CN114592154B - Production method of 10.9-grade niobium microalloyed cold forging steel - Google Patents
Production method of 10.9-grade niobium microalloyed cold forging steel Download PDFInfo
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Abstract
The invention discloses a production method of 10.9-grade niobium microalloyed cold forging steel, and belongs to the technical field of steel for fasteners. Mixing iron-containing raw materials, sequentially carrying out electric furnace smelting, LF furnace refining, RH vacuum degassing, large round billet continuous casting, square billet rolling and high-speed wire rod rolling treatment to obtain a hot rolled wire rod, and carrying out annealing processing treatment on the hot rolled wire rod to obtain the cold forging steel; the iron-containing raw material comprises not less than 95.5wt% of Fe, 0.035wt% to 0.045wt% of Ti, 0.04wt% to 0.08wt% of Nb and 0.0003wt% to 0.0008wt% of B, wherein 29 is more than or equal to (Ti + Nb)/10 × B is more than or equal to 6; the high-speed wire rolling comprises the steps of rolling wires by a roughing mill and a medium mill, controlling the temperature of a wire feeding reducing and sizing unit to be not lower than 800 ℃, and cooling the wires to the spinning temperature of not lower than 720 ℃ through a water tank. The invention can save 40% of the traditional spheroidizing annealing time, and the cold forging steel prepared by the method has good strength, plasticity and toughness and good fatigue property.
Description
Technical Field
The invention belongs to the technical field of steel for fasteners, and particularly relates to a production method of 10.9-grade niobium microalloyed cold forging steel.
Background
The cold heading steel is used as a general basic part, is large in quantity and wide in variety, is widely applied to various industries of national economy, is used for millions of tons at present in China, is 45 million tons only in 2010 of the automobile industry, and is increased in a trend of increasing year by year, wherein the most commonly used fastener in the automobile industry is a 10.9-grade high-strength fastener which is used for fasteners of automobile engines, power transmission systems, directional operation systems, braking systems and the like, and is particularly an automobile safety part and a key part, in order to ensure high reliability and safety of automobiles, the high-strength fastener generally needs to be subjected to tempering treatment to obtain good impact resistance, low-temperature impact toughness and strong fatigue performance, and spheroidizing annealing is used as the most important ring in the manufacturing process of the high-strength fastener, so that the organization and mechanical performance after final tempering treatment are influenced, the automobile safety is directly related, and the time and energy consumption in the whole processing process is often required to be more than 30 hours.
In recent years, manufacturers at home and abroad produce annealing-free or annealing-simplified cold forging steel products, the purpose of annealing simplification is realized by a method of obtaining an ultrafine grained ferrite + pearlite structure through a low-temperature rolling technology, and the purpose of reducing annealing by obtaining a bainite structure through conventional rolling is not reported. Chinese application patent CN201810147729.X provides an alloy cold heading steel with excellent delayed fracture resistance and a production method thereof, the alloy cold heading steel comprises, by weight, 0.37% -0.41% of C, 0.15% -0.30% of Si, 0.75% -0.95% of Mn, 0.90% -1.20% of Cr, 0.15% -0.30% of Mo and 0.05% -0.15% of W, and one of V and Nb elements, wherein V is 0.030% -0.060%, nb is 0.010% -0.030%, and the balance is Fe and inevitable impurities. The medium carbon chromium molybdenum alloy cold heading steel wire rod with ferrite and pearlite structures and without a full decarburized layer is produced by the reasonable design of chemical components and the production processes of continuous casting and rolling, heating, controlled rolling and controlled cooling.
Chinese application patent CN201911247314.0 provides high weather-resistant cold heading steel for 10.9-grade fasteners and a production method thereof, and belongs to the technical field of cold heading steel production. The main chemical components and the mass percentage content are as follows: c:0.33 to 0.43%, si: 0.20-0.50%, mn: 0.35-0.55%, cr:0.60% -1.00%, ni:0.50% -0.80%, cu:0.20% -0.40%, V:0.01% -0.10%, alt:0.015% -0.040%, RE:0.01% -0.10%, P: 0.010-0.030 percent of the total weight of the alloy, less than or equal to 0.0015 percent of O, less than or equal to 0.006 percent of N, and the balance of Fe and inevitable impurities. The tensile strength Rm is more than or equal to 1040MPa, the yield strength Rp0.2 is more than or equal to 940MPa, the elongation A after fracture is more than or equal to 9 percent, the surface shrinkage rate Z is more than or equal to 48 percent, the yield ratio is more than or equal to 0.9, the requirements of 10.9-grade fastener steel grades are met, and the high weather resistance is high, the production and the use are convenient, but the simplification of an annealing process cannot be realized.
