JP2019206743A - Steel for induction hardening, shaped material of induction hardening component and induction hardening component - Google Patents

Abstract

To provide a steel for induction hardening having excellent machinability, surface fatigue strength and bending fatigue strength.SOLUTION: A steel for induction hardening comprises, in mass%, C: 0.40-0.70%, Si: 0.15-2.10%, Mn: 0.30-1.15%, Cr: 0.01-less than 0.50%, S: 0.005-0.070%, N: 0.0020-0.0200%, Al: 0.005-0.100%, P: less than 0.050%, with the balance being Fe and impurities, its chemical composition satisfying the following formulae, and its ferrite volume fraction being 40% or less. 290C+50Si+430≥631.0. C+(1/7) Si+(1/5) Mn+(1/9) Cr+V+(1/25) Mo≤0.900. (1+0.7Si)×(1+3.3333Mn)×(1+2.16Cr)×(1+3.00Mo)×(1+1.73 V)×(1+0.365Cu)×(1+0.363 Ni)≥3.80. 9.7Mn+32.4Cr≤25.9.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a steel for induction hardening, a shape material for induction hardening parts, and an induction hardening part.

  A mechanical structure component used for a power transmission component typified by a differential gear may be subjected to surface hardening treatment for the purpose of improving surface fatigue strength and bending fatigue strength.

  Typical surface hardening treatments include carburizing treatment, nitriding treatment, and induction hardening treatment. In the carburizing treatment, the surface of the base material is hardened by increasing the carbon surface. The carburizing process is mainly applied to gears, CVT (continuously variable transmission) parts, and CVJ (constant velocity joint) parts. The carburizing process is mainly a batch process in a gas atmosphere, and is heated and held at around 930 ° C. for several hours or more. Therefore, much energy and cost are spent. Further, in actual operation, there is a problem that it is difficult to inline. In actual operation, there was another problem that carburizing efficiency was low in the case of large parts.

  On the other hand, induction hardening can harden only a necessary part. Therefore, it is possible to shorten the surface curing treatment time and energy, and it is very advantageous for environmental cleanup. Therefore, induction hardening is often performed on components used for power transmission components. Hereinafter, induction-hardened parts are referred to as induction-hardened parts.

  The power transmission component is also manufactured by machining such as cutting. Therefore, high machinability is also required for induction hardening steel, which is a material for induction hardening parts.

  Patent Document 1 (Japanese Patent Laid-Open No. 2007-131471), Patent Document 2 (Japanese Patent Laid-Open No. 2007-332440) and Patent Document 3 (Japanese Patent Laid-Open No. 2004-156071) disclose induction hardened steel.

  The steel for induction hardening of Patent Document 1 is mass%, C: 0.35 to 0.65%, Si: 0.50% or less, Mn: 0.65 to 2.00%, P: 0.015%. Hereinafter, S: 0.003 to 0.080%, Mo: 0.05 to 0.50%, Al: 0.10% or less, N: 0.0070% or less, and O (oxygen): 0.0020% or less The balance is composed of Fe and impurities, and martensite has a structure that occupies 70% or more in area fraction. When the intensity | strength of the steel materials for induction hardening increases by this, it is described in patent document 1. FIG.

  The steel material for induction hardening of patent document 2 is the mass%, C: 0.35-0.6%, Si: 0.01-1.0%, Mn: 0.2-1.8%, S: 0 0.001 to 0.15%, Al: 0.001 to 0.05%, N: 0.002 to 0.020%, P: 0.025% or less, O: 0.0025% or less, and Cr: 1.8% or less, Mo: 1.5% or less, Ni: 3.5% or less, B: 0.006% or less, V: 0.5% or less, Nb: 0.04% or less, Ti : 0.2% or less, 1 type or 2 types or more, the balance being iron and inevitable impurities, the hardness of the hardened layer is HV550 or more after induction hardening, and the ferrite volume fraction of the core Is 50% or less, and the index A defined by the formula is -11 or more. If the low cycle fatigue characteristics are enhanced by this, it is described in Patent Document 2.

The molded part for induction hardening of Patent Document 3 is mass%, C: 0.5 to 0.7%, Si: 0.1 to 1.5%, Mn: 0.2 to 1.5%, Cr: Contains 0 to 1.5%, V: 0 to 0.10%, S: 0.002 to 0.05%, Al: 0.01 to 0.04%, N: 0.005 to 0.012% And the balance is formed of Fe and impurities, and is a molded part in which Ti in the impurities is 0.003% or less, O is 0.0015% or less, and P is 0.020% or less. The average minor axis of ferrite is 8 μm or less, and A = (Mn _MIN / Mn _AVE ) (Mn _MIN : lower limit value (mass%) of Mn concentration in the surface layer region, Mn _AVE : average value (mass%) of Mn concentration) Mn having an A value of 0.80 or more, an aspect ratio of 3 or less, and a minor axis of 10 μm or more The number of inclusions other than is two / mm ² or less. Thus, Patent Document 3 describes that the rolling fatigue life is excellent.

JP 2007-131871 A JP 2007-332440 A Japanese Patent Laid-Open No. 2004-156071

  However, in Patent Document 1, since the area fraction of martensite is 70% or more, workability, particularly machinability, is low.

  In Patent Document 2, high cycle fatigue strength such as surface fatigue strength in which surface hardness works directly does not necessarily increase. Furthermore, bainite is included in the previous structure, the core hardness representing the structure before induction hardening is high, and the machinability is low.

  In patent document 3, the upper limit prescription | regulation of alloy element addition is high, and material hardness increases. As a result, machinability may be low.

  Moreover, in the conventional induction-hardening component, although the average hardness of the induction-hardened part is high, there exists a site | part with low hardness locally. In this case, there were many events in which the surface fatigue strength and the rotational bending fatigue strength were reduced due to the fracture starting point of the low hardness portion. This phenomenon is a peculiar event in induction-hardened parts, and cannot be solved by using any of the methods disclosed in Patent Documents 1 to 3.

  An object of the present invention is to provide a steel for induction hardening having high surface fatigue strength and bending fatigue strength, and a shape of an induction-hardened component, which has excellent machinability and suppresses local hardness reduction after induction hardening. It is to provide materials and induction-hardened parts.

The steel for induction hardening according to the present embodiment is mass%, C: 0.40 to 0.70%, Si: 0.15 to 2.10%, Mn: 0.30 to 1.15%, Cr: 0. 0.01 to less than 0.50%, S: 0.005 to 0.070%, N: 0.0020 to 0.0200%, Al: 0.005 to 0.100%, P: less than 0.050%, Mo: 0 to 1.00%, Ni: 0 to 1.00%, Cu: 0 to 1.00%, Ca: 0 to 0.005%, Mg: 0 to 0.005%, Te: 0 to 0 2000%, Zr: 0 to 0.0050%, rare earth elements: 0 to 0.0050%, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0 to 0.35%, A chemical group consisting of Sb: 0 to 0.0150%, Pb: 0 to 0.5000%, and the balance: Fe and impurities and satisfying the formulas (1) to (4) It has a ferrite volume fraction of 40% or less.
290C + 50Si + 430 ≧ 631.0 (1)
C + (1/7) Si + (1/5) Mn + (1/9) Cr + V + (1/25) Mo ≦ 0.900 (2)
(1 + 0.7Si) × (1 + 3.3333Mn) × (1 + 2.16Cr) × (1 + 3.00Mo) × (1 + 1.73V) × (1 + 0.365Cu) × (1 + 0.363Ni) ≧ 3.80 (3)
9.7 Mn _θ + 32.4Cr _θ ≦ 25.9 (4)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the expressions (1) to (3). The Mn concentration (mass%) in cementite is substituted for Mn _θ in the formula (4), and the Cr concentration (mass%) in cementite is substituted for Cr _θ in the formula (4).

The base material of the induction-hardened component according to the present embodiment is mass%, C: 0.40 to 0.70%, Si: 0.15 to 2.10%, Mn: 0.30 to 1.15%, Cr: 0.01 to less than 0.50%, S: 0.005 to 0.070%, N: 0.0020 to 0.0200%, Al: 0.005 to 0.100%, P: 0.050 %: Mo: 0 to 1.00%, Ni: 0 to 1.00%, Cu: 0 to 1.00%, Ca: 0 to 0.005%, Mg: 0 to 0.005%, Te: 0 to 0.2000%, Zr: 0 to 0.0050%, rare earth elements: 0 to 0.0050%, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0 to 0.00. 35%, Sb: 0 to 0.0150%, Pb: 0 to 0.5000%, and the balance: Fe and impurities, satisfying the formulas (1) to (4) It has a chemical composition, the ferrite volume fraction of 40% or less.
290C + 50Si + 430 ≧ 631.0 (1)
C + (1/7) Si + (1/5) Mn + (1/9) Cr + V + (1/25) Mo ≦ 0.900 (2)
(1 + 0.7Si) × (1 + 3.3333Mn) × (1 + 2.16Cr) × (1 + 3.00Mo) × (1 + 1.73V) × (1 + 0.365Cu) × (1 + 0.363Ni) ≧ 3.80 (3)
9.7 Mn _θ + 32.4Cr _θ ≦ 25.9 (4)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the expressions (1) to (3). The Mn concentration (mass%) in cementite is substituted for Mn _θ in the formula (4), and the Cr concentration (mass%) in cementite is substituted for Cr _θ in the formula (4).

The induction-hardened component according to the present embodiment includes a quenched portion that is a portion where induction hardening has been performed and an unquenched portion that is a portion where induction hardening has not been performed. In the quenched portion, the martensite volume fraction is 90% or more. An unquenched part is mass%, C: 0.40-0.70%, Si: 0.15-2.10%, Mn: 0.30-1.15%, Cr: 0.01-0. Less than 50%, S: 0.005 to 0.070%, N: 0.0020 to 0.0200%, Al: 0.005 to 0.100%, P: less than 0.050%, Mo: 0 to 1 0.00%, Ni: 0 to 1.00%, Cu: 0 to 1.00%, Ca: 0 to 0.005%, Mg: 0 to 0.005%, Te: 0 to 0.2000%, Zr : 0 to 0.0050%, rare earth elements: 0 to 0.0050%, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0 to 0.35%, Sb: 0 to 0 0.150%, Pb: 0 to 0.5000%, and the balance: Fe and impurities, having a chemical composition satisfying the formulas (1) to (4). In the unquenched part, the ferrite volume fraction is 40% or less.
290C + 50Si + 430 ≧ 631.0 (1)
C + (1/7) Si + (1/5) Mn + (1/9) Cr + V + (1/25) Mo ≦ 0.900 (2)
(1 + 0.7Si) × (1 + 3.3333Mn) × (1 + 2.16Cr) × (1 + 3.00Mo) × (1 + 1.73V) × (1 + 0.365Cu) × (1 + 0.363Ni) ≧ 3.80 (3)
9.7 Mn _θ + 32.4Cr _θ ≦ 25.9 (4)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the expressions (1) to (3). The Mn concentration (mass%) in cementite is substituted for Mn _θ in the formula (4), and the Cr concentration (mass%) in cementite is substituted for Cr _θ in the formula (4).

