Search Steel

Gear Materials

1-Types of Gear Materials

S45C (Carbon Steel for Structural Machine Usage)

S45C is one of the most commonly used steel, containing moderate amounts of carbon (0.45% ). S45C is easily obtainable and is used in the production of spur gears, helical gears, gear racks, bevel gears and worm gears.

Heat Treatment and Hardness

Heat Treatment	Hardness
None	less than 194HB
Thermal Refining	225 – 260HB
Induction Hardening	45 – 55HRC

SCM440 (Chrome-molybdenum Alloy Steel)

An alloy steel containing moderate amounts of carbon (0.40% ). It also contains chrome / molybdenum. SCM440 has more strength than S45C and is used with thermal-refining or induction-hardening treatment for producing gears.

Heat Treatment and Hardness

Heat Treatment	Hardness
Thermal Refining	225 – 260HB
Induction Hardening	45 – 60HRC

SCM415 (Chrome-molybdenum Alloy Steel)

SCM415 is one of the most commonly used low-carbon alloy steel (C = 0.15%). Generally, it is carburized for use. It has more strength than S45C or SCM440. Surface hardness should be between 55 and 60HRC for use.

SUS303 (Stainless Steel：18Cr-8Ni Stainless Steel)

Since it is called “stainless steel”, it is a rust-resistant steel. This authentic stainless steel is basically non-magnetic. Most commonly used for gears in applications where rust contamination is undesirable, such as in food-processing machinery. There is a similar stainless steel called SUS304 which has more corrosion resistance than SUS303.

Copper Alloy Casting

Frequently used as a material for worm wheels. Phosphor bronze casting (CAC502) or aluminum-bronze casting(CAC702) are commonly used. For mating worms, iron metals such as S45C/SCM44/SCM415 are used. To prevent galling / seizure by slippage, different materials are used for each of the paired worm and worm wheel.

Worm gears

2- Heat Treatments

What is Quenching?

Quenching is a treatment performed on steel, applying rapid cooling after heating at high temperature (Approximate 800C). Quenching is applied to adjust the hardness of steel. There are several types of quenching in accordance with cooling conditions; oil quenching, water quenching, and spray quenching. After quenching, tempering must be applied to give toughness back to the steel, that might become brittle. Quenching cannot harden genuine steel, however, quenching can work for steel containing more than 0.35% carbon.

What is Thermal Refining?

Thermal Refining is a heat treatment applied to adjust hardness / strength / toughness of steel. This treatment involves quenching and tempering. Since machining is applied to products after thermal refining, the hardness should not be raised too high in quenching.

What is Induction Hardening?

Induction Hardening is a heat treatment performed to harden the surface of the steel containing carbon more than 0.35%, such as S45C or SCM440. For gear products, induction hardening is effective to harden tooth areas including tooth surface and the tip, however, the root may not be hardened in some cases. The precision of gears declines by induction hardening. To encourage the gear accuracy, grinding must be applied.

Heating Coil (Gear and High frequency inductor (coil))

What is Carburizing ?

Carburizing is a heat treatment performed to harden only the surface of low-carbon steel. The surface, in which carbon is present and penetrated the surface, gets especially hardened. Inner material structure (with low-carbon C=0.15%) is also hardened by some level of carburizing, however, it is not as hard as the surface. The precision of carburized gears declines by 1 grade or so, due to deformation (dimensional change) or distortion. To encourage the gear accuracy, grinding is essential.

Carburizing Furnace

Carbon layer by carburizing

What is Nitriding ?

Nitriding is a heat treatment performed to harden the surface by introducing nitrogen into the surface of steel. If the steel alloy includes aluminum, chrome, and molybdenum, it enhances nitriding and hardness can be obtained. A representative nitride steel is SACM645 (Aluminum chromium molybdenum steel).

