JP2004300458A - Steel for high-frequency induction hardening superior in low-temperature impact resistance at high-frequency induction hardened portion, and steel bar - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a low-temperature impact resistance at a high-frequency induction hardened portion, while maintaining a high quenching hardness of the high-frequency induction hardened portion. <P>SOLUTION: The steel having the low-temperature impact resistance balanced with the high quenching hardness of the high-frequency induction hardened portion comprises 0.30-0.5% C, 0.01% or more but less than 0.40% Si, 0.05-1.5% Mn, 0.06% or less (excluding 0%) S, 0.010% or less (excluding 0%) P and the balance Fe with unavoidable impurities. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００４６】
【表２】

【００４７】
表１〜２及び図４〜５から明らかなように、Ｓ及びＰを所定量以下に制限すると、歯部の低温靭性が急激に改善される。なお割れ発生速度を所定値以上（例えば５ｋｍ／秒以上）とすることをも目的とする場合には、表１〜２及び図６から明らかなように、硫化物系介在物を少なくする必要がある。
【００４８】
なお実験Ｎｏ．１３より明らかなように、Ｃ量が不足すると歯部硬さも不足する。また実験Ｎｏ．２８より明らかなように、Ｓｉが過剰になると割れ発生速度が所定値未満（例えば５ｋｍ／秒未満）となる。
【００４９】
【発明の効果】
本発明によれば、高周波焼入部硬さを確保するために所定量のＣ、Ｓｉ、及びＭｎが添加された特定の成分系の鋼において、Ｓ及びＰを所定量以下に低減しているため、低温耐衝撃特性を著しく向上することができる。
【図面の簡単な説明】
【図１】図１は実施例の試験片の概略上面図である。
【図２】図２は実施例の試験片の概略正面図である。
【図３】図３は実施例の試験片の概略側面図である。
【図４】図４はＳ量と割れ発生速度との関係を示すグラフである。
【図５】図５はＰ量と割れ発生速度との関係を示すグラフである。
【図６】図６は硫化物系介在物の個数と割れ発生速度との関係を示すグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a steel for induction hardening excellent in low-temperature impact resistance of an induction hardened part useful for manufacturing an induction hardened part such as a steering rack and a gear (particularly, a part whose teeth are induction hardened). The present invention relates to a steel bar, and an induction hardened component manufactured from the steel for induction hardening, the steel bar or the like.
[0002]
[Prior art]
Parts having teeth such as steering racks and gears are induction hardened to increase wear resistance and the like. For example, the teeth of the steering rack are increased in hardness to about 600 HV. By the way, in general, as the hardness of steel increases, the impact resistance decreases, but in recent years, despite the fact that it has a high tooth hardness, there is a demand for parts that can also have excellent impact resistance. ing. If the impact resistance can be enhanced, it is possible to prevent cracks in the teeth even when the vehicle rides on a curb.
[0003]
In particular, the steering rack is a component that determines the traveling direction of the vehicle, and if the teeth are broken, it becomes difficult to control the traveling direction. Therefore, it is strongly required that both high tooth hardness and excellent tooth impact resistance be achieved. In addition, since the impact resistance tends to decrease as the temperature becomes lower, there is a demand for a component that can achieve excellent tooth impact resistance even in an extremely cold region such as North America where the temperature is about -40 ° C. I have. In recent automobiles, the power steering unit has shifted from hydraulic control to electric control. In the case of hydraulic control, the steering rack is warmed by a high oil temperature. However, since such warming cannot be expected in electric control, the demand for improving the shock resistance at low temperatures is further increasing.
[0004]
Patent Literature 1 discloses a high-toughness non-heat treated steel for direct cutting. However, high toughness referred to in this document means that toughness comparable to that of tempered material can be maintained without quenching and tempering after rolling. There is no teaching about. Further, this non-heat-treated steel does not add much alloying elements such as Cr, V, and Nb, but does not consider P.
[0005]
Patent Document 2 discloses a non-heat treated steel bar having excellent low-temperature toughness. However, this document also attempts to solve the problem that low temperature toughness is inferior to tempered steel when tempering of ferritic / pearlite type steel is omitted, and the low temperature toughness is exceptional. Not something. This non-heat treated steel also contains Cr, V, and the like, but does not consider P.