  The steel for induction hardening, the material for induction hardening parts and the induction hardening parts of the present invention are excellent in machinability and suppress high local fatigue strength and bending by suppressing local hardness reduction after induction hardening. Has fatigue strength.

FIG. 1 is a plan view of a roller pitching test piece produced in the example. FIG. 2 is a schematic diagram of a roller pitching test. FIG. 3 is a side view of the Ono type rotating bending fatigue test piece produced in the example.

  In order to increase the surface fatigue strength and bending fatigue strength of the induction-hardened component, the C content may be increased. For example, if the C content is 0.40% by mass or more, high surface fatigue strength and bending fatigue strength can be obtained. However, if the C content is increased, the hardness of the steel for induction hardening before cutting increases, and the machinability decreases.

  Therefore, the present inventors have made various studies in order to achieve both high surface fatigue strength and bending fatigue strength and machinability in induction hardening steel. As a result, the following knowledge was obtained.

[About surface fatigue strength and bending fatigue strength]
The inventors further investigated the surface fatigue strength and the bending fatigue strength. As a result, the following knowledge was obtained.

(A) The hardness of the induction-hardened component surface has a correlation with the C content and the Si content in the steel. Further, the higher the hardness of the induction-hardened component surface, the higher the surface fatigue strength. Therefore, the present inventors conducted various investigations on the relationship between the C content and Si content in steel and the surface fatigue strength. As a result, it was found that the surface fatigue strength can be increased if the C content and the Si content in the steel satisfy the formula (1).
290C + 50Si + 430 ≧ 631.0 (1)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formula (1).
It is defined as FN1 = 290C + 50Si + 430. The present inventors have found that the value of FN1 substantially corresponds to the Vickers hardness of the surface of the induction-quenched part tempered at 300 ° C. after induction hardening.

  Further, it is generally known that the surface fatigue strength of the induction-hardened component in the roller pitting fatigue test has a positive correlation with the 300 ° C. tempering hardness. When the relationship between the surface fatigue strength in the roller pitting fatigue test and the Vickers hardness after tempering at 300 ° C. was investigated, the surface fatigue strength was satisfactory when the Vickers hardness after tempering at 300 ° C. was 631.0 Hv or more. I understood that. That is, when the FN1 is 631.0 or more, the surface fatigue strength is satisfactory. On the other hand, if the value of FN1 is less than 631.0, the surface fatigue strength is lowered, and pitching may occur.

(B) When the induction-hardened part includes an incompletely hardened structure, there is a portion having locally low hardness. In this case, the surface fatigue strength and the bending fatigue strength are reduced as compared with the case where a completely quenched structure is obtained. In order to suppress the incompletely quenched structure, it is necessary to limit the contents of Si, Mn, Cr, Mo, V, Cu, and Ni related to hardenability to an appropriate range. Therefore, the present inventors conducted various investigations on the relationship between these elements and the surface fatigue strength and bending fatigue strength. As a result, it has been found that if the content of these elements satisfies the formula (3), generation of an incompletely quenched structure can be suppressed, and surface fatigue strength and bending fatigue strength can be increased.
(1 + 0.7Si) × (1 + 3.3333Mn) × (1 + 2.16Cr) × (1 + 3.00Mo) × (1 + 1.73V) × (1 + 0.365Cu) × (1 + 0.363Ni) ≧ 3.80 (3)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formula (3).
FN3 = (1 + 0.7Si) × (1 + 3.3333Mn) × (1 + 2.16Cr) × (1 + 3.00Mo) × (1 + 1.73V) × (1 + 0.365Cu) × (1 + 0.363Ni). FN3 is an index of hardenability of induction hardening steel. As FN3 increases, the hardenability increases. As a result of investigating the relationship between FN3 and the incompletely quenched structure generated during induction hardening, it was found that if FN3 was 3.80 or more, the incompletely quenched structure was not generated during induction hardening. That is, if FN3 is 3.80 or more, generation of an incompletely quenched structure during induction hardening can be suppressed. On the other hand, when FN3 is less than 3.80, the hardenability is lowered and an incompletely hardened structure may be generated.

[Machinability]
The contents of C, Si, Mn, Cr, V, and Mo affect the hardness of the steel before induction hardening. Moreover, when the hardness of steel exceeds a certain limit value, machinability is extremely lowered. Therefore, in order to ensure good machinability, it is necessary to control the hardness of the steel within an appropriate range. Therefore, the present inventors conducted various investigations on the relationship between the contents of C, Si, Mn, Cr, V, and Mo and machinability. As a result, it has been found that if the content of these elements satisfies the formula (2), the machinability can be improved.
C + (1/7) Si + (1/5) Mn + (1/9) Cr + V + (1/25) Mo ≦ 0.900 (2)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formula (2).

  It is defined as FN2 = C + (1/7) Si + (1/5) Mn + (1/9) Cr + V + (1/25) Mo. FN2 is an index of hardness of induction hardening steel. When FN2 exceeds the limit value, the machinability is extremely lowered. When the relationship between FN2 and machinability was investigated, it was found that if FN2 was 0.900 or less, good machinability could be satisfied. That is, if FN2 is 0.900 or less, good machinability can be obtained. On the other hand, if FN2 exceeds 0.900, the machinability is extremely lowered. A preferable upper limit of FN2 is 0.890.

[About variation in hardness of induction hardened parts surface]
However, even when the above expressions (1) to (3) are satisfied, the surface fatigue strength and the bending fatigue strength may still be low. Therefore, the present inventors have conducted various studies on methods for further increasing the surface fatigue strength and the bending fatigue strength.

  As a result of investigating the parts for induction hardening with low surface fatigue strength and bending fatigue strength, it was found that there was variation in hardness even in the quenched parts subjected to induction hardening. In the induction hardening component, if there is a locally low hardness portion (hereinafter also referred to as hardness variation), the surface fatigue strength and the bending fatigue strength are reduced. The present inventors considered that the reason for this is that if there is a variation in hardness, a fracture occurs starting from a low hardness portion.

  Therefore, the present inventors further studied a method for suppressing the hardness variation of the induction hardening component in order to increase the surface fatigue strength and the bending fatigue strength. As a result, it was found that cementite remained undissolved in the hard part. Furthermore, when cementite in the hard part was examined, it was found that the Mn concentration and the Cr concentration were high.

  Further investigation by the present inventors revealed that, in mass%, C: 0.40 to 0.70%, Si: 0.15 to 2.10%, Mn: 0.30 to 1.15%, Cr: 0 0.01 to less than 0.50%, S: 0.005 to 0.070%, N: 0.0020 to 0.0200%, Al: 0.005 to 0.100%, P: less than 0.050%, Mo: 0 to 1.00%, Ni: 0 to 1.00%, Cu: 0 to 1.00%, Ca: 0 to 0.005%, Mg: 0 to 0.005%, Te: 0 to 0 2000%, Zr: 0 to 0.0050%, rare earth elements: 0 to 0.0050%, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0 to 0.35%, In an induction hardening steel having a chemical composition comprising Sb: 0 to 0.0150%, Pb: 0 to 0.5000%, and the balance: Fe and impurities. Te, if there is Mn and Cr in the cementite, it was found that increasing the temperature (solution temperature) required cementite forms a solid solution.

  Therefore, the present inventors considered that the variation in hardness is caused by the variation in the amount of dissolved C during high-frequency heating. Specifically, it is as follows. In the case of furnace heating performed by carburizing treatment or the like, since heating at a high temperature is performed for a long time, the equilibrium state shown in the equilibrium diagram of the chemical composition is obtained, and cementite can be completely dissolved. Thereby, the dispersion | variation in the amount of solute C can be suppressed. However, heating by quenching at high frequency heating is very short and non-equilibrium compared to furnace heating. Therefore, cementite remains undissolved after high-frequency heating, and the amount of solid solution C varies. As a result, hardness variation occurs.

  The solution temperature of cementite in the steel for induction hardening influences the amount of solid solution C during induction heating. Mn and Cr in cementite increase the solution temperature of cementite. When Mn and Cr are contained in the cementite, the cementite remains undissolved even after induction heating, and hardness variation occurs on the induction-hardened component surface.

  From the above knowledge, the present inventors considered that the hardness variation of the induction-hardened component surface can be suppressed by suppressing the Mn concentration and the Cr concentration in cementite within appropriate ranges.

As described above, the hardness variation on the surface of the induction-hardened component correlates with the surface fatigue strength and the bending fatigue strength. Therefore, the present inventors conducted various investigations on the relationship between the Mn concentration and Cr concentration in cementite and the surface fatigue strength and bending fatigue strength in induction hardening steel. As a result, it has been found that if the Mn concentration and the Cr concentration in cementite satisfy Equation (4), the hardness variation of the surface of the induction-hardened component can be suppressed and the surface fatigue strength and the bending fatigue strength can be increased.
9.7 Mn _θ + 32.4Cr _θ ≦ 25.9 (4)
Here, Mn concentration (mass%) in cementite is substituted for Mn _θ in formula (4), and Cr concentration (mass%) in cementite is substituted for Cr _θ in formula (4). The

FN4 = is defined as 9.7Mn θ + 32.4Cr _θ. FN4 is an indicator of the solution temperature of cementite. The larger the FN4, the higher the solution temperature. That is, the cementite tends to remain undissolved even after induction hardening, and the hardness variation is likely to occur. If FN4 exceeds 25.9, undissolved cementite remains after induction hardening. As a result, hardness variation occurs.

