Industrial atmospheric corrosion resistant high-strength steel and production method

Abstract

A high-strength steel resistant to industrial atmospheric corrosion, the components and wt% of which are: C: 0.02-0.04%, Si: 0.20-0.30%, Mn: 0.3-0.5%, Cu: 0.1-0.3%, Cr: 1.5-2.0%, Sb: 0.15-0.2%, Nb: 0.02-0.03%, Ti: 0.05-0.08%, P: 0.06-0.09%, S≤0.002%, N: 0.01-0.03%; production method: converter smelting, RH treatment, casting into billets; heating the billets; rough rolling; finish rolling; laminar cooling; coiling and standby. The metallographic structure of the present invention is bainite + pearlite, the grain size is not less than 10, the inclusion level is ≤0.5 level; the yield strength R t0.5 700~750MPa, tensile strength R m 800~860MPa, yield strength ratio R t0.5 / R m ≤0.9, elongation after break A 50mm ≥20%, -20℃ impact energy KV2≥100J, industrial atmospheric corrosion resistance rate is not higher than 15% relative to Q345 steel.

Description

Technical Field

[0001] The invention relates to atmospheric corrosion resistant steel and a production method thereof, in particular to high-strength structural steel resistant to industrial atmospheric corrosion and a production method thereof. Background Art

[0002] my country has many metallurgical, coal-fired power generation, and chemical industrial enterprises, which naturally cause a large amount of acidic gases such as sulfur dioxide and nitrogen dioxide in the atmosphere. However, these acidic gases are highly corrosive to steel materials, which will cause mechanical equipment, steel structure buildings, etc. to fail due to corrosion, resulting in huge economic losses. In order to improve the acidic atmospheric corrosion resistance of steel, domestic and foreign scholars have added an appropriate amount of one or several alloy elements on the basis of ordinary carbon steel to improve the atmospheric corrosion resistance of steel, and developed atmospheric corrosion-resistant steel, also known as weathering steel. Common acidic atmospheric corrosion-resistant steels are mainly 09CuPCrNi and 09CuPTiRe systems, as well as new steels developed on the basis of these two systems by increasing the content of alloy elements such as Cu, Cr, Ni, and Mo. At present, the highest grade of weathering steel specified in the GB / T 4171-2008 "Weathering Structural Steel" standard is Q550NH, with a yield strength of 550MPa, and the highest grade of high weathering steel is Q355GNH, with a yield strength of 355MPa. However, when actually used in industrial atmospheric environments, these steels do not show more obvious corrosion resistance than ordinary carbon steel. The results of laboratory accelerated tests show that the corrosion rate of Q550NH weathering steel relative to ordinary carbon steel Q345 is about 50%, while that of Q355GNH high weathering steel is increased to about 45%. Moreover, as human beings' requirements for low carbon and environmental protection increase, the demand for high-strength and lightweight industrial atmospheric corrosion-resistant steel is growing. Therefore, it is of great significance to improve the strength and industrial atmospheric corrosion resistance of industrial atmospheric corrosion-resistant steel through alloy element blending and organizational control, so as to improve the lightweight rate and service life of weather-resistant structural steel in industrial atmospheric environments.

[0003] After searching: the document with Chinese patent application number CN202210823918.0 discloses "A kind of high-phosphorus high-performance weathering steel without coating and its preparation method and application". The chemical composition includes: C: 0.020%~0.040%, Si: 0.20%~0.30%, Mn: 0.20%~0.30%, Cu: 0.20%~0.60%, P: 0.25%~0.50%, S≤0.01%, Ni: 0.10%~0.15%, Cr: 0.25%~0.55%, and the rest is Fe and unavoidable impurity elements; used in rural atmospheric environment and / or industrial atmospheric environment; using high content of P and Cu to form a passivation film covering the surface of weathering steel, thereby preventing SO in the atmospheric environment 2The invention has a high phosphorus content, and excessive phosphorus has a bad effect on the low temperature toughness and welding performance of the steel plate.

[0004] The document with Chinese patent application number CN202010325456.0 discloses "A 500MPa coating-free weathering steel and its manufacturing method". The chemical composition includes: 0.05wt%≤C≤0.09wt%; 0.2wt%≤Si≤0.35wt%; 1.30wt%≤Mn≤1.50wt%; 0<S≤0.015wt%; 0<P≤0.018wt%; 0.020wt%≤Nb≤0.050wt%; 0.01wt%≤Ti≤0.035wt%; 0.45wt%<Cr≤0.50wt%; 0.30wt%≤Ni≤0.40wt%; 0.30wt%≤Cu≤0.35wt%; 0.1wt%≤Mo≤0.25wt%; 0.02wt%≤Als≤0.05wt%; 0.03wt%≤Sb≤0.05wt%; the rest are iron and other inevitable impurities; it can adapt to the environment of wet heat, dryness, atmosphere, industrial pollution and other environments without painting. This patent adds precious metals such as Ni and Mo, which is not conducive to the large-scale application and promotion of steel plates.