[0006]
Patent Literature 3 discloses a high-strength, high-toughness non-heat treated steel material, and describes that it is used for automobile parts and mechanical structural parts. However, the high toughness referred to in this document also means that the toughness reduction when the conventional tempered steel is made to be a non-heat treated steel can be improved, and the impact resistance characteristics at the time of induction hardening, the low temperature impact resistance characteristics, etc. There is no teaching. Further, a large amount of Cu, Ni, V, etc. is added to this non-heat treated steel. In Patent Document 3, as comparative examples, C: about 0.3 to 0.4%, Si: 0.22%, Mn: about 0.8%, S: about 0.02%, Al: about 0 A steel with a P content of 0.008% or 0.016% is disclosed in steel of 0.025% (Steel X, Y). However, these steels X and Y are comparative examples and are steels denied to be used for automobile parts and mechanical structural parts. Moreover, the toughness when P is as large as 0.016% (steel X; uE ₂₀ = 107 to 146 J /) is higher than the toughness when P is as small as 0.008% (steel Y; uE ₂₀ = 90 to 115 J / cm ² ). cm ² ) is better.
[0007]
Patent Document 4 contains Si: 0.40 to 1.50% and Nb: 0.005 to 0.050%, and is manufactured by performing hot rolling, quenching, and tempering under predetermined conditions. A high-hardness wear-resistant steel excellent in low-temperature toughness is disclosed. According to this document, it is necessary to reduce the grain size in order to obtain toughness with a high-hardness material of HB500 or more. However, since high toughness cannot be obtained with as-quenched material, low-temperature tempering is necessary. Teach that it is necessary to suppress temper embrittlement and temper softening by adding Si and Nb in combination. Further, this document teaches that P ≦ 0.010% and S ≦ 0.005% assuming that P and S are harmful impurities that lower the low-temperature toughness. However, the low-temperature toughness described in Patent Document 4 is only the low-temperature toughness of a quenched and tempered steel. When induction hardening is performed, the grain size of the induction hardened structure becomes extremely fine (for example, the grain size number is at least 10 or more), so that the toughness is better than that of normal quenched and tempered steel. In the case of induction hardening steel in which the crystal grain size is fine and the toughness is originally high, as to how to improve the impact resistance at low temperature, Patent Document 4 does not disclose any method. There is no place to teach. Moreover, in the examples section of Patent Document 4, the amounts of P and S are always small, and there is no teaching about the criticality. Further, Cr, Ti, Mo and the like are added to the steel of Patent Document 4.
[0008]
Patent Literature 5 discloses a structural / structural high-strength steel having high toughness. However, the toughness described in this document is also the toughness as a normal quenched and tempered material, and there is no teaching about the toughness (particularly low-temperature toughness) of the induction hardened portion where the toughness behavior differs. In addition, Ta is added to the steel of Patent Document 5. This reference discloses a steel having C: 0.32%, Si: 0.30%, Mn: 0.67%, P: 0.007%, and S: 0.018% as comparative materials. However, as is apparent from the comparative example, the use of the steel was denied.
[0009]
As described above, the steels of Patent Literatures 1 to 5 are not steels for induction hardening, and thus do not teach how low-temperature impact resistance of the induction hardened portion is.
[0010]
On the other hand, Patent Document 6 discloses an induction hardening steel. Further, Patent Document 6 discloses that P and S reduce toughness, that is, P is set to 0.010% or less and S is set to 0.030% or less. However, Patent Document 6 is an invention for improving the fatigue limit, and the effects of P and S on the toughness and the amount thereof are only described from the viewpoint of improving the fatigue limit. Therefore, there is no teaching in Patent Document 6 for improving the low-temperature impact resistance of the induction hardened portion. In Patent Document 6, in order to obtain high surface strength by induction hardening, the content of Si is set to 0.40% or more, and specifically, about 1% is added.
[0011]
[Patent Document 1]
Japanese Patent No. 3036061 (Claim 1, page 2, left column, lines 8-11)
[Patent Document 2]
JP-A-6-17126 (Claims 1-2, paragraphs 0006, 0009, 0041)
[Patent Document 3]
JP-A-2002-160285 (Claim 1, paragraphs 0002 to 0007, Table 1-1, Table 1-2, Table 2-2)
[Patent Document 4]
Japanese Patent Application Laid-Open No. 8-41535 (Claim 1, Paragraph 0009, Paragraph 0013, Examples)
[Patent Document 5]
JP-B-39-28873 (Claim 1, page 2, right column, third line, table 1)
[Patent Document 6]
JP-A-60-169544 (Claim 1, page 3, upper left line 6 to upper right line 3, page 2, upper right column line 20 to lower left column line 4, line 5 lower left column line 12, Upper right column, 4th line)
[0012]
[Problems to be solved by the invention]
An object of the present invention is to improve the low-temperature impact resistance of the induction-quenched portion while maintaining the high quenching hardness of the induction-quenched portion. The present invention is to provide an induction hardened part manufactured from the company.