Heat treatment of gears (Carburizing, Induction hardening, Nitriding)

When mating gears transmit power, both tooth flanks are in sliding contact and rolling contact. In other words, the pressure which the tooth flank get is same as the pressure when a cylinder slides while rolling on a flat surface. The tooth flank needs to have durability against such pressure.

However, some rigid materials such as ceramic are vulnerable to impacts and break easily. Bending force is frequently applied to the dedendum and impact may be generated when gears start moving. The material of gear needs to be tenacious in order to achieve high durability against external forces and impact.

Therefore, gears need to be hard on the outside and tenacious inside just like a Japanese sword. Heat treating is the method to give such characteristics.

Types of heat treatment for gears are :

Carburizing
Induction hardening
Nitriding

Let’s see the details and characteristics of each type.

1. Carburizing

A typical treatment for gears made of low-carbon steel like S15CK.

After being penetrated by “carbon” just like the name, the metal surface is quenched and tempered to harden. The thickness of the hardened layer is 0.2mm to 2mm depending on gear size.

In the past, people used to cover metal with crushed carbon before sealing and heating. In Europe, products were dipped in molten sodium cyanide-based inorganic salts at high temperature, but the toxicity of sodium cyanide was a problem. Currently, gas carburization in which products are heated in carbon dioxide gas, methane, propane and steam are mainly used. Although the gas carburization is expensive because large special equipment is needed, a large volume of products can be processed effectively.

Carburizing is usually performed after gear is cut and gear teeth are formed. After that, tooth surface is lapped and ground to finish.

2. Induction hardening

A typical treatment for gears made of medium-carbon steel like S45C.

The eddy current flows by electromagnetic induction when the metal gear, wound with wire, is electrified. The induction hardening takes advantage of the property of the eddy current which concentrates at the metal surface and heats metal.

As the common method for induction hardening, the electric current is applied to the wired coil overlaid on the gear tooth formed by cutting.

Induction hardening varies in the precision widely and fewer products can be processed at once compared to other methods like carburizing. On the other hand, this method is suited to process products with gear and axis integrated or large gears because the gear tooth can be hardened partially.

3. Nitriding

Frequently used for gears made of steel which contains chrome or molybdenum. Among the various kinds of steel which are suitable for nitriding, aluminum-containing steel produces particularly a powerful effect and are called “nitride steel”.

In nitration, gears are heated in nitrogen gas to form a layer of iron nitride of 0.1mm to 1mm thickness on the gear surface.

The nitriding can give hardness higher than carburizing and induction hardening, but the layer hardened by nitriding is thinner than other heat treatments. Meanwhile, the temperature necessary for nitriding is relatively low, 500 to 600 degrees Celsius. In contrast, products need to be heated up to 800 degrees Celsius in carburizing and induction hardening. Therefore, nitriding causes no quenching cracks or distortion unlike other heat treatments.

Generally, the nitriding is carried out in the final step of processing gears as it doesn’t cause deformation and gives high hardness.

Table: Types of Gear Materials

The table lists the mechanical properties and characteristics of gear materials most commonly used.

Material : Carbon Steel for Structural Machine Usage
JIS Material No. : S15CK
Tensile Strength N/mm2 More than : 490
Elongation (%) More than : 20
Drawability (%) More than : 50
Hardness HB : 143-235
Characteristics, heat treatments applied : Low-carbon steel. High hardness obtained by Carburizing.

Material : Carbon Steel for Structural Machine Usage
JIS Material No. : S45C
Tensile Strength N/mm2 More than : 690
Elongation (%) More than : 17
Drawability (%) More than : 45
Hardness HB : 201-269
Characteristics, heat treatments applied : Most commonly used medium-carbon steel. Thermal refined / induction hardened.

Material : Alloy steel for Machine Structural Use
JIS Material No. : SCM435
Tensile Strength N/mm2 More than : 930
Elongation (%) More than : 15
Drawability (%) More than : 50
Hardness HB : 269-331
Characteristics, heat treatments applied : Medium-carbon alloy steel (C content: 0.3-0.7%). Thermal refined and induction hardened. High strength (High bending strength / High surface durability). Used in gear manufacturing, except for worm gear.