[0005] The document with Chinese patent application number CN201611138247.5 discloses "A low alloy weathering steel and its preparation method and application". The chemical composition and mass percentage content are as follows: C: 0.02-0.05%; Mn: 0.6-1.00%; Cu: 0.20-0.40%; Ni: 0.15-0.50%; Nb: 0.04-0.07%; Ti: 0.005-0.015%; Si: 0.30-0.60%; Al≤0.02%; P≤0.02%; S≤0.08%; the rest is Fe and unavoidable impurities. By increasing the content of low-cost alloying element Si to reduce the amount of higher-cost alloying elements Cr and Ni, the synergistic effect between alloying elements is utilized to reduce the use of high-cost alloying elements, thereby maximizing cost-effectiveness. At the same time, it has good comprehensive mechanical properties and is suitable for application requirements such as bridges in industrial marine atmospheric environments. This patent adds the precious metal Ni, and the addition of higher Si and Mn is not conducive to the steel's resistance to industrial atmospheric corrosion.

[0006] The document with Chinese patent application number CN201110456872.5 discloses "A low-cost all-weather weathering steel". The alloy composition and weight percentage content are: C: 0.12-0.2%, Si: 0.4-0.5%, Mn: 1.2-2.0%, S≤0.02%, P: 0.045-0.075%, Cu: 0.30-0.40%, and the rest is Fe. By alloying Cu, Mn, P, etc., and simply adjusting the content of some elements of ordinary low-carbon steel (Q235 steel), without changing the production process of Q235 steel, low-cost weathering steel with good resistance to coastal atmospheric corrosion, industrial atmospheric corrosion and coastal industrial atmospheric corrosion can be produced. The addition of higher Si and Mn in this patent is not conducive to the steel's resistance to industrial atmospheric corrosion.

[0007] The document with Chinese patent application number CN200610035800.2 discloses "A method for producing 700MPa grade VN microalloyed high-strength atmospheric corrosion resistant steel based on thin slab continuous casting and rolling process". The chemical composition range of molten steel is (wt.%): C: ≤0.08%; Si: 0.25-0.75%; Mn: 0.8-2.0%; P: 0.070-0.150%; S: ≤0.040%; Cu: 0.25-0.60%; Cr: 0.30-1.25wt%; Ni: ≤0.65%; V: 0.05-0.20%; N: 0.015-0.030%. The steel plate can stably obtain high strength, high formability, high weather resistance and good welding performance. The metallurgical composition of the steel is relatively simple, and the alloying production cost is low. It is an ideal plate for the production of containers, railway carriages and industrial facilities that require high weather resistance and strength. However, due to the addition of high Si and Mn in this document, it is not conducive to the steel's resistance to industrial atmospheric corrosion.

[0008] The above literature application did not report its industrial atmosphere resistance performance data. Summary of the invention

[0009] The present invention aims to overcome the shortcomings of the prior art and provide a method for improving the industrial atmospheric corrosion resistance of steel by synergistic action of alloy elements such as Cu, Cr, P, Sb, and N, and adopting Nb and Ti microalloying, combined with controlled rolling and controlled cooling process, to obtain not only the yield strength R t0.5 700~750MPa, tensile strength R m 800~860MPa, yield strength ratio R t0.5 / R m ≤0.9, elongation after break A 50mm ≥20%, -20℃ impact energy KV 2 ≥100J, and its industrial atmospheric corrosion resistance rate is not higher than 15% relative to Q345 steel, and its production method.

[0010] Measures to achieve the above objectives:

[0011] A high-strength steel resistant to industrial atmospheric corrosion, the components and weight percentages of which are: C: 0.02-0.04%, Si: 0.20-0.30%, Mn: 0.3-0.5%, Cu: 0.1-0.3%, Cr: 1.5-2.0%, Sb: 0.15-0.2%, Nb: 0.02-0.03%, Ti: 0.05-0.08%, P: 0.06-0.09%, S≤0.002%, N: 0.01-0.03%, and the rest are Fe and unavoidable impurities; the metallographic structure is bainite + pearlite, the grain size is not less than 10, and the inclusion level is ≤0.5; mechanical properties: yield strength R t0.5 700~750MPa, tensile strength R m 800~860MPa, yield strength ratio R t0.5 / R m ≤0.9, elongation after break A 50mm ≥20%, -20℃ impact energy KV 2 ≥100J, the industrial atmospheric corrosion resistance rate is not higher than 15% relative to Q345 steel.