[0013]
[Means for Solving the Problems]
The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, in order to secure the induction hardened portion hardness, a predetermined amount of C, Si, and Mn-added steel of a specific component system added. Surprisingly, they found that S and P had a very large effect on the low-temperature impact resistance, that is, only by reducing S and P, the low-temperature impact resistance sharply improved at a certain value. Completed the invention. As far as the present inventors know, steel of the above-mentioned specific component is used for induction hardened parts (particularly, induction hardened parts requiring low-temperature toughness, such as steering racks and gears used in extremely cold regions). There is no example.
[0014]
That is, the steel for induction hardening, which is excellent in the low-temperature impact resistance of the induction hardened portion according to the present invention, has C: 0.30 to 0.5% (mean% by mass, the same applies hereinafter), and Si: 0.01%. Above, less than 0.40%, Mn: 0.05 to 1.5%, S: 0.06% or less (excluding 0%), P: 0.010% or less (excluding 0%) The gist is that the balance consists of Fe and unavoidable impurities (for example, 0.05% or less of Al and 0.02% or less of N). This induction hardening steel further contains Pb: 0.3% or less (excluding 0%), Bi: 0.2% or less (excluding 0%), Te: 0.1% or less (0%). , Mg: 0.01% or less (excluding 0%), Ca: 0.01% or less (excluding 0%), REM: 0.01% or less (excluding 0%), Zr: 0.3% or less (not including 0%) may be appropriately contained. Preferred steel for induction hardening is one having an average of 22 or less sulfide-based inclusions having a major axis of 30 μm or more per 2 mm × 2 mm field of view. The portion of the sulfide-based inclusions having a depth D / 8 in the direction is as described above.
[0015]
The present invention also includes an induction hardened part obtained from the steel for induction hardening (such as a steel bar).
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
The steel for induction hardening of the present invention contains predetermined amounts of C, Si, Mn, P, and S, with the balance being Fe and unavoidable impurities. Hereinafter, the amounts of the respective components and the reasons for the limitations will be described.
[0017]
C: 0.30-0.5%
C is an element necessary to secure the hardness of the induction hardened portion. The C content is at least 0.30%, preferably at least 0.33%, more preferably at least 0.35%, especially at least 0.38%. On the other hand, when C is excessive, it becomes brittle and the fatigue strength decreases. Therefore, C is set to 0.5% or less, preferably 0.48% or less, and more preferably about 0.45% or less.
[0018]
Si: 0.01% or more and less than 0.40% Si is an element necessary for improving the hardenability and ensuring the hardness of the induction hardened portion. The amount of Si is 0.01% or more, preferably 0.1% or more, more preferably 0.15% or more, and particularly 0.18% or more. On the other hand, when Si is excessive, not only does the machinability deteriorate, but also the low-temperature impact resistance decreases. Therefore, the Si content is less than 0.40%, preferably 0.35% or less, and more preferably 0.30% or less.
[0019]
Mn: 0.05-1.5%
Mn is also an element necessary for improving hardenability. The Mn content is at least 0.05%, preferably at least 0.3%, more preferably at least 0.5%, especially at least 0.7%. On the other hand, if Mn is excessively added, burning cracks may occur. Therefore, the Mn content is 1.5% or less, preferably 1.3% or less, more preferably 1.0% or less.
[0020]
S: 0.06% or less (excluding 0%)
S is a very important element for the present invention. Conventionally, S is known as an element that lowers toughness, but its relationship with low-temperature impact resistance is not known. Even more, low-temperature impact resistance sharply improves at a predetermined S content. That was a complete surprise. Considering this criticality, the amount of S is set to 0.06% or less, preferably 0.058% or less, and more preferably 0.055% or less. On the other hand, setting S to 0% involves technical difficulty. In addition, since S forms sulfide-based inclusions with Mn and improves machinability, it is preferable that S is large from this viewpoint. Therefore, the S content is more than 0%, preferably 0.01% or more, more preferably 0.03% or more, particularly 0.04% or more (for example, 0.045% or more).
