CN109852893B - Low-temperature high-toughness refractory steel and preparation method thereof - Google Patents
Low-temperature high-toughness refractory steel and preparation method thereof Download PDFInfo
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Abstract
The invention relates to low-temperature high-toughness refractory steel, which comprises the following chemical components in percentage by weight: 0.01 to 0.12%, Mn: 0.30-1.60%, Si: 0.10-0.50%, Al: 0.010-0.050%, Cu: 0.02-0.05%, Cr: 0.10-0.90%, Mo: 0.10-0.80%, Ti: 0.005-0.060%, Nb: 0.005-0.080%, Ni: 0.05-0.30 percent of the total weight of the alloy, less than or equal to 0.0040 percent of B, less than or equal to 0.025 percent of P, less than or equal to 0.0020 percent of S, and the balance of Fe and inevitable impurities. The invention adds one or more microalloy elements to obtain good fire resistance and low-temperature toughness in a certain proportion. The yield strength of the steel at 600 ℃ is greater than 2/3 of the yield strength required by the room temperature standard, the impact energy at-40 ℃ is more than or equal to 120J, and the steel has excellent forming property, cold bending property, welding property and the like.
Description
Technical Field
The invention belongs to the technical field of steel rolling, and relates to low-temperature high-toughness refractory steel and a preparation method thereof.
Background
The yield strength of ordinary structural steel for construction at 600 c will drop below 1/2 of the room temperature yield strength, thereby losing the load-bearing capacity. Existing building standards specify that steel structures be protected with fire-resistant thermal insulation coatings. However, the work of spraying the fireproof heat-insulating coating is harmful to the health of workers, the construction period is prolonged, and the construction cost of the steel structure is increased. In addition, the spatter from the operation of spraying the refractory heat-insulating coating also causes environmental pollution.
The temperature in winter in northern China can reach-20 ℃ at the lowest, and can reach-40 ℃ in partial areas, the impact toughness of a steel structure for construction can be rapidly reduced in severe cold weather, and particularly, the steel structure is easy to break suddenly under the action of certain impact load under the extremely cold weather condition, so that major safety accidents are caused. In order to adapt to northern cold weather conditions and enhance the safety of high-rise buildings, a low-temperature high-toughness refractory steel which has higher strength at high temperature and good impact toughness at low temperature is urgently needed.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide low-temperature high-toughness refractory steel and a preparation method thereof, and the low-temperature high-toughness refractory steel has better refractory performance and low-temperature toughness.
The invention provides low-temperature high-toughness refractory steel which comprises the following chemical components in percentage by weight: 0.01 to 0.12%, Mn: 0.30-1.60%, Si: 0.10-0.50%, Al: 0.010-0.050%, Cu: 0.02-0.05%, Cr: 0.10-0.90%, Mo: 0.10-0.80%, Ti: 0.005-0.060%, Nb: 0.005-0.080%, Ni: 0.05-0.30 percent of the total weight of the alloy, less than or equal to 0.0040 percent of B, less than or equal to 0.025 percent of P, less than or equal to 0.0020 percent of S, and the balance of Fe and inevitable impurities.
The preparation method of the low-temperature high-toughness refractory steel comprises the following steps of:
a steel making process: smelting and casting into a slab according to the following chemical composition and weight percentage:
wherein C: 0.01 to 0.12%, Mn: 0.30-1.60%, Si: 0.10-0.50%, Al: 0.010-0.050%, Cu: 0.02-0.05%, Cr: 0.10-0.90%, Mo: 0.10-0.80%, Ti: 0.005-0.060%, Nb: 0.005-0.080%, Ni: 0.05-0.30 percent of the total weight of the alloy, less than or equal to 0.0040 percent of B, less than or equal to 0.025 percent of P, less than or equal to 0.0020 percent of S, and the balance of Fe and inevitable impurities;
a heating procedure: controlling the furnace chamber atmosphere of the heating furnace, reducing the generation of casting blank iron scale, ensuring the uniform heating temperature, and controlling the discharging temperature of the plate blank to be 1160-1200 ℃;
a rolling procedure: the rough rolling pass is controlled by selecting a 3+3 mode, and the final rolling temperature is greater than or equal to 800 ℃;
a cooling process: adopting an intermittent cooling mode, starting spraying water to carry out laminar cooling when the steel plate is discharged from a finishing mill, and reducing the water spraying amount by half;
a coiling step: the coiling temperature is greater than or equal to 400 ℃.
