A 450mpa grade nickel-free marine atmosphere corrosion resistant steel plate and a production method thereof

Abstract

The application belongs to the technical field of marine atmospheric corrosion resistant steel plate, and discloses a 450MPa grade nickel-free marine atmospheric corrosion resistant steel plate and a production method thereof, which comprises the following chemical components in percentage by weight: C: 0.02-0.04%, Si: 0.20-0.60%, Mn: 0.30-0.80%, P≤0.020%, S≤0.008%, Cu: 0.20-0.65%, W: 0.03-0.25%, Sn: 0.05-0.30%, Ti: 0.03-0.08%, and the rest is iron and inevitable impurities. The application improves the corrosion resistance of the steel through Cu, W and Sn, and inhibits the "copper brittleness" defect caused by the composite addition of Cu and Sn in the steel through Ti, and controls the steel to be a ferrite single-phase structure, so that the steel has good mechanical properties, corrosion resistance, welding performance and cost advantage, the yield strength of the steel is greater than or equal to 450MPa, the tensile strength is 550-750MPa, the elongation is greater than or equal to 22%, the impact energy KV2 at-40℃ is greater than or equal to 60J, and the corrosion rate is only 65% or less of that of SPA-H weathering steel.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of marine atmospheric corrosion resistant steel plate, and particularly relates to a 450MPa grade nickel-free marine atmospheric corrosion resistant steel plate and a production method thereof. BACKGROUND

[0002] The common problem faced by marine engineering steels in the service process is serious corrosion in marine environment. A large number of salt particles are carried in the marine atmosphere. When these salt particles fall on the surface of the steel structure, an electrolyte film is generated due to deliquescence, and the conductivity of the electrolyte is increased and the protective property of the corrosion product is destroyed due to the dissolution of the salt in the liquid film, thereby promoting the microcell reaction of atmospheric corrosion and greatly accelerating the corrosion process.

[0003] In order to delay atmospheric corrosion, the current marine atmospheric corrosion resistant steel usually adds 1-3% of Ni. For example, Japan developed 1.5Ni-Mo series and 2.5Ni series nickel-based high weathering steels, 0.1% Cu-1.0% Ni-0.05% Ti series marine environment corrosion resistant steel plates, 1.5% Ni-0.3% Mo series marine environment corrosion resistant steel plates, etc. Many domestic steel enterprises have also developed 3% Ni series corrosion resistant steels. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a 450MPa grade nickel-free marine atmospheric corrosion resistant steel plate and a production method thereof, which can improve the corrosion resistance of the steel by Cu, W and Sn, inhibit the "copper brittleness" defect of the steel by Ti, and control the steel to be a ferrite single-phase structure, so that the steel has good mechanical properties, corrosion resistance, welding performance and cost advantage.

[0005] To solve the technical problems proposed in the present application, the present application provides a 450MPa grade nickel-free marine atmospheric corrosion resistant steel plate, which has the following chemical composition by weight percentage: C: 0.02-0.04%, Si: 0.20-0.60%, Mn: 0.30-0.80%, P≤0.020%, S≤0.008%, Cu: 0.20-0.65%, W: 0.03-0.25%, Sn: 0.05-0.30%, Ti: 0.03-0.08%, and the rest is iron and inevitable impurities.

[0006] Preferably, the chemical composition of the steel plate includes the following by weight percentage: C: 0.02-0.03%, Si: 0.25-0.45%, Mn: 0.40-0.65%, P≤0.015%, S≤0.005%, Cu: 0.25-0.50%, W: 0.05-0.20%, Sn: 0.05-0.20%, Ti: 0.05-0.08%, and the rest is iron and inevitable impurities.

[0007] In the above scheme, the chemical composition of the steel plate satisfies Ti / C≥1.5 and Ti / (Cu+Sn)≥0.1.

[0008] In the above scheme, the carbon equivalent CEV of the steel plate is ≤0.22%, and the calculation formula of the carbon equivalent CEV is: CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15, wherein C, Mn, Cr, Mo, V, Ni and Cu are the weight percentages of the respective elements.

