CN111101068A - Low-nickel-content atmospheric corrosion resistant steel and preparation method thereof - Google Patents
Low-nickel-content atmospheric corrosion resistant steel and preparation method thereof Download PDFInfo
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C22C33/06—Making ferrous alloys by melting using master alloys
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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Abstract
The invention discloses low-nickel-content atmospheric corrosion resistant steel and a preparation method thereof, wherein the low-nickel-content atmospheric corrosion resistant steel consists of C, Si, Mn, S, P, Cu, Al, Ni, Cr, Ca, N, Fe and other inevitable impurities, is strengthened by adding low-nickel elements and other microalloy elements in a composite manner, can achieve the purpose of improving the corrosion resistance of the steel through reasonable proportioning, and meanwhile, has excellent forming performance, cold bending performance, welding performance and the like, and can reduce the cost.
Description
Technical Field
The invention relates to the technical field of steel preparation, and particularly provides low-nickel-content atmospheric corrosion resistant steel and a preparation method thereof.
Background
In general, corrosion of metals under natural environmental conditions is referred to as atmospheric corrosion, and thus steels that are resistant to corrosion under natural environmental conditions are referred to as atmospheric corrosion resistant steels. The atmospheric corrosion resistant steel is a low-cost low-alloy steel having corrosion resistance superior to that of ordinary carbon steel in the atmosphere and containing only a small amount of alloying elements (Cu, P, Cr, Ni, Mo, Nb, RE … …, etc.) of several percent. Such as: the container is exposed to the atmosphere for long-term operation, atmospheric corrosion is one of the main reasons for container damage, the container made of common carbon steel has poor atmospheric corrosion resistance and short service life, maintenance is required when the container is operated for two or half years, overhaul is required for five years, and the adoption of the atmospheric corrosion resistant steel is an effective measure for prolonging the service life of the container.
The rust layer structure of the weather-resistant steel is divided into two layers, the outer rust layer is continuous and compact α -FeOOH and gamma-FeOOH, the inner rust layer is an amorphous delta-FeOOH layer (stable rust layer) rich in alloy elements such as Cu and P, and the inner rust layer and the outer rust layer are both provided with Fe3O 4.
In order to achieve the purpose of corrosion resistance, 0.15-0.25% of Ni is added into the conventional corrosion-resistant steel, and Cu, Cr, P, RE, Mo and the like are added in a compounding manner, so that the manufacturing cost of an enterprise is increased, the production profit is reduced, particularly, the competition is very strong in the domestic steel market at present, the profit of the enterprise is greatly compressed, and the survival crisis is faced in many cases, so that research and development of alternative materials capable of meeting the actual production manufacturing and performance requirements of containers and other corrosion-resistant structural members and the like are urgently needed to reduce the production cost of the enterprise.
Disclosure of Invention
In view of the above, the invention aims to provide low-nickel-content atmospheric corrosion resistant steel and a preparation method thereof, so as to solve the problems of high cost, poor formability and weldability, easy generation of copper brittleness defect, poor obdurability matching and the like of the conventional corrosion resistant steel.
The invention provides low-nickel-content atmospheric corrosion resistant steel, which comprises the following components in percentage by mass: c: 0.06-0.12%, Si: 0.20 to 0.50%, Mn: 0.30-0.50%, S: 0.001-0.005%, P: 0.07 to 0.12%, Cu: 0.20-0.60%, Al: 0.015 to 0.06%, Ni: 0.03-0.10%, Cr: 0.30-0.70%, Ca: 0.0010-0.0050%, N: 0.0010-0.0060% and the balance of Fe and other inevitable impurities.