In the preparation method of the low-temperature high-toughness refractory steel, the raw material adopts the fine scrap steel in the steelmaking process, and S is less than or equal to 0.005 percent when the raw material is pretreated and enters a furnace.
In the preparation method of the low-temperature high-toughness refractory steel, oxygen is blown only once when the converter decarburization treatment is carried out during the converter smelting in the steelmaking process; the steel tapping adopts low-carbon low-phosphorus ferromanganese, ferrosilicon, ferromolybdenum and high-chromium alloying; blowing by using argon when the converter pours the molten steel into the steel ladle, wherein the aluminum content of the steel ladle is 0.005-0.015%; the N of the steel ladle is required to be less than or equal to 25ppm, slag is blocked and steel is tapped, and the amount of slag entering the steel ladle is strictly controlled.
In the preparation method of the low-temperature high-toughness refractory steel, when external refining is carried out in the steelmaking process, the LF treatment process is required to keep micro-positive pressure, the increase of N in LF is strictly controlled, and the increase of N is required to be less than or equal to 10 ppm; the LF adopts active lime and fluorite to produce reducing slag with good fluidity, controls the argon blowing strength and avoids the exposure of molten steel; and performing calcium treatment after RH treatment, increasing soft blowing time and controlling inclusions in molten steel.
In the preparation method of the low-temperature high-toughness refractory steel, protective pouring is carried out in the whole process of continuous casting in the steelmaking process, an argon purging tundish is adopted before casting, no molten steel is exposed in the pouring process, the water mouth suction N is strictly controlled, and the increase of the N is controlled to be less than or equal to 5 ppm; high-alkalinity tundish slag is adopted to facilitate the removal of inclusions in steel; the pouring process of the molten steel adopts a soft reduction function, so that the internal quality of a casting blank is guaranteed; the constant drawing speed is kept in the steel casting process; controlling the temperature of the tundish according to the superheat degree of less than or equal to 30 ℃; after the continuous casting billet is poured, stacking and slow cooling are carried out to ensure that the casting billet is slowly cooled, and rolling is carried out after 72 hours.
The low-temperature high-toughness refractory steel and the preparation method thereof have the beneficial effects that:
(1) compared with the refractory steel of the same grade, the composition design adopts the design of low C and no V, and the proper amount of Cr, Mo, Ni and Cu alloy elements, so that various indexes on the mechanical property meet the requirements, and particularly, the impact toughness is particularly excellent. The high-performance refractory brick still has good refractory performance on the premise of not adding V element, has high product competitiveness and has good economic benefit.
(2) The yield strength of the low-temperature high-toughness fire-resistant steel at 600 ℃ is greater than 2/3 of the yield strength required by the room temperature standard, and the index requirement of fire resistance safety of modern building structural steel is met.
(3) Compared with common structural steel of the same grade, the low-temperature high-toughness fire-resistant steel produced by the process meets all index requirements except the normal-temperature mechanical property, all mechanical properties meet the requirements, the yield strength of the low-temperature high-toughness fire-resistant steel at 600 ℃ is greater than 2/3 of the yield strength required by the room-temperature standard, the index requirements of fire resistance safety of modern building structural steel are met, particularly, the impact toughness is particularly excellent, and the physical impact energy can reach more than or equal to 200J at-40 ℃.
