CN109957724B - Wire rod for cold heading and method for manufacturing same - Google Patents
Wire rod for cold heading and method for manufacturing same Download PDFInfo
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- CN109957724B CN109957724B CN201810795127.5A CN201810795127A CN109957724B CN 109957724 B CN109957724 B CN 109957724B CN 201810795127 A CN201810795127 A CN 201810795127A CN 109957724 B CN109957724 B CN 109957724B
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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
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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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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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
- C21D2201/00—Treatment for obtaining particular effects
- C21D2201/05—Grain orientation
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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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- Organic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
The invention provides a wire rod for cold heading and a manufacturing method thereof, wherein excellent cold workability can be ensured even without spheroidizing annealing heat treatment. A wire rod for cold heading according to one embodiment of the present invention includes, in wt%: 0.01% to less than 0.15%, Si: 0.3% or less, Mn: 0.2% to 0.75%, P: 0.03% or less, S: 0.03% or less, sol.Al: 0.01 to 0.05%, Cr: 0.5% or less, Ti: 0.005% to 0.05%, N: 0.01% or less, and the balance Fe and other impurities, and satisfying the following formula (1), wherein the average grain size of ferrite surrounded by ferrite grain boundaries having a difference in crystal orientation of 15 DEG or more is 15 to 40 mu m, { (A/4) + [ (B x 30)/(2A +40) ] } × (C/3) ≥ 700 … … formula (1) wherein A represents the average equivalent circle diameter (mu m) of the ferrite grain boundaries having a difference in crystal orientation of 15 DEG or more, B represents the area fraction (area%) of the ferrite grain boundary grains having a difference in crystal orientation of 15 DEG or more with respect to the entire ferrite phase, and C represents the average hardness (Hv) of the ferrite phase.
Description
Technical Field
The present invention relates to a wire rod for cold heading and a method for manufacturing the same. More particularly, the present invention relates to a wire rod for cold heading suitable for use as an automobile material or a material for mechanical parts and a method for manufacturing the same.
Background
The common wire rod product is manufactured into a final product by carrying out hot rolling, cold drawing, spheroidizing heat treatment, cold drawing, cold heading, rapid cooling and tempering on the wire rod.
Cold working methods are widely used as automobile materials and materials for machine parts such as bolts and nuts because of their excellent productivity as compared with hot working methods or mechanical cutting methods and their great effect of reducing heat treatment costs.
However, in order to manufacture machine parts by cold working, it is necessary that deformation resistance is low and ductility is excellent at cold working. If the deformation resistance of steel is high, the life of a tool used in cold working is reduced, and if the ductility of steel is low, the steel is likely to crack at the time of cold working, which causes defective products.
Therefore, the spheroidizing annealing heat treatment is performed on the cold-working wire rod before the cold working. When the spheroidizing annealing heat treatment is performed, the steel softening deformation resistance is reduced, the ductility is improved, and the cold workability can be improved. However, when the spheroidizing annealing heat treatment is performed, the cost increases and the manufacturing efficiency decreases. Therefore, there is a need for development of a wire rod that can ensure excellent cold workability without further performing spheroidizing annealing heat treatment.
Disclosure of Invention
Technical problem
The invention aims to provide a wire rod which can ensure excellent cold workability even without spheroidizing annealing heat treatment and a manufacturing method thereof.
Technical scheme
A wire rod for cold heading according to one embodiment of the present invention includes, in wt%: 0.01% to less than 0.15%, Si: 0.3% or less, Mn: 0.2% to 0.75%, P: 0.03% or less, S: 0.03% or less, sol.Al: 0.01 to 0.05%, Cr: 0.5% or less, Ti: 0.005% to 0.05%, N: 0.01% or less, and the balance Fe and other impurities, and satisfying the following formula (1), wherein the average grain size of ferrite surrounded by ferrite grain boundaries having a crystal orientation difference of 15 DEG or more is 15 to 40 [ mu ] m.
{ (A/4) + [ (B × 30)/(2A +40) ] } × (C/3) ≧ 700 … … formula (1)
Wherein A represents the average equivalent circle diameter (μm) of ferrite grain boundaries having a difference in crystal orientation of 15 ° or more, B represents the area fraction (area%) of ferrite grain boundary grains having a difference in crystal orientation of 15 ° or more with respect to the entire ferrite phase, and C represents the average hardness (Hv) of the ferrite phase.