The invention also provides a preparation method of the low-nickel-content atmospheric corrosion resistant steel, which comprises the following steps:
1) pretreatment of molten iron
Pretreating molten iron to ensure that the mass ratio of S in the molten iron fed into the converter is less than or equal to 0.003 percent, and feeding the molten iron into the converter after completely slagging off;
2) smelting in a converter
Smelting refined scrap steel and molten iron; the converter draws carbon for one time, and avoids point blowing; the steel tapping adopts ferrosilicon, high manganese, ferrochromium and nickel-copper alloy, the argon of the steel ladle is swept before the steel tapping, the steel tapping hole is controlled, the free flow is avoided, and the mass content of Al in the steel ladle is 0.015-0.030%; the mass content of N in the steel ladle is less than or equal to 0.0030 percent;
3) LF refining
The LF treatment process keeps micro-positive pressure, and the N increase amount is less than or equal to 10 ppm; the LF adopts active lime and fluorite to produce reducing slag, controls the argon blowing strength and avoids the exposure of molten steel; calcium treatment is carried out by adopting calcium silicate wires, and 400-500 m CaSi wires are fed, so that inclusions are fully spheroidized, and the product performance is improved;
4) continuous casting
Protective pouring is carried out in the whole process, argon is adopted to purge the tundish before pouring, no molten steel is exposed in the pouring process, N is strictly controlled to be absorbed at a water port, and the increase of N is controlled to be less than or equal to 5 ppm; high-alkalinity slag inclusion is adopted to facilitate the removal of inclusions in steel; the constant drawing speed is kept in the steel casting process; the control target of the continuous casting superheat degree is not more than 30 ℃;
5) heating in a furnace
The tapping temperature is 1150-1220 ℃, and the heating time is more than or equal to 150 minutes;
6) hot continuous rolling, rolling and coiling to obtain the target steel
Selecting a 3+3 mode for control in the rough rolling pass; the finishing temperature is as follows: more than or equal to 860 ℃; the coiling temperature is more than or equal to 500 ℃, and the cooling mode adopts the rear-end continuous mode.
Preferably, in the step 4), the steel casting process is performed under a soft reduction function.
Further preferably, in the step 5), the atmosphere and the temperature rise speed in the furnace are controlled, when the temperature of the slab reaches the copper melting point, the gas amount is increased, the temperature rise speed is increased, and the high-temperature in-furnace time is shortened, so that the enrichment of Cu on the grain boundary and the slab surface is reduced.
Further preferably, in the step 5), the tapping temperature is 1170-1210 ℃.
More preferably, the step 6) further comprises the step of performing small scale removal after the F1 and F2 machines.
Further preferably, in the step 6), the finish rolling compression ratio is more than or equal to 3.5, so that the metallographic structure and the physical property of a finished product are improved, and the product quality is improved.
The low-nickel-content atmospheric corrosion resistant steel provided by the invention is mainly used for manufacturing containers, railway vehicles, bridges, ships, automobiles, boilers, buildings and the like.
The low-nickel-content atmospheric corrosion resistant steel provided by the invention is reinforced by adding the low-nickel element and other microalloy elements in a composite manner, and simultaneously, the elements are controlled according to the proportion, so that the aim of improving corrosion resistance can be achieved, and the specific embodiment is as follows:
1) reducing the conductivity of the rust layer, and precipitating and covering the surface of the steel by the rust layer;
2) the phase structure and the variety of the rust layer are influenced, and the growth of the rust layer is hindered;
3) delaying rust crystallization;
4) accelerating the uniform dissolution of steel;
5) the alloying elements and their compounds block cracks and defects.
The low-nickel-content atmospheric corrosion resistant steel provided by the invention also has excellent forming performance, cold bending performance, welding performance and the like.
The steel comprises the following chemical element components in content ranges and functions:
c: c is the most economic strengthening element in low-carbon steel, but the plasticity and impact toughness of the steel are reduced and the cold forming performance and the welding performance are deteriorated due to the excessively high content of C, so the content of C in the steel is reduced as much as possible on the premise of ensuring the strength, and the content of C is controlled within 0.12 wt%.
