TW200821393A - A high strength steel used for springs and a high strength heat-treated steel wire used for springs - Google Patents

Abstract

The present invention provides a high strength steel used for springs and a high strength heat-treated steel wire used for springs having a tensile strength of more than 2000 MPa which are coiled in an as-cold state and having adequate atmospheric strength and coiling workability. The steel and steel wire contain, in mass, C: 0.5 -0.9%, si: 1.0 -3.0%, Mn: 0.1 -1.5%, Cr: 1.0 -2.5%, V: more than 0.15% and less than 1.0%, Al ≤ 0.005%, and a restrained N content of less than 0.007%, and further contain one or more of Nb: 0.001 to less than 0.01%, Ti: 0.001 to less than 0.005%, and the balance being Fe and unavoidable impurities, and having a tensile strength more than 2000 MPa, and satisfying an area ratio of cementite spheroidal carbides and alloying spheroidal carbides of the circle equivalent diameter of 0.2μm of less than 7%, an existing density of the circle equivalent diameter of 0.2μm of less than 1 piece /μm <SP>2<SP>, and former austenite grain size number of more than 10, and the volume of retained austenite of less than 15 mass %.

Description

200821393 IX. Description of the Invention: Technical Field of the Invention The present invention relates to a steel for spring and a heat-treated steel wire for spring which can be taken up in the cold and has high strength and high toughness. Background Art Along with the weight reduction and high performance of automobiles, the spring has been made high-strength, and high-strength steel having a tensile strength of more than 1500 MPa after heat treatment is used for the bomb. In recent years, steel wires having a tensile strength exceeding 1900 MPa have also been required. This is because even if it is subjected to stress relief annealing and nitriding treatment during spring production, it is slightly softened by heating, and it can ensure the hardness of the material which can be used as a spring. In addition, 'the nitriding treatment and shot peening treatment (sh〇tpeening) will be the same as the hardness of the surface layer. The durability of the elastic yellow fatigue is greatly improved. The sagging characteristics of the spring are not determined by the hardness of the surface layer, but the internal strength of the elastic material. Or the hardness of the big towel shirt. Therefore, it is important to finally form a component that can maintain the internal hardness extremely high. 2〇^ The method of the following has been proposed: adding V, Nb, Mo and other elements to solidify when sweating, producing fine carbides that will precipitate during tempering, thereby: reading the material of the index, reading Highly resistant to the following (for the paste, see Japanese Unexamined Japanese Patent Publication No. 57-32353). In the other method of manufacturing steel ring spring (10) s_g), the austenite field of steel is reheated and coiled, followed by quenching and tempering.

Green,,,, and indirect take; &amp;, so that the cold-rolled coils of the high-strength steel that has been quenched and fired are pre-rolled. If it is taken by cold, _ line manufacturing = oil tempering treatment and high-frequency treatment which can be rapidly heated and rapidly cooled can be used to reduce the old austenite grain size of the spring material, and as a result, a bullet with excellent damage characteristics can be obtained. basket for carrying soil. In addition, in the production line of the magazine, the equipment such as the heating furnace can be made simple, and the factory of the miscellaneous money can reduce the benefits of the preparation of the county. Therefore, the cold room of the magazine has recently progressed. During the inspection, the spring phase is thinner than the lower miscellaneous wire (4), and (4) is introduced into the cold coil for the above. However, the strength of the steel wire for winding the spring is increased, and it is broken when it is taken up in the cold, and it is not formed into a spring shape. So far, the strength and the workability have not been taken into consideration, and it has been necessary to take advantage of the strength of the industry, such as heating and winding, and quenching and tempering after winding. In addition, when the high-strength heat-treated steel wire is subjected to cold-rolling and nitriding to ensure strength, it is considered that it is effective to add a large amount of alloying elements such as ν, Nb or the like to the steel in order to precipitate fine carbides. However, once it is added in a large amount, it cannot be solid-melted under heating at the time of quenching, and it grows to a coarse state and becomes a so-called unmelted carbide, which is a cause of breakage during cold coiling. 2〇 Therefore, it is also possible to look at the technology of unmelting carbides. In addition to the above alloying elements, there are also inventions for controlling a plurality of cementite-centered carbides present in steel to improve performance (for example, refer to Japanese Laid-Open Patent Publication No. 2002-180198). SUMMARY OF THE INVENTION j 200821393 - 5 DISCLOSURE OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION The object of the present invention is to provide a heat-treated steel wire for spring which can be wound up in a cold room and which can achieve sufficient atmospheric strength and coiling workability and has a tensile strength of 2000 MPa or more. Used as the spring steel for the steel wire. The inventors of the present invention have found that by controlling the N which has not been noticed so far, even if an alloying element is added, the generation of unmelted carbides can be suppressed, and the toughness and the processability can be ensured, and the high strength and the take-up property can be developed. Heat treated steel wire for springs. That is, the gist of the present invention is as follows. (1) A high-strength spring steel containing C·10 0.9·5 to 0.9%, Si: 1.0 to 3.0%, Μη: 0.1 to 1.5%, Cr: 1·〇 to 2.5%, by mass% , V: more than 〇15~1.0% or less, and A1: 0.005% or less, and the limit N: 0.007% or less 'more Nb: 0.001 to less than 0.01%, Ti: 0.001 to less than 0.005% of one or two The residual part consists of iron and unavoidable impurities. (2) The steel for high-strength springs of (1) further contains one or two of %·· w: 0.05 to 0.5% and Mo: 0.05 to 0.5% by mass%. (3) The steel for high-strength springs of (1) or (2) further contains, by mass%, Ni: 0.05 to 3.0%, Cu: 0.05 to 0.5%, Co: 0.05 to 3·0%, and B. One or two or more of 0.0005 to 0.006%. (4) The high-strength spring steel according to any one of (1) to (3), which further contains Te: 0.0002 to 0.01%, Sb: 0.0002 to 0.01%, Mg: 0.0001 〜 0.0005%, Zr: 0.0001 to 0.0005%, Ca·· 0.0002 to 0·01%, and Hf: 0.0002 to 0.01%, one or more. (5) A heat-treated steel wire for high-strength springs, having a steel composition such as 〇) to (4) in 200821393, a tensile strength of 2000 MPa or more, and a spherical carbide in the carburizing system of the mirror surface And the alloy-based spheroidal carbides have an occupied area ratio of 7% or less and a circular equivalent diameter of 0·2 μηι or more and a density of 1/gm 2 or less; The austenite grain 5 degree number is 1 (&gt; or more, and the retained austenite is 15 mass% or less.

Fig. 1 is an explanatory diagram for explaining the effect of reducing the 1^13 addition of the shellfish (the relationship between the tempering temperature and the Charpy impact value). In Fig. 2, (a) is a photograph showing an observation example of unmelted carbide of a scanning electron microscope, (8) is an example of an alloy-free undissolved carbide ray element, and (c) shows a carburizing system. Example of melting carbide Υ2 ray element analysis. [Mode] The best mode for carrying out the invention The inventors of the present invention defined the chemical composition in order to obtain high strength, and at the same time controlled the shape of the carbide in the steel by heat, thereby inventing a steel wire which can ensure sufficient winding of 4 inches. Suitable for the manufacture of springs. The paper shows its details as follows. First, the reason for limiting the chemical composition and composition range of the high-strength magazine 20 will be explained. C-series - an element that has a large influence on the basic strength of steel. So far, = has obtained sufficient strength to make it 〇.5~〇.9%. If small · _ can not get ^ full strength. In particular, in order to improve the performance of (4), nitriding is omitted, and it is necessary to confirm that a sufficient spring strength is required to be 5% or more of the c paste to be over-eutectoid solid, and a large amount of coarse cementite is precipitated, and the conductivity is remarkably lowered. 8 200821393 This - phenomenon also causes a reduction in the take-up characteristics. Furthermore, the relationship with the micro-organism is also known as the area where the right side is less than 〇·5%, because the amount of carbide is small, and the distribution of the broken material is locally smaller than that of other parts (hereinafter, referred to as a thin carbide domain). The rate is easy ~ plus 'difficult to obtain full strength and character or take-up (extension 5 生). Here, it is preferably 0.55% or more, and more preferably 0.6% or more from the viewpoint of the balance of strength-winding. On the other hand, when the amount of C is large, the carbides of the alloy system and the carburizing system tend to be difficult to be solidified during quenching heating. When the heating temperature in the heat treatment is high and the heating time is short, the strength and the coiling property are insufficient. There are also many situations. In addition, the 10 un-carbide will also affect the carbide thinning field. If the solid c in the steel forms the unresolved stone reversal in the steel, the substantial c area of the carbide will decrease as described above. Furthermore, if the amount of C is increased, it is known that the morphology of the martensite in the case of tempering is generally in the medium carbon steel, and the morphology of the layer will be changed to the meniscus Martin. Body 15 martensite). As a result of research and development, it was found that the carbide distribution of the tempered Martin body structure resulting from the tempering of the meniscus body is lower than that of the layered Martin body. Therefore, it is also possible to increase the amount of c and increase the meniscus body and the unmelted carbide, resulting in an increase in the lean range of carbides. Therefore, it should be less than 7%. It is more preferably less than 65%, which makes it easier to reduce the 20 carbide thin domains.

