KR100398375B1 - A method of manufacturing as-rolled wire rods for - Google Patents

Abstract

The present invention relates to a method for producing a high frequency quenching wire used in automobile steering device parts and the like; The purpose of this method is to manufacture a high-strength high-strength non-coated steel wire that has the same processing characteristics and mechanical properties as steel wire without omitting hardening-treatment heat treatment by appropriately adjusting steel components and controlling hot wire rolling and cooling conditions. In providing.

The present invention is, in weight%, C: 0.30-0.60%, Si: 0.10-0.40%, Mn: 0.8-2.0%, Cr: 0.03-1.0%, V: 0.03-0.15%, Ti: 0.010-0.040%, Hot wire material by heating steel with Al: 0.01-0.10%, P: 0.030% or less, S: 0.020-0.10%, N: 0.005-0.030% and the remaining Fe and other unavoidable impurities to 1000-1150 ℃ After rolling and winding in the form of a coil, the 550-750 ° C section is cooled at a rate of 0.1-1.0 ° C / sec, and cold drawn at a cross-sectional reduction rate of 5.0-30%. Make that technical point.

Description

Manufacturing method of non-coarse steel wire for high frequency quenching {A METHOD OF MANUFACTURING AS-ROLLED WIRE RODS FOR}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing high frequency quenched wire rods used in automobile steering device parts and the like, and more particularly, to a method for manufacturing non-coated steel wire rods without the hardening-treatment heat treatment performed after hot wire rolling.

Wire rods are used in various mechanical parts and are also applied to the rack bar 10, which is a gear shaft of the automobile steering apparatus shown in FIG. In order to use the wire rod as a rack bar, the wire rod should be cut to form gears, and then subjected to high frequency quenching heat treatment and sorrow heat treatment to give abrasion resistance to the gear portion. Usually, the wire used for high frequency quenching heat treatment is called high frequency quenching wire, and cold wire workability (cutting workability and drilling workability), high frequency quenchability and mechanical properties are important.

S45C, a mechanical structural carbon steel shown in Table 1, is commonly used as a high-frequency hardened wire rod, and the manufacturing method is cold drawn after hot-rolled steel, followed by quenching-treating heat treatment to secure proper strength and toughness. Doing. As such, the wire produced by quenching-seal heat treatment is referred to as a tempered steel wire.

Steel grade Chemical composition (% by weight) C Si Mn P S S45C 0.42-0.48 0.15-0.35 0.60-0.90 Less than 0.030 Less than 0.035

On the other hand, since the mid-70s, non-coarse steel wire rods have been developed and widely used in Europe and Japan, which can significantly reduce cost by eliminating the hardening-seal heat treatment.

Non-coated steel wire is a steel that has been developed so that the alloy design is appropriate and high strength tough material is manufactured through controlled rolling and controlled cooling to omit the quenching-thinning heat treatment process following hot forging or cold forging. Examples of the non-coarse steel wire include the techniques proposed in Japanese Patent Application Laid-Open Nos. 84-136420 and 95-54040.

Steel disclosed in Japanese Unexamined Patent Publication No. 84-136420 increases manganese (Mn) content compared to conventional carbon steel for mechanical structure to increase strength without deterioration of toughness, and adds about 0.1% of vanadium (V), a precipitation hardening element. Therefore, during the hot forging, the vanadium carbonitride [V (CN)] is finely precipitated in the ferrite matrix to increase the strength, thereby eliminating the subsequent hardening and annealing process.

However, this wire rod is suitable to be used as a material for making a specific shape part through hot forging, but it is not suitable for use as a cold work material because of its poor machinability or drilling ability.

In addition, the non-coarse steel wire developed by Daedong Special Steel Co., Ltd. and proposed in Japanese Laid-Open Patent Publication No. 94-54040 improves the strength and toughness of the steel by significantly lowering the carbon content and improving the microstructure in order to improve cold workability. Niobium is added in small amounts. This non-coated steel wire is suitable for use in cold drawing and forging materials, but it does not contain free cutting elements, which makes it unsuitable for cutting. It also has low carbon content and poor high frequency quenchability.

So far, the proposed non-coated steel wire can reduce cost by omitting quenching-concern heat treatment, but there is a problem in that it cannot be used as a wire for high frequency quenching due to poor cutting processability or high frequency hardening.

The present inventors have developed a non-manufactured steel wire rod for automobile parts which is manufactured by performing surface hardening by high frequency quenching after cold drawing and cutting without hot-rolled material by hardening and treating the hot rolled material. In order to do so, studies and experiments have been carried out and the present invention has been proposed based on the results.

