KR100256349B1 - The manufacturing method for low carbon steel wire rod with excellent wire drawing property - Google Patents

Abstract

PURPOSE: A method for manufacturing a mild steel wire rod for ultra fine wire having superior rod drawability is provided not only to decrease distribution of non-metallic inclusions influencing adverse effect on the generation of the snapping of a wire during the wire drawing of the ultra fine wire but also solve the problems of coarsening during annealing heat treatment, and formation and growth of the crystal grains by properly controlling aluminum constituent in the steel and a temperature of the heat treatment during the annealing heat treatment after the wire drawing. CONSTITUTION: In a method for manufacturing a mild steel wire rod for ultra fine wire, the method for manufacturing a mild steel wire rod having superior rod drawability comprises the processes of wire drawing the wire rod after manufacturing a steel billet comprising 0.003 to 0.05 wt.% of C, 0.1 to 0.3 wt.% of Mn, 0.02 wt.% or less of P, 0.02 wt.% or less of S, 0.03 to 0.08 wt.% of Al, and a balance of Fe and inevitable impurities into a wire rod; and finally wire drawing the annealing heat treated wire rod after annealing heat treating the drawn wire rod in the temperature range of 630 to 680 deg.C.

Description

Manufacturing method of mild steel wire with excellent drawability

1 is an optical microscope observation picture according to the annealing heat treatment temperature of the present invention and the comparative material.

The present invention relates to a method for manufacturing a fine steel wire rod for ultrafine wires, and more particularly, to a method for producing a fine steel wire rod for fine wire strands excellent in workability.

Among the mild steel wires, the steel grades used for the use of ultra fine wires (0.5 mm dia or less) include SWRM6M1 and SWRM6B.These steel grades are used for annealing wires, galvanized wire mesh, and welding materials used between nails and nails. have. Since these steel grades are drawn in the ultra fine wire and used according to the characteristics of each application, the steel grades should have excellent quality characteristics. The freshness mentioned here is evaluated based on the disconnection rate during the fresh processing, and the less the disconnection rate, the better the freshness.

Fine steel wire rod is usually 5.5mm Wire rod of 1.2-1.6mm Fresh and annealing (750 ℃) 0.4mm It is manufactured by final drawing until the end, and zinc plating is used during the drawing process according to the characteristics of each application.

However, if the purpose of the mild steel wire is to be used for micro wire, the influence of non-metallic inclusions cannot be excluded as a detrimental effect on freshness. This is because when a mild steel wire is used for ultra fine wire, if a large amount of non-metallic inclusion exists, it is very likely to cause disconnection during drawing due to the generation and propagation of microcracks at the interface between the non-metallic inclusion and the base metal during the drawing process. Strict management of nonmetallic inclusions is required. In order to reduce the distribution of these nonmetallic inclusions, it is most important to reduce the content of molten steel oxygen because oxygen in the molten steel is the main factor for forming oxide-based nonmetallic inclusions. Therefore, as a means for reducing the oxide-based non-metallic inclusions, it is possible to consider a method of reducing the oxygen remaining in the molten steel during steelmaking by adding a small amount of Al and Ca as a deoxidizer.

In the case of the conventional materials, since the mild steel wire is manufactured without using deoxidizers such as Al and Ca, the oxygen content in the hand is quite high. This results in a large distribution of oxide-based nonmetallic inclusions. Therefore, when the non-metallic inclusions are excessively distributed in the wire rod when the mild steel wire is used for the use of the ultra-fine wire, it is difficult to use the ultra-fine wire because of the excessive disconnection during the drawing process.

Oxygen content in the material can be reduced by adding deoxidizing agents such as Al and Ca during steelmaking, but when Al content is high, grain coarsening and abnormal grains are generated during annealing heat treatment after drawing due to Al-based precipitates that precipitate during annealing heat treatment. Rather, they have a more detrimental effect on freshness than non-metallic inclusions. Therefore, in order to use mild steel wire for ultra fine wire, it is necessary to suppress grain coarsening and abnormal grain formation during annealing and heat treatment after drawing. .

