CN114752847B - Annealing-free high-strength cold forging steel and manufacturing method thereof - Google Patents
Annealing-free high-strength cold forging steel and manufacturing method thereof Download PDFInfo
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- CN114752847B CN114752847B CN202110031191.8A CN202110031191A CN114752847B CN 114752847 B CN114752847 B CN 114752847B CN 202110031191 A CN202110031191 A CN 202110031191A CN 114752847 B CN114752847 B CN 114752847B
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
- B21J5/00—Methods for forging, hammering, or pressing; Special equipment or accessories therefor
- B21J5/002—Hybrid process, e.g. forging following casting
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- C—CHEMISTRY; METALLURGY
- 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
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- C—CHEMISTRY; METALLURGY
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- C—CHEMISTRY; METALLURGY
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention discloses annealing-free high-strength cold forging steel which contains the following chemical elements in percentage by mass besides Fe and inevitable impurity elements: c:0.32-0.35%, si:0.1-0.3%, mn:0.60-0.7%, cr:0.15-0.19%, ti:0.01-0.03%, B:0.0015 to 0.003 percent of the total weight of the components, and less than or equal to 0.006 percent of N; the microstructure of the non-annealed high-strength cold forging steel comprises ferrite and degenerated pearlite, wherein the phase proportion of the ferrite is more than or equal to 55%. In addition, the invention also discloses a manufacturing method of the annealing-free high-strength cold forging steel, which comprises the following steps: smelting, casting and hot rolling, wherein in the hot rolling step: controlling the finish rolling temperature to be 780-830 ℃, the reducing sizing temperature to be 780-810 ℃ and the high-speed wire spinning temperature to be 760-800 ℃; and cooling the coiled wire in a heat-insulating cover at a cooling speed of less than 1.5 ℃/s. The annealing-free high-strength cold heading steel can be produced without annealing, has excellent performance, and can be effectively used for producing fasteners such as bolts, screws, pins, nuts and the like.
Description
Technical Field
The invention relates to a steel material and a manufacturing method thereof, in particular to cold forging steel and a manufacturing method thereof.
Background
Cold heading steel is a steel material formed by one or more times of impact loading at room temperature, and has high requirements on cold forming performance of the material.
At present, cold heading steel has been widely used for producing standard parts (fasteners) such as bolts, screws, pins, nuts, and the like. In the prior art, the common fastener production process flow is as follows: annealing cold heading steel wire rods, pickling, phosphating, drawing, spheroidizing annealing, cold heading, quenching and tempering heat treatment, surface treatment and packaging. In the above fastener processing process, in order to ensure the cold heading performance of the material, the material is usually subjected to spheroidizing annealing operation.
In the prior art, the metallographic structure of the material after carbon steel spheroidizing annealing is ferrite and spheroidized carbide, the tensile strength of the material is generally not more than 530MPa, the surface shrinkage is more than 45 percent, and the material has good cold working performances such as cold heading and the like and can be effectively used for producing fasteners.
However, it should be noted that the spheroidizing annealing process has negative effects of higher energy consumption, greater environmental pressure and higher production cost on the whole fastener processing process. Thus, there is a need to provide a cold heading steel material for high strength fastener properties that can be directly cold headed without spheroidizing annealing.
Disclosure of Invention
The invention aims to provide novel annealing-free high-strength cold forging steel, which adopts reasonable chemical composition design, and improves the content of ferrite in a metallographic structure after hot rolling of a material by adding Mn and trace elements such as Cr, B, ti and the like on the basis of carbon steel, and ensures the strength and the hardenability of the steel after quenching and tempering by a user. The annealing-free high-strength cold heading steel has the advantages of tensile strength of not more than 560MPa, surface shrinkage of not less than 50%, excellent performance, low production cost, low environmental protection pressure and excellent cold deformation capability.
In order to achieve the aim, the invention provides the annealing-free high-strength cold forging steel which comprises the following chemical elements in percentage by mass in addition to Fe and inevitable impurity elements:
C：0.32-0.35％，Si：0.1-0.3％，Mn：0.60-0.7％，Cr：0.15-0.19％，Ti：0.01-0.03％，B：0.0015-0.003％，N≤0.006％；
the microstructure of the annealing-free high-strength cold forging steel comprises ferrite and degenerated pearlite, wherein the phase proportion of the ferrite is more than or equal to 55%.
