KR100979006B1 - Wire Rods Having Superior Strength And Ductility For Drawing And Method For Manufacturing The Same - Google Patents

Abstract

There is provided a wire rod for drawing excellent in strength and ductility and a method of manufacturing the same.

The wire rod for drawing superior in strength and ductility is in weight%, C: 0.87 to 1.0%, Mn: 0.1 to 0.60%, Si: 0.3 to 1.0%, S: 0.010% or less (not including 0%), P : 0.011% or less (does not contain 0%), Cr: 0.1-0.5%, N: 0.007% or less (does not contain 0%), and is composed of the remaining Fe and other unavoidable impurities, the content of the Si, Cr This satisfies the following formula, 0.6 ≦ Si + Cr ≦ 1.2 (Si and Cr mean weight% of the corresponding element), and is characterized by including a pearlite structure.

High strength, high ductility, layer spacing, heat treatment

Description

Wire rod having excellent strength and ductility and manufacturing method {Wire Rods Having Superior Strength And Ductility For Drawing And Method For Manufacturing The Same}

The present invention relates to a high-strength high-ductility wire for wire used in tire cords, wire ropes, piano wires, bridge steel wires, and the like and a method of manufacturing the same. Specifically, the present invention relates to a wire rod for wire drawing having a high ductility as well as a high ductility by miniaturization of a pearlite layered structure by controlling the content of C and simultaneously adding Si and Cr in combination.

In general, there are three methods for obtaining high strength wire for drawing.

First, it is possible to increase the strength of the material itself by adding a large amount of reinforcing elements. Representative examples of such reinforcing elements include carbon. As the strength of the required wire rods increased, the carbon content gradually increased from the vacancy zone to the vacancy zone and from the vacancy zone to the over-vacancy zone. If the carbon content is increased, the strength of the material can be improved as the fraction of hard cementite is increased in the wire rod and the lamellar spacing of the pearlite structure becomes dense.

Secondly, the wire rod for drawing is that the rolled wire is drawn and heat treated to be processed into a final wire, the strength can be significantly improved by the work hardening during processing. When the wire is processed, the lamellar spacing of the pearlite structure can be miniaturized, the work hardening coefficient increases, the work can be hardened due to the accumulation of dislocations, and the like.

Third, the strength can be improved by increasing the fresh strain of the material separately from the above. This is because the fresh strain of the material is closely related to the ductility of the material, and as the material itself is easily disconnected during wire drawing, the easier it is to improve the strength.

However, since the above methods are not acting independently but are related to each other to change the strength of the wire rod, it may be limited to increase the strength by controlling them independently.

In addition, when a large amount of alloying elements are simply added to improve the strength of the wire, problems such as disconnection may occur due to poor ductility of the wire in the subsequent wire manufacturing process after wire rod rolling. That is, as the carbon content increases, the strength may be improved, but the ductility is rather reduced.

An object of the present invention is to provide a wire rod for high strength and high ductility by miniaturization of a pearlite layered structure and a method for producing the same by controlling the content of C and simultaneously adding Si and Cr.

The wire rod for drawing excellent in strength and ductility of the present invention for achieving the above object, in weight%, C: 0.87 ~ 1.0%, Mn: 0.1 ~ 0.60%, Si: 0.3 ~ 1.0%, S: 0.010% or less ( Does not contain 0%), P: 0.011% or less (does not contain 0%), Cr: 0.1-0.5%, N: 0.007% or less (does not contain 0%), with the rest of Fe and other unavoidable impurities It is formulated, the content of Si, Cr satisfies the following formula, 0.6 ≤ Si + Cr ≤ 1.2 (Si and Cr means the weight percent of the element), characterized in that it comprises a pearlite structure.

The present invention has a useful effect of properly controlling the content of C and at the same time by adding a combination of Si and Cr to provide a wire for a wire having a high strength as well as a high ductility and a manufacturing method thereof.

The present inventors have carefully examined the relationship between the carbon content and the strength of the wire rod, which have been added in a large amount in order to improve the strength of the wire rod, and have come to the following conclusion.