The Si system is an essential element for ensuring spring strength, hardness, and sag resistance. When the amount is too small, the necessary strength and sag resistance are insufficient. Therefore, the lower limit is 1%. Further, Si has an effect of spheroidizing and refining the grain boundary carbide-based precipitates, and the positive addition has an effect of reducing the grain boundary occupation area ratio 200821393 of the grain boundary precipitates. However, if it is added too much, it will not only harden the material but also embrittle it. Here, in order to prevent embrittlement after quenching and tempering, 3.0% is used as an upper limit. Furthermore, Si is also an element which contributes to tempering and softening resistance. When it is desired to form a high-strength wire, it is preferable to add a certain amount. Specifically, it is advisable to add 5 plus 2%. On the other hand, in order to obtain the stability of the coilability, it is preferable to remove the oxygen by 2.6% or less, 10 15 Μη, and to fix S in the steel to become MnS, thereby improving the hardenability and obtaining sufficient hardness after heat treatment, and is often used. . To ensure this stability, 〇·1% is the lower limit. Further, in order to prevent embrittlement caused by Μη, the upper limit is made 2.0%. Furthermore, in order to balance strength and take-up, it is preferable to use 33 to 1%. In addition, when the take-up is prioritized, it is effective to be 1.0% or less.

Cr is an effective element for improving the hardenability and temper softening resistance. Furthermore, in the nitriding treatment which can be seen in recent high-strength valve springs, it not only ensures tempering hardness, but also is an effective element for increasing the hardness of the surface layer after nitriding and the depth of the hardened layer. However, an increase in the amount of addition will not only result in an increase in cost, but also a coarsening of cementite which is visible after quenching and tempering. In addition, there is also the effect of stabilizing and coarsening the 5 to the gangue. As a result, the wire is brittle and there is a disadvantage that it is easy to break when being wound up. Therefore, if you add &amp; if it is not 0.1/❶ or more, the effect is not clear. In addition, the embrittlement will become significantly upper limit. However, in the present invention, by controlling N to control the carbide, a large amount of Cr can be added, and the addition of Cr for nitriding treatment for those who are easy to obtain high strength can deepen the hardened layer due to nitridation. Therefore, it is preferable to add 1·1〇/0 or more, and it is preferable to add 1.2% or more if it is desired to cooperate with the conventional nitriding of the strength bomb. 20 200821393 Since Cr inhibits the cementite from melting due to heating, in particular, when the amount of c is as high as 00.55%, the amount of Cr is suppressed to suppress the generation of coarse carbides, and it is easy to achieve both strength and coilability. Therefore, it should be added in an amount of less than 2%. It is more preferably 1.7% or less. (5) Two precipitation hardenings which are hardened by precipitation of carbides during tempering, etc. v can be used for surface hardening at the time of hardening and nitriding of steel wires at tempering temperatures. Further, it has an effect of suppressing coarsening of the austenite grain size due to generation of nitrides, carbides, and carbonitrides, and is preferably added. However, heretofore, nitrides, carbides, and carbonitrides of v are also produced at austenitizing temperature A3 of steel of 10, and when they are insufficient in appearance, they are likely to remain as undissolved carbides (nitrides). The unmelted carbide not only causes the breakage of the spring when it is wound up, but also consumes V" uselessly, reduces the § temper softening resistance and the secondary precipitation hardening effect caused by the added V, and degrades the spring performance. Therefore, it has hitherto been industrially preferred to be less than 15%. However, in the present invention, it is possible to suppress the generation of μ nitrides, carbides, and carbonitrides having an austenitizing temperature of eight or more points by controlling the amount of lanthanum. Therefore, V can be added in a relatively large amount so that the amount of addition of V is more than k〇.15/, and is less than 1%. If the amount of addition is less than 〇, the hardness of the nitrided layer is increased and the depth of the nitrided layer is increased. The effect of adding V is reduced, and it is impossible to ensure sufficient fatigue (four) longness of the conventional steel. In addition, if the addition amount is more than 丨.0%, coarse un-solidified inclusions will be produced, in addition to lowering the toughness, and Mo The same volume (4) was born with cold shouting, and the material became the original g] of the broken line when the wire was broken and pulled. Therefore, it is the upper limit of the ease of stability in the Wei industry. The nitride, carbide and carbonitride of the mouth V are in steel. The austenitizing temperature sound &quot;, will account for the above, it will not solidify It is easy to remain as an unmelted carbide (nitrogen 11 200821393). Therefore, in consideration of the nitrogen-control ability of the industrial industry today, it is industrially preferable to be 5% or less, and more preferably 〇4% or less. On the other hand, the surface hardening treatment of nitriding is most heated to a temperature above 3 °C, in order to suppress the hardening of the outer surface layer and the softening of the inner hardness caused by nitriding, 5 need to be added more than 0.15%, and 0.2% should be added. Above. A1 is a deoxidizing element, which will affect the production of oxides. Especially in the high-strength valve, the hard oxides centered on Ah 〇3 are easy to be the starting point of damage and need to be avoided. Therefore, it is very important to strictly control the amount of A1. In particular, when the tensile strength exceeds 21 MPa as the heat-treated steel wire, the fatigue strength is not reduced to 10, and strict control of the oxide generating element is required. In the present invention, A1: 0·005% or less is defined. This is because if it exceeds 5%, the oxide of the main body of Α2〇3 will be easily generated, and the oxide will be broken, and sufficient fatigue strength and quality stability cannot be ensured. High fatigue strength Preferably, it is 0.003% or less. 15 In the present invention, the control of bismuth is a great point, and the present invention defines a strict limit value of 1^0.007%. This is due to the new function in the spring steel. The reason for controlling the enthalpy and the reasons for the definition of the present invention are as follows. In steel, the influence of bismuth is: 丨) exists as a solid solution 纯 in pure granulated iron, suppressing the dynamics of the translocation in pure granulated iron, so that pure Hardening of granular iron; 2) Nitride is produced by alloys such as D, Nb V, Ai 'Β, etc., which have an effect on the properties of steel. The mechanism is as follows. 3) Iron-based carbides that affect cementite etc. The precipitation action affects the properties of the steel. In the spring steel, the strength is ensured by the alloying elements such as C and Si and V, and the hardening effect of the solid-melting N is very high. On the other hand, in consideration of the cold working of the elastic crystal (volume 12 200821393), the deformation of the processing zone is suppressed by suppressing the indexing dynamics, and the processing zone is embrittled, so that the winding processing property is lowered. (―) When the material is heated, it will produce a secret carbonized material, which will become the core and easily grow in size. Furthermore, from the viewpoint of cementite, this slave high spring is tempered in terms of its required strength. In addition, in the defined elements of the first paragraph of the patent scope, v is difficult to precipitate in steel at high temperatures. Things. The chemical composition becomes a nitride 5 main body at a high temperature, and it is converted into carbonitrides and carbides by cooling. Therefore, the nitride produced at the two temperatures tends to become the precipitated core of the tantalum carbide. Wei blade

Mechanical properties such as ductility of steel have an impact. N also affects the production of carbides, and 10 temperatures are tempered at 300 to 5 Torr. In the case of spring steel, the form of the iron-based carbide generated during tempering is complicatedly converted into ε-carbide and θ-carbide (so-called cementite hC). Therefore, the smaller the amount of N, the more 35G~· can be obtained. In the present invention, in order to reduce the harmfulness of N, the amount of N is limited to Ng 0.007%. Further, as described later, any one or two of T^^Nb may be added in a trace amount. When the amount of N can be suppressed to 0.003% or less, it is possible to obtain good performance without adding any one or two of butyl filling, and it is industrially stable and 7 is 0.003% or less, so that the manufacturing cost is It is unfavorable in view of the above. Therefore, one or two of "2" are added in a small amount. When TbtNb is added, since the elements are nitrided at a constant temperature to substantially reduce the amount of solid-melted nitrogen, the same effect as reducing the amount of addition of N can be obtained. Therefore, the upper limit of the amount of addition of n amount can also be increased. However, if the amount of N exceeds 007%, the amount of nitride produced by v, 1^1&gt; or 1^ will increase, resulting in an increase in unmelted carbide, or 13 200821393 increasing the hard intermediate such as TiN, resulting in toughness The lowering of the fatigue endurance characteristics and the winding characteristics is lowered, so the upper limit of the amount of N is limited to 007.007%. That is, even if one or two of Ti and Nb are added, if the amount of N is too large or Ti or Nb is too large, a nitride of Ti or Nb is still generated, which is harmful, and the amount of Ti 5 or added is still small. Therefore, the upper limit of the amount of N is preferably 〇·〇〇5〇/〇 or less, more preferably 0.004% or less. Through such precise N control, it is possible to suppress the generation of V-based nitride while suppressing the embrittlement of pure iron, and to suppress the generation and growth of unmelted carbide. In addition, controlling the form of iron-based carbides can improve the character. That is, when N exceeds 〇·〇〇7%, V-based nitride is likely to be generated, and a large amount of undissolved 10-decarburized carbide is generated, and the steel is embrittled due to the form of pure granular iron and carbide. As described above, when Ti or Nb is added, the ease of heat treatment or the like is also considered, and it is preferably 0.005% or less. Further, the lower limit of the amount of n is preferably as small as possible, but it is easy to be mixed from the atmosphere in the steel making step or the like, and it is preferable to use 0.0015% or more in consideration of the production cost and the ease of the nitrogen removal step.