Material : Alloy steel for Machine Structural Use
JIS Material No. : SCM440
Tensile Strength N/mm2 More than : 980
Elongation (%) More than : 12
Drawability (%) More than : 45
Hardness HB : 285-352
Characteristics, heat treatments applied : Medium-carbon alloy steel (C content: 0.3-0.7%). Thermal refined and induction hardened. High strength (High bending strength / High surface durability). Used in gear manufacturing, except for worm wheels.

Material : Alloy steel for Machine Structural Use
JIS Material No. : SNCM439
Tensile Strength N/mm2 More than : 980
Elongation (%) More than : 16
Drawability (%) More than : 45
Hardness HB : 293-352
Characteristics, heat treatments applied : Medium-carbon alloy steel (C content: 0.3-0.7%). Thermal refined and induction hardened. High strength (High bending strength / High surface durability). Used in gear manufacturing, except for worm wheels.

Material : Alloy steel for Machine Structural Use
JIS Material No. : SCr415
Tensile Strength N/mm2 More than : 780
Elongation (%) More than : 15
Drawability (%) More than : 40
Hardness HB : 217-302
Characteristics, heat treatments applied : Low-carbon Alloy Steel (C content below 0.3%). Surface-hardening treatment applied (Carburizing, Nitriding, Carbo-nitriding, etc.) High strength (Bending strength / Surface durability).

Material : Alloy steel for Machine Structural Use
JIS Material No. : SCM415
Tensile Strength N/mm2 More than : 830
Elongation (%) More than : 16
Drawability (%) More than : 40
Hardness HB : 235-321
Characteristics, heat treatments applied : Low-carbon Alloy Steel (C content below 0.3%). Surface-hardening treatment applied (Carburizing, Nitriding, Carbo-nitriding, etc.) High strength (Bending strength / Surface durability).

Material : Alloy steel for Machine Structural Use
JIS Material No. :SNC815
Tensile Strength N/mm2 More than : 980
Elongation (%) More than : 12
Drawability (%) More than : 45
Hardness HB : 285-388
Characteristics, heat treatments applied : Low-carbon Alloy Steel (C content below 0.3%). Surface-hardening treatment applied (Carburizing, Nitriding, Carbo-nitriding, etc.) High strength (Bending strength / Surface durability).

Material : Alloy steel for Machine Structural Use
JIS Material No. : SNCM220
Tensile Strength N/mm2 More than : 830
Elongation (%) More than : 17
Drawability (%) More than : 40
Hardness HB : 248-341
Characteristics, heat treatments applied : Low-carbon Alloy Steel (C content below 0.3%). Surface-hardening treatment applied (Carburizing, Nitriding, Carbo-nitriding, etc.) High strength (Bending strength / Surface durability).

Material : Alloy steel for Machine Structural Use
JIS Material No. : SNCM420
Tensile Strength N/mm2 More than : 980
Elongation (%) More than : 15
Drawability (%) More than : 40
Hardness HB : 293-375
Characteristics, heat treatments applied : Low-carbon Alloy Steel (C content below 0.3%). Surface-hardening treatment applied (Carburizing, Nitriding, Carbo-nitriding, etc.) High strength (Bending strength / Surface durability).

Material :Rolled Steel for General Structures
JIS Material No. : SS400
Tensile Strength N/mm2 More than : 400
Elongation (%) More than : –
Drawability (%) More than : –
Hardness HB : –
Characteristics, heat treatments applied : Low strength. Low cost.

Material :Gray Cast Iron
JIS Material No. : FC200
Tensile Strength N/mm2 More than : 200
Elongation (%) More than : –
Drawability (%) More than : –
Hardness HB : Less than 223
Characteristics, heat treatments applied : Low strength than steel. Suitable for bulk production.

