CN115852106A - Spheroidizing annealing method for medium-low carbon alloy cold heading steel - Google Patents
Spheroidizing annealing method for medium-low carbon alloy cold heading steel Download PDFInfo
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- CN115852106A CN115852106A CN202211539741.8A CN202211539741A CN115852106A CN 115852106 A CN115852106 A CN 115852106A CN 202211539741 A CN202211539741 A CN 202211539741A CN 115852106 A CN115852106 A CN 115852106A
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Abstract
The invention relates to a spheroidizing annealing method of medium and low carbon alloy cold forging steel, which comprises the steps of carrying out drawing deformation on the medium and low carbon alloy cold forging steel after acid washing, phosphorization and saponification, carrying out spheroidizing annealing on a cold-drawn wire rod, heating the wire rod to 700-720 ℃, preserving heat for 6h, cooling to 680 ℃ at the speed of 5-10 ℃/h, then cooling to 250-300 ℃ at the speed of 100 ℃/h, preserving heat for 2h, and then discharging the spheroidized alloy steel wire after slow cooling. The carbide particles with proper coarsening distribution state is obtained by improving the spheroidizing annealing process, the material strength is reduced, the plasticity is increased, and the comprehensive mechanical property is obviously improved. The spheroidized medium and low carbon alloy cold heading steel after spheroidizing annealing has good spheroidizing structure and can not crack in the subsequent cold heading process; has the characteristics of simple process, good effect and the like. By controlling the cooling and temperature speed, the distribution condition of carbide particles in the steel after spheroidization is changed, so that the carbide particles are more uniformly distributed in the matrix and inside crystal grains, and the segregation of the carbide at the grain boundary is reduced, thereby enhancing the plasticity.
Description
Technical Field
The invention relates to the technical field of spheroidizing annealing, in particular to a spheroidizing annealing method of medium and low carbon alloy cold heading steel.
Background
Spheroidizing annealing is annealing in which carbide in steel is spheroidized to obtain a structure of spherical or granular carbide uniformly distributed on a ferrite matrix. Spheroidizing annealing is mainly used for eutectoid steels and hypereutectoid steels to obtain a spheroidized structure (called a spheroidized structure because of not necessarily eutectoid components) similar to granular pearlite, thereby reducing hardness, improving machinability, and preparing the structure for quenching. The spheroidized structure not only has better plasticity and toughness than the flaky structure, but also has slightly lower hardness. When a workpiece with a spheroidized structure is machined, the cutter can avoid cutting hard and brittle cementite and can pass through soft ferrite, so that the service life of the cutter is prolonged, and the machinability of steel is improved.
In the prior art, the raw material for producing 8.8-grade and higher high-strength standard parts is usually medium-carbon steel or medium-low carbon alloy cold heading steel in a hot rolling state, and the raw material is required to bear larger total deformation amount in the cold heading process production process of the standard parts, so that the raw material is required to have good plasticity and lowest hardness. The room temperature structure of the cold heading steel wire rod in the hot rolling state is ferrite and lamellar pearlite structures with higher strength and hardness, which are not beneficial to the cold heading processing of a standard part, easily causes cold heading cracking and reduces the utilization rate of raw materials.
In the wire rod reforming process, spheroidizing annealing treatment is needed after cold drawing so as to reduce the hardness, improve the plasticity and improve the processability. The product obtained by the existing spheroidizing annealing process has higher strength and lower plasticity, and the cold-formed part also has the quality problems of higher hardness and the like.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a spheroidizing annealing method of medium-low carbon alloy cold forging steel, which obtains a properly coarsened carbide particle distribution state by improving a spheroidizing annealing process, reduces the material strength, increases the plasticity and obviously improves the comprehensive mechanical property.
