KR20110075629A - Wire rod for miniblock spring and method for manufacturing the wire rod - Google Patents

Abstract

PURPOSE: A mini-block spring steel wire rod and a manufacturing method thereof are provided to manufacture a spring without heat treatment, thereby reducing costs and improving productivity. CONSTITUTION: A billet is heated at 1000°C or higher and subject to rough rolling, intermediate finish rolling, final finish rolling, and reduction/size control rolling. The rolled billet is wound on a laying head at a temperature of 880-920°C. The billet is cooled in a cooling zone comprising a conveyor and one or more slow-cooling covers so that a wire rod is produced.

Description

Wire rod for miniblock spring and method for manufacturing the wire rod

The present invention relates to a method for manufacturing a mini-block spring steel wire mainly used in automobile suspensions, and more particularly, to a mini-block spring steel wire having excellent peeling workability and a method of manufacturing the same.

As shown in FIG. 1, the mini block spring has a difference of, for example, about 5 mmφ or more in the diameter of the tip and center portion.

As such, there is a difference of about 5 mmφ or more in the diameter of the tip and center of the mini block spring. Therefore, in the case of the mini block spring steel wire rod, a considerable amount of material must be scraped off when processing the mini block spring.

For this reason, how well the material (wire) is cut without variation is one of the very important quality characteristics. This is also referred to as the peeling (peeling) workability of the material (wire) in general, when cutting the material, the hardness of the surface is low, the less the amount of bite wear, the better the peeling workability.

In addition, how straight the material is processed during the filling (straightness) and how uniform the shape of the resulting chips is also closely related to the peeling processability.

Since the conventional miniblock spring steel wire has a high hardness and a large variation, it is subjected to annealing heat treatment before processing to ensure excellent peeling workability.

In general, the annealing heat treatment was performed by placing the entire coil in a batch, and the time and cost in this process were the main cause of the cost competitiveness of the customer.

Although many attempts have been made to omit the annealing heat treatment in this background, it is difficult to omit the heat treatment due to the cooling deviation between the TOP and BOTTOM portions of the coil and the occurrence of low temperature tissue generated at the center. .

The customer developed a titanium bite, which increased its wear resistance. Nevertheless, it was difficult to use the conventional mini block spring steel wire without heat treatment.

Therefore, there is a demand for the development of mini block spring steel wire having excellent peeling workability without heat treatment.

The present invention is to provide a mini-block spring steel wire having excellent peeling workability without heat treatment by appropriately controlling the wire rolling temperature and cooling conditions, and a manufacturing method thereof.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention is in weight%, C: 0.52 to 0.58%, Si: 1.2 to 1.6%, Mn: 0.6 to 0.8%, Cr: 0.60 to 0.80%, V: 0.10 to 0.15%, P: 0.025% or less, S: It relates to a miniblock spring steel wire which is composed of less than 0.015%, the remaining Fe and other unavoidable impurities, the structure consists of 3-15 vol.% Ferrite and the remaining pearlite, and has an HRC hardness value of 26.9 to 27.3. .

As for the lamellar layer space | interval of the said pearlite, 0.3-0.6 micrometer is preferable.

In addition, the present invention is a weight%, C: 0.52 ~ 0.58%, Si: 1.2 ~ 1.6%, Mn: 0.6 ~ 0.8%, Cr: 0.60 ~ 0.80%, V: 0.10 ~ 0.15%, P: 0.025% or less, S: 0.015% or less, the billet composed of the remaining Fe and other unavoidable impurities is heated at 1000 ° C or higher, and then subjected to rough rolling, intermediate finishing rolling, final finishing rolling, reduction and dimensional control rolling (Reducing and Sizing Milling). As a method of manufacturing a wire rod by winding in a head, it is cooled in a cooling stand equipped with a conveyor and one or more slow cooling covers.

The winding temperature is 880 ~ 920 ℃, and the cooling rate of the wire rod in the cooling zone is 0.45 ~ 1.0 ℃ / sec (s) relates to a method for producing a mini-block spring steel wire.

As described above, according to the present invention, by providing a mini-block spring steel wire having excellent peeling workability without heat treatment, spring processing can be performed without heat treatment, resulting in cost reduction, productivity improvement, and quality improvement. Can be.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

First, the composition of the billet will be described.

The C is a very effective element to increase the strength, and should be added at least 0.52% to secure the strength, but the increase in strength due to the increase of the C content is not suitable for securing the inherent properties of the spring steel such as deformation resistance, so the upper limit thereof is 0.58%. It is desirable to limit.

