3.3 Gear materials and Heat treatments
Refer to Table 5 for suitable materials and its method of heat treatment for load. Also refer to Table 6 for hardness
range of heat treatment.
Table 5. Loads, Materials and Heat treatment methods
LoadLight load

Material number

Light impact load and minutewear off

S35C ～ S45C

Thermal refining (Quenching and Tempering)

Slight wear resistance needed

S15CK

Carburizing, Quenching and Tempering (Depthof hardness 0.2 to 0.4mm)

S35C ～ S45C

Induction hardening is lightly applied after Thermal refining. Hardness of Tooth tip is HRC47 to56 (1)SCM415SCr415

Carburizing, Quenching and Tempering (Depthof hardness 0.6 to 1.0). Surface hardness is fromHRC 55 to 60.

S40C ～ S45C

Induction hardening(2) is applied after Thermal
refining. Depth of hardness should be slightlydeeper. Apply Induction hardening to Rootdiameter. Hardness of Tooth tip surface isHRC47-56(1).

SCM435
SCM440

Nitriding treatment, Gas nitrocarburizing, Tufftriding and etc. are applied after Thermal refining.

Special impact resistance ifneeded

SNC815
SNCM420
SNCM815Carburizing, Quenching and Tempering. Surface
Hardness from HRC 58 to 64

Wear resistance needed

SNCM420
SCM421
SCM822

Carburizing, Quenching and Tempering. Surface
hardness is for HRC 62 and above

Wear resistance and Fatigue
strength needed

S45C
S48C

Apply Induction hardening(2) to area of root diameter after Thermal refining. Hardness of Tooth tip
is HRC 56-60(1)Sand burning resistanceneededNitriding steel

Apply Nitration treatment after Thermal refining

Alloyed steel SCM435

Apply Nitration treatment after Thermal refining

Anti-corrosion needed

Austenite, Ferrite, Martenstic group, Stainlesssteel

Consider other properties together with Anticorrosion when selecting suitable heat treatment.

Heat resistance needed

Fe-Cr-Ni Alloy

Apply suitable Heat treatment as required

Medium strength and wear
resistance needed

Medium load

Fatigue strength needed

Heavy Load

Special load

Note(1) Area of tooth flank near Bottomland is HRC 5-10 lower than HRC47-56.
(2) Motor generator system (MG) with low frequency is suitable for relatively large size gear.

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Methods of heat treatment

Table 6. Hardness of Heat treatment
Name of steelsNickel-chrome steel

Nickel chrome
molybdenum steel

Chrome steel

Chromemolybdenum steel

Carbon steel

SurfaceInduction hardhardness ofCase hardening
ening HRC
HRC

Core hardnessof Casehardening HBMaterial
numbers

Hardness forThermal
refining Hs

Full quenching
Hs

SNC631

37-40

50-55

50-55

--

SNC836

38-42

50-55

50-55

-

-

SNC415-

-

-

55-60

217-321

SNC815-

-

-

58-64

285-388

SNCM439

43-51

65-70

-

--

SNCM447

45-53

65-70

-

-

-

SNCM220

-

-

-

58-64

248-341

SNCM415-

-

-

58-64

255-341

SNCM420---58-64

293-375

SNCM815---58-64311-375

SCr415---58-64

217-300

SCr420---58-64

235-320

SCM435

37-40

45-50

45-50

-

-

SCM440

38-42

50-55

(50-53)(2)--

SCM415---58-64

235-321

SCM420---58-64

262-341

SCM421---

58-64

285-263

S15CK---

55-62(3)

131(4)

S35C

25-35

35-45

35-40

-

-

S45C

31-40

45-55

40-45

-

-S55C

33-42

55-65

45-50

--Note(1) Refer to Table 5 for Load, Material and Heat treatment. Core hardness is equivalent to Thermal refining hardness.
(2) Applying Induction hardening to teeth is not advisable.
(3) Hardness is (50-53) for water cooling and 50 - 55 is for oil cooling.
(4) Maximum hardness.

Guide
Table 7. Sizes of tooth and depth of Carburizing
Module mm

Range fromm1.0 tom1.5

Range fromm1.5 tom2.0

Range fromm2.0 tom2.75

Range fromm2.75 tom4.0

Range fromm4.0 tom6.0

Range fromm6.0 tom9.0

Range fromm9.0 tom12.0

Depth of Carburizing
mm

0.2-0.5

0.4-0.7

0.6-1.0

0.8-1.21.0-1.4

1.2-1.7

1.3-2.0

Note: Depth of Carburizing is rough outline for standard value for Gas carburizing. Solid or liquid Carburizing adopts a smaller amount than the abovechart.

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