JPH0430462B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is a piano wire class B SWP-B (JIS G3522)
The present invention relates to a high-strength spring steel wire that has excellent stiffness properties and hydrogen embrittlement properties and has a long spring life, and a method for manufacturing the same. [Prior art] Piano wire and hard steel wire are used as spring materials by cold wire drawing, and the tensile strength of spring steel wire after strain relief annealing after wire drawing is 160 to 200 Kgf at 4 mmφ. /
It was about ^mm2 . However, in order to reduce the weight and improve the reliability of springs, it is desired to increase the tension, reduce non-deformable inclusions, and improve the settling characteristics. As a means to solve these problems, high tensile strength wire rods of various component systems have been proposed. For example,
The low alloy steel containing Si, Mn, Ni, Cr, W, and V, "high carbon wire steel with high strength and toughness" shown in Publication No. 86211 and Noboru Yamakoshi et al.
A number of alloyed steels have been proposed since before, such as ``Effects of Addition of Alloying Elements on the Mechanical Properties of High Carbon Steel Wire'' published in Vol. 23, No. 3 (1973). However, although many component systems have been proposed, few have been industrially mass-produced. This is because the addition of alloying elements increases non-deformable inclusions and does not improve fatigue properties, and the patenting process is not successful, making it difficult to obtain a fine pearlite structure suitable for wire drawing. Among steel wires for springs, where fatigue and setness are particularly important, the size that requires weight reduction is relatively thick, 2 to 8 mmφ. High-strength steel wire has a higher strength than piano wire, which has the highest strength and is currently in practical use, and can be stably produced industrially.Also, there are applications where the operating atmosphere is 200 to 350℃, and it can be used at low temperatures for long periods of time. Unlike heat-resistant cold-drawn steel wire with little strength loss even when heated, and high-strength steel wire that is further quenched and tempered, spring steel wire has high strength and is less affected by hydrogen embrittlement during electroplating. is desired. [Problems to be Solved by the Invention] The present invention has been made in order to satisfy these conventional demands, and has been developed to provide a wire with heat-settling characteristics that is between that of piano wire and low-alloy steel oil-tempered wire. A further object of the present invention is to provide a high-strength spring steel wire that exhibits less hydrogen embrittlement during electroplating, and a method for manufacturing the same. [Means and effects for solving the problems] The gist of the means for solving the above problems is (1) specifying the component system, that is, combining Si and Cr to improve heat resistance and stiffness properties. We aim to improve In addition, O, S regulations are carried out, and one or more of Ca, Mg, Ba, and Sr, singly or in combination, are
By adding 0.0005 to 0.005%, non-deformable inclusions are reduced to 20μ or less; (2) the steel wire has a drawn fiber structure with excellent stiffness properties and low hydrogen embrittlement; and (3) these steels This is a manufacturing method that combines wire composition, patenting conditions, post-patenting standing conditions, and a wire drawing method. Based on the outline of the means for solving the problems of the present invention as described above, the gist of the present invention is as follows. (1) C: 0.70 to 1.00% Si: 0.50 to 2.00% Mn: 0.40 to 0.70% Cr: 0.40 to 1.00% P: 0.025% or less, N: 0.005% or less In steel consisting of the balance iron and unavoidable impurities S: 0.015% or less, O: 0.0050% or less, Ca,
Contains 0.0005 to 0.005% of one or more of Mg, Ba, and Sr, singly or in total, and has a drawn fiber structure with non-deformable inclusions of 20 μ or less. Excellent stiffness properties and low hydrogen embrittlement. Steel wire for high strength springs. (2) C: 0.70 to 1.00% Si: 0.50 to 2.00% Mn: 0.40 to 0.70% Cr: 0.40 to 1.00% P: 0.025% or less N: 0.0050% or less In steel with balance iron and unavoidable impurities S: 0.015 % or less, O: 0.0050% or less, Ca,
900 to 1000 steel wire rods containing 0.0005 to 0.005% of one or more of Mg, Ba, and Sr, singly or in total, and with non-deformable inclusions of 20μ or less.
After heating to ℃, perform a patenting treatment in a lead bath or the like at 570 to 650℃, followed by conditions such that K=t×T/20 is 25 to 500 at temperature T (℃) and time t (hr). A method for manufacturing a high-strength spring steel wire having a wire drawing fiber structure, which comprises leaving it to stand or heating it to release hydrogen in the steel, and then drawing 55 to 95% of the wire. Conventional high-carbon, low-alloy steels have a high C content and also add Cr, V, and W, which tend to form carbides, slow pearlite transformation, and are prone to micro-segregation.
