500℃ at a cooling rate of 16.8℃ / s (the thermal simulation test shows that the B s Temperature is about 600℃), then air-cooled, and the time from the time when the surface temperature of the steel plate is measured to the time when it cools to 250℃ is 250s, and even with the accelerated cooling time, it is no more than 600s; no bending straightening is used during the whole cooling process;

[0038] (4) Finishing: Use a flattening machine to flatten the surface, then use flame cutting to trim and cut to size.

[0039] Table 1 Rolling passes, steel plate surface temperature and descaling conditions of Example 1

[0040] .

[0041] Table 2 Rolling passes, steel plate surface temperature and descaling conditions of Example 2

[0042] .

[0043] Table 3 Rolling passes, steel plate surface temperature and descaling conditions of Example 3

[0044] .

Claims

1. A method for producing an atmospheric corrosion resistant steel plate, characterized in that: The weight percentage of steel is C=0.03%~0.08%, Si≤0.60%, Mn=0.50%~1.50%, P≤0.025%, S≤0.005%, Al=0.01%~0.06%, Cu=0.30%~0.60%, Ni=0.30%~1.0%, Cr=0.30%~0.60%, Mo≤0.50%, Ti≤0.03%, Nb≤0.10%, V≤0.10%, the balance is Fe and unavoidable impurity elements; The key process steps include: (1) Heating: Before heating, flame cleaning is used to remove the primary iron oxide scale on the surface of the continuous casting billet, and the removal depth is not less than 2mm; Then use a walking beam heating furnace to heat, control the residual oxygen content in the furnace to ≤2.5%, control the furnace temperature to ≤1250℃, and the furnace time to ≤300min; (2) Rolling: After the ingot is removed from the heating furnace, it is initially descaled. The descaling high-pressure water pressure is ≥22MPa and the descaling speed is ≤1.0m / s. After the initial descaling, the surface temperature of the slab is above 1100℃. Then the slab is swung and air-cooled for 60~180s before rolling. During the rolling process, high-pressure water descaling is performed. The first pass is not descaling, and the second pass is descaling. When the slab surface temperature is higher than 1000℃ or lower than 900℃, descaling is performed every 30~60s. When the slab surface temperature is between 900~1000℃ or the descaling interval is ≥60s, high-pressure water descaling is performed before each rolling pass. (3) Cooling: After rolling, the steel plate is cooled until the surface temperature is lower than A r1 Air cooling is performed before ±5℃. A r1 It is the starting temperature of the transformation of supercooled austenite to pearlite; the steel plate continues to cool and the surface temperature is controlled within the range of 570~250℃ for no more than 600s; no bending straightening is used during the entire cooling process; (4) Finishing: Use flame cutting to trim and cut to size.

2. The method for producing an atmospheric corrosion resistant steel plate according to claim 1, characterized in that: In step (2), when the surface temperature of the slab after initial descaling is between 1150 and 1200°C, the slab is swung in air to cool to a temperature for 1 to 2 minutes; when the surface temperature of the slab after initial descaling is between 1100 and 1150°C, the slab is swung in air to cool to a temperature for 2 to 3 minutes.

3. The method for producing an atmospheric corrosion resistant steel plate according to claim 1, characterized in that: In step (2), the reduction rate of the final rolling pass is controlled to be less than 5%.

4. The method for producing an atmospheric corrosion resistant steel plate according to claim 1, characterized in that: In step (3), the rolled steel plate is air-cooled and then accelerated to a temperature of 5°C / s. B s The following, among which B s is the starting temperature of bainite transformation.

5. The method for producing an atmospheric corrosion resistant steel plate according to claim 1, characterized in that: In step (4), if the plate shape is not good, use a flattening machine to flatten it.

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