KR20150078190A - Improved durability coil spring composition - Google Patents

Abstract

The present invention relates to a composition used for a spring requiring excellent toughness, fatigue life, and corrosion resistance. More specifically, the present invention relates to a coil spring composition having improved durability, which is composed of 0.5-0.55 wt% of C, 1.4-1.7 wt% of Si, 0.3-0.5 wt% of Ni, 0.01-0.04 wt% of Nb, 0.25-0.35 wt% of Cu, 0.0005-0.0025 wt% of B, a remaining amount of Fe, and impurities based on the total weight of the composition. Therefore, the coil spring composition improves the strength with an increase in a bonding force between microstructures; improves the toughness by refining the microstructures through Nb and the like; and improves general fatigue life, corrosion fatigue life, and corrosion resistance.

Description

Improved durability coil spring composition Abstract:

The present invention relates to a composition for use in springs and the like that require excellent toughness, fatigue life, and corrosion resistance, and more particularly to a composition for improving the durability including silicon (Si), boron (B) and niobium To a coil spring composition.

An automobile combines various devices and parts to facilitate movement, and the suspension among the devices of the automobile is also referred to as a suspension device. The coil spring of the shock absorber, which is a component of the automotive suspension system, is made by winding a coil of steel material. It is installed between the vehicle body and the axle and mainly supports the weight of the vehicle body. At the same time, And absorbs shocks and vibrations to reduce the transmission of the body to the role.

However, the coil spring is highly likely to be damaged by corrosion fatigue cracks after paint peeling in the lower contact zone of the spring due to the snow removing agent such as calcium chloride and potassium chloride in a cold weather environment.

In addition to the discomfort of the driver due to the vibration and noise of the vehicle caused by the breakage of the coil spring, a large accident may occur if a part of the broken spring damages the rotating tire. Significant importance is emerging.

Generally, the spring material can be classified according to its operating stress (at full blow). In the past, domestic and overseas automobile makers mainly applied 110K (kgf) class steel as coil spring material. However, since 2000, 120K class high stress coil spring has been applied due to light weight needs due to improvement of fuel efficiency.

The current 120K class coil spring is a high-strength spring material developed for light weight and ease of layout. However, the fatigue life of the above-mentioned material is excellent, but the corrosion durability is weakened due to the concentration of stress when a surface notch due to corrosion flaw occurs due to reduction in spring outer diameter, number of turns,

In order to overcome such disadvantages, the technique of reinforcing the design of the spring material with the double coating and the urethane hose has been developed. However, there is a disadvantage that the cost competitiveness of the product is deteriorated due to an increase in manufacturing cost.

Disclosure of Invention Technical Problem [8] The present invention has been made to solve the problems of the prior art, and it is an object of the present invention to improve the durability and corrosion resistance of a spring composition at low cost by setting an optimal constituent component and its content.

In order to achieve the above object, the coil spring composition according to the present invention comprises 0.5 to 0.55% by weight of carbon (C), 1.4 to 1.7% by weight of silicon (Si), 0.3 to 0.5% by weight of nickel 0.01 to 0.04% by weight of niobium (Nb), 0.25 to 0.35% by weight of copper (Cu), 0.0005 to 0.0025% by weight of boron (B) and the balance of iron (Fe) and unavoidable impurities.

The composition may further comprise 0.55 to 0.75 wt% of manganese (Mn), 0.6 to 0.8 wt% of chromium (Cr), 0.05 to 0.10 wt% of vanadium (V) and 0.02 to 0.06 wt% of aluminum desirable.

Further, it is preferable that the composition further contains 0.017 wt% or less of phosphorus (P) and 0.01 wt% or less of sulfur (S).

Meanwhile, the coil spring composition according to the present invention comprises 0.53% by weight of carbon (C), 1.5% by weight of silicon (Si), 0.4% by weight of nickel (Ni), 0.03% by weight of niobium (Nb) 0.3 wt% of boron (B), 0.6 wt% of manganese (Mn), 0.7 wt% of chromium (Cr), 0.08 wt% of vanadium (V) and 0.04 wt% of aluminum (Al) (Fe).