[0009] In the above scheme, the microstructure of the steel plate is ferrite.

[0010] In the above scheme, the yield strength of the steel plate is ≥450MPa, the tensile strength is 550-750MPa, the elongation is ≥22%, the impact energy KV2 at -40℃ is ≥60J, and the corrosion rate is only 65% or less than that of SPA-H weathering steel.

[0011] The application also provides a production method of the 450MPa-grade nickel-free marine atmosphere corrosion resistant steel plate, which comprises the steps of smelting a casting blank, heating the casting blank, rolling, and cooling.

[0012] In the above scheme, the air excess coefficient is controlled to be 0.80-0.93 when the casting blank is heated, and the heating temperature is 1200-1240℃.

[0013] In the above scheme, the rolling comprises rough rolling and finish rolling, the rough rolling final rolling temperature is 1000-1040℃, the finish rolling initial rolling temperature is ≤940℃, and the finish rolling final rolling temperature is 830-870℃.

[0014] In the above scheme, the cooling adopts two-stage laminar flow cooling, the first stage is cooled to an intermediate temperature of 660-700℃ at a rate of 80-180℃ / s, and the second stage is cooled to a coiling temperature at a rate of 30-80℃ / s.

[0015] Further, air cooling is performed between the first stage and the second stage of the laminar flow cooling, and the air cooling time is ≥10s.

[0016] Further, the coiling temperature is 600-640℃.

[0017] The main alloy element content of the application is based on the following principles:

[0018] C: is a cheap solid solution strengthening element, but too high C will deteriorate the welding performance of the steel, and promote pearlite transformation, thereby reducing the impact toughness and corrosion resistance of the steel. In order to improve the welding performance of the steel, inhibit the formation of pearlite structure, and improve the corrosion resistance and impact toughness of the steel, the C content in the steel of the application is 0.02-0.05%.

[0019] Si: Silicon in steel accelerates carbon to austenite segregation, purify ferrite, avoid the formation of coarse carbide when cooling, while the solid solution of silicon can also improve the corrosion resistance of steel, but too high silicon element will form Fe2SiO4 in high temperature rolling process, increase the adhesion of iron oxide skin, deteriorate the surface quality of steel plate, therefore the Si content range is controlled at 0.20-0.60%.

[0020] Mn: The appropriate amount of Mn is added in steel, which can not only improve the strength of steel through solid solution strengthening of Mn, but also reduce the phase transition temperature of steel, refine the grain, and improve the comprehensive performance of steel. The Mn content in the steel of the present application is designed to be 0.30%-0.80%.

[0021] P, S: Phosphorus in steel has the effect of easily causing segregation, which has a huge damaging effect on the impact toughness and elongation of steel. Sulfur is a harmful element in steel, and the sulfide inclusions generated not only seriously affect the mechanical properties of steel, but also seriously deteriorate the corrosion resistance of steel. However, too low upper limit of P and S will significantly increase the production cost of steel, therefore, P≤0.020%, S≤0.008% in the present application.

[0022] Cu: It is the main element for resisting industrial atmosphere corrosion, and when the content reaches 0.20% or more, it significantly improves the atmospheric corrosion resistance of steel. However, Cu is easy to accumulate on the surface of steel and form a Cu-rich liquid phase that penetrates the austenite grain boundary at high temperatures, reducing the binding force of the austenite grain boundary, and forming "copper brittleness" defects on the surface and edge of the steel plate during rolling. Therefore, the Cu content in the present application is controlled in the range of 0.20-0.65%.

[0023] W: The presence of W can form WC to reduce the C content, increase the pure ferrite area, and improve the corrosion resistance; in addition, the complex carbide of W forms a layer of corrosion-resistant film on the ferrite grain boundary, further improving the corrosion resistance of the steel. However, too high W content will significantly increase the production cost, therefore the W content is designed to be 0.03-0.25%.