Further, according to an embodiment of the present invention, B: 0.006% or less, and can satisfy the following formula (2).
0 < 0.31Ti +1.4B-N < 0.004 … … type (2)
Further, according to an embodiment of the present invention, the following formula (3) may be satisfied.
0.8 ≦ [ (Si + Mn + Cr)/10C + Ti/C ] ≦ 2.3 … … type (3)
Further, according to an embodiment of the present invention, the microstructure is composed of pearlite and ferrite, and a fraction of the ferrite in an area fraction may be 80% or more.
A method of manufacturing a wire rod for cold heading according to another embodiment of the present invention includes: a step of heating a billet having a component content satisfying the following formulae (1) and (2), the billet containing C in wt%: 0.01% to less than 0.15%, Si: 0.3% or less, Mn: 0.2% to 0.75%, P: 0.03% or less, S: 0.03% or less, sol.Al: 0.01 to 0.05%, Cr: 0.5% or less, Ti: 0.005% to 0.05%, B: 0.006% or less, N: 0.01% or less, and the balance Fe and other unavoidable impurities; a step of hot rolling the heated billet at a finish rolling temperature of 920 ℃ to 1020 ℃; and a step of coiling and cooling the hot-rolled wire rod.
0.8 ≦ [ (Si + Mn + Cr)/10C + Ti/C ] ≦ 2.3 … … formula (1)
0 < 0.31Ti +1.4B-N < 0.004 … … type (2)
Further, according to an embodiment of the present invention, the cooling step may include a first cooling step of cooling from a finish rolling temperature to a temperature range lower than a coiling temperature at a cooling rate of 5 ℃/s to less than 20 ℃/s in the hot rolling.
Further, according to an embodiment of the present invention, the cooling step may further include a second cooling step of cooling from the coiling temperature to less than 750 ℃ at a cooling rate of 2 ℃/s to less than 5 ℃/s after the first cooling step.
Further, according to an embodiment of the present invention, the cooling step may further include a third cooling step of cooling from 750 ℃ to 650 ℃ at a cooling rate of 1 ℃/s to less than 2 ℃/s after the second cooling step.
Further, according to an embodiment of the present invention, the cooling step may further include a fourth cooling step of cooling from 650 ℃ to less than 400 ℃ at a cooling rate of less than 0.8 ℃/s (excluding 0 ℃/s) after the third cooling step.
Further, according to an embodiment of the present invention, the heating temperature in the step of heating the billet may be 1000 ℃ to 1150 ℃.
Further, according to an embodiment of the present invention, the reeling temperature in the reeling step may be 800 ℃ to 880 ℃.
Effects of the invention
The wire rod and the manufacturing method thereof according to the embodiment of the present invention can provide a wire rod in which deformation resistance at the time of cold working can be suppressed even if the spheroidizing annealing heat treatment is omitted.
Detailed Description
The following provides a detailed description of embodiments of the invention. The following embodiments are provided to fully convey the technical idea of the present invention to those skilled in the art to which the present invention pertains. The present invention is not limited to the following embodiments, and can be implemented in other ways.
A wire rod for cold heading according to one embodiment of the present invention includes, in wt%: 0.01% to less than 0.15%, Si: 0.3% or less, Mn: 0.2% to 0.75%, P: 0.03% or less, S: 0.03% or less, sol.Al: 0.01 to 0.05%, Cr: 0.5% or less, Ti: 0.005% to 0.05%, N: 0.01% or less, and the balance Fe and other impurities, and the following formula (1).
{ (A/4) + [ (B × 30)/(2A +40) ] } × (C/3) ≧ 700 … … formula (1)
Wherein A represents the average equivalent circle diameter (μm) of ferrite grain boundaries having a difference in crystal orientation of 15 ° or more, B represents the area fraction (area%) of ferrite grain boundary grains having a difference in crystal orientation of 15 ° or more with respect to the entire ferrite phase, and C represents the average hardness (Hv) of the ferrite phase.
Further, the wire rod for cold heading according to one embodiment of the present invention may further include B: 0.006% or less, and can satisfy the following formula (2).
