EN31 Steel

What is EN31 Steel?

EN31 steel is a high-carbon, chromium alloy steel specifically known for its exceptional hardness, wear resistance, and high fatigue strength. It is primarily used in applications requiring high dimensional accuracy and excellent surface quality, notably in bearing manufacturing and various automotive and engineering components. Its properties are significantly enhanced through specific heat treatments.

What are Key Characteristics and Properties of EN31 Steel?

A. Chemical Composition

• Carbon (C): 0.90-1.20% (Crucial for hardness)
• Silicon (Si): 0.10-0.35%
• Manganese (Mn): 0.25-0.75%
• Chromium (Cr): 1.00-1.65% (Contributes to wear resistance and hardenability)
• Phosphorus (P): 0.025-0.050% max
• Sulfur (S): 0.015-0.050% max
• Nickel (Ni): Present in some compositions (e.g., 0.25% in ASTM A295 52100)
• Molybdenum (Mo): Present in some compositions (e.g., 0.1% in ASTM A295 52100)

B. Mechanical Properties

• Hardness: Up to 63-66 HRC (Rockwell C) after appropriate heat treatment. Typical annealed hardness is max. 207 HB (Brinell).
• Tensile Strength: Approximately 750 N/mm²
• Yield Stress: Approximately 450 N/mm²
• Reduction of Area: Approximately 45%
• Elongation: Approximately 30%
• Modulus of Elasticity: Approximately 190-215 GPa (215,000 N/mm²)
• Compressive Strength: High
• Abrasion Resistance: Excellent

C. Physical Properties

Thermal Expansion Coefficient: 11.9 µm/m°C (annealed, @ 23-280°C)

Density: 7.81 g/cm³ (or 7.8 Kg/m³)

Melting Point: Approximately 1424°C – 1540°C

Thermal Conductivity: 44.5-46.6 W/(m*K) (at various temperatures)

What are Equivalent Grades and Standard?

• British (BS 970:1991): 535A99
• British (BS 970:1955): EN31
• German (DIN): 100Cr6 / 1.3505
• French (AFNOR): 100C6
• Swedish (SS): 2258
• American (SAE / AISI): 52100

IV. Manufacturing and Supply

A. Forms Available

• Round Bars (Bright, Hot Rolled, Cold Drawn, Centerless Peeled, Centerless Ground)
• Forging (Round, Flat)
• Sheet, Coil, Profiled Strip
• Deformed steel, Flat steel
• Mould, Steel wire

B. Surface Finishes

• Bright: Smooth, polished surface, enhancing usability in precision applications where high dimensional accuracy and excellent surface quality are required.

C. Certifications

• Often supplied with cast and analysis certification, in accordance with ISO 9001:2015 registration.

• tungsten electrode can surface-harden EN31. Cryogenic treatment (shallow at -50°C, deep at -196°C) further improves hardness by transforming retained austenite to plate martensite and precipitating carbide particles. Maximum hardness is achieved with specific current, electrode angles, and soaking periods (e.g., 200A, 45° electrode tip, 15h soaking at -190°C).

D. Welding Performance

• Can be produced to meet EN31 Alloy Steel welding performance standards, or customized to customer requests.

VI. Applications

• Bearings: Ball and roller bearings (primary application due to high hardness and wear resistance).
• Automotive Components: Heavy-duty gears, shafts, pinions, camshafts, gudgeon pins, front automobile axles, obverse axle beam, axle periodicals, crankshafts, steering components.
• Machine Components: Wear-resisting machine parts, machining components.
• Tools: Taps, gauges, swaging dies, ejector pins, press tools (especially those not requiring more complex quality).
• Other Engineering Applications: Connectors between pipes, sockets in pressure regulators, tiller blades.

VII. Suppliers and Manufacturers

Jaiganeshsteel is the supplier and manufacturer of EN31 steel in Delhi & whole India.