Nb will produce nitrides, carbides, and carbonitrides, the nitrides of which are produced at higher temperatures than v. Therefore, when cooling, a nitride is generated to consume N in the steel, and generation of a v-based nitride can be suppressed. As a result, temper softening resistance and workability can be ensured because the generation of v-based unmelted carbides can be suppressed. Further, in addition to suppressing the coarsening of the austenite grain size caused by the Nb-based carbonitride, the surface layer hardening at the time of hardening and nitriding of the steel wire at the tempering temperature can be utilized. However, if the amount of addition is too large, it is easy to leave the &Nl-nitride-based nitride as the core unmelted carbide, so it is necessary to avoid a large amount of addition. Specifically, if the amount of Nb added is less than 〇 〇〇 1%, the effect of addition is hardly observed. In addition, if 200821393 is 0.01% or more, the addition of ruthenium will cause coarse unsolidified inclusions. In addition to lowering the toughness, it is similar to Mo, and it is easy to generate supercooled structure, which is easy to cause breakage and wire breakage. Therefore, it is less than 0.01% which is industrially easy to operate stably.

Fig. 1 is a graph showing the results of measuring the impact values of the materials of the chemical components shown in Table 1, and the results of measuring the impact values of the samples A and B which were heat-treated by the method of the examples described later. As can be seen from Fig. 1, the addition of a trace amount of ^^ to control the steel of N as a whole can obtain a higher impact value. Table 1 Chemical composition (mass%) C Si Μη PS Cr Mo VW Nb N s-Al Sample A 0.61 2.20 0.53 0.002 0.004 1.21 0.13 0.20 0.16 0.0049 0.002 Sample B 0.61 2.21 0.54 0.002 0.004 1.19 0.13 0.20 0.16 0.009 0.0050 0.002 10 When Ti is added in the invention, the amount thereof is 0.001% or more and less than 0·005/〇. In addition to the deoxidizing element, Ti is also a nitride or sulfide generating element, which affects the generation of oxides, nitrides, and sulfides. Therefore, a large amount of addition tends to generate a hard oxide or a nitride, and if it is inadvertently added, hard carbides are generated to lower the fatigue durability. As with A1, the special 15 is in the high-strength spring, and the unevenness of the fatigue strength is lowered compared with the fatigue limit of the spring itself. If the amount of Ti is large, the incidence of the inclusion is broken. Increase, and must control its amount so that it is less than 〇〇〇5%. On the other hand, Ti will produce TiN at a high temperature in the molten steel, thus reducing the effect of sol. N in the molten steel. The technical point of the present invention is to suppress the generation of V-based nitride by limiting n 2 , and further control the growth of v-based unmelted carbide. Therefore, if the temperature of the V-based nitride generation temperature is exceeded in advance to eliminate the consumption of N in 200821393, the growth of the chemical compound can be suppressed and the growth of the compound can be achieved. That is, adding Tl can reduce the temperature of the :::❹ lifetime, and the step-by-step ‘solution 5

10, the view that the system does not dissolve carbonitrides and oxides produces ΓΓ addition, but the addition of trace amounts can reduce the nitrides, which can be said to reduce unmelted carbides. The addition amount is above. If the content is 1%, the effect of consuming N is not obtained, and the effect of suppressing the V system is not converted to carbide, and the improvement effect of reading can not be expressed. However, the amount of Ti added is preferably 3% or less. One

The steel of the present invention has the above-mentioned components as a basic component and can improve the composition of the steel properties. That is, when it is desired to strengthen the temper softening resistance = add one or two of W and (10). w not only improves the hardenability, but also produces carbides in the steel, which has the effect of increasing the strength and effectively imparting tempering resistance. Therefore, it is best to add. The _ phase is lower than the lower temperature to produce carbides, and it is not easy to produce unmelted carbides. Further, temper softening resistance can be imparted by precipitation hardening. That is, even in the case of nitriding and stress relieving annealing, the internal hardness is not greatly lowered. If the addition amount is less than 5%, the effect will not be obtained, and 0.5% or more will produce coarse carbides, but it will damage the mechanical properties such as ductility of 2〇, so the addition amount of W is 〇.〇5~ 〇5%. If it is more convenient to consider the ease of heat treatment, etc., it is preferable. Especially in the case of avoiding the disadvantages such as supercooled tissue after rolling, and at the same time obtaining the maximum temper softening resistance, it is more preferable to add 0.15% or more.

In addition to improving the hardenability, Mo will become a carbide precipitate at a temperature of tempering and nitriding temperature of 16 200821393, and can be used for temper softening resistance. Therefore, even if the tempering at the temperature of the tempering and the heat treatment such as stress relief annealing or nitriding incorporated in the step are not softened, the strength can be exhibited. This phenomenon can suppress the reduction of the internal hardness of the elastic yellow after nitriding, and can make the heating setting treatment (h〇t 5 setting) and stress relief annealing easier, and can improve the final fatigue characteristics of the spring. That is, the tempering temperature at the time of controlling the strength can be increased. The tempering temperature enthalpy is advantageous for reducing the grain boundary area ratio of grain boundary carbides. That is, the grain boundary carbides which are deposited in a film form are spheroidized by high temperature tempering, and are effective in lowering the grain boundary area ratio. In addition, M〇 will produce other Mo-based carbides in the steel with the infiltrated carbon. In particular, since it has a lower precipitation temperature than v, it has an effect of suppressing coarsening of carbides. If the amount added is below 0 05%, no effect is observed. However, if the amount of addition is too large, it is easy to cause a supercooled structure in the softening heat treatment such as rolling and drawing, and it is liable to cause breakage and breakage during wire drawing. That is to say, when pulling the wire, it is preferable to make the steel wire by the toughening portion to become a pure granular iron-pearlite structure and then pull the wire. However, since the Mo-based element can impart extremely hardenability, the increase in the amount of addition will prolong the time until the completion of the pearlite transformation, and it is easy to generate a supercooled structure in the cooling and toughening process after rolling. When the line breaks, or if the crack is present inside, the characteristics of the final product 20 are greatly deteriorated. If Mo exceeds 0.5%, the hardenability increases and it is industrially difficult to produce a pure granulated iron-pearlite structure, so this is the upper limit. In order to suppress the man-made structure which is reduced in manufacturability in the rolling and drawing process, and it is easy to stabilize the emulsion and the wire in the industry, it is preferably 0.4% or less, and more preferably 〇 2%. 17 200821393 Furthermore, W and Mo are mixed with V, Nb, and Ti (four) which have the same effect of strengthening temper softening resistance, and nitrides are generated as described above with respect to V, Nb, and di, and it is easy to use it as a core. The carbide grows, w&amp;M〇 hardly produces nitride, so it is not affected by the amount of N, and can be added to enhance softening resistance. In other words, 5 v, Nb, and Tl can also enhance the softening resistance, but if the intention is to prevent the addition of the unmelted stone anodized material while enhancing the softening resistance, the amount of addition is naturally limited. Therefore, it is necessary to add a system in which W or Mo which does not cause unmelted carbides and which requires high softening resistance, which does not generate nitrides, precipitates at a lower temperature, and functions as a precipitation strengthening element. In addition, when the optimum balance between softening resistance and workability cannot be obtained by controlling carbides under the consideration of 10 strength and workability, one of Ni, CU, Co, and B is added to strengthen the matrix to ensure strength. Or two or more. Νι improves hardenability and can be stabilized by heat treatment to increase strength. In addition, the ductility of the substrate can be improved to improve the take-up property. However, since the retained austenite is increased at the time of quenching and tempering, the sag and the uniformity of the material are poor after the spring is formed. When the amount is 0.5% or less, the effect is not exhibited in the high strength and the ductility. On the other hand, it is not preferable to add a large amount of Ni. When the content is 3.0% or more, the retained austenite is increased to cause a significant disadvantage, and the effect of hardenability and ductility is saturated, which is disadvantageous in terms of cost and the like. 20 For Cu* §, Cu can also be added to prevent decarburization. The decarburization layer will reduce the fatigue life after the spring is processed, and it needs to be reduced as much as possible. In addition, the decarburization layer can be removed by a peeling process called peeling to remove the surface layer. In addition, the same effect as Ni has an effect of improving corrosion resistance. By suppressing the decarburization layer, the life of the baby is lost and the step of peeling is omitted. Decarburization suppression of cu 18 200821393 The effect and the effect of improving the corrosion resistance can be exhibited at 05% or more. However, if Ni is added as described later, if it exceeds 〇·5%, it will easily cause damage due to embrittlement. Therefore, the lower limit is 〇.〇5% and the upper limit is 〇5%. Although Cu addition hardly causes mechanical properties at room temperature, if Cu is added in excess of 〇·3%, 5 will deteriorate hot rolling properties and cause cracking on the surface of the scale after rolling. Therefore, it is advisable to prevent the rolling delay from cracking depending on the amount of (11) added to [ 〕 &lt; [Ni%]. Within the range of 3% or less of ClM^〇e, no rolling delay is caused, so it is not necessary to prevent rolling. The purpose of extending the scar is to limit the amount of addition.