0 < 0.31Ti +1.4B-N < 0.004 … … type (2)
Further, the wire rod for cold heading according to one embodiment of the present invention may further satisfy the following formula (3).
0.8 ≦ [ (Si + Mn + Cr)/10C + Ti/C ] ≦ 2.3 … … type (3)
The effects and contents of the respective components contained in the wire rod for cold heading according to the present invention are explained below. The% of the following components is expressed by weight%.
The content of C (carbon) is 0.01% to less than 0.15%.
C is an element for improving the strength of the wire rod. In order to improve the strength of the wire rod, C needs to be contained by 0.01% or more, and more preferably 0.03% or more. However, if the C content is too large, the deformation resistance of the steel may sharply increase, thereby causing deterioration of cold forgeability. Therefore, the upper limit of the C content is limited to 0.14%, and more preferably, the upper limit of the C content is limited to 0.12%.
The content of Si (silicon) is 0.3% or less.
Si is an element useful as a deoxidizer. However, if the Si content is too large, the deformation resistance of the steel is sharply increased due to solid solution strengthening, thereby resulting in deterioration of cold forgeability. Therefore, the upper limit of the Si content is limited to 0.3%, and more preferably, the upper limit of the Si content may be 0.2%.
The content of Mn (manganese) is 0.2-0.75%.
Mn is an element useful as a deoxidizer and a desulfurizer. For this effect, Mn is preferably contained at 0.2% or more, and more preferably at 0.3% or more. However, if the Mn content is too large, the strength of the steel itself becomes too high, and the deformation resistance of the steel sharply increases, thereby resulting in deterioration of cold forgeability. Therefore, the upper limit of the Mn content is limited to 0.75%, and more preferably, the upper limit of the Mn content may be 0.7%.
The content of P (phosphorus) is less than or equal to 0.03 percent.
P is an impurity inevitably contained, and segregates to grain boundaries to reduce the toughness of the steel and also to cause a reduction in delayed fracture resistance. Therefore, the P content is preferably controlled to be as low as possible. In theory, it is more advantageous to control the P content to 0%, but P is inevitably contained in the manufacturing process. Therefore, it is important to control the upper limit of the P content, which is limited to 0.03% in the present invention.
The content of S (sulfur) is less than or equal to 0.03 percent.
S is an inevitable impurity, segregates to grain boundaries to reduce ductility of the steel, forms sulfides in the steel, and deteriorates delayed fracture resistance and stress relaxation properties. Therefore, the S content is preferably controlled to be as low as possible. In theory, it is more advantageous to control the S content to 0%, but S is inevitably contained in the production process. Therefore, it is important to control the upper limit of the S content, which is limited to 0.03% in the present invention.
Al (soluble aluminum) content is 0.01% to 0.05%.
Al is an element useful as a deoxidizer. In the present invention, in order to have such an effect, Al needs to be contained by 0.01% or more, preferably Al may be contained by 0.015% or more, and more preferably Al may be contained by 0.02% or more. However, if the Al content is too large, the formation of AlN increases the austenite grain refining effect, which may result in a decrease in cold forgeability. Therefore, the upper limit of the Al content in the present invention is limited to 0.05%.
The content of Cr (chromium) is less than or equal to 0.5 percent.
Cr plays a role of promoting ferrite and pearlite transformation at the time of hot rolling. In addition, Cr prevents the steel from excessively improving the strength and precipitates in the form of carbide in the steel, thereby reducing the amount of solid-solution carbon and contributing to the reduction of dynamic strain aging caused by the solid-solution carbon. However, if the Cr content is too large, the strength of the steel itself becomes too high, and the deformation resistance of the steel sharply increases, thereby resulting in deterioration of cold forgeability. Therefore, the upper limit of the Cr content is limited to 0.5%, and more preferably, the Cr content may be 0.4% or less.
The content of Ti (titanium) is 0.005% to 0.05%.
