JP6420656B2 - Spring steel, spring and method for producing them - Google Patents

Description

  The present invention relates to a spring steel suitable for use, for example, as a material for automobile parts, and more particularly to a spring steel and a spring having extremely fine tempered martensite, and a method for producing them.

  For example, tempered martensitic steel is widely used in spring steel, which is a material for automotive parts, from the balance between strength and toughness. In recent years, there has been an increasing demand for higher strength and lower cost of springs. As a technology for achieving high strength and high toughness of low-cost steel that does not depend on the addition of expensive alloying elements, the fineness of tempered martensite grains has been reduced. It is well known that conversion is effective.

  The prior austenite grain size and thus martensite can be refined by appropriately selecting the temperature and holding time in the austenite region at the time of quenching, but there is a limit to refinement by simply selecting the heat treatment conditions. Therefore, various studies have been conducted to obtain a finer martensitic steel material by appropriately selecting the starting structure before the austenite transformation.

  In the technique described in Patent Document 1, the grain size number of the prior austenite is set to ## by holding and quenching a spring steel having a sorbite structure by patenting for a short time (1 to 10 s) in the austenite region. A steel wire having a thickness of 11 to # 15 and a maximum thickness of the block in the tempered martensite being 600 nm or less is disclosed.

  In the technique of Patent Document 2, fine martensite obtained by ausforming a medium-low carbon steel is plastically processed at a tempering temperature to form fine tempered martensite (fine ausformed martensite). Furthermore, the steel material which has the fine martensite whose prior austenite particle size is 1.1-3.0 micrometers is disclosed by hold | maintaining this structure | tissue in an austenite region for 1 second-30 minutes and quenching.

JP 2003-213372 A JP 2002-003943 A

Li Z D, Miyamoto G, Yang Z G, et al. Nucleation of austenite from pearlitic structure in an Fe-0.6C-1Cr alloy.Scr Mater, 2009, 60: 485-488

  Each of the above technologies uses a microstructure having a fine substructure as a structure before quenching, thereby generating fine austenite grains originating from the microstructure at the time of reverse austenite transformation, and obtaining fine martensite by quenching therefrom. It is aimed at. However, in the technique of Patent Document 1, sorbite generated by the patenting process is quenched, and the crystal orientation difference between colonies and lamellar structures in the same block of pearlite constituting this structure is small, and the reverse transformation from pearlite to austenite. It is known that a relatively large block boundary is preferential for the recrystallized nuclei (see Non-Patent Document 1), and there is a limit to the remarkable refinement effect.

  Moreover, in the technique described in Patent Document 2, tempered martensite finely divided by two plastic workings is quenched by reverse transformation to austenite, but the crystal orientation of tempered martensite is a variant selected from austenite grains. The crystal orientation is limited by the law, and crystal grains obtained by reversely transforming tempered martensite to austenite have a high probability of taking the same orientation, and it is difficult to form large-angle grain boundaries. .

  Any prior art pre-quenching structures are affected by the initial coarse austenite grain size and / or crystallographic orientation to obtain it, and when these structures are transformed back to austenite In addition, there remains a common problem that it is difficult to achieve conditions for generating fine austenite grains with random crystal orientations.

  The present invention has been made in view of the above circumstances, and by using a fine grain structure having a random crystal orientation not affected by the prior austenite grains before obtaining the structure as a quenching starting structure, the above-described conventional The object is to provide spring steel with tempered martensite finer than the technology.

  As a result of intensive studies to obtain finer tempered martensite than the conventional ones, the inventors have made it a starting idea to nanosize the structure before heating it to the austenite region for quenching. Was converted into martensite and hot plastic working was performed in a state where the high dislocation density of martensite was maintained, and it was found that equiaxed nanoferrites were generated by dynamic recrystallization using the dislocations as recrystallization nuclei. And by quenching this structure for a very short time, martensite composed of fine prior austenite grain boundaries reflecting the size of nanoferrite grains and its substructure is obtained, and this structure is tempered. As a result, it was found that tempered martensite maintaining the fine prior austenite grain boundaries and the substructure can be obtained.

  The spring steel of the present invention was made based on the above findings, and in mass%, C: 0.10 to 0.90%, Si: 0.10 to 2.50%, Mn: 0.10 to 2 0.000%, Cr: 0.10 to 2.00%, the balance being composed of Fe and inevitable impurities, the structure is composed of martensite or tempered martensite, and the block in the martensite or tempered martensite The average thickness is 200 nm or less. In the following description, the above elements are in the same component range.