In general, as the strength of drawing wire increases, the carbon content increases from the suba pore to the super pore area. When the carbon content is above a certain level, the improvement in strength is no longer expected. The strength no longer increases or rather decreases.

Therefore, the upper limit of the carbon is limited to a range that allows sufficient fresh processing amount without continuously increasing the content of carbon, while the addition of other alloying elements, particularly Si and Cr, results in a finer layered structure of pearlite. The strength and ductility of the wire rod can be secured.

Hereinafter, the composition range of the steel component of the present invention will be described.

Content of carbon (C): 0.87 ~ 1.0% (hereinafter, by weight)

When C is a key element for securing strength or the content thereof is more than 1.0%, the cross-sectional reduction rate (RA) of the steel is reduced, and ultimately, the strength increase due to fresh processing cannot be expected, while less than 0.87%. It can be difficult to secure the targeted intensity. Therefore, the content of C is preferably limited to 0.87 ~ 1.0%.

Manganese (Mn) content: 0.1 ~ 0.6%

The Mn is an effective element for increasing hardenability or an element with a high central segregation, and when Mn exceeds 0.6%, it is very likely to cause low temperature tissue. If less than 0.1%, the effect of the addition may not appear sufficiently. Therefore, the content of Mn is preferably limited to 0.1% ~ 0.6%.

Silicon (Si) content: 0.3 ~ 1.0%

Si is an element which plays a very important role in the present invention together with Cr. In the case of C, the strength increases as the amount added increases, but the amount of fresh processing decreases, eventually limiting the increase in strength. Above the pore composition, coarse cementite cement is precipitated to provide a major cracking location in the wire. . The addition of Si does not encourage the formation of cementite cementite in the range of pore formation, and increases the strength by strengthening solid solution. Since Si is used as a deoxidizer in the steelmaking process, it is included in the steel in small amounts, and more than 0.3% is added to increase the strength and ductility. However, when added in excess of 1.0%, the ductility of the lamella ferrite is drastically reduced, which worsens the fresh workability. Therefore, the content of Si is preferably limited to 0.3 ~ 1.0%.

Content of chromium (Cr): 0.1 ~ 0.5%

Cr is an element which plays a very important role in the present invention together with Si, thereby improving strength and ductility by miniaturizing the layered structure of pearlite. If the Cr content is less than 0.1%, there is no sufficient effect of miniaturization of the layered tissue. If the content of Cr is more than 0.5%, the constant temperature transformation rate is lowered, thereby degrading productivity. Therefore, the content of Cr is preferably limited to 0.1 to 0.5%.

Content of silicon (Si) + content of chromium (Cr): 0.6 ~ 1.2%

The Si and Cr is effectively added to the composite, when the addition of 0.6 to 1.2% by the sum of the weight of the two elements will increase both strength and ductility. If it is less than 0.6%, the increase in strength is not preferable, whereas if it is more than 1.2%, the ductility may decrease, so the sum of the content of Si and Cr is preferably limited to 0.6 to 1.2%.

S: 0.010% or less (without 0%), P: 0.011% or less (without 0%), N: 0.007% or less (without 0%)

S, P, and N are impurity elements present in the manufacture of wire rods, and in the presence of a large amount, embrittlement of the material leads to disconnection during drawing, so it is limited to 0.010%, 0.011%, and 0.007%, respectively.

Furthermore, the wire rod excellent in strength and ductility may contain Ni. This is because Ni increases the plastic deformation of cementite during fresh processing by operating one additional cement system slip system, and the content range is preferably 0.3 to 1.0%.

The present invention is composed of Fe and other unavoidable impurities in addition to the above components.

In the case of the wire rod having the composition range as described above, the tensile strength of the wire rod is 1300 MPa or more and the cross-sectional reduction rate is 30% or more.

Hereinafter, the structure of the wire rod of this invention is demonstrated.

The layer spacing of the pearlite structure of the wire rod having the above composition range is 130 nm or less.

After LP (Lead Patenting) heat treatment, the lamellar spacing of the pearlite structure is 50 nm or less.

The smaller the laminar spacing of the pearlite structure, the higher the strength of the wire rod.

