KR100368224B1 - Manufacturing method of high strength steel for wire rod and wire rod with excellent freshness - Google Patents

Abstract

The present invention relates to a high-strength steel for wire rods and a method for producing a wire rod excellent in freshness; Its purpose is to control the chemical composition design of steel and / or continuous controlled cooling conditions in the manufacture of high strength wires, thereby suppressing the generation of cornerstone cementite and low temperature tissues, which cause breakage during drawing, thereby reducing the payload before drawing. High strength steel for wire rods with excellent cold drawability, which can produce high strength steel wire with tensile strength of 215kg / mm2 or more and cross section reduction rate of 30% or more by cold wire processing of over 85% It is to provide a method for manufacturing a wire rod using this.

The present invention for achieving the above object by weight% carbon: 0.85-0.95%, silicon: 0.4-1.2%, manganese: 0.4-0.7%, chromium: 0.2-0.4%, vanadium: 0.04-0.10%, titanium: 0.01 -0.05%, phosphorus: 0.02% or less, sulfur: 0.02% or less, the high-strength steel for wire rods, characterized in that consisting of residual Fe and unavoidable impurities,

In addition, the present invention after heating the raw material made of the high-strength steel in the range of 900-1050 ℃ hot-rolled wire, the average cooling rate from the cooling start temperature of 850-950 ℃ to 500 ℃ 5-12 ℃ / sec The present invention relates to a method for producing a high strength wire rod having excellent freshness, characterized by continuous controlled cooling.

Description

High-strength steel for wire rod and manufacturing method of wire rod with excellent freshness

The present invention relates to a high-strength steel for the production of steel wire, high-strength cable (cable), high-strength wire rope, or piano wire for concrete reinforcement, and a method for producing a high-strength wire using the same, more specifically during the wire processing It relates to a high-strength steel excellent in workability and a method for producing a high-strength wire using the same.

Generally, vacant steel wires or super-vacuum steel wires that are inexpensive and easily manufactured are mainly used for concrete reinforcing steel wires, high strength cables, high strength wire ropes, piano wires, etc., which require high strength depending on application characteristics. It is becoming. These steel wires usually use a heat treatment called patterning and a cold strain with a total reduction of 85% or more from wires with a wire diameter of 8-13 mm, in order to have a suitable strength and wire diameter to suit commonly used properties. After that, it is made of steel wire having the size and strength required for the properties of the final product.

In recent years, as the use environment of the material is becoming more severe and the construction of the large-scale giant building structures is increasing, the strength required for these steel wires is increased sharply compared with the past, and ultra high strength is required. For this reason, the strength of steel wires is increased by increasing the carbon content, adding alloying elements, optimizing the wire rod manufacturing process, and improving the drawing process.

As a method of increasing the strength in the high-carbon steel for drawing, the cementite fraction increase in pearlite, which is the main microstructure of the steel wire, the layer spacing, and the method of strengthening the ferrite solid solution in pearlite by the addition of solid elements.

The cementite fraction is increased by increasing the carbon content of the material, and the finer perlite layer spacing increases the carbon content of the material, the addition of alloying elements to improve the hardenability of the material, and the increase in the cooling rate of the wire during the manufacture of the wire. It is done by

In the case of drawing the high strength steel wire manufactured by the above method, the most important thing is to obtain a pearlite structure having a fine layer spacing in order to secure excellent drawing processability. In order to obtain such fine pearlite, generally, heat treatment called patenting is performed during drawing or drawing. In addition to the purpose of obtaining fine pearlite suitable for drawing, the patented heat treatment is also used to relax extreme work hardening and to secure the ductility required for continuous drawing. Such patenting heat treatment is generally performed in a lead (Pb) bath, which causes problems such as environmental pollution, increased device cost, and reduced productivity. Therefore, although the research on the heat treatment method using a different medium, the most preferred method is to develop a high-strength wire that can be cold drawn directly without such a heat treatment.

In addition, the method of increasing carbon content and adding alloying elements for high strength in high carbon steels is effective in improving the carbon content in high carbon steels in addition to the effect of lowering the ductility and fresh workability due to the high strength of the material. Increasing the segregation of the core in the billet and wire rod, which is a material, promotes the formation of cornerstone cementite. Unlike other products, the material used for concrete reinforcing steel wire, high-strength wire rope or piano wire is 8-13mm wire diameter of wire rod, and the cooling speed is relatively slow when manufacturing wire rod. Inhibition is not easy. On the other hand, the addition of the alloying element causes the problem of low temperature structure, such as martensite in the continuous cooling process in the wire rod manufacture due to the increase in hardenability (hardenability) with the pearlite fine.

