KR100435460B1 - A method for manufacturing steel wire for steel cord - Google Patents

Abstract

The present invention relates to a method for producing a steel cord steel wire, by reducing the carbon content and adding a suitable alloying element after drawing the wire only one time, the high-strength fine wire can be produced 270kg / mm ² or more It is an object of the present invention to provide a method for manufacturing steel wire for steel cords.

The present invention provides a method for producing a steel wire for steel cords,

By weight% C: 0.4-0.65%, Mn: 0.1-1.0%, Si: 0.1-1.0%, Cr: 0.3% or less, B: 100 ppm or less, remaining Fe and other unavoidable impurities, wherein Ti, Nb , At least one selected from the group consisting of elements of V is hot rolled to a steel sheet containing 0.02% or less, and then continuously cooled at a cooling rate of 10 to 30 ° C./sec to form a cornerstone ferrite fraction of 10% or less, Cementite fraction is fresh with 6 ~ 10% wire rod, then heated at 900 ~ 1050 ℃, austenitized and quenched, and is incubated with fine pearlite in the temperature range of 500 ~ 650 ℃, and then to 0.15 ~ 0.3mm The manufacturing method of the steel wire for steel cords characterized by wet drawing is made into the technical summary.

Description

Manufacturing method of steel wire for steel cord {A METHOD FOR MANUFACTURING STEEL WIRE FOR STEEL CORD}

The present invention relates to a method for manufacturing steel cord steel wire used as a rubber tire reinforcement for trucks, buses, passenger cars, etc. More specifically, intermediate heat treatment (patenting, patenting) performed to give ductility of the material during drawing The manufacturing method of the steel wire for steel cords which shortened a process twice to one time.

Steel cords are manufactured by twisting steel wires, and are commonly used as rubber tire reinforcement materials for trucks, buses and passenger cars.

Steel wire for steel cord is hot rolled carbon steel and alloy steel with more than 0.7% C and controlled cooling to secure pearlite structure, and then processed by wire processing 30 ~ 70% After repeating the process of obtaining (usually twice), the final wet drawing to produce 0.15 ~ 0.3mm. In this case, the intermediate heat treatment process generally performed during drawing is performed to control the deformed structure formed after the drawing is carried out to some extent so that drawing can be done to the final diameter of the final product. have.

Therefore, in order to improve the strength by shortening the intermediate heat treatment or by increasing the amount of drawing, the freshness of the steel must be premised.

As a conventional technique for improving the freshness of carbon steel, in many cases, methods for securing the freshness of high carbon steel by miniaturizing austenite grains in high carbon steel of 0.7% or more have been proposed. For example, US Patent 5156692 relates to a method of securing high strength high ductility by controlling the grain size of austenite to about 5 mm by applying deformation at high temperature, and controls the grain size of austenite to control colony and pearly phase. This is to improve the freshness according to the miniaturization of the interlayer spacing.

In addition, JP-A-6-136452 and the like are methods for inhibiting growth of austenite crystal grains by precipitating AlN during a paytenting process. However, the method of miniaturizing the austenite grain size described above is difficult to apply in the medium-carbon steel because it increases the fraction of ferrite in the case of medium-carbon steel, causing the deterioration of freshness.

In addition, Japanese Laid-Open Patent Publication No. Hei 4-325627 has a problem in which a large amount of Si is added to steel to achieve strength and ductility due to solid solution strengthening, or when a large amount of Si is added, it promotes decarburization during rolling.

In addition, the Japanese Patent Application Laid-Open No. (63) -63-4039 and (Hyeong-ho) 4-346619 are representative examples of a conventional method for manufacturing a high strength wire rod having excellent ductility by addition of alloying elements and cooling rate control. .

The Japanese Laid-Open Patent Publication No. 63-4039 has a weight% of steel containing C: 0.7-0.95, Si: 0.2-0.5, Mn: 0.4-0.7, V: 0.05-0.2, and Ni 0.05-0.5%. The method of securing the ductility at the time of manufacturing the ultra fine wire of about 0.3 mm by repeating the drawing and the patting process is disclosed.

Japanese Unexamined Patent Application Publication No. Hei 4-346619 discloses at least 60% freshness after pitting the carbon steel containing C: 0.6-1.1%, Si: 0.1-0.2% and Mn: 0.1-2.0% by weight. And to maintain a 300 ~ 3600 seconds in the range of 50 ~ 200 ℃ to recover the degradation of the ductility due to strain aging at the time of drawing relates to a method for producing an excellent steel wire, because it does not fundamentally increase the ductility of the steel wire during the drawing, There is a problem in increasing freshness without heat treatment.