1. What are the primary distinguishing properties of EN31 steel that make it suitable for its main applications?
   • EN31 steel is a high-carbon, chromium alloy steel primarily known for its excellent hardness, wear resistance, and high fatigue strength. These properties make it ideal for applications requiring precision and durability.
2. List three equivalent international grades for EN31 steel.
   • Three equivalent international grades for EN31 steel are German DIN 100Cr6, American SAE/AISI 52100, and British BS 970:1991 535A99. These designations indicate similar chemical compositions and mechanical properties.
3. Explain the significance of the “Bright” finish for EN31 round bars.
   • The “Bright” finish refers to a smooth, polished surface on EN31 round bars. This finish is crucial for precision applications as it enhances usability, provides high dimensional accuracy, and ensures excellent surface quality.
4. Briefly describe the annealing process for EN31 steel and its purpose.
   • Annealing EN31 steel involves heating it slowly to 780-810°C, soaking it thoroughly, and then cooling it slowly in a furnace. Its purpose is to soften the steel, relieve internal stresses, and improve machinability, typically resulting in a maximum hardness of 207 HB.
5. What is the typical hardening temperature range for EN31 steel and what quenching medium is commonly used?
   • EN31 steel is typically hardened by heating it slowly to a temperature range of 800-820°C. After thorough soaking, it is commonly quenched in oil to achieve the desired hardness.
6. How does tempering affect the hardness of EN31 steel, and what is the general temperature range for tempering?
   • Tempering reduces the brittleness of EN31 steel after hardening and influences its final hardness. Generally performed between 150-300°C, higher tempering temperatures result in a lower final hardness.
7. Identify three common applications of EN31 steel in the automotive industry.
   • In the automotive industry, EN31 steel is commonly used for heavy-duty gears, shafts, and pinions. It is also found in components like camshafts, gudgeon pins, and various parts requiring high wear resistance.
8. What are the main elements contributing to the high hardness and wear resistance of EN31 steel?
   • The high hardness and wear resistance of EN31 steel are primarily attributed to its significant carbon content, which provides the hardness, and its chromium content, which enhances wear resistance and hardenability.
9. What are some of the challenges associated with machining EN31 steel, particularly when aiming for dimensional accuracy and surface quality?
   • Machining EN31 steel is challenging due to its inherent high hardness and wear resistance. Achieving precise dimensional accuracy and an outstanding surface finish often requires specialized techniques like Wire Electrical Discharge Machining (WEDM).
10. Describe one method used to further enhance the surface hardness of EN31 steel beyond conventional heat treatment.
    • One method to further enhance EN31 steel’s surface hardness is Gas Tungsten Arc (GTA) surface hardening combined with cryogenic treatment. This process, especially deep cryogenic treatment, transforms retained austenite and precipitates carbide particles, significantly increasing surface hardness.