[0021]
P: 0.010% or less (excluding 0%)
P is an extremely important element for the present invention, like S. It was completely surprising that the low-temperature impact resistance sharply improved at a predetermined P amount. Considering this criticality, the P content is set to 0.010% or less, preferably 0.009% or less, and more preferably 0.008% or less. On the other hand, if P is excessively reduced, the effect is saturated, and the cost of removing P only increases. Therefore, the P content is more than 0%, preferably 0.003% or more, more preferably 0.005% or more, and particularly 0.007% or more.
[0022]
Inevitable impurities The inevitable impurities include those derived from raw materials (such as iron ore), those derived from pig iron and steelmaking methods, those derived from recycled steel, and the like, such as Al, N, and O. It is a target. Since Al and N are particularly important, they are preferably set in the following ranges.
[0023]
Al: 0.05% or less (excluding 0%)
Al is sometimes added for deoxidation, and in such a case, it always remains in the steel. However, when the amount of Al increases, the amount of oxide-based inclusions increases and the fatigue characteristics deteriorate. Although the reason is not clear, there is a tendency that as the amount of Al increases, the low-temperature toughness decreases. Therefore, the Al content is preferably 0.05% or less, more preferably 0.03% or less, and particularly preferably 0.025% or less.
[0024]
N: 0.02% or less (excluding 0%)
When N is increased, hot workability is reduced, and surface defects of the steel material are increased. Although the reason is not clear, low-temperature toughness tends to decrease as N increases. Therefore, the N content is preferably 0.02% or less, more preferably 0.01% or less, and particularly 0.008% or less. It is technically difficult to set N to 0%. In addition, it is desirable to increase the amount of N from the viewpoint of improving the chip disposability during cutting. Therefore, the N content is, for example, 0.001% or more, preferably 0.003% or more, and more preferably 0.004% or more.
[0025]
The steel as described above is the most preferable steel from the viewpoint of production cost because it can achieve both the hardness of the induction hardened portion and the low-temperature impact resistance, despite the small number of components. Further, if necessary, other elements such as Pb, Bi, Te, Mg, Ca, REM, Zr, etc. may be added alone or in combination of two or more. These elements contribute to improving the machinability of steel. Preferred addition amounts are as follows.
[0026]
Pb: 0.3% or less (excluding 0%)
Bi: 0.2% or less (excluding 0%)
If Pb and Bi (and Te, which will be described later) are added excessively, flaws are likely to occur during rolling, so it is desirable to add Pb and Bi while paying attention to this point. Pb is, for example, 0.3% or less, preferably 0.2% or less, and more preferably 0.1% or less. Bi is, for example, 0.2% or less, preferably 0.15% or less, and more preferably 0.1% or less. On the other hand, from the viewpoint of improvement in machinability, it is more desirable. Therefore, Pb is, for example, 0.01% or more, preferably 0.03% or more, and more preferably 0.05% or more. Bi is, for example, 0.01% or more, preferably 0.03% or more, and more preferably 0.05% or more.
[0027]
These Pb and Bi (and Te described later) can be added alone or in combination.
[0028]
Mg: 0.01% or less (excluding 0%)
Ca: 0.01% or less (excluding 0%)
REM: 0.01% or less (excluding 0%)
Zr: 0.3% or less (excluding 0%)
Te: 0.1% or less (excluding 0%)
Mg, Ca, and REM are difficult to remain in the steel even if added in large amounts, and the effect is saturated even if Zr is added in large amounts, so that all of them increase the cost. Therefore, Mg is, for example, 0.01% or less, preferably 0.005% or less, and more preferably 0.003% or less. Ca is, for example, 0.01% or less, preferably 0.005% or less, and more preferably 0.003% or less. REM is, for example, 0.01% or less, preferably 0.005% or less, and more preferably 0.003% or less. Zr is, for example, 0.3% or less, preferably 0.2% or less, and more preferably 0.1% or less.
[0029]
As in the case of Pb and Bi, if Te is excessively added, flaws are likely to occur during rolling. Therefore, Te is, for example, 0.1% or less, preferably 0.05% or less, and more preferably 0.02% or less.
[0030]
On the other hand, Mg, Ca, REM, Zr, and Te are preferably as large as possible from the viewpoint of improving machinability. In particular, since Ca, Zr, and Te make MnS spherical, the length of the sulfide-based inclusions can be shortened (the advantages of this will be described in detail later). Therefore, Mg is, for example, 0.0001% or more, preferably 0.0005% or more, and more preferably 0.0010% or more. Ca is, for example, 0.0001% or more, preferably 0.0005% or more, and more preferably 0.0008% or more. REM is, for example, 0.0001% or more, preferably 0.0003% or more, and more preferably 0.0005% or more. Zr is, for example, 0.01% or more, preferably 0.03% or more, and more preferably 0.05% or more. Te is, for example, 0.001% or more, preferably 0.002% or more, and more preferably 0.003% or more.