Cu: cu is the most outstanding element for improving the weather resistance of steel, and plays a role in activating a cathode in the atmospheric corrosion process, so that an anode is passivated, the corrosion speed is reduced, the uniform dissolution of steel and the oxidation speed of Fe2+ can be accelerated, the generation of a uniform gamma-FeOOH rust layer and the conversion of the gamma-FeOOH rust layer to amorphous delta-FeOOH are promoted, a compact protective film is formed and is enriched in the protective film, and the corrosion resistance effect is achieved.
Cu has the obvious effect of counteracting the harmful effect of sulfur in low-carbon steel. Has the advantages that: the higher the sulfur content in the steel, the more pronounced the relative effect of Cu on reducing the corrosion rate. The corrosion of the steel with higher sulphur content is higher than that of the steel with lower sulphur content, and when the Cu content is increased to 0.3 wt%, the corrosion of the two kinds of steel with sulphur content is reduced to the same level.
Cu is also a solid solution strengthening element, which can improve the strength of steel.
The Cu is hot brittle, when the continuous casting billet is heated in a furnace, oxidizing gas and steel materials generate oxidation reaction, so that the iron content of the surface layer is reduced, the Cu content is relatively increased until the Cu content exceeds the solubility in iron, and the Cu is dispersed along a grain boundary after being precipitated to form a network-shaped Cu-rich phase. As the heating temperature of the steel material is higher than the melting point (1083 ℃) of Cu, the Cu-rich phase is in a molten state, and when the Cu-rich phase reaches a certain degree, surface cracking is caused in the hot rolling process, and a Cu brittle crack defect is formed. In order to improve the quality of the weathering steel sheet, certain measures must be taken to prevent the occurrence of such defects. The corrosion resistance of the steel under an acid environment can be improved by adding a certain amount of Cu into the steel, the Cu has an obvious effect of offsetting the harmful effect of S in the steel, the content of S in the steel is higher, the relative effect of reducing the corrosion rate of the alloy element Cu is more obvious, and the hot workability of the steel is reduced by adding Cu, so that the content of Cu is limited within the range of 0.20-0.60 wt%.
P: p is an element capable of improving the weather resistance of steel, and in an electrolyte solution formed on the surface of the steel, the P can promote the uniform dissolution of the steel, avoid pitting corrosion, contribute to forming a uniform rust layer on the surface of the steel and promote the formation of an amorphous hydroxyl compact protective film. Meanwhile, under the high temperature condition, the P inevitably generates the 'upslope diffusion' effect on the surface layer, and the depth and the concentration of the P-rich layer diffused in the upslope are continuously increased along with the increase of the heating temperature and the extension of the heat preservation time, so that the catalytic action on the amorphous layer is improved, the content of the P in the steel substrate is reduced, and the harmful action of the P is reduced. The P content of the weathering steel is controlled to be more than 0.07-0.12 wt%.
Cr can form a compact oxide film on the surface of steel, improves the passivation capability of the steel, and has a particularly obvious effect when Cr and Cu are added into the steel at the same time, the Cr content is improved to facilitate refining α -FeOOH, when the Cr content in α -FeOOH of a rust layer/metal interface exceeds 5%, corrosive anions, particularly Cl ions, can be effectively inhibited from invading, and simultaneously, the Cr element is added to prevent the conversion of Fe3+ to Fe2+ in the dry-wet alternating process, so that the corrosion resistance of the steel is improved.
Ni: by adopting low nickel-copper composite reinforcement, copper-nickel compounds with higher melting points can be generated among the crystals, the Cu enrichment layer on the surface of the steel is converted into the Cu-Ni enrichment layer, the melting point is increased to over 1200 ℃ from 1083 ℃, and the defect of 'Cu brittleness' can be effectively prevented. The preferable Ni content of the invention is 0.03-0.10 wt%.