The present invention provides a method for producing a high-strength non-coated steel wire for high-frequency quenching that exhibits the same processing characteristics and mechanical properties as those of a crude steel wire without omitting hardening-treatment heat treatment by appropriately adjusting steel components and controlling hot wire rolling and cooling conditions. To provide, the purpose is.

1 is a schematic diagram of a vehicle steering apparatus

Figure 2 is a microstructure photograph of the invention steel.

In order to achieve the above object, the manufacturing method of the non-coated steel wire of the present invention, in weight%, C: 0.30-0.60%, Si: 0.10-0.40%, Mn: 0.8-2.0%, Cr: 0.03-1.0%, V ; 0.03-0.15%, Ti: 0.010-0.040%, Al: 0.01-0.10%, P: 0.030% or less, S: 0.020-0.10%, N: 0.005-0.030% and the remaining Fe and other unavoidable impurities The resulting steel is heated to 1000-1150 ℃, hot rolled and coiled, then cooled to 550-750 ℃ at a rate of 0.1-1.0 ℃ / sec. It is constructed by drawing.

As described above, the cold drawn wire is subjected to cutting and finally subjected to high frequency quenching and thinning to harden the surface.

Hereinafter, the present invention will be described in detail.

The present invention is characterized in that [S] is managed at an appropriate level to secure the cutting property of the wire rod, while appropriately controlling other components to secure mechanical properties, which will be described for each component as follows.

The carbon (C) is a major element that determines the strength of the material. If the carbon content is too low, it is impossible to secure the required strength. If the carbon content is too high, the required toughness and ductility cannot be secured. Therefore, the carbon content is preferably limited to 0.30-0.60%.

Silicon (Si) is added up to 0.40% in order to increase the strength by solid solution strengthening, but if it is added more than that, surface decarburization of the material occurs. In order to ensure the required strength and to sufficiently deoxidize, it is preferable to add 0.10% or more.

Manganese (Mn) is added more than 0.8% to increase the strength of steel due to the increase in hardenability and solid solution, but decreases the toughness when added more than 2.0%. Therefore, in order to obtain the required strength without significantly reducing the toughness, the content of the manganese is preferably limited to 0.8-2.0%.

Chromium (Cr) is an element necessary to ensure good quenching properties, in particular, to strengthen the matrix structure to increase the strength and also improve the wear resistance and corrosion resistance. In order to obtain such an effect, it is necessary to add 0.03% or more, but when it is added more than 1.0%, toughness is lowered and the price of the material is expensive, so it is preferable to limit the addition range to 0.03-1.0%.

Vanadium (V) combines with carbon and nitrogen in steel to form vanadium carbonitrides. The fine vanadium carbonitride produced during the cooling process is very effective in improving the strength. In order to obtain the required effect, it is necessary to add at least 0.03% or more, but if it is added more than 0.15%, the strength is increased more than necessary and the toughness and ductility are lowered. Therefore, it is preferable to limit the addition range to 0.03-0.15%.

Titanium (Ti) combines with nitrogen in steel to form titanium nitride. Titanium nitride improves the impact toughness of the steel by inhibiting austenite grain growth during reheating. If the amount of titanium added is too small, the absolute amount of titanium nitride is difficult to effectively inhibit grain growth, and if the amount exceeds a certain amount, the effect is saturated or rather reduced. Therefore, the appropriate addition amount is preferably in the range of 0.010-0.040%.

Aluminum (Al) is added for deoxidation and also to form aluminum nitride to refine the austenite to improve the impact toughness of the steel. If the added amount is small, the required effect is not obtained. If the added amount is large, the effect is saturated. Therefore, the added amount is preferably limited to the range of 0.01-0.10%.

Phosphorus (P) is segregated at the austenite grain boundary and degrades toughness, so the upper limit is preferably limited to 0.030%.

Sulfur (S) combines with manganese in the steel to form manganese sulfide. Manganese sulfide improves the free machinability of steel. In order to acquire such an effect, it is preferable to add 0.020% or more. However, since sulfur reduces impact toughness, it is preferable to limit the upper limit to 0.10%.

Nitrogen (N) combines with titanium, vanadium and aluminum in steel to form titanium nitride vanadium nitride and aluminum nitride, thereby improving strength and toughness. If the addition amount is small, such an effect cannot be obtained. If the addition amount is too large, the effect is saturated, so the addition range is preferably 0.005-0.030%.

Reheating the steel composition as described above is hot wire re-rolling, the reheating temperature is preferably 1000-1150 ℃. The reason for this is that the reheating temperature of 1000 ° C or higher can re-introduce the coarse precipitated vanadium nitride, and if it exceeds 1150 ° C, the austenite becomes coarse and the decarburization becomes severe.