Ti is a carbonitride forming element, and when Ti is contained in the steel, it is advantageous for the fixation of C and N, and may be advantageous for cold forgeability. However, if a large amount of microscopic Ti (C, N) precipitates are precipitated, the matrix strength by precipitation strengthening increases rapidly, and there is a possibility that cold forgeability deteriorates. Therefore, the content, size and distribution of Ti need to be appropriately controlled. If the Ti content is less than 0.005%, the C, N fixing effect is insufficient. On the contrary, if the Ti content is more than 0.05%, there is a problem that Ti precipitates are formed in a large amount. Therefore, the content of Ti in the present invention is limited to 0.005% to 0.05%, and more preferably, the content of Ti may be 0.005% to 0.03%.
The content of N (nitrogen) is less than or equal to 0.01 percent.
N is an inevitable impurity, and if the content of N is too large, the amount of solid solution nitrogen increases, and the deformation resistance of the steel increases sharply, thereby deteriorating cold forgeability. In theory, it is more advantageous to control the content of N to 0%, but N is inevitably contained in the manufacturing process. Therefore, it is important to control the upper limit of the N content, and in the present invention, the upper limit of the N content is limited to 0.01%, preferably the upper limit of the N content may be 0.008%, and more preferably the upper limit of the N content may be 0.007%.
The content of B (boron) is less than or equal to 0.006%.
B is a nitride-forming element, and when B is contained in the steel, fixation of solid-solution N is facilitated, and cold forgeability may be facilitated. However, when used in combination with Ti, the effects thereof may be lost, and therefore, it is necessary to use them in an appropriate combination. Further, if the B content is too large, BN precipitates are formed at grain boundaries, which may adversely affect the ductility of the steel, and therefore, the upper limit of the B content needs to be controlled. The upper limit of the content of B is limited to 0.006%, preferably the upper limit of the content of B may be 0.005%, more preferably the upper limit of the content of B may be 0.004%.
According to an embodiment of the present invention, the contents of Ti, B, and N may satisfy the following formula (2).
0 < 0.31Ti +1.4B-N < 0.004 … … type (2)
If the value of the formula (2) is less than 0, the deformation resistance of the steel may increase sharply, resulting in deterioration of cold forgeability. If the value of formula (2) is greater than 0.004, excessive precipitates may be precipitated, which may result in a reduction in the ductility of the steel. Thus, according to one embodiment of the present invention, the value of equation (2) is limited to 0 to 0.004.
According to one embodiment of the present invention, the contents of Si, Mn, Cr, C, and Ti satisfy the following formula (3).
0.8 ≦ [ (Si + Mn + Cr)/10C + Ti/C ] ≦ 2.3 … … type (3)
If the value of formula (3) is less than 0.8, the content of C is too large, which may result in deterioration of cold forgeability. On the contrary, if the value of the formula (3) is more than 2.3, the deformation resistance of the steel may be sharply increased, possibly resulting in deterioration of cold forgeability. Therefore, the value of formula (3) is limited to 0.8 to 2.3.
The wire rod according to one embodiment of the present invention may include ferrite (ferrite) and pearlite (pearlite) as a microstructure. The fraction of ferrite may be 80% or more (excluding 100%) by area fraction. Pearlite may contain 20% or less (excluding 0%) by area fraction. This structure ensures excellent cold workability and also ensures strength after drawing.
Further, according to an embodiment of the present invention, the average grain size of the ferrite may be 15 μm to 40 μm, and preferably, the average grain size of the ferrite may be 20 μm to 35 μm. If the ferrite average grain size is less than 15 μm, the grain boundary becomes finer, the strength increases, and the cold forgeability may decrease. Conversely, when the average grain size of ferrite is larger than 40 μm, the strength may be decreased.
The average particle diameter is an average equivalent circular diameter (equivalent circular diameter) of crystal grains detected by observing a cross section of the wire rod in the longitudinal direction.
Further, the microstructure of the wire rod according to one embodiment of the present invention may satisfy the following formula (1). In the present invention, it was confirmed through further experiments that cold forgeability is improved when the average circle-equivalent diameter (a) of ferrite grain boundaries having a difference in crystal orientation of 15 ° or more, the proportion (B) of ferrite grain boundary grains having a difference in crystal orientation of 15 ° or more, and the average hardness (C) of the ferrite phase satisfy the following formula (1).
{ (A/4) + [ (B × 30)/(2A +40) ] } × (C/3) ≧ 700 … … formula (1)
If the value of formula (1) is less than 700, cold forgeability may be reduced.