The above object of the present invention is achieved by the following technical solutions:
a spheroidizing annealing method of medium and low carbon alloy cold forging steel is characterized in that the medium and low carbon alloy cold forging steel is subjected to drawing deformation after being subjected to acid washing, phosphorization and saponification, spheroidizing annealing is carried out on a cold-drawn wire rod, the wire rod is heated to 700-720 ℃, the temperature is kept for 6h, the wire rod is cooled to 680 ℃ at the speed of 5-10 ℃/h, then the wire rod is cooled to 250-300 ℃ at the speed of 100 ℃/h, the temperature is kept for 2h, and then the spheroidized alloy steel wire is slowly cooled and taken out of a furnace.
The present invention in a preferred example may be further configured to: the diameter of the cold-drawn wire is 5.5-15mm.
The present invention in a preferred example may be further configured to: the medium and low carbon alloy cold forging steel comprises the following chemical components in percentage by weight: 0.12 to 0.22 percent of C, 0.15 to 0.32 percent of Si, 0.24 to 0.55 percent of Mn0.20 percent, less than or equal to 0.20 percent of Cr, less than or equal to 0.03 percent of P, less than or equal to 0.05 percent of S, less than or equal to 0.06 percent of AI, less than or equal to 0.25 percent of Ni, less than or equal to 0.20 percent of Cu, and the balance of Fe and impurity elements.
The present invention in a preferred example may be further configured to: and in the step of drawing deformation, cold drawing deformation is carried out for one or two passes.
The present invention in a preferred example may be further configured to: when spheroidizing annealing treatment is carried out, introducing nitrogen, simultaneously opening an exhaust valve, heating to 750-780 ℃ along with the furnace, and heating for 150min; and (3) keeping the temperature of the medium-low carbon alloy cold forging steel in a spheroidizing annealing furnace at 700-720 ℃ for 6h, and conveying protective atmosphere into the spheroidizing annealing furnace in the constant temperature process.
The present invention in a preferred example may be further configured to: the flow rate regulation range of nitrogen gas delivery is 25-30m 3 /h。
The present invention in a preferred example may be further configured to: the flow rate of the protective atmosphere is regulated within the range of 12-18m 3 /h。
The present invention in a preferred example may be further configured to: the protective atmosphere is methanol high-temperature pyrolysis gas or natural gas catalytic pyrolysis gas.
In summary, the invention includes at least one of the following beneficial technical effects:
the invention discloses a spheroidizing annealing method of medium-low carbon alloy cold forging steel, which obtains a properly coarsened carbide particle distribution state by improving a spheroidizing annealing process, reduces the material strength, increases the plasticity and obviously improves the comprehensive mechanical property. The spheroidized medium and low carbon alloy cold heading steel after spheroidizing annealing has good spheroidizing structure and can not crack in the subsequent cold heading process; has the characteristics of simple process, good effect and the like. By controlling the cooling and temperature speed, the distribution condition of carbide particles in the steel after spheroidization is changed, so that the carbide particles are more uniformly distributed in the matrix and inside crystal grains, and the segregation of the carbide at the grain boundary is reduced, thereby enhancing the plasticity.
Detailed Description
The technical solution in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application; it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all embodiments, and all other embodiments obtained by those of ordinary skill in the art without any inventive work based on the embodiments in the present application belong to the protection scope of the present application.
The first embodiment is as follows:
the invention discloses a spheroidizing annealing method of medium and low carbon alloy cold forging steel, which comprises the steps of carrying out drawing deformation on the medium and low carbon alloy cold forging steel after acid washing, phosphorization and saponification, carrying out spheroidizing annealing on a cold-drawn wire rod, heating the wire rod to 700-720 ℃, preserving heat for 6h, cooling to 680 ℃ at the speed of 5-10 ℃/h, then cooling to 250-300 ℃ at the speed of 100 ℃/h, preserving heat for 2h, and then discharging the spheroidized alloy steel wire after slow cooling. The diameter of the cold-drawn wire is 5.5-15mm.
