KR20150089845A - Spring and method of manufacturing the same - Google Patents

Abstract

Disclosed in the present specification is a spring and a manufacturing method thereof. According to the present invention, the spring is composed of 0.52-0.54 wt% of C, 1.40-1.50 wt% of Si, 0.6-0.7 wt% of Mn, 0.01 wt% or less of P, 0.005 wt% or less of S, 0.65-0.75 wt% of Cr, 0.15-0.25 wt% of Ni, 0.01-0.03 wt% of Mo, 0.06-0.08 wt% of V, 0.02-0.03 wt% of Ti, 0.15-0.25 wt% of Cu, 0.03-0.05 wt% of Al, 0.005 wt% or less of B, 0.001 wt% or less of O, 0.005 wt% or less of N, and the remaining amount of Fe and impurities.

Description

[0001] SPRING AND METHOD OF MANUFACTURING THE SAME [0002]

More particularly, the present invention relates to a spring having excellent durability and impact toughness, and a method of manufacturing the spring.

The spring absorbs shocks and vibrations transmitted from the outside to prevent it from being transmitted to other parts.

For example, it effectively absorbs and disperses shocks and vibrations transmitted from the road surface when the vehicle is driven in a vehicle suspension system.

Since these springs must be strong against fatigue, high tensile strength is basically required, and hardness and impact toughness should be excellent.

As a background technique related to the present invention, Korean Patent Registration No. 10-0328087 (published on Apr. 17, 2002) discloses a steel for a high-stress spring having excellent cutting workability and a method for manufacturing a spring using the steel. .

An object of the present invention is to provide a spring having excellent strength, hardness and impact toughness and suppressing surface decarburization by using cold spring forming, and a method for producing the same.

The method of manufacturing a spring according to an embodiment of the present invention includes the steps of (a) 0.52 to 0.54% of carbon (C), 1.40 to 1.50% of silicon (Si) (Mo): 0.01 to 0.03%, and the content of phosphorus (P) is not more than 0.01%, the content of sulfur (S) is not more than 0.005%, the content of chromium (Cr) is 0.65 to 0.75% (B): 0.005% by weight or less, and the content of boron (B) is 0.06 to 0.08%, the content of vanadium (V) is 0.06 to 0.08%, the content of titanium is 0.02 to 0.03%, the content of copper is 0.15 to 0.25% Forming a steel wire in a cold shape from a cold steel wire comprising oxygen (O): 0.001% or less, nitrogen (N): 0.005% or less, and remaining iron (Fe) and unavoidable impurities; And (b) post-treating the molded product.

The step (a) may include a step of subjecting the steel wire to a high-frequency heat treatment, a step of molding the high-frequency heat-treated product in a cold spring shape, and a step of blanching the cold-formed product.

In addition, the step (b) may include a step of pre-setting the formed product by applying a compressive force, a step of sharpening the surface by shot peening the primary preset product, And a second pre-setting step of applying compression force to the shot-pinned product.

In order to achieve the above object, the spring according to an embodiment of the present invention includes 0.52 to 0.54% of carbon (C), 1.40 to 1.50% of silicon (Si), 0.6 to 0.7% of manganese (Mn) P: 0.01% or less, S: 0.005% or less, Cr: 0.65-0.75%, Ni: 0.15-0.25, molybdenum: 0.01-0.03% (O): 0.06 to 0.08%, titanium (Ti): 0.02 to 0.03%, copper (Cu): 0.15 to 0.25% (HRC): 50 or more, and an impact value of 50J or more. The tensile strength is 1900 MPa or more, the elongation is 10% or more, and the hardness .

According to the method of manufacturing a spring according to the present invention, a spring having excellent tensile strength, hardness and impact toughness can be manufactured through controlling an alloy component such as molybdenum, a spring forming process, and a post-process process control.

Therefore, the spring according to the present invention is usefully applied to suspension devices of automobiles and the like.