[0031]
Mg, Ca, REM, Zr, and Te (for example, Ca, Zr, and Te) may be added alone or in combination of two or more.
[0032]
Further, in the steel of the present invention, it is desirable that the length of sulfide-based inclusions (such as MnS) is controlled. Since the sulfide-based inclusions that have been extended for a long time cause brittle fracture, the sulfide-based inclusions are shortened in order to maximize the effect of improving the low-temperature impact resistance by reducing P and S. Specifically, the sulfide-based inclusions having a major axis of 30 μm or more are, for example, 22 or less, preferably 20 or less, more preferably 15 or less, and particularly 10 or less per 2 mm × 2 mm visual field. .
[0033]
The number means an average value when the sulfide-based inclusions in the steel are uniformly measured at a plurality of locations, and the more the number of the measured locations, the more accurate the value.
[0034]
The steel of the present invention is preferably a steel bar (particularly a steel bar for a steering rack) as described later. When cutting the steering rack, a portion having a depth D / 8 in the diameter (D) direction from the surface of the steel bar (hereinafter, referred to as a D / 8 portion) corresponds to a substantially central portion of the tooth. Therefore, in a steel bar, D / 8 parts of the sulfide-based inclusions need only be controlled within the above range.
[0035]
The length of the sulfide-based inclusion can be controlled by adjusting the cooling rate during casting. When controlling the length of the sulfide-based inclusions within the above range, the cooling rate is, for example, about 0.3 to 9 ° C / min, preferably about 0.6 to 6 ° C / min, and more preferably about 1.0 to 6 ° C / min. It is recommended to select from a range of about 4 ° C./sec.
[0036]
Since the steel of the present invention can secure the hardness of the induction hardened part and can also improve the low-temperature impact resistance of the induction hardened part, the steel is hardened by induction hardened parts (particularly, teeth) such as steering racks and gears (particularly, steering racks). It is suitable for manufacturing parts whose parts are induction hardened.
[0037]
The form of the steel of the present invention is not particularly limited, but is preferably a steel bar in consideration of its intended use.
[0038]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples. However, the present invention is not limited to the following Examples, and may be appropriately modified within a range that can be adapted to the purpose of the preceding and the following. It is of course possible to carry out them, and all of them are included in the technical scope of the present invention.
[0039]
Experimental example 1
After casting steel having the composition shown in Tables 1-2, hot rolling and cooling, it is quenched (heating temperature: 860 ° C, cooling condition: water cooling) and tempered (heating temperature: 600 ° C, holding time: 1 hour). Thus, a steel bar having a diameter of 30 mm was obtained. For the experimental system C (No. 8 to No. 12), the size and number of MnS were adjusted by adjusting the cooling rate during casting between 0.01 and 12.0 ° C./sec. For other steels, the cooling rate was 2.5 ° C./sec.
[0040]
The bar was cut to form a convex portion (tooth portion), thereby processing into a test piece shape shown in FIGS. FIG. 1 is a schematic top view of the test piece, FIG. 2 is a schematic front view, and FIG. 3 is a schematic side view. That is, this test piece has one tooth portion formed at the center of the upper surface, and the rest is cut flush. The tooth portion has a width of 4 mm at the upper surface, a width of 6 mm at the base portion, and a height of 5 mm, and the R of the rising portion of the tooth is 0.5 mm. Next, the teeth were induction hardened [Coil used: Surface hardening (diameter 30 mm, thickness 2 mm), voltage: 4.0 kV, current: 4.5 A, maximum power of equipment: 200 kW, frequency: 40 kHz, heating method: moving hardening , Moving speed: 3.5 mm / sec, cooling: using a mixed medium of soluble oil and water], and then tempering (heating temperature: 180 ° C, holding time: 30 minutes) to obtain a test piece.
[0041]
The number of sulfide-based inclusions in the bar and the low-temperature toughness of the test were evaluated as follows. The hardness of the teeth of the test piece was also measured.