Mn was added in combination. This significantly impeded wire drawability. To prevent this, Mn was kept low and Si and Cr were combined as alloying elements. By combining Si, which does not form carbides, with a carbide-forming element, deterioration in wire drawability could be prevented. It was found that the combination of Si and Cr further improved heat resistance and stiffness properties. Fatigue is important in spring applications. In low-alloy steel, non-deformable inclusions serve as starting points for fatigue and significantly worsen fatigue life. In order to minimize non-deformed inclusions, we have found that controlling O and adding trace amounts of Ca, Mg, Ba, and Sr are effective. As a result, the oxide-based inclusions become easily deformed, and those larger than 20 μm no longer appear, and the sulfide size of the deformed inclusions becomes smaller. This effect becomes more pronounced due to the S regulation. Fatigue life is determined by the propagation of cracks, and P was regulated to reduce the propagation speed. N was regulated to prevent toughness deterioration due to strain aging during strain relief annealing. Regulation of P and S will be even more effective. As a result of research into the reason why various low-alloy steels have been developed but have not been used industrially, an important fact has been discovered. These are the patenting conditions and the time from after patenting to wire drawing. Conventionally, little importance has been placed on the heating temperature during patenting. For low-alloy steels, it has been thought that it is best to perform pearlite transformation by quenching in a lead bath immediately after austenite transformation at the lowest possible temperature. This is because it was thought that crystal grain growth occurs after austenitization and that the reduction of area after pearlite transformation decreases. Although there was no problem with ordinary carbon steel, it was found that there was a serious problem with low alloy steel. When the austenitizing temperature is low, the reduction is high, but undissolved carbide of about 0.1 to 0.2 μ remains in most cases less than 1 μ. If these minute undissolved carbides remain, the toughness will be extremely deteriorated during strain relief annealing after wire drawing. This fact was discovered through a detailed study of the fiber structure after wire drawing. Therefore, we found it necessary to increase the heating temperature during patenting. Furthermore, even with a pearlite structure, if the isothermal transformation temperature is low, the pearlite lamellar structure is misaligned and sufficient wire drawability cannot be ensured. Therefore, the isothermal transformation temperature was regulated. It has thus been found that by increasing the heating temperature during patenting, the reduction of area immediately after patenting is low, but gradually recovers. This is due to hydrogen absorption during heating. It is almost negligible in carbon steel, but it is noticeable in low alloy steel. With low alloy steel, the reduction of area cannot be increased to 30% or more unless this is left or heat treated after the patenting process. Based on many years of research, K = temperature T (℃) and time t (hr).
It was found that it was necessary to leave or heat under conditions such that t×T/20 was 25 or more. The treatment is left at 20℃ for 25 hours or more. The time can be shortened by increasing the temperature. Lead patented material is wire-drawn to achieve a specified strength, but because the lower limit of the lead bath temperature is regulated, the tensile strength is low and unless wire-drawn to a level higher than 55%, the piano wire will be class B SWP-B. Unable to secure equivalent or higher tensile strength. The above lead bath may be any salt bath or the like. In addition, this wire drawing process forms a fibrous structure, which, in combination with the effects of the component system, results in a high-strength steel wire for springs that has excellent settling properties and less hydrogen embrittlement. The above is the basic idea of the present invention. Next, the reasons for limiting the chemical components, non-deformable inclusions, patenting conditions, post-patenting processing conditions, and wire drawing conditions of the present invention will be explained. C is a basic element for strength and microstructure. If the content is less than 0.70%, it is impossible to manufacture spring steel wire with a tensile strength equal to or higher than that of SWP-B.
C was 0.70% or more. When C exceeds 1.00%, Si,