The invention relates to a production method and a processing method of 10.9-grade niobium microalloyed cold forging steel. Comprises the following components in percentage by weight: 0.40 to 0.50 percent of C, 0.10 to 0.20 percent of Si, 0.60 to 0.80 percent of Mn, 0.30 to 0.50 percent of Cr, 0.35 to 0.55 percent of Mo, less than or equal to 0.025 percent of P, less than or equal to 0.025 percent of S, 0.04 to 0.08 percent of Nb, 0.0003 to 0.0008 percent of B, 0.035 to 0.045 percent of Ti, 0.015 to 0.040 percent of Alt, less than or equal to 0.015 percent of P, less than or equal to 0.015 percent of S, less than or equal to 0.0015 percent of O and less than or equal to 0.006 percent of N. The balance of Fe and other inevitable impurities. The invention also provides a production method and a processing method of the steel, a bainite and ferrite dual-phase structure is obtained through microalloying and controlled rolling and controlled cooling, the deep processing spheroidizing annealing time can be saved by nearly 40 percent, and the spheroidizing grade is 4-6 grade; the mechanical property after heat treatment reaches 10.9 grades, and the alloy has good strength, plastic toughness and fatigue property.
Therefore, there is a need to design a method for producing grade 10.9 cold forging steel, which can effectively simplify the annealing process and reduce the annealing time.
Disclosure of Invention
1. Problems to be solved
Aiming at the problem that the annealing time is long because the subsequent annealing process cannot be effectively simplified in the production process of 10.9-grade cold forging steel in the prior art, the invention provides a production method of 10.9-grade niobium microalloyed cold forging steel; the bainite and ferrite microstructure is obtained by controlling the contents of niobium, titanium, boron and other microalloy elements in steel and controlling rolling and cooling, and the problem of long annealing time of the existing cold heading steel production process can be effectively solved.
2. Technical scheme
In order to solve the problems, the technical scheme adopted by the invention is as follows:
the invention relates to a production method of 10.9-grade niobium microalloyed cold forging steel, which comprises the steps of mixing iron-containing raw materials, sequentially carrying out electric furnace smelting, LF furnace refining, RH vacuum degassing, large round billet continuous casting, square billet rolling and high-speed wire rod rolling treatment to obtain a hot rolled wire rod, and carrying out annealing processing treatment on the hot rolled wire rod to obtain the cold forging steel; the iron-containing raw material comprises not less than 95.5wt% of Fe, 0.035wt% to 0.045wt% of Ti, 0.04wt% to 0.08wt% of Nb and 0.0003wt% to 0.0008wt% of B, wherein 29 is more than or equal to (Ti + Nb)/10 × B is more than or equal to 6; the high-speed wire rolling comprises the steps of rolling wires by a roughing mill and a medium mill, controlling the temperature of a wire feeding reducing and sizing unit to be not lower than 800 ℃, and cooling the wires to the spinning temperature of not lower than 720 ℃ through a water tank.
In order to realize the purpose of simplifying spheroidizing annealing by a bainite and ferrite dual-phase microstructure, the invention adds strong carbide forming elements such as Cr, mo, B and the like to ensure hardenability and easily obtain a bainite structure, and simultaneously adds refined grain elements such as Nb, ti and the like to inhibit grain growth and generate dispersed and precipitated carbonitride to refine austenite grains to improve toughness and obtain good fatigue strength.
Further, in order to ensure sufficient hardenability, a fine-grained bainite structure is obtained, and (Ti + Nb)/10 × b =8 to 25 is preferable.
The specific elements have the following functions in the invention:
cr can effectively improve the hardenability of steel and delay bainite transformation so as to obtain required high strength, and the hardness of bainite ferrite can be obviously improved through solid solution strengthening; meanwhile, cr can also reduce the activity of C, can reduce the decarburization tendency of the surface of steel in the heating, rolling and forging processes, and is beneficial to obtaining high fatigue resistance. However, since too high a content deteriorates toughness and cold workability of steel, the Cr content is controlled to be 0.30wt% to 0.50wt%.