  Further, the present invention is a spring steel as an intermediate for producing the spring steel described above, and in mass%, C: 0.10 to 0.90%, Si: 0.10 to 2.50%, Mn : 0.10 to 2.00%, Cr: 0.10 to 2.00%, the balance is composed of Fe and inevitable impurities, the structure is composed of two phases of equiaxed ferrite and spherical cementite, The average crystal grain size of equiaxed ferrite is 1000 nm or less. By quenching the spring steel, martensite having an average block thickness of 200 nm or less can be produced. By tempering the martensite, tempered martensite having an average block thickness of 200 nm or less is produced. be able to.

  In the present invention, in addition to the above composition, Cu: 0.05 to 0.40%, V: 0.05 to 0.25%, Ni: 0.10 to 0.70%, B: 0 to 0.00. One or two or more of 005%, Ti: 0.05 to 0.11%, and Mo: 0.25 to 0.35% can be contained. In the following description, the above elements are in the same component range.

  The present invention is also a spring manufactured from the above spring steel, such as a suspension spring, a valve spring, a clutch damper spring, a disc spring, a stabilizer, or a torsion bar. Of the various springs as described above, those that can be composed of martensite depending on the components of the spring steel to be used can be increased in strength and toughness by refining crystal grains, and the present invention can be applied. .

Next, this invention is a manufacturing method of the said spring steel, Comprising: In mass%, C: 0.10-0.90%, Si: 0.10-0.50%, Mn: 0.10-2 A quenching step of quenching a steel material having a composition of 0.000%, Cr: 0.10 to 2.00%, the balance being Fe and inevitable impurities from an austenite region of Ac3 point or higher to produce martensite; The steel material is heated to 500 to 650 ° C. at a rate of 2 ° C./second or more, held for 0 to 5 seconds, and then subjected to a hot plastic working step of performing plastic working with an equivalent strain of 0.7 or more. To do. This manufacturing method is a method for manufacturing an intermediate for manufacturing the spring steel of the present invention.

Furthermore, the present invention is another method for producing the spring steel, wherein the temperature of the spring steel produced by the production method is increased to austenite region of Ac3 point or higher at a rate of 25 ° C./second or more. It is characterized by performing an extremely short time quenching step of rapidly cooling after holding for 2 seconds and generating fine martensite, and a tempering step of heating and holding the spring steel. Depending on the component (for example, C amount) of the spring steel, it may be used as it is. In that case, the tempering step can be omitted.

  According to the present invention, since the average thickness of blocks in martensite or tempered martensite is 200 nm or less, it is possible to achieve high strength and high toughness of inexpensive steel that does not depend on the addition of expensive alloy elements, etc. The effect is obtained. Moreover, according to this invention, the spring steel which can manufacture the above martensites or tempered martensites can be obtained.

It is a figure which shows the manufacturing process of the spring steel of embodiment. It is a figure which shows the EBSD-IPF map in the Example of this invention. It is a figure which shows the EBSD-IPF map in the comparative example of this invention. It is a figure which shows the EBSD-IPF map in the other comparative example of this invention.

  Hereinafter, embodiments of the method for producing spring steel of the present invention will be described together with the grounds for limiting the numerical values of the present invention. In the following description, “%” means “mass%”.

1. Material component C: 0.10 to 0.90%
C contributes to strength improvement. If the C content is less than 0.10%, the effect of improving the strength cannot be obtained sufficiently, so that the fatigue resistance and sag resistance are insufficient. On the other hand, when the content of C exceeds 0.90%, the toughness is lowered and cracking is likely to occur. For this reason, content of C shall be 0.10-0.90%.

Si: 0.10 to 2.50%
Si is effective for deoxidation of steel and contributes to improvement of strength and resistance to temper softening. If the Si content is less than 0.10%, these effects cannot be obtained sufficiently. On the other hand, if the Si content exceeds 2.50%, the toughness is lowered and cracks are likely to occur, and decarburization is promoted to cause a reduction in the wire surface strength. For this reason, content of Si shall be 0.10-2.50%.

Mn: 0.10 to 2.00%
Mn contributes to improvement of hardenability. If the Mn content is less than 0.10%, it becomes difficult to ensure sufficient hardenability, and the effect of S fixation (MnS generation) that is harmful to ductility becomes poor. On the other hand, when the content of Mn exceeds 2.00%, ductility is lowered and cracks and surface scratches are likely to occur. For this reason, content of Mn shall be 0.10 to 2.00%.