Even with Cr-added steel, wire breakage during wire drawing due to reticulated cementite cannot be prevented, so the C content was set at 1.00% or less. Next is Si, and the hardening effect of ferrite becomes noticeable when Si is 0.50% or more. However, if it exceeds 2.00%, it is impossible to achieve a reduction of more than 30% no matter what patenting conditions are used, making wire drawing difficult. Mn is an element that prevents hot embrittlement and is 0.20%
Otherwise, the occurrence of surface flaws cannot be prevented. and,
In order to increase the tensile strength to 200Kgf/mm ² or more, it is necessary to add 0.40% or more. Mn slows pearlite transformation and tends to undergo micro-segregation. Therefore,
The Mn content was set to 0.70% or less so that pearlite transformation, including micro-segregation parts, can be completed within 5 minutes of holding the lead bath. As mentioned above, by combining Si, which does not form carbides, and Cr, which is a carbide forming element, deterioration of wire drawability can be prevented, and heat resistance and set property are further improved. This effect can be obtained at Cr of 0.40~
It is in the range of 1.00%. P was set to 0.025% or less, at which the effect of reducing the crack propagation speed during fatigue is significant. S was set at 0.015% or less to prevent hot embrittlement and to expect refinement of sulfide size by adding Ca, Mg, Ba, and Sr. O was set to 0.0050% or less, which can be modified into deformed inclusions by adding Ca, Mg, Ba, and Sr. This reduces the size of non-deformed inclusions to 20μ or less. Ca, Mg, Ba, and Sr are all elements that react with O and S, and have the same effect. Therefore, single addition and combined addition can be treated equally. It is also highly effective when added in small amounts. When added in large amounts, harmful giant undeformed inclusions of CaO, MgO, BaO, and SrO are formed. Effective under simultaneous regulation of S and O. Promotes deformation of oxide inclusions,
In order to suppress the formation of non-deformed inclusions of 20μ or more and to reduce the size of sulfides, 0.0005% or more is required. If it exceeds 0.005%, it becomes the starting point of fatigue.
Huge non-deformed inclusions larger than 20μ appear. In this way, fine adjustment is an important point. When patenting steel wire rods with this composition, the heating temperature is
The generation of undissolved carbides cannot be prevented unless the temperature exceeds 900°C. However, if the temperature exceeds 1000℃, the austenite crystal grains will become coarser, the drawing will deteriorate, and even if left untreated, the temperature will not exceed 30%, so the heating temperature should be adjusted to 900℃ or higher.
The temperature was 1000℃. Furthermore, unless the lead bath temperature is 570°C or higher, a well-shaped fine pearlite structure with good wire drawability cannot be obtained. However, if the temperature exceeds 650°C, the strength of the patenting material decreases and it is impossible to obtain a high-strength steel wire of 200 Kgf/mm ² or more even by wire drawing, so the lead bath temperature was set at 570 to 650°C. Even under such patenting conditions, the aperture immediately after is 20 to 30%. After patenting, it is necessary to release the hydrogen absorbed during heating by leaving it to stand or by heat treatment. This leaving treatment increases the aperture to 30% or more.
It was found that temperature and time are important parameters for hydrogen release. As a result of research, the temperature T
(°C) and time t (hr), K=t×T/20 was found to be the most suitable parameter for determining the temperature and time of the standing treatment. Tests with varying temperatures and times showed that if this parameter was 25 or higher, the aperture was definitely 30% or higher. Therefore, the parameter K was limited to 25 or more. The larger K becomes, the more the aperture recovers, but there is a tendency for it to become saturated at around 500. Therefore, the value of K was set from 25, which allows the aperture to recover to 30% or more due to the effect of neglect, to 500, which saturates the effect. This leaving or heat treatment is extremely important as it also affects the spring properties after wire drawing. It is necessary to leave or heat the wire after patenting, and the drawing will not recover if it is left or heated after drawing. The wire drawing process cold-works the patented material and increases its tensile strength. 55% even in high carbon low alloy steel
If the above wire drawing process is not performed, piano wire B class SWP
- It is impossible to manufacture high-strength steel wire for springs that is equal to or higher than B. However, if the degree of wire drawing is increased, the tensile strength will increase, but the number of twists will deteriorate to 20 times or less, so the degree of wire drawing was set at 55 to 99%. [Example] Next, an example according to the present invention will be shown. Example 1 looks at the influence of ingredients. Table 1 shows the chemical composition of the inventive steel and comparative steel used in Example 1, and Table 2 shows a list of properties of the spring steel wire prototyped using the steel materials. The symbols in Tables 1 and 2 correspond. The spring steel wire prototyped using A in Table 1 is A in Table 2. Both are 9.0mm