The Mo in the steel mainly has the functions of improving hardenability and bainite transformation, and simultaneously can obviously improve the tempering resistance of the steel, so that the carbide Mo is formed 2 C has trapping effect on hydrogen and can improve the delayed fracture resistance of the steel, so that the content of added Mo is 0.35-0.55 wt%.
Nb mainly plays a role of fine grain reinforcement, and can improve corrosion resistance, improve low-temperature properties of steel, and improve resistance to tempering and delayed fracture resistance of high-strength steel while improving strength because grains are finer. The Nb range can be controlled between 0.04wt% and 0.08wt%.
The B element can greatly improve the hardenability, and the boron in the steel can be partially gathered at the austenite crystal boundary during quenching only when the boron exists in a solid solution form, so as to inhibit ferrite nucleation, thereby improving the hardenability of the steel. However, if the B content is too high, it forms a compound with oxygen and nitrogen in the steel, which not only does not improve hardenability but also reduces the toughness of the material. Therefore, the boron content in the steel is controlled to 0.0003wt% to 0.0008wt%.
Ti and N, C element in the steel form Ti (C, N) precipitated phase which has the effect of inhibiting grain growth in the heating process, meanwhile, titanium carbide formed by the Ti element can pin austenite grain boundary refined grains, toughness is improved, and the titanium carbide has stronger trapping effect on hydrogen, so that delayed fracture resistance of the steel can be improved, but overhigh Ti content is easy to generate large-grain TiN inclusion by liquation, and fatigue performance of the steel is reduced, therefore, the Ti content is controlled to be 0.035-0.045%.
Al is a main deoxidizing element in steel, an AlN precipitated phase formed by Al and N in steel has the effect of inhibiting grain growth, the AlN precipitated phase is insufficient due to too low Al content and cannot inhibit the grain growth, and the purity of the steel is easily reduced due to too high Al content, so that the Al content is controlled to be 0.035wt% -0.045 wt%.
Preferably, the iron-containing raw material also comprises 0.40-0.50 wt% of C, 0.10-0.20 wt% of Si, 0.60-0.80 wt% of Mn, 0.30-0.50 wt% of Cr, 0.35-0.55 wt% of Mo, 0-0.015 wt% of P, 0-0.025 wt% of S and 0.015-0.040 wt% of Alt.
Preferably, the annealing process includes: annealing, drawing, cold heading, quenching and tempering heat treatment, thread rolling and blackening to process the fastener; the annealing is to heat the wire rod to 700-725 ℃, keep the temperature for 4.5-5.5 h, cool the wire rod to 640-700 ℃ at 15-25 ℃/h, keep the temperature for 3.5-4.5 h, cool the wire rod to 500-550 ℃ at 15-25 ℃/h, and take the wire rod out of the furnace, wherein the total annealing time is 19-21 h.
Preferably, the quenching and tempering heat treatment adopts oil quenching at 850-910 ℃ and tempering at 540-560 ℃.
Preferably, the high-speed wire rod rolling comprises: the heating temperature is controlled to be 1050-1150 ℃, the soaking time is more than 30min, the heated casting blank is descaled by high pressure water and then enters a continuous rolling mill set for rolling, and the starting rolling temperature is 950-1050 ℃; controlling the temperature of the incoming wire reducing sizing mill unit to be 820-860 ℃, and rapidly cooling the incoming wire reducing sizing mill unit to the spinning temperature of 750-780 ℃ through a water tank; after air cooling for a certain time, when the temperature of the loose coil is reduced to 640-670 ℃, a fan is adopted for rapid cooling, the cooling rate is 3 ℃/3-6 ℃/3, the loose coil is cooled to 500-540 ℃ and then enters a heat preservation cover for slow cooling, the cooling rate is 0.5 ℃/3-0.9 ℃/3, the loose coil is collected and hooked when the temperature is 430-460 ℃, and then the loose coil is air cooled to room temperature for packaging and weighing.
Preferably, the content of C in the electric furnace end point of the electric furnace smelting is controlled to be 0.06wt% -0.20 wt%, and P is less than or equal to 0.010wt%; the electric furnace smelting comprises slag-stopping and tapping, wherein about 1/5 of molten steel is tapped, refining slag and lime are added, about 1/3 of molten steel is tapped, and a deoxidizer and an alloy are added in the following sequence: aluminum iron, slag charge, silicomanganese, high carbon ferrochrome, ferromolybdenum and carburant, and after tapping, uniformly throwing aluminum particles on the steel slag surface according to the slag discharge amount.