Co may also lower the hardenability, but may increase the high temperature strength. Further, since 10 can hinder the generation of carbides, it has an effect of suppressing the problem of coarse cracking in the present invention. Therefore, coarsening of carbides containing cementite can be suppressed. Therefore, it is advisable to add. If you want to add it, if it is below 0 05%, the effect will be very small. However, if a large amount is added, the hardness of the pure iron phase increases and the ductility is lowered, so that the upper limit is 3.0%. In the industry, 安 5% or less can obtain stable performance. B is effective for improving the quenching element and purifying the austenite grain boundary. Elements such as p, s, which are segregated to the grain boundary and cause a decrease in toughness, can be harmless by the addition of ^, and the destruction characteristics are improved. At this time, if 8 and ^^ are combined to produce 3 instruments, the effect is lost. In order to make the effect clear, the addition amount is 〇.〇〇〇5% as the lower limit, and 0.0060% of the effect 20 fruit 臻 saturation is the upper limit. However, even if a very small amount of BN is generated, embrittlement will occur, and sufficient attention should be paid not to cause BN to be produced. Therefore, it is preferably 〇3 or less, and it is more preferable to fix the free N by a nitride generating element such as Ti or Nb, and to make B: 0.0010 〇 〇〇 〇 2 〇%. These Ni, Cu, Co and lanthanum are mainly effective for strengthening the pure iron phase of the matrix 19 200821393. In order to achieve the best balance between softening resistance and workability due to the control of carbide in consideration of strength and workability, it is an effective element to ensure strength by matrix strengthening. In addition, in order to achieve higher performance and stability of performance, one or two or more of Te, 5 Sb, Mg, Zr, and money may be added as an element for controlling oxide and sulfide forms.

Te has an effect of spheroidizing MnS. If the thickness is less than 〇·0〇〇2%, the effect is not clear. However, if it exceeds 0.01%, the toughness of the matrix is lowered, and the disadvantage of causing thermal cracking or reducing fatigue durability becomes remarkable. Therefore, 〇〇1% is used. 10 limits.

Sb has an effect of spheroidizing MnS. If it is less than 0.0002%, the effect is not clear 'But if the right exceeds 〇·〇1%, the matrix property will be lowered, and the disadvantage of causing thermal cracking or reducing fatigue durability will become significant. Therefore, Π% is the upper limit. 0 15 Mg will produce oxides in molten steel with a higher temperature than MnS.

MnS is already present in the molten steel when it is produced. Therefore, it can be used as a precipitation nucleus of MnS, thereby controlling the distribution of MnS. In addition, in the number distribution, the Mg-based oxide is more finely dispersed in the molten steel than the Si and A1-based oxides which are common in the conventional steel, so the MnS having the Mg-based oxide as the core is finely dispersed in the steel 20 in. Therefore, even if the S content is the same, the distribution of MnS will be different depending on the presence or absence of Mg, and the addition of these will make the MnS particle size finer. Even if it is a trace amount, the effect can be fully obtained, and if Mg is added, MnS will be refined. However, when it exceeds 0.0005%, in addition to the formation of hard oxides, sulfides such as MgS will start to be produced, resulting in a decrease in fatigue strength and a decrease in the windability. Therefore, order 20 200821393

The amount of Mg added is from 0.0001 to 0.0005%. When used for high-strength magazines, it should be 0.0003% or less. Although these elements are very small, they can be added in an amount of 0.0001% by using a multi-purpose fire resistant material. Further, by strictly selecting the auxiliary raw material, it is possible to control the amount of addition of Mg by using an auxiliary material having a small amount of ruthenium. 5 Zr is an oxide and sulfide generating element. In the spring steel, the oxide is finely dispersed, and the precipitated nucleus of MnS is formed in the same manner as Mg. Thereby improving fatigue durability and increasing ductility to improve the take-up property. If it is less than 〇 〇〇〇 1%, the effect is not obtained. Further, when the addition exceeds 〇·0005%, the hard oxide is generated, and even if the sulfide is finely dispersed, the problem due to the oxide is likely to occur. Further, if a large amount is added, ZrN 'ZrS-specific nitrides and sulfides are generated in addition to the oxide, which is a manufacturing problem and reduces the fatigue and long-lasting characteristics of the magazine, so that it is 0.0005% or less. When using a high-strength magazine, the addition amount should be 0.0003% or less. Although these elements are trace amounts, they can be controlled by strictly selecting auxiliary materials and precisely controlling refractories. 15 For example, when the ladle, the tundish, the nozzle, etc. are in contact with the molten steel for a long time, the Zr refractory can be used to add the degree of the melon to the molten steel of 200t. Further consideration of this point may be made by adding an auxiliary material within a defined range. The analysis method of Zr in steel is as follows: 2 g can be taken from the portion of the steel to be measured which is not affected by the surface scale, and then the sample is treated in the same manner as in JIS g 1237-1997, Attachment 3 20, and then determined by ICP. . At this time, the ICP calibration curve is set to be suitable for a small amount of Zr.

Ca-based oxides and sulfides produce elemental stones. In the spring steel, MnS can be spheroidized, thereby suppressing the MnS length as a starting point of fracture such as fatigue and making it harmless. If the effect is less than 00002%, it will not be married. If the addition of 21200821393 is more than 0.01%, not only the yield is not good, but also sulfides such as oxides and CaS will be produced, which will cause manufacturing problems and reduce the fatigue durability of the spring. Therefore, it is made 0.01% or less. The amount of addition is preferably 1% or less of 〇·〇〇.

Hf is an oxide generating element and will become a precipitated nucleus of MnS. Therefore, 5 is finely dispersed, and Zr is an element for generating oxides and sulfides. In the spring steel, the oxide is finely dispersed, and like Mg, it becomes a precipitated core of MnS. Thereby, the fatigue durability is improved and the ductility is increased to improve the take-up property.

If it is less than 0.0002%, the effect is not clear, and if it is added more than 0. 01%, not only the yield is not good, but also oxides and nitrides and sulfides such as ZrN and ZrS are generated, causing manufacturing problems and causing springs. The fatigue and long-term characteristics are reduced, so it is made 0.01% or less. The addition amount is preferably 3% or less. The preferred range of other ingredients is described below. Although p and S are not included in the definition of the scope of application for patents, it is necessary to impose 15 restrictions. Although p will harden the steel, segregation will occur and the material will be embrittled. In particular, p which is segregated to the austenite grain boundary will be delayed due to a decrease in the impact value and intrusion of hydrogen. Therefore, it is less suitable. Here, it is preferable to make P: 0.015% or less in which the embrittlement tendency becomes remarkable. Further, when the tensile strength of the heat-treated steel is more than 2150 MPa, it is preferably less than 〇·〇10/0 〇 * 8 and ? The same, if stored in steel will make the steel embrittled. Although it is possible to reduce the noise by Μη, it will also reduce the damage characteristics due to the shape of the inclusions. Especially in high-strength steel, trace amounts of MnS are also likely to cause damage, and s are extremely reduced. It should be less than 0.015% after the adverse effect becomes significant. Further, when the tensile strength of the heat-treated steel wire is more than 215 MPa, the strength is preferably less than 0.01%. Let t-Ο be 0.0002~0.01%. The steel contains oxides and solids generated by the deoxidation step. However, if the total amount of oxygen (t_0) is large, it means that there are many oxide inclusions. Although the size of the oxide-based inclusions is small, it does not affect the performance of the yellowing, but if a large amount of large oxides are present, the spring performance will be greatly affected. If the amount of oxygen exceeds 1% of the force, the spring performance will be significantly reduced, so the upper limit should be 0.01%. Further, although the amount of oxygen is preferably small, the effect is also saturated to less than 0.0002%, so it is preferable to use this as the lower limit. If it is considered that the practical deacidification step is easy, it should be adjusted to 10 0.0005 to 0.005%. In the present invention, the tensile strength should be 2 MPa or more. The tensile strength is higher. The fatigue characteristics of the yellowing tend to increase. Further, even when a surface hardening treatment such as vaporization is applied, the higher the basic strength of the steel wire, the more fatigue characteristics and droop characteristics can be obtained. On the other hand, if the strength is high, the winding 15 is lowered, and it becomes difficult to manufacture a spring. Therefore, it is important not only to increase the strength but also to impart a ductile ductility. From the viewpoints of fatigue and sagging, although the strength of the steel wire is required, the tensile strength TS-2000 MPa is the lower limit. In the case of applying a higher-strength bomb, it is better to have a higher strength, preferably 22 〇〇Mpa or more, and when applied to a 2 〇-return spring, it is suitable for 2250, 2300 MPa or more and does not damage the volume. The range of the properties is increased. As for the undissolved carbide, although C and other so-called alloying elements such as Mn'Ti, v, and Nb are added to obtain high strength, elements such as nitrides, carbides, and carbonitrides are formed by adding a large amount of these. When it is easy to remain 23 200821393 Unmelted carbide. Unmelted Fresh slain is generally spherical and is divided into alloy elements and carburizing bodies. ', / Figure 2 _ atypical observations. The first system) shows an example of an untransformed carbide of a scanning electron micromirror, (8) an X-ray analysis example of an undissolved carbide X of an alloy system, and (4) shows an undissolved carbide of a carburizing system. X-ray halogen analysis example. According to the figures, there are two types of needle-like structures and globular structures having a matrix in the steel. In general, it is known that a steel system forms a needle-like structure of a Martin body through a bonfire, and then generates a carbide by tempering, thereby taking into consideration the strength and the character. However, in the present invention, as shown in the second section (X, Υ of the phantom, 0 does not necessarily have only needle-like structure, and many spherical structures may remain. The globular structure is an unmelted carbide, and its distribution will be The influence of the steel wire of the spring is greatly affected. Therefore, the so-called unmelted carbide refers not only to nitrides, carbides and carbonitrides produced by the above alloys (so-called alloy-based spheroidal carbides (X) ), also includes a carburized system spherical 15 carbide (Y) containing Fe carbide (cementite) as a main component. Figures 2(b) and 2(c) show examples of EDX installed in SEM. The conventional invention only pays attention to carbides of alloying elements such as V and Nb, and an example thereof is the second (b) graph, characterized in that the Fe peak in the carbide is small and the alloy peak (in this example, V) is large. Strictly speaking, many of the alloy-based carbides (X) are composite carbides (i.e., carbonitrides) with 20 nitrides. Here, the alloys are carbides, nitrides, and alloys thereof. The spheroidal precipitates are collectively referred to as alloy-based spheroidal carbides. It has been found in the present invention that not only conventional alloying elements are found. Spherical carbides, as shown in Fig. 2©, Fe3C with a diameter of less than 3μηη and its composite 24 200821393 The precipitation form of the so-called carburizing system carbides of some microalloying elements is also important. If the high strength of the steel wire above the conventional steel wire and the processing of the spheroidal carbide of the carburizing system of 3 μηι or less are large, the workability will be greatly impaired. Thereafter, as described above, it will be spherical and shown in the second figure. The carbides in which Fe and C are the main components of 5 are referred to as carburized carbides of the carburizing system. Moreover, the same analytical results can be obtained even by the replicating method under a transmission electron microscope. The carbide is considered to be a carbide that is not sufficiently solidified during the quenching and tempering process of the oil tempering treatment and the high-frequency treatment, and which is spheroidized and grown or reduced in the bonfire tempering step. The carbonization of the size H) The strength and the nature of the quenching and tempering are completely unhelpful, but will deteriorate. In other words, it is only necessary to add C which is a source of strength by fixing c in the steel, and it is coarsened to become a stress concentration source, and the mechanical properties of the steel wire are lowered. Here, the alloy-based spheroidal carbide and the carburizing system 15 spherical carbides are defined as follows, and the following limitations are important in order to eliminate the disadvantages caused by such. The area ratio of the circle-equivalent diameter of 0·2 μm or more is 7% or less, and the density of the circle-equivalent diameter of 0·2 μm or more is Η@/μπι2 or less. When the steel is quenched and tempered for cold-rolling, the unmelted spheroidal carbides 20 affect the winding characteristics, i.e., the bending characteristics until rupture. Heretofore, in general, in order to obtain high strength, not only c is added, but alloy elements such as &amp; ν are added in a large amount. However, if the strength is too high, there will be a disadvantage that the deformation energy is insufficient and the coiling characteristics are deteriorated. The reason for this is considered to be the coarse carbides in the steel. In the mirror-polished sample, 25 200821393 etching methods were applied to picar and electrolysis, and the alloys and carburizing systems of these steels were observed, but the detailed observation and evaluation of the dimensions were required. It is observed by a scanning electron microscope at a magnification of 3000 times or more. Here, the target alloy is a spherical carbide and a spheroidal carbide system of a dream carbon system is equivalent to a diameter of 2 μm or more. In general, carbides in 5 steel are indispensable for ensuring the strength and temper softening resistance of steel', but the effective particle size is below 〇·1μπΐ, and conversely, if it exceeds 1μη1, the strength and austenite grain size are Micro-reduction does not contribute, but only the deformation characteristics can be deteriorated. However, the prior art has never recognized this importance in detail, and only pays attention to the alloy-based carbides of V, Nb, etc., and seems to think that the circle is equivalent to 3 μπι or less. Carbides of bismuth (especially carburized spheroidal carbides) are harmless. The mirror-polished sample is electrolytically etched, and the alloy system and the carburization system carbide are observed by a scanning electron microscope to reach 10 fields of view. The area ratio of the spheroidal carbide is more than 7%. Sex will be extremely degraded and will be used as an upper limit. Further, in the present invention, the point of the θ gold system and the carburized system spheroidal carbide having a circular diameter of 2 μm or more as a target of attention is not limited to the size, and the number 3 is also a major factor. Therefore, the scope of the present invention is defined in consideration of the two. In other words, if the number of spheroidal carbides having a circle-equivalent diameter of 0.2 μm or more is extremely large and the density exceeds 1/μηι 2 in the mirror surface, the deterioration of the winding characteristics is remarkable, so that it is an upper limit. On the other hand, if the size of the carbide exceeds 3 μm, the influence of the size will become larger, and it is preferable to not exceed this limit. The reason why the old austenite grain size number is above 10 is that the old austenite grain size and carbide are in the case of a steel wire based on the tempered martin body structure 26 200821393