Further, in the annealing-free high-strength cold forging steel provided by the invention, the mass percentages of all chemical elements are as follows:
c:0.32-0.35%, si:0.1-0.3%, mn:0.60-0.70%, cr:0.15-0.19%, ti:0.01-0.03%, B:0.0015-0.003 percent and less than or equal to 0.006 percent of N; the balance being Fe and other unavoidable impurities.
According to the technical scheme, the annealing-free high-strength cold forging steel is based on the carbon steel, mn and trace elements such as Cr, B and Ti are added to improve the content of ferrite in a metallographic structure of the hot-rolled material, and the strength and the hardenability of the steel after quenching and tempering by a user are ensured.
The design principle of each chemical element of the annealing-free high-strength cold forging steel is as follows:
c: in the annealing-free high-strength cold forging steel, C is the most main element influencing the cold plastic deformation of steel, and the higher the carbon content is, the higher the strength of the steel is, and the lower the plasticity is. In order to ensure that the steel can reach the strength and toughness performance of 8.8-grade fasteners after quenching and tempering, the mass percent of the element C in the annealing-free high-strength cold forging steel is controlled to be between 0.32 and 0.35 percent.
Of course, in some preferred embodiments, the mass percentage of C may be controlled to be between 0.32 and 0.34% in order to secure a higher ferrite proportion of the hot rolled material.
Si: in the non-annealed high-strength cold forging steel of the present invention, si is a residue of a deoxidizer during steel smelting, which can secure a lower oxygen content of the steel. However, it should be noted that when the content of Si element in the steel is too high, the plasticity of the steel material is adversely affected, and particularly, the cold plastic deformation of the steel is adversely affected. Therefore, in the annealing-free high-strength cold forging steel, the mass percent of Si element is controlled between 0.1 and 0.3 percent.
Mn: in the annealing-free high-strength cold forging steel, mn is a common strengthening element in the steel, can effectively improve the strength of the steel, and simultaneously, compared with C, the alloy strengthening effect of Mn causes much smaller plasticity loss, so that the steel can obtain better toughness matching by ensuring certain Mn content. However, it should be noted that the content of Mn element in steel should not be too high, and too high content of Mn element will adversely affect the plasticity and structure control of steel. Therefore, in the annealing-free high-strength cold forging steel of the present invention, the mass percentage of the Mn element is controlled to be 0.60 to 0.70%.
Of course, in some preferred embodiments, the mass percentage of Mn may be controlled to be between 0.60 and 0.65% for better practical effects.
Cr: in the annealing-free high-strength cold forging steel, cr can be used as a ferrite forming element in the steel, has a certain promotion effect on improving the proportion of ferrite in a hot-rolled metallographic structure, and can effectively improve the hardenability of the steel. However, the content of Cr element in steel should not be too high, and too high Cr not only makes it difficult to obtain low strength of hot rolled material, but also greatly increases production cost. Therefore, in the annealing-free high-strength cold forging steel, the mass percent of Cr is controlled to be 0.15-0.19%.
Ti: in the annealing-free high-strength cold forging steel, oxides, nitrides and carbides of Ti can form mass points at a higher temperature to ensure that B in the steel plays an effective role, and meanwhile, equiaxial crystallization of a molten steel solidification structure is facilitated, and the mass points can also inhibit growth of austenite grains in a subsequent hot working process. However, it should be noted that the content of Ti element in steel should not be too high, and too high Ti may affect the morphology of inclusions in steel, thereby affecting the impact plasticity and fatigue resistance of steel, and may also affect the smooth pouring of molten steel. Therefore, in the annealing-free high-strength cold forging steel, the mass percent of Ti element is controlled between 0.01 and 0.03 percent.
Of course, in some preferred embodiments, the mass percentage of Ti may be controlled between 0.01 and 0.02% for better performance.