Material : Nodular Graphite Cast Iron
JIS Material No. : FCD500-7
Tensile Strength N/mm2 More than : 500
Elongation (%) More than : 7
Drawability (%) More than : –
Hardness HB : 150-230
Characteristics, heat treatments applied : Ductile Cast Iron with high strength. Used in the manufacturing of large casting gears.

Material : Stainless Steel
JIS Material No. :SUS303
Tensile Strength N/mm2 More than : 520
Elongation (%) More than : 40
Drawability (%) More than : 50
Hardness HB : Less than 187
Characteristics, heat treatments applied : Has more machinability than SUS304. Increases seizure resistant.

Material : Stainless Steel
JIS Material No. : SUS304
Tensile Strength N/mm2 More than : 520
Elongation (%) More than : 40
Drawability (%) More than : 60
Hardness HB : Less than 187
Characteristics, heat treatments applied : Most commonly used stainless Steel. Used for food processing machines etc.

Material : Stainless Steel
JIS Material No. : SUS316
Tensile Strength N/mm2 More than : 520
Elongation (%) More than : 40
Drawability (%) More than : 60
Hardness HB : Less than 187
Characteristics, heat treatments applied : Has corrosion resistance against salty seawater, better than SUS304.

Material : Stainless Steel
JIS Material No. : SUS420J2
Tensile Strength N/mm2 More than : 540
Elongation (%) More than : 12
Drawability (%) More than : 40
Hardness HB : More than 217
Characteristics, heat treatments applied : Martensitic stainless steel, quenching can be applied.

Material : Stainless Steel
JIS Material No. : SUS440C
Tensile Strength N/mm2 More than : –
Elongation (%) More than : –
Drawability (%) More than : –
Hardness HB : More than 58HRC
Characteristics, heat treatments applied : High hardness can be obtained by quenching. High surface durability.

Material : Nonferrous Metals
JIS Material No. : C3604
Tensile Strength N/mm2 : 335
Elongation (%) More than : –
Drawability (%) More than : –
Hardness HB : More than 80HV
Characteristics, heat treatments applied : Free-Cutting Brass. Used in manufacturing of small gears.

Material : Nonferrous Metals
JIS Material No. : CAC502
Tensile Strength N/mm2 : 295
Elongation (%) More than : 10
Drawability (%) More than : –
Hardness HB : More than 80
Characteristics, heat treatments applied : Phosphor bronze casting. Suitable for worm wheels.

Material : Nonferrous Metals
JIS Material No. : CAC702
Tensile Strength N/mm2 : 540
Elongation (%) More than : 15
Drawability (%) More than : –
Hardness HB : More than 120
Characteristics, heat treatments applied : Aluminum-bronze casting. Used for worm wheels etc.

Material : Engineering Plastics
JIS Material No. : MC901
Tensile Strength N/mm2 : 96
Elongation (%) More than : –
Drawability (%) More than : –
Hardness HB : 120HRR
Characteristics, heat treatments applied : Used for machined gears. Lightweight. Anti-rust.

Material : Engineering Plastics
JIS Material No. : MC602ST
Tensile Strength N/mm2 : 96
Elongation (%) More than : –
Drawability (%) More than : –
Hardness HB : 120HRR
Characteristics, heat treatments applied : Used for machined gears. Lightweight. Anti-rust.

Material : Engineering Plastics
JIS Material No. : M90
Tensile Strength N/mm2 : 62
Elongation (%) More than : –
Drawability (%) More than : –
Hardness HB : 80HRR
Characteristics, heat treatments applied : Used for injection-molded gears. Suitable for bulk production at low cost. Applied for use with light load.

Source: https://khkgears.net/

ASTM A387 Grade 11: Chemical Composition, Properties, Equivalent grades

Introduction

The ASTM A387 specification is the Standard Specification for Pressure Vessel Plates, Alloy Steel, Chromium-Molybdenum intended primarily for use in welded boilers and pressure vessels designed for elevated temperature service.