[0024] Sn: Sn can form Cu2Sb and SnO2 films on the surface of steel, which are insoluble in water, acid and alkali solutions, improve the rust layer resistance + charge transfer resistance value during corrosion, and form Sn(OH)Cl precipitates in marine atmospheric environment, improve the rust layer density, block the further penetration of erosive Cl - , and improve the corrosion resistance of steel. However, the melting point of Sn is low, which significantly aggravates the "copper brittleness" defects of steel, and deteriorates the surface quality and edge quality of steel plate. In order to minimize the adverse effects of Sn and fully utilize its beneficial effects, the Sn content is designed to be 0.05-0.30%.

[0025] Ti: Ti forms TiC second phase particles in the steel, hinders the growth of austenite grains, significantly refines the austenite grains, increases the austenite grain boundary area, reduces the penetration depth of the Cu and Sn-rich liquid phase on the surface of the steel matrix in the austenite grain boundary, thereby effectively inhibiting the occurrence of the "copper brittleness" defect caused by the combined addition of Cu and Sn in the steel. On the other hand, the addition of Ti plays a certain strengthening role, which can reduce the design value of C under the premise of maintaining the original strength level, and fix C as TiC, further inhibit the transformation of C-rich austenite to pearlite, form a single-phase ferrite structure, avoid the galvanic corrosion formed between different structures in the conventional ferrite-pearlite steel, thereby further improving the corrosion resistance of the steel. In addition, the TiC particles formed by the addition of Ti hinder the grain growth in the heat-affected zone during welding, thereby improving the welding performance of the steel. However, Ti higher than 0.08% can easily lead to tensile strength exceeding the upper limit, therefore, the content of Ti is designed to be 0.03-0.08%, and Ti / C≥1.5 is controlled to inhibit the transformation of pearlite and form a single-phase ferrite structure, and Ti / (Cu+Sn)≥0.1 is controlled to inhibit the "copper brittleness" caused by the combined addition of Cu and Sn.

[0026] CEV: Carbon equivalent can predict the degree of cold cracking (hydrogen-induced cracking) of the steel during welding, the higher the carbon content, the more likely it is to produce cold cracking (hydrogen-induced cracking) during welding. Therefore, the carbon equivalent CEV of the present application is controlled to be ≤0.22%, the hardenability of the steel plate is small, and the steel plate has excellent weldability.

[0027] The technical concept of the main process parameters of the production method of the present application is as follows:

[0028] The positive effect of the air excess coefficient of the billet heating being 0.80-0.93 is to form an appropriate reducing atmosphere, avoid the enrichment of Cu and Sn caused by the excessive oxidation of the surface of the billet, and thereby inhibit the occurrence of the "copper brittleness" defect. When the air excess is less than the range, the combustion of the gas is insufficient, which leads to the content of harmful substances such as CO in the exhaust gas of the heating furnace exceeding the standard; when the air excess coefficient is greater than the range, the surface of the billet is excessively oxidized, which leads to the enrichment of Cu and Sn, and cannot effectively inhibit the occurrence of the "copper brittleness" defect.

[0029] The positive effect of the billet heating temperature being 1200-1240℃ is that the austenitization is sufficient within the temperature range. When the temperature is less than the minimum value of the range, the austenitization of the steel can be insufficient, and when the temperature is greater than the range, the austenite grains can be coarse.

[0030] The final rolling temperature of the rough rolling is 1000-1040℃, which can obtain a uniform and fine structure, when the temperature is less than the range, it is easy to cause the generation of mixed crystals; when the temperature is greater than the range, the structure is relatively coarse.

[0031] The open rolling temperature of finish rolling is less than or equal to 940 DEG C, and the rolling is controlled in the non-recrystallization zone to obtain uniform and fine structure and avoid forming mixed crystal structure in the partial recrystallization zone.

[0032] The finish rolling temperature is 830-870 DEG C, and a lower temperature is adopted in the austenite zone to increase dislocation in the deformed austenite and promote the formation of fine grain transformation structure and improve the strength and toughness.