B: in the annealing-free high-strength cold forging steel, B is also a ferrite forming element, and the hardenability of the steel can be effectively improved by adding a proper amount of B element into the steel. The content of B element in steel is not too high, and excessive B has certain harm to steel quality. Therefore, in the present invention, the mass percentage of B is controlled to be between 0.0015 and 0.003%.
N: in the annealing-free high-strength cold forging steel, the content of N element in the steel is not too high, the radius of N atoms is far smaller than that of metal elements, and the N atoms can form solid solution in the steel by interstitial atoms, so that the cold forging deformation of the steel is not facilitated. Therefore, in the annealing-free high-strength cold forging steel, the mass percent of the N element is controlled to be less than or equal to 0.006 percent.
Further, in the annealing-free high-strength cold forging steel, the mass percentage of each chemical element also meets at least one of the following conditions:
0.55％≤C+0.5Mn-0.2Cr≤0.65％；
0.0015％≤B+Ti/4-N≤0.005％。
in the annealing-free high-strength cold forging steel, the mass percentage of a single chemical element in the steel is controlled, and simultaneously, C, mn and Cr in the annealing-free high-strength cold forging steel can be preferably controlled to meet the following requirements: 0.55 percent to 0.5 percent of C +0.2 Mn-0.2Cr to 0.65 percent. The limited relation can improve the percentage content of ferrite after the material is subjected to hot rolling and slow cooling, thereby ensuring the strength and the hardenability of the material. In the above formula, C, mn and Cr respectively represent the mass percentage of each corresponding element.
Accordingly, in order to secure hardenability of the material, the function of the B element is sufficiently exerted, and the B, ti and N elements in the annealing-free high-strength cold heading steel may also be preferably controlled to satisfy: b + Ti/4-N is more than or equal to 0.0015% and less than or equal to 0.005%, and in the formula, B, ti and N respectively represent the mass percentage content of each corresponding element.
Further, in the annealing-free high strength cold heading steel according to the present invention, among inevitable impurity elements: s is less than or equal to 0.015 percent; and/or P is less than or equal to 0.02 percent.
In the technical scheme, the P element has extremely strong work hardening effect on steel, has serious segregation in the steel, and easily causes the wire rod to break when drawing and crack when cold heading. Therefore, in the annealing-free high-strength cold forging steel of the invention, the P element is required to be controlled to be P less than or equal to 0.02%. Accordingly, S is also a harmful element in steel, and S deteriorates hot workability of steel and has a negative effect on corrosion resistance of materials, so that the content of S in steel is controlled to be less than or equal to 0.015%.
It should be noted that both P and S are impurity elements in steel, and the content of the impurity elements in the non-annealed high-strength cold heading steel should be reduced as much as possible in order to obtain a steel material with better performance and better quality when the technical conditions allow.
Furthermore, in the annealing-free high-strength cold forging steel, the hardenability index DI is more than or equal to 0.85.
In the technical scheme, in order to ensure the hardenability of the annealing-free high-strength cold heading steel, the DI value of the hardenability index of the annealing-free high-strength cold heading steel is more than or equal to 0.85, namely the hardenability index is not lower than that of a material with similar carbon content which can be cold-deformed after conventional spheroidizing annealing.
Further, in the annealing-free high-strength cold forging steel, the performances of the steel meet the following requirements: the tensile strength is less than or equal to 560MPa, and the surface shrinkage is more than or equal to 50 percent.
Accordingly, another object of the present invention is to provide a method for manufacturing an annealing-free high strength cold heading steel, which has high production efficiency and low production cost. The manufacturing method can effectively manufacture the annealing-free high-strength cold forging steel without annealing on the premise of not increasing investment and production cost.
In order to achieve the above object, the present invention provides a method for manufacturing the non-annealed high strength cold heading steel, comprising the steps of: smelting, casting and hot rolling, wherein in the hot rolling step: controlling the finish rolling temperature to be 780-830 ℃, the reducing sizing temperature to be 780-810 ℃ and the high-speed wire spinning temperature to be 760-800 ℃; and cooling the coiled wire in a heat-insulating cover at a cooling speed of less than 1.5 ℃/s.