Here, the abnormal grain growth refers to grain growth in which specific grains grow coherently.

Techniques related to abnormal grain formation and growth control in conventional annealing heat treatment include Yamazaki <Japanese Iron and Steel, CAMP '80 -S1246 P646> and Ochiai et al. (Iii) No. 319 (1985) P 44).

Yamajiki et al. Argued that the amount of Al in the iron and steel, CAMP '80 -S1246 P646, had a decisive effect on the formation of anomalous grains rather than the Al / N ratio, and they indicated that the sol-Al content was less than 0.020%. In the case of -killed steel, since sol-Al content occurs at 750 ℃ in the range of 0.003-0.006%, annealing treatment should be performed at 750 ℃ or below, or sol-Al content should be maintained at 0.003% or above 0.006%. It has been reported that the formation of abnormal grains can be suppressed.

Ochiai et al., In 日本 製 鐵 硏 寇 No. 329 (1985) P44, argued that it is necessary to select an appropriate range of Al or Al / N ratio to prevent the occurrence of abnormal grains in low-carbon steel grades. He thinks that continuous cast steel with low Al content has a larger tendency of abnormal grains than Al-killed steel with high Al content, because the Al / N ratio enters the hazardous area because there is little Al even if the N content is changed. In case of selecting Al / N ratio, if it is less than 1, it will inevitably be more than 7 because it has a big influence on quality characteristics.Increasing Al amount as a means to increase Al / N ratio is a burden of price increase. It has been argued that it is necessary to prevent intake nitrogen in the nitrogen blowing, refining and continuous casting processes.

The conventional materials mentioned above cannot be used for ultrafine wires due to the formation of abnormal grains when the Al content is high. In addition, when the Al content is low, the generation of abnormal grains is suppressed, but there is a disadvantage that the disconnection rate is high when the ultra fine wire is drawn due to the excessive distribution of coarse nonmetallic inclusions.

Accordingly, the present inventors have solved the above problems and conducted research and experiments to produce a fine steel wire rod for excellent fine wire drawing, when the addition of 0.03-0.07% Al element, it is possible to control the oxygen content in the molten steel It can be confirmed that the distribution of oxide-based nonmetallic inclusions can be reduced, and that grain size coarsening and abnormal grain formation and growth can be suppressed during annealing heat treatment when the annealing heat treatment temperature is in the range of 630-680 ° C. during the annealing heat treatment after drawing. Based on this, the present invention has been proposed.

According to the present invention, while appropriately controlling the aluminum component in steel and the heat treatment temperature during annealing after annealing, reducing the distribution of non-metallic inclusions that have a detrimental effect on the occurrence of disconnection during ultrafine wire drawing, grain coarsening and annealing of grains during annealing and The purpose of the present invention is to provide a method for producing a fine steel wire rod for excellent wire drawing, which has solved growth.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In the manufacturing method of the ultra-fine stranded steel wire rod, the weight%, carbon (C): 0.003-0.05%, manganese (Mn): 0.1-0.3%, phosphorus (P): 0.02% or less, sulfur (S) : Less than 0.02%, aluminum (Al): 0.03-0.08% balance: Fe and a billet of steel composed of inevitable impurities are made of wire rod, and then freshly annealed and heat-treated at a temperature range of 630-680 ° C. The present invention relates to a method for producing a mild steel wire rod having excellent drawing property by drawing.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The above object of the present invention is to control the composition of the steel and the annealing heat treatment temperature as described above, to reduce the distribution of oxide-based non-metallic inclusions that are harmful to the drawability during ultra-fine wire drawing, coarsening grains, annealing grains during annealing heat treatment And it becomes possible to suppress growth, and the solution is possible.

In the present invention, the carbon content is preferably limited to the range of 0.003-0.005% by weight (hereinafter referred to as '%'), because it is difficult to secure sufficient strength of the material at 0.003% or less, and strength at 0.05% or more. This is because the toughness and ductility decrease with increasing.