Cr: 0.10 to 2.00%
Cr is effective in preventing decarburization, contributes to improvement in strength and resistance to temper softening, and is effective in improving fatigue resistance. It is also effective in improving warm sag resistance. If the Cr content is less than 0.10%, these effects cannot be sufficiently obtained. On the other hand, when the content of Cr exceeds 2.00%, the toughness decreases, and cracks and surface scratches are likely to occur. For this reason, in this invention, content of Cr shall be 0.10 to 2.00%.

These additive elements are the minimum necessary elements for constituting the present invention, and other elements may be further added. That is, in the present invention, Cu: 0.05 to 0.40%, Ni : 0.10 to 0.70%, B: B: more than 0 %, which is generally used as a component composition of spring steel One or more of 0.005% or less , Ti: 0.05 to 0.11%, Mo: 0.25 to 0.35% can be contained.

2. Manufacturing Method FIG. 1 is a view showing a manufacturing process of the spring steel of the embodiment. In the manufacturing process shown in this figure, quenching of steel, hot plastic working, extremely short time quenching, and tempering are sequentially performed. Hereinafter, these manufacturing processes will be described.

2-1. Quenching First, a steel material having an arbitrary structure such as a wrought material is heated to an austenite region of Ac3 point or higher and held for a sufficient time for the structure to transform into austenite. Next, first quenching is performed in which martensite is generated by quenching from the austenite region. By this quenching, the hardness of the steel material is set to 700 to 750 HV, for example.

-Cooling rate from austenite region In this quenching, the cooling rate is arbitrary as long as austenite can be transformed into martensite. For example, a steel material containing 0.85% Mn can be set to 100 ° C./second or more, and a steel material containing 0.30% Mn can be set to 300 ° C./second or more. The cooling method is arbitrary. For example, the steel material heated in the austenite region can be immersed in oil or water, or water mist can be jetted onto the steel material for rapid cooling.

2-2. Next, hot plastic working is performed on the steel material. Hot plastic working is rolling, forging, extrusion, drawing, etc., for example. In hot plastic working, equiaxed nanoferrite is generated by using recrystallization as a recrystallization nucleus by dynamic recrystallization from a state where a high dislocation density of martensite is maintained. Therefore, unlike the technique described in Patent Document 2, there is no influence of the grain size and crystal orientation of the prior austenite generated during the first quenching. By this hot plastic working, a two-phase structure of equiaxed ferrite having an average crystal grain size of 1000 nm or less and spherical cementite is formed, and an intermediate for manufacturing the spring steel of the present invention is manufactured. In this hot plastic working, in order to work from a state where the dislocation density of martensite is maintained as much as possible, the heating rate is fast and the holding time is shortened as follows.

(1) Temperature rise rate in hot plastic working: 2 ° C./second or more The temperature rise rate up to the hot plastic working temperature is 2 ° C./second or more in order to maintain the dislocation density of martensite.

(2) Heating temperature in hot plastic working: 500-650 ° C
When the heating temperature is less than 500 ° C., processing with an equivalent strain of 0.7 or more, which will be described later, becomes impossible due to material cracking due to the processing limit. On the other hand, when the heating temperature exceeds 650 ° C., it becomes difficult to obtain equiaxed ferrite having an average particle size of 1000 nm or less due to the disappearance of dislocations and grain growth. Therefore, the heating temperature for hot plastic working is set to 500 to 650 ° C.

(3) Holding time from reaching the heating temperature to the start of processing: 0 to 5 seconds When the heating temperature for hot plastic processing is reached, plastic processing is started within 5 seconds. If it exceeds 5 seconds, it will be difficult to obtain equiaxed ferrite having an average particle size of 1000 nm or less due to the disappearance of dislocations and grain growth. By this hot plastic working, dynamic recrystallization occurs and equiaxed nanoferrite having an average particle diameter of 1000 nm or less is generated with dislocations as recrystallization nuclei. When the processing is completed, it is desirable to cool the steel material by putting it in water. The average particle diameter of equiaxed ferrite is a circle-equivalent mean particle diameter obtained by determining the diameter of a circle from the area of equiaxed ferrite.