Detailed Description
Ordinary structural steel for construction has good strength at room temperature, but as the temperature increases, the yield strength of the steel material decreases to below 1/2 of the room temperature yield strength, thereby losing the load-bearing capacity. The fire resistance of steel is judged internationally by the japanese standards: if the yield strength of the steel at 600 ℃ is greater than 2/3, which is the room temperature yield strength, the steel has fire resistance properties. The refractory steel of the invention has better refractory performance by adding Mo, Cr, Cu, Ni and other alloy elements into the steel.
The impact energy of the common structural steel for the building is required to be more than or equal to 27J, the ductile-brittle transition temperature is-20 ℃, and the material is easy to generate brittle fracture under the action of impact load in the environment with the temperature lower than-20 ℃. According to the low-temperature high-toughness refractory steel, the Nb microalloying element is added into the steel, and the cooling speed is controlled in the processing process, so that the grain structure is refined, and the impact energy of a final product object at-40 ℃ is more than or equal to 200J, so that the low-temperature high-toughness refractory steel has good low-temperature toughness.
In order to obtain good fire resistance and low-temperature toughness, the low-temperature high-toughness refractory steel must have good purity and low C content of molten steel, and special alloy addition is designed.
The invention relates to low-temperature high-toughness refractory steel, which comprises the following chemical components in percentage by weight: 0.01 to 0.12%, Mn: 0.30-1.60%, Si: 0.10-0.50%, Al: 0.010-0.050%, Cu: 0.02-0.05%, Cr: 0.10-0.90%, Mo: 0.10-0.80%, Ti: 0.005-0.060%, Nb: 0.005-0.080%, Ni: 0.05-0.30 percent of the total weight of the alloy, less than or equal to 0.0040 percent of B, less than or equal to 0.025 percent of P, less than or equal to 0.0020 percent of S, and the balance of Fe and inevitable impurities.
According to the low-temperature high-toughness refractory steel, a plurality of microalloy elements are added, so that the low-temperature high-toughness refractory steel has good refractory performance and low-temperature toughness in a certain proportion. The yield strength of the refractory steel at 600 ℃ is greater than 2/3 of the yield strength required by the room temperature standard, the impact energy at-40 ℃ is more than or equal to 120J, and the refractory steel has excellent forming performance, cold bending performance, welding performance and the like.
The fire-resistant mechanism of steel: the Mo element added into the refractory steel can remarkably increase the stability of the undercooled austenite in a pearlite transformation region, thereby being beneficial to the formation of bainite or MA structures. Therefore, at a lower cooling speed, the refractory steel has a mixed structure of ferrite, bainite and MA, and the phase boundary of the mixed structure can effectively block dislocation movement, so that the high-temperature strength of the steel is improved.
Molybdenum and niobium are both strong carbide forming elements. Mo favors the formation of more fine stable carbides (Mo)2C) The carbide is Fe3C is more stable and is difficult to decompose and grow up at high temperature. Niobium forms a fine second phase of NbC in the steel and has a high structural stability. The fine dispersed Nb (C, N) can hinder the migration of crystal boundary, improve the growth temperature of crystal grains, achieve the fine crystal effect, and the refined crystal grains can effectively prevent the expansion of cracks, thereby improving the low-temperature toughness of the refractory steel.
After the steel is added with trace elements such as copper, chromium, nickel and the like, a compact protective film with strong adhesiveness is formed on the surface of the steel, so that the corrosion is prevented from diffusing and developing inwards, and a matrix below the rust layer is protected to slow down the corrosion speed. An amorphous spinel type oxide compact layer with the thickness of about 50-100 mu m is formed between the rust layer and the matrix, and the compact oxide film prevents oxygen and water in the air of the external environment from permeating into the steel matrix, slows down the deep development of rust to steel materials and improves the corrosion resistance of the steel materials.