Further, it is preferable to manufacture the coil spring using the coil spring composition.

As described above, the effect of the present invention having the above-described structure is that the content of silicon (Si) is adjusted and boron (B) or the like is added to increase the bonding strength between the microstructures, (Nb) and the like can be added to improve the toughness of the microstructure to further improve toughness, corrosion fatigue life and corrosion resistance.

1 is a perspective view of a coil spring mounted on a suspension.
2 is a photograph showing the crystal grains of a conventional spring.
3 is a photograph showing the microfined grain of the spring according to the present invention.
4 is a photograph showing the fatigue wavefront.
Fig. 5 is a photograph showing the mouth-wave plane.
6 is a photograph showing the depth of corrosion of the comparative example.
7 is a photograph showing the corrosion depth of the embodiment.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings and the like.

The present invention relates to a coil spring composition having improved durability.

1 is a perspective view of a coil spring mounted on a suspension. In the coil spring composition with improved durability according to the present invention, foreign matter such as a lubricant such as calcium chloride and potassium chloride, sand or the like may be introduced between the lower portion of the spring 10 and the sheet 11, The present invention is an invention that compensates for the disadvantages of conventional springs in which a surface is scratched and a spring is corroded and damaged due to damaged coatings and flaws.

The coil spring composition according to the present invention can suppress the occurrence of scratches on the surface of the spring caused by a snow remover or sand due to the improvement of strength and toughness and can prevent corrosion of the spring exposed by scratches on the surface of the spring, It is possible to improve corrosion resistance, etc.

Generally, 120K ultra super high strength steel is applied to a spring or the like, and it is possible to increase the spring strength or the like by a combined effect of carbon (C), nickel (Ni) and copper (Cu) Although there is an advantage, there is a disadvantage that toughness and the like can be deteriorated.

Therefore, it is desirable to make the spring structure finer in order to simultaneously improve the strength and toughness of the spring. In particular, the present invention reduces the content of silicon (Si) to less than the content of conventional spring compositions, increases the bonding force between the microstructure of the composition by newly adding boron (B), and newly adds niobium (Nb) The strength of the spring can be improved and the toughness can be improved.

division unit Conventional
Spring composition According to the invention
Spring composition C weight% 0.46-0.50 0.50 to 0.55 Si weight% 2.00 ~ 2.20 1.40 to 1.70 Mn weight% 0.55-0.75 0.55-0.75 Cr weight% 0.60 to 0.80 0.60 to 0.80 Ni weight% 0.25-0.35 0.30-0.50 V weight% 0.05 to 0.10 0.05 to 0.10 Nb weight% - 0.01 to 0.04 Cu weight% 0.20-0.30 0.25-0.35 Al weight% 0.02 to 0.06 0.02 to 0.06 B weight% - 0.0005 to 0.0025 P weight% 0.017 or less 0.017 or less S weight% 0.010 or less 0.010 or less Fe weight% Remainder Remainder

Table 1 is a table comparing the composition of the conventional spring composition with that of the spring composition according to the present invention.

As shown in the above table, the present invention is characterized in that carbon (C), silicon (Si), nickel (Ni), niobium (Nb), copper (Cu), boron (B) (Mn), chromium (Cr), vanadium (V), aluminum (Al), and the like. The present invention may further comprise phosphorus (P) and sulfur (S) as auxiliary components.

More specifically, the content of each component is 0.5 to 0.55 wt% of carbon (C), 1.4 to 1.7 wt% of silicon (Si), 0.3 to 0.5 wt% of nickel (Ni) (Mn), 0.6 to 0.8% by weight of chromium (Cr), 0.6 to 0.8% by weight of vanadium (B), 0.01 to 0.04% by weight of copper (Cu), 0.25 to 0.35% 0.05 to 0.10 wt% of aluminum (V), 0.02 to 0.06 wt% of aluminum (Al), 0.017 wt% or less of phosphorus (P), 0.01 wt% or less of sulfur and the balance iron (Fe).