[0033] After rolling, two-stage laminar flow cooling is adopted. According to the TTT curve, the nose temperature corresponding to the shortest time of ferrite transformation of the composition is about 660-700 DEG C. Therefore, the super-fast cooling technology is adopted to cool at a speed of 80-180 DEG C / s to 660-700 DEG C after rolling, and the ferrite phase transformation occurs rapidly. After the ferrite transformation occurs, the TiC solid solubility drops sharply, and the nanoscale dispersed fine TiC is rapidly precipitated. According to the strip speed, the air cooling time is kept as long as possible, and then water cooling is entered again, and the coiling is carried out at 600-640 DEG C, so that the pearlite transformation can be avoided, and the fine ferrite is obtained.

[0034] Compared with the prior art, the beneficial effects of the present application are:

[0035] The present application mainly improves the corrosion resistance of the steel through the Cu, W and Sn compound, and inhibits the "copper brittleness" defect caused by the compound addition of Cu and Sn in the steel through Ti, and reduces the C content under the premise of ensuring the strength to form TiC combined with C, form ferrite single-phase structure, further improve the corrosion resistance and welding performance, so that the steel plate has good mechanical properties, corrosion resistance, welding performance and cost advantage, the yield strength of the steel plate is greater than or equal to 450 MPa, the tensile strength is 550-750 MPa, the elongation is greater than or equal to 22%, the impact energy A KV at -40 DEG C is greater than or equal to 60 J, and the corrosion rate is only less than or equal to 65% of that of SPA-H weathering steel. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 It is the metallographic microstructure diagram of the steel plate of example 1 of the present application. DETAILED DESCRIPTION

[0037] In order to better understand the present application, the content of the present application will be further illustrated below in combination with examples, but the content of the present application is not limited to the following examples.

[0038] Examples 1-6

[0039] The chemical composition of the 450 MPa grade nickel-free marine atmosphere corrosion resistant steel plate in examples 1-6 is shown in table 1.

[0040] Table 1

[0041]

[0042] The production method of the 450 MPa grade nickel-free marine atmosphere corrosion resistant steel plate in Examples 1-6 is as follows:

[0043] 1) Smelting the cast blank: the molten iron is smelted by converter, refined by LF furnace, and then cast into a blank;

[0044] 2) Heating the cast blank: the air excess coefficient is controlled to be 0.80-0.93, and the heating temperature is 1200-1240℃;

[0045] 3) Rolling: including rough rolling and finish rolling, the rough rolling final rolling temperature is 1000-1040℃, the finish rolling opening rolling temperature is ≤940℃, and the finish rolling final rolling temperature is 830-870℃;

[0046] 4) Cooling: after rolling, two-stage laminar cooling is adopted, the first stage is cooled to an intermediate temperature of 660-700℃ at a rate of 80-180℃ / s, then air-cooled for ≥10s, and then the second stage is cooled to 600-640℃ for coiling at a rate of 30-80℃ / s, to obtain the 450 MPa grade nickel-free marine atmosphere corrosion resistant steel plate.

[0047] Table 2

[0048]

[0049] Comparative Example

[0050] The comparative example is SPA-H weathering steel, and the chemical components include, by weight percentage: C: 0.128%, Si: 0.303%, Mn: 0.53%, P: 0.085%, S: 0.012%, Cu: 0.31%, Cr: 0.42%, Ni: 0.12%, and the carbon equivalent CEV=0.33%.

[0051] The mechanical properties of the steels in Examples 1-6 and the comparative example are tested, and the cyclic immersion corrosion test is carried out according to TB / T 2375-1993 "Railway Weathering Steel Cyclic Immersion Corrosion Test Method", and the test parameters are set as follows: the immersion solution is 3.5% NaCl solution by mass fraction, the temperature is 45±2℃, the humidity is 70±5%, the test time is 72h, and the corrosion resistance of the tested steel is tested. The results are shown in Table 3.