The average hardness value C is (Hv,1/2d + Hv,1/4d)/2, Hv,1/2d and Hv,1/4d respectively represent the hardness of the wire measured from the surface of the wire to the position 1/2d and 1/4d in the diameter (d) direction of the wire on a cross section perpendicular to the longitudinal direction of the wire.
A method of manufacturing a wire rod for cold heading according to one embodiment of the present invention is described in detail below.
The steel sheet satisfying the above composition is heated. At this time, the heating temperature may be 1000 ℃ to 1150 ℃, and preferably the heating temperature may be 1030 ℃ to 1130 ℃. If the heating temperature is less than 1000 ℃, the heat distortion resistance increases, and the productivity may be lowered. Conversely, if the heating temperature is higher than 1150 ℃, ferrite grains become coarse, possibly resulting in a reduction in ductility.
Then, hot rolling was performed to obtain a wire rod. At this time, the finish rolling temperature may be 920 ℃ to 1020 ℃, and preferably, the finish rolling temperature may be 930 ℃ to 1000 ℃. If the finish rolling temperature is lower than 920 ℃, the strength may be increased due to the ferrite grain refinement, and the deformation resistance may be increased. Conversely, if the finish rolling temperature is higher than 1020 ℃, ferrite grains become coarse, possibly resulting in a reduction in ductility.
Then, the wire rod was wound and cooled. At this time, the winding temperature of the wire may be 800 to 880 ℃, and preferably, the winding temperature of the wire may be 820 to 860 ℃. If the coiling temperature is less than 800 ℃, the martensite in the surface layer portion generated during cooling is not recovered by heat recovery, but tempered martensite is generated, and further hard and brittle steel is generated, which may cause a decrease in cold forgeability. On the contrary, if the coiling temperature is higher than 880 ℃, thick scale is formed on the surface, there is a possibility that a problem occurs in removing scale, and productivity is lowered because the cooling time becomes long.
Cooling may be performed sequentially as described below.
The cooling step may include a first cooling step of cooling from the finish rolling temperature to a temperature range lower than the coiling temperature at a cooling rate of 5 ℃/s to less than 20 ℃/s in the hot rolling. The first cooling step may be carried out together with the coiling.
A second cooling step of cooling from the coiling temperature to less than 750 ℃ at a cooling rate of 2 ℃/s to less than 5 ℃/s after the first cooling step may be included.
A third cooling step of cooling from 750 ℃ to 650 ℃ at a cooling rate of 1 ℃/s to less than 2 ℃/s after the second cooling step may be included.
A fourth cooling step may be included after the third cooling step from 600 ℃ to less than 400 ℃ at a cooling rate of less than 0.8 ℃/s (excluding 0 ℃/s).
The present invention will be described in detail below by way of examples, but the following examples are only illustrative of the present invention and are not intended to limit the scope of the present invention.
Examples
After heating a steel sheet having the composition of Table 1 below at 1100 ℃ for 3 hours, hot-rolled into
A wire rod is manufactured. At this time, the finish rolling temperature was 950 ℃ and the rolling ratio was 80% kept constant. Then, the wire rod was manufactured by cooling to 850 ℃ through the first cooling step (CR1) and winding, and then cooling through the second cooling step (CR2), the third cooling step (CR3), and the fourth cooling step (CR 4). The cooling process is shown in table 2 below.
[ Table 1]
[ Table 2]
Then, the cooled wire rods were subjected to drawing amounts of 10%, 20%, and 30% to produce steel wires, and the cold forgeability was evaluated and shown in table 3 below. For the evaluation of cold forgeability, after a compression test of a true strain of 0.85 was performed on a slit compression sample, whether or not cracks were generated was evaluated, and the generation of cracks was represented by "GO" and the absence of cracks was represented by "NG".
[ Table 3]
From table 3, it was confirmed that the microstructure, the average size of ferrite grain boundaries surrounded by grain boundaries having a crystal orientation difference of 15 ° or more, the ferrite fraction, and the average hardness of the ferrite phase satisfy the ranges of the present invention, and the cold forgeability is excellent for invention examples 1 to 4 satisfying the alloy composition and the manufacturing conditions according to one example of the present invention.