Si: si is generally added as a deoxidizer, and can improve the strength of the steel material, and Si forms a corrosion-resistant coating in the atmospheric environment, thereby improving the corrosion resistance of the steel. The addition of more than 0.5 wt% lowers the toughness of the steel, so that the present invention controls the Si content to 0.20 to 0.50 wt%.
Ca: the trace Ca is added into the atmospheric corrosion resistant steel to improve the overall corrosion resistance of the steel and effectively avoid the phenomenon of rust liquid sagging during use. The addition of a trace amount of Ca into the steel can form CaO and CaS which are dissolved in a thin electrolyte film on the surface of the steel, so that the alkalinity of a corrosion interface is increased, the corrosivity of the corrosion interface is reduced, and the conversion of a rust layer into a compact protective coating with good protection is promoted. The invention controls the content of Ca at 0.0010-0.0050 wt%.
S: the S content and the form of the sulfide are main factors affecting the moldability, and the greater the amount of the sulfide, the longer the size, and the less favorable the moldability. It is well known that plastic deformation of metals is always accompanied by crack formation and propagation processes, and that if there is a sharp interface of sulfide inclusions with the matrix on the propagating crack surface, the sulfide strongly promotes crack propagation leading to the formation of macrocracks. On the other hand, the sulfides generally have good deformability and are elongated into strips or chains during rolling, the existence of such elongated inclusions causes anisotropy of the mechanical properties of the strip, and the data indicate that a major part (about 80%) of the anisotropy of the strip is caused by the deformed sulfides, and the remaining 20% is caused by the elongated strip structure during rolling deformation. The key to improve the formability of SPA-H steel is to reduce the sulfur content as much as possible, and the invention controls the S content to 0.0010-0.0050 wt%. .
Al: al is an element added in steel as a deoxidizer, a certain amount of aluminum is added into molten steel, aluminum and oxygen react to generate aluminum oxide under the condition of high temperature, the aluminum oxide floats on the surface of the molten steel in the form of residues, and then the residues are removed to control the oxygen content in the molten steel, thereby playing an important role in reducing impurities in the steel and improving the quality of the steel. In the invention, the content range of Al is controlled to be 0.015-0.060 wt%.
N: the addition of N in the steel smelting is beneficial to removing harmful gas impurities and mechanical impurities generated in the steel smelting, the steel performance is improved, and the steel quality is improved, however, if the content of N is too high, the impact toughness of the steel is influenced, so the content of N is controlled to be 0.0010-0.0060 Wt%.
The low-nickel atmosphere corrosion resistant steel provided by the invention is a special steel developed for containers and other corrosion resistant structural members. The steel is a novel material which is in contact with the atmosphere for a long time, the salt spray accelerated corrosion test (relative to Q235B) is less than or equal to 60 percent, the strength index of the material reaches the index of the original atmospheric corrosion resistant steel, and the atmospheric corrosion resistant passivation coating on the surface of the material is slightly damaged. The manufacturing cost of the steel is far lower than that of the original atmospheric corrosion resistant steel, the steel can meet the technical performance requirements when being applied to containers and other corrosion resistant structural members, the manufacturing cost of enterprises can be reduced, the economic benefits of related industries are improved, and the development and scientific and technical progress of container industries are promoted. Meanwhile, the consumption of expensive metal nickel can be saved, a large amount of cost is saved, and the environmental pollution and energy consumption caused by non-ferrous metallurgy are reduced.
The low-nickel-content atmospheric corrosion resistant steel and the preparation method thereof have the advantages that:
(1) in the aspect of chemical component design, the low nickel content is added, the molten steel is pure, and the cost is saved on the basis of ensuring excellent performance;
(2) atmospheric corrosion resistance, and meets the use requirements of users;
(3) on the aspect of mechanical property, each index meets the requirement, and the margin is sufficient;
(4) in the aspect of plate shape control, measures such as reasonable higher heating temperature, higher coiling temperature and the like are adopted in the preparation method to ensure that the plate shape is excellent.