The preparation method of the low-temperature high-toughness refractory steel comprises the following steps of:
a steel making process: smelting and pouring into a plate blank according to the following chemical compositions in percentage by weight:
wherein C: 0.01 to 0.12%, Mn: 0.30-1.60%, Si: 0.10-0.50%, Al: 0.010-0.050%, Cu: 0.02-0.05%, Cr: 0.10-0.90%, Mo: 0.10-0.80%, Ti: 0.005-0.060%, Nb: 0.005-0.080%, Ni: 0.05-0.30 percent of the total weight of the alloy, less than or equal to 0.0040 percent of B, less than or equal to 0.025 percent of P, less than or equal to 0.0020 percent of S, and the balance of Fe and inevitable impurities;
a heating procedure: controlling the furnace chamber atmosphere of the heating furnace, reducing the generation of casting blank iron scale, ensuring the uniform heating temperature, and controlling the discharging temperature of the plate blank to be 1160-1200 ℃;
a rolling procedure: the rough rolling pass is controlled by selecting a 3+3 mode, and the final rolling temperature is greater than or equal to 800 ℃;
a cooling process: adopting an intermittent cooling mode, starting spraying water to carry out laminar cooling when the steel plate is discharged from a finishing mill, and reducing the water spraying amount by half;
a coiling step: the coiling temperature is greater than or equal to 400 ℃.
In the specific implementation, in the steelmaking process, the raw materials adopt refined scrap steel, and when the raw materials are pretreated and fed into a furnace, S is less than or equal to 0.005 percent.
In the specific implementation, only one time of oxygen blowing is carried out when the decarburization treatment of the converter is carried out during the smelting of the converter in the steelmaking process; the steel tapping adopts low-carbon low-phosphorus ferromanganese, ferrosilicon, ferromolybdenum and high-chromium alloying; blowing by using argon when the converter pours the molten steel into the steel ladle, wherein the aluminum content of the steel ladle is 0.005-0.015%; the N of the steel ladle is required to be less than or equal to 25ppm, slag is blocked and steel is tapped, and the amount of slag entering the steel ladle is strictly controlled.
In the specific implementation, when the external refining is carried out in the steelmaking process, the LF treatment process is required to keep micro-positive pressure, the increase of N in LF is strictly controlled, and the increase of N is required to be less than or equal to 10 ppm; the LF adopts active lime and fluorite to produce reducing slag with good fluidity, controls the argon blowing strength and avoids the exposure of molten steel; and performing calcium treatment after RH treatment, increasing soft blowing time and controlling inclusions in molten steel.
During specific implementation, protective pouring is carried out in the whole process of continuous casting in the steelmaking process, an argon purging tundish is adopted before casting, 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 tundish slag is adopted to facilitate the removal of inclusions in steel; the pouring process of the molten steel adopts a soft reduction function, so that the internal quality of a casting blank is guaranteed; the constant drawing speed is kept in the steel casting process; controlling the temperature of the tundish according to the superheat degree of less than or equal to 30 ℃; after the continuous casting billet is poured, stacking and slow cooling are carried out to ensure that the casting billet is slowly cooled, and rolling is carried out after 72 hours.
Example 1
Smelting and pouring into slab blanks according to the following chemical compositions and weight percentages thereof
C: 0.06%, Mn: 0.8%, Si: 0.12%, Al: 0.030%, Cu: 0.31%, Cr: 0.32%, Mo: 0.4%, Ti: 0.008%, Nb: 0.03%, Ni: 0.13%, B: 0.0002%, P: 0.01%, S: 0.001%, and the balance of Fe and inevitable impurities;
and then the plate blank is sequentially subjected to a heating process, a rolling process, a cooling process and a coiling process to obtain the low-temperature high-toughness refractory steel.
Example 2
Smelting and pouring into slab blanks according to the following chemical compositions and weight percentages thereof
C: 0.1%, Mn: 1.4%, Si: 0.28%, Al: 0.025%, Cu: 0.40%, Cr: 0.55%, Mo: 0.35%, Ti: 0.030%, Nb: 0.01%, Ni: 0.18%, B: 0.0001%, P: 0.012%, S: 0.002%, and the balance of Fe and inevitable impurities;
and then the plate blank is sequentially subjected to a heating process, a rolling process, a cooling process and a coiling process to obtain the low-temperature high-toughness refractory steel.