In the technical scheme, the manufacturing method of the annealing-free high-strength cold heading steel utilizes the existing equipment and process, and controls the finish rolling temperature, the diameter reducing and sizing temperature, the spinning temperature, the cooling temperature of the wire rod after spinning and the cooling speed of the wire rod in the heat-insulating cover through the optimized design of chemical components and production process on the premise of not increasing investment and production cost, so that the metallographic structure appearance of the annealing-free high-strength cold heading steel and the proportion of ferrite are effectively controlled, and the production of the annealing-free hot rolled wire rod of the annealing-free cold heading steel is realized.
The manufacturing method of the annealing-free high-strength cold heading steel can manufacture the annealing-free high-strength cold heading steel without annealing, thereby not only reducing the production cost, but also avoiding the pollution of annealing to the environment.
In the technical scheme, the manufacturing method of the annealing-free high-strength cold forging steel provided by the invention is characterized in that the rolling process parameters are optimally set, and the rolling-controlled and cold-controlled production process is adopted for production, so that the pearlite lamellar structure of the annealing-free high-strength cold forging steel is changed on the basis of ensuring higher ferrite proportion, and the dense long lamellar distribution is changed into sparse short rod distribution, so that the cold processing performance of the material is improved.
It should be noted that, in the above technical solution, the coil rod of the non-annealed high strength cold heading steel according to the present invention is obtained after the hot rolling step, and in some embodiments, the coil rod may be further processed through the drawing, cold heading and heat treatment steps.
Further, in the manufacturing method of the present invention, in the hot rolling step, the heating temperature of the high-speed wire-rolled wire rod is controlled to 850 to 920 ℃.
Further, in the manufacturing method of the present invention, after the hot rolling step, the method further includes the steps of: drawing, cold heading and heat treatment.
Compared with the prior art, the annealing-free high-strength cold forging steel and the manufacturing method thereof have the advantages and beneficial effects that:
compared with the prior art, in the chemical composition design of the annealing-free high-strength cold forging steel, the content of ferrite in a metallographic structure after hot rolling of a material is improved by adding Mn and trace elements such as Cr, B and Ti on the basis of a carbon steel, and the strength and hardenability of a steel after quenching and tempering treatment by a user are ensured. The annealing-free high-strength cold heading steel has the tensile strength of not more than 560MPa, the surface shrinkage rate of not less than 50 percent, excellent performance, can be produced without annealing, and can be effectively used for producing fasteners such as bolts, screws, pins, nuts and the like.
Correspondingly, the manufacturing method of the annealing-free high-strength cold heading steel has higher production efficiency and low production cost, and the production method utilizes the existing equipment and process to control the finish rolling temperature, the reducing sizing temperature, the spinning temperature and the cooling speed of the coil rod in the heat-insulating cover through the optimized design of chemical components and production process on the premise of not increasing investment and production cost, thereby controlling the metallographic structure appearance and ferrite phase proportion of the annealing-free high-strength cold heading steel and realizing the production of the hot rolled coil rod of the annealing-free cold heading steel.
Drawings
FIG. 1 is a metallographic structure diagram of an annealing-free high-strength cold-heading steel according to example 4.
FIG. 2 is a metallographic structure diagram of a comparative steel plate according to comparative example 1.
Detailed Description
The non-annealed high strength cold heading steel and the method for manufacturing the same according to the present invention will be further explained and illustrated with reference to specific examples, which, however, should not be construed to unduly limit the technical scope of the present invention.
Examples 1 to 6 and comparative example 1
The annealing-free high-strength cold forging steel of the embodiment 1-6 is prepared by the following steps:
(1) Smelting and casting were carried out according to the chemical compositions shown in tables 1-1 and 1-2: adopting an electric arc furnace or a converter for rough smelting; in order to reduce the oxygen content of the molten steel and control the inclusion, the alkalinity of the slag of the ladle refining furnace is controlled to be 4.0-6.5, and the retention time of yellow and white slag is more than 30 minutes; when necessary, carrying out VD or RH vacuum refining degassing treatment on the molten steel; and the fully killed molten steel is cast into steel ingots or steel billets under the condition of no oxidation protection.