Preferably, the LF furnace refining comprises: and (3) blowing argon from the bottom of the steel ladle in the whole process, adding premelted refining slag and lime for slagging, wherein the alkalinity R = 3-6, the white slag time is more than or equal to 20 minutes, and adding alloy before and in the middle period of refining according to the analysis result of components before entering the LF furnace to adjust the contents of Si, mn, cr, mo, V and Nb within the respective ranges.
Preferably, the RH vacuum degassing comprises: in the early stage of vacuum, if the vacuum degree is less than or equal to 100 Pa, the vacuum maintaining time is more than or equal to 10 minutes, and if the vacuum degree is less than or equal to 200 Pa, the vacuum maintaining time is more than or equal to 15 minutes; the holding time is more than or equal to 10 minutes in the later period of vacuum; according to the analysis result of the components in the early stage of vacuum, if the components need to be adjusted in the middle stage, the vacuum is kept for more than 5 minutes after the adjustment; carrying out calcium line feeding treatment after vacuum breaking; and carrying out soft argon blowing treatment before leaving the station, wherein the soft blowing time is more than or equal to 15min.
Preferably, the round billet continuous casting includes: the casting method is characterized in that 380 large round billet continuous casting is adopted, whole-course protection casting is carried out, a protective sleeve and argon seal are adopted between a steel ladle and a tundish, the tundish uses a molten steel covering agent and argon blowing protection, an immersion type water gap is adopted between the tundish and a crystallizer, and the primary cooling water flow is 100m 3 /h～130m 3 The water amount of the secondary cooling is 1.0L/kg-1.4L/kg, the superheat degree in the casting process is controlled at 10-40 ℃, the drawing speed is 1.9 mm/min-2.2 mm/min, and a casting blank is obtained.
Preferably, the billet rolling process comprises: controlling the temperature of a 380-size round billet in a soaking section of a heating furnace at 1200-1300 ℃, controlling the total heating time at 250-350 min, controlling the initial rolling temperature at 1100150 ℃, performing pile cooling after rolling at the pile cooling temperature of more than or equal to 400 ℃, and performing surface and end grinding treatment on 150 square billets after rolling.
3. Advantageous effects
Compared with the prior art, the invention has the beneficial effects that:
according to the production method of the 10.9-grade niobium microalloyed cold forging steel, a bainite and ferrite double-phase microstructure is obtained through microalloying, controlled rolling and controlled cooling, and the bainite content is more than or equal to 80%. Compared with the prior wire rod with ferrite and pearlite group structure obtained by low-temperature rolling, the spheroidizing annealing time can be saved by 40 percent, the spheroidizing grade is 4-6 grade, and fasteners with larger deformation such as hexagon socket head cap bolts, flange face bolts and the like are manufactured; mechanical Properties R after Heat treatment m Not less than 1000MPa and yield ratio R P0.2 /R m More than or equal to 0.9 percent, elongation A after fracture more than or equal to 18 percent, reduction of area Z more than or equal to 52 percent, and normal temperature impact absorption power KU 2 The fatigue strength is more than or equal to 70J, and the fatigue strength is more than or equal to 450MPa, and the high-strength plastic-toughness steel has high strength, high toughness and high fatigue performance.
Drawings
FIG. 1 is a schematic view showing a microstructure 500X (bainite + small amount of ferrite) of cold heading steel according to the present invention;
FIG. 2 is a schematic view of a cold heading steel spheroidized structure grade 4 according to the present invention;
FIG. 3 is a schematic diagram of the cold heading steel annealing process of the present invention.
Detailed Description
The following detailed description of exemplary embodiments of the invention refers to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration exemplary embodiments in which the invention may be practiced, and in which features of the invention are identified by reference numerals. The following more detailed description of the embodiments of the invention is not intended to limit the scope of the invention, as claimed, but is presented for purposes of illustration only and not limitation to describe the features and characteristics of the invention, to set forth the best mode of carrying out the invention, and to sufficiently enable one skilled in the art to practice the invention. It will, however, be understood that various modifications and changes may be made without departing from the scope of the invention as defined in the appended claims. The detailed description and drawings are to be regarded as illustrative rather than restrictive, and any such modifications and variations are intended to be included within the scope of the present invention as described herein. Furthermore, the background is intended to be illustrative of the state of the art as developed and the meaning of the present technology and is not intended to limit the scope of the invention or the application and field of application of the invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs; the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
The invention is further described with reference to specific examples.