The medium and low carbon alloy cold heading steel comprises the following chemical components in percentage by weight: 0.12 to 0.22 percent of C, 0.15 to 0.32 percent of Si, 0.24 to 0.55 percent of Mn0.20 percent, less than or equal to 0.20 percent of Cr, less than or equal to 0.03 percent of P, less than or equal to 0.05 percent of S, less than or equal to 0.06 percent of AI, less than or equal to 0.25 percent of Ni, less than or equal to 0.20 percent of Cu, and the balance of Fe and impurity elements.
And in the step of drawing deformation, cold drawing deformation is carried out for one or two passes. When spheroidizing annealing treatment is carried out, introducing nitrogen, opening an exhaust valve, heating to 750-780 ℃ along with the furnace, and heating for 150min; and (3) keeping the temperature of the medium-low carbon alloy cold forging steel in the spheroidizing annealing furnace at 700-720 ℃ for 6h, and conveying protective atmosphere into the spheroidizing annealing furnace in the constant temperature process. The flow rate regulation range for nitrogen delivery is 25-30m3/h. The flow rate of the protective atmosphere is adjusted within the range of 12-18m3/h. The protective atmosphere is methanol high-temperature cracking gas or natural gas catalytic cracking gas.
Before the process is improved, a large amount of fine granular carbides are aggregated and distributed in an adhesive manner along the crystal boundary of massive ferrite, and the quantity of carbide particles in the crystal is very small. The distribution position corresponds to the height of the region where the original pearlite is located, which shows that although the appearance of the original lamellar pearlite disappears and is transformed into fine grained pearlite through spheroidizing annealing, the dispersion precipitation of carbide particles is not realized. Since the particles are aggregated at the grain boundaries, the grain boundaries are weakened, which is disadvantageous to spheroidizing annealing. Lateral carbide accumulation is an important cause of higher annealing hardness. After the process is improved, the phenomenon of carbide grain boundary segregation basically disappears, the overall dispersivity is improved, part of particles are coarsened and grown, and the spheroidization effect is good.
The comparison result of the mechanical properties of the medium-low carbon alloy cold forging steel before and after the process improvement is shown in table 1.
| Class of the Process | Tensile strength/MPa | Elongation after Break (%) | Reduction of area (%) |
| Before improvement | 385 | 36 | 73 |
| After improvement | 335 | 36 | 82 |
Analysis shows that after the process is improved, the tensile strength of the medium-low carbon alloy cold forging steel is reduced from 385MPa to 335MPa, the elongation after fracture is kept unchanged, and the reduction of area is increased from 73% to 82%. This shows that after the process is improved, the strength of the material is reduced, the plasticity is increased, and the comprehensive mechanical property is better.
The key of the spheroidizing annealing process is that the material is heated and insulated at the temperature of 20-30 ℃ above Ac1, so that the material is partially austenitized, a large number of undissolved carbide particles are remained in austenite, and the carbide can be re-precipitated by taking the undissolved particles as a core in the subsequent cooling process and is aggregated and grown, thereby realizing the spheroidizing of the carbide.
Before the process is improved, the conventional one-stage spheroidizing annealing is adopted, and due to the factors such as cooling speed, heat preservation time and the like, carbon elements after austenitizing cannot be fully diffused in a matrix, so that undissolved particles cannot be fully precipitated by taking the undissolved particles as cores in the cooling process. After the process is improved, the heat preservation time of the original heat preservation section is shortened from original 10 hours to 6 hours under the premise that the temperature of the original heat preservation section is basically unchanged, and the temperature is gradually reduced to about 680 ℃ at an extremely slow cooling speed. For medium and low carbon alloy cold forging steel, ar1=680 ℃, therefore, in the process of slow cooling, the material is basically in an austenite region, pearlite type transformation hardly occurs, but as the temperature is gradually reduced, the solubility product of carbide is in a descending trend while carbon is diffused in a matrix, and the precipitation of second phase particles in the subsequent cooling process is facilitated. Then, cooling to 250-300 ℃ at a relatively high speed and keeping the temperature for 2 hours, similar to the low-temperature tempering aging process. The new carbide can be precipitated in the temperature range, and the precipitated carbide realizes partial aggregation and coarsening and is in a state of uniform and dispersed distribution of fine particles.