The presence of such a cementite cementite or low temperature structure acts as a cause of disconnection during cold drawing, and thus has an effect of rapidly lowering the wire workability of the wire rod. Therefore, for the manufacture of high strength wire rods that can be cold drawn directly without patenting heat treatment, the design of chemical components to improve the strength of materials that can be produced in wire rod stellmor cooling facilities and the continuous control in wire rod cooling facilities Cooling conditions must be set.

Conventional techniques for producing high strength steel wire with excellent freshness through the continuous control cooling include Japanese Patent Application Laid-Open No. Hei 4-100772, Hei 4-254526, Hei 6-271937, and the like. .

In Japanese Patent Application Laid-Open No. 4-100772, in a steel containing C: 0.9-1.1%, Si: 0.15-1.5%, Mn: 0.3-0.6%, and Cr: 0.1-0.5%, the wire is 750 after rolling. The critical carbon content that does not precipitate cementite cementite when cooled from -950 ℃ is expressed as a function of the cooling rate up to 550 ℃. Since the content of manganese is limited to 0.3-0.6%, it is difficult to apply to a material having a relatively large wire diameter requiring high strength containing 0.6% or more of manganese. In addition, the carbon content of the application range is 0.9-1.1%, and the concentration of carbon in the center segregation of wire rods manufactured from BLUM manufactured by casting is generally 1.1 times higher than that of other parts. Since formation of cementite cementite in the large diameter wire containing is inevitable, it is difficult to apply.

Japanese Patent Laid-Open No. 4-254526 discloses hot carbon steel in the production of high carbon steel containing C: 0.9-1.3%, Si: 0.1-2.0%, Mn: 0.2-1.3%, Cr: 0.1-0.8%. The critical cooling start temperature at which the cornerstone cementite does not precipitate during continuous cooling after rolling is set for the component content, and there is no specific limitation on the cooling rate, which is the main element of the continuous cooling. As in -100772, it contains more than 1.0% of carbon, so it is difficult to apply cementite cementite in large diameter wires with a diameter of 8-13mm because it is an unavoidable phenomenon.

Japanese Patent Laid-Open No. 6-271937 includes C: 0.9-1.2%, Si: 0.5-2.0%, Mn: 0.2-1.0%, Al: 0.02-0.07%, and N: 0.003-0.015%. In the production of carbon steel, there is no specific limitation on the cooling rate, which is the main element of continuous cooling after hot rolling, and as in the Japanese Patent Publications, it contains more than 1.0% of carbon, so the diameter range of 8-13mm in continuous cooling is applied. It is difficult to apply cementite cementite production in large diameter wires because of unavoidable phenomenon.

In order to solve the problems of the prior arts, the present inventors have repeatedly conducted research and experiments and propose the present invention based on the results. The present invention provides a steel chemical composition design and / or continuous control in manufacturing a high strength wire rod. By controlling the cooling conditions appropriately and suppressing the formation of cornerstone cementite and low temperature tissue which causes disconnection when drawing, 215kg by cold drawing more than 85% of total section reduction rate even if the drawing is done directly without the patenting process before drawing An object of the present invention is to provide a high-strength steel for wire rods having excellent cold drawing processability and a method of manufacturing wire rods using the same, which can manufacture high-strength steel wire having a tensile strength of 30 mm or more and a reduction ratio of 30% or more.

The present invention for achieving the above object by weight% carbon: 0.85-0.95%, silicon: 0.4-1.2%, manganese: 0.4-0.7%, chromium: 0.2-0.4%, vanadium: 0.04-0.10%, titanium: 0.01 -0.05%, phosphorus: 0.02% or less, sulfur: 0.02% or less, and a high-strength steel for wire rods, characterized in that consisting of residual Fe and unavoidable impurities,

In addition, the present invention after heating the raw material made of the high-strength steel in the range of 900-1050 ℃ hot-rolled wire, the average cooling rate from the cooling start temperature of 850-950 ℃ to 500 ℃ 5-12 ℃ / sec The present invention relates to a method for producing a high strength wire rod having excellent freshness, characterized by continuous controlled cooling.

Next, the present invention will be described in detail. First, the composition of high-strength steel that satisfies the conditions of the present invention will be described in detail, and then a method of manufacturing a high-strength wire using the high-strength steel will be described in detail.