Chrome Molybdenum steel plate, also known as Chrome Moly, is a versatile material widely used in various industries, including the oil and gas industry, nuclear industry, and fossil fuel power stations. The addition of molybdenum in the alloy composition enhances its strength and enables it to withstand higher working temperatures, while the presence of chromium enhances its corrosion resistance and resistance to oxidation.

The superior temperature tensile strength and anti-corrosive properties of Chrome Moly make it an ideal choice for applications involving saltwater exposure.

Equivalent steel grades

ASTM A387 Grade 11 equivalent steel grades:

Country	USA	USA	European	UK (British Standard)
Standards	ASTM	ASME	EN 10028	BS
Grade	A387 Grade 11	SA387 Grade 11	13CrMoSi5-5	621B

Chemical Composition

The chemical composition of AISI A387 grade 11 alloy steel is as follows:

Element Content (%)

Iron, Fe 96.16-97.6

Chromium, Cr 1.0-1.50

Silicon, Si 0.50-0.80

Manganese, Mn 0.40-0.65

Molybdenum, Mo 0.45-0.65

Carbon, C 0.050-0.17

Phosphorous, P 0.035

Sulfur, S 0.035

Mechanical Properties

The mechanical properties of AISI A387 grade 11 alloy steel are as follows:

Tensile strength 515-690 Mpa/ 74700-100000 psi.

Yield strength 310 Mpa/ 45000 psi.

Rupture strength (@575 °C, time 3.60e+8 sec/1070 °F, time 100000 hour) 37.0 - 48.0 Mpa/ 5370 - 6960 psi

Elastic modulus 190-210 Gpa/ 27557-30458 ksi.

Poisson's ratio 0.27-0.30.

Elongation at break (In 50 mm) 22.00%.

Applications

ASTM A387 Grade 11 steel is characterised by good weldability. ASTM A387 Grade 11 steel is used for manufacturing boilers, pressure vessels and pipes for the transportation of hot liquids. ASTM A387 Grade 11 steel also offer good properties at high and low temperatures. ASTM A387 Grade 11 steel is always supplied in the normalised and tempered condition.

ASTM A278 class 35C Properties and Aplications

ASTM A278 class 35C is a grade of carbon steel and low alloy steel castings that has a minimum tensile strength of 35,000 psi (240 MPa), a minimum yield strength of 22,000 psi (150 MPa), and a minimum elongation of 22%. This grade of cast steel is commonly used in general-purpose applications that require good strength and toughness, as well as resistance to wear and corrosion.

In ASTM A278, the letter "C" following the numerical value, such as "35C", indicates that the material is a carbon steel casting. The "C" designation is used to distinguish carbon steel castings from other types of castings, such as alloy steel or stainless-steel castings, which may have different chemical compositions and mechanical properties.

In the case of ASTM A278 class 35C, the material is a carbon steel and low alloy steel casting with a minimum tensile strength of 35,000 psi, a minimum yield strength of 22,000 psi, and a minimum elongation of 22%. The specific chemical composition of the material includes carbon, manganese, silicon, phosphorus, sulfur, and potentially other trace elements.

Note:

It is important to note that ASTM A278 class 35C is a grade of carbon steel and low alloy steel castings, not gray iron. Gray iron is a different type of cast iron that is characterized by its gray color, which is due to the presence of graphite flakes in the microstructure.

ASTM A278 does include several grades of gray iron castings, including classes 30, 35, and 40. These grades of gray iron have different mechanical properties and are used in a variety of applications, such as engine blocks, gears, and machine tool bases.

Compared to gray iron, steel castings such as ASTM A278 class 35C typically have higher strength and toughness, as well as better resistance to wear and corrosion. The specific choice of material will depend on the specific requirements of the application, including the operating conditions, the design of the component, and the required properties of the material.