The implementation principle of the embodiment is as follows: the invention discloses a spheroidizing annealing method of medium-low carbon alloy cold forging steel, which obtains a properly coarsened carbide particle distribution state by improving a spheroidizing annealing process, reduces the material strength, increases the plasticity and obviously improves the comprehensive mechanical property. The spheroidized structure of the medium and low carbon alloy cold heading steel after spheroidizing annealing is good, and the medium and low carbon alloy cold heading steel cannot crack in the subsequent cold heading process; has the characteristics of simple process, good effect and the like. By controlling the cooling and temperature speed, the distribution condition of carbide particles in the steel after spheroidization is changed, so that the carbide particles are more uniformly distributed in the matrix and inside crystal grains, and the segregation of the carbide at the grain boundary is reduced, thereby enhancing the plasticity.
The embodiments of the present invention are preferred embodiments of the present invention, and the scope of the present invention is not limited by these embodiments, so: all equivalent changes made according to the structure, shape and principle of the invention are covered by the protection scope of the invention.
Claims (8)
1. A spheroidizing annealing method of medium and low carbon alloy cold forging steel is characterized by comprising the following steps: the medium and low carbon alloy cold forging steel is subjected to drawing deformation after acid washing, phosphorization and saponification, spheroidizing annealing treatment is carried out on the cold-drawn wire rod, the wire rod is heated to 700-720 ℃, the temperature is kept for 6h, the wire rod is cooled to 680 ℃ at the speed of 5-10 ℃/h, then the wire rod is cooled to 250-300 ℃ at the speed of 100 ℃/h, the temperature is kept for 2h, and then the spheroidized alloy steel wire is discharged after slow cooling.
2. The spheroidizing annealing method of the medium and low carbon alloy cold heading steel according to claim 1, wherein the diameter of the cold-drawn wire rod is 5.5-15mm.
3. The spheroidizing annealing method of the medium-low carbon alloy cold forging steel as claimed in claim 1, wherein the medium-low carbon alloy cold forging steel comprises the following chemical components in percentage by weight: 0.12 to 0.22 percent of C, 0.15 to 0.32 percent of Si, 0.24 to 0.55 percent of Mn0.20 percent, less than or equal to 0.20 percent of Cr, less than or equal to 0.03 percent of P, less than or equal to 0.05 percent of S, less than or equal to 0.06 percent of AI, less than or equal to 0.25 percent of Ni, less than or equal to 0.20 percent of Cu, and the balance of Fe and impurity elements.
4. The spheroidizing annealing method of the medium and low carbon alloy cold heading steel according to claim 1, wherein in the step of drawing deformation, the drawing deformation is carried out in one or two passes.
5. The spheroidizing annealing method of the medium and low carbon alloy cold forging steel according to claim 1, characterized in that, during the spheroidizing annealing treatment, nitrogen is introduced, simultaneously an exhaust valve is opened, the temperature is raised to 750-780 ℃ along with the furnace, and the temperature raising time is 150min; and (3) keeping the temperature of the medium-low carbon alloy cold forging steel in a spheroidizing annealing furnace at 700-720 ℃ for 6h, and conveying protective atmosphere into the spheroidizing annealing furnace in the constant temperature process.
6. The spheroidizing annealing method of the medium-low carbon alloy cold forging steel according to claim 5, wherein the flow rate of the nitrogen gas is adjusted within a range of 25-30m 3 /h。
7. The spheroidizing annealing method of the medium-low carbon alloy cold forging steel according to claim 5, wherein the flow rate of the protective atmosphere is adjusted within the range of 12-18m 3 /h。
8. The spheroidizing annealing method of the medium-low carbon alloy cold forging steel according to claim 1, wherein the protective atmosphere is methanol high-temperature pyrolysis gas or natural gas catalytic pyrolysis gas.
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