The effects are as follows:
(1) the special steel with low nickel content and atmospheric corrosion resistance produced by the process completely meets the use requirements of users with excellent performance and good plate shape and quality;
(2) the low-nickel-content atmospheric corrosion resistant special steel produced by the technology reduces the cost of enterprises, embodies higher finished product quality and yield and has good economic benefit;
(3) the general institute of iron and steel verifies that the atmospheric environment exposure test and the salt spray corrosion test of the low-nickel-content atmospheric corrosion resistant steel are good, the technical specification requirements are met, and the use requirements of users are met.
Detailed Description
The invention will be further explained with reference to specific embodiments, without limiting the invention.
The invention provides low-nickel-content atmospheric corrosion resistant steel which comprises the following components in percentage by mass: c: 0.06-0.12%, Si: 0.20 to 0.50%, Mn: 0.30-0.50%, S: 0.001-0.005%, P: 0.07 to 0.12%, Cu: 0.20-0.60%, Al: 0.015 to 0.06%, Ni: 0.03-0.10%, Cr: 0.30-0.70%, Ca: 0.0010-0.0050%, N: 0.0010-0.0060% and the balance of Fe and other inevitable impurities.
The invention also provides a preparation method of the low-nickel-content atmospheric corrosion resistant steel, which comprises the following steps:
1) pretreatment of molten iron
Pretreating molten iron to ensure that the mass ratio of S in the molten iron fed into the converter is less than or equal to 0.003 percent, and feeding the molten iron into the converter after completely slagging off;
2) smelting in a converter
Smelting refined scrap steel and molten iron; the converter draws carbon for one time, and avoids point blowing; the steel tapping adopts ferrosilicon, high manganese, ferrochromium and nickel-copper alloy, the argon of the steel ladle is swept before the steel tapping, the steel tapping hole is controlled, the free flow is avoided, and the mass content of Al in the steel ladle is 0.015-0.030%; the mass content of N in the steel ladle is less than or equal to 0.0030 percent;
3) LF refining
The LF treatment process keeps micro-positive pressure, and the N increase amount is less than or equal to 10 ppm; the LF adopts active lime and fluorite to produce reducing slag, controls the argon blowing strength and avoids the exposure of molten steel; calcium treatment is carried out by adopting a calcium-silicon wire, and a CaSi wire is fed for 400-500 m, preferably 450 m, so that inclusions are fully spheroidized, and the product performance is improved;
4) continuous casting
Protective pouring is carried out in the whole process, argon is adopted to purge the tundish before pouring, no molten steel is exposed in the pouring process, N is strictly controlled to be absorbed at a water port, and the increase of N is controlled to be less than or equal to 5 ppm; high-alkalinity slag inclusion is adopted to facilitate the removal of inclusions in steel; the constant drawing speed is kept in the steel casting process; the control target of the continuous casting superheat degree is not more than 30 ℃; preferably, the steel casting process has the function of soft reduction; the continuous casting billet is subjected to hot conveying and hot charging, and the residual slab is placed in a slow cooling area in a warehouse;
5) heating in a furnace
The tapping temperature is 1150-1220 ℃, the target tapping temperature is 1170-1210 ℃, and the heating time is more than or equal to 150 minutes;
6) hot continuous rolling, rolling and coiling to obtain the target steel
Selecting a 3+3 mode for control in the rough rolling pass; load distribution of a finish rolling model is well done, and rolling stability is guaranteed; the finishing temperature is as follows: more than or equal to 860 ℃; the coiling temperature is more than or equal to 500 ℃, the cooling mode adopts the rear-stage continuity, wherein, the medium-high temperature coiling can obtain fine and uniform tissues, and according to the actual condition of the surface of the strip steel, the strip steel can be selectively thrown into F1 and F2 machines for small scale removal.