The carbon (C) serves to increase the strength and hardness of the material and to precipitate the carbide. The carbon (C) is preferably 0.5 to 0.55% by weight based on the total weight of the composition. If the amount of carbon (C) is less than 0.5% by weight, the strength of the composition may be rapidly lowered. If the amount of carbon (C) is more than 0.55% by weight, the toughness of the composition may be lowered.

The silicon (Si) serves to increase the hardness of the composition, and the silicon (Si) is preferably 1.4 to 1.7% by weight based on the total weight of the composition. If the amount of silicon (Si) is less than 1.4% by weight, sufficient hardness of the composition can not be secured. If the amount of silicon (Si) exceeds 1.7% by weight, toughness of the composition may be lowered.

The nickel (Ni) serves to improve the corrosion resistance and the like of the composition, and the nickel (Ni) is preferably 0.3 to 0.5% by weight based on the total weight of the composition. If the amount of nickel (Ni) is less than 0.3 wt%, it may be difficult to ensure sufficient abrasion resistance. If the amount of nickel (Ni) exceeds 0.5 wt%, the increase in manufacturing cost is greater than the increase in corrosion resistance There is a problem that economical efficiency is deteriorated.

The niobium (Nb) serves to improve the toughness and the corrosion rate of the composition by refining the crystal grains. The niobium (Nb) is preferably 0.01 to 0.04% by weight based on the total weight of the composition. If the niobium (Nb) content is less than 0.01% by weight, sufficient toughness improvement and corrosion rate can not be delayed. If the niobium content exceeds 0.04% by weight, So that the economical efficiency may be lowered.

The copper (Cu) serves to improve the corrosion resistance of the composition, and the copper (Cu) is preferably 0.25 to 0.35% by weight based on the total weight of the composition. If the amount of copper (Cu) is less than 0.25 wt%, it may be difficult to ensure sufficient corrosion resistance. If the amount of copper (Cu) is more than 0.35 wt%, heat brittleness may occur.

The boron (B) plays a role of retarding corrosion and the like through grain boundary strengthening, and the boron (B) is preferably 0.0005 to 0.0025% by weight based on the weight of the whole composition. Here, when the boron (B) 0.0005% by weight, less than, not to obtain a corrosion delay effect satisfactory, when the boron (B) is more than 0.0025% by weight and a boron compound, such as Fe ₂₃ (CB) ₆ is generated The content of boron (B) is reduced, and the boron compound becomes a starting point of fatigue failure and the strength of the composition may be lowered.

The manganese (Mn) serves to improve the strength of the composition, and is preferably 0.55 to 0.75% by weight based on the total weight of the composition. If the manganese (Mn) content is less than 0.55% by weight, the effect of improving the strength of the composition may not be sufficient. If the manganese content is more than 0.75% by weight, knit structure may be formed in the composition.

The chromium (Cr) serves to improve the oxidation resistance of the composition and is preferably 0.6 to 0.8% by weight based on the weight of the entire composition. When the chromium (Cr) content is less than 0.6% by weight, it may be difficult to improve the oxidation resistance, and when it is more than 0.8% by weight, the brittleness of the composition may be increased.

The vanadium (V) serves to improve the toughness and resilience of the composition and is preferably 0.05 to 0.10% by weight based on the weight of the entire composition. If the vanadium (V) content is less than 0.05% by weight, it may be difficult to ensure sufficient toughness and resilience of the composition. If the vanadium (V) content exceeds 0.10% by weight, vanadium (V) carbide may be generated to reduce the strength of the composition.

The aluminum (Al) added as a deoxidizer is preferably 0.02 to 0.06 wt%, more preferably 0.02 wt% or less, more preferably 0.02 wt% or less, more preferably 0.02 wt% or less, .

The coil spring composition having improved durability according to the present invention is preferably applied to a spring requiring high strength, toughness and corrosion resistance, and more particularly, it is preferably applied to a coil spring for an automobile.