  Furthermore, the ferrite volume fraction of the steel for induction hardening affects the amount of solute C during induction heating. In the induction hardening, since the heat treatment time is short, the diffusion time of C is also short. Therefore, the time for the carbide to dissolve is shortened. As a result, the ferrite volume fraction tends to be high. However, if the ferrite volume fraction is too high, ferrite remains in the structure after induction hardening. If the ferrite volume fraction is too high, low carbon martensite is generated. As a result, extreme hardness variations occur. Therefore, the present inventors further conducted various investigations on the relationship between the ferrite volume fraction of the steel for induction hardening, the surface fatigue strength, and the bending fatigue strength. As a result, it was found that if the ferrite volume fraction is 40% or less, the hardness variation of the surface of the induction-hardened component can be suppressed and the surface fatigue strength and the bending fatigue strength can be increased.

  If the ferrite volume fraction exceeds 40%, ferrite remains in the surface layer structure after induction hardening. If the ferrite volume fraction exceeds 40%, low carbon martensite is further generated in the structure after induction hardening. In these cases, a part having extremely low hardness is generated and hardness variation occurs.

  From the above, in order to increase machinability and suppress hardness variations, and to increase the surface fatigue strength and bending fatigue strength of parts after induction hardening, the relationship between the contents of C and Si is appropriate. Value, and in order to ensure proper hardenability, the content of C, Si, Mn, Cr, Mo, V, Cu, Ni is set to an appropriate range, and the ferrite volume fraction is limited to an appropriate range. In addition, it is preferable that the Mn concentration and Cr concentration in the cementite are set to appropriate values, and the contents of C, Si, Mn, Cr, V, and Mo related to the material hardness are set to an appropriate range. I found out.

The induction-quenched steel according to the present embodiment completed based on the above knowledge is mass%, C: 0.40 to 0.70%, Si: 0.15 to 2.10%, Mn: 0.30 to 1. 15%, Cr: 0.01 to less than 0.50%, S: 0.005 to 0.070%, N: 0.0020 to 0.0200%, Al: 0.005 to 0.100%, P: Less than 0.050%, Mo: 0 to 1.00%, Ni: 0 to 1.00%, Cu: 0 to 1.00%, Ca: 0 to 0.005%, Mg: 0 to 0.005% , Te: 0 to 0.2000%, Zr: 0 to 0.0050%, rare earth elements: 0 to 0.0050%, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0 -0.35%, Sb: 0-0.0150%, Pb: 0-0.5000%, and the balance: Fe and impurities, and the formula (1) Has a chemical composition that satisfies the equation (4), a ferrite volume fraction of 40% or less.
290C + 50Si + 430 ≧ 631.0 (1)
C + (1/7) Si + (1/5) Mn + (1/9) Cr + V + (1/25) Mo ≦ 0.900 (2)
(1 + 0.7Si) × (1 + 3.3333Mn) × (1 + 2.16Cr) × (1 + 3.00Mo) × (1 + 1.73V) × (1 + 0.365Cu) × (1 + 0.363Ni) ≧ 3.80 (3)
9.7 Mn _θ + 32.4Cr _θ ≦ 25.9 (4)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the expressions (1) to (3). The Mn concentration (mass%) in cementite is substituted for Mn _θ in the formula (4), and the Cr concentration (mass%) in cementite is substituted for Cr _θ in the formula (4).

  The chemical composition of the induction hardening steel is selected from the group consisting of Mo: 0.01 to 1.00%, Ni: 0.05 to 1.00%, and Cu: 0.05 to 1.00%. You may contain 1 type, or 2 or more types.

  The chemical composition of the steel for induction hardening is as follows: Ca: 0.0003 to 0.005%, Mg: 0.0003 to 0.005%, Te: 0.0003 to 0.2000%, Zr: 0.0003 to 0 One or two or more selected from the group consisting of .0050% and rare earth elements: 0.0003 to 0.0050% may be included.

  The chemical composition of the induction hardening steel is selected from the group consisting of Ti: 0.005 to 0.200%, Nb: 0.005 to 0.200%, and V: 0.005 to 0.35%. 1 type (s) or 2 or more types may be contained.

  The chemical composition of the induction hardening steel may include one or more selected from the group consisting of Sb: 0.0003 to 0.0150% and Pb: 0.0100 to 0.5000%.

The base material of the induction-hardened component according to the present embodiment is mass%, C: 0.40 to 0.70%, Si: 0.15 to 2.10%, Mn: 0.30 to 1.15%, Cr: 0.01 to less than 0.50%, S: 0.005 to 0.070%, N: 0.0020 to 0.0200%, Al: 0.005 to 0.100%, P: 0.050 %: Mo: 0 to 1.00%, Ni: 0 to 1.00%, Cu: 0 to 1.00%, Ca: 0 to 0.005%, Mg: 0 to 0.005%, Te: 0 to 0.2000%, Zr: 0 to 0.0050%, rare earth elements: 0 to 0.0050%, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0 to 0.00. 35%, Sb: 0 to 0.0150%, Pb: 0 to 0.5000%, and the balance: Fe and impurities, satisfying the formulas (1) to (4) It has a chemical composition, the ferrite volume fraction of 40% or less.
290C + 50Si + 430 ≧ 631.0 (1)
C + (1/7) Si + (1/5) Mn + (1/9) Cr + V + (1/25) Mo ≦ 0.900 (2)
(1 + 0.7Si) × (1 + 3.3333Mn) × (1 + 2.16Cr) × (1 + 3.00Mo) × (1 + 1.73V) × (1 + 0.365Cu) × (1 + 0.363Ni) ≧ 3.80 (3)
9.7 Mn _θ + 32.4Cr _θ ≦ 25.9 (4)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the expressions (1) to (3). The Mn concentration (mass%) in cementite is substituted for Mn _θ in the formula (4), and the Cr concentration (mass%) in cementite is substituted for Cr _θ in the formula (4).

  The chemical composition of the base material of the induction-hardened component is selected from the group consisting of Mo: 0.01 to 1.00%, Ni: 0.05 to 1.00%, and Cu: 0.05 to 1.00%. You may contain the 1 type (s) or 2 or more types selected.

  The chemical composition of the shape of the induction-hardened component is as follows: Ca: 0.0003 to 0.005%, Mg: 0.0003 to 0.005%, Te: 0.0003 to 0.2000%, Zr: 0.00. You may contain 1 type, or 2 or more types selected from the group which consists of 0003-0.0050% and rare earth elements: 0.0003-0.0050%.

  The chemical composition of the base material of the induction-hardened component is a group consisting of Ti: 0.005 to 0.200%, Nb: 0.005 to 0.200%, and V: 0.005 to 0.35%. You may contain 1 type, or 2 or more types selected from these.

  The chemical composition of the base material of the induction-hardened component contains one or more selected from the group consisting of Sb: 0.0003 to 0.0150% and Pb: 0.0100 to 0.5000%. Also good.

The induction-hardened component according to the present embodiment includes a quenched portion that is a portion where induction hardening has been performed and an unquenched portion that is a portion where induction hardening has not been performed. In the quenched portion, the martensite volume fraction is 90% or more. An unquenched part is mass%, C: 0.40-0.70%, Si: 0.15-2.10%, Mn: 0.30-1.15%, Cr: 0.01-0. Less than 50%, S: 0.005 to 0.070%, N: 0.0020 to 0.0200%, Al: 0.005 to 0.100%, P: less than 0.050%, Mo: 0 to 1 0.00%, Ni: 0 to 1.00%, Cu: 0 to 1.00%, Ca: 0 to 0.005%, Mg: 0 to 0.005%, Te: 0 to 0.2000%, Zr : 0 to 0.0050%, rare earth elements: 0 to 0.0050%, Ti: 0 to 0.200%, Nb: 0 to 0.200%, V: 0 to 0.35%, Sb: 0 to 0 0.150%, Pb: 0 to 0.5000%, and the balance: Fe and impurities, having a chemical composition satisfying the formulas (1) to (4). In the unquenched part, the ferrite volume fraction is 40% or less.
290C + 50Si + 430 ≧ 631.0 (1)
C + (1/7) Si + (1/5) Mn + (1/9) Cr + V + (1/25) Mo ≦ 0.900 (2)
(1 + 0.7Si) × (1 + 3.3333Mn) × (1 + 2.16Cr) × (1 + 3.00Mo) × (1 + 1.73V) × (1 + 0.365Cu) × (1 + 0.363Ni) ≧ 3.80 (3)
9.7 Mn _θ + 32.4Cr _θ ≦ 25.9 (4)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the expressions (1) to (3). The Mn concentration (mass%) in cementite is substituted for Mn _θ in the formula (4), and the Cr concentration (mass%) in cementite is substituted for Cr _θ in the formula (4).

  The chemical composition of the induction-hardened component is selected from the group consisting of Mo: 0.01 to 1.00%, Ni: 0.05 to 1.00%, and Cu: 0.05 to 1.00% 1 You may contain a seed or two or more sorts.

  The chemical composition of the induction-hardened component is as follows: Ca: 0.0003 to 0.005%, Mg: 0.0003 to 0.005%, Te: 0.0003 to 0.2000%, Zr: 0.0003 to 0.00. One or two or more selected from the group consisting of 0050% and rare earth elements: 0.0003 to 0.0050% may be contained.

  The chemical composition of the induction-hardened part is selected from the group consisting of Ti: 0.005 to 0.200%, Nb: 0.005 to 0.200%, and V: 0.005 to 0.35%. You may contain 1 type, or 2 or more types.

  The chemical composition of the induction-hardened component may contain one or more selected from the group consisting of Sb: 0.0003 to 0.0150% and Pb: 0.0100 to 0.5000%.

  The steel for induction hardening of the present invention, the shape material of the induction hardening component, and the induction hardening component are excellent in machinability and have excellent surface fatigue strength by suppressing local hardness reduction after induction hardening. Has bending fatigue strength characteristics.

  Hereinafter, the induction hardening steel, the shape material of the induction hardening component, and the induction hardening component will be described in detail. “%” Regarding an element means mass% unless otherwise specified.

