JP4319808B2 - Manufacturing method of steel wire for valve spring - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a valve spring steel wire material having excellent quality such as fatigue resistance suitable as a material for a valve spring used in an engine for automobiles and the like.
[0002]
[Prior art]
Conventionally, this kind of valve spring steel wire rod is generally produced by the steps shown in the upper part of FIG. That is, after annealing a rolled material having a composition defined in, for example, SAE 9254, obtained by melting, casting and rolling by a conventional method, shave (SV) is performed to perform a decarburized layer or Remove surface scratches. Then, lead patenting (LP) or the like as soft annealing is performed, the structure of the entire steel is given a fine and uniform pearlite structure to impart drawability and strength, and the scale generated by the previous heat treatment is removed by pickling. Next, the surface of the surface is coated with a phosphate film or lime film in order to increase the lubrication effect, and then the wire is drawn at a drawing rate of around 70% and processed into product dimensions, and finally an oil temper treatment is performed. Thus, the mechanical properties are adjusted, and the production of the valve spring steel wire ends. In place of lead patenting (LP), induction high frequency heating (IH) or low temperature annealing (LA) may be employed for the purpose of softening the surface of the steel wire rod.
[0003]
In addition, the valve spring steel wire manufactured by the wire manufacturer in this way is subjected to various processes such as coiling, brewing, nitriding, shot peening, strain relief annealing, and setting by the spring manufacturer, and the valve spring as the final product. It becomes.
[0004]
By the way, the shaving process is provided assuming that an abnormality such as a decarburized layer (ferrite decarburized layer) or a surface flaw occurs on the ground iron surface of the wire for some reason in the history of the previous process. It is. As is well known, abnormalities in the surface layer part of the steel rail (hereinafter referred to as abnormal layers) such as decarburized layers and surface flaws adversely affect fatigue characteristics (fatigue strength), which is an important required performance of valve springs, and are eliminated. This is essential in the manufacturing process. A shaving device is equipped on the line of this process, and the steel bar surface layer is forcibly scraped over about 0.3 mm through the peeling dies of the valve spring steel wire rod, and the abnormal layer is thereby removed. Will be removed together. In order to facilitate such shaving processing, the surface of the wire is usually softened beforehand by an annealing furnace.
[0005]
However, in the production of such conventional steel wire for valve springs, a large amount of power is consumed to drive the shaving device, and the peeling die must be frequently replaced, and a prior annealing process is also required. Furthermore, in the shaving process, troubles due to die sticking sometimes occur, which may cause product defects.
[0006]
[Problems to be solved by the invention]
As described above, in the manufacture of conventional steel wire for valve springs, the operation and maintenance cost of the equipment is increased, the productivity is low, and the method is not sufficient in terms of ensuring quality such as fatigue resistance. There wasn't.
[0007]
The present invention has been made in view of such a technical background.In the production of a steel wire for valve springs, the process is simplified, the operation and maintenance costs of the equipment are low, the productivity is high, and the resistance is high. An object of the present invention is to provide a method capable of stably producing a product having excellent quality such as fatigue.
[0008]
[Means for Solving the Problems]
Therefore, as a means for solving the above-mentioned problems, the present invention according to claim 1 is obtained by continuously casting a molten steel whose components are adjusted and used for a valve spring to obtain a billet, which is hot-rolled. C: Rolled steel wire for valve spring having 0.51% by weight or more is immersed in a strong acid solution selected from nitric acid, hydrofluoric acid or hydrofluoric acid, and the surface layer of the steel line material is removed by chemical cutting. Then, a method for producing a steel wire for a valve spring is proposed, which is characterized by performing soft annealing, pickling, drawing, and quenching and tempering.
[0009]
Moreover, the present invention according to claim 2 has C: 0.51% by weight or more obtained by continuously casting molten steel having a component adjusted for use as a valve spring into a billet and hot rolling it. Rolled steel wire for valve springs is immersed in a strong acid solution selected from nitric acid, hydrofluoric acid or hydrofluoric acid to remove the steel surface layer of the steel gland material by chemical cutting, and then softened and pickled. The present invention proposes a method of manufacturing a steel wire for a valve spring, which is characterized by performing wire drawing.