Si is an element necessary for securing strength and deformation resistance of spring steel, and in order to obtain such an effect, it should be added at least 1.2%. However, Si promotes surface decarburization in heating furnaces and cooling zones during wire fabrication, so the upper limit thereof is 1.6%. It is desirable to limit.

The Mn is an element that is beneficial for securing strength by improving hardenability in spring steel. Therefore, when the Mn content is less than 0.6%, it is difficult to obtain sufficient strength and hardenability required as a high strength wire, and when it exceeds 0.8%, the toughness is lowered, so the Mn content is preferably limited to 0.6 to 0.8%. Do.

The Cr should be added at least 0.60% because it affects the oxidation resistance, temper softening and quenching properties of the steel depending on the content thereof.

However, if the content is too large, the upper limit thereof is limited to 0.80% because it adversely affects deformation resistance, which is one of the main characteristics of spring steel.

The V is an element that improves the spring characteristics by forming a carbon / nitride alone or in combination to cause precipitation hardening. It is desirable to limit the V content to not more than 0.10% and not more than 0.15% to improve the grain size control and the fatigue properties of the spring.

It is preferable to limit the P to 0.025% or less because P is segregated at the grain boundaries and the toughness is lowered to reduce the workability.

The S is preferably limited to 0.015% or less, which is a generally controllable level in the steelmaking process because it forms an emulsion.

The billet formed as described above is made of a wire rod for the spring through a heating, rolling and cooling process, the manufacturing process will be described below.

The billet is heated to a heating temperature of 1000 ℃ or more, the heated billet is wound in a laying head through rough rolling, intermediate finishing rolling, final finishing rolling and reduction and dimensional control rolling.

The temperature measured as soon as it is wound in this laying head is called the winding temperature, which is very important as the initial temperature of the cooling process that determines the properties of the wire rod.

Therefore, the physical properties of the wire rod can be greatly changed depending on how the temperature is managed.

In the present invention, in order to reduce the hardness of the wire rod, the winding temperature is limited as high as possible because the higher the winding temperature, the transformation starts in the high temperature region in the continuous cooling curve of the wire rod. Its lamellar spacing is wider than the resulting tissue.

However, if the coiling temperature is too high, it may cause serious surface scratches of the material due to the decrease of the amount of cooling water in the cooling process.

Therefore, in the present invention, the winding temperature is limited to 880 ~ 920 ℃.

The wire wound as described above is cooled, wherein the cooling rate is preferably limited to 0.45 ~ 1.0 ℃ / s (s).

When the cooling rate is less than 0.45 ° C / s, not only is it difficult to control due to the characteristics of the equipment, but also the productivity is lowered, and when the cooling rate exceeds 1.0 ° C / s, the hardness is increased to decrease the peeling workability.

Examples of the method of controlling the cooling rate of the wire rod are not particularly limited, but examples thereof include a conveyor speed of the cooling stand and a method of controlling the slow cooling cover condition of the wire rod cooling stand.

The cooling stand that can be used in the present invention is not particularly limited, but a conventional Stelmor cooling stand or the like can be preferably used in the present invention.

The conveyor speed of the cooling stand of the wire rod will be described.

The conveyor speed of the Stelmor cooling stage is the most important factor in determining how much it will be affected by the blowing and the stocking density in the cooling stage.

In the present invention, it is preferable not to blow air in the cooling zone.

In the absence of blowing, the conveyor speed is limited to the pile density of the wire rod. As the conveyor speed decreases, the pile density of the wire rod increases. In this case, the slow cooling effect is maximized due to the radiant heat between the rings. .

However, since the rolling speed of the wire rod is constant, if the dimension is small, the amount of material wound up is relatively large, so that the conveyor speed can be unconditionally caused by abnormal operation.

Therefore, it is preferable to limit the maximum speed of the conveyor to 0.15 m / s or more, which is a conveyor speed capable of normal operation and maximizing pile load density.

However, when the conveyor speed exceeds 0.2 m / s, the slow cooling effect is lowered to increase the hardness and the peeling workability is reduced, it is preferable to limit the conveyor speed to 0.15 ~ 0.20 m / s.

Next, the slow cooling cover conditions of the wire rod cooling stand will be described.

The slow cooling cover, which is a facility to compensate for the poor slow cooling ability of the Stelmor cooling table, is generally used in the case of spring steel in order to complete the transformation within a predetermined section and minimize the reheating effect in the cover. I have been working open.

However, as a result of several tests of the present inventors, it was confirmed that operating with the slow cooling cover all closed is more effective in improving the peeling workability of the mini block spring steel.

According to the test results, in the present invention, it is preferable to operate the slow cooling cover in the cooling stand in a closed state.