- The same is true for the basic properties of the steel. That is, the smaller the old austenite grains are pinched, the better the fatigue characteristics and the curling property. However, no matter how small the austenite grains are pinched, if the amount of the above-mentioned carbides is more than the prescribed amount, the effect is small. — Generally speaking, in order to make the Aussie diameter smaller, the heating temperature of the cake fire is reduced, but this will increase the above-mentioned untransformed carbide. Therefore, it is important to finally make the steel wire that balances the surface (4) with the old austenite grain. In the case of the definition of carbide satisfaction, if the old austenite grain diameter number is not full, New Zealand is fully evasive, so the old austenite grain number is defined as! The nickname is above. 10 When applied to higher strength springs, the fine particle size is appropriate 15

20, &quot;, release&gt;1 Wang Hao Even the 12th or above will be able to balance high strength and take-up. The reason why the retained austenite is 15% by mass or less is that the retained austenite remains in the vicinity of the segregation zone, the prior austenite grain boundary, and the subgrain. The retained austenite will be a martensite due to a phase change caused by the reinforcement, and if a phase is generated during the spring forming, a high hardness portion is locally generated in the material, and the coil as a spring is turned low. In addition, the wire bomb is surface-strengthened by shot peening or setting treatment (four) deformation, but when the process includes most of the steps of applying such plastic deformation, the addition of the spring in the early stage will cause the strain to break. Lowering, so that the processability and the yellowing damage characteristics during use are reduced. In addition, it is also expected to be damaged during winding when it is inevitable deformation in the sanitary industry. Further, the sanitary napkins such as nitriding and stress-relieving annealing are also slowly decomposed to cause a change in mechanical properties, resulting in a decrease in strength or a decrease in take-up property. Therefore, minimizing the reduction of retained austenite and inhibiting the processing of the Martin body will increase the read. 27 200821393 Specifically, if the amount of retained austenite exceeds 15% (% by mass), the sensitivity of the nail is increased.' «In the case of coiling and other operations, the damage is caught. The amount of retained austenite will vary depending on the amount of alloying elements such as C and Μη and the heat conditions. Therefore, not only the composition design, but also the heat treatment conditions are important. If the temperature of the Martin body (starting temperature Ms point, end temperature Mf|i) becomes low μ / the fire is not produced at a relatively low temperature, the Martin body cannot be produced, and the residual _ austenite will easily remain. Industrial quenching uses water or oil, but 1° inhibition of retained austenite requires a high degree of heat treatment control. Specifically, it is necessary to maintain the cold portion of the cold medium at a low temperature, to maintain the low temperature after cooling, and to make the phase change to a Martin body for a long period of time. Since the industrial line is treated by a continuous production line, the temperature of the cooling refrigerant easily rises to near 100 ° C, but should be maintained below 60 ° C, and is preferably maintained at a low temperature of 4 ° C or less. To fully promote the Martin phase transition, it is necessary to maintain Is above the cooling medium, and it is important to ensure the retention time after cooling. #再者' In addition to the definition of such carbides, the distribution of carbides should be avoided in comparison with other parts. Specifically, in the meniscus and its tempered structure, the distribution of carbides is less than that of other parts, resulting in inhomogeneity of the microstructure, which adversely affects fatigue strength and workability. EXAMPLES Evaluation Items: In order to evaluate the applicability of the present invention to springs, the evaluation item showed tensile strength 28 200821393 degrees, hardness after annealing, impact value, and tensile strength measured in tensile test directly linked to spring durability, strong Sound Wei Gu -, year _ X Yue Yu shows that the durability is more and more ambiguous. In addition, the plastic deformation dynamics of the material at the same time as the tensile strength is measured, is a spring processing *., shoulder material (winding characteristics) evaluation # mark. The larger the shrinkage rate, the easier it is to process. For example, the higher the strength, the lower the shrinkage rate. According to the example of Xizhi Steel, if the initial rate of _ 15 ^ ^ is light, the shrinkage rate of 10 15 exceeds 鸠'. Other diameters are difficult to achieve obstacles in industrial mass production. The formed sheet is made by quenching and tempering the wmm reading, and after 22_Pa, it is made according to the test piece of the melon Z _9, and the strength is calculated from the breaking load according to the JISZ. Further, in recent years, the spring has been increased in strength, and a hardening treatment by nitriding was applied to the surface layer. The ratification system heats the spring to a fineness of ~ ~ fine in a nitriding atmosphere to keep the surface layer hardened. At this time, the inside is not heated due to the intrusion of nitrogen, and the annealing softens. It is very important to suppress the softening. Therefore, the evaluation of the post-mortem hardness of the _ reduction is used. In addition, in order to evaluate the processability and damage resistance of the material, Charpy is used as a miscellaneous item. In general, materials with good impact values are considered to be 20 forces and = bad properties (including fatigue characteristics) are also good. In addition, materials that are brittle are not bad, so materials with high toughness are considered to be excellent in workability. In the example, the Charpy impact value of the same material as that of the tensile X after quenching and tempering has been measured. The Charpy impact value will also be affected by the austenite granules. Therefore, the austenite grain size of the same material is also determined. This 29 200821393 outside the 'Xiabi impact test piece transmission ^ u 尺 驰 驰 m cross section of the symplectic; &quot; such as the heat treatment material of 111 to take out the so-called half) material, apply a 2mm U notch processing. In addition, the spring is finer and thinner, and the degree is short.