Hereinafter, the manufacturing method of the wire rod of this invention is demonstrated.

By weight%, C: 0.87 ~ 1.0%, Mn: 0.1 ~ 0.60%, Si: 0.3 ~ 1.0%, S: 0.010% or less (not including 0%), P: 0.011% or less (not including 0%) Cr: 0.1-0.5%, N: 0.007% or less (does not contain 0%), the remaining Fe and other inevitable impurities, the content of Si, Cr is the following formula, 0.6 ≤ Si + Cr To obtain a fine and homogeneous pearlite structure, the steel sheets satisfying ≤ 1.2 (Si and Cr mean weight% of the corresponding element) are heated and rolled to 1100 to 1300 ° C for homogenization and to secure hot rolling temperature. Cool to 20 ° C / s.

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

Example 1

Tensile strength (TS), cross-sectional reduction rate (RA) of a wire rod manufactured by heating and rolling a steel sheet having a composition range as shown in Table 1 at 1100 to 1300 ° C and then cooling to 10 to 20 ° C / s, lamellar of pearlite structure The stratified spacing was measured.

Comparative steels 1 to 6 show the tensile strength of the wire rod 1119 ~ 1249MPa, the cross-sectional reduction rate is less than 30% except for the comparative steel 1. Comparative steel 1 is 0.82C steel, which has a high cross-sectional reduction rate due to low carbon content, but the strength is very low as 1119MPa, which is not suitable for high strength steel.

On the other hand, the inventive steels 1 to 5 show a strength of 1300 MPa or more, and a section reduction rate of 30% or more. Comparing the inventive steel 1 with the comparative steel 4, as a result of increasing the Si content, the tensile strength increased by 121 MPa and the sectional reduction rate increased by 6.6%. Increasing the Si content in the inventive steels 1 to 3 it can be seen that the strength increases without a significant decrease in the cross-sectional reduction rate. However, in the case of Comparative Steel 7, the strength is increased when 1.5% Si is added, but C is added in excess of 1.0% so that the cross-sectional reduction rate is drastically reduced to 19.3%.

Even when 0.496% Cr was added as invented steel 4, it showed excellent strength and ductility of 1364 MPa in tensile strength and 38.7% in section reduction rate.

In addition, the sum of the Si and Cr content shows a tensile strength of 1300MPa or more and a section reduction rate of 30% or more in a range of 0.6 to 1.2% by weight.

In addition, in the case of the inventive steel 5, when the 0.5 wt% Ni is added, the tensile strength is increased by 79 MPa, and the section reduction rate is increased by 3.2%.

The inventive steels are characterized in that the lamellar spacing of the pearlite structure in the wire state is 130 nm or less, and the excellent strength and the rate of reduction of the cross section are due to this.

division Ingredient (% by weight) TS (MPa) RA (%) Layer spacing
(nm) C Mn Si Cr Ni Si + Cr Inventive Steel 1 0.92 0.297 0.513 0.200 - 0.713 1361 35.8 124 Inventive Steel 2 0.97 0.294 0.513 0.200 - 0.713 1385 32.4 128 Invention Steel 3 0.92 0.294 0.995 0.198 - 1.193 1464 36.2 88 Inventive Steel 4 0.96 0.296 0.304 0.496 - 0.800 1364 38.7 127 Inventive Steel 5 0.96 0.297 0.300 0.301 0.500 0.601 1328 32.3 122 Comparative Steel 1 0.82 0.296 0.180 - - 0.180 1119 35.6 132 Comparative Steel 2 0.93 0.328 0.204 - - 0.204 1208 29.5 157 Comparative Steel 3 0.98 0.297 0.214 - - 0.214 1216 25.0 142 Comparative Steel 4 0.93 0.298 0.202 0.198 - 0.400 1240 29.2 139 Comparative Steel 5 0.97 0.297 0.200 0.200 - 0.400 1249 29.1 145 Comparative Steel 6 0.98 0.294 0.202 0.102 - 0.304 1219 25.6 134 Comparative Steel 7 1.02 0.297 1.512 0.198 - 1.710 1512 19.3 132

Example 2

Table 2 below shows the tensile strength and lamellar spacing of the steel produced by the method of Example 1 at 1050 ° C. and then heat treated with LP at 550 ° C. in the bath bath temperature.