In addition, Japanese Patent Application Laid-Open No. 4-254526 discloses cementite cementite after hot rolling a steel composed of C: 0.9% to 1.3%, Si: 0.1 to 2.0% and Cr: 0.1 to 1.3% by weight. Quenching the cementite cementite by cooling the temperature range where is generated and cooling to a temperature at which the pearlite transformation is completed at a rate of 8 ° C./sec or less or by quenching to a pearlite transformation temperature and then maintaining a constant temperature. It is about how to improve. However, this method is not applied when C is less than 0.9% because the cementite cementite is not formed, and there is a problem that it is difficult to control the cooling rate by dividing the cooling rate into two stages during cooling after actual rolling.

Recently, efforts have been made to reduce the number of heat treatments generally performed twice in the steel wire manufacturing process due to the energy saving effect by eliminating or shortening the intermediate heat treatment and reducing the environmental problem by using Pb. In Japanese Laid-Open Patent No. 5-156370, hot-rolled steels containing C: 0.9 to 1.1wt%, Si: 0.4wt% or less, Mn: 0.5wt% or less, Cr: 0.1 to 0.3wt% to 4.5-6.5mm After cooling to a temperature range of 800 ~ 1100 ℃ to a temperature range of 450 ~ 550 ℃ at a cooling rate of 50 ℃ / sec or more, the transformation is completed at a temperature range of 450 ~ 550 ℃, and at this time for about 120 seconds at a temperature of 450 ℃ or more. Disclosed is an invention for cooling to room temperature after holding. According to the present invention, the cementite maintains a cementite form having an aspect ratio of 10 or less, and thus the heat treatment can be shortened once due to a low work hardening rate and improved ductility. However, this invention is difficult to control by the air cooling method performed at the time of manufacture of a wire rod in the control method of a microstructure after rolling, and requires special facilities, such as a salt bath instead of air, and there exists a problem of a productivity fall and a cost increase.

On the other hand, deterioration of freshness during drawing is due to cracks occurring during processing, and these cracks occur at grain boundary cementite which is present at the ferrite / pearlite interface and grain boundary alone in the structure composed of ferrite / pearlite and of cementite in pearlite single phase structure. Since it is caused by a crack, it is known that high carbon steel with many cementite fractions has low freshness compared with low carbon steel.

Accordingly, the present inventors in Korea Patent Application No. 95-56693, by reducing the amount of carbon to reduce the cementite fraction, and at the same time to control the increase in the ferrite fraction and the transformation behavior accompanying the decrease in the amount of carbon, the location of cracks during fresh processing It has been disclosed that the present invention provides excellent freshness by reducing the grain boundary cementite and ferrite / pearlite interface and reducing the fraction of cementite in the pearlite single phase. However, this method has to raise the heating temperature or the laying head temperature in order to make austenite coarse, so that the cost increases and it is difficult to manufacture high strength steel wire. Therefore, Korean Patent Application No. 98-43340 discloses a method of manufacturing a high strength and high ductility wire rod having excellent freshness without increasing heating temperature or laying head temperature by adding an appropriate alloying element. Controlling the ferrite fraction by controlling the cooling rate is limited to only the fresh material is difficult to apply to products that must be applied in the middle, such as steel wire for steel essential.

In order to solve the above problems, the present inventors have repeatedly conducted research and experiments and proposed the present invention based on the results. It is an object of the present invention to provide a method for producing a steel cord steel wire that can produce a high-strength ultrafine wire of 270 kg / mm ² or more by performing the tenting only once.

1 is a microstructure after heat treatment of the invention and comparative materials

The present invention provides a method for producing a steel wire for steel cords,

By weight% C: 0.4-0.65%, Mn: 0.1-1.0%, Si: 0.1-1.0%, Cr: 0.3% or less, B: 100 ppm or less, remaining Fe and other unavoidable impurities, wherein Ti, Nb , At least one selected from the group consisting of elements of V is hot rolled to a steel sheet containing 0.02% or less, and then continuously cooled at a cooling rate of 10 to 30 ° C./sec to form a cornerstone ferrite fraction of 10% or less, Cementite fraction is fresh with 6 ~ 10% wire rod, then heated at 900 ~ 1050 ℃, austenitized and quenched, and is incubated with fine pearlite in the temperature range of 500 ~ 650 ℃, and then to 0.15 ~ 0.3mm It relates to a method for producing a steel wire for steel cord, characterized in that the wet drawing.

Hereinafter, the present invention will be described in detail.

First, the reason for setting the steel component will be described.

The C is the most effective element to increase the strength, the amount of addition changes depending on the use, but less than 0.4% of the base structure becomes a ferrite, this structure is much easier to increase the fraction than pearlite, so it is difficult to secure high strength In addition, the lower limit was set to 0.4%. On the other hand, if the content exceeds 0.65%, the pearlite fraction becomes 95% or more without the addition of alloying elements, but the lamination occurs when the freshness increases due to the increase in the cementite fraction, so 0.65 wt% is set as the upper limit. Therefore, the C content is preferably set to 0.4 to 0.65%.