The embodiment provides a production method of 10.9-grade niobium microalloyed cold forging steel, which is used as an embodiment 1, the method comprises the following specific operation steps of firstly mixing iron-containing raw materials, wherein the content of each element in the iron-containing raw materials is shown in table 1, and the rest components are iron, and then sequentially carrying out electric furnace smelting → LF furnace refining → RH vacuum treatment → 380 large round billet continuous casting → 150 square billet rolling → high-speed wire rod rolling:
(1) Electric furnace smelting: controlling the C content to be 0.06wt% and the P content to be 0.004wt% at the electric furnace end point; and (3) slag stopping and tapping, wherein about 1/5 of molten steel is tapped, refining slag and lime are added, about 1/3 of molten steel is tapped, and a deoxidizer and an alloy are added, wherein the sequence is as follows: aluminum iron → slag charge → silicomanganese → high carbon ferrochrome → ferromolybdenum → carburant, after tapping, according to the amount of slag, a proper amount of aluminum particles are uniformly thrown to the surface of the steel slag.
(2) Refining in an LF furnace: argon is blown from the bottom of the steel ladle in the whole process, and the flow of the argon is based on that the molten steel does not splash to the steel-tapping ladle; adding premelted refining slag and lime for slagging, wherein the alkalinity is R3.3, the white slag time is 25 minutes, and adding alloy before and during refining according to the analysis result of components before entering the LF furnace to adjust the contents of Si, mn, cr, mo, V and Nb to the proportion of each element.
(3) RH vacuum degassing: the vacuum degree in the early stage of vacuum is 100 Pa, the vacuum maintaining time is 13 minutes, and the vacuum maintaining time in the later stage is 10 minutes. According to the analysis result of the composition in the early stage of vacuum, if the composition adjustment is required in the middle stage, the vacuum holding time of more than 5 minutes must be ensured after the adjustment. And (5) performing calcium wire feeding treatment after vacuum breaking. And carrying out soft argon blowing treatment before the station is out, wherein the soft blowing time is 20min.
(4) Continuous casting of 380 large round billets: in order to obtain good surface quality, preparation is made for subsequent drawing, large round billet continuous casting is adopted, whole-process protective casting is carried out, a protective sleeve and argon sealing are adopted between a steel ladle and a tundish, the tundish is protected by using a molten steel covering agent and blowing argon, an immersion type water gap is adopted between the tundish and a crystallizer, and primary cooling water flow is 105m 3 And h, the secondary cooling specific water amount is 1.21L/kg, the superheat degree in the casting process is controlled at 35 ℃, the drawing speed is 2.0mm/min, and a defect-free casting blank is obtained.
(5) 150 square billet rolling: the temperature of a 380-inch round billet in a soaking section of a heating furnace is controlled to be 1200 ℃, the total heating time is controlled to be 320min, the initial rolling temperature is controlled to be 1100 ℃, the post-rolling dump cooling temperature is 420 ℃, the surface and end grinding treatment is carried out 150 degrees after the rolling, good surface quality is provided for the subsequent high-speed wire rolling, and the surface decarburization sensitivity of a wire rod is reduced.
(6) Rolling the high-speed wire rods: in order to meet the requirement of a rolling process and enable carbon and nitride to be dissolved in austenite, the heating temperature is controlled to be 1050 ℃, soaking time is 35min to ensure that Nb and Ti elements are fully dissolved, the heated casting blank is descaled by high-pressure water and then enters a continuous rolling mill set for rolling, and the rolling temperature is 970 ℃. In order to obtain a two-phase microstructure of bainite and ferrite, controlling the temperature of a wire inlet reducing sizing mill set to 842 ℃, and rapidly cooling the wire inlet reducing sizing mill set to a spinning temperature of 770 ℃ through a water tank; after air cooling for a certain time, the temperature of the loose coil is reduced to 640-670 ℃, a fan is used for rapid cooling, the cooling rate is 3 ℃/3-6 ℃/3, the generation of a pearlite structure is avoided, the loose coil enters a heat preservation cover for slow cooling after being cooled to 500-540 ℃, the cooling rate is 0.5 ℃/3-0.9 ℃/3, the generation of a martensite structure is avoided, the subsequent drawing and other deep processing are influenced, the loose coil is coiled and hooked when the temperature is 400-440 ℃, and then the loose coil is air cooled to room temperature, packaged and weighed.