After reheating as described above, the hot wire is re-rolled and wound in a coil form, and then cooled. In this case, it is preferable to cool the phase transformation section at 550-750 ° C. at a cooling rate of 0.1-1.0 ° C./sec. If the cooling rate is slower than 0.1 DEG C / sec, the ferrite and pearlite structures become too coarse to reduce the strength and toughness, and the vanadium carbonitride precipitated during the cooling process is too grown to effectively contribute to the strength increase. And when the cooling rate is faster than 1.0 ℃ / sec is generated low temperature transformation tissue makes the steel vulnerable.

Wire rods manufactured in this way are cold drawn to fit the final product dimensions in order to generate compressive residual stresses on the wire surface.

After the cold drawing, the wire is cut to the appropriate length, and after the necessary cutting process, the surface is hardened by high frequency quenching and thinning treatment.

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

Example 1

Chemical compositions of the inventive steel and conventional steel applied to the embodiment of the present invention are shown in Table 2 below.

division Chemical composition (% by weight) Remarks C Si Mn P S Cr Mo Al V Nb Ti N Invention steel 0.45 0.24 0.19 0.016 0.044 0.08 - 0.032 0.10 - 0.016 0.015 Conventional Steel 1 0.43 0.25 0.85 - 0.025 0.13 - - 0.10 - - 0.01 Japanese Patent Laid-Open Conventional Steel 2 0.15 0.25 1.15 - - 0.12 0.02 - 0.11 0.015 - - Japanese Patent Laid-Open

The steel, as shown in Table 2, was charged into a heating furnace, heated for 1 hour and 30 minutes, and extracted. At this time, the extraction temperature was 1050 ° C. The extracted steel was rolled to a diameter of 25, 27, 30mm using a hot wire rolling mill, and then wound in a coil form. The wound wire rod was cooled in a 550-750 ° C. section at a cooling rate of 0.25-0.30 ° C./sec using a cooling system.

2 shows a microstructure of the inventive steel that has completed hot wire rolling and adjusted cooling as described above.

The steel of the present invention shown in FIG. 2 shows a good microstructure composed of fine ferrite and pearlite without the presence of low temperature transformation tissue harmful to the material such as bainite.

In addition, the tensile strength and hardness performance of the invention steel and conventional steel by wire diameter in the state of finishing hot wire rolling as described above are shown in Table 3 below.

division Tensile Strength (kg / mm ² ) Elongation (%) Hardness (HRc) Impact value (kg.m / cm ² ) Invention steel 86-96 12-18 21.4-24.3 5.5-7.0 Conventional Steel 1 85-90 12-14 15.7-22.2 5.0-6.0 Conventional Steel 2 69-78 17-22 15.2-20.5 7.0-9.0

As shown in Table 3, it can be seen that the mechanical properties of the inventive steel produced according to the present invention are improved compared to the conventional steel.

As described above, the wire wound in the coil state was cold drawn in a cold state at a reduction rate of about 5-15%, and then cut to a predetermined length. After that, gear processing was performed on one side of the wire rod and the wire rod center was drilled in the longitudinal direction to manufacture a rack bar which is a vehicle steering device part. The surface of the shaft and the gear was subjected to high frequency quenching and heat treatment to improve wear resistance. The physical properties of the rack bar manufactured according to the present invention are shown together in Table 4 below as standard values of the properties of the wire rod (tempered steel wire) subjected to heat treatment.

division standard Invention steel Material straightness 0.40 / 1000mm or less 0.26 / 1000-0.30 / 1000mm Bending direction after broach processing Forward direction Forward direction Dental Hardness (HRc) 58-62 58.5-59.0 Shaft hardness 55-64 60-61

As shown in Table 4, it can be seen that the inventive steel has an equivalent physical property or higher than that of the existing tempered steel wire.

As described above, the present invention can provide a method for manufacturing high-frequency annealed nonferrous steel wire that is cost-saving and simplifies the manufacturing process, and the provided non-ferrous steel wire has a useful effect that can be applied to automobile rack bars and the like.

Claims (1)

By weight%, C: 0.30-0.60%, Si: 0.10-0.40%, Mn: 0.8-2.0%, Cr: 0.03-1.0%, V: 0.03-0.15%, Ti: 0.010-0.040%, Al: 0.01- Steel wire composed of 0.10%, P: 0.030% or less, S: 0.020-0.10%, N: 0.005-0.030% and the remaining Fe and other unavoidable impurities are heated to 1000-1150 ° C for hot wire re-rolling and coil shape. After winding in the 550-750 ℃ section at a rate of 0.1-1.0 ℃ / sec, and then cold drawn at a cross-sectional reduction rate of 5.0-30% of the high-frequency quenching amorphous steel wire manufacturing method.