Heat treatment. It is known that it is easy to leave unconverted carbides, and the workability is lowered. In the present invention, the blade is also made into a wire-cutting wire, and the wire is heat-treated to determine the distribution of the material and the austenite. Body size. In general: If the heating temperature is low and the time is short, the austenite grain size will shrink, but the tendency to increase the carbonization of the unresolved carbide should be evaluated to balance the two. As a result, since the system is expressed in tensile strength and elongation, and the two are used as the evaluation, the cross-sectional area of the fine-diameter material having a size of 5 mm or less is small, and the dynamic deformation of the plastic deformation is more obvious than the shrinkage ratio. Details of the heat treatment conditions of the evaluation material are described below. The tensile test was carried out according to JIS, and a test piece of parallel region p 6 mm was prepared, and the tensile strength and elongation were measured. After quenching and tempering, mirror polishing was carried out, and the amount of retained austenite was measured by X 15 ray. As for the hardness after annealing, it was subjected to mirror polishing after heat treatment, and the Vickers hard hardness from the surface to the radius of 1/2 was measured at three points, and the average value thereof was used as the hardness after annealing. Regarding the material manufacturing method (Wire-rod), the inventive example 16 of the present invention was melted in a 2t-vacuum melting furnace, and then rolled into an ingot. At this time, in the inventive example, the series 20 was kept at a high temperature of 12 ° C or higher for a certain period of time. Any subsequent case is rolled from 0 to 13 mm. In the other examples, after melting in a 16 kg vacuum melting furnace, forging was performed to φ 13 mm x 600 mm, followed by heat treatment. At this time, the temperature is maintained at a high temperature of 1200 ° C or higher for a certain period of time, and then heat-treated to a desired strength. 30 200821393 As for the heat treatment method, when the test piece is made, if it is not specifically described, it is not: 1200 Cxl5mm - after air cooling, it is heated by 95 (rc for 〇 minutes, and then it is heated to the wrong groove of 650 C, and even 95 (rCxl〇mii^ after heat, put 60. Quenching oil tank quenching, after which, in the invention example, the tempering temperature is adjusted so that the tensile strength exceeds 2200 MPa. The tensile strength, shrinkage and Charpy impact of this heat treatment are measured. The tempering temperature varies depending on the chemical composition, but in the present invention, the tensile strength is 2200 MPa or more and the chemical component is applied with heat treatment. On the other hand, in the comparative example, heat treatment is applied only in accordance with the tensile strength. The mold 10 is annealed at 400 ° C x 2 〇 min, and the hardness is measured to evaluate the softening resistance. In addition, if the φ 4 mm wire used for the evaluation of the limestone is not specifically described, it is 1200 ° C x 15 min - after air cooling, by cutting The processing was performed at p 1 〇mm, and after heating at 950 C for 10 minutes, the wrong tank heated to 650 ° C was charged, and the wire was further drawn to p4 mm to be thinned, and then heated at 950 ° C for 5 minutes, 15 Put the oil tank quenched at 6 °C Then, the tempering temperature is adjusted so that the tensile strength exceeds 2200 MPa. In addition, in the Nakamura-type rotational bending test, the stress exceeding the load rotation number of 1 〇 7 is the fatigue strength. 31 Table 2 Chemical composition (mass%) No. C Si Μ Ρ S Ν Cr V A1 Ti Nb Inventive Example 1 0.58 2.22 0.66 0.008 0.004 0.0011 1.17 0.22 0.003 0.007 2 0.65 1.93 0.44 0.007 0.007 0.0022 L41 0.25 0.002 0.008 3 0.71 2.23 0.81 0.003 0.003 0.0017 1.17 0.23 0.003 0.006 4 0.76 1.89 0.51 000.005 0.0021 1.23 0.26 0.003 0.005 5 0.81 1.94 0.54 0.00 0.008 0.0012 1.18 0.25 0.002 0.004 6 0.66 1.89 0.63 0.005 0.009 0.0017 1.10 0.18 0.001 0.007 7 0.68 2.10 0.77 0.004 0.003 0.0032 1.40 0.28 0.001 0.003 0.005 8 0.66 2.02 0.42 0.008 0.006 0.0049 1.40 0.24 0.002 0.004 9 0.67 2.00 0.83 0.001 0.004 0.0021 1.18 0.29 0.002 0.004 10 0.66 2.05 0.86 0.004 0.009 0.0038 1.38 0.24 &lt;0.001 0.003 11 0.69 1.80 0.67 0.005 0.002 0.0037 1.48 0.26 0.002 0.004 12 0.61 2.04 0.76 0.008 0.006 0.0046 1.31 0.28 0.003 0.004 13 0.69 2.17 0.43 0.007 0.008 0.0056 1.12 0.24 0.002 0.002 14 0.65 1.91 0.48 0.009 0.008 0.0025 1.16 0.26 0.002 0.003 15 0.61 1.86 0.68 0.002 0.005 0.0041 1.16 0.30 0.002 0.004 16 0.62 2.05 0.56 0.006 0.005 0.0047 1.43 0.21 0.002 0.008 17 0.69 2.11 0.65 0.007 0.008 0.0019 1.50 0.27 0.004 0.009 18 0.66 2.23 0.79 0.007 0.006 0.0055 Ϊ.37 0.25 0.001 0.004 19 0.62, 2.22 0.71 0.008 0.003 0.0055 1.44 0.24 0.003 0.006 20 0.63 1.95 0.43 0.002 0.003 0.0040 1.20 0.22 0.002 0.005 21 0.69 2.08 0.65 0.006 0.004 0.0026 1.35 0.20 0.003 0.003 22 0.66 1.94 0.82 0.007 0.004 0.0024 1.45 0.27 0.002 0.009 23 0.68 2.08 0.89 0.006 0.008 0.0053 1.26 0.29 0.001 0.005 24 0.63 1.86 0.42 0.009 0.005 0.0048 1.17 0.20 0.003 0.001 0.005 25 0.69 2.00 0.87 0.005 0.005 0.0020 1.26 0.25 0.002 0.003 0.004 32 200821393 Table 3

Chemical composition (mass%) No. Mo W Ni Cu Co B Ca Zr Hf Te Sb Mg 1 0.10 0.18 0.0003 0.0003 2 0.25 0.16 0.0003 0.0005 3 0.17 0.16 0.0002 0.0003 4 0.18 0.15 0.0002 0.0004 5 0.20 0.21 0.0003 0.0003 6 0.20 0.18 0.0002 0.0002 7 0.22 0.17 0.0002 0.0004 8 0.0003 0.0003 9 0.0001 0.0003 10 0.15 0.16 11 0.15 0.16 Hair 12 0.25 0.15 Ming 13 0.21 0.17 0.0004 Example 14 0.15 0.21 0.0003 15 0.16 0.17 0.0003 0.0003 16 17 0.0001 18 0.16 0.0003 19 0.11 0.0003 20 0.15 0.20 21 0.19 0.17 0.0002 22 0.08 0.14 0.0003 23 0.13 0.20 0.0002 0.0003 24 0.0002 0.0005 25 0.0003 0.0004 33 Table 4 Chemical composition (mass%) No. C Si Μη Ρ S Ν Cr V A1 Ti Nb Inventive example 26 0.67 2.07 0.48 0.008 0.001 0.0041 1.49 0.24 0.001 0.001 0.004 27 0.70 2.26 0.81 0.008 0.00 8 0.0058 1.24 0.24 0.001 0.001 0.002 28 0.68 1.86 0.85 0.005 0.005 0.0049 1.10 0.23 0.002 0.004 0.006 29 0.67 2.24 0.48 0.008 0.002 0.0029 1.20 0.30 0.002 0.004 0.002 30 0.66 1.85 0.78 0.005 0.008 0.0026 1.47 0.29 0.002 0.002 0.002 31 0.62 2.11 0.54 0.007 0.005 0.0034 1.42 0.23 0.002 0.002 0.009 32 0.61 1.80 0.25 0.007 0.005 0.0028 1.24 0.28 0.002 0.001 0.007 33 0.65 2.01 0.26 0.002 0.003 0.0038 1.10 0.20 0.002 0.004 0.001 34 0.68 2.11 0.28 0.003 0.005 0.0034 1.11 0.24 0.003 0.004 0.001 35 0.63 1.82 0.15 0.008 0.008 0.0043 1.28 0.24 0.002 0.004 0.009 36 0.70 2.15 0.26 0.002 0.008 0.0054 1.39 0.20 0.001 0.004 0.004 37 0.68 2.20 0.12 0.004 0.003 0.0029 1.17 0.25 0.001 0.004 0.005 40 0.64 1.92 0.42 0.002 0.004 0.0025 1.26 0.28 0.003 0.004 0.002 41 0.62 2.04 0.77 0.002 0.009 0.0036 1.24 0.29 0.001 0.002 0.009 42 0.67 2.10 0.70 0.003 0.007 0.0036 1.11 0.21 0.002 0.004 0.003 43 0.64 2.00 0.79 0.008 0.003 0.0028 1.31 0.20 0.001 0.004 0.009 44 0.67 2.13 0.86 0.004 0.004 0.0053 1 .36 0.22 0.003 0.004 0.004 45 0.62 2.07 0.47 0.004 0.009 0.0041 1.32 0.22 0.003 0.002 0.006 46 0.69 2.28 0.60 0.006 0.005 0.0047 1.43 0.28 0.003 0.002 0.008 47 0.68 2.26 0.68 0.005 0.009 0.0040 1.24 0.23 0.002 0.003 0.004 48 0.82 2.22 0.74 0.008 0.005 0.0019 1.16 0.18 0.003 0.002 49 0.77 2.19 0.80 0.003 0.005 0.0015 1.12 0.22 0.002 0.007 50 0.68 2.06 0.71 0.004 0.008 0.0025 1.33 0.17 0.002 0.006 51 0.61 2.50 0.75 0.006 0.003 0.0015 1.05 0.42 0.003 0.008 34 200821393 Table 5