The hot-rolled wire rod is produced by the method, and the diameter of the hot-rolled wire rod is reduced
The hot rolling of the wire rod is carried out in sequence: acid cleaning → isothermal spheroidizing annealing (20 h) → acid cleaning → phosphating → first drawing
→ isothermal spheroidizing annealing (20 h) → acid washing → phosphorization → second drawing 13.7mm → fine wire finished product → cold heading → 880 ℃ quenching → 530 ℃ tempering → rolling wire → blackening → flange face bolt finished product. As shown in fig. 3, in the isothermal spheroidizing annealing process in this embodiment, the wire rod is heated to 725 ℃, kept for 5h, cooled to 700 ℃ at 7.14 ℃/h, kept for 4h, then slowly cooled to 550 ℃ at 20 ℃/h, and taken out of the furnace, and the total annealing time is 20h. Wherein the quenching and tempering heat treatment adopts oil quenching at 900 ℃ and tempering at 550 ℃.
Finally, the microstructure before annealing contains bainite and a small amount of ferrite, as shown in fig. 1, wherein the bainite content and the grain size are shown in table 3; the microstructure after the annealing process is shown in fig. 2, and the specific mechanical property data are shown in table 4.
TABLE 1 chemical composition and organization (wt%) of inventive and comparative examples
TABLE 2 steelmaking Process according to the examples of the invention
TABLE 3 wire rod Rolling Process of examples of the invention and comparative examples
TABLE 4 mechanical properties after quenching and tempering heat treatment of inventive examples and comparative examples
In addition, the present invention provides comparison of the production methods of cold heading steels of examples 2 to 5 and comparative examples 1 to 7, and the difference between each example and comparative example is the difference in parameters between tables 1 to 4.
In comparative example 1, the diameter is measured
The hot rolling of the wire rod is carried out in sequence: acid cleaning → isothermal spheroidizing annealing (33.5 h) → acid cleaning → phosphating → first drawing
→ isothermal spheroidizing annealing (33.5 h) → acid washing → phosphorization → second drawing 13.7mm → fine wire finished product → cold heading → 880 ℃ quenching → 530 ℃ tempering → rolling wire → blackening → flange face bolt finished product.
In comparative examples 1 to 7: in the comparative example 1 and the comparative example 2, cr and B elements are not added, the bainite content of the microstructure obtained by adopting the same controlled rolling and controlled cooling process is lower than or equal to 80%, and the spheroidization grade is grade 3 by adopting the same spheroidization annealing process, so that the spheroidization effect is influenced. The comparative example 3 is that Mo element is not added, on one hand, the bainite content of the microstructure obtained after the same controlled rolling and controlled cooling process is lower than or equal to 80 percent, the spheroidization grade is 3 grade by adopting the same spheroidization annealing process, and on the other hand, the strength can reach 1000MPa only when the tempering temperature of the quenching and tempering process is lower, but the ductility and toughness are insufficient. Comparative example 4 is a microalloy element containing no Nb or Ti, and has a significantly large grain size and insufficient ductility and toughness as compared with the examples. Comparative example 5 is (Ti + Nb)/10 × b is not in the preferred range, the bainite content obtained is insufficient, and at the same time, the grain size is not fine enough, and the properties after spheroidizing annealing are poor. Comparative example 6 is a steel product obtained using the chemical composition and production process of example 1, and the performance obtained using the conventional spheroidizing annealing process is comparable to the performance obtained using the simplified annealing process of the present invention. Comparative example 7 is that the chemical components of the same furnace number in example 1 are adopted, a microstructure with pearlite and ferrite as main components is obtained according to a low-temperature rolling process, and by adopting the spheroidizing annealing process, the spheroidizing structure is grade 3, and the spheroidizing effect is poor.
Comparing the examples with the comparative examples, it can be seen that after annealing treatment is carried out by the spheroidizing annealing process of the present invention, the tensile, impact and fatigue test samples are firstly processed into the blank of the standard test sample, then the blank is subjected to oil quenching at 880 ℃ and 130 ℃, and is naturally cooled with air after being tempered at 530 ℃. The mechanical properties after heat treatment are shown in Table 4, the strength of the examples is more than 1000MPa, the elongation is more than 18%, the face shrinkage is more than 52%, and the normal temperature impact absorption energy KU 2 More than or equal to 70J and more than or equal to 450MPa. In the comparative example, under the condition that defects exist in the steel smelting or rolling process, if the spheroidizing annealing process with shorter time is forcibly adopted, various problems of mechanical property reduction are caused, and if cold forging steel with excellent performance is obtained, the annealing process cannot be simplified. The cold forging steel prepared by the production method has better strength, toughness and fatigue property on the premise of saving annealing time.