Si is an element necessary for deoxidation of steel, and if the content is too small, the deoxidation effect is not sufficient, so Si should be added at least 0.1%. In addition, Si is an effective ferrite solid solution strengthening element, and the interval between the pearlite layer is fine during continuous cooling, and the strength is reduced when heat-treating the drawn material.However, when excessively added, decarburization occurs during heating for hot rolling and scale removal for drawing It was difficult to set the upper limit to 1%. Therefore, it is preferable to add 0.1 to 1.0% of said Si.

The Mn forms MnS together with sulfur in the material as well as the deoxidation effect in the manufacture of steel, thereby preventing red brittleness due to sulfur, so 0.1% or more should be added. In addition, Mn is a very effective element to increase the strength of the material and refine the pearlite interlayer spacing, but when added in excess, Mn increases the likelihood of segregation and decreases the critical cooling rate at which martensite is generated. Since it significantly lowered, the upper limit was limited to 1.0%. Therefore, it is preferable to add 0.1 to 1.0% of the Mn.

The Cr is an element that is very effective in increasing the hardenability of steel to refine the pearlite to increase the strength and ductility, but when it is added, it may cause martensite during cooling of the material. Therefore, the content should be set to 0.3% or less. desirable.

The B has an effect of suppressing the formation of ferrite by increasing the hardenability of the material, and promotes the growth of cementite in pearlite, and serves to suppress microdefects generated at the ferrite / cementite interface during freshness. However, when excessively added, it forms a nitride by combining with nitrogen, so that bursting occurs during hot rolling, and when the improvement of the hardenability of the material exceeds 0.01%, it is not greatly improved. Therefore, the content is set to 0.01% or less. It is desirable to.

It is preferable that 1 or more types of said Ti, Nb, and V are added in 0.02% or less. The reason is that the elements combine with C and N to form carbonitrides to maximize the effect of B. However, when excessively added, a large amount of precipitate lowers the ductility of the ferrite and increases the strength of martensite. This is because cold tissue can be generated.

Next, the reason for setting the manufacturing conditions will be described.

As described above, after the steel is formed to have the alloy component system of the present invention, it is manufactured as a billet, hot rolled, and then cooled to manufacture the wire, wherein the cooling rate is in the range of 10 to 30 ° C./sec, and the The microstructure preferably has a cornerstone ferrite fraction of 10% or less and a cementite fraction of 6-10%. The reason is that when the cooling rate is less than 10 ℃ / sec, despite the addition of the alloying element, the superfine ferrite precipitation is excessive, so that it is easy to reduce the strength and delamination at the final wire diameter, whereas when the cooling rate exceeds 30 ℃ / sec This is because martensite is precipitated and there is a problem that disconnection occurs during the drawing process.

Thereafter, the primary fresh processing with a processing amount of 2.5 ~ 3.5, then austenitized at 900 ~ 1050 ℃, and subjected to a patented heat treatment in a lead bath maintained in the temperature range of 500 ~ 650 ℃ for constant temperature transformation of fine pearlite It is desirable to. The fresh processing amount is set to 2.5 to 3.5 because it is advantageous to prevent the occurrence of delamination due to harsh processing during the primary drawing and to limit the processing amount of the final drawing to 4 or less for the properties of the final product.

In addition, the heating temperature for the austenitization is preferably set to 900 ~ 1050 ℃, the reason is that below 900 ℃ the size of the austenite grain is too fine to increase the ferrite fraction after transformation, exceeding 1050 ℃ In this case, the austenite grains are so coarse that the ductility of the material is lowered.

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

(Example 1)

Steel slabs having a chemical composition as shown in Table 1 were continuously cast into 160 × 160 mm billets, heated at 1050 ° C., hot rolled, and continuously cooled to 25 ° C./sec to prepare wire rods having a diameter of 5.5 mm. Next, the cornerstone ferrite, cementite fraction and mechanical properties of the specimens were measured and shown in Table 2 below.

division C Si Mn Cr B Ti Conventional Steel 0.70 0.3 0.4 － － － Comparative Steel 1 0.52 0.3 0.4 Inventive Steel 1 0.52 0.3 0.4 0.2 Inventive Steel 2 0.53 0.3 0.7 － 0.0013 0.01 Invention Steel 3 0.62 0.6 0.4 0.0023 0.01

division Manufacture conditions Measurement result Heating temperature (℃) Cooling rate (℃ / sec) Tensile Strength (kg / ㎡) Cross section reduction rate (%) Cornerstone ferrite fraction (%) Conventional Conventional Steel 1050 25 105.6 48 2 Comparative Material 1 Comparative Steel 1 1150 85.3 59 6 Comparative Material 2 1050 81.9 56.4 24 Invention 1 Inventive Steel 1 88 58.7 7 Invention 2 Inventive Steel 2 98 63 2 Invention 3 Invention Steel 3 102 52 5.5

As can be seen in Table 2, although the present invention material was controlled to be less than 10% of the cornerstone ferrite fraction even if the heating temperature is low, in the case of the comparative material (1) to control the amount of the cornerstone ferrite to 10% or less 1150 ℃ or more High temperature heating was needed.