Meanwhile, the coil spring manufactured using the coil spring composition according to the present invention can be manufactured through a hot spring manufacturing process or a cold spring manufacturing process.

The hot spring manufacturing process includes: a first step of cutting and heating the composition material; A second step of hot-molding the heated material; A third step of tempering the shaped body; A fourth step of shot-peening the tempered molding; And a fifth step of coating the shot peened molding; And the like.

In addition, the cold spring manufacturing process may include a first step of applying a composition material using high frequency waves; A second step of tempering the so-called material using a high frequency wave; A third step of cold-molding the tempered material; A fourth step of shot-pinning the cold-formed article; And a fifth step of coating the shot peened molding; And the like.

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are merely illustrative of the present invention and that the scope of the present invention is not construed as being limited by these embodiments.

Examples of the coil spring composition having improved durability according to the present invention were prepared by referring to the following Table 2, and physical properties and fatigue life, etc. of the conventional comparative examples were compared, and the results are summarized in Table 3 below.

division unit Comparative Example Example C weight% 0.48 0.53 Si weight% 2.1 1.5 Mn weight% 0.6 0.6 Cr weight% 0.7 0.7 Ni weight% 0.3 0.4 V weight% 0.08 0.08 Nb weight% - 0.03 Cu weight% 0.25 0.3 Al weight% 0.04 0.04 B weight% - 0.0015 Fe weight% Remainder Remainder

Table 2 is a table comparing the contents of the components and the components of Comparative Examples and Examples, and Comparative Examples and Examples were produced by referring to the table.

division Grain size
(탆) The tensile strength
(MPa) Impact toughness
(J / cm2) simple
Fatigue life corrosion
Fatigue life Comparative Example 33 1960 52 570,000 times 200,000 times Example 13 2058 60 74,000 times 250,000 times

Table 3 is a table summarizing the grain size, tensile strength, impact toughness, simple fatigue life, and corrosion fatigue life in the corrosion environments of the comparative example and the example. The size of the crystal grains was measured by an electron microscope for the cut surfaces of the comparative examples and the examples. The smaller the grain size is, the finer the texture is, and the more the texture is finer, the better the toughness.

More specifically, FIG. 2 is a photograph showing the crystal grains of the conventional spring, and FIG. 3 is a photograph showing the minute crystal grains of the spring according to the present invention. As shown in the figure, the conventional spring crystal grains have an average diameter of about 33 탆, while the average diameter of the spring crystal grains according to the present invention is about 13 탆, which is about 40% smaller than that of the comparative example. This means that the microstructure of the example is about 60% more fine than that of the microstructure of the comparative example, which is related to the improvement of impact toughness and the like of the examples.

Further, in the case of tensile strength, it was confirmed that the example was improved by about 5% as compared with the comparative example, but the impact toughness was improved by about 15% in the examples.

The simple fatigue life was measured by repeating loads of the comparative example and the example until breakage by applying a repeated load of 20 to 120 kgf / mm 2. The larger the number of times, the longer the simple fatigue life.

On the other hand, when a load is repeatedly applied to the spring without the influence of the external environment, the spring of the fatigue damage portion 20, which is the maximum stress concentration portion of the spring, is cut off and the broken wavefront can observe the stripe wavefront as shown in FIG. The simple fatigue life of the comparative example is 570,000 times, while the embodiment shows a simple fatigue life of 740,000 times, which is 30% higher than that of the comparative example.

The corrosion fatigue life in the above corrosive environment is such that the corrosion of the base material is accelerated due to peeling off of the spring due to the calcium chloride or sand on the cold weather road, and the cyclic loading of 20 to 120 kgf / Were measured. When the spring is repetitively loaded in the environment with foreign matter, the corrosion of the base material accelerates and the spring of the corrosion fatigue damage portion (21) is damaged by the corrosion stress crack, and the broken wave surface is observed can do. At this time, the corrosion fatigue life in the corrosion environment was 200,000 times in the comparative example, whereas it was 250,000 times in the embodiment, and it was confirmed that the corrosion fatigue life was improved by about 25% as compared with the comparative example.