The continuous casting billet is subjected to hot conveying and hot charging, and the surface quality of the casting billet is strictly checked during charging. As the steel contains Cu, in order to prevent the finished product plate from edge rolling and cracking caused by cracking of the surface of a casting blank during heating, as an improvement of the technical scheme, in the step 5), the atmosphere in the furnace and the heating speed are controlled, when the temperature of the plate blank reaches 1083 ℃ of the melting point of copper, the coal gas amount is increased, the heating speed is accelerated, the high-temperature in-furnace time is shortened, the enrichment of Cu on the crystal boundary and the surface of the blank is reduced, the heating time is averagely more than 2 hours and 30 minutes, the tapping temperature is 1150-1220 ℃, and the target tapping temperature is 1210-1210 ℃.
As an improvement of the technical scheme, in the step 6), the finish rolling compression ratio is more than or equal to 3.5, so that the metallographic structure and the physical property of a finished product are improved, and the product quality is improved.
The rust layer on the surface of the low-nickel-content atmospheric corrosion resistant steel provided by the invention generally needs more than 2 years, the low-nickel-content atmospheric corrosion resistant special steel generates the same corrosion as common carbon steel in the initial corrosion stage, the advantage is not large, holes and cracks exist in the rust layer, so that a corrosion medium is easy to permeate, the corrosion medium is directly contacted with a matrix, and the corrosion is accelerated, so that the corrosion rates of the carbon steel in the initial corrosion stage and the low-nickel-content weathering steel are both large. With the progress of corrosion, the alloying elements in the low nickel content atmosphere corrosion resistant steel gradually act: reducing the conductivity of the rust layer, and precipitating and covering the surface of the steel by the rust layer; inhibiting the growth of rust layer and postponing the crystallization of rust; accelerating the uniform dissolution of steel and hindering the rapid growth of corrosion products, accelerating the healing of defects, blocking the channel of a corrosion medium directly contacting with a substrate, densifying a rust layer, controlling the diffusion of the corrosion process, reducing the corrosion speed and finally forming a stable inner and outer rust layer.
The production process of the low-nickel-content atmospheric corrosion resistant steel provided by the invention adopts low-nickel-copper composite reinforcement, so that a copper-nickel compound with a higher melting point can be generated between crystals, a Cu enrichment layer on the surface of the steel is converted into a Cu-Ni enrichment layer, the melting point is increased to over 1200 ℃ from 1083 ℃, and the defect of 'Cu brittleness' can be effectively prevented.
In addition, Cr and Ni elements reduce the carbon content of eutectoid points and improve the stability of super-cooled austenite, so that more and finer pearlite can be obtained by the steel at the same cooling speed, and the strength of the steel is improved.
The low-nickel-content atmospheric corrosion resistant steel has the advantages that the price is far lower than that of the traditional atmospheric corrosion resistant steel, and the atmospheric corrosion resistant steel has the characteristic of atmospheric corrosion resistance.
The thickness of the special steel provided by the invention is preferably 1.2 mm-12.0 mm, the width is preferably 900 mm-2150 mm, and the special steel can be widely applied to container bodies and other corrosion-resistant structural members. Can effectively prevent the parts directly contacted with the container body and other corrosion-resistant structural parts from being corroded.
Example 1
Preparing the low-nickel-content atmospheric corrosion resistant steel according to the following mass percentages: c: 0.06-0.12%, Si: 0.20 to 0.50%, Mn: 0.30-0.50%, S: 0.001-0.005%, P: 0.07 to 0.12%, Cu: 0.20-0.60%, Al: 0.015 to 0.06%, Ni: 0.03-0.10%, Cr: 0.30-0.70%, Ca: 0.0010-0.0050%, N: 0.0010-0.0060% and the balance of Fe and other inevitable impurities.