[0010]
Further, in the present invention according to claim 3, the depth of dissolution and removal of the surface layer of the ground metal is 0.03 mm or more. The production of the steel wire for valve spring according to claim 1 or 2, A method is proposed.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the contents of the present invention will be described in detail and specifically with a focus on the characteristic portions.
The present inventors use existing equipment and processes to remove abnormal layers such as decarburized layers and surface flaws generated on the surface of the steel core for valve springs without mechanical cutting by the conventional shaving process. However, we conducted intensive research and examination on methods to remove them relatively easily and effectively.
[0012]
As a result, an idea was obtained that the abnormal layer could be chemically welded by utilizing the pickling equipment in the above-described pickling process. Based on such an idea, when experiments were conducted using various solutions, it was found that this abnormal layer was relatively easy by immersing the steel wire in a specific strong acid solution for a certain period of time, that is, by chemical cutting with a strong acid solution. It was confirmed that it was dissolved and removed in order to complete the present invention.
[0013]
That is, the strong acid solution is a solution obtained by adding an appropriate amount of water to a strong acid selected from nitric acid, hydrofluoric acid or hydrofluoric acid, as described in the claims. The nitric acid solution is 10% or more nitric acid, the hydrofluoric acid solution is 10% or more nitric acid and 2% or more hydrofluoric acid, and the hydrofluoric acid solution is 10% or more sulfuric acid and 2% or more hydrofluoric acid.
[0014]
By the way, as a result of investigations by the inventors, it has been found that the above-mentioned decarburized layer and abnormal layer including scratches extend to a depth of 0.02 to 0.05 mm from the surface of the steel wire. Therefore, the above-mentioned chemical cutting with the strong acid solution in the present invention is continuously performed until these abnormal layers are surely disappeared from the ground iron. Specifically, this is continued until the surface layer is dissolved and removed over a depth of at least 0.03 mm, preferably 0.05 mm, from the surface of the ground iron. Of course, if the surface layer is deleted more deeply than necessary, the yield loss of the steel wire increases, so it is preferable to terminate the process before the depth to be deleted exceeds 1 mm.
[0015]
Further, the specific processing time for removing the abnormal layer in this way usually depends on the concentration of the strong acid solution and the processing temperature, but usually requires 2 minutes or more.
Furthermore, it is desirable to continue the treatment for 5 minutes or longer if it is possible to completely eliminate the abnormal layer. By the way, because the conventional pickling is intended to remove scales etc., the treatment is completed in about 1 minute at most, even if the treatment is carried out using the same strong acid solution used in the present invention. It is impossible to get rid of. In addition, it is desirable to continue this process for a very long time because the dissolution removal depth exceeds 1 mm as described above, resulting in a yield loss and further hindering productivity. I can't say that. Therefore, the treatment is usually 15 minutes or less, preferably 10 minutes or less. Of course, this is not the case when the abnormal layer reaches about 1 mm. In addition, what is necessary is just to immerse in the form of a coil-shaped wire material similarly to the conventional pickling process in these applications. It is also recommended to increase the efficiency by adopting a method in which a steel wire is immersed in a strong acid solution for a certain period of time and then pulled, washed with water, and immersed again.
[0016]
Now, an outline of the entire manufacturing process according to the present invention will be described with reference to FIG . First, in a conventional manner, molten steel that has been melted and component-adjusted for a valve spring is continuously cast into a billet, which is hot-rolled to obtain a steel wire having a diameter of 6.4 to 9.0 mm. The component (% by weight) is preferably silicon chrome steel corresponding to SAE 9254 as described below, but may be any component steel as long as it can be used for valve springs such as chrome vanadium steel and manganese chrome boron steel. .
