JPS593535B2 - Mild steel wire rod for ultra-fine wire - Google Patents

Description

[Detailed description of the invention] Conventionally, mild steel wire rods drawn to a diameter of 093 mm or less have a diameter of 5 mm or less.
A wire rod with a diameter of 0.05 mm is hot rolled, the oxidized scale on the surface of the wire is peeled off, and a wire drawing pretreatment is performed to process the wire rod to a diameter of about 192 mm.

This is usually called primary wire drawing, but since wire drawing after that causes a large amount of work hardening, it is not possible to process the wire to O, 3 mrnφ or less unless it is softened by annealing at about 650° C. for 1 to 2 hours.
The wire drawing after the primary wire drawing is usually called secondary wire drawing, but in order to perform the secondary wire drawing process, the primary wire drawing must be subjected to intermediate annealing, pickling, and lubrication. did not become.

As a result, the cost of intermediate annealing, pickling, coating, and other lubrication treatments before secondary wire drawing increases, and the pickling process involves pollution problems such as waste acid treatment, which has the drawback of making the cost extremely high. . The purpose of the present invention is to overcome the drawbacks of the conventional technology in the production of ultra-fine wire rods with a diameter of 0.3 mm or less, omit the intermediate treatment, and improve wire drawability so that direct drawing from primary wire drawing to ultra-fine wire is possible. The object of the present invention is to provide a mild steel wire rod for ultra-fine wires that can improve ductility after wire drawing, extend die life, reduce wire breakage, and improve workability and safety.

The gist of the present invention is as follows. That is, Co, less than 2% by weight, SiO, less than 2% by weight,
Mn0.05-0.30%, Ai, 0.005% or less, NO
. 0,040% or less, and the carbon equivalent Ceq shown by the following formula (1) is 0,907% or less, the remainder consists of Fe and unavoidable impurities, and is characterized by being capable of being drawn directly from rolled wire rods. wire.

There were various problems that the inventors had to overcome before they were able to achieve the present invention.

First, conventionally, rimmed steel has been used as the material for mild steel wire rods for ultra-fine wires. As a result, segregation at the head of the steel ingot is large, making it impossible to obtain uniform quality over the entire length of the material. Therefore, in order to obtain uniform quality, it is necessary to use continuously cast slabs.

However, in continuous casting, when molten steel with a C content of 0.04% or more is injected, blowholes cannot be prevented from occurring in the slab unless it is made into killed steel, which increases the cost of cleaning the slab. Furthermore, if 0.010% or more of Al is added to make killed steel,
In addition to the problem of closing the nozzle of the tundish due to the generated Al2O3, a large amount of N is absorbed from the atmosphere, and the ferrite crystal grains of the resulting wire become small. Due to the small size of the ferrite crystal grains and the solid solution hardening of Al and N, the strength of the rolled wire rod and the strength after wire drawing are increased, and there is a risk of embrittlement during processing. In addition, for aluminum and killed steel, the degree of recrystallization is affected by the temperature increase rate during annealing after wire drawing, and there is a risk that the mechanical properties will fluctuate greatly. On the other hand, when using silicon and killed steel, the strength and work hardening rate increase due to solid solution hardening of Si, resulting in a decrease in ductility and poor bending workability.
This results in a reduction in die life.

As described above, since it is impossible to draw a wire to a diameter of 0.3 mm or less by direct drawing with conventional materials, the present inventors developed a wire that is uniform over the entire length and can be drawn directly into an ultra-fine wire. In order to manufacture mild steel wire rods, we have conducted extensive research on the composition system and manufacturing method, and have confirmed that we can manufacture slabs with fewer harmful inclusions and blowholes using a composition system that produces wire rods with good wire drawability. We were able to obtain a unique wire rod for ultra-fine wires that can be drawn directly from rolled wire rods, which could not be obtained even with ordinary agglomerated materials up until now.

In order to improve the wire drawability of mild steel wire rods, and in particular to make it possible to draw them into ultra-fine wires of 0.3 mm or less, it is first necessary to prevent process embrittlement and aging embrittlement to the maximum extent possible. However, there has been no previous research from this perspective.