After heating the φ wire to 950℃, quenching it in a 590℃ lead bath,
It was left at ℃ for 48 hours. K=48. Then I drew the wire. The area reduction rate of each stage of wire drawing is approximately 20%,
Wire was drawn to 4.0mmφ (area reduction rate 80%). After wire drawing, heating was performed at 350°C for 30 minutes to remove strain. Characteristics were determined in this state. Torsion test span length 400mm
(=100d). The presence or absence of undissolved carbides was determined by cutting a longitudinal section sample from the fracture surface after the torsion test.
It was checked using a scanning electron microscope at a magnification of 10,000 times or more. For the fatigue test, a Takeshi Nakamura rotary bending fatigue testing machine was used to draw an S-N curve and determine the fatigue limit. We also checked the fracture surface in the finite fatigue life region to check for the presence of non-metallic inclusions. Hydrogen embrittlement was evaluated by accelerated testing. immersed in 3% _{H2SO4 solution} ;
A DC current of 15 mA/cm ² was applied to force hydrogen charge. A stress of 60 Kgf/mm ² was applied. Those that did not break after 100 hours were judged to have no hydrogen embrittlement. To evaluate heat resistance, the tensile strength residual rate after heating at 350°C for 1000 hours was investigated. In addition, the tensile strength residual rate is expressed by the following formula. Tensile strength residual rate (%) = Tensile strength after heating / Tensile strength before heating x 100 There is a correlation between the tensile strength residual rate and spring fatigue.
The higher the residual tensile strength, the less the fatigue. To reduce fatigue, set the tensile strength residual rate to 90.
% or more. In Table 1, symbols A to R are the steels of the present invention,
X1 to X12 are comparative steels. All of the steels of the present invention have a drawn fiber structure and have a tensile strength of 200Kgf/mm ²
The number of twists is 20 times or more, the fatigue limit is 40 kgf/mm ² or more, there is no hydrogen embrittlement, and the tensile strength residual rate is 90% or more. In the steel of the present invention, A, E, J, K, L, M,
N is the addition of two elements among Ca, Mg, Ba, and Sr, B,
C, H, and I are added with three elements of Ca, Mg, Na, and Sr; C, D, and F are added with four elements of Ca, Mg, Ba, and Sr; O is added with Ca alone; P is added with Mg alone. addition,
Q is the addition of Ba alone, and R is the addition of Sr alone.
It can be seen that Ca, Mg, Ba, and Sr are effective whether added alone or in combination. All comparative steels have a tensile strength of 200 Kgf/mm ² or more, but the number of twists is 20 or less, and the fatigue limit is 40 Kgf/mm ² or less. No non-deformed inclusions were detected on the fatigue fracture surface of the steel of the present invention. Among the comparative steels, S, O, Ca, Mg,
In cases where Ba and Sr are outside the scope of the present invention, fatigue fracture surfaces may be affected.
Non-deformed inclusions larger than 20μ were present. X1 is N
Since it is high at 0.0062%, the number of twists is low at 13 times. X
3 has a high P of 0.040%, and X4 has a high S of 0.040%, so the number of twists is less than 20 and the fatigue limit is 40Kgf/
It is low, less than mm ² , and non-deformed inclusions are seen on the fatigue fracture surface. In addition, undissolved carbides are seen in X7 and X8 containing V and W, and the number of twists is extremely low.
Due to the undissolved carbide, the fatigue limit is also low at 40Kgf/mm ² or less. X4 with high S, X2 with high O, Ca, Mg,
With the addition of four elements Ba and Sr, the total is 0.0055%
5. Addition of three elements, Ca, Mg, and Ba, increases the total
When adding 0.0056% of X9, two elements of Ba and Sr, the total amount is 0.0055% of X10, and when adding Ca alone, the amount of addition is
0.0051% of X11, conversely, with the addition of two elements Ca and Mg, the total is as low as 0.0003%, X6, Ca, Mg, Ba,
With the addition of four elements, Sr, the total is as low as 0.0004%
Regarding No. 2, non-deformed inclusions of 20μ or more were detected on the fatigue fracture surface, and the fatigue limit was low. X7,X
Since No. 8 is not Si-Cr based, its tensile strength residual rate is 90% or less. Further, when springs manufactured from the steels A to R of the present invention were subjected to chromium electroplating, no breakage due to hydrogen embrittlement occurred, as in the accelerated test results.