  In the present embodiment, the induction hardening steel refers to a material that is subjected to induction hardening in order to obtain an induction hardening component. The material may be subjected to normalization. The shape material of the induction-hardened component is a material obtained by hot forging steel for induction hardening and processing it into a rough shape of the induction-hardened component. In addition, the induction hardening component refers to a product obtained by subjecting induction hardening steel to induction hardening (however, it may be tempered after induction hardening). Induction-hardened parts are assumed to be parts that require high surface fatigue strength and bending fatigue strength. The induction hardening component is, for example, a differential gear used for power transmission for automobiles. The induction-hardened component according to this embodiment is obtained by subjecting the steel for induction hardening according to this embodiment to induction hardening with a maximum heating temperature of 850 to 1100 ° C.

  The induction-hardened component includes a quenched portion and an unquenched portion.

  A quenching part is the site | part heated at the time of induction hardening. In the quenched portion, the martensite volume fraction is 90% or more.

  An unquenched part is a part of an induction-hardened part that is not affected by heating during induction hardening. Since it is composed mainly of ferrite pearlite, the ferrite volume fraction is 40% or less, and Vickers It refers to a part having a hardness of 350 Hv or less.

[About induction hardening steel]
[Chemical composition]
The chemical composition of the steel for induction hardening according to the present embodiment contains the following elements.

C: 0.40 to 0.70%
Carbon (C) increases the bending fatigue strength and surface fatigue strength of steel. C further reduces the ferrite volume fraction in the structure before induction hardening, improves the hardening ability during induction hardening, and increases the depth of the hardened layer. If the C content is less than 0.40%, these effects cannot be obtained. On the other hand, if the C content exceeds 0.70%, not only the machinability and forgeability are significantly impaired, but also the possibility of occurrence of quenching cracks during induction hardening increases. Therefore, the C content is 0.40 to 0.70%. The minimum with preferable C content is 0.45%, More preferably, it is 0.50%. The upper limit with preferable C content is 0.68%.

Si: 0.15 to 2.10%
Silicon (Si) increases the temper softening resistance of the surface hardened layer and increases the surface fatigue strength after quenching. If the Si content is less than 0.15%, this effect cannot be obtained. On the other hand, when the Si content exceeds 2.10%, decarburization during forging and induction hardening becomes significant. When decarburization occurs, surface fatigue strength and bending fatigue strength decrease. Therefore, the Si content is 0.15 to 2.10%. A preferable lower limit of the Si content is 0.50%. The upper limit with preferable Si content is 1.95%.

Mn: 0.30 to 1.15%
Manganese (Mn) increases the hardenability of the steel. Mn further combines with sulfur (S) in the steel to form MnS, thereby detoxifying S in the steel. Thereby, hot ductility is ensured. If the Mn content is less than 0.30%, these effects cannot be obtained. On the other hand, if the Mn content exceeds 1.15%, the material becomes too hard and the machinability of the steel decreases. If the Mn content exceeds 1.15%, it further dissolves in cementite and raises the solution temperature of cementite. As a result, in the case of over-dissolution, cementite remains undissolved by induction hardening, resulting in hardness variations. Therefore, the Mn content is 0.30 to 1.15%. The minimum with preferable Mn content is 0.40%, More preferably, it is 0.50%, More preferably, it is 0.60%, More preferably, it is 0.75%. The upper limit with preferable Mn content is 1.10% or less, More preferably, it is 1.00% or less.

Cr: 0.01 to less than 0.50% Chromium (Cr) increases the hardenability of steel. Cr further increases the hot ductility of the steel. If the Cr content is less than 0.01%, these effects cannot be obtained. On the other hand, if the Cr content is 0.50% or more, the Cr concentration dissolved in the cementite increases, and the solution temperature of the cementite increases. As a result, undissolved cementite is produced. If undissolved cementite is present, a solid solution C deficiency or an incompletely quenched structure that causes hardness variations after induction hardening occurs. As a result, the surface fatigue strength decreases. Moreover, when the range of Formula (2) is exceeded in balance with another alloy element, raw material hardness becomes high and machinability falls. Therefore, the Cr content is 0.01 to less than 0.50%. When raising the hardenability and tensile strength of steel, the minimum with preferable Cr content is 0.03%, More preferably, it is 0.10%. When the surface fatigue strength is further increased, the upper limit of the Cr content is preferably 0.40%, more preferably 0.30%, further preferably 0.20%, and further preferably 0.15%. It is.

S: 0.005-0.070%
Sulfur (S) combines with Mn in the steel to form MnS and enhances the machinability of the steel. If the S content is 0.005% or less, this effect cannot be obtained. On the other hand, if the S content exceeds 0.070%, the bending fatigue strength of the steel decreases. If the S content exceeds 0.070%, when performing a magnetic particle flaw detection test on a hot forged product after induction hardening, a pseudo pattern tends to be generated on the surface of the hot forged product. Therefore, the S content is 0.005% to 0.070%. When raising the machinability of steel, the minimum with preferable S content is 0.010%, More preferably, it is 0.015%. The upper limit with preferable S content is 0.050%, More preferably, it is 0.030%.

N: 0.0020 to 0.0200%
Nitrogen (N) combines with nitride-forming elements such as Al in the steel to form nitrides. Thereby, the austenite structure at the time of induction hardening is refined. As a result, the bending fatigue strength is increased. If the N content is less than 0.0020%, this effect cannot be obtained. On the other hand, if the N content exceeds 0.0200%, the hot ductility of the steel is significantly reduced. Therefore, the N content is 0.0020 to 0.0200%. When obtaining the sizing by suppressing the grain coarsening of the steel, the preferable lower limit of the N content is 0.0040%, more preferably 0.0060, and further preferably 0.0080%. The upper limit with preferable N content is 0.010%.

Al: 0.005 to 0.100%
Aluminum (Al) precipitates and disperses in the steel as a nitride, thereby refining the austenite structure during induction hardening. Al further increases the hardenability and increases the depth of the hardened layer. Al further improves machinability. Further, Al forms a compound with N during nitriding, and increases the N concentration in the surface layer portion. Thereby, surface fatigue strength is raised. When the Al content is less than 0.005%, these effects cannot be obtained. On the other hand, if the Al content exceeds 0.100%, transformation to austenite is difficult to complete during high-frequency heating, and the hardenability decreases. Therefore, the Al content is 0.005 to 0.100%. A preferable lower limit of the Al content is 0.010%. The upper limit with preferable Al content is 0.010%.

P: Less than 0.050% Phosphorus (P) is an unavoidable impurity. That is, the P content is more than 0%. If the P content is 0.050% or more, the toughness decreases. If the P content is 0.050% or more, the crack propagation is further promoted and the bending fatigue strength is lowered. Accordingly, the P content is less than 0.050%. The upper limit with preferable P content is 0.040%. The P content is preferably as low as possible. However, since the dephosphorization process takes time and cost, the preferable lower limit of the P content is 0.0001% in view of industrial productivity.

  The balance of the chemical composition of the steel for induction hardening according to this embodiment is composed of Fe and impurities. Here, an impurity means what is mixed from the ore as a raw material, a scrap, or a manufacturing environment when manufacturing the said steel for induction hardening industrially.

[Arbitrary elements]
The induction hardening steel of the present embodiment may further contain one or more selected from the group consisting of Mo, Ni, and Cu instead of part of Fe.

Mo: 0 to 1.00%
Molybdenum (Mo) is an optional element and may not be contained. That is, the Mo content may be 0%. When contained, Mo increases the temper softening resistance of the quenched layer. As a result, the surface fatigue strength increases. Mo further strengthens the hardened layer. As a result, bending fatigue strength increases. However, if the Mo content exceeds 1.00%, the above effect is saturated and the economy is impaired. Therefore, the Mo content is 0 to 1.00%. The minimum with preferable Mo content is 0.01%, More preferably, it is 0.05%. The upper limit with preferable Mo content is 0.30%, More preferably, it is 0.25%.

Ni: 0 to 1.00%
Nickel (Ni) is an optional element and may not be contained. That is, the Ni content may be 0%. When contained, Ni is concentrated on the surface of the induction hardening steel when it is oxidized, and suppresses the subsequent oxidation reaction. However, if the Ni content exceeds 1.00%, the machinability decreases. Therefore, the Ni content is 0 to 1.00%. The minimum with preferable Ni content is 0.05%, More preferably, it is 0.10%. The upper limit with preferable Ni content is 0.80%, More preferably, it is 0.60%.

Cu: 0 to 1.00%
Copper (Cu) is an optional element and may not be contained. That is, the Cu content may be 0%. When contained, Cu concentrates on the surface of the steel for induction hardening when oxidized, and suppresses the subsequent oxidation reaction. However, if the Cu content exceeds 1.00%, the effect is saturated in terms of mechanical properties. If the Cu content exceeds 1.00%, the hot ductility is further lowered, so that wrinkles are easily formed during rolling. Therefore, the Cu content is 0 to 1.00%. The minimum with preferable Cu content is 0.05%, More preferably, it is 0.10%. The upper limit with preferable Cu content is 0.80%, More preferably, it is 0.60%.

  The induction hardening steel of this embodiment may further contain one or more selected from the group consisting of Ca, Mg, Te, Zr, and rare earth elements instead of a part of Fe. .

Ca: 0 to 0.005%
Calcium (Ca) is an optional element and may not be contained. That is, the Ca content may be 0%. When contained, Ca suppresses stretching of MnS during rolling. As a result, bending fatigue strength increases. However, if the Ca content exceeds 0.005%, the effect is saturated. If Ca content exceeds 0.005%, hot ductility will fall further. Therefore, the Ca content is 0 to 0.005%. The minimum with preferable Ca content is 0.0003%, More preferably, it is 0.0005%. The upper limit with preferable Ca content is 0.0030%, More preferably, it is 0.0025%.

Mg: 0 to 0.005%
Magnesium (Mg) is an optional element and may not be contained. That is, the Mg content may be 0%. When contained, Mg suppresses stretching of MnS during rolling. As a result, bending fatigue strength increases. However, if the Mg content exceeds 0.005%, the effect is saturated. If Mg content exceeds 0.005%, hot ductility will fall further. Therefore, the Mg content is 0 to 0.005%. The minimum with preferable Mg content is 0.0003%, More preferably, it is 0.0005%. The upper limit with preferable Mg content is 0.0030%, More preferably, it is 0.0025%.