Glossary of Key Terms: EN31 Steel

• Alloy Steel: Steel that has had small amounts of one or more alloying elements (other than carbon) added to it to improve its properties. EN31 is an alloy steel with chromium, nickel, and molybdenum.
• Annealing: A heat treatment process that alters the microstructure of a material to soften it, relieve internal stresses, and improve ductility and machinability. For EN31, this typically involves slow heating and cooling in a furnace.
• Austenite: A metallic, non-magnetic allotrope of iron or a solid solution of iron and alloying elements, existing at high temperatures. In EN31, retained austenite can be transformed during cryogenic treatment.
• Bearing Steel: A class of steel specifically designed for use in ball and roller bearings, characterized by high hardness, wear resistance, and fatigue strength, such as EN31.
• Bright Finish: A smooth, polished surface quality on steel products, achieved through processes like cold drawing or centerless grinding, which improves dimensional accuracy and aesthetic appeal for precision applications.
• Carbide Particles: Hard, brittle compounds of carbon with a less electronegative element (like chromium in EN31). Their presence contributes significantly to wear resistance and hardness, especially after heat treatment.
• Carbon (C): A key alloying element in steel; its percentage primarily determines the hardness and strength of the steel. Higher carbon content, as in EN31, leads to greater hardness.
• Chromium (Cr): An alloying element that enhances the hardenability, wear resistance, and corrosion resistance of steel. It is a critical component in EN31 steel.
• Cryogenic Treatment: A post-heat treatment process where materials are cooled to very low temperatures (e.g., -50°C for shallow, -196°C for deep). This process can further transform retained austenite into martensite and precipitate fine carbides, increasing hardness and wear resistance.
• Ductility: The ability of a material to deform plastically under tensile stress without fracturing, allowing it to be drawn into a wire or hammered into a thin sheet. EN31 possesses good ductility despite its high strength.
• Fatigue Strength: The maximum stress that a material can withstand for a specified number of cycles without failing. EN31 is known for its high fatigue strength, making it suitable for dynamically loaded components.
• Forging: A manufacturing process involving shaping metal using localized compressive forces. For EN31, specific temperature ranges (e.g., 1000-1050°C) and slow cooling are required.
• Gas Tungsten Arc (GTA): An arc welding process that uses a non-consumable tungsten electrode to produce the weld. It can be used for surface hardening processes, as mentioned with EN31.
• Hardening: A heat treatment process that increases the hardness of a metal, typically by heating to a high temperature followed by rapid cooling (quenching). For EN31, this is done around 800-820°C and usually involves oil quenching.
• Hardness (HRC/HB): Resistance of a material to localized plastic deformation, measured using scales like Rockwell C (HRC) or Brinell (HB). EN31 exhibits high HRC values after hardening and tempering.
• Heat Treatment: A series of industrial and metalworking processes used to alter the physical and sometimes chemical properties of a material, such as steel, through heating and cooling.
• Kerf Width: The width of the material removed by a cutting process, often discussed in the context of machining accuracy, especially with methods like Wire Electrical Discharge Machining (WEDM).
• Martensite: A very hard and brittle crystalline structure formed in steel during quenching, resulting from the rapid cooling of austenite. Cryogenic treatment can induce further martensite formation in EN31.
• Modulus of Elasticity (Young’s Modulus): A measure of the stiffness of an elastic material. It is the ratio of stress to strain in the elastic region. EN31 has a high modulus of elasticity.
• Normalizing: A heat treatment process similar to annealing but typically involves cooling in air. It refines the grain structure and reduces internal stresses, preparing the steel for subsequent processes.
• OEM Auto Components: Original Equipment Manufacturer automotive components, referring to parts made for vehicles by the company that originally manufactured the vehicle. EN31 is used in these components.
• Quenching: The rapid cooling of a metal (e.g., in oil or water) after heating to high temperatures, typically done during hardening to freeze the microstructure and achieve high hardness.
• Retained Austenite: Austenite that remains untransformed in the microstructure of steel after quenching to room temperature. It can reduce hardness and stability but can be transformed through further treatments like cryogenic cooling.
• Stress Relieving: A heat treatment process where a material is heated to a moderate temperature (below its critical range) and held there for a period, then slowly cooled to reduce residual internal stresses without significantly altering microstructure or hardness.
• Swaging Dies: Tools used in the swaging process, which involves shaping metal by hammering or pressing it into a specific form. EN31 is suitable for these dies due to its wear resistance.
• Tempering: A heat treatment process performed after hardening to reduce brittleness and increase toughness by heating the steel to a specific temperature below its critical point and then cooling it.
• Tensile Strength: The maximum stress that a material can withstand while being stretched or pulled before breaking.
• Thermal Conductivity: A measure of a material’s ability to conduct heat.
• Wear Resistance: The ability of a material to resist the removal of material from its surface by mechanical action such as friction, rubbing, or erosion. EN31 excels in this property.
• Wire Electrical Discharge Machining (WEDM): A non-conventional machining process that uses a thin wire electrode to cut a workpiece with electrical discharges (sparks). It is effective for complex shapes and hard materials like EN31.
• Yield Stress: The stress at which a material begins to deform plastically (permanently).