The carbon is the most effective and economical element to increase the strength, and has an effect on the hardenability, strength, work hardening rate, impact toughness, fatigue properties of the material. If the content is less than 0.85%, it is difficult to secure a target tensile strength of 215kg / mm2 and more than 30% of cross section, even after cold drawing with a total cross section reduction rate of 85% or more. Since the carbon concentration in the central segregation area is higher than 1.05%, the production of cornerstone cementite is inevitable when the wire rod cooling equipment, such as the wire rod cooling equipment, is made of wire rod 8-13mm in diameter. There is concern. Therefore, in the present invention, the content of carbon is preferably 0.85-0.95%.

The silicon is used as a deoxidizer and is an element having a high solubility strengthening effect in solid solution, which is effective for improving strength and affects delayed fracture, impact toughness and fatigue resistance. It also has the effect of suppressing the formation of saltpeter cementite. If the content is less than 0.4%, the effect of deoxidation and solid solution strengthening is not sufficient. If the content exceeds 1.2%, the cold workability decreases, which makes it difficult to draw fresh, and the weldability of the material is increased, the deformation resistance is increased during hot rolling, and the decarburization is increased. Problems such as weakening of descale treatment during fresh processing occur. Therefore, in the present invention, the silicon content is preferably 0.4-1.2%.

The manganese is used as a deoxidizing agent and improves the hardenability and strength of the material and is an element having the effect of preventing the generation of cracks due to sulfur by combining with sulfur (S) in the steel. In particular, when the wire diameter of the manufactured wire is large, the effect of forming fine pearlite due to improvement of the hardenability of the material is great. If the content is less than 0.4%, it is not sufficient to show the effect of improving the hardenability. If the content is higher than 0.7%, the wire rod generated when the local hardenability of the material due to segregation is added and the alloy element with the hardenability is added simultaneously. Since the production of low-temperature tissues promotes the production, disconnection may occur due to the fresh processing. Therefore, in the present invention, the content of manganese is preferably 0.4-0.7%.

The chromium, like manganese, has an effect of improving the hardenability and miniaturizing the spreadlite layer spacing, thereby improving the strength, and preventing decarburization and graphitization. If the content is less than 0.2%, the effect of strength improvement is not sufficient. If the content is more than 0.4%, it is more likely that low temperature structure is formed during wire rod production due to the increase of hardenability. This facilitates the creation of low temperature tissue, which may result in disconnection during fresh processing. Therefore, in the present invention, the content of chromium is preferably 0.2-0.4%.

The vanadium is an element having a large austenite grain size refinement effect, a solid solution strengthening effect, and a precipitation strengthening effect. The vanadium is an element having a great effect on quenchability, fatigue characteristics, strength, impact toughness, and delayed fracture resistance. It also has the effect of suppressing the formation of saltpeter cementite. If the content is less than 0.04%, a sufficient amount is not solubilized so that the effect of improving the hardenability of the material is not sufficient, so that it is not easy to obtain a fine pearlite structure, and the austenite grain refining effect and precipitation strengthening effect are not sufficient, and 0.10% If it exceeds, the effect is saturated and it is uneconomical. The excessive precipitation of vanadium carbonitride in the ferrite rapidly strengthens the ferrite in the pearlite, thereby reducing the ductility, thereby reducing the fresh workability. Therefore, in this invention, it is preferable to make content of vanadium into 0.04-0.10%.

Titanium is an element having an effect similar to vanadium, and is particularly an element that greatly affects austenite grain refining. If the content is less than 0.01%, the austenite grain refining effect is not sufficiently exhibited. If the content exceeds 0.05%, the addition effect is saturated, which is no longer effective for reducing the austenite grain, and when excessively added, deformation during hot rolling There is a problem of increasing resistance. Therefore, in the present invention, it is preferable to make the content of titanium 0.01-0.05%.

The phosphorus (P) and sulfur (S) is preferably at most 0.02%. When the phosphorus exceeds 0.02%, the grain boundary segregation is reduced to lower the toughness. When the sulfur exceeds 0.02%, the grain is segregated into a low melting point element to reduce the toughness and form an emulsion to have a harmful effect during the fresh processing Because.

Next, a method of manufacturing a high strength wire using the high strength steel as described above will be described in detail.

In the present invention, the material made of the high-strength steel is heated in the range of 900-1050 ℃ hot-rolled wire.

In the case where the heating temperature is lowered below 900 ° C., the load of the rolling roll increases due to an increase in the hot deformation resistance according to the reduction of the rolling temperature of the raw material during hot rolling, resulting in a decrease in the roll life. In addition, in the case where the heating temperature is higher than 1050 ° C, decarburization which is easy to occur in the silicon-rich steel is accelerated, and decarburization of the material is increased, and colony of pearlite generated when the pearlite is transformed due to the increase of austenite grain size. (colony) The particle size is large, the fresh workability is lowered, and there is a problem of causing a decrease in wire quality, such as a winding failure and surface defects during wire winding. Therefore, in this invention, it is preferable to perform the heating for wire rod hot rolling at 900-1050 degreeC.