Te: 0 to 0.2000%
Tellurium (Te) is an optional element and may not be contained. That is, the Te content may be 0%. When contained, Te suppresses stretching of MnS during rolling. As a result, bending fatigue strength increases. However, if the Te content exceeds 0.2000%, the effect is saturated. If Te content exceeds 0.2000%, hot ductility will fall further. Accordingly, the Te content is 0 to 0.2000%. The minimum with preferable Te content is 0.0003%, More preferably, it is 0.05%. The upper limit with preferable Te content is 0.15%, More preferably, it is 0.10%.

Zr: 0 to 0.0050%
Zirconium (Zr) is an optional element and may not be contained. That is, the Te content may be 0%. If contained, Zr precipitates and disperses in the steel as a nitride, thereby refining the austenite structure during induction hardening. However, if the Zr content exceeds 0.0050%, the precipitates become coarse and the fatigue strength is greatly reduced. If the Zr content exceeds 0.0050%, the steel further becomes brittle. Therefore, the Zr content is 0 to 0.0050%. The minimum with preferable Zr content is 0.0003%, More preferably, it is 0.0005%, More preferably, it is 0.0010%. The upper limit with preferable Zr content is 0.0045%, More preferably, it is 0.0040%.

Rare earth elements: 0-0.0050%
The rare earth element (REM) is an optional element and may not be contained. That is, the REM content may be 0%. When contained, REM suppresses stretching of MnS during rolling. As a result, bending fatigue strength increases. However, if the REM content exceeds 0.0050%, the effect is saturated. If the REM content exceeds 0.0050%, the formation of a composite oxide of oxide and sulfide is further promoted, and the inclusion size is increased. As a result, the fatigue strength is greatly reduced. Therefore, the REM content is 0 to 0.0050%. The minimum with preferable REM content is 0.0003%, More preferably, it is 0.0005%. The upper limit with preferable REM content is 0.0045%, More preferably, it is 0.0040%.

  In this specification, REM means yttrium (Y) having an atomic number of 39, lanthanum (La) having an atomic number of 57, which is a lanthanoid to lutetium (Lu) having an atomic number of 71, and an atomic number having an atomic number of 89. It is one or more elements selected from the group consisting of actinium (Ac) to atomic number 103 Lorencium (Lr). Moreover, the REM content in this specification is the total content of these elements. In adding these elements, the effect does not change at all even if misch metal containing these elements is used.

  The induction hardening steel of this embodiment may further contain one or more selected from the group consisting of Ti, Nb, and V instead of a part of Fe.

Ti: 0 to 0.200%
Titanium (Ti) is an optional element and may not be contained. That is, the Ti content may be 0%. When contained, Ti precipitates and disperses in the steel as a nitride, thereby refining the austenite structure during induction hardening. However, if the Ti content exceeds 0.200%, the precipitates become coarse and the fatigue strength decreases. If the Ti content exceeds 0.200%, the steel further becomes brittle. Therefore, the Ti content is 0 to 0.200%. The minimum with preferable Ti content is 0.005%, More preferably, it is 0.010%. The upper limit with preferable Ti content is 0.150%, More preferably, it is 0.100%.

Nb: 0 to 0.200%
Niobium (Nb) is an optional element and may not be contained. That is, the Nb content may be 0%. When Nb is contained, Nb precipitates and disperses in the steel as a nitride, thereby refining the austenite structure during induction hardening. However, if the Nb content exceeds 0.200%, the effect is saturated and the economy is impaired. Therefore, the Nb content is 0 to 0.200%. The minimum with preferable Nb content is 0.005%, More preferably, it is 0.010%. The upper limit with preferable Nb content is 0.100%, More preferably, it is 0.050%.

V: 0 to 0.35%
Vanadium (V) is an optional element and may not be contained. That is, the V content may be 0%. When contained, V precipitates and disperses in the steel as a nitride, thereby refining the austenite structure during induction hardening. However, if V content exceeds 0.35%, the effect will be saturated and economical efficiency will be impaired. Therefore, the V content is 0 to 0.35%. The minimum with preferable V content is 0.005%, More preferably, it is 0.010%. The upper limit with preferable V content is 0.30%, More preferably, it is 0.25%.

  The induction hardening steel of the present embodiment may further contain one or more selected from the group consisting of Sb and Pb instead of part of Fe.

Sb: 0 to 0.0150%
Antimony (Sb) is an optional element and may not be contained. That is, the Sb content may be 0%. When contained, Sb has a strong surface segregation tendency and suppresses oxidation due to adsorption of oxygen from the outside. However, if the Sb content exceeds 0.0150%, the toughness and hot ductility of the steel decrease. Therefore, Sb content is 0 to 0.0150%. The minimum with preferable Sb content is 0.0003%, More preferably, it is 0.0005%, More preferably, it is 0.0010%. The upper limit with preferable Sb content is 0.0100%, More preferably, it is 0.0080%.

Pb: 0 to 0.5000%
Lead (Pb) is an optional element and may not be contained. That is, the Pb content may be 0%. When contained, Pb increases the machinability of the steel. However, if the Pb content exceeds 0.5000%, the toughness and hot ductility of the steel decrease. Therefore, the Pb content is 0 to 0.5000%. The minimum with preferable Pb content is 0.0100%, More preferably, it is 0.0400%. The upper limit with preferable Pb content is 0.4000%, More preferably, it is 0.3500%.

[Regarding Formula (1)]
The chemical composition further satisfies formula (1).
290C + 50Si + 430 ≧ 631.0 (1)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formula (1).

  It is defined as FN1 = 290C + 50Si + 430. FN1 is an index of the hardness of the steel surface. FN1 substantially corresponds to the Vickers hardness of the surface of the induction-quenched part tempered at 300 ° C. after induction hardening. The durability of the induction-hardened component in the roller pitting fatigue test has a positive correlation with the 300 ° C. tempering hardness. If FN1 is 631.0 or more, sufficient surface fatigue strength can be obtained on the assumption that other conditions are satisfied. If FN1 is less than 631.0, the surface fatigue strength may be reduced and pitching may occur. A preferred lower limit of FN1 is 640.0. A preferable upper limit of FN1 is 665.0.

[Regarding Formula (2)]
The chemical composition further satisfies formula (2).
C + (1/7) Si + (1/5) Mn + (1/9) Cr + V + (1/25) Mo ≦ 0.900 (2)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formula (2).

  It is defined as FN2 = C + (1/7) Si + (1/5) Mn + (1/9) Cr + V + (1/25) Mo. FN2 is an index of the hardness of the induction-hardened component. If FN2 is 0.900 or less, good machinability can be obtained. On the other hand, when FN2 exceeds 0.900, machinability is extremely reduced. A preferred lower limit of FN2 is 0.800. A preferable upper limit of FN2 is 0.890.

[Regarding Formula (3)]
The chemical composition further satisfies formula (3).
(1 + 0.7Si) × (1 + 3.3333Mn) × (1 + 2.16Cr) × (1 + 3.00Mo) × (1 + 1.73V) × (1 + 0.365Cu) × (1 + 0.363Ni) ≧ 3.80 (3)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formula (3).

  FN3 = (1 + 0.7Si) × (1 + 3.3333Mn) × (1 + 2.16Cr) × (1 + 3.00Mo) × (1 + 1.73V) × (1 + 0.365Cu) × (1 + 0.363Ni). FN3 is an index of hardenability of induction hardening steel. If FN3 is 3.80 or more, generation of an incompletely quenched structure during induction hardening can be suppressed. On the other hand, when FN3 is less than 3.80, the hardenability is lowered, and an incompletely hardened structure may be generated. A preferred lower limit of FN3 is 4.00. A preferable upper limit of FN2 is 15.00.

[Regarding Formula (4)]
The steel for induction hardening according to this embodiment satisfies the formula (4).
9.7 Mn _θ + 32.4Cr _θ ≦ 25.9 (4)
Here, the concentration (mass%) of Mn in cementite is substituted for Mn _θ in the formula (4). For Cr _θ in formula (4), the concentration (mass%) in cementite is substituted.

  In addition, said cementite is cementite of the steel for induction hardening.

FN4 = is defined as 9.7Mn θ + 32.4Cr _θ. FN4 is an index of hardness variation. Induction hardening is an extremely short time heating compared with furnace heating, and is in a non-equilibrium state. Therefore, variation in the amount of solid solution C occurs because cementite remains undissolved. As a result, hardness variation occurs.

  By increasing the solution temperature of cementite and controlling the Mn concentration and Cr concentration in the cementite that affect the undissolved cementite to below appropriate values, the undissolved cementite can be reduced. Thereby, hardness variation can be suppressed. Thereby, surface fatigue strength and bending fatigue strength increase.

  If FN4 is 25.9 or less, undissolved carbide during induction hardening does not remain. On the other hand, when FN4 exceeds 25.9, the solution temperature of cementite rises and undissolved carbides may remain. A preferred lower limit of FN4 is 3.00. A preferable upper limit of FN4 is 20.00.

[Method for measuring Mn concentration and Cr concentration in cementite]
Mn concentration (mass%) and Cr concentration (mass%) in cementite are measured by electrolytic extraction residue. Specifically, it is as follows. A test specimen for measurement is taken from an arbitrary position of the induction hardening steel. The test piece is electrolyzed using a 10% AA-based electrolytic solution (10% acetylacetone, 1% tetraammonium chloride-methanol). After electrolysis, the residue is collected with a 0.2 μm filter. The mass of the collected residue is measured. Further, an acid decomposition treatment is performed on the collected residue. After the acid decomposition treatment, ICP-AES (High Frequency Inductively Coupled Plasma Atomic Spectroscopy) is performed to measure the mass of Fe, Cr, and Mn in the residue. Assuming that all the residues are M ₃ C type carbides, that is, cementite, the masses of Mn and Cr in the cementite are calculated. From the obtained results, the Cr concentration and the Mn concentration dissolved in the cementite are calculated.