1 schematically shows a method of manufacturing a spring according to an embodiment of the present invention.
Fig. 2 schematically shows a method of manufacturing a spring when cold spring forming is used.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

Hereinafter, a spring according to a preferred embodiment of the present invention and a method of manufacturing the same will be described in detail with reference to the accompanying drawings.

spring

The spring according to the present invention is, for example, a coil spring which comprises 0.52 to 0.54% of carbon (C), 1.40 to 1.50% of silicon (Si), 0.6 to 0.7% of manganese (Mn) (Mo): 0.01 to 0.03%, vanadium (V): 0.06 to 0.08%, and the like. (B): 0.005 wt% or less, and oxygen (O): 0.001 wt% or less, and titanium (Ti): 0.02 to 0.03%, copper (Cu): 0.15 to 0.25% , And nitrogen (N): 0.005% or less.

The rest of the alloying components are composed of iron (Fe) and unavoidable impurities generated in the steelmaking process.

Hereinafter, the role and content of each component included in the spring according to the present invention will be described.

Carbon (C)

Carbon (C) contributes to securing the strength of the spring through incineration.

The carbon preferably comprises 0.52 to 0.54 weight% of the total weight of the spring. When the content of carbon is less than 0.52% by weight, the incombustibility is insufficient. On the contrary, when the carbon content exceeds 0.54% by weight, impact toughness is deteriorated.

Silicon (Si)

The role of silicon in the springs is enhanced in the ferrite to enhance the strength of the base material and also to improve fatigue properties and resistance to permanent deformation through stabilization of the epilone carbide precipitates.

The silicone is preferably added in an amount of 1.4 to 1.5% by weight based on the total weight of the spring. If the addition amount of silicon is less than 1.4% by weight, the effect of adding silicon may be insufficient. On the contrary, when the amount of silicon added exceeds 1.5% by weight, there is a fear of surface decarburization in the high-frequency heat treatment.

Manganese (Mn)

Manganese (Mn) contributes to securing strength by improving the incombustibility in the manufacture of springs.

The manganese is preferably added in an amount of 0.6 to 0.7% by weight based on the total weight of the spring. If the manganese content is less than 0.6 wt%, the effect of the addition is insufficient. On the other hand, when the amount of manganese added exceeds 0.7% by weight, the impact toughness is degraded.

Phosphorus (P), sulfur (S)

Phosphorus (P) is segregated at crystal grain boundaries, which causes a decrease in impact toughness. In the present invention, the content of phosphorus is limited to not more than 0.01% by weight of the total weight of the spring.

Sulfur (S) segregates as a low-melting point element to lower the impact toughness and form an emulsion, which has a detrimental effect on the spring characteristics. Therefore, the content of sulfur in the present invention is limited to 0.005% by weight or less.

Chromium (Cr)

Chromium lowers the diffusion rate of carbon to suppress surface decarburization and contributes to securing strength in manufacturing springs through improved ingotability.

The chromium is preferably added in an amount of 0.65 to 0.75% by weight based on the total weight of the spring. When the addition amount of chromium is less than 0.65% by weight, the effect of addition is insufficient. On the other hand, when the addition amount of chromium exceeds 0.75% by weight, the brittleness may increase and the resistance to permanent deformation may deteriorate.

Nickel (Ni)

Nickel (Ni) contributes to improving the incombustibility and impact toughness.

The nickel is preferably added in an amount of 0.15 to 0.25 wt% of the total weight of the spring. When the addition amount of nickel is less than 0.15% by weight, the effect of the addition is insufficient. Conversely, when the addition amount of nickel exceeds 0.25% by weight, the fatigue characteristics may be deteriorated.

Molybdenum (Mo)

Molybdenum (Mo) contributes to improvement of strength at room temperature and high temperature, improvement of impact toughness, and also contributes to enhancement of resistance to permanent deformation.

The molybdenum is preferably added in an amount of 0.01 to 0.03% by weight based on the total weight of the spring. If the addition amount of molybdenum is less than 0.01% by weight, the effect of the addition is insufficient. On the other hand, if the amount of molybdenum added exceeds 0.03% by weight, the moldability may be deteriorated in the production of springs.

Vanadium (V)

Vanadium (V) forms carbonitride and contributes to grain refinement.

The vanadium is preferably added in an amount of 0.06 to 0.08% by weight based on the total weight of the spring. When the addition amount of vanadium is less than 0.06% by weight, the effect of the addition is insufficient. On the contrary, when the addition amount of vanadium exceeds 0.08% by weight, the fatigue characteristics of the spring may be deteriorated by the formation of coarse carbonitride.