The present inventors have obtained a mild steel wire rod for ultra-fine wires that can be directly drawn based on knowledge from the viewpoint of preventing work embrittlement and aging embrittlement. First, the reasons for limiting the mild steel wire rod components in the present invention will be explained.

C: C is an element necessary to some extent to ensure strength, but for the purpose of the present invention, other Mn is required to ensure this strength.
* Possible by appropriately adding 81 etc.
C is not an absolutely necessary element.

Therefore, industrially, from the economic point of view of melting, 0.002
The lower limit is approximately %, but there is no lower limit due to the necessity of the material. On the other hand, when C increases, the amount of solid solute C and pearlite increases, which suppresses the growth of ferrite crystal grain size, resulting in a decrease in workability and ductility.Furthermore, in the case of continuous casting, C
An increase in the amount causes the generation and growth of bubbles during solidification of molten steel, resulting in the deterioration of the surface quality of the slab.

In order to prevent such defects in materials and manufacturing, it is necessary to limit the upper limit of C to 0.02%. As described above, by regulating the C content to less than 0.02%, even when the oxygen content is as high as 200 ppm, a good slab can be obtained by continuous casting, and it can be processed at the same level or better than ordinary steel ingots. It has now become possible to obtain a material for mild steel wire with good properties. Si: Si is an element necessary for strength and deoxidation of steel, but it has a large effect on solid solution hardening and work hardening, and if it exceeds 0.03%, it may cause defects such as shortening of the life of drawing dies and occurrence of defective bending. Therefore, it should be limited to less than 0.02 factor.

Mn: Mn is an element necessary for the strength of steel, deoxidation, and composition adjustment of inclusions, but for the purpose of the present invention, deoxidation can be supplemented by vacuum degassing, etc. It is possible to supplement with elements.

On the other hand, if the addition amount exceeds 0.30, excessive pearlite formation, solid solution hardening and work hardening will occur, making wire drawing to a high area reduction ratio impossible. 30
The upper limit was Carbon equivalent Ceq: [%Si)+C%Mn) Ceq-(chi)+?(Information) If the carbon equivalent Ceq exceeds 0.07%, work hardening and work embrittlement will be large, and the mechanical properties will deteriorate. deterioration, wire breakage increases, and direct drawing to ultra-fine wire becomes difficult.

An example is shown in FIG. Figure 1 shows the primary wire drawing of 5.5 mm diameter processed with MD-borak and 800 m with 15 dies.
The relationship between the degree of work and the carbon equivalent in which the twist value shows a minimum value is shown from the change in twist value with respect to the degree of wire drawing when wire is drawn under the same conditions up to 0.6 φ at a wire drawing speed of /Min. It is something that As is clear from Figure 1, the lower the degree of wire drawing, which indicates the minimum twist value, the more embrittled the material is due to wire drawing. It can be seen that the line limit is large. In the experiment based on Fig. 1, a material with a Ceq of 0.10 was drawn at a wire drawing speed of 800 m/M from a 5.5 mm diameter using a continuous double deck wire drawing machine.
It was possible to directly draw the wire to 0.6 vtmφ or less without any breakage using 15 dies. From this figure, it can be seen that when Ceq is 0.07% or less, the wire drawability becomes clearly good. Al: A is an effective element as a deoxidizing agent, but if it exceeds 0.005, the tundish nozzle will be clogged, and hard Al2O will form.
0.00 because it involves difficulties in material manufacturing and wire drawing processing, such as the formation of 3 and the refinement of ferrite crystal grains by AlN.
It was limited to 5% or less.

N: N combines with Al to precipitate A[N, suppressing the growth of crystal grains, and also causes work embrittlement and age embrittlement due to solid solution nitrogen, so it must be 0.0040% or less. be.

The mild steel wire rod for ultra-fine wire according to the present invention has the above-mentioned limited components and the remainder consisting of Fe and unavoidable impurities. The basic experiment results are as follows.