[0052] Table 3

[0053]

[0054] Table 3 shows that the yield strength of the steel of the embodiment of the present application is greater than or equal to 450 MPa, the tensile strength is 550-750 MPa, the elongation is greater than or equal to 22%, and the impact energy KV2 at-40℃ is greater than or equal to 60 J, which shows excellent mechanical properties, especially good toughness and plasticity, and the overall performance is better than that of the ordinary SPA-H weathering steel; and the corrosion rate in a 3.5% NaCl solution is significantly lower than that of the ordinary SPA-H weathering steel, and is only 65% or less of that of the SPA-H weathering steel, which shows that the corrosion resistance is significantly improved compared with the ordinary SPA-H weathering steel. In summary, the steel of the present application has good mechanical properties, corrosion resistance, welding performance and cost advantage.

[0055] The above embodiments are merely examples for clearly illustrating but not limiting the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art, and all the embodiments do not need to be exhausted here, and thus the obvious changes or variations still fall within the protection scope of the present application.

Claims

1. A 450MPa grade nickel-free marine atmospheric corrosion resistant steel plate, characterized in that: Its chemical composition by weight percentage includes: C: 0.02~0.04%, Si: 0.20~0.60%, Mn: 0.30~0.80%, P≤0.020%, S≤0.008%, Cu: 0.20~0.65%, W: 0.03~0.25%, Sn: 0.05~0.30%, Ti: 0.038~0.08%, and the rest is iron and inevitable impurities; among which, Ti / C ≥1.5, Ti / (Cu+Sn) ≥0.1; The metallographic structure of the steel plate is ferrite, with a yield strength of ≥450 MPa, a tensile strength of 550-750 MPa, an elongation of ≥22%, an impact energy KV2 of ≥60 J at -40°C, and a corrosion rate of less than 65% of that of SPA-H weathering steel; The production method of the 450MPa grade nickel-free marine atmospheric corrosion-resistant steel plate comprises the following steps: Rolling: including rough rolling and finishing rolling, the rough rolling finishing temperature is 1000~1040℃, the finishing rolling start temperature is ≤940℃, and the finishing rolling finishing temperature is 830~870℃; Cooling: After rolling, two-stage laminar cooling is adopted. The first stage is cooled at a rate of 80~180℃ / s to an intermediate temperature of 660~700℃, and the second stage is cooled at a rate of 30~80℃ / s to 600~640℃ for coiling.

2. The 450MPa grade nickel-free marine atmospheric corrosion resistant steel plate according to claim 1, characterized in that: The chemical composition of the steel plate includes, by weight percentage, C: 0.02-0.03%, Si: 0.25-0.45%, Mn: 0.40-0.65%, P≤0.015%, S≤0.005%, Cu: 0.25-0.50%, W: 0.05-0.20%, Sn: 0.05-0.20%, Ti: 0.05-0.08%, and the rest is iron and unavoidable impurities.

3. The 450MPa grade nickel-free marine atmospheric corrosion resistant steel plate according to claim 1, characterized in that: The carbon equivalent CEV of the steel plate is ≤0.22%.

4. A method for producing a 450 MPa grade nickel-free marine atmosphere corrosion resistant steel plate according to any one of claims 1 to 3, characterized in that: The following steps are involved: 1) Smelting and casting: The molten iron is smelted in a converter and refined in a LF furnace before being cast into billets; 2) Billet heating: heating temperature 1200~1240℃; 3) Rolling: including rough rolling and finishing rolling, the rough rolling finishing temperature is 1000~1040℃, the finishing rolling start temperature is ≤940℃, and the finishing rolling finishing temperature is 830~870℃; 4) Cooling: After rolling, two-stage laminar cooling is adopted. The first stage is cooled at a rate of 80~180℃ / s to an intermediate temperature of 660~700℃, and the second stage is cooled at a rate of 30~80℃ / s to 600~640℃ for coiling to obtain 450MPa grade nickel-free marine atmospheric corrosion resistant steel plate.

5. The method for producing a 450MPa grade nickel-free marine atmospheric corrosion resistant steel plate according to claim 4, characterized in that: When the slab is heated, the excess air coefficient is controlled to be 0.80-0.

93.

6. The method for producing a 450MPa grade nickel-free marine atmospheric corrosion resistant steel plate according to claim 4, characterized in that: Air cooling is performed between the first section and the second section of the laminar cooling, and the air cooling time is ≥10s.

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