(2) Hot rolling: controlling the finish rolling temperature to be 780-830 ℃; reducing the diameter temperature to 780-810 ℃; the high-speed wire spinning temperature is 760-800 ℃; cooling the wire rod after spinning to 700-730 ℃, and entering a stelmor cooling line heat-preserving cover, wherein the cooling speed of the wire rod is less than 1.5 ℃/s.
(3) And (4) drawing.
(4) And (5) cold heading.
(5) And (6) heat treatment.
In the step (2), the hot rolled wire rod corresponding to the embodiment can be obtained after the hot rolling step, the hot rolled wire rod is subjected to acid pickling, phosphorization and saponification, a steel wire with the surface meeting the cold heading requirement is manufactured by drawing the surface reduction rate within 5%, and the steel wire is subjected to cold heading, thread rolling, heat treatment, surface bluing or coating to obtain the cold heading steel fastener corresponding to the embodiment.
The chemical element components and the related process design of the annealing-free high-strength cold forging steel of the embodiments 1 to 6 meet the requirements of the design specification of the invention. The comparative sample of comparative example 1 is a material which can be cold headed only after spheroidizing treatment in the market, and the design of chemical element components thereof has parameters which do not satisfy the design requirements of the present invention.
Tables 1 to 1 and tables 1 to 2 show the mass percentage ratios of the respective chemical elements of the non-annealed high strength cold heading steels of examples 1 to 6 and the comparative steel sheet of comparative example 1.
TABLE 1-1. (wt%, balance Fe and unavoidable impurities other than P, S)
Tables 1-2.
Note: in the above table, DI = (0.171 +0.001 × C +0.265 × C) × (1 +3.333 × Mn) × (1 +0.7 × Si) × (1 +2.16 × Cr), where C, mn, si and Cr in the above formula each represent a numerical value before the percentage content of each corresponding element by mass; c, mn and Cr in the C +0.5Mn-0.2Cr formula respectively represent the mass percentage content of each corresponding element; b, ti and N in the B + Ti/4-N formula respectively represent the mass percentage content of each corresponding element.
Table 2 lists the specific process parameters for the non-annealed high strength cold heading steels of examples 1-6.
Table 2.
The obtained finished products of the non-annealed high-strength cold-heading steels of examples 1 to 6 and the comparative sample of comparative example 1 were sampled, and observation and mechanical property tests were performed, and the obtained observation results and mechanical property detection results are listed in table 3.
The relevant mechanical property test method is as follows:
(1) And (3) tensile test testing: under room temperature conditions, according to GB/T228.1 part 1 of tensile test of metallic materials: the test was carried out by the method "Room temperature test method".
(2) It should be noted that, when the microstructures of the non-annealed high strength cold-heading steels of examples 1 to 6 and the comparative sample of comparative example 1 were observed, the phase ratio of ferrite in the microstructures of each of the examples and the comparative steel could be obtained by a colorimetric method.
Table 3 lists the observation results and performance test results of the non-annealed high strength cold heading steels of examples 1 to 6 and the comparative steel sheet of comparative example 1.
Table 3.
As can be seen from Table 3, compared with the comparative steel sheet of comparative example 1 in the prior art, the non-annealed high-strength cold heading steels of examples 1-6 of the present invention all have tensile strengths of not more than 560MPa, surface shrinkages of not less than 50%, strengths significantly lower than those of conventional products, better plasticity of materials, higher ferrite proportion, and mechanical properties close to those of conventional products after spheroidizing annealing (about 530 MPa).
FIG. 1 is a metallographic structure diagram of an annealing-free high-strength cold-heading steel according to example 4.
FIG. 2 is a metallographic structure diagram of a comparative steel plate according to comparative example 1.
As can be seen from the combination of fig. 1 and 2, the lamellar structure of pearlite in the anneal-free high strength cold heading steel of example 4 is partially degraded compared to the conventional hot rolled material of comparative example 1. In the embodiment shown in fig. 1, the microstructure of the non-annealed high strength cold heading steel of example 4 includes ferrite and degenerated pearlite, in which the phase proportion of ferrite is 62%.