Chemical composition (mass%) No. Mo W Ni Cu Co B Ca Zr Hf Te Sb Mg 26 0.14 0.0003 0.0003 27 0.24 0.0002 0.0003 28 0.24 0.19 29 0.17 0.22 0.0002 30 0.16 0.21 0.0003 31 0.19 0.18 0.0001 0.0004 32 0.23 0.20 0.0003 0.0003 33 0.18 0.16 0.0001 0.0002 34 0.14 0.20 0.0001 0.0003 35 0.12 0.21 0.0002 Inventive Example 36 0.15 0.19 0.0003 37 0.21 0.18 0.0002 0.0005 40 0.23 0.14 0.2 0.0001 0.0004 41 0.15 0.14 0.07 0.0002 0.0004 42 0.12 0.17 0.15 0.0002 0.0004 43 0.10 0.16 0.0006 0.0002 0.0005 44 0.16 0.22 0.0005 0.0002 0.0005 45 0.21 0.18 0.0001 0.0005 0.0005 46 0.11 0.16 0.0001 0.002 0.0003 47 0.09 0.19 0.0003 0.001 0.0002 48 0.21 0.0001 0.0004 49 0.16 0.0003 0.0004 50 0.0002 0.0004 51 0.0002 0.0004 35 Table 6 Chemical composition (mass%) No. C Si Μη Ρ S Ν Cr V A1 Ti Nb ratio Example 52 0.65 2.05 0.67 0.007 0.001 0.0056 1.25 0.28 0.003 53 0.82 1.81 0.85 0.007 0.006 0.0066 1.09 0.52 0.002 54 0.65 1.30 0.79 0.002 0.007 0.0080 1.31 0.24 0.002 0.003 55 0.65 1.79 1.18 0.003 0.011 0.0100 1.35 0.26 0.001 0.007 56 0.62 1.76 0.97 0.008 0.008 0.0040 1.21 0.55 0.001 0.044 57 0.63 2.44 0.76 0.004 0.005 0.0041 1.11 0.20 0.002 0.011 58 0.65 2.12 1.10 0.007 0.003 0.0049 1.18 0.29 0.001 0.018 0.07 59 0.66 1.88 1.20 0.009 0.008 0.0027 1.38 0.27 0.001 0.021 60 0.65 1.90 1.01 0.010 0.011 0.0087 1.42 0.29 0.002 0.033 61 0.68 2.13 0.41 0.006 0.001 0.0036 1.45 0.25 0.001 0.046 62 0.69 1.93 1.09 0.006 0.009 0.0049 1.28 0.25 0.004 0.022 63 0.70 1.86 0.45 0.005 0.012 0.0040 1.32 0.28 0.012 0.003 64 0.64 2.34 1.12 0.001 0.009 0.0022 1.30 0.25 0.007 0.007 65 0.68 2.01 0.56 0.008 0.007 0.0050 1.29 0.06 0.001 0.003 66 0.68 1.86 0.60 0.008 0.006 0.0050 1.49 0.10 0.001 0.006 67 0.67 2.49 1.16 0.007 0.009 0.0021 0.76 0.21 0.003 0.008 68 0.66 2.38 0.50 0.006 0.004 0.0053 0.65 0.21 0.002 0.007 69 0.67 1.74 0.58 0.009 0.003 0.0052 1.31 0.28 0.001 0.009 70 0.68 1.49 1.18 0.005 0.007 0.0059 1.11 0.24 0.003 0.004 71 0.69 2.66 0.87 0.005 0.009 0.0057 1.12 0.27 0.002 0.003 72 0.62 1.47 0.99 0.010 0.004 0.0037 1.27 0.27 0.002 0.006 73 0.65 1.79 0.85 0.003 0.002 0.0054 1.40 0.21 0.003 0.007 74 0.48 1.38 1.06 0.011 0.008 0.0034 1.13 0.29 0.001 0.007 75 0.64 0.52 1.07 0.011 0.005 0.0024 1.43 0.23 0.003 0.006 76 0.45 1.23 0.88 0.007 0.012 0.0051 1.18 0.29 0.002 0.005 77 0.64 0.96 1.14 0.004 0.002 0.0055 1.18 0.23 0.002 0.007 36 200821393 Table 7

There is a cable without a wire, there is a tensile tensile stretching Ί a rotating residual tensile annealing, a tensile impact 1 area rate, a number of strength extensions, bending Ί strength hardness &amp; shrinkage value No. % / μπι2 MPa % # MPa % MPa HV % J/cm2 # 1 0.37 0.12 2312 7.3 12 915 6.2 2253 580 38.2 53 10 2 0.32 0.30 2347 8.9 12 917 9.3 2254 601 343 57 11 '3 0.20 0.05 2325 6.8 11 923 7.7 2262 576 41.7 56 10 4 0.20 0.38 2325 7.0 12 906 7.6 2290 612 42.5 54 11 5 0.06 0.46 2310 7.3 11 907 8,2 2308 613 39.6 53 10 6 0.28 035 2296 8.9 12 895 7.6 2251 598 45.0 55 10 7 0.40 0.27 2324 6.1 13 902 10.3 2255 599 37.8 53 11 8 0.02 0.03 2328 6.5 12 897 10.2 2259 601 46.9 51 10 9 0.20 0.15 2288 8.9 12 902 10.2 2259 605 46.9 53 10 10 0.25 0.35 2301 8.4 13 902 8.8 2269 582 35.5 61 11 11 0.38 0.08 2331 6.3 12 919 11.4 2248 602 45.0 51 10 12 12 8 8 8 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 15 0.04 0.30 2299 10.2 11 894 7.6 2276 585 42.5 54 10 16 0.23 0.15 2328 6.8 13 898 8.5 2261 600 45.0 59 10 17 0.52 0.05 2322 10.2 12 892 10.9 2280 584 34.0 61 11 18 0.48 0.25 2307 7.3 12 914 10.6 2273 586 33.1 49 10 Ϊ9 0.28 0.08 2290 7.2 13 925 7.2 2260 586 44.1 53 10 20 0.12 0.14 2301 6.4 13 899 8.0 2285 583 43.7 48 12 21 0.06 0.22 2320 6.1 12 909 9.4 2265 586 47.2 49 11 22 0.23 0.25 2340 7.1 13 919 8.7 2254 604 45.6 53 11 23 0.31 0.19 2319 6.7 13 901 10.3 2258 585 35.0 49 10 24 0.31 0.23 2306 6.5 12 914 8.7 2262 591 38.7 52 11 25 0.41 0.40 2315 8.7 13 897 9.4 2263 588 35.5 58 11 37 200821393 Table 8

There are no wires in the cable, there is a tensile stretching, γ, a rotating residue, a tensile annealing, a tensile impact, a γ area ratio, a strength extension curve, a strength, a hardness, and a shrinkage value. No. % / μιη2 MPa % # MPa % MPa HV % J/cm2 # 26 0.21 0.36 2302 7.4 12 928 6.7 2241 592 34.6 51 10 27 0.32 0.14 2299 7.1 13 919 8.2 2272 579 46.2 51 11 28 0.43 0.04 2321 8.0 11 904 8.2 2255 587 39.9 68 10 29 0.29 0.27 2306 6.4 11 910 9.9 2281 593 36.4 56 10 30 0.03 0.22 2330 6.9 12 909 10.1 2279 605 35.3 54 11 31 0.05 0.38 2303 6.9 12 922 7.5 2289 608 36.5 63 10 32 0.21 0.20 2315 8.0 12 927 7.5 2251 588 33.5 52 10 33 0.40 0.15 2338 6.9 11 902 9.3 2254 591 39.4 56 10 34 0.11 0.04 2335 7.7 13 904 11.6 2248 599 35.4 50 11 35 0.45 0.11 2328 9.1 13 909 10.8 2282 593 39.2 48 11 round 36 0.41 0.27 2320 7.4 12 913 10.7 2273 591 33.0 66 11 37 0.30 0.12 2318 8.0 11 914 11.8 2251 592 43.9 57 10 Ming 40 0.52 0.39 2346 8.1 11 914 7.7 2271 601 38.5 51 10 1 eve 1J 41 0.28 0.16 2312 8.1 11 922 8.1 2273 579 44.7 53 10 42 0.10 0.10 2321 7.4 12 908 7.2 2257 588 41.9 47 10 43 0.44 0.02 2326 8.7 13 922 11.6 2284 587 37.5 62 11 44 0.22 0.05 2325 10.0 13 891 11.0 2255 601 44.0 56 11 45 0.18 0.11 2307 6.4 13 897 9.2 2290 597 46.3 57 11 46 0.01 0.21 2335 6.9 13 910 11.5 2271 590 37.8 48 11 47 0.36 0.07 2319 9.3 11 908 8.6 2253 596 38.3 51 10 48 0.01 0.36 2315 9.8 11 895 11.5 2279 603 32.5 55 10 49 0.44 0.11 2330 8.3 12 905 10.8 2251 594 40.0 59 10 50 0.46 0.07 2277 7.7 12 923 9.6 2249 586 35.6 50 10 51 1.12 0.61 2310 7.7 12 880 11.1 2242 590 40.6 55 10 38 200821393