[Ferrite volume fraction: 40% or less]
Further, in the steel for induction hardening according to the present embodiment, the ferrite volume fraction is 40% or less. In the induction hardening, since the heat treatment time is short, the diffusion time of C is also short. Therefore, the time for the carbide to dissolve is shortened. As a result, the ferrite volume fraction tends to be high. However, if the ferrite volume fraction exceeds 40%, ferrite remains in the structure after induction hardening. When the ferrite volume fraction exceeds 40%, the generation of low carbon martensite further occurs. As a result, extreme hardness variations occur. As a result, the surface fatigue strength decreases. Therefore, the ferrite volume fraction is 40% or less. The upper limit with a preferable ferrite volume fraction is 35%, More preferably, it is 30%. A preferable lower limit of the ferrite volume fraction is 5%.

  In the present embodiment, the balance of the microstructure is bainite and / or pearlite. The volume fraction of bainite is preferably 10% or less. If the volume fraction of bainite is 10% or less, the steel can be prevented from becoming too hard. Therefore, it can suppress that machinability falls.

[Measurement method of ferrite volume fraction]
A specimen for microstructural observation is taken from the induction hardening steel. Of the surface of the test piece, a cross section (hereinafter referred to as an observation surface) perpendicular to the axial direction of the induction hardening steel is polished. The observation surface after polishing is etched using a nital etchant. In the etched observation plane, the ferrite is specified. The area ratio of the identified ferrite is measured by a point calculation method based on JIS G 0555 (2003). Since the measured area ratio is considered to be equal to the volume fraction, this is defined as the ferrite volume fraction (vol%). The volume fraction of bainite can be measured similarly.

[Shape of induction hardening parts]
The shape material of the induction-hardened component is obtained by hot forging steel for induction hardening and processing it into a rough shape of the induction-hardened component. Therefore, the chemical composition of the base material of the induction-hardened component according to this embodiment is the same as the chemical composition of the steel for induction hardening according to this embodiment. Therefore, the chemical composition of the base material of the induction-hardened part satisfies the formulas (1) to (3). The base material of the induction-hardened component of the present embodiment further satisfies the formula (4). Further, in the base material of the induction-hardened component of the present embodiment, the ferrite volume fraction is 40% or less.

  The method of measuring the Mn concentration and the Cr concentration in cementite of the shape material of the induction-hardened component according to the present embodiment is the same as that for induction hardening steel. The observation method of the microstructure of the base material of the induction-hardened component according to the present embodiment is the same as that of the steel for induction hardening.

  [Induction hardening parts]

  The induction-hardened component according to the present embodiment is a mechanical structural component used for a power transmission component typified by a differential gear.

  The induction-hardened component according to the present embodiment includes a quenched portion that is a portion where induction hardening has been performed and an unquenched portion that is a portion where induction hardening has not been performed.

  In the quenched portion, the martensite volume fraction is 90% or more. The martensite volume fraction in the quenched portion can be measured from the contrast by observing the structure. In the unquenched part, the ferrite volume fraction is 40% or less.

  Even if induction hardening is performed on the steel for induction hardening according to the present embodiment, the chemical composition does not change. Therefore, the chemical composition of the induction hardening component according to this embodiment is the same as the chemical composition of the induction hardening steel according to this embodiment. Therefore, the chemical composition of the induction-hardened part satisfies the formulas (1) to (3). The unquenched part of the induction-hardened component according to the present embodiment further satisfies the formula (4).

  In addition, the induction-hardened component according to the present embodiment is obtained by induction-quenching the steel for induction hardening according to the present embodiment. Therefore, the induction-hardened component according to the present embodiment does not have a heterogeneous abnormal surface layer including residual γ, nitride, and grain boundary oxidation. Alternatively, in the induction-hardened component according to the present embodiment, the generation of the surface abnormal layer is suppressed to the minimum. The induction-hardened component according to the present embodiment further has a Vickers hardness of 631 Hv or more at a depth of 50 μm from the surface even after tempering at 300 ° C.

  When measuring the Mn concentration and the Cr concentration in cementite in an induction-hardened component, a test specimen for measurement is taken from an unquenched portion, which is a portion that has not been induction-hardened. The subsequent procedure is the same as in the case of the induction hardening steel.

  When measuring the ferrite volume fraction in an induction-hardened component, a test specimen for measurement is taken from an unquenched portion, which is a portion that has not been subjected to induction hardening. The subsequent procedure is the same as in the case of the induction hardening steel.

[Production method]
[Method of manufacturing induction hardening steel]
An example of the manufacturing method of the steel for induction hardening of this embodiment is as follows. In addition, the manufacturing method of the steel for induction hardening of this embodiment is not limited to this. However, the manufacturing method described below is a suitable example of the method for manufacturing the steel for induction hardening according to the present embodiment.

[Casting process]
In the casting process, slab (slab or bloom) or steel ingot (ingot) is produced by using a molten steel by a known casting method. The casting method is, for example, a continuous casting method or an ingot-making method. For example, the casting conditions are as follows. A 220 × 220 mm square mold is used. The superheat of the molten steel in the tundish (difference between the molten steel temperature and the solidification temperature of the molten steel) is set to 10 to 50 ° C. The casting speed is set to 1.0 to 1.5 m / min. The slab or the steel ingot satisfies the chemical composition and formulas (1) to (3).

[Hot working process]
In the hot working step, hot working is performed on the slab or steel ingot produced in the casting step to produce the steel for induction hardening according to the present embodiment. The steel for induction hardening of this embodiment is, for example, a steel bar and a wire. Below, an example of the manufacturing method in case the steel for induction hardening is a bar steel and a wire is shown.

  The hot working process includes a finish rolling process for performing finish rolling. The finish rolling is, for example, finish rolling using a continuous rolling mill. In a continuous rolling mill, for example, a horizontal stand having a pair of horizontal rolls and a vertical stand having a pair of vertical rolls are alternately arranged in a line.

  In the hot working step, for example, the billet is heated at a heating temperature of 1250 to 1300 ° C. for 1.5 hours or more and then hot rolled at a finishing temperature of 900 to 1100 ° C. The above heating temperature and heating time mean the average temperature in the furnace and the in-furnace time, respectively. The finishing temperature of hot rolling means the surface temperature of the bar and wire at the final stand outlet of a rolling mill having a plurality of stands.

  After finish rolling, it cools in air | atmosphere on the conditions from which a cooling rate becomes below cooling. The cooling after finish rolling may be any of air cooling, oil cooling, and water cooling. However, in order for the Mn concentration and the Cr concentration in the cementite to satisfy the formula (4), the cooling is performed as follows as an example, although it depends on the amount of each element added. In the temperature range from 700 ° C., which is the start temperature of cementite formation, to 300 ° C., which is the lower limit temperature for alloy element diffusion, the average cooling rate is preferably 0.1-1.0 ° C./second. When the average cooling rate in the temperature range of 700 ° C. to 300 ° C. is less than 0.1 ° C./second, the Mn concentration and the Cr concentration in the cementite increase, and the formula (4) may not be satisfied. In this case, hardness variation occurs. When the average cooling rate in the temperature range of 700 ° C. to 300 ° C. exceeds 1.0 ° C./second, the amount of bainite and martensite produced increases. In this case, machinability may be reduced. The cooling rate after finish rolling refers to the cooling rate at the surface of the steel bar and wire.

  The adjustment of Mn concentration and Cr concentration in cementite is not limited to the above production method. If it satisfies said chemical composition and Formula (1)-Formula (4), it will not specifically limit to said manufacturing method.

  Normalizing treatment may be performed on the steel bar and wire rod after finish rolling. When performing the normalizing process, the cooling rate in the normalizing process is as described above.

  The induction hardening steel is manufactured by the above manufacturing process.

[Manufacturing method of induction hardening parts]
The above-mentioned induction hardening steel (bar steel or wire) is hot forged to produce a rough shaped material for induction hardening parts (for example, differential gear). The manufactured shaped material is allowed to cool in the atmosphere.

  A tempering treatment or a normalizing treatment may be performed on the shaped material after being allowed to cool. The conditions for the normalizing treatment are as follows, for example. The shaped material after being allowed to cool is heated at 850 ° C. for 1 hour. The shaped material after heating is cooled. The cooling method may be any of air cooling, oil cooling, and water cooling. However, depending on the amount of each element added, in the temperature range from 700 ° C., which is the cementite formation start temperature, to 300 ° C., which is the lower limit temperature for alloy element diffusion, the average cooling rate is 0.1-1.0 ° C. / The second is preferred. When the average cooling rate in the temperature range of 700 ° C. to 300 ° C. is less than 0.1 ° C./second, the Mn concentration and the Cr concentration in the cementite increase, and the formula (4) may not be satisfied. In this case, hardness variation occurs. When the average cooling rate in the temperature range of 700 ° C. to 300 ° C. exceeds 1.0 ° C./second, the amount of bainite and martensite produced increases. In this case, machinability may be reduced.

[Method of manufacturing induction-hardened parts]
An example of the manufacturing method of the induction hardening component using the steel for induction hardening of this embodiment is as follows.

  Machining is performed on the base material to form the base material into a predetermined shape. Machining is, for example, cutting or drilling.

  Induction hardening is performed on the shaped material after machining to harden the surface of the shaped material. Thereby, a surface hardened layer is formed on the surface of the base material. Finishing is performed on the induction-hardened material. The finishing process is grinding or polishing.

  In the induction hardening, the quenching temperature (maximum heating temperature) is set to 850 to 1100 ° C., and cooling is performed from this temperature range. When the quenching temperature is less than 850 ° C., the material cannot be sufficiently quenched by induction quenching. In this case, pro-eutectoid ferrite appears and the hardness of the surface hardened layer becomes non-uniform. As a result, the surface fatigue strength does not increase. Further, when the quenching temperature is less than 850 ° C., the surface layer portion is not sufficiently austenitic, and a desired quenching layer depth cannot be obtained. On the other hand, when the quenching temperature exceeds 1100 ° C., the surface layer portion is significantly oxidized, and the smoothness of the surface properties is not sufficiently ensured. In this case, the surface fatigue strength decreases. Moreover, in order to fully austenite the surface layer, it is preferable that the time when the temperature is 850 ° C. or higher is 0.5 second to 1 minute.

  The induction-hardened component is manufactured by the above process. The induction hardened component has the same chemical composition as the induction hardening steel of this embodiment. Insoluble cementite does not remain in the hardened surface layer of the induction-hardened component manufactured by the above process.