Copper (Cu)

Copper (Cu) contributes to securing strength through solid solution strengthening and serves to prevent the formation of corrosion pits.

The copper is preferably added in an amount of 0.15 to 0.25 wt% of the total weight of the spring. When the addition amount of copper is less than 0.15% by weight, the effect of the addition is insufficient. On the contrary, when the addition amount of copper exceeds 0.25 wt%, the surface quality of the spring surface can be lowered by surface thickening.

Titanium (Ti), aluminum (Al)

Titanium (Ti) plays a role in making carbonitride and making crystal grains finer.

The titanium is preferably added in an amount of 0.02 to 0.03% by weight based on the total weight of the spring. When the addition amount of titanium is less than 0.02% by weight, the effect of the addition is insufficient. On the other hand, when the amount of titanium added exceeds 0.03% by weight, coarse carbonitrides are formed.

Aluminum (Al) acts as a deoxidizing agent and contributes to grain refinement like titanium.

The aluminum is preferably added in an amount of 0.03 to 0.05 wt% of the total weight of the spring. When the addition amount of aluminum is less than 0.03% by weight, the effect of addition is insufficient. On the contrary, when the added amount of aluminum exceeds 0.05% by weight, coarse carbonitride is formed.

Boron (B)

The addition of boron (B) has the effect of increasing the strength by increasing the corrosion resistance by improving densification of the rust formed on the surface, improving the incombustibility. However, when the addition amount of boron exceeds 0.005% by weight of the total weight of the spring, the carbonitride-based precipitate is coarsened and adversely affects the fatigue characteristics, so it is preferable to limit it to 0.005% or less.

Oxygen (O), nitrogen (N)

Oxygen (O) becomes a nonmetallic inclusion (oxide), which causes the fatigue characteristics of the spring to deteriorate. Therefore, the content of oxygen in the present invention is limited to 0.001 wt% (10 wt ppm) or less of the total weight of the spring.

Nitrogen (N) forms a nitride by bonding with titanium, aluminum or the like to contribute to grain refinement, but if it is contained in large amounts, fatigue characteristics are deteriorated due to coarsening of nitride.

In the present invention, the content of nitrogen is limited to 0.005 wt% (50 wt ppm) or less of the total weight of the spring.

The spring according to the present invention can exhibit a tensile strength of 1900 MPa or more, an elongation of 10% or more, a Rockwell hardness (HRC) of 50 or more, and an impact value of 50 J or more by the above-described alloy component and the spring forming process and post-

How to make spring

Hereinafter, a method of manufacturing a spring according to the present invention will be described.

1 schematically shows a method of manufacturing a spring according to an embodiment of the present invention.

Referring to FIG. 1, a method of manufacturing a spring according to the present invention includes a spring forming step (S110) and a post-processing step (S120).

The spring forming step S110 forms the steel wire having the above-described alloy composition into a spring shape, for example, a coil spring shape. Forming, cold forming such as the example shown in Fig. 2 can be applied.

The post-treatment step S120 is performed to improve the elastic limit of the spring and the surface hardness. This post-processing step may include pre-setting, shot peening as in the example shown in Fig.

Fig. 2 schematically shows a method of manufacturing a spring when cold spring forming is used.

Referring to FIG. 2, the illustrated spring manufacturing method includes a high frequency heat treatment step S311, a cold spring forming step S312, a bake processing step S313, a first pre-setting step S321, a shot peening step S322, And a second pre-setting step S323.

In the high-frequency heat treatment step (S311), the steel wire having an alloy component according to the present invention is heat-treated by using a high frequency. The high-frequency heat treatment may include quenching and sintering by high frequency.

In the cold spring forming step S312, it is formed into a cold shape at a cold temperature, more preferably at a normal temperature.

In the bake processing step S313, the increased brittleness is removed by the high frequency heat treatment and the cold forming. The bake processing may be performed by, for example, maintaining the quenched product at 350 to 600 ° C for 1 to 3 hours.

Thereafter, the first pre-setting step S321, the shot peening step S322, and the second pre-setting step S323 are performed.