Figure 2 shows the effect of changes in carbon equivalent on tensile strength during the primary wire drawing of 5.5 mm diameter for the present invention steel A, conventional aluminum-killed steel C, and rimmed steel B under the same rolling and cooling conditions. It is a correlation diagram for comparison.

As is clear from Fig. 2, for all steel types, as Ceq decreases, the solid solution amount and pearlite amount decrease, ferrite crystal grains grow, and the tensile strength decreases, and the limit is almost the same as the conventional one. Almost the same level as rimmed steel. This is because in the steel of the present invention, precipitation of AlN is small due to the reduction of N and Al, so that crystal grains can grow sufficiently after rolling. Next is the diameter D.

The degree of wire drawing when drawing from φ to Dφ (ε=2
FIG. 3 shows a correlation diagram comparing the influence of changes in 1nDJL on tensile strength D between the steel of the present invention and the conventional rimmed steel.

From FIG. 3, it was found that the steel of the present invention had a lower work hardening rate than the conventional rimmed steel. This is because the steel of the present invention has larger ferrite crystal grains than the rimmed steel, as shown in FIGS. 4A, B, C, and D in both the surface layer and the center, respectively. Next, a correlation diagram comparing the influence of the change in the degree of wire drawing (ε=21n') on the twist value of the wire drawn material between the steel of the present invention and the conventional rimmed steel, which have almost the same tensile strength, is shown in Figure 5. As shown in the figure.

As is clear from FIG. 5, the torsion value of the present invention is extremely larger than that of conventional rimmed steel on the reduced area ratio side, and its minimum value is on the high area reduction side. .

As is clear from the comparison diagrams from Figures 2 to 5 above,
Coupled with the low work hardening rate, the steel of the present invention is less susceptible to work embrittlement due to wire drawing, and has extremely good wire drawability.For this reason, it can be directly drawn from rolled material to ultra-fine wire. This shows that it is a material that can

Examples Steels A, B, C, D of the present invention having the chemical components shown in Table 1
All comparative steels I, J, K, L, M, N, and O, except comparative steel L, were melted in a converter, degassed, poured into a 250 mm mold, and plume cast by continuous casting. A piece was produced.

Comparative steel L is a rimmed steel that was melted in a converter and then poured into a 11J normal mold, and was rolled into a plume of 250 Ichida, which is the same as other plume slabs produced by continuous casting. These blooms were rolled into 80 Tomota billets, then rolled into 5.5 diameter wire rods, and uniformly cooled in a Stelmor processing line.

As is clear from Table 1, the invention steel (4) and (B
) is an ultra-low carbon material, (Q and 0 are CO.Oxs materials (Q is a material with Al and N equal to the rimmed steel of comparison steel K, 0 is a material with slightly higher Al and N) Although the comparative steels are similar to the inventive steel, (I) has a higher Mn than the limited range of the inventive steel, and (.J) has a higher Si,
The wholesaler is rimmed steel with high Mn, υ is higher in C than the limiting value, and M is S1? All of them are high in Mn9N, N is high in Al and N, and (0) is a material with high N.

In most of the steels of the present invention, Al is limited, so the first
As shown in the table, although the oxygen content is high, there are almost no blowholes, and the surface of the slab requires only minor maintenance.Also, due to the high oxygen content, non-metallic inclusions are oxide-based inclusions. Although there are somewhat many inclusions, they are small inclusions of 3 μm or less, as is clear from the micrograph shown in FIG. 6A. Table 2 shows a comparison table of the ferrite crystal grain size and tensile test value of the rolled material between the steel of the present invention and the comparative steel.

That is, the ferrite crystal grains of the steel of the present invention are large, approximately 20μ or more in both the surface and center, while the grain sizes of the comparative steels are small, about 14μ, because l and N are not controlled. Rimmed steel of steel K has a surface area of 20μ.
Although it is weak and large, it is 14μ in the center. The tensile strength of the steel of the present invention is lower than that of the comparative steel, and the reduction of area is large, indicating that the steel has good wire drawability.