(4) Equivalent strain: 0.7 or more In hot plastic working, the equivalent strain is 0.7 or more. When the equivalent strain is less than 0.7, the dynamic recrystallization using the intragranular dislocations of martensite as the recrystallization nucleus is poor, and it becomes difficult to produce equiaxed nanoferrites.

2-3. Extremely short time quenching Spring steel having a two-phase structure of equiaxed ferrite and spherical cementite is heated to an austenite region of Ac3 or higher, and when it reaches the heating temperature, it is rapidly cooled as soon as possible to transform into martensite. By transforming equiaxed ferrite grains with fine random and completely random crystal orientation into austenite, fine austenite reflecting the ferrite grain size before transformation is generated, and further quenched to form fine martensite.

(1) Temperature rise rate in quenching for a very short time: 25 ° C./second or more The temperature rise rate is 25 ° C./second or more to prevent nanoferrite and austenite crystal grains reversely transformed from nanoferrite from coarsening.

(2) Heating temperature in extremely short time quenching The heating temperature in very short time quenching is the austenite region of Ac3 point or higher, and the two-phase structure of nanoferrite and spherical cementite is completely austenite. The heating temperature can be set to 850 to 900 ° C., for example.

(3) Time from reaching the heating temperature to cooling: 0 to 2 seconds When reaching the heating temperature for quenching, quench within 0 to 2 seconds. Thus, by quenching in an extremely short time, coarsening of austenite crystal grains can be prevented. In order to completely transform austenite into martensite, the rapid cooling rate can be, for example, a steel material containing 0.85% Mn at 100 ° C./second or more, and a steel material containing 0.30% Mn is It may be 300 ° C./second or more. The cooling method is arbitrary. For example, the steel material can be rapidly cooled by immersing the steel material in water or oil, or by jetting water mist on the steel material.

2-4. Tempering For tempering, optimum tempering conditions can be arbitrarily selected for each application as a spring. For example, in the case of spring steel for automobile suspension springs, it can be held at 390 to 420 ° C. for 60 minutes. By this tempering, tempered martensite maintaining the fine prior austenite grain boundaries reflecting the nanoferrite crystal grain size can be obtained. Depending on the spring steel components, tempering can be omitted and the steel can be used after being quenched for a very short time. The structure in this case is martensite, and the average thickness of the block of the structure is 200 nm or less.

3. Molding When molding a coil spring having a large ratio of coil diameter to wire diameter, molding is performed after extremely short time quenching or tempering. On the other hand, when forming a coil spring having a small ratio of the coil diameter to the wire diameter or a spring that requires pressing, cutting, plastic working, etc., the forming is performed after the hot plastic working. And after shaping | molding, it quenches for a short time and tempering as needed.

1. Production Conditions The present invention will be described in more detail below with reference to examples.
Steel materials A to F (stretched materials) made of the chemical components shown in Table 1 were heated to 900 ° C. and held for 10 minutes, and then poured into oil and quenched. Next, hot plastic working was performed on the steel materials A to F under the conditions shown in Table 2. The hot plastic working was forging, and a steel material having a height of 12 mm was compressed once to a height of 6 mm or less. Next, the steel materials A to F having a two-phase structure of equiaxed ferrite and spherical cementite were quenched for a very short time under the conditions shown in Table 2 and then tempered at 415 ° C. for 60 minutes. Thus, samples of Production Examples 1 to 14 were produced.

  A sample of Comparative Example 1 was produced under the same conditions as in Production Example 1 except that only the heating was performed without performing the plastic working in the hot plastic working. Moreover, the sample of Comparative Examples 2-7 was obtained by quenching and tempering a general wrought steel material composed of a mixed structure of ferrite and pearlite and having the same components as the steel materials A to F under normal conditions. It was. For example, in the case of the steel material A, the steel material was heated to 940 ° C. at a temperature increase rate of 2 ° C./second and held for 10 minutes, and then poured into oil for quenching. Moreover, in tempering, it hold | maintained at 415 degreeC for 60 minutes.

2. Measuring method [Grain size after hot plastic working]
Observe the structure of the samples of Production Examples 1 to 14 using a FE-SEM analyzer (Field Emission Scanning Electron Microscopy, JSM-7000F manufactured by JEOL Ltd.) and use the dedicated image analysis software to crystal equiaxed ferrite. The particle size was determined. In this case, when the tilt angle of the crystal orientation is 5 degrees or more, the boundary is the grain boundary, and when it is less than 5 degrees, the boundary is within the same crystal grain. The crystal grain size was measured for 1000 or more crystal grains per field of view. This crystal grain size is a value converted from the area of equiaxed ferrite to the diameter of a circle. The average crystal grain size of the equiaxed ferrite thus obtained is also shown in Table 2.