【table】

【table】

【table】

[Table] Example 2 examines the influence of wire drawing conditions.
The chemical composition of the wire used was C: 0.85%, Si: 0.99
%, Mn: 0.51%, Cr: 0.50%, P: 0.010%,
S: 0.005%, O: 0.0020%, N: 0.0030%,
Ca: 0.0008%, Mg: 0.0005%. 9.0mmφ,
The wire drawing conditions and spring steel wire properties were investigated using 5.8mmφ wire rod. The investigation method after wire drawing to 4.0 mmφ is the same as in Example 1. b, f, and g are the steels of the present invention. This is patenting at a heating temperature of 900℃ or higher and a lead bath temperature of 570℃ or higher, and after patenting, the wire is left at a temperature of K25 or higher until wire drawing. 4.0
The area reduction rate down to mmφ is also 80%. The tensile strength after strain relief annealing is also about 200 Kgf/mm ² , the number of twists is 20 or more, and the fatigue limit is 40 Kgf/mm ² or more. a, c,
d, e, and h are comparative steels. The heating temperature for a is 850
At low temperatures, undissolved carbides appear and the number of twists is extremely low. In case c, the lead bath temperature is as low as 565°C, so the tensile strength is high, but the number of twists is low. Also, the fatigue limit is 30
It has decreased to Kgf/ ^mm2 . In cases d and e, the number of twists is 20 times or less because there is little left processing after patenting. h satisfies the patenting conditions, but the tensile strength is 180 kg due to insufficient wire drawing.
f/mm ² cm ² and the fatigue limit was 35Kgf/mm ² , which did not reach the target.

【table】

[Table] In Example 3, the performance as a spring steel wire with different area reduction ratios and different tensile strengths was tested. The chemical composition of the wire rod used was: C: 0.87%, Si: 1.01%, Mn: 0.46%, Cr: 0.53%, P: 0.020%, S: 0.007%, O: 0.0030%, N: 0.0039%, Ca: 0.0002%, Mg: 0.0005%. Wire diameter is 11.0mm, 10.0mm, 9.0mm and 8.0
The wire was drawn to 4.0 mm using four types of mm. Table 4 shows the patenting conditions, standing time, wire drawing area reduction ratio, tensile strength, number of twists, etc. of each of the four types. As you will see, SWP―
The tensile strength of B4.0mm is 185-200Kgf/ ^mm2 ,
It can be seen that even higher strength is obtained from this intermediate level. In addition, the number of twists satisfies the 20 twists specified by the JIS standard until the wire drawing area reduction rate is 84%.
If the area reduction rate is higher than this, the area will decrease rapidly. Next, in order to confirm the performance as a spring, tests were conducted on the resistance to set in a heated state, the time strength in a spring durability test, and the resistance to set in this time.
The spring was formed using a general-purpose automatic forming machine with the spring specifications shown in Table 5, and subjected to end face grinding and low-temperature strain relief annealing. At this time, despite the high strength, there were no problems such as poor formability or breakage during processing, and a good spring could be processed. Of the spring tests,
A long-term heating tightening test was conducted to confirm the resistance to set in temperature at elevated temperatures. The conditions at this time were that after spring forming, low-temperature strain relief annealing was performed at 360°C for 20 minutes, and then end face grinding was performed. The test was conducted at 150℃, 200℃ and 250℃ in a hot air circulation oven with a constant tightening stress of 70Kgf/ ^mm2 .
Heat tightening was performed for a long time of 64 hours, and the residual shear strain at that time was measured. As a result, as shown in Figure 1, the residual shear strain is significantly superior to that of SWP-B, which is in practical use, although it differs depending on the tensile strength level.
%, which shows the features of this steel grade. Next, in order to confirm the durability performance as a spring, a test was conducted at 1800 rpm using a spring fatigue tester.
The test spring used was a spring with the same spring specifications as above.
Four conditions were selected for low-temperature strain relief annealing from 360°C to 420°C, and the heating time was 20 min. The test conditions were an average stress of 60 kgf/mm ² and the stress amplitude was changed. The number of test pieces at each stress amplitude was four, and the number of times until breakage was investigated. In addition, for springs that did not break until ¹⁰⁷ times, the test was stopped after this number of times, and the residual shear strain was examined. In addition, each spring was subjected to low-temperature strain relief annealing, shot peening, and further low-temperature strain relief annealing at 250°C for 15 minutes, using general-purpose equipment and normal conditions. However, the shot grain uses 0.60mm cut wire, arc height 0.35mmA, coverage
It was over 90%. Therefore, as a comparative steel wire to examine the features of the steel of the present invention, we used a piano wire for high-strength valve springs (edited by the Spring Technology Study Group, Spring Papers No. 25, wire diameter
4.0mm, tensile strength 189Kgf/mm ² , low temperature strain relief annealing at 360×20min),
It can be seen that all of the four types of tensile strength have excellent durability limits (hereinafter simply referred to as durability limits) after 10 ⁷ cycles (Figure 2). Table 6 shows the relationship between the residual shear strain and stress amplitude of unbroken springs whose test was stopped at the durability limit, by tensile strength.
There are remarkable features in the stiffness characteristics of the spring.