Table 9 There are pull wires without wires, there is density, tensile stretching, T. Rotation, residual tensile annealing, tensile impact, T, area ratio, strength, elongation, bending, strength, hardness, shrinkage, value, No. %, /μπι2 MPa %, #MPa % MPa HV % J/cm2 # 52 9.2 0.41 2311 L9 11 895 10.2 2242 583 19.3 49 10 53 7.0 0.70 2308 2.1 12 904 8.6 2236 588 16.1 51 11 54 8.7 0.37 2306 2.0 12 924 8.8 2230 590 16.3 52 12 55 7.5 0.61 2275 2.0 12 903 10.1 2243 585 22.2 50 10 56 7.8 0.44 2292 2.0 13 889 9.1 2241 578 19.5 53 11 57 4.8 1.56 2270 8.4 11 890 9.9 2228 590 23.5 20 10 58 7.7 0.71 2280 3.3 13 892 10.7 2224 579 20.0 52 11 59 7.7 0.27 2275 3.8 13 899 11.3 2238 575 17.1 53 11 60 2.4 1.11 2308 3.5 13 912 7.8 2250 598 20.2 20 11 61 8.7 2.23 2271 3.9 11 871 8.3 2235 590 14.9 20 10 62 7.2 0.62 2285 3.3 11 889 11.8 2260 577 15.6 20 10 Comparison 63 0.25 0.39 2298 2.0 13 780 8.0 2232 580 14.5 48 11 64 0.21 0.44 2296 2.1 12 790 7.2 2263 590 21.9 53 11 65 0.08 0.49 2293 2.7 9 911 6.9 2263 550 18.3 19 8 66 0.11 0.40 2316 2.1 11 895 11.5 2260 533 13.3 19 10 67 0.40 0.41 2303 4.1 11 887 7.2 2215 518 14.0 23 10 68 0.43 0.30 2303 2.6 12 900 7.6 2239 522 19.0 23 10 69 1.20 0.02 2306 8.1 13 883 15.5 2231 575 25.9 21 10 70 0.16 0.18 2306 9.8 13 898 16.1 2243 593 25.2 20 11 71 0.06 0.34 2294 7.0 11 907 16.0 2226 592 27.3 20 10 72 0.13 0.39 2275 1.9 8 783 6.3 2231 580 18.3 21 7 73 0.17 0.40 2295 2.7 8 798 10.7 2252 594 22.2 19 7 74 0.12 0.42 2197 10.9 13 748 8.9 2228 542 41.7 51 11 75 0.24 0.24 2260 6.2 12 775 8.3 2213 536 35.5 53 10 76 0.07 0.07 2177 6.7 12 762 10.4 2222 528 39.6 54 10 77 0.16 0.37 2164 10.6 12 737 11.3 2248 552 37.8 57 10 Tables 2 to 9 show the chemical composition of the invention and the carburized system, the lean area ratio of the carburized system, and the possession of the spheroidal carbide of the alloy system/carburizing system when treated by φ 4 mm. Area ratio, round equivalent diameter 0 · 2~3 μ m carburizing system ball 5-shaped carbide exists in density, round equivalent diameter exceeds 3μπι carburizing system spherical carbon 39 200821393 Degree, maximum oxide diameter, old austenite grain number, residual austenite amount (% by mass), tensile strength obtained, hardness after annealing, impact value, and shrinkage measured in tensile test. That is, Tables 2 and 3 show the chemical components of the inventive examples Νο·1 to 25, and Tables 4 and 5 show the composition of the invention Νο·26~51. Table 6 shows the chemical compositions of Comparative Examples Νο·52~77. Next, Table 7 shows inventive examples Ν1·1 to 25, and Table 8 shows the characteristics of each of Invention Examples 26 to 51 with and without a pull wire. Further, Table 9 shows the characteristics of the comparative examples νο·52 to 77 in the presence of the pull wire and the no pull wire. The following is a description of the comparative example. 10 In the invention example, even a heat-treated material having no wire can exhibit good performance in impact resistance and softening resistance and tensile properties after annealing, and further, even the heat-treated material after the wire is included The tensile properties and the carbide distribution in the range were obtained to obtain good performance, but the following examples were outside the definition and thus did not exhibit sufficient performance. 15 Examples 52 and 53 are not containing any of Ti and Nb, and a large amount of V and Cr are added to produce an unmelted carbide having a nitride as a core, so that the shrinkage rate and the tensile line in the tensile test are obtained. The latter extension is lower, resulting in reduced processability. In Examples 54 and 55, although Ti and Nb were added, the unmelted carbide having 20 nitride as the core was generated due to too much N, so the shrinkage ratio in the tensile test and the elongation after the drawing were low, resulting in processing. Reduced sex. Examples 56 to 59 are examples in which N is added and Ti is fixed to TiN, but the amount of ruthenium added is too large, and the disadvantage caused by ΤιΝ is remarkable. Therefore, the distribution of inclusions is increased, and as a result, the shrinkage rate in the tensile test and the elongation after the drawing are low, 40 200821393 causes the workability to decrease. In Example 57, the heating temperature at the time of quenching was lowered, and thus a large amount of undissolved carbide was produced. Examples 60 to 62 are examples in which Nb is added. However, since the amount of addition is too large, many unmelted carbides are observed, and the shrinkage ratio in the tensile test and the elongation after the drawing are low, resulting in a decrease in workability. In the examples 63 and 64, the oxides were increased due to the excessive amount of A1, and the fatigue characteristics were lowered. In the case of Examples 65 and 66, the amount of V added was too small. At this time, the hardness after the annealing of the simulated nitride was extremely low, the grain size of the prior austenite was coarser, and the fatigue property was lowered. In the actual nitriding, compared with the inventive example in which a defined amount of V is added, the surface hardness is not lowered or the nitriding depth is shallow at the same nitriding time, and the performance after the nitriding treatment is different. In Examples 67 and 68, the amount of addition of Cr was too small, and the hardness after annealing of the simulated nitriding was low, and the surface hardened layer during nitriding was thinned to deteriorate the fatigue characteristics. In Examples 69 to 71, the cooling temperature was higher at the time of quenching, and the cooling time was also short. The amount of retained austenite was increased. Therefore, in addition to the insufficient hardness after annealing, practically, some operations were caused by stress. The phase change causes 20 embrittlement and the workability is lowered. In Examples 72 and 73, the heating temperature at the time of quenching was too high, the grain size of the prior austenite was increased, the impact value was lowered, and the fatigue characteristics were lowered. In Examples 74 to 77, when C or Si was less than a defined amount, the tensile strength after annealing was lowered, and the fatigue strength could not be secured. 41 200821393 INDUSTRIAL APPLICABILITY The steel system of the present invention makes the carburization system in the steel wire for cold coiling spring and the occupied area ratio, the existence density, the austenite grain size, and the residual spheroidal carbide of the alloy system. When the amount of the bulk is reduced, the high strength of the strength of 2 〇〇〇]^^^ or more can be achieved, and the coilability can be ensured to produce a spring having high strength and excellent fracture characteristics. [Circular simple description]

10 The West Su system is used to illustrate the effect of reducing the time added (the relationship between tempering temperature and Charpy (the Chalpym hit value). Lai Jingzhi's unsolved line element resolver, (4) shows that the infiltration is not 2 (four) X-ray element analysis example of X. X-ray of each deuterated compound Y [Description of main component symbols] (none) 42

Claims (1)

200821393 X. Patent application scope: 1. A high-strength spring steel containing, by mass%: C: 0.5~0.9%, Si: 1.0~3.0%, -5 Mn: 0·1~1.5%, 'Cr : 1.0 to 2.5%, V: more than 0.15 to 1.0% or less, and A1: 0.005% or less; and the limit N: 0.007% or less, 10 further contains Nb: 0.001 to less than 0.01%, and Ti · · 0.001 to less than 0.005% One or two, the remainder consists of iron and unavoidable impurities. 2. If the high-strength spring steel of the first application of the patent scope is in the mass%, it further contains: 15 W: 0.05 to 0.5%, and Mo: one or two of 0.05 to 0.5%; and contained by mass%: Ni: 0.05 to 3.0%, 20 Cu: 0.05 to 0.5%, Co: 0.05 to 3.0%, and B: 0.0005~ One or more of 0.006%; and contained in mass%: 43 200821393 Te : 0.0002 to 0.01%, Sb: 0.0002 to 0.01%, Mg: 0.0001 to 0.0005%, Zr ·· 0.0001 to 0.0005%, 5 Ca: one or two or more of 0.0002 to 0.01%, and Hf: 0.0002^0.01%. 3. A kind of heat-treated steel wire for high-strength spring, which has the steel component of the first or second item of the patent application, the tensile strength of which is more than 2000 MPa, and the spherical carbide and alloy of the carburizing system occupied by the mirror surface In the case of spheroidal carbides, the content of the spheroidal carbide is less than or equal to 7% or less, and the density of the circle is more than 2 μm 2 or less, and the prior austenite is less than or equal to 2 μm 2 or less. The particle size number is 10 or more, and the retained austenite is 15 15% by mass or less. 44