In the present invention, even if the wire rod hot rolling is performed in the range of 8-13 mm wire diameter, the object can be achieved.

In the present invention, after the hot rolling, continuous control cooling is performed at an average cooling rate of 850-950 ° C from 500 ° C to 500 ° C.

The reason for setting the cooling start temperature to 850-950 ° C is as follows. In other words, at the cooling start temperature lower than 850 ℃, the cooling start temperature is close to the cornerstone cementite precipitation temperature range, and during continuous cooling, the foundation stone cementite precipitation occurs in a short time, so that the cooling is continuously performed in the Stelmore cooling system, which is a wire rod cooling system. This is because it is difficult to control the cooling because the cementite cementite precipitates at the beginning of the start.At the cooling start temperature higher than 950 ° C, the austenite particles are coarsened and the colony particle diameter of the pearlite produced when the pearlite is transformed becomes fresh. This is because it lowers the quality of wire rods such as winding failure and surface defects when the wire is wound.

In the continuous cooling, the reason for setting the average cooling rate from the cooling start temperature to 500 ° C. as 5-12 ° C./sec is as follows. That is, if the average cooling rate is less than 5 ℃ / sec during the wire rod manufacturing, the time required for the precipitation and growth of the cementite cementite at the austenite grain boundary is sufficient, the formation of the cementite cementite significantly larger than the cementite in pearlite In addition, the pearlite transformed from austenite also has a coarse layer spacing, making it difficult to obtain high strength and causing a decrease in fresh processing. When the average cooling rate exceeds 12 ° C / sec, carbon and manganese in the center of the wire rod are The low-temperature structure which degrades fresh workability arises because sufficient time for perlite transformation in the area | region where alloy elements, such as these were concentrated, is not made. Therefore, in the present invention, it is preferable to perform continuous control cooling with the average cooling rate from the cooling start temperature to 500 ° C as 5-12 ° C / sec.

On the other hand, the wire rod manufactured by the method of the present invention as described above is drawn into a commercialized product, the draw speed at the time of such drawing is in the range of 100-400m / min as the drawing speed in the final product line It is desirable to. If the drawing speed is less than 100m / min, productivity in the drawing process is low and economical, if it exceeds 400m / min, fatal defect during drawing due to the increase of carbon content for the high strength of the material and the addition of alloying elements such as silicon This is because there is a risk of causing occurrence of delamination.

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

Example 1

To prepare a 50kg ingot containing a chemical component as shown in Table 1. The prepared ingot was melted under vacuum induction and homogenized at 1250 ° C. for 8 hours, hot rolled at a rolling ratio of 15: 1, and then maintained at 900 ° C. for 5 minutes and then cooled at 3 ° C./sec, 7 as shown in Table 2 below. It changed to 15 degree-C / sec and cooled and obtained wire rod. After the cross section cutting of the obtained wire rod was examined by the biopsy to check whether the cementite cementite (C) and the low-temperature structure (M) bainite or martensite were generated and the results are shown in Table 2 below. At this time, the histology was a scanning electron microscope (Scanning Electron Microscope, SEM) at 2000 times magnification.

C Mn Si P S Cr V Ti Invention 1 0.87 0.61 0.61 0.005 0.003 0.25 0.082 0.020 Invention 2 0.91 0.61 0.40 0.006 0.003 0.24 0.083 0.021 Invention 3 0.89 0.55 1.02 0.005 0.004 0.26 0.062 0.015 Invention 4 0.90 0.59 0.80 0.005 0.003 0.35 0.041 0.018 Invention 5 0.85 0.045 0.59 0.005 0.004 0.25 0.079 0.050 Comparative Material 1 1.30 0.53 0.90 0.005 0.003 - - - Comparative Material 2 0.95 0.55 0.22 0.005 0.003 - - - Comparative Material 3 0.98 0.71 0.87 0.005 0.003 - - 0.030 Comparative Material 4 0.92 0.81 1.41 0.003 0.005 - - -