  Hereinafter, the present invention will be specifically described by way of examples. The conditions in the examples are one condition example adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to this one condition example. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

[experimental method]
Steels having chemical compositions shown in Tables 1 and 2 were melted with 150 kg ingots. The ingot was heated at a heating temperature of 1200 to 1250 ° C. for 1.5 hours or more. Hot forging was performed on the heated ingot to produce a steel bar having a diameter of 30 to 100 mm.

  Normalization was performed on the manufactured steel bars. The conditions for normalization were as follows. The manufactured steel bar was heated at 850 ° C. for 1 hour. The heated steel bar was cooled by air cooling, oil cooling or water cooling. The average cooling rate was adjusted from a temperature range of 700 ° C., which is the cementite formation start temperature, to a temperature range of 300 ° C., which is a lower limit temperature for alloy element diffusion, in a range of 0.1-1.0 ° C./second. The average cooling rate of each test number was as described in the “Normalized cooling rate” column of Tables 3 and 4. As described above, induction hardening steels of Test No. 1 to Test No. 56 were manufactured.

[Machinability evaluation test]
The machinability was evaluated using the induction hardening steel of each test number. First, in order to evaluate the drill machinability, a test piece was collected from the center of a steel bar having a diameter of 30 to 100 mm and cut into a test piece for machinability evaluation having a cylindrical cross section and a height of 21 mm.

  The tool used was a drill of Fujikoshi Co., Ltd., model number SD3.0. The feed amount per rotation was 0.25 mm, and the drilling depth of one hole was 9 mm. A water-soluble cutting oil was used as the lubricant. Drill drilling tests were conducted to evaluate the machinability of induction hardening steels of each test number.

  As an evaluation index, a maximum cutting speed VL1000 capable of cutting up to a cumulative hole depth of 1000 mm was adopted. It was evaluated that 40 m / min or more was excellent in machinability at the maximum cutting speed VL1000. When the maximum cutting speed VL1000 was less than 40 m / min, the machinability was evaluated to be poor, and Table 3 and Table 4 indicate x.

  In addition, among what evaluated that it was excellent in machinability, 50 m / min or more was shown in A, Table 3, and Table 4 with the maximum cutting speed VL1000. Tables 3 and 4 show the maximum cutting speed VL45 to 49 m / min. Tables 3 and 4 show the maximum cutting speed VL of 40 to 44 m / min.

[Measurement of Cr concentration and Mn concentration in cementite]
Mn concentration (mass%) and Cr concentration (mass%) in cementite were measured by electrolytic extraction residue. Specifically, it was as follows. A test specimen for measurement was taken from an arbitrary position of the remaining material of the drill specimen. The test piece was electrolyzed using a 10% AA electrolyte (10% acetylacetone, 1% tetraammonium chloride-methanol). After electrolysis, the residue was collected with a 0.2 μm filter. The mass of the collected residue was measured. Furthermore, an acid decomposition treatment was performed on the collected residue. After the acid decomposition treatment, ICP-AES (high frequency inductively coupled plasma atomic spectroscopy) was performed to measure the mass of Fe, Cr, and Mn in the residue. The mass of Cr and Mn in cementite was calculated on the assumption that all the residues were M ₃ C type carbides, that is, cementite. From the obtained results, Cr concentration and Mn concentration dissolved in cementite were calculated.

  In addition, hot forging was performed on the induction hardening steel of each test number, and the shape material of the induction hardening component obtained by performing the same cooling method was the same as the induction hardening steel. Results were obtained. Similarly, the Cr concentration and the Mn concentration dissolved in cementite were also measured for the induction-quenched parts described later. However, the test piece was collected from the unquenched part.

[Ferrite volume fraction measurement]
A test piece for observing the microstructure was taken from the remaining material of the drill test piece of each test number. Of the surface of the test piece, a cross section (hereinafter referred to as an observation surface) perpendicular to the axial direction of the remaining material was polished. The observation surface after polishing was etched using a nital etchant. In the etched observation surface, ferrite was identified. The area ratio of the identified ferrite was measured by a point calculation method based on JIS G 0555 (2003). The measured area ratio was considered to be equal to the volume fraction, and this was defined as the ferrite volume fraction (vol%).

  In addition, hot forging was performed on the induction hardening steel of each test number, and the shape material of the induction hardening component obtained by performing the same cooling method was the same as the induction hardening steel. Results were obtained. The ferrite volume fraction was measured in the same manner for the induction-quenched parts described later. However, the test piece was collected from the unquenched part.

[Roller pitching fatigue test]
A test piece for roller pitting fatigue test for evaluation of surface fatigue strength was processed from induction hardening steel of each test number. When the test piece had a diameter of less than 80 mm, it was collected from the center and processed. In the case of a diameter of 80 mm or more, processing was performed so that 1/4 of the diameter was the center.

  The test piece for roller pitting fatigue test had the shape shown in FIG. Numerical values in FIG. 1 indicate dimensions. The test piece for the roller pitting fatigue test was cylindrical, and had a parallel part with a diameter of 26 mm in the center. The diameter of the roller pitting fatigue test specimen other than the parallel portion was 22 mm. The test piece for the roller pitting fatigue test was the small roller test piece 200 in FIG.

  The small roller test piece 200 was subjected to induction hardening at a heating temperature of 1000 ° C. × 20 seconds, and then tempered at 150 ° C. for 1 hour, and the surface fatigue strength was evaluated by a roller pitching test. Specifically, it is as follows.

  FIG. 2 is a schematic diagram of a roller pitching test. As shown in FIG. 2, the small roller test piece 200 was rotated while pressing the large roller test piece 100 against the small roller test piece 200 with the above surface pressure. The small roller test piece 200 was a roller pitching test piece prepared in the preparation of the test piece. As the large roller test piece 100, a steel having a chemical composition corresponding to SCM722 defined in JIS G 4053 (2016) and subjected to surface polishing after carburizing was used. The radius of the large roller test piece 100 was 130 mm.

In the roller pitting fatigue test, the large roller test piece 100 was pressed against the small roller test piece 200 with a surface pressure of various Hertz stresses. The circumferential speed direction of both roller test pieces at the contact portion is the same direction, and the slip rate is -40% (the peripheral speed of the contact portion is 40% greater for the large roller test piece 100 than for the small roller test piece 200). The test was carried out with rotation. The oil temperature of ATF (AT lubricating oil) supplied as a lubricating oil to the contact portion was 80 ° C., and the contact stress between the large roller test piece 100 and the small roller test piece 200 was 3000 to 3300 MPa. When the number of test censoring is 10 million times ( ¹⁰⁷ times) and the number of rotations reaches 10 million without causing pitching in the small roller test piece 200, the surface fatigue strength is sufficiently high. It was judged that durability (roller pitching fatigue durability) was sufficiently secured. Among those judged to have high surface fatigue strength, 3300 MPa durability is shown in A and Tables 3 and 4. The 3200 MPa durability is shown in B and Tables 3 and 4. Table 3 and Table 4 show the 3100 MPa durability. 3000 MPa durability is shown in D and Tables 3 and 4. Those in which pitching occurred until the number of revolutions reached 10 million were evaluated as having low surface fatigue strength, and are shown as x in Tables 3 and 4.

  The occurrence of pitching was detected by a vibrometer provided in the testing machine, and after the vibration was detected, the rotation of both roller test pieces was stopped to confirm the occurrence of pitching and the number of rotations.

[Ono type rotating bending fatigue test]
The Ono rotary bending test piece for bending fatigue strength evaluation shown in FIG. 3 was processed from the induction hardening steel of each test number. The test piece had a 9 mm cross-sectional diameter at the notch bottom. The Ono rotary bending test piece was subjected to induction hardening at 1000 ° C. for 5 seconds and then tempered at 150 ° C. for 1 hour.

Using the Ono rotary bending test piece after induction hardening, an Ono rotary bending fatigue test was performed. In the Ono type rotating bending fatigue test, the load load is adjusted so as to obtain a predetermined bending stress, the number of test aborts is 10 million times (10 ⁷ times), and the Ono type rotating bending fatigue test piece is 10 million times without breaking. When the number of rotations was reached, it was judged that the bending fatigue strength was sufficiently high and the bending fatigue strength was sufficiently secured. Even when it is judged that the bending fatigue strength is sufficiently secured, the 680 MPa durability is shown in A and Tables 3 and 4. The 665 MPa durability is shown in B and Tables 3 and 4. 650 MPa durability is shown in Tables 3 and 4 with C. Those fractured before reaching the number of rotations of 10 million times were evaluated as having low bending fatigue strength, and shown in Table 3 and Table 4 as x.

[Test results]
The test results are shown in Tables 3 and 4.

  With reference to Tables 1 to 4, test numbers 2, 3, 6, 7, 9, 12, 13, 16, 17, 20, 21, 24 to 28, 30, 31, 33, 34, 36, 37, In 39-53, the chemical composition was appropriate, and FN1-FN3 was also appropriate. Therefore, it was excellent in machinability, surface fatigue strength, and bending fatigue strength. Furthermore, since manufacturing conditions were appropriate, FN4 and ferrite volume fraction were appropriate. Therefore, since it was excellent in surface fatigue strength and bending fatigue strength, it can be judged that the hardness variation after induction hardening could be suppressed.

  On the other hand, in test number 1, the C content was too high. Therefore, machinability was low. Furthermore, fire cracks occurred.

  In test number 4, the C content was too low. Therefore, the surface fatigue strength and bending fatigue strength characteristics were low.

  In test number 5, the Si content was too high. Therefore, the surface fatigue strength and bending fatigue strength characteristics were low.

  In test number 8, the Mn content was too low. Therefore, evaluation was not performed because thermal forging cracks occurred.

  In test number 10, it did not contain Cr. Furthermore, FN3 was less than 3.80. Therefore, evaluation was not performed because thermal forging cracks occurred.

  In test number 11, the S content was too high. Therefore, the bending fatigue strength was low.

  In test number 14, the S content was too low. Therefore, machinability was low.

  In test number 15, the N content was too high. Therefore, evaluation was not performed because thermal forging cracks occurred.

  In test number 18, the N content was too low. Therefore, the bending fatigue strength was low.

  In test number 19, the Al content was too high. Therefore, the surface fatigue strength and the bending fatigue strength were low.

  In test number 22, the Al content was too low. Therefore, the bending fatigue strength was low.

  In test number 23, the P content was too high. Therefore, the bending fatigue strength was low.