[0042]
[Number of sulfide inclusions]
A portion having a depth D / 8 in the diameter (D) direction from the surface of the steel bar (hereinafter, referred to as a D / 8 portion) is cut in parallel with the rolling direction, and the cross section is image-analyzed (LUZEX manufactured by Nireco Co., Ltd.). Using F), a 2 mm × 2 mm visual field was observed at a magnification of 100, and the major axis of the sulfide-based inclusions in the visual field was measured. The measurement was performed by binarizing the observed image. The image data is captured in RGB and adjusted to R: 125/180, G: 110/180, B: 120/180, and the gray level is set so that the MnS-based inclusions can be sufficiently distinguished from the matrix by the brightness. Adjusted each time. The number of sulfide-based inclusions having a major axis of 30 μm or more was counted.
[0043]
[Low temperature toughness]
After the test piece was cooled to a temperature of -40 ° C, it was placed on a test table with its convex portion facing upward. A cylindrical steel weight (diameter: 300 mm, weight: 100 kg) was dropped from above onto the convex portion. The weight was dropped from various heights, and the speed (crack speed at the time of collision) when a crack was generated in the convex portion (teeth portion) was examined. The presence or absence of cracks was visually checked.
[0044]
The results are shown in Tables 1 and 2. In Tables 1 and 2 below, experimental system A (experimental system with varied S content; No. 1 to 3), experimental system B (experimental system with varied P content; No. 4 to 7 and No. 1). ) And experimental system C (experimental systems in which the number of sulfide-based inclusions was changed; Nos. 8 to 12 and No. 1) are shown in FIGS.
[0045]
[Table 1]

[0046]
[Table 2]

[0047]
As is clear from Tables 1 and 2 and FIGS. 4 and 5, when S and P are limited to predetermined amounts or less, the low-temperature toughness of the tooth portion is rapidly improved. In addition, when the purpose is to increase the crack generation rate to a predetermined value or more (for example, 5 km / sec or more), it is necessary to reduce the amount of sulfide-based inclusions as is clear from Tables 1 and 2 and FIG. is there.
[0048]
Experiment No. As is clear from FIG. 13, when the amount of C is insufficient, the hardness of the teeth is also insufficient. Experiment No. As is clear from FIG. 28, when the amount of Si is excessive, the crack generation speed becomes less than a predetermined value (for example, less than 5 km / sec).
[0049]
【The invention's effect】
According to the present invention, in order to secure the hardness of the induction hardened part, in a specific component steel to which a predetermined amount of C, Si, and Mn is added, S and P are reduced to a predetermined amount or less. In addition, the low-temperature impact resistance can be significantly improved.
[Brief description of the drawings]
FIG. 1 is a schematic top view of a test piece of an example.
FIG. 2 is a schematic front view of a test piece of an example.
FIG. 3 is a schematic side view of a test piece of an example.
FIG. 4 is a graph showing the relationship between the S content and the crack generation rate.
FIG. 5 is a graph showing the relationship between the P content and the crack generation rate.
FIG. 6 is a graph showing the relationship between the number of sulfide-based inclusions and the crack generation rate.

Claims (6)

In mass%,
C: 0.30 to 0.5%,
Si: 0.01% or more, less than 0.40%,
Mn: 0.05-1.5%,
S: 0.06% or less (excluding 0%),
P: contains 0.010% or less (excluding 0%),
Induction hardening steel excellent in low-temperature impact resistance of the induction hardened portion, the balance being Fe and unavoidable impurities. The steel for induction hardening according to claim 1, wherein Al: 0.05% or less and N: 0.02% or less (excluding 0%). further,
Pb: 0.3% or less (excluding 0%),
Bi: 0.2% or less (excluding 0%),
Te: 0.1% or less (excluding 0%),
Mg: 0.01% or less (excluding 0%),
Ca: 0.01% or less (excluding 0%),
REM: 0.01% or less (excluding 0%),
3. The steel for induction hardening according to claim 1, wherein the steel contains at least one selected from the group consisting of Zr: 0.3% or less (excluding 0%). The steel for induction hardening according to any one of claims 1 to 3, wherein the average number of sulfide-based inclusions having a major diameter of 30 µm or more is 22 or less per 2 mm × 2 mm visual field. A steel bar having the component composition according to any one of claims 1 to 3, wherein a sulfide-based inclusion having a major axis of 30 µm or more is present in a portion having a depth of D / 8 in the diameter (D) direction from the surface of the steel bar. The number of steel bars is 22 or less per 2 mm × 2 mm field of view. An induction hardened part obtained from the steel for induction hardening or the steel bar according to claim 1.

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