C: 0.51 to 0.59%, Si: 1.20 to 1.60%, Mn: 0.60 to 0.90%, P: 0.035% or less S: 0.040% or less, Cr: 0,60-0.90%
[0017]
Without annealing the coiled rolled steel wire obtained in this way, it is led to an existing pickling tank conventionally used in the pickling process, to one or more strong acid solutions selected from nitric acid, hydrofluoric acid or hydrofluoric acid. It is immersed and the abnormal layer which exists in the surface layer layer of steel wires, such as the above-mentioned decarburization layer and a surface crack, is chemically cut and removed. The details of this chemical cutting process are as described above.
[0018]
Next, the steel wire that has undergone the above chemical cutting is subjected to lead patenting (LP) to make the entire structure completely pearlite, thereby imparting excellent wire drawability and strength in the subsequent wire drawing step. By the way, as described above, instead of this lead patenting, it has been described that induction high-frequency heating (IH) or low-temperature annealing (LA) may be conventionally used for the purpose of softening the surface of the steel wire. Since the shaving process (SV) is eliminated, the phenomenon that the surface of the steel wire is hardened does not occur, so that these processes can be omitted.
Next, in order to remove scale generated on the surface of the steel wire by heat treatment of lead patenting (LP), pickling is performed with a sulfuric acid or hydrochloric acid solution in a pickling tank.
[0019]
And after performing a film | membrane process similarly to the past and performing surface lubrication, it draws to the product size of diameter 5.1-7.3mm through the wire drawing apparatus in which the wire drawing die was incorporated.
[0020]
The steel wire rod that has become austenite (γ) due to the heat generated by wire drawing is also unwound from the coil in the same manner as before and continuously supplied to the oil temper equipment, where it is quenched by oil cooling, Subsequently, tempering is performed using a lead bath or the like to give and adjust the final characteristics as a steel wire for a valve spring to obtain a product, that is, an oil tempered wire.
[0021]
As mentioned above, although the case where the oil temper wire was made into object was demonstrated about the manufacturing process of the steel wire for valve springs which concerns on this invention, this invention can be applied effectively also to what is called a hard drawing wire. In the production of hard drawn wire, the other steps are the same except that the quenching and tempering steps after the wire drawing process, which is the last step in the case of an oil tempered wire, are omitted. Accordingly, the hard drawn wire is inferior to the oil tempered wire in terms of performance such as fatigue strength, but has an advantage that it can be manufactured at low cost, and is preferably used depending on the application.
[0022]
(Example)
The example (test example) which concerns on this invention is given to the following, and the outstanding effect is clarified.
In a conventional manner, molten steel that has been melted and adjusted for components for valve springs is continuously cast into billets and hot rolled to obtain a diameter of 15.56 mm (long and short) The average diameter of the steel wire was used as a test material.
[0023]
Test material: SAE9254
C: 0.58%, Mn: 0.7%, P: 0.01%, S: 0.01%,
Cu: 0.01%, Ni: 0.02%, Cr: 0.68%,
Mo: 0.01%, Al: 0.002%, Ti: 0.0006%,
N: 0.0045%, O: 0.0024%
[0024]
And when this test material was decarburized, a decarburized layer was formed on the surface layer portion of the base steel as shown in the outermost white portion of FIG. 2 (A) over a depth (layer thickness) of 0.02 mm. It was confirmed that it was formed. Moreover, as a result of observing the surface layer part of the test material of the same test material, as shown by the black unevenness on the outermost surface of FIG. 3A, there is a large wrinkle scratch reaching a depth of 0.03 mm. It was also found out.