Steel grade used Cooling rate (℃ / sec) Microstructure Inventive Example 1 Invention 1 7 P Inventive Example 2 Invention 2 7 P Inventive Example 3 Invention 3 7 P Inventive Example 4 Invention 4 7 P Inventive Example 5 Invention 5 7 P Comparative Example 1 Comparative Material 1 7 P + C Comparative Example 2 Comparative Material 2 7 P + C Comparative Example 3 Comparative Material 3 7 P + C + M Comparative Example 4 Comparative Material 4 7 P + M Comparative Example 5 Invention 1 15 P + M Comparative Example 6 Invention 2 15 P + M Comparative Example 7 Invention 3 3 P + C Comparative Example 8 Invention 4 3 P + C Comparative Example 9 Invention 5 15 P + M Comparative Example 10 Comparative Material 1 3 P + C Comparative Example 11 Comparative Material 2 3 P + C Comparative Example 12 Comparative Material 3 3 P + C Comparative Example 13 Comparative Material 4 3 P + C

As can be seen in Table 2, when manufactured by the alloy component and the cooling rate satisfying the conditions of the present invention (Invention Example 1-5), while the microstructure is composed of a complete pearlite suitable for cold drawing In the case of an alloy component of the present invention and / or outside the cooling rate range (Comparative Examples 1-13), it may be found that even though it contains a fine pearlite structure, it contains cornerstone cementite or martensite that is harmful to cold drawing.

Example 2

50 kg of ingots having the chemical composition as shown in Table 1 were melted under vacuum induction, processed after homogenization at 1250 ° C. for 8 hours, welded to a wire rod 160 × 160 mm billet, and heated and extracted at 1000 ° C. for 1 hour and 20 minutes at the wire rod factory. Hot rolling was carried out. After hot rolling, the laying head temperature was set to 850 ° C., and a wire diameter of 11 mm was manufactured by controlling the cooling rate in the wire stealmo cooling system.

After the pre-treatment such as descaling of the wire rods, coating of lubricant, etc. (when using the steel grades of the comparative materials 1, 2 and 3 in Table 3 below, the patenting is performed, and the rest is not performed). Cold drawing was performed in a continuous drawing machine with a drawing speed of 120m / min up to 4.28mm (cold processing rate of 85%).

The wire rod manufactured as described above and a portion of the finished final product line were taken and subjected to a uniaxial tensile test of a tensile speed of 5 mm / min in a tensile tester, and the measured tensile strength and cross-sectional reduction rate are shown in Table 3 below.

Steel grade used Wire rod Fresh Wire diameter (mm) Tensile Strength (kg / ㎡) Wire diameter (mm) Tensile Strength (kg / ㎡) Cross section reduction rate (%) Inventive Example A Invention 1 11 142.1 4.28 220.2 44.8 Inventive Example B Invention 2 11 141.8 4.28 217.8 43.4 Inventive Example C Invention 3 11 148.2 4.28 231.2 36.5 Inventive Example D Invention 4 11 145.6 4.28 226.9 38.4 Inventive Example E Invention 5 11 140.2 4.28 215.3 48.4 Comparative Example A Comparative Material 1 11 157.3 monorail - - Comparative Example B Comparative Material 2 11 139.5 5.0 196.0 58.5 Comparative Example C Comparative Material 3 11 147.4 5.0 203.9 50.3 Comparative Example D Comparative Material 4 11 150.2 5.0 212.4 21.6

As can be seen from Table 3, in the case of the invention example (AE) that satisfies the conditions of the present invention, the tensile strength at least 215kg / ㎠ or more and the cross-sectional reduction rate 30 when cold drawing is more than 85% without performing the patenting More than% could be secured.

As described above, according to the present invention, by controlling the steel composition and the continuous controlled cooling conditions, even if the wire is drawn directly without performing the patenting process before the wire drawing, the cold drawing is not less than 215kg / mm 2 or more due to the cold drawing of 85% or more. Since high-strength steel wire having a tensile strength and a reduction ratio of 30% or more can be manufactured, a large-strength wire rod having a high strength such as a wire diameter of 8-13 mm can be manufactured at a lower cost.

Claims (3)

In weight%, carbon: 0.85-0.95%, silicon: 0.4-1.2%, manganese: 0.4-0.7%, chromium: 0.2-0.4%, vanadium: 0.04-0.10%, titanium: 0.01-0.05%, phosphorus: 0.02% or less , Sulfur: 0.02% or less, high strength steel for wire rod, characterized in that it is composed of residual Fe and unavoidable impurities In the method of manufacturing a high strength wire rod, After heating the raw material of the high-strength steel of claim 1 in the range of 900-1050 ℃ hot-rolled wire, the average cooling rate from the cooling start temperature of 850-950 ℃ to 500 ℃ to 5-12 ℃ / sec Method for producing high strength wire rods having excellent freshness, characterized by continuous controlled cooling The method of claim 2, The wire rod hot rolling is a method for producing high strength wire rods having excellent freshness, characterized in that the wire diameter is in the range of 8-13mm.