The method of measuring corrosion fatigue life after damaging the spring of a road environment in such a cold season includes a first step of spraying a sufficient amount of sand having a diameter of 1 to 3 mm to the spring; A second step of inducing paint peeling of the corrosion fatigue failure portion (21) of the spring by applying a repeated load of 3 to 40,000 times to the spring in the state that the sand exists, thereby abrading the seat and the spring; A third step of spraying salt water with a 5% NaCl solution for 15 days (360 hours) to form a corrosion flaw on the base material of the spring; A fourth step of repeating a cycle of 5 min after 5 min of salt water spraying with a 5% NaCl solution and 25 min of drying; And a fifth step of applying a repeated load until the spring is broken; And the like.

In order to confirm the effect of improving the corrosion resistance of the present invention in which the contents of nickel (Ni) and copper (Cu) are increased, the corrosion rates and corrosion depths of the comparative examples and the embodiments were compared.

The corrosion rates were compared by comparing the measured current density by applying a voltage after immersing the comparative example and the example in a 5% sodium chloride (NaCl) solution.

The higher the current density, the faster the erosion rate. The measured current density of the comparative example is 4.38 × 10 ^-6 A / cm 2, and the current density of the embodiment is 3.48 × 10 ^-6 A / cm 2. It can be seen that the current density of the measured example is about 20% less than the current density of the comparative example, which shows that the corrosion rate of the example is about 20% less than the corrosion rate of the comparative example.

The corrosion depths were compared with the corrosion depths of Comparative Examples and Examples after salt spraying on the surfaces of Comparative Examples and Examples for about 360 hours with 5% NaCl solution at room temperature of about 35 ° C.

FIG. 6 is a photograph showing the corrosion depth of the comparative example, and FIG. 7 is a photograph showing the corrosion depth of the embodiment. As shown in the figure, the corrosion depth of the comparative example is about 0.38 mm, while the corrosion depth of the embodiment is about 0.29 mm. The corrosion depth of the above example was about 23% lower than the corrosion depth of the comparative example.

Therefore, it was confirmed that the examples according to the present invention have excellent tensile strength, impact toughness, simple fatigue life and corrosion fatigue life, and corrosion resistance and corrosion resistance are improved due to low corrosion rate and low corrosion depth.

Although the present invention has been described in connection with the specific embodiments of the present invention, it is to be understood that the present invention is not limited thereto. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. Various modifications and variations are possible.

10: spring
11: Sheet
20: fatigue damage portion
21: Corrosion fatigue damage part

Claims (5)

(Si) 1.4 to 1.7% by weight, nickel (Ni) 0.3 to 0.5% by weight, niobium 0.01 to 0.04% by weight, copper (Cu) 0.25 to 0.35% by weight of boron (B), 0.0005 to 0.0025% by weight of boron (B) and the balance iron (Fe) and unavoidable impurities.
The method according to claim 1,
The composition further comprises 0.55 to 0.75 wt% of manganese (Mn), 0.6 to 0.8 wt% of chromium (Cr), 0.05 to 0.10 wt% of vanadium (V), and 0.02 to 0.06 wt% of aluminum (Al) Lt; / RTI >
The method according to claim 1,
Wherein the composition further comprises 0.017 wt% or less of phosphorus (P) and 0.01 wt% or less of sulfur (S).
0.53 wt% of carbon (C), 1.5 wt% of silicon (Si), 0.4 wt% of nickel (Ni), 0.03 wt% of sodium niobate, 0.3 wt% of copper, 0.3 wt% of boron (B) Characterized in that it comprises 0.0015% by weight of cerium, 0.6% by weight of manganese (Mn), 0.7% by weight of chromium (Cr), 0.08% by weight of vanadium (V) and 0.04% Coil spring composition.
A coil spring produced by using the coil spring composition according to any one of claims 1 to 4.

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