TABLE 1 comparison of mechanical Properties of refractory steels and common structural steels
TABLE 2 impact test of fire-resistant steel series
As can be seen from Table 1, the high temperature properties of the fire resistance test steels of example 1 and the fire resistance test steels of example 2 both satisfy the high temperature fire resistance requirement, and the design goal that the steels can resist fire is achieved. As the steel of the embodiment 1 is added with more alloy, the strength of the steel of the embodiment 1 is higher than that of the steel of the embodiment 2, and compared with Q345B common hot-rolled structural steel, the test steels of the embodiment 1 and the embodiment 2 have better impact toughness, and as can be seen from the table 2, the test steels of the embodiment 1 and the embodiment 2 still have good impact toughness at-60 ℃, which indicates that the refractory steel of the invention still does not reach the ductile-brittle transition temperature point at-60 ℃, and meets the service conditions of low-temperature service in northern areas.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the scope of the present invention, which is defined by the appended claims.
Claims (1)
1. The preparation method of the low-temperature high-toughness refractory steel is characterized by comprising the following steps of:
a steel making process: smelting and casting into a slab according to the following chemical composition and weight percentage:
wherein C: 0.01 to 0.12%, Mn: 0.30-1.60%, Si: 0.10-0.50%, Al: 0.010-0.050%, Cu: 0.02-0.05%, Cr: 0.10-0.90%, Mo: 0.10-0.80%, Ti: 0.005-0.060%, Nb: 0.005-0.080%, Ni: 0.05-0.30 percent of the total weight of the alloy, less than or equal to 0.0040 percent of B, less than or equal to 0.025 percent of P, less than or equal to 0.0020 percent of S, and the balance of Fe and inevitable impurities;
a heating procedure: controlling the furnace chamber atmosphere of the heating furnace, reducing the generation of casting blank iron scale, ensuring the uniform heating temperature, and controlling the discharging temperature of the plate blank to be 1160-1200 ℃;
a rolling procedure: the rough rolling pass is controlled by selecting a 3+3 mode, and the final rolling temperature is greater than or equal to 800 ℃;
a cooling process: adopting an intermittent cooling mode, starting spraying water to carry out laminar cooling when the steel plate is discharged from a finishing mill, and reducing the water spraying amount by half;
a coiling step: the coiling temperature is more than or equal to 400 ℃;
in the steelmaking process, the raw material adopts refined scrap steel, and when the raw material is pretreated and fed into a furnace, S is less than or equal to 0.005 percent;
in the steelmaking process, oxygen blowing is only carried out once when the decarburization treatment of the converter is carried out during the smelting of the converter; the steel tapping adopts low-carbon low-phosphorus ferromanganese, ferrosilicon, ferromolybdenum and high-chromium alloying; blowing by using argon when the converter pours the molten steel into the steel ladle, wherein the aluminum content of the steel ladle is 0.005-0.015%; the N of the steel ladle is required to be less than or equal to 25ppm, slag is blocked and steel is tapped, and the amount of slag entering the steel ladle is strictly controlled;
when the external refining is carried out in the steelmaking procedure, the LF treatment process is required to keep micro-positive pressure, the increase of N in LF is strictly controlled, and the increase of N is required to be less than or equal to 10 ppm; the LF adopts active lime and fluorite to produce reducing slag with good fluidity, controls the argon blowing strength and avoids the exposure of molten steel; performing calcium treatment after RH treatment, increasing soft blowing time and controlling inclusions in molten steel;
protective pouring is carried out in the whole process during continuous casting in the steelmaking process, argon is adopted to purge a tundish before casting, 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 tundish slag is adopted to facilitate the removal of inclusions in steel; the pouring process of the molten steel adopts a soft reduction function, so that the internal quality of a casting blank is guaranteed; the constant drawing speed is kept in the steel casting process; controlling the temperature of the tundish according to the superheat degree of less than or equal to 30 ℃; after the continuous casting billet is poured, stacking and slow cooling are carried out to ensure that the casting billet is slowly cooled, and rolling is carried out after 72 hours.
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