[0012] Preferably, the weight percentage of Sb is 0.15-0.18%.

[0013] Preferably, the weight percentage of N is 0.013-0.026%.

[0014] Preferably, the weight percentage of P is between 0.063% and 0.086%.

[0015] A method for producing high-strength steel resistant to industrial atmospheric corrosion, comprising the following steps:

[0016] 1) Converter smelting, conventional vacuum calcium treatment, and casting into billets;

[0017] 2) Heat the ingot and control the heating temperature of the ingot to be between 1160 and 1200°C;

[0018] 3) The starting temperature of rough rolling is 1050-1100°C, the ending temperature of rough rolling is 890-950°C, and the total reduction rate is 75-85%;

[0019] 4) The starting temperature of finishing rolling is 860-880°C, the ending temperature of finishing rolling is 800-830°C, the cumulative reduction rate of finishing rolling is not less than 70%, and the steel plate is rolled into 2-10 mm thick steel plate after 5-10 passes;

[0020] 5) performing laminar cooling to 500-600° C. at a cooling rate of 25-30° C. / s;

[0021] 6) Coil up and set aside.

[0022] The functions and mechanisms of various raw materials and main processes in the present invention are:

[0023] Carbon (C): Carbon is the most economical and basic strengthening element. The addition of carbon can reduce the addition amount of other precious alloys, but carbon has a negative impact on the ductility, corrosion resistance and welding performance of steel. Therefore, the carbon content of the present invention is limited to 0.02-0.04%.

[0024] Silicon (Si): Silicon plays a role in deoxidation and solid solution strengthening in steel, but excessive addition of silicon will reduce the plasticity, toughness and weldability of the steel. Therefore, the silicon content of the present invention is limited to 0.20-0.25%.

[0025] Manganese (Mn): Manganese plays a role in solid solution strengthening in steel, compensating for the strength loss caused by low carbon or ultra-low carbon. However, too much manganese can easily cause structural segregation and the formation of MnS inclusions, resulting in reduced mechanical properties and corrosion resistance of the steel. Therefore, the manganese content of the present invention is limited to 0.3-0.4%.

[0026] Copper (Cu): Copper is not only a solid solution strengthening element, but also can significantly improve the performance of steel in resisting industrial atmospheric corrosion. On the one hand, the copper element makes the rust layer show ion selection characteristics to repel anions from corroding the steel substrate. On the other hand, it cooperates with the phosphorus element to make the rust layer more dense and block the corrosive medium, thereby slowing down corrosion. However, too much copper can cause hot brittleness of steel. Therefore, the copper content of the present invention is limited to 0.1-0.3%.

[0027] Chromium (Cr): Chromium can be enriched in the corrosion product film layer, making the α-FeOOH crystals refined, which is conducive to the formation of a dense protective inner rust layer and improving the atmospheric corrosion resistance. However, adding a large amount of chromium will reduce the toughness and welding performance of the steel. The chromium content of the present invention is limited to 1.5% to 2.0%.

[0028] Antimony (Sb): Antimony has a significant effect on improving the corrosion resistance of steel in industrial atmospheres. Antimony generates stable Sb in the rust layer. 2 O 3 , Sb 2 O 5 Oxides promote the conversion of γ-FeOOH in the rust layer into α-FeOOH and Fe 3 O 4 , improve the stability of the rust layer, and improve the compactness and continuity of the rust layer. However, when the Sb addition exceeds 0.2%, the corrosion resistance shows a downward trend. Therefore, the antimony content of the present invention is limited to 0.18-0.2%, and preferably the weight percentage of Sb is 0.15-0.18%.

[0029] Niobium (Nb): Niobium can significantly refine grains and play a role in precipitation strengthening, making steel have high strength and high toughness. Adding niobium to low-alloy steel can effectively improve its corrosion resistance. However, too high niobium is not good for the impact toughness of the weld. Therefore, the niobium content of the present invention is limited to 0.02-0.03%.

[0030] Titanium (Ti): Titanium is beneficial to the deoxidation of steel and reduces inclusions in steel. Titanium can also improve the impact toughness of steel. Titanium is also a corrosion-resistant alloying element. After addition, it can increase the self-corrosion potential of steel and is beneficial to the steel's resistance to industrial atmospheric corrosion. However, when the titanium content exceeds a certain value, the precipitation strengthening effect of TiC will be apparent, reducing the low-temperature toughness of steel. The titanium content of the present invention is limited to 0.05-0.08%.