In the first pre-setting step S321, a compressive load is applied to the result of the completion of the quenching / punching process to cause a certain permanent deformation, thereby increasing the elastic limit of the spring.

In the shot peening step (S322), hard particles are sprayed on the first pre-set result to remove the oxide film on the surface of the material and to improve the hardness by annealing the surface.

In the second pre-setting step S323, as in the case of the first presetting, compression load is applied to the result of the completion of the shot peening to induce permanent deformation of a certain portion, thereby increasing the elastic limit of the spring.

In the case of the spring according to the present invention, it is manufactured through cold spring forming. Unlike hot spring forming, it is important to prevent surface decarburization in cold spring forming. Accordingly, in the present invention, the addition amount of silicon (Si) is lowered to prevent surface decarburization. Boron was added to increase the amount of silicon and the amount of copper added to compensate for the lowering of the strength.

As a result, the surface decarburization was prevented, and a spring having excellent strength, hardness, and impact characteristics was produced.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

1. Manufacture of springs

After subjecting the steel wire having the alloy composition shown in Table 1 to high-frequency heat treatment using high-frequency induction heating, the steel wire was subjected to cold spring forming at room temperature, bake treatment to be held at 400 ° C for 2 hours, primary presetting, shot peening, The springs according to Examples 1 to 2 and Comparative Examples 1 and 2 were produced.

[Table 1]

2. Property evaluation

The specimens prepared according to Examples 1 to 2 and Comparative Examples 1 to 4 were tested for cracking, tensile test, Rockwell hardness and impact toughness. The results are shown in Table 2.

[Table 2]

In the case of the spring according to the first and second embodiments which satisfy the alloy component range according to the present invention, the tensile strength is 1900 MPa or more, the elongation is 10% or more, the Rockwell hardness (HRC) is 50 or more, And no surface decarbonization layer was formed.

On the other hand, in the case of the spring according to Comparative Example 1 in which molybdenum was not added, the strength was relatively low and the impact value was less than 50J.

Also, in the case of the spring according to Comparative Example 2 in which molybdenum was excessively added, it was confirmed that a crack occurred in the spring.

Also, in the case of the spring according to Comparative Example 3 in which silicon was excessively added in an amount of 2.1 wt%, a surface decarbonization layer was formed in comparison with other specimens.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.

Claims (5)

(S): not more than 0.01% by weight of phosphorus (P), not more than 0.01% by weight of phosphorus (M) (V): 0.06 to 0.08%, titanium (Ti): 0.02 to 0.08%, and the like. (B): 0.005 wt% or less, oxygen (O): 0.001 wt% or less, nitrogen (N): 0.005 wt% or less Forming a steel wire made of remaining iron (Fe) and unavoidable impurities into a spring shape; And
(b) post-processing the formed product.
The method according to claim 1,
The step (a)
Heating the steel wire to form a spring shape in the hot state;
Performing a quenching process on the molded product;
And squeezing the result of the quenching process.
The method according to claim 1,
The step (a)
Subjecting the steel wire to high-frequency heat treatment,
Forming a resultant product of the high-frequency heat treatment in a cold-spring shape;
And squeezing the resultant molded product in the cold state.
The method according to claim 1,
The step (b)
A first pre-setting step of applying a compressive force to the molded product,
Performing a shot peening of the primary pre-set result to train the surface,
And applying a compressive force to the result of the shot peening to perform second presetting.
(S): not more than 0.005% by mass (%) of carbon (C), 0.5 to 0.54% of carbon (C), 1.40 to 1.50% , 0.65 to 0.75% of chromium (Cr), 0.15 to 0.25 of nickel (Ni), 0.01 to 0.03% of molybdenum (Mo), 0.06 to 0.08% of vanadium (V), 0.02 to 0.03% of titanium (Ti) (B): 0.005 wt% or less, oxygen (O): 0.001 wt% or less, nitrogen (N): 0.005 wt% or less, and the balance iron (Fe) and inevitable impurities, and exhibits a tensile strength of 1900 MPa or more, an elongation of 10% or more, a Rockwell hardness (HRC) of 50 or more, and an impact value of 50 J or more.

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