Next, the steels of the present invention and comparative steels were drawn under the conditions shown in Table 3, and the wire drawability was investigated. Table 4 shows the results.

As is clear from Table 4, all of the steels of the present invention are on the high side with respect to wire drawing workability, where the torsion value is minimal, and are materials with far less work embrittlement than the comparative steels. It is shown that. In addition, the wire drawing limit value is determined based on the occurrence of wire breakage, but all steels of the present invention have a wire drawing limit value of 0.22+u+φ
It was found that wire drawing is possible up to the following (ε=6.43 or more). Next, 1.20 m of these test wire drawn materials
Fig. 7 shows the results of an investigation of the dependence of the tensile strength on the heating rate for the steel of the present invention and the conventional steel. In other words, the temperature dependence of the tensile strength of the steel of the present invention is much smaller than that of the conventional rimmed steel and killed steel. This means that wire rods are normally annealed while being wound into a coil, so the temperature increase rate within the coil varies greatly, but the steel of the present invention has such a large temperature increase rate variation. This shows that almost uniform mechanical properties can always be obtained even when the As is clear from the examples above, the mild steel wire rod for ultra-fine wire according to the present invention had the composition and carbon equivalent limited to an appropriate pressure, and therefore was able to achieve the following great effects.

(a) Since the raw material for wire rods can be manufactured using a continuous casting method with a high yield, uniform wire rods can be supplied.

(Exposure) In wire drawing processing, 0.3011LTAφ or more. It is possible to directly draw the lower ultra-fine wire from the rolled wire by eliminating conventional intermediate treatments such as intermediate annealing, pickling, and lubrication.

09 The mild steel wire rod according to the present invention has a small work hardening rate and its nonmetallic inclusions are fine, making it possible to extend the die life and significantly reducing wire breakage accidents, which is combined with the effects of (a) and (b). This has made it possible to improve productivity and significantly reduce costs.

(d) The components of the wire material became uniform due to (a), and the dependence of the tensile strength after annealing on the heating rate was small, so uniformity of product quality could be ensured.

As is clear from the above description, according to the present invention, by promoting the growth of ferrite crystal grain size and improving wire drawability and drawing toughness after wire drawing, rolled wire rods can be made from primary wire drawing to ultra-fine wire. A mild steel wire rod for ultra-fine wires that can be directly drawn without intermediate treatment and without wire breakage can be obtained.

[Brief explanation of drawings]

Figure 1 shows the degree of wire drawing (ε-2An
Correlation diagram showing the influence of carbon equivalent on D0/D), 2nd
The figure is a correlation diagram showing the influence of carbon equivalent on the tensile strength of a 5.5 mm diameter rolled wire rod. Figure 3 shows the relationship between the tensile strength of the wire rod and the degree of wire drawing for the invention steel A and the conventional rimmed steel. Figure 4 A, B, C, and D show the surface layers A, B, and center C of the steel of the present invention and the conventional rimmed steel, respectively.
, D. Micrograph (magnification: 200) showing the size of ferrite crystal grains in Fig. 5 compares the relationship between twist value and degree of wire drawing in inventive steel A and conventional rimmed steel B with the same tensile strength. Figures 6A and B are micrographs (magnification: 200) comparing non-metallic inclusions in the invention steel and conventional rimmed steel, respectively. Figure 7 shows the relationship between the invention steel A and the conventional rimmed steel B. FIG. 2 is a correlation diagram showing the influence of the temperature increase rate on the tensile strength of killed steel C.

Claims (1)

[Claims] 1. C: less than 0.02%, Si: 0.02% by weight
less than, Mn: 0.05-0.03%, Al: 0.005
% or less, N: 0.0040% or less, and the carbon equivalent Ceq shown by the following formula is 0.07% or less, the balance consists of Fe and unavoidable impurities, and it is characterized by being able to be drawn directly from a rolled wire rod. Mild steel wire rod for ultra-fine wire. Ceq=[%C]+([%Si]+[%Mn])/5