It is preferable to limit the manganese content to 0.1-0.3% because it is difficult to expect deoxidation effect below 0.1%, and above 0.3%, it is difficult to secure the target strength after final drawing due to work hardening during drawing processing. Because it is difficult.

It is preferable to limit the upper limit to 0.02% because phosphorus (P) is segregated at grain boundaries and degrades toughness. Sulfur (S) is detrimental in toughness and forms an emulsion, which is detrimental to freshness during ultrafine wire drawing. It is preferable to limit the upper limit to 0.02% because

Aluminum is a deoxidizer and an element that reduces the distribution of oxide-based nonmetallic inclusions while reducing the oxygen content of molten steel in the present invention, and the content thereof is preferably limited to 0.03-0.08% because the deoxidation effect is less than 0.03%. This is because it is difficult to reduce the distribution of oxide nonmetallic inclusions, and at 0.08%, the deoxidation effect is saturated and the possibility of forming coarse oxide nonmetallic inclusions during steelmaking is high, which may adversely affect the fresh workability. .

On the other hand, in the present invention, after forming the steel as described above, after manufacturing the billet of the steel such as wire rod drawing (primary drawing) and annealing heat treatment in the temperature range of 630-680 ℃, and then the final drawing (secondary drawing Processing) to produce a fine steel wire rod for the fine wire, the reason is as follows.

The annealing temperature after the first drawing is limited to the range of 630-680 ℃ before the second drawing. The recrystallization is not completely completed when the heat treatment temperature is below 630 ℃. This is because it may affect the homogeneous deformation and deleteriously affect the freshness. Above 680 ° C, Al-based precipitates are unevenly deposited at grain boundaries or dislocation cells, resulting in grain coarsening and abnormality. This is because it causes the formation and growth of grains, which adversely affects fresh workability.

Here, the wire rod is usually 5.5mm Primary wire is 1.2mm ~ 1.6mm To fresh up to the range of, the secondary fresh is 0.4mm It says to be fresh.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

After holding the billet formed as shown in Table 1 at 1100 ° C. for 2 hours and rapidly rolling with a wire rod of 5.5 mm in diameter, the rolled wire rod product having a diameter of 5.5 mm was rapidly cooled to 880 ° C. by water spraying and wound up at 500 ° C. It was prepared by slow cooling after cooling to an average cooling rate of 1.2 ℃ / sec until.

Subsequently, the wire rod having a diameter of 5.5 mm manufactured as described above was firstly freshened to a diameter of 1.2 mm, and then 4 at 650 ° C. for the inventive materials (1, 2) and 750 ° C. for the comparative materials (1, 2). After the annealing heat treatment by time, the secondary drawing (final drawing) at the final drawing speed of 500m / min to 0.4mm in diameter.

As such, the tensile properties in the wire state of the wire rods, the tensile properties after the wire processing, and the ferrite grain size (hereinafter referred to as 'FGS') after drawing and annealing heat treatment were measured and the results are shown in Table 2 below. Shown in

In Table 2, the tensile properties in the wire rod state of the inventive material (1,2) and the comparative material (1,2) and the tensile properties after the drawing process were investigated using a tensile tester. FGS is to investigate the grain growth behavior during annealing heat treatment. FGS was measured in wire rod state and FGS in annealing heat treatment state after wire drawing. The measurement method was linear intercept method (Iinear intercept method). Was the rolling direction.

Table 2 above shows the mechanical properties and FGS of the invention material (1, 2) and the comparative material (1, 2) before and after the wire, and the mechanical properties and effects of the FGS of the invention material (1, 2) are compared with the comparative material ( There was no difference between the two groups. However, the tensile strength of the inventive materials (1,2) is about 2-4kg / mm ² lower than that of the comparative materials (1,2) and the cross-sectional reduction rate is about 3-6% higher than that of the comparative materials (1,2). It is judged that the carbon content is low on the alloy composition of the present invention. As a result, in the case of the present invention, it can be seen that there is no change in FGS compared to the comparative material after the freshness and after the addition of Al.