The invention has been described in detail hereinabove with reference to specific exemplary embodiments thereof. It will, however, be understood that various modifications and changes may be made without departing from the scope of the invention as defined in the appended claims. The detailed description and drawings are to be regarded as illustrative rather than restrictive, and any such modifications and variations are intended to be included within the scope of the present invention as described herein. Furthermore, the background is intended to be illustrative of the state of the art as developed and the meaning of the present technology and is not intended to limit the scope of the invention or the application and field of application of the invention.
More specifically, although exemplary embodiments of the invention have been described herein, the invention is not limited to these embodiments, but includes any and all embodiments modified, omitted, combined, e.g., between various embodiments, adapted and/or substituted, as would be recognized by those skilled in the art from the foregoing detailed description. The limitations in the claims are to be interpreted broadly based the language employed in the claims and not limited to examples described in the foregoing detailed description or during the prosecution of the application, which examples are to be construed as non-exclusive. Any steps recited in any method or process claims may be executed in any order and are not limited to the order presented in the claims. The scope of the invention should, therefore, be determined only by the appended claims and their legal equivalents, rather than by the descriptions and examples given above.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control. When a rate, pressure, temperature, time, or other value or parameter is expressed as a range, preferred range, or as a range defined by a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. For example, a range of 1 to 50 should be understood to include any number, combination of numbers, or subrange selected from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50, and all fractional values between the above integers, e.g., 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, and 1.9. With respect to sub-ranges, specifically consider "nested sub-ranges" that extend from any endpoint within the range. For example, nested sub-ranges of exemplary ranges 1-50 may include 1-10, 1-20, 1-30, and 1-40 in one direction, or 50-40, 50-30, 50-20, and 50-10 in another direction.
Claims (8)
1. A production method of 10.9-grade niobium microalloyed cold forging steel is characterized in that after iron-containing raw materials are mixed, electric furnace smelting, LF furnace refining, RH vacuum degassing, large round billet continuous casting, square billet rolling and high-speed wire rod rolling are sequentially carried out to obtain a hot rolled wire rod, and annealing processing is carried out on the hot rolled wire rod to obtain the cold forging steel; wherein the annealing treatment comprises: annealing, drawing, cold heading, quenching and tempering heat treatment, thread rolling and blackening to process the fastener; the annealing is to heat the wire rod to 700-725 ℃, keep the temperature for 4.5h to 5.5h, cool the wire rod to 640-700 ℃ at a speed of 15 ℃/h-25 ℃/h, keep the temperature for 3.5h to 4.5h, cool the wire rod to 500-550 ℃ at a speed of 15 ℃/h-25 ℃/h, and discharge the wire rod from the furnace, wherein the total annealing time is 19h to 21h;
the high-speed wire rod rolling comprises: the heating temperature is controlled to be 1050-1150 ℃, the soaking time is more than 30min, the heated casting blank is descaled by high-pressure water and then enters a continuous rolling unit for rolling, and the initial rolling temperature is 950-1050 ℃; controlling the temperature of the incoming wire reducing sizing mill unit to be 820-860 ℃, and rapidly cooling the incoming wire reducing sizing mill unit to the spinning temperature of 750-780 ℃ through a water tank; after air cooling for a certain time, when the temperature of the loose coil is reduced to 640-670 ℃, rapidly cooling by using a fan at a cooling rate of 3-6 ℃/s, cooling to 500-540 ℃, then slowly cooling in a heat-preservation cover at a cooling rate of 0.5-0.9 ℃/s, collecting the coil and hooking when the temperature is reduced to 430-460 ℃, and then air cooling to room temperature, packaging and weighing;
the iron-containing raw material comprises not less than 95.5wt% of Fe, 0.035wt% to 0.045wt% of Ti, 0.04wt% to 0.08wt% of Nb and 0.0003wt% to 0.0008wt% of B, wherein 29 is (Ti + Nb)/10B is not less than 6; the high-speed wire rolling comprises the steps of rolling wires by a roughing mill and a medium mill, controlling the temperature of a wire feeding reducing and sizing unit to be not lower than 800 ℃, and cooling the wires to the spinning temperature of not lower than 720 ℃ through a water tank.