[Tempered martensite crystal grain size]
The old austenite grain boundaries of tempered martensite in the samples of Production Examples 1-14 and Comparative Examples 1-7 were observed with the FE-SEM analyzer, and the crystal grain size of the prior austenite was determined by the counting method of JIS G 0551. The crystal grain size was measured by adjusting the magnification so that 50 or more crystal grains were taken into the circle region. The average crystal grain size of the prior austenite thus obtained is also shown in Table 2.

[Average thickness of blocks in tempered martensite]
A block in the tempered martensite is identified from the EBSD-IPF maps of the samples of Production Examples 1 to 14 and Comparative Examples 1 to 7 using an EBSD analyzer (Electron Backscatter Diffraction, OSL Ver.5.31 manufactured by TSL Co., Ltd. is used). The thickness of the block was obtained by analysis. The measurement conditions at this time were acceleration voltage: 15 kV, CL: 12, WD: 20 mm, and measurement step: 0.050 μm. In this case, when the tilt angle of the crystal orientation is 5 degrees or more, the boundary is defined as a block boundary, and when it is less than 5 degrees, the boundary is within the same block. In addition, each block was elliptically approximated by the image analysis software for 1000 or more blocks per field of view, the short axis length was defined as the block thickness, and the average thickness was measured. The grain at the edge of the map was excluded from the analysis. The above measurement results are also shown in Table 2. In Table 2, values that depart from the scope of the present invention are underlined.

3. Evaluation As shown in Table 2, in Production Examples 1 to 7 that satisfy all the production conditions of the present invention, the average grain size of equiaxed ferrite after hot plastic working is 1000 nm or less, and the average thickness of the block is 200 nm or less. became. Moreover, the average crystal grain size (old austenite average grain size) of tempered martensite became 1000 nm or less. Therefore, in Production Examples 1 to 7, it is inferred that the balance between strength and toughness is good.

  Production Examples 15 and 16 are examples in which tempering was not performed in Production Examples 1 and 2. Tempering mainly has the effect of recovery of dislocations in martensite and precipitation of carbides, so that the crystal orientation and grain boundaries are approximately maintained before and after tempering. Therefore, in Production Examples 15 and 16 in which tempering is not performed, the old austenite average particle diameter and the average thickness of the blocks are Production Examples 1 and 2 or less, the old austenite average particle diameter is 1000 nm or less, and the block average thickness is 200 nm or less. It became. Therefore, it is presumed that the balance between strength and toughness is good even when tempering is omitted.

  On the other hand, in Comparative Example 1, equiaxed ferrite was not generated because hot plastic working was not performed. As a result, the average thickness of the block exceeded 400 nm, and the average crystal grain size of tempered martensite was 1000 nm. Beyond.

  Further, in Comparative Examples 2 to 7 in which ordinary tempered materials were normally quenched and tempered, fine equiaxed ferrite was not used, so the average thickness of the block exceeded 400 nm, and the average crystal grain size of tempered martensite was It exceeded 1000 nm.

  2 is an EBSD-IPF map in Production Example 1, FIG. 3 is an EBSD-IPF map in Comparative Example 1, and FIG. 4 is an EBSD-IPF map in Comparative Example 2. From comparison of these figures, it can be seen that the spring steel of the present invention (FIG. 2) has very fine crystal grains.

  Next, in Production Example 8 where the rate of temperature increase in hot plastic working is less than 2 ° C./second, the dislocation density of martensite is not maintained, so the average grain diameter of equiaxed ferrite after hot plastic working is 1000 nm. Exceeded. As a result, the average thickness of the block increased slightly and exceeded 200 nm, and the average crystal grain size of tempered martensite exceeded 1000 nm.

  In Production Example 9 where the time from reaching the heating temperature to the start of processing exceeds 5 seconds, the average particle diameter of equiaxed ferrite after hot plastic working is 1000 nm because of the disappearance of dislocations and grain growth in martensite. Beyond. As a result, the average thickness of the block slightly increased and exceeded 200 nm, and the average crystal grain size of tempered martensite exceeded 1000 nm.