The preparation method comprises the following steps:
1) pretreatment of molten iron
Pretreating molten iron to ensure that the mass of S in the molten iron fed into the converter is less than or equal to 0.003 percent, and feeding the molten iron into the converter after slagging off and slag removing;
2) smelting in a converter
Smelting refined scrap steel and molten iron; the converter draws carbon for one time, and avoids point blowing; the steel tapping adopts ferrosilicon, high manganese, ferrochromium and nickel-copper alloy, the argon of the steel ladle is swept before the steel tapping, the steel tapping hole is controlled, the free flow is avoided, and the mass content of Al in the steel ladle is 0.015-0.030%; the mass content of N in the steel ladle is less than or equal to 0.0030 percent;
3) LF refining
The LF treatment process keeps micro-positive pressure, and the N increase amount is less than or equal to 10 ppm; the LF adopts active lime and fluorite to produce reducing slag, controls the argon blowing strength and avoids the exposure of molten steel; calcium treatment is carried out by adopting a calcium-silicon wire, and a CaSi wire is fed for 450 meters, so that inclusions are fully spheroidized, and the product performance is improved;
4) continuous casting
Protective pouring is carried out in the whole process, argon is adopted to purge the tundish before pouring, no molten steel is exposed in the pouring process, N is strictly controlled to be absorbed at a water port, and the increase of N is controlled to be less than or equal to 5 ppm; high-alkalinity slag inclusion is adopted to facilitate the removal of inclusions in steel; the soft reduction function is put into the steel casting process; the constant drawing speed is kept in the steel casting process; controlling the superheat degree of continuous casting to be not more than 30 ℃, carrying out hot overheating loading on the plate blank, and placing the rest plate blank in a slow cooling area in a warehouse;
5) heating in a furnace
The tapping temperature is 1150 ℃, the heating time is 150 minutes, the alloying elements can be fully ensured to be melted, so that the high-strength steel has better product of strength and elongation and good plate shape during rolling, the requirements of the rolling process are met, the furnace chamber atmosphere of the heating furnace is controlled, the generation of casting blank iron scale is reduced, the heating temperature is ensured to be uniform, and a foundation is provided for ensuring the plate shape;
6) hot continuous rolling, rolling and coiling to obtain the steel plate
Selecting a 3+3 mode for control in the rough rolling pass; adjusting the load distribution of the finish rolling model to ensure the rolling stability; the finishing temperature is as follows: 860 ℃; the coiling temperature is 500 ℃, a fine and uniform tissue can be obtained, and a sixth group of opening cooling and intermittent cooling modes are adopted in a cooling mode; selectively throwing the steel strip into an F1 machine or an F2 machine for small scale removal according to the actual condition of the surface of the steel strip; meanwhile, the control of the cooling water amount between the racks is optimized and adjusted, wherein in the step 6), the finish rolling compression ratio is more than or equal to 3.5, the metallographic structure and the physical property of the steel can be improved, and the quality of a final product is improved;
example 2
Preparing the low-nickel-content atmospheric corrosion resistant steel according to the following mass percentages: c: 0.06-0.12%, Si: 0.20 to 0.50%, Mn: 0.30-0.50%, S: 0.001-0.005%, P: 0.07 to 0.12%, Cu: 0.20-0.60%, Al: 0.015 to 0.06%, Ni: 0.03-0.10%, Cr: 0.30-0.70%, Ca: 0.0010-0.0050%, N: 0.0010-0.0060% and the balance of Fe and other inevitable impurities.
The preparation method differs from example 1 in that:
in the step 5), the tapping temperature is 1220 ℃, and the heating time is 180 minutes;
in step 6), the finish rolling temperature: 900 ℃; coiling temperature: at 550 ℃.
The steel having the composition in the target range (SPAH-D) obtained in examples 1 and 2 and conventional atmospheric corrosion resistant steel Q235 were subjected to atmospheric environment exposure test and salt spray corrosion test by the iron and Steel research institute, and the test results are shown in tables 1 and 2.
TABLE 1 results of atmospheric exposure test (0.5 years)
Table 2: salt spray corrosion test results
And (4) conclusion: according to analysis of results of an atmospheric environment exposure test and a salt spray corrosion test, the low-nickel-content atmospheric corrosion resistance of the invention has higher corrosion resistance compared with Q235.