[0031] Phosphorus (P): On the one hand, phosphorus works synergistically with copper to strengthen the steel's resistance to industrial atmospheric corrosion; on the other hand, after phosphorus is enriched in the rust layer, it has the effect of anode depolarization and stabilizing the rust layer, making the rust layer more dense and stable, and becoming a protective barrier on the steel surface to block chloride ions. However, too high a phosphorus content has a bad effect on the low-temperature toughness and welding performance of the steel plate. Therefore, the present invention controls the phosphorus content to be limited to 0.06-0.09%, preferably: the weight percentage content of P is 0.063-0.086%.

[0032] Sulfur (S): Sulfur is a harmful element in steel. The generated manganese sulfide inclusions will not only reduce the mechanical properties of the steel, but also reduce the steel's resistance to industrial atmospheric corrosion. Therefore, the present invention controls the sulfur content to ≤ 0.002%.

[0033] Nitrogen (N): Nitrogen forms fine dispersed nitrides with elements such as Al, Ti, and Nb in steel, which can refine grains and improve strength on the one hand, and improve corrosion resistance on the other hand. However, it is difficult to add nitrogen in steel smelting, and nitrogen dissolves in ferrite to produce strain aging, reduce the cold workability of steel, and cause embrittlement of the weld affected zone. Therefore, the present invention controls the nitrogen content to 0.01-0.03%, and preferably the weight percentage of N is 0.013-0.026%.

[0034] The present invention adopts a low C, low Si, and low Mn basic component system to reduce structural segregation and inclusions in the steel, improve the cleanliness of the steel, and is beneficial to the mechanical properties and corrosion resistance of the steel. The addition of elements such as Cu, Cr, and P plays a synergistic role. On the one hand, the steel of the present invention has a lower reaction activity in the early stage of corrosion, and on the other hand, it promotes the formation of a dense and stable rust layer on the surface of the steel of the present invention after corrosion. In addition, Sb and N elements are added, which react with corrosive media such as sulfur dioxide and nitrogen dioxide in the industrial atmosphere to generate products with a stable rust layer, further improving the protectiveness of the rust layer. The rust layer formed by the steel of the present invention has a high barrier effect on the penetration of corrosive media such as sulfur dioxide and nitrogen dioxide in the industrial atmosphere, thereby greatly improving the steel's resistance to industrial atmospheric corrosion.

[0035] The present invention treats molten steel with nitrogen and combines niobium and titanium microalloying to form a large number of fine, dispersed non-metallic inclusions, induce ferrite nucleation, and cooperates with TMCP process technology to prepare and a faster cooling rate of 20-25°C / s to finally obtain fine bainite + pearlite structure. Fine bainite structure + pearlite steel has higher strength and toughness, making up for the toughness loss caused by high phosphorus.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] (1) In the prior art, expensive Ni is generally added, and a relatively high content of Cr (>2%) is added to improve the corrosion resistance of the steel. In the present invention, no Ni is added, and the Cr content is relatively low and within the standard range.

[0038] (2) The alloy elements of the present invention, such as Cu, Cr, P, Sb, and N, synergistically improve the corrosion resistance of the steel in the industrial atmosphere, and the corrosion resistance is greatly improved compared with the prior art, that is, compared with the corrosion rate of Q345, the relative corrosion rate of the present invention is reduced from 40% of the existing Q355GNH to no more than 15%. The industrial atmospheric corrosion rate of the present invention does not exceed 30% of the corrosion rate of Q550NH, and does not exceed 37.5% of the corrosion rate of Q355GNH.

[0039] (3) The present invention adopts Nb and Ti microalloying, combined with controlled rolling and controlled cooling process, to obtain a steel with high strength (yield strength R t0.5 700~750MPa, tensile strength R m 800~860MPa), low yield strength ratio (yield strength ratio R t0.5 / R m ≤0.9) and excellent toughness (elongation after fracture A 50mm ≥20%, -20℃ impact energy KV 2≥100J). The maximum yield strength of weathering steel in existing standards is 550MPa. The high-strength steel resistant to industrial atmospheric corrosion of the present invention will greatly reduce the amount of steel used and has good application economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The metallographic structure diagram with inclusions of the present invention;

[0041] Figure 2 It is the metallographic structure diagram of the present invention. DETAILED DESCRIPTION

[0042] The present invention is described in detail below:

[0043] Table 1 is a list of chemical components of various embodiments and comparative examples of the present invention;

[0044] Table 2 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0045] Table 3 is a table of performance test results of various embodiments of the present invention and comparative examples.