Inventive steel 1 can be seen that the tensile strength increased by 88MPa by the increase of Si compared with the comparative steel 4. It also shows that the tensile strength is superior to the comparative steel 5 having higher carbon content. Due to the composite addition of Si and Cr, it shows excellent strength even after LP heat treatment, and it can be seen that the layer spacing is about 26 nm compared to that of the comparative steel. This is because the rate of nucleation is increased by increasing the vacancy temperature upon addition of Si element, thereby increasing the supercooling rate.

division
Ingredient (% by weight) The tensile strength
(MPa) Layer spacing
(nm) C Mn Si Cr Si + Cr Inventive Steel 1 0.92 0.297 0.513 0.200 0.713 1483 26 Comparative Steel 4 0.93 0.298 0.202 0.198 0.400 1395 51 Comparative Steel 5 0.97 0.297 0.200 0.200 0.400 1403 54

Example 3

Table 3 below shows the physical properties of the steel wire after the wire is manufactured by the method of Example 1 and Example 2. The drawing was performed with the same strain rate of 3.2% or more, and the final wire diameter was 2.7mm.

In the case of the inventive steel 1, the tensile strength, the number of torsional recovery, and the fatigue characteristics are all higher than those of the comparative steel 4 and the comparative steel 5.

In the case of the torsion recovery, it shows that the steel or the ductility of the steel wire is excellent while maintaining the excellent strength. Excellent ductility can lower the wire disconnection rate during wire drawing, and delamination can be suppressed.

In addition, the fatigue characteristics indicate that the service life is increased and the durability is increased, and the invention steel has a value of about twice.

Therefore, it can be seen that the wire rod by the composite addition of Si and Cr has excellent ductility and fatigue characteristics as well as strength even after drawing.

division Tensile Strength (MPa) Number of twists Hunter Fatigue (Times) Inventive Steel 1 3870 52 119,270 Comparative Steel 4 3830 45 72,000 Comparative Steel 5 3860 44 66,000

1 is a graph showing the tensile strength and the cross-sectional reduction rate as the content of C increases.

Figure 2 is a graph showing the tensile strength and the cross-sectional reduction rate of the wire rod for the composition range.

Claims (7)

By weight%, C: 0.87 ~ 1.0%, Mn: 0.1 ~ 0.60%, Si: 0.3 ~ 1.0%, S: 0.010% or less (not including 0%), P: 0.011% or less (not including 0%) ), Cr: 0.1-0.5%, N: 0.007% or less (not including 0%), Ni: 0.3-1.0%, remaining Fe and other inevitable impurities, and the content of Si, Cr is Satisfies the formula: 0.6 < Si + Cr < A wire rod for excellent strength and ductility, characterized by a reduction rate of 30% or more. delete delete delete The wire rod for excellent strength and ductility according to claim 1, wherein the layered spacing of the pearlite structure is 50 nm or less after LP (Lead Patenting) heat treatment. The wire rod for excellent strength and ductility according to claim 1, wherein the wire is twisted at least 50 times after the wire is drawn. By weight%, C: 0.87 ~ 1.0%, Mn: 0.1 ~ 0.60%, Si: 0.3 ~ 1.0%, S: 0.010% or less (not including 0%), P: 0.011% or less (not including 0%) ), Cr: 0.1-0.5%, N: 0.007% or less (not including 0%), Ni: 0.3-1.0%, remaining Fe and other inevitable impurities, and the content of Si, Cr is The steel sheet satisfying the formula, 0.6 ≤ Si + Cr ≤ 1.2 (Si and Cr refer to the weight% of the corresponding element) was heated and rolled to 1100 ~ 1300 ℃ and then cooled to 10 ~ 20 ℃ / s to include a pearlite structure And a wire rod having a layer spacing of 130 nm or less, a tensile strength of 1300 MPa or more, and a cross-sectional reduction rate of 30% or more.

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