Equivalent grades

There are several equivalent grades to ASTM A278 class 35C, which may vary depending on the country or region. Some of the equivalent grades are:

BS3100 grade A4
DIN 1681 grade GS45
EN 10293 grade G35

Chemical composition

The chemical composition of ASTM A278 class 35C castings typically includes:

Carbon (C): 0.25% max
Manganese (Mn): 0.70-1.00%
Silicon (Si): 0.15-0.50%
Phosphorus (P): 0.035% max
Sulfur (S): 0.040% max

Additionally, this grade of cast steel may also contain trace amounts of other elements, such as copper (Cu), nickel (Ni), and chromium (Cr), depending on the specific composition and intended application.

The properties of ASTM A278 class 35C castings are determined by a combination of its chemical composition, microstructure, and processing conditions. Generally, this grade of cast steel exhibits good strength, toughness, and wear resistance, as well as good machinability and weldability. However, the exact properties of the material can vary depending on the specific casting process and heat treatment used, as well as the quality of the casting itself.

Mechanical properties

The mechanical properties of ASTM A278 class 35C castings are specified in the ASTM A278 standard. The typical mechanical properties of this grade of cast steel are:

Tensile strength: minimum 35,000 psi (240 MPa)
Yield strength: minimum 22,000 psi (150 MPa)
Elongation: minimum 22%
Hardness: maximum 217 Brinell (HB)

It is important to note that the actual mechanical properties of the casting may vary depending on factors such as the casting process, section size, cooling rate, and heat treatment. The mechanical properties of the casting can be tested and verified through various methods such as tensile testing, impact testing, and hardness testing. The specific mechanical properties required for a particular application will depend on the operating conditions and the design requirements of the component.

Applications

ASTM A278 class 35C castings are commonly used in a variety of general-purpose applications that require good strength, toughness, and resistance to wear and corrosion. Some of the typical applications of this grade of cast steel include:

Valves: ASTM A278 class 35C castings are commonly used in the manufacturing of valve bodies, stems, and other components that require good mechanical properties and resistance to wear and corrosion.
Fittings: This grade of cast steel is also used in the manufacturing of fittings such as pipe elbows, tees, and reducers, which are used in various piping systems.
Flanges: ASTM A278 class 35C castings are often used in the manufacturing of flanges, which are used to connect piping systems and other equipment.
Pump, and compressor components: This grade of cast steel is also used in the manufacturing of casings, impellers, and other components that require good strength and resistance to wear and corrosion.
Mining equipment: ASTM A278 class 35C castings are commonly used in the manufacturing of various mining equipment such as dragline buckets, excavator buckets, and crusher liners.

Overall, ASTM A278 class 35C castings are widely used in various industrial applications that require good mechanical properties and resistance to wear and corrosion. The specific application of this grade of cast steel will depend on a variety of factors, including the operating conditions, the design of the component, and the required properties of the material.

SA240 gr 321 Properties and Aplications

SA240 gr 321 is a type of stainless steel produced in accordance with ASTM A240 standard, which is often used in high-temperature and corrosive environments.

SS 321 Plate Equivalent grades

JIS G4304	ASTM	UNS	KS	EN10095	AS	CNS
SUS321	321	S32100	STS321	1.4541	321	321

Chemical composition:

Type	Grade
Type	ASTM (A240M)	Others (JIS)	C	Si	Mn	P	S	Ni	Cr
Austenitic Steels
Austenitic Steels	321	SUS321	≤0.08	≤0.75	≤2.00	≤0.045	≤0.030	9.0/12.0	17.0/19.0

Titanium (Ti): a minimum of 5 times the carbon (C) content, but not more than 0.70%.

Physical Properties

Grade	Density (kg/m3)	Elastic Modulus (GPa)	Mean Coefficient of Thermal Expansion (μm/m/°C)			Thermal Conductivity (W/m.K)		Specific Heat 0-100 °C (J/kg.K)	Electrical Resistivity (nΩ.m)
			0-100 °C	0-315 °C	0-538 °C	at 100 °C	at 500 °C
321	8027	193	16.6	17.2	18.6	16.1	22.2	500	720