2. The method for producing 10.9-grade niobium microalloyed cold forging steel according to claim 1, wherein (Ti + Nb)/10B = 8-25.
3. The production method of 10.9-grade niobium microalloyed cold forging steel according to claim 1, wherein the iron-containing raw material further comprises 0.40-0.50 wt% of C, 0.10-0.20 wt% of Si, 0.60-0.80 wt% of Mn, 0.30-0.50 wt% of Cr, 0.35-0.55 wt% of Mo, 0-0.015wt% of P, 0-0.025wt% of S and 0.015-0.040 wt% of Alt.
4. The production method of 10.9-grade niobium microalloyed cold forging steel according to claim 3, wherein the quenching and tempering heat treatment is carried out by oil quenching at 850-910 ℃ and tempering at 540-560 ℃.
5. The method for producing 10.9-grade niobium microalloyed cold forging steel according to any one of claims 1~4, wherein the electric furnace end point control C content of the electric furnace smelting is 0.06wt% to 0.20wt%, and P is less than or equal to 0.010wt%; the electric furnace smelting comprises slag-stopping and tapping, wherein 1/5 of molten steel is tapped by adding refining slag and lime, and 1/3 of molten steel is tapped by adding deoxidizer and alloy, and the sequence is as follows: aluminum iron, slag charge, silicomanganese, high carbon ferrochrome, ferromolybdenum and carburant, and after tapping, uniformly throwing aluminum particles on the steel slag surface according to the slag discharge amount.
6. The method for producing 10.9 niobium microalloyed cold forging steel according to any one of claims 1~4, wherein the LF furnace refining comprises: argon is blown at the bottom of the ladle in the whole process, premelted refining slag and lime are added for slagging, the alkalinity R =3~6, the white slag time is more than or equal to 20 minutes, and alloy is added before and in the middle period of refining according to the analysis result of components before entering the LF furnace to adjust the contents of Si, mn, cr, mo, V and Nb within the respective ranges.
7. The method for producing niobium microalloyed cold forging steel grade 10.9 as claimed in 1~4 wherein the RH vacuum degassing comprises: in the early stage of vacuum, if the vacuum degree is less than or equal to 100 Pa, the vacuum maintaining time is more than or equal to 10 minutes, and if the vacuum degree is more than 100 Pa and less than or equal to 200 Pa, the vacuum maintaining time is more than or equal to 15 minutes; the holding time is more than or equal to 10 minutes in the later period of vacuum; according to the analysis result of the components in the early stage of vacuum, if the components are required to be adjusted in the middle stage, the vacuum is kept for more than 5 minutes after the adjustment; carrying out calcium line feeding treatment after vacuum breaking; and carrying out soft argon blowing treatment before the station is out, wherein the soft argon blowing time is more than or equal to 15min.
8. The method for producing 10.9 niobium microalloyed cold forging steel according to any one of claims 1~4, wherein the continuous casting of the large round billet comprises the following steps: the casting method is characterized in that 380 large round billet continuous casting is adopted, whole-course protection casting is carried out, a protective sleeve and argon seal are adopted between a steel ladle and a tundish, the tundish uses a molten steel covering agent and argon blowing protection, an immersion type water gap is adopted between the tundish and a crystallizer, and the primary cooling water flow is 100m 3 /h~130m 3 H, controlling the secondary cooling specific water amount to be 1.0-1.4L/kg, controlling the superheat degree to be 10-40 ℃ in the casting process, and controlling the pulling speed to be 1.9-2.2 mm/min to obtain a casting blank;
the square billet rolling process comprises the following steps: controlling the temperature of a 380-size round billet in a soaking section of a heating furnace at 1200-1300 ℃, controlling the total heating time at 250min-350min, controlling the rolling temperature at 1100 +/-50 ℃, carrying out pile cooling after rolling, wherein the pile cooling temperature is more than or equal to 400 ℃, and carrying out surface and end grinding treatment on 150 square billets after rolling.
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| CN103789621A (en) * | 2012-11-03 | 2014-05-14 | 无锡市森信精密机械厂 | Preparation process of bainite structure steel for high-strength fastener |
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