【table】

【table】

【table】

[Table] Example 4 is a steel wire for springs that is small in diameter and aimed at high strength, particularly in cases where resistance to set is important and time strength under high stress is required. The ingredients were the same as in Example 3, the wire diameter was 7.0 mm, patented, and left as in the previous example.
The wire was drawn to 2.0mm. The patenting conditions, standing time, and wire drawing area reduction rate at this time are shown in Table 7.
As shown in Table 8, the tensile strength was 271Kg.
f/mm ² and twisted 21 times. In this way, a high-strength steel wire with toughness significantly higher than SWP-B (205 to 225 Kgf/mm ² ) was obtained. Compression springs shown in Table 9 were manufactured from this, and fatigue tests were conducted on the springs. As in Example 3, spring processing was carried out using a general-purpose automatic forming machine, but despite the high strength, no troubles such as breakage were observed. In the fatigue test, after the end face grinding treatment, low-temperature strain relief annealing was performed at 400°C for 15 minutes, shot peening was performed, and further low-temperature annealing was performed at 225°C for 110 minutes. The shot peening conditions were a 0.60 mm cut wire, an arc height of 0.35 mm A, and a coverage of 95% or more. The fatigue test was conducted at an average stress of 80Kgf/mm ² and a stress amplitude of 45Kgf/mm ² , with an average life of 6×10 ⁶ , 5
The average residual shear strain at ×10 ⁶ hours was 0.008%.