  In test number 29, FN1 was less than the lower limit of formula (1). Therefore, the surface fatigue strength was low.

  In test number 32, FN2 exceeded the upper limit of formula (2). Therefore, machinability was low.

  In test number 35, FN3 was less than the lower limit of formula (3). Therefore, the surface fatigue strength and the bending fatigue strength were low.

  In test number 38, FN4 exceeded the upper limit of formula (4). Therefore, the surface fatigue strength and the bending fatigue strength were low. Therefore, it is considered that the hardness variation after induction hardening occurred. Although the added amount of Cr and the added amount of Mn are within the scope of the present application, it is considered that they were relatively high and the cooling rate after normalization was relatively slow.

  In test number 54, the cooling rate after normalization was slow. Therefore, FN4 exceeded the upper limit of Formula (4). As a result, the surface fatigue strength and the bending fatigue strength were low. Therefore, it is considered that the hardness variation after induction hardening occurred.

  In test number 55, the ferrite fraction was too high. Therefore, the surface fatigue strength and the bending fatigue strength were low. Therefore, it is considered that the hardness variation after induction hardening occurred.

  In test number 56, the Cr content was too low. Therefore, evaluation was not performed because thermal forging cracks occurred.

  The embodiments of the present invention have been described above. However, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately changing the above-described embodiment without departing from the spirit thereof.

  The steel for induction hardening according to the present embodiment is excellent in machinability and has excellent surface fatigue strength and bending fatigue strength when an induction hardening component is obtained.

100 Large roller specimen 200 Small roller specimen

Claims (15)

% By mass
C: 0.40 to 0.70%,
Si: 0.15 to 2.10%,
Mn: 0.30 to 1.15%,
Cr: 0.01 to less than 0.50%,
S: 0.005-0.070%,
N: 0.0020 to 0.0200%,
Al: 0.005 to 0.100%,
P: less than 0.050%,
Mo: 0 to 1.00%,
Ni: 0 to 1.00%,
Cu: 0 to 1.00%,
Ca: 0 to 0.005%,
Mg: 0 to 0.005%,
Te: 0 to 0.2000%,
Zr: 0 to 0.0050%,
Rare earth elements: 0-0.0050%,
Ti: 0 to 0.200%,
Nb: 0 to 0.200%,
V: 0 to 0.35%,
Sb: 0 to 0.0150%,
Pb: 0 to 0.5000%, and
Remainder: Steel for induction hardening comprising Fe and impurities, having a chemical composition satisfying formulas (1) to (4), and having a ferrite volume fraction of 40% or less.
290C + 50Si + 430 ≧ 631.0 (1)
C + (1/7) Si + (1/5) Mn + (1/9) Cr + V + (1/25) Mo ≦ 0.900 (2)
(1 + 0.7Si) × (1 + 3.3333Mn) × (1 + 2.16Cr) × (1 + 3.00Mo) × (1 + 1.73V) × (1 + 0.365Cu) × (1 + 0.363Ni) ≧ 3.80 (3)
9.7 Mn _θ + 32.4Cr _θ ≦ 25.9 (4)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formulas (1) to (3), and Mn concentration in the cementite is substituted for Mn _θ in the formula (4). (Mass%) is substituted, and Cr concentration in the cementite (mass%) is substituted for Cr _θ in the formula (4). The induction hardening steel according to claim 1,
The chemical composition is
Mo: 0.01 to 1.00%,
Ni: 0.05-1.00%, and
Cu: Steel for induction hardening containing one or more selected from the group consisting of 0.05 to 1.00%. Induction hardening steel according to claim 1 or claim 2,
The chemical composition is
Ca: 0.0003 to 0.005%,
Mg: 0.0003 to 0.005%,
Te: 0.0003 to 0.2000%,
Zr: 0.0003 to 0.0050%, and
Rare earth element: Steel for induction hardening containing one or more selected from the group consisting of 0.0003 to 0.0050%. The steel for induction hardening according to any one of claims 1 to 3,
The chemical composition is
Ti: 0.005 to 0.200%,
Nb: 0.005 to 0.200%, and
V: Steel for induction hardening containing one or more selected from the group consisting of 0.005 to 0.35%. The steel for induction hardening according to any one of claims 1 to 4,
The chemical composition is
Sb: 0.0003 to 0.0150%, and
Pb: Steel for induction hardening containing at least one selected from the group consisting of 0.0100 to 0.5000%. % By mass
C: 0.40 to 0.70%,
Si: 0.15 to 2.10%,
Mn: 0.30 to 1.15%,
Cr: 0.01 to less than 0.50%,
S: 0.005-0.070%,
N: 0.0020 to 0.0200%,
Al: 0.005 to 0.100%,
P: less than 0.050%,
Mo: 0 to 1.00%,
Ni: 0 to 1.00%,
Cu: 0 to 1.00%,
Ca: 0 to 0.005%,
Mg: 0 to 0.005%,
Te: 0 to 0.2000%,
Zr: 0 to 0.0050%,
Rare earth elements: 0-0.0050%,
Ti: 0 to 0.200%,
Nb: 0 to 0.200%,
V: 0 to 0.35%,
Sb: 0 to 0.0150%,
Pb: 0 to 0.5000%, and
Remainder: A material for induction-hardened parts, comprising Fe and impurities, having a chemical composition satisfying the formulas (1) to (4), and having a ferrite volume fraction of 40% or less.
290C + 50Si + 430 ≧ 631.0 (1)
C + (1/7) Si + (1/5) Mn + (1/9) Cr + V + (1/25) Mo ≦ 0.900 (2)
(1 + 0.7Si) × (1 + 3.3333Mn) × (1 + 2.16Cr) × (1 + 3.00Mo) × (1 + 1.73V) × (1 + 0.365Cu) × (1 + 0.363Ni) ≧ 3.80 (3)
9.7 Mn _θ + 32.4Cr _θ ≦ 25.9 (4)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formulas (1) to (3), and Mn concentration in the cementite is substituted for Mn _θ in the formula (4). (Mass%) is substituted, and Cr concentration in the cementite (mass%) is substituted for Cr _θ in the formula (4). It is the shape material of the induction-hardened component according to claim 6,
The chemical composition is
Mo: 0.01 to 1.00%,
Ni: 0.05-1.00%, and
Cu: A base material for induction-hardened parts, containing one or more selected from the group consisting of 0.05 to 1.00%. A base material of the induction-hardened component according to claim 6 or 7,
The chemical composition is
Ca: 0.0003 to 0.005%,
Mg: 0.0003 to 0.005%,
Te: 0.0003 to 0.2000%,
Zr: 0.0003 to 0.0050%, and
Rare earth element: A shape material for induction-hardened parts containing one or more selected from the group consisting of 0.0003 to 0.0050%. It is a shape material of the induction-hardened component according to any one of claims 6 to 8,
The chemical composition is
Ti: 0.005 to 0.200%,
Nb: 0.005 to 0.200%, and
V: A base material for induction-hardened parts, containing one or more selected from the group consisting of 0.005 to 0.35%. It is a base material of the induction-hardened component of any one of Claims 6-9,
The chemical composition is
Sb: 0.0003 to 0.0150%, and
Pb: A base material for induction-hardened parts, containing at least one selected from the group consisting of 0.0100 to 0.5000%. A quenching portion that is a portion where induction hardening has been performed;
Including an unquenched portion that is a portion where induction hardening has not been performed,
In the quenched portion, the martensite volume fraction is 90% or more,
The unquenched part is
% By mass
C: 0.40 to 0.70%,
Si: 0.15 to 2.10%,
Mn: 0.30 to 1.15%,
Cr: 0.01 to less than 0.50%,
S: 0.005-0.070%,
N: 0.0020 to 0.0200%,
Al: 0.005 to 0.100%,
P: less than 0.050%,
Mo: 0 to 1.00%,
Ni: 0 to 1.00%,
Cu: 0 to 1.00%,
Ca: 0 to 0.005%,
Mg: 0 to 0.005%,
Te: 0 to 0.2000%,
Zr: 0 to 0.0050%,
Rare earth elements: 0-0.0050%,
Ti: 0 to 0.200%,
Nb: 0 to 0.200%,
V: 0 to 0.35%,
Sb: 0 to 0.0150%,
Pb: 0 to 0.5000%, and
Remainder: Induction-hardened component that consists of Fe and impurities, has a chemical composition that satisfies the formulas (1) to (4), and has a ferrite volume fraction of 40% or less.
290C + 50Si + 430 ≧ 631.0 (1)
C + (1/7) Si + (1/5) Mn + (1/9) Cr + V + (1/25) Mo ≦ 0.900 (2)
(1 + 0.7Si) × (1 + 3.3333Mn) × (1 + 2.16Cr) × (1 + 3.00Mo) × (1 + 1.73V) × (1 + 0.365Cu) × (1 + 0.363Ni) ≧ 3.80 (3)
9.7 Mn _θ + 32.4Cr _θ ≦ 25.9 (4)
Here, the content (mass%) of the corresponding element is substituted for each element symbol in the formulas (1) to (3), and Mn concentration in the cementite is substituted for Mn _θ in the formula (4). (Mass%) is substituted, and Cr concentration in the cementite (mass%) is substituted for Cr _θ in the formula (4). The induction-hardened component according to claim 11,
The chemical composition is
Mo: 0.01 to 1.00%,
Ni: 0.05-1.00%, and
Cu: An induction-hardened component containing one or more selected from the group consisting of 0.05 to 1.00%. The induction-hardened component according to claim 11 or 12,
The chemical composition is
Ca: 0.0003 to 0.005%,
Mg: 0.0003 to 0.005%,
Te: 0.0003 to 0.2000%,
Zr: 0.0003 to 0.0050%, and
Rare earth element: Induction-hardened component containing one or more selected from the group consisting of 0.0003 to 0.0050%. The induction-hardened component according to any one of claims 11 to 13,
The chemical composition is
Ti: 0.005 to 0.200%,
Nb: 0.005 to 0.200%, and
V: An induction-hardened component containing one or more selected from the group consisting of 0.005 to 0.35%. The induction-hardened component according to any one of claims 11 to 14,
The chemical composition is
Sb: 0.0003 to 0.0150%, and
Pb: induction-hardened part containing one or more selected from the group consisting of 0.0100 to 0.5000%.