[0025]
Therefore, chemical cutting treatment according to the present invention was performed using this test material. That is, the test material was placed in the first pickling tank and immersed in a hydrofluoric acid solution (hydrofluoric acid: 3-4%, sulfuric acid: 15-18%, remaining water, liquid temperature: 44.3 ° C.) for 5 minutes. . Next, the test material was pulled up from the first pickling tank, transferred to the second pickling tank, washed with shower water, and then a sulfuric acid hydrofluoric acid solution having the same concentration (hydrofluoric acid: 3 to 4%, sulfuric acid: 15-18%, remaining water, liquid temperature: 46.8 ° C.). Further, after returning to the first pickling tank and immersing in a low-concentration hydrofluoric acid solution (hydrofluoric acid: 1%, sulfuric acid: 2%, remaining water, liquid temperature: 29.9 ° C.) for 5 minutes, this is pulled up. Finally, it was washed with shower water. In this process, a high concentration sulfuric acid hydrofluoric acid solution was used in order to remove the same depth (0.3 mm) as conventional shaving in a short time. The treatment with the high-concentration hydrofluoric acid solution was divided into two steps, and a three-step treatment was adopted in which water washing was sandwiched between them, followed by treatment with the low-concentration hydrofluoric acid solution and water washing. This is because, when treated with a high-concentration solution, chemical cutting with hydrofluoric acid proceeds rapidly and locally, and the hydrofluoric acid deteriorates, while the surface of the base iron is uniformly distributed to the desired depth. This is because it becomes difficult to dissolve and remove.
[0026]
Thus, when the diameter of the test material subjected to the chemical cutting treatment was measured, it was 15.29 mm, which was 0.27 mm smaller than the diameter before the treatment, and the surface layer portion of the base iron was dissolved and removed by this thickness. I found out. That is, this means that the decarburized layer over the depth of 0.02 mm and the wrinkle damage reaching the depth of 0.03 mm found in the surface layer portion of the steel before the treatment were completely removed.
[0027]
And as a result of observing the state of the surface with a microscope to confirm the state of removal of these abnormal layers after the treatment, as shown in FIG. 2 (B) and FIG. 3 (B), It can be seen that all wrinkle scratches disappeared, and a smooth surface of the iron surface appeared.
[0028]
【The invention's effect】
As described above, according to the present invention, when manufacturing a steel wire for a valve spring, an abnormal layer such as a decarburized layer and a surface flaw generated and remaining on the surface layer portion of the steel wire material is provided without using mechanical shaving. The pickling equipment can be removed relatively easily and reliably. In addition, according to the present invention, the process can be simplified such that annealing before shaving is not necessary, and the operation and maintenance costs of the equipment are low, and productivity can be maintained high. Furthermore, according to the present invention, it is possible to stably produce a product excellent in quality such as fatigue resistance, which is important as a steel wire for a valve spring, and achieves an excellent technical contribution in this field.
[Brief description of the drawings]
FIG. 1 is a process diagram showing a conventional steel wire for valve springs and a method for manufacturing a valve spring.
FIG. 2 is a schematic diagram showing a state of a micrograph (corrosion present, × 100) in which a cross section of the surface layer of the base metal in the width direction of the test material before and after the chemical cutting treatment of Example 1 is observed.
3 is a schematic diagram showing a state of a micrograph (no corrosion, x100) in which a cross section of the surface layer of the base iron in the width direction of the test material before and after the treatment of Example 1 is observed. FIG.
FIG. 4 is a process diagram illustrating a steel wire for a valve spring and a method for manufacturing the valve spring according to the present invention .

Claims (3)

A rolled steel wire for valve springs having a C: 0.51% by weight or more obtained by continuously casting molten steel, which has been prepared and component-adjusted for a valve spring, into a billet and hot rolling the steel , Then, it is immersed in a strong acid solution selected from hydrofluoric acid or hydrofluoric acid to remove the surface layer of the steel wire material by chemical cutting, and then softened, annealed and pickled, and then drawn, and further quenched and tempered. The manufacturing method of the steel wire for valve springs characterized by performing these. A rolled steel wire for valve springs having a C: 0.51% by weight or more obtained by continuously casting molten steel, which has been prepared and component-adjusted for a valve spring, into a billet and hot rolling the steel , The steel wire is soaked in a strong acid solution selected from hydrofluoric acid or hydrofluoric acid to remove the surface layer of the steel wire by chemical cutting, and then subjected to soft annealing, pickling, and wire drawing. A method for manufacturing a steel wire for a valve spring. The method for producing a steel wire for a valve spring according to claim 1 or 2, wherein the dissolution removal depth of the surface layer is 0.03 mm or more.

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