The wire rod manufactured as described above has a structure composed of 3-15 vol.% Of ferrite and the remaining pearlite.

When the content of the ferrite is less than 3 Vol.%, The ductility is lowered and the peeling workability is poor. Therefore, the ferrite should contain 3Vol.% Or more, but it is difficult to include the ferrite in excess of 15Vol.%.

Therefore, the content of the ferrite is preferably limited to 3 ~ 15 Vol.%.

As for the lamellar layer space | interval of the said pearlite, 0.3-0.6 micrometer is preferable.

When the lamellar layer spacing of the pearlite is less than 0.3 μm, the hardness is increased to reduce the peeling workability. When the pearlite is more than 0.6 μm, the toughness decreases and the workability is poor.

In addition, the wire rod has an HRC hardness value of 26.9 ~ 27.3.

When the hardness exceeds 27.3, the hardness is increased and the peeling workability is inferior. Therefore, the hardness is preferably limited to 27.3 or less, but it is difficult to control the hardness to less than 26.9.

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

(Example)

After rolling a 160 × 160 mm2 spring steel billet having a composition as shown in Table 1 with a 15.5 mmφ wire rod, winding and cooling it under the winding temperature and cooling conditions shown in Table 2, and then cutting the wire rod in a cross-section in the cross section C direction HRC hardness (Rockwell hardness), lamellar lamellar spacing and ferrite fraction of nine points were measured, and the results are shown in Table 2 below.

The conventional material (1-2) of the following Table 2 is to cover only two or two of the slow cooling covers as shown in FIG. 2 and to cool the wire rod [Fig. 2 (a)]. In the case of -3), the wire rods are cooled by covering all the slow cooling covers (FIG. 2 (b)).

Composition (% by weight) C Si Mn P S Al Cr V N (ppm) 0.54 1.45 0.65 0.007 0.005 0.003 0.67 0.11 45

Specimen No. Coiling temperature
(℃) conveyor
Speed (m / s) Average cooling
Speed (℃ / s) HRC Hardness Lamera Layered
Thickness (㎛) ferrite
Fraction (%) Conventional material 1 852 0.30 1.32 28.7 0.15 Less than 3 Conventional material 2 860 0.30 1.35 28.3 0.15 Less than 3 Invention 1 908 0.17 0.72 27.2 0.35 7.8 Invention Material 2 910 0.19 0.76 27.2 0.52 8.0 Invention 3 903 0.15 0.56 27.3 0.50 10.2

As shown in Table 2, the wire rod (inventive material 1-3) manufactured under the conditions according to the present invention has an HRC hardness value of 27.2 to 27.3, compared with the conventional material (1-2) produced under conventional conditions. It can be seen that is lowered.

In addition, it can be seen that the inventive material (1-3) has a larger lamellar layer spacing and a larger ferrite fraction than the conventional material (1-2).

1 is an example of a conventional mini block spring

2 is a schematic view showing cooling equipment conditions for producing conventional materials and invention materials, (a) relates to conventional materials, and (b) relates to invention materials.

Claims (4)

By weight%, C: 0.52 to 0.58%, Si: 1.2 to 1.6%, Mn: 0.6 to 0.8%, Cr: 0.60 to 0.80%, V: 0.10 to 0.15%, P: 0.025% or less, S: 0.015% or less , Miniblock spring steel wire, composed of the remaining Fe and other unavoidable impurities, the structure consisting of 3-15 vol.% Ferrite and the remaining pearlite, and having an HRC hardness value of 26.9-27.3. The mini block spring steel wire according to claim 1, wherein the lamellar layer spacing of the pearlite is 0.3 to 0.6 mu m. By weight%, C: 0.52 to 0.58%, Si: 1.2 to 1.6%, Mn: 0.6 to 0.8%, Cr: 0.60 to 0.80%, V: 0.10 to 0.15%, P: 0.025% or less, S: 0.015% or less , The billet composed of the remaining Fe and other unavoidable impurities is heated at 1000 ℃ or higher, and then wound in a laying head through rough rolling, intermediate finishing rolling, final finishing rolling and reduction and dimensional control rolling. As a method of producing a wire rod by cooling in a cooling stand equipped with one or two or more slow cooling cover, The winding temperature is 880 ~ 920 ℃, and the cooling rate of the wire rod in the cooling zone is 0.45 ~ 1.0 ℃ / second (s) The manufacturing method of the mini-block spring steel wire. 4. The mini block spring steel wire rod according to claim 3, wherein the cooling speed of the wire rod is controlled by controlling the speed of the conveyor at 0.15 to 0.2 m / s and cooling the wire rod with all of the slow cooling cover closed. Manufacturing method.

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