  In Production Example 10 in which the heating temperature in the hot plastic working is less than 500 ° C., cracking occurred in the material when processing with an equivalent strain of 0.7 was performed. On the other hand, in Production Example 11 where the heating temperature exceeded 650 ° C., the average grain diameter of equiaxed ferrite exceeded 1000 nm due to the disappearance of dislocations and grain growth. As a result, the average thickness of the block slightly increased and exceeded 200 nm, and the average crystal grain size of tempered martensite exceeded 1000 nm.

  In Production Example 12 in which the equivalent strain in hot plastic working was less than 0.7, equiaxed ferrite was not generated because of the lack of dynamic recrystallization using relocation nuclei in the intragranular dislocations of martensite. As a result, the average thickness of the block exceeded 200 nm, and the average crystal grain size of the tempered martensite exceeded 1000 nm.

  In Production Example 13 in which the rate of temperature increase in extremely short-time quenching is less than 25 ° C./second, and Production Example 14 in which the time from reaching the heating temperature to cooling exceeds 2 seconds, from nanoferrite and nanoferrite The reverse transformed austenite crystal grains became coarse, the average thickness of the block exceeded 200 nm, and the average crystal grain size of tempered martensite exceeded 1000 nm.

  The present invention is applicable to suspension springs for automobiles, valve springs, clutch damper springs, disc springs, stabilizers, torsion bars, and the like.

Claims (11)

  In mass%, C: 0.10 to 0.90%, Si: 0.10 to 2.50%, Mn: 0.10 to 2.00%, Cr: 0.10 to 2.00%, the balance being A spring steel having a composition comprising Fe and inevitable impurities, having a structure composed of martensite or tempered martensite, and an average thickness of blocks in the martensite or tempered martensite being 200 nm or less.   The spring steel according to claim 1, wherein an average thickness of blocks in the martensite or the tempered martensite is 150 nm or less.   In mass%, C: 0.10 to 0.90%, Si: 0.10 to 2.50%, Mn: 0.10 to 2.00%, Cr: 0.10 to 2.00%, the balance being A spring steel having a composition composed of Fe and inevitable impurities, the structure is composed of two phases of equiaxed ferrite and spherical cementite, and the mean crystal grain size of the equiaxed ferrite is 1000 nm or less. In addition to the above components, Cu: 0.05 to 0.40%, Ni : 0.10 to 0.70%, B: more than 0 % and 0.005% or less , Ti: 0.05 to 0.11% Mo: From 0.25 to 0.35%, 1 type or 2 types or more are contained, The spring steel in any one of Claims 1-3 characterized by the above-mentioned. In mass%, C: 0.10 to 0.90%, Si: 0.10 to 2.50%, Mn: 0.10 to 2.00%, Cr: 0.10 to 2.00%, the balance being A steel material having a composition composed of Fe and inevitable impurities is quenched from an austenite region at Ac3 or higher to produce martensite, and the steel material is heated to 500 to 650 ° C at a rate of 2 ° C / second or more. And holding the steel material for 0 to 5 seconds and then performing a plastic working process with an equivalent strain of 0.7 or more, and raising the temperature of the steel material to the austenite region of the Ac3 point or more at a rate of 25 ° C./second or more. The method for producing spring steel according to claim 1, wherein after holding for 2 seconds, a quenching process is performed in which the steel is rapidly cooled to produce fine martensite.   The method for producing spring steel according to claim 5, wherein a tempering step of heating and holding the steel material is performed after the ultra-short time quenching step. In mass%, C: 0.10 to 0.90%, Si: 0.10 to 2.50%, Mn: 0.10 to 2.00%, Cr: 0.10 to 2.00%, the balance being A steel material having a composition composed of Fe and inevitable impurities is quenched from an austenite region at Ac3 or higher to produce martensite, and the steel material is heated to 500 to 650 ° C at a rate of 2 ° C / second or more. A method for producing spring steel according to claim 3, wherein a hot plastic working step of performing plastic working with an equivalent strain of 0.7 or more is performed after holding for 0 to 5 seconds.   The method for producing spring steel according to claim 5 or 6, wherein the ultra-short time quenching step is performed by high frequency heating.   The method for producing spring steel according to any one of claims 5 to 8, wherein the hot plastic working step is performed by any of rolling, drawing, extrusion, or forging. A spring comprising the spring steel according to any one of claims 1 to 4. The spring according to claim 10 , wherein the spring is a suspension spring, a valve spring, a clutch damper spring, a disc spring, a stabilizer, or a torsion bar.

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