[0046] Table 4 is a statistical table of immersion corrosion rates of various embodiments of the present invention and comparative examples.

[0047] Each embodiment of the present invention is produced according to the following steps

[0048] 1) Converter smelting, conventional vacuum calcium treatment, and casting into billets;

[0049] 2) Heat the ingot and control the heating temperature of the ingot to be between 1160 and 1200°C;

[0050] 3) The starting temperature of rough rolling is 1050-1100°C, the ending temperature of rough rolling is 890-950°C, and the total reduction rate is 75-85%;

[0051] 4) The starting temperature of finishing rolling is 860-880℃, the ending temperature of finishing rolling is 800-830℃, and the cumulative reduction rate of finishing rolling is not less than

[0052] 70%, after 5 to 10 passes, it is rolled into 2 to 10 mm thick steel plates;

[0053] 5) performing laminar cooling to 500-600° C. at a cooling rate of 25-30° C. / s;

[0054] 6) Coil up and set aside.

[0055] Table 1 List of values ​​of various embodiments and comparative examples of the present invention (wt%)

[0056]

[0057] Table 2 Process parameters of various embodiments and comparative examples of the present invention

[0058]

[0059]

[0060] Table 3 Statistical table of transverse main mechanical properties of various embodiments of the present invention and comparative examples

[0061]

[0062] Table 4 Statistical table of cyclic immersion corrosion rates of various embodiments of the present invention and comparative examples

[0063]

[0064]

[0065] Note: The 3-day immersion corrosion rate of the embodiment and comparative example was obtained in a solution containing 0.01 mol / L sodium bisulfite according to the TB / T 2375-1993 "Test Method for Periodic Immersion Corrosion of Weathering Steel for Railways". The average corrosion rate of plain carbon steel Q345 is 3.15 mm / a, and the calculation formula of the corrosion rate of the embodiment and comparative example relative to Q345 is: average corrosion rate of the embodiment or comparative example / 3.15 mm / a×100%.

[0066] This specific implementation is only the best example and is not a restrictive implementation of the technical solution of the present invention.

Claims

1. A high-strength steel resistant to industrial atmospheric corrosion, wherein the components and weight percentages are: C: 0.02-0.028%, Si: 0.233-0.30%, Mn: 0.3-0.39%, Cu: 0.16-0.19% or Cu: 0.27-0.30%, Cr: 1.5-2.0%, Sb: 0.15-0.2%, Nb: 0.02-0.03%, Ti: 0.05-0.08%, P: 0.082-0.09%, S≤0.002%, N: 0.015-0.03%, and the rest are Fe and unavoidable impurities; the metallographic structure is bainite + pearlite, the grain size is not less than 10, and the inclusion level is ≤0.5; mechanical properties: yield strength R t0.5 700~750MPa, tensile strength R m 800~860MPa, yield strength ratio R t0.5 / R m ≤0.9, elongation after break A 50mm ≥20%, -20℃ impact energy KV2≥100J, cyclic immersion corrosion rate relative to Q345 steel does not exceed 15%; The cyclic immersion corrosion rate of the industrial atmospheric corrosion resistant high-strength steel is tested according to the standard TB / T 2375-1993 "Test method for periodic immersion corrosion of weathering steel for railway use", and the 3-day cyclic immersion corrosion rate is obtained in a 0.01 mol / L sodium bisulfite solution.

2. The high-strength steel resistant to industrial atmospheric corrosion according to claim 1, characterized in that: The weight percentage of Sb is between 0.15 and 0.18%.

3. A method for producing high-strength steel resistant to industrial atmospheric corrosion as claimed in claim 1, comprising the steps of: 1) Converter smelting, conventional vacuum calcium treatment, and casting into billets; 2) Heat the ingot and control the heating temperature of the ingot to be between 1160 and 1195°C; 3) The starting temperature of rough rolling is 1050-1100°C, the ending temperature of rough rolling is 890-950°C, and the total reduction rate is 75-85%; 4) The starting temperature of finishing rolling is 860-869℃, the ending temperature of finishing rolling is 800-818℃, and the cumulative reduction rate of finishing rolling is not less than 70%. 5~10 passes to roll into 2~10mm thick steel plates; 5) Perform laminar cooling to 565-600°C at a cooling rate of 25.4-30°C / s; 6) Coil up and set aside.

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