On the other hand, the present invention is low in strength compared to the conventional material, but it can be seen that the cross-sectional reduction rate that can evaluate the ductility of the material is significantly increased. In order to prove this, Table 3 below shows the critical strain of delamination when the 5.5 mm specimen is drawn.

division Critical strain Conventional 2.5 Comparative Material 1 3.5 or more Invention 1 3.5 or more Invention 2 3.5 or more Invention 3 3.2

As shown in Table 3, it can be seen that the delamination does not occur even by the high fresh processing of the deformation amount 3 or more except for the conventional material. Therefore, it can be seen that the conventional material does not have the wire workability for omitting the petenting once.

At this time, the amount of wire deformation (e) is a value calculated by 2ln (D _o / D), D _o is the wire diameter of the fresh material, D means the wire diameter after the wire.

(Example 2)

The comparative material (1) and the inventive material (2) of the above example were first drawn to 0.96 mm, heated at 950 ° C., and then deposited in a lead (Pb) bath to control the transformation temperature to 580 ° C. Then, the microstructure was observed and the results are shown in FIG.

As shown in FIG. 1, the comparative material (FIG. 1B) was found to have a large amount of cornerstone ferrite in comparison with the present invention material (FIG. 1A), and the ductility was about 51%, compared to 58.6% of the inventive steel.

Next, the specimens were drawn in the conditions as shown in Table 4 below, and the physical properties thereof are shown in Table 4 below.

division Fresh Process Tensile Strength (kg / ㎡) Cross section reduction rate (%) Delamination occurrence Conventional Example 1 Conventional 5.5mmΦ → 3.3mmΦ → patterning → 1.4mmΦ → patterning → bloss plating → 0.2mmΦ 275 35 radish Conventional Example 2 5.5mmΦ → 2.4mmΦ → Patterning → 0.6mmΦ → Patterning → Blass Plating → 0.15mmΦ 260 38 radish Comparative Example 1 Comparative Material 1 5.5mmΦ → 0.96mmΦ → Patterning → Blass Plating → 0.15mmΦ 278 33 U Inventive Example 1 Invention 1 5.5mmΦ → 0.96mmΦ → Patterning → Blass Plating → 0.15mmΦ 278 42 radish Inventive Example 2 Invention 2 5.5mmΦ → 0.96mmΦ → Patterning → Blass Plating → 0.15mmΦ 280 45 radish Inventive Example 3 Invention 3 5.5mmΦ → 1.5mmΦ → Patterning → Blass Plating → 0.28mmΦ 290 40 radish

As shown in Table 4, the prior art examples (1), (2) was able to secure a tensile strength of 260 ~ 300kg / mm ² in the ultra-fine wire of 0.3mm or less after the heat treatment twice in the freshness. In this case, it can be seen from Example 1 that the increase in the amount of drawn processing to shorten the heat treatment, the delamination occurs in the primary drawing is difficult to commercialize.

However, in the case of the present invention, it can be seen that similar strength can be obtained without omitting such a pattening heat treatment once and no delamination occurs.

As described above, according to the present invention, in the manufacturing method of steel cord steel wire, the high strength wire can be manufactured even if the heating treatment is performed only once, so that the heat treatment, pickling, and lubricant coating process performed during the drawing process can be omitted. It has an effect.

Claims (1)

In the manufacturing method of steel wire for steel cord, By weight% C: 0.4-0.65%, Mn: 0.1-1.0%, Si: 0.1-1.0%, Cr: 0.3% or less, B: 100 ppm or less, remaining Fe and other unavoidable impurities, wherein Ti, Nb , At least one selected from the group consisting of elements of V is hot rolled to a steel sheet containing 0.02% or less, and then continuously cooled at a cooling rate of 10 to 30 ° C./sec to form a cornerstone ferrite fraction of 10% or less, Cementite fraction is fresh with 6 ~ 10% wire rod, then heated at 900 ~ 1050 ℃, austenitized and quenched, and is incubated with fine pearlite in the temperature range of 500 ~ 650 ℃, and then to 0.15 ~ 0.3mm Manufacturing method of steel wire for steel cord, characterized by wet drawing