In conclusion, compared with the prior art, in the chemical composition design of the annealing-free high-strength cold forging steel, on the basis of the carbon steel, mn, trace Cr, B, ti and other elements are added to improve the content of ferrite in a metallographic structure of the material after hot rolling, and the strength and the hardenability of the steel after quenching and tempering by a user are ensured. The annealing-free high-strength cold heading steel has the tensile strength of not more than 560MPa, the surface shrinkage rate of not less than 50 percent, excellent performance, can be produced without annealing, and can be effectively used for producing fasteners such as bolts, screws, pins, nuts and the like.
It should be noted that the combination of the features in the present application is not limited to the combination described in the claims of the present application or the combination described in the specific examples, and all the features described in the present application may be freely combined or combined in any manner unless contradicted by each other.
It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. It is apparent that the present invention is not limited to the above embodiments and similar changes or modifications can be easily made by those skilled in the art from the disclosure of the present invention and shall fall within the scope of the present invention.
Claims (8)
1. The annealing-free high-strength cold forging steel is characterized by further comprising the following chemical elements in percentage by mass in addition to Fe and inevitable impurity elements:
C：0.32-0.35％，Si：0.1-0.3％，Mn：0.60-0.7％，Cr：0.15-0.19％，
Ti：0.01-0.03％，B：0.0015-0.003％，N≤0.006％；
the mass percentage of each chemical element also satisfies: c +0.5Mn-0.2Cr is more than or equal to 0.55 percent and less than or equal to 0.65 percent; b + Ti/4-N is more than or equal to 0.0015% and less than or equal to 0.005%;
the microstructure of the annealing-free high-strength cold forging steel comprises ferrite and degenerated pearlite, wherein the phase proportion of the ferrite is more than or equal to 55%;
the annealing-free high-strength cold heading steel is prepared by the following steps: controlling the finish rolling temperature to be 780-830 ℃, the reducing sizing temperature to be 780-810 ℃ and the high-speed wire spinning temperature to be 760-800 ℃; and cooling the coiled wire in a heat-insulating cover at a cooling speed of less than 1.5 ℃/s.
2. The annealing-free high-strength cold forging steel as claimed in claim 1, wherein the chemical elements are, by mass:
c:0.32-0.35%, si:0.1-0.3%, mn:0.60-0.7%, cr:0.15-0.19%, ti:0.01-0.03%, B:0.0015-0.003 percent and less than or equal to 0.006 percent of N; the balance being Fe and other unavoidable impurities.
3. The annealing-free high strength cold heading steel as claimed in claim 1 or 2, wherein among inevitable impurity elements: s is less than or equal to 0.015 percent; and/or P is less than or equal to 0.02 percent.
4. The annealing-free high strength cold heading steel as claimed in claim 1 or 2, wherein the hardenability index DI is 0.85 or more.
5. The annealing-free high strength cold heading steel as claimed in claim 1 or 2, wherein the properties satisfy: the tensile strength is less than or equal to 560MPa, and the surface shrinkage is more than or equal to 50 percent.
6. The method for manufacturing the annealing-free high strength cold heading steel as claimed in any one of claims 1 to 5, comprising the steps of: smelting, casting and hot rolling, wherein in the hot rolling step: controlling the finish rolling temperature to be 780-830 ℃, the reducing sizing temperature to be 780-810 ℃ and the high-speed wire spinning temperature to be 760-800 ℃;
and cooling the coiled wire in a heat-insulating cover at a cooling speed of less than 1.5 ℃/s.
7. The manufacturing method according to claim 6, wherein in the hot rolling step, the heating temperature of the high-speed wire-rolled wire rod is controlled to be 850-920 ℃.
8. The manufacturing method according to claim 6 or 7, further comprising, after the hot rolling step, the step of: drawing, cold heading and heat treatment.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202110031191.8A CN114752847B (en) | 2021-01-11 | 2021-01-11 | Annealing-free high-strength cold forging steel and manufacturing method thereof |
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