In comparative example 1, the cooling rate in the third cooling step was 0.7 ℃/s and did not satisfy the range of the present invention, and the value of formula (1) was 700 or less and did not satisfy the range of the present invention, and cracks were generated at a drawing amount of 30%, and therefore, cold workability was poor.
In comparative example 2, the values of formula (2) and formula (3) do not satisfy the range of the present invention, the cooling rates in the first cooling step, the second cooling step, and the third cooling step do not satisfy the range of the present invention, the value of formula (1) does not satisfy the range of the present invention, the size of ferrite grains does not satisfy the range of the present invention, and cracks are generated at a drawing amount of 30%, so that cold workability is poor.
In comparative example 3, the content of C did not satisfy the range of the present invention, and the values of formula (2) and formula (3) did not satisfy the range of the present invention, and the cooling rates of the second cooling step and the fourth cooling step did not satisfy the range of the present invention, so the ferrite fraction did not reach 80%, and the value of formula (1) did not satisfy the range of the present invention. Therefore, cracks were generated at the drawing amounts of 20% and 30%, and cold workability was poor.
In comparative example 4, the content of C did not satisfy the range of the present invention, and the values of formula (2) and formula (3) did not satisfy the range of the present invention, the cooling rates of the first cooling step and the fourth cooling step did not satisfy the range of the present invention, and the ferrite grain size did not satisfy the range of the present invention, so the ferrite fraction did not reach 80%, and the value of formula (1) did not satisfy the range of the present invention. Therefore, cracks were generated at the drawing amounts of 20% and 30%, and cold workability was poor.
The exemplary embodiments of the present invention have been described above, but the present invention is not limited thereto, and those skilled in the art can make various changes and modifications within a scope not exceeding the concept and scope of the claims.
Claims (7)
1. The utility model provides a wire rod for cold-heading which characterized in that:
the wire consists of the following components in weight percent, C: 0.01% to less than 0.15%, Si: 0.3% or less, Mn: 0.2% to 0.75%, P: 0.03% or less, S: 0.03% or less, sol.Al: 0.01 to 0.05%, Cr: 0.5% or less, Ti: 0.005% to 0.05%, N: less than or equal to 0.01%, the balance Fe and other impurities,
the ferrite surrounded by ferrite grain boundaries having a crystal orientation difference of 15 DEG or more has an average grain diameter of 15 to 40 [ mu ] m and satisfies the following formula (1),
{ (A/4) + [ (B × 30)/(2A +40) ] } × (C/3) ≧ 700 … … formula (1)
Wherein A represents the average equivalent circle diameter of ferrite grain boundaries having a difference in crystal orientation of 15 DEG or more in terms of μm, B represents the area fraction of ferrite grain boundary grains having a difference in crystal orientation of 15 DEG or more in terms of area% relative to the entire ferrite phase, and C represents the average hardness of the ferrite phase in terms of Hv.
2. The wire rod for cold heading according to claim 1, wherein:
the wire further comprises B: less than or equal to 0.006 percent,
and satisfies the following formula (2):
0 is more than or equal to 0 [0.31Ti +1.4B-N ] is more than or equal to 0.004 … … formula (2).
3. The wire rod for cold heading as claimed in claim 1 or 2, wherein:
the wire satisfies the following formula (3):
0.8 ≦ [ (Si + Mn + Cr)/10C + Ti/C ] ≦ 2.3 … … formula (3).
4. The wire rod for cold heading according to claim 1, wherein:
the microstructure is composed of pearlite and ferrite, and the fraction of ferrite in terms of area fraction is 80% or more.