【table】

【table】

[Table] Example 5 is an example of a cold-drawn steel wire in which this steel type has heat resistance and set resistance, and can be attached. In general, among spring steel wires, excluding stainless steel wires, carbon steel wires and low alloy steel wires require plating after spring processing in order to improve their corrosion resistance, which is a drawback. Currently, for this purpose, piano wire and hard steel wire are most commonly electrogalvanized after spring processing. However, Si-Cr steel oil-tempered wire (SWOSC-V) is the most common material that has heat resistance, fatigue resistance, and high strength; There are examples where it is used with As is well known, oil tempered wire is a heat-treated steel wire, so
JIS also explains that hydrogen embrittlement is likely to occur during plating pretreatment and electroplating processes and should generally be avoided. This indicates that there is currently no material that is heat resistant and resistant to set and can be practically electroplated after spring processing. That is, this is because a high-strength material that is made of low-alloy steel and has high strength, and has a tensile strength equal to or higher than class B piano wire, has not been put into practical use. Therefore, we conducted a fatigue test on springs electroplated using this steel type to confirm the brittleness of plating. The test material was the material shown in Example 3 with the highest tensile strength of 220 Kgf/mm ² . This was based on the expectation that the effects of glare would be more pronounced in higher strength materials. A spring that was formed according to the spring specifications shown in Example 3 and then subjected to low-temperature strain relief annealing under the same conditions was used as a test material. As shown in Figure 3, the test spring was galvanized to a thickness of 10μ, which is currently in practical use, and then tested. As a comparison material, in order to confirm the brittleness of plating, a spring that had been subjected to low-temperature strain relief annealing without plating was used. As shown in Fig. 4, the results show that there is no difference in the fatigue limit, which shows the same tendency as the piano wire and hard steel wire that are currently in practical use, and is sufficiently durable for practical use. Example 5 is a comparison with the oil tempered wire described in Example 4 to test whether it is possible to put into practical use a spring that is free from plating brittleness and can withstand high stress. The comparison steel wire was an oil-tempered Si-Cr steel wire, which is currently in practical use and has the largest diameter and highest strength. Although there is currently a demand for plating with this Si-Cr steel oil-tempered wire, it cannot be put to practical use due to the brittleness of plating, and the current situation is that it relies on painting. The sample material was chosen to have a large diameter of 8.0 mm. The chemical composition used was the same steel number as in Example 3, and the product was manufactured under the manufacturing conditions shown in Table 10. Si as the same 8.0mm comparison steel wire
- Spring processing and plating were performed using 182 kgf/mm ² Cr steel oil tempered wire and 175 kgf/mm ² equivalent to class B piano wire according to the spring specifications shown in Figure 5. In addition, in order to examine the effects of plating, a comparative test was also conducted with springs before and after plating. The test was conducted at 100 rpm with an average stress of 60 Kgf/mm ² and a stress amplitude of 45 Kgf/mm ² to determine the number of repetitions until the spring broke. As a result, as shown in Figure 6, there is no difference between this steel type, which is a cold-drawn steel wire, and piano wire type B (equivalent), regardless of the presence or absence of plating, but in the case of oil-tempered wire, brittleness due to plating is observed. .

[Table] As described above, it can be seen how excellent the present invention is as a high-strength spring steel wire and a manufacturing method thereof. According to the present invention, even high carbon, low alloy steel can be produced stably industrially by combining not only the component system but also the patenting conditions, standing or heat treatment after patenting, and wire drawing.

[Brief explanation of drawings]

FIG. 1 shows the relationship between heating temperature and residual shear strain for the steel wire of the present invention and the comparative steel wire. A, B,
C and D are steel wires of the present invention, and E and F are comparison steel wires.
FIG. 2 shows the relationship between the stress amplitude and the number of repetitions of the steel wire of the present invention and the comparison steel wire. A, B, C,
D is the steel wire of the present invention, and G is the comparison steel wire. FIG. 3 shows the electrogalvanizing process and its conditions. FIG. 4 is an SN diagram comparing the presence and absence of plating of the steel of the present invention. FIG. 5 shows the steps from forming the spring to plating. FIG. 6 shows a comparison of the time strength of the present invention steel and two comparative steel wires used as comparative materials, with and without plating.

Claims (1)

[Claims] 1 C: 0.70 to 1.00% Si: 0.50 to 2.00% Mn: 0.40 to 0.70% Cr: 0.40 to 1.00% P: 0.025% or less N: 0.0050% or less Steel consisting of balance iron and inevitable impurities In S: 0.015% or less, O: 0.0050% or less, Ca,
Contains 0.0005 to 0.005% of one or more of Mg, Ba, and Sr, singly or in total, and has a drawn fiber structure with non-deformable inclusions of 20 μ or less. Excellent stiffness properties and low hydrogen embrittlement. Steel wire for high strength springs. 2 C: 0.70-1.00% Si: 0.50-2.00% Mn: 0.40-0.70% Cr: 0.40-1.00% P: 0.025% or less N: 0.0050% or less In steel with balance iron and inevitable impurities S: 0.015% or less , O: 0.0050% or less, Ca,
A steel wire containing 0.0005 to 0.005% of one or more of Mg, Ba, and Sr alone or in total and with non-deformable inclusions of 20 μ or less is heated to 900 to 1000 °C and then heated to 570 to 650 °C. Patenting treatment is performed in a lead bath or the like, and then the steel is left to stand or heated under conditions such that K=t×T/20 is 25 to 500 at a temperature T (°C) and a time t (hr). After releasing hydrogen, 55-95
1. A method for producing a high-strength spring steel wire having a drawn fiber structure, which comprises performing a wire drawing process of 10%.