Example 2

In order to confirm the distribution of oxide-based nonmetallic inclusions harmful to freshness during ultra-fine wire drawing, the distribution of oxide-based nonmetallic inclusions was investigated with respect to the inventive materials (1,2) and comparative materials (1,2) of Example 1. The results are shown in Table 3 below.

Here, the distribution of the nonmetallic inclusions of the inventive material (1, 2) and the comparative material (1, 2) was usually measured by an image analyzer using the SEP 1570 method which is commonly used in evaluating the distribution of oxide-based inclusions.

As can be seen in Table 3, in the case of the comparative material (1,2), the K (3) value of the oxide shows a value of 42-48, while in the case of the invention material (1,2), the K (3) value is Since the level is about 5-7, it can be seen that the distribution of non-metal oxide inclusions is small. This is due to the oxygen content directly affecting the distribution of nonmetallic inclusions. The K (3) value at this time is the value of KL Number (the larger the inclusion size, the larger the inclusion size), and the weight of the inclusions multiplied by the weight used in the SEP 1570 method for all inclusions 3 to 10. Therefore, the smaller the K (3) value, the less nonmetallic inclusions are distributed. On the other hand, in the distribution of sulfides, the invention materials (1,2) were less than the comparative materials (1,2).

Example 3

In order to confirm the structure change of the invention material and the comparative material according to the annealing heat treatment temperature change during the annealing heat treatment of the wire after the primary drawing, the wires of the invention material (1) and the comparative material (1) of Example 1 were 650 ° C and 750, respectively. Annealing heat treatment for 4 hours at a temperature of ℃ ℃ and observed the change in the structure with an optical microscope and the results are shown in Figure 1 (a) for the invention material (1) and Figure 1 (b) for the comparative material (1) Shown in

As can be seen in Figure 1, when the heat treatment at the heat treatment temperature range of 650 ℃ of the present invention, the crystal grains of both the invention material (1) and the comparative material (1) was not observed, but the heat treatment temperature is within the scope of the present invention In the case of the deviation of 750 ℃, the comparative material (1) did not generate abnormal grains, but the inventive material (1) can be seen that the abnormal grains are observed. Therefore, in the case of the invention material (1) it can be seen that the same normal structure as the comparative material (1) can be secured within the temperature range of 630-680 ℃ which is the heat treatment condition of the present invention.

Example 4

In order to evaluate the drawability of the inventive material and the comparative material, the drawability of the inventive material (1, 2) and the comparative material (1, 2) of Example 1 was evaluated by the disconnection rate, and the results are shown in Table 4 below.

As can be seen in Table 4, the invention material (1,2) satisfying the scope of the present invention, the disconnection rate is 0.1 per ton compared to the case of the comparative material (1,2) that does not satisfy the scope of the present invention On the other hand, in the case of the comparative material (1, 2), the disconnection rate of the present invention material (1, 2) was improved two to three times. Accordingly, it can be seen that the freshness of the inventive material (1,2) is superior to that of the comparative material (1,2).

As described above, the present invention reduces the distribution of harmful non-metallic inclusions having a great influence on the occurrence of disconnection during the fine wire drawing, and has excellent fine workability, which solves both grain coarsening and abnormal grain formation and growth during annealing heat treatment. There is an effect that can provide a method for producing a mild steel wire rod.

Claims (1)

In the method for producing a fine steel wire rod for ultrafine wire, in weight%, carbon (C): 0.003-0.05%, manganese (Mn): 0.1-0.3%, phosphorus (P): 0.02% or less, sulfur (S): 0.02% Hereinafter, a billet of steel composed of aluminum (Al): 0.03-0.08%, balance: Fe and unavoidable impurities is prepared by wire, and then annealed and heat-treated at a temperature range of 630-680 ° C., followed by final drawing. Method for producing a mild steel wire rod excellent in drawability, characterized in that it comprises.