Claims (7)
1. The low-nickel-content atmospheric corrosion resistant steel is characterized by comprising the following components in percentage by mass: c: 0.06-0.12%, Si: 0.20 to 0.50%, Mn: 0.30-0.50%, S: 0.001-0.005%, P: 0.07 to 0.12%, Cu: 0.20-0.60%, Al: 0.015 to 0.06%, Ni: 0.03-0.10%, Cr: 0.30-0.70%, Ca: 0.0010-0.0050%, N: 0.0010-0.0060% and the balance of Fe and other inevitable impurities.
2. The method for preparing the low-nickel-content atmospheric corrosion resistant steel as claimed in claim 1, characterized by comprising the following steps:
1) pretreatment of molten iron
Pretreating molten iron to ensure that the mass ratio of S in the molten iron fed into the converter is less than or equal to 0.003 percent, and feeding the molten iron into the converter after completely slagging off;
2) smelting in a converter
Smelting refined scrap steel and molten iron; the converter draws carbon for one time, and avoids point blowing; the steel tapping adopts ferrosilicon, high manganese, ferrochromium and nickel-copper alloy, the argon of the steel ladle is swept before the steel tapping, the steel tapping hole is controlled, the free flow is avoided, and the mass content of Al in the steel ladle is 0.015-0.030%; the mass content of N in the steel ladle is less than or equal to 0.0030 percent;
3) LF refining
The LF treatment process keeps micro-positive pressure, and the N increase amount is less than or equal to 10 ppm; the LF adopts active lime and fluorite to produce reducing slag, controls the argon blowing strength and avoids the exposure of molten steel; calcium treatment is carried out by adopting calcium silicate wires, and 400-500 m CaSi wires are fed, so that inclusions are fully spheroidized, and the product performance is improved;
4) continuous casting
Protective pouring is carried out in the whole process, argon is adopted to purge the tundish before pouring, no molten steel is exposed in the pouring process, N is strictly controlled to be absorbed at a water port, and the increase of N is controlled to be less than or equal to 5 ppm; high-alkalinity slag inclusion is adopted to facilitate the removal of inclusions in steel; the constant drawing speed is kept in the steel casting process; the control target of the continuous casting superheat degree is not more than 30 ℃;
5) heating in a furnace
The tapping temperature is 1150-1220 ℃, and the heating time is more than or equal to 150 minutes;
6) hot continuous rolling, rolling and coiling to obtain the target steel
Selecting a 3+3 mode for control in the rough rolling pass; the finishing temperature is as follows: more than or equal to 860 ℃; the coiling temperature is more than or equal to 500 ℃, and the cooling mode adopts the rear-end continuous mode.
3. A method of producing a low nickel atmosphere corrosion resistant steel as claimed in claim 2, characterised in that: in the step 4), the soft reduction function is put into the steel casting process.
4. A method of producing a low nickel atmosphere corrosion resistant steel as claimed in claim 2, characterised in that: and 5) controlling the atmosphere and the heating speed in the furnace, increasing the gas amount, accelerating the heating speed and shortening the high-temperature in-furnace time when the temperature of the plate blank reaches the copper melting point so as to reduce the enrichment of Cu on the crystal boundary and the surface of the blank.
5. A method of producing a low nickel atmosphere corrosion resistant steel as claimed in claim 2, characterised in that: in the step 5), the tapping temperature is 1170-1210 ℃.
6. A method of producing a low nickel atmosphere corrosion resistant steel as claimed in claim 2, characterised in that: step 6), further comprising the steps of F1 and F2 post-machine small scale removal.
7. A method of producing a low nickel atmosphere corrosion resistant steel as claimed in claim 2, characterised in that: in the step 6), the finish rolling compression ratio is more than or equal to 3.5.
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