5. A method for manufacturing a wire rod for cold heading, comprising:
a step of heating a billet having a component content satisfying the following formulae (1) and (2), the billet consisting of the following components in% by weight, C: 0.01% to less than 0.15%, Si: 0.3% or less, Mn: 0.2% to 0.75%, P: 0.03% or less, S: 0.03% or less, sol.Al: 0.01 to 0.05%, Cr: 0.5% or less, Ti: 0.005% to 0.05%, B: 0.006% or less, N: 0.01% or less, and the balance Fe and other unavoidable impurities;
0.8 ≦ [ (Si + Mn + Cr)/10C + Ti/C ] ≦ 2.3 … … formula (1)
0 < 0.31Ti +1.4B-N < 0.004 … … type (2)
A step of hot rolling the heated billet at a finish rolling temperature of 920 ℃ to 1020 ℃;
a step of coiling the hot-rolled wire rod and a step of cooling the hot-rolled wire rod;
the cooling step includes a first cooling step of cooling from a finish rolling temperature to a temperature range lower than a coiling temperature at a cooling rate of 5 ℃/s to less than 20 ℃/s in the hot rolling,
a second cooling step of cooling from the coiling temperature to less than 750 ℃ at a cooling rate of 2 ℃/s to less than 5 ℃/s after the first cooling step,
a third cooling step of cooling from 750 ℃ to 650 ℃ at a cooling rate of 1 ℃/s to less than 2 ℃/s after the second cooling step, and
a fourth cooling step of cooling from 650 ℃ to below 400 ℃ at a cooling rate of less than 0.8 ℃/s exclusive of 0 ℃/s after the third cooling step.
6. The manufacturing method of a wire rod for cold heading as claimed in claim 5, wherein:
the heating temperature in the step of heating the blank is 1000 ℃ to 1150 ℃.
7. The manufacturing method of a wire rod for cold heading as claimed in claim 5, wherein:
the coiling temperature in the coiling step is 800 ℃ to 880 ℃.
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| Application Number | Priority Date | Filing Date | Title |
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| KR1020170178711A KR102042062B1 (en) | 2017-12-22 | 2017-12-22 | Steel wire rod for cold forging and methods for manufacturing thereof |
| KR10-2017-0178711 | 2017-12-22 |
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| CN109957724A CN109957724A (en) | 2019-07-02 |
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| CN111647794B (en) * | 2020-04-17 | 2021-09-24 | 江阴兴澄特种钢铁有限公司 | Steel wire rod and wire rod packing steel wire and manufacturing method thereof |
| CN113025908B (en) * | 2021-03-09 | 2022-04-26 | 马鞍山钢铁股份有限公司 | Cold heading steel hot-rolled wire rod for torsion bar of automobile safety belt and production method thereof |
| CN113737099B (en) * | 2021-09-09 | 2022-06-10 | 广东韶钢松山股份有限公司 | Tool steel suitable for large-deformation cold machining forming and preparation method thereof, and sleeve and preparation method thereof |
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| JPS5773169A (en) * | 1980-10-24 | 1982-05-07 | Central Glass Co Ltd | Sealed metallic wire rod for reinforcing glass |
| JPS60245722A (en) * | 1984-05-21 | 1985-12-05 | Kawasaki Steel Corp | Manufacture of high tensile wire rod |
| JPH0759738B2 (en) * | 1988-10-17 | 1995-06-28 | 新日本製鐵株式会社 | Ultra-high-strength PC steel wire or steel bar excellent in uniform elongation and method for producing the same |
| JPH08232046A (en) * | 1995-02-23 | 1996-09-10 | Nippon Steel Corp | High strength steel wire excellent in twisting crack resistance |
| JP3844443B2 (en) * | 2002-04-12 | 2006-11-15 | 新日本製鐵株式会社 | Profile wire for reinforcing submarine optical fiber cable |
| JP2007327084A (en) * | 2006-06-06 | 2007-12-20 | Kobe Steel Ltd | Wire rod having excellent wire drawability and its production method |
| KR101382664B1 (en) * | 2009-11-17 | 2014-04-07 | 신닛테츠스미킨 카부시키카이샤 | Steel wire for low temperature annealing and producing method thereof |
| MX344834B (en) * | 2010-08-30 | 2017-01-09 | Kobe Steel Ltd | Steel wire material for high-strength spring which has excellent wire-drawing properties and process for production thereof, and high-strength spring. |
| JP5704717B2 (en) * | 2011-06-23 | 2015-04-22 | 株式会社神戸製鋼所 | Machine structural steel for cold working, method for producing the same, and machine structural parts |
| KR101714916B1 (en) * | 2015-11-12 | 2017-03-10 | 주식회사 포스코 | Wire rod having excellent cold forging characteristics and method for manufacturing same |
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| KR102042062B1 (en) | 2019-11-08 |
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