Introduction and Grade Overview

65G spring steel is a manganese-enhanced high-carbon spring steel designed to develop high strength and a strong elastic response after quenching and tempering. The grade is widely associated with springs, leaf springs, resilient machine elements, agricultural components and wear-loaded parts.

65Mn steel follows the same basic metallurgical concept. It combines approximately 0.65% carbon with a controlled manganese level that improves hardenability compared with plain carbon steels containing a lower manganese percentage.

The principal characteristics of the ST65G, 65G and 65Mn family include:

• High tensile strength after heat treatment
• High elastic limit
• Good fatigue resistance under controlled cyclic loading
• Good wear resistance
• Better hardenability than lower-manganese carbon spring steels
• Suitability for flat, round, coiled and strip spring components
• Sensitivity to overheating, decarburisation and improper quenching
• Limited weldability
• Limited atmospheric corrosion resistance

The final performance of 65G steel and 65Mn steel depends heavily on section thickness, surface quality, decarburisation control, quenching uniformity and tempering temperature.

Alternative Names, Spellings and Designations

The following names are commonly used for this material family:

ST65G is not normally a separate metallurgical grade from 65G. It is generally used as a searchable or catalogue-style variation of the Russian 65Г designation.

ST65G, 65G, 65Г and 65Mn Naming Explanation

ST65G, 65G and 65Г generally refer to the same Russian spring-steel designation written in different scripts or catalogue formats.

The Cyrillic letter Г is transliterated as G and represents manganese. Therefore:

• 65Г is the Russian designation.
• 65G is its common Latin transliteration.
• ST65G is an extended search or catalogue form.
• 65Mn is the Chinese grade designation using the chemical symbol Mn for manganese.

65G and 65Mn have very similar nominal carbon, silicon and manganese ranges. However, they are controlled by different standards and may have different limits for phosphorus, sulphur, nickel, copper, dimensions, testing and delivery condition.

Steel Grade Designation Explained

The grade designation describes the approximate carbon level and the principal alloying element.

For Russian 65Г steel:

• 65 indicates an average carbon level close to 0.65%.
• Г indicates manganese.
• The absence of a following number means that manganese is present at a relatively low alloying level rather than at several whole percentage points.

For Chinese 65Mn steel:

• 65 represents approximately 0.65% carbon.
• Mn identifies manganese as the characteristic alloying element.

Both systems describe a high-carbon manganese spring steel rather than an austenitic high-manganese steel.

Meaning of 65 in the Grade Name

The number 65 does not represent hardness, tensile strength or product thickness. It indicates the approximate carbon content expressed in hundredths of a percent.

A nominal value of 65 therefore corresponds to approximately 0.65% carbon. The specified carbon range for both 65G and 65Mn is generally 0.62–0.70%.

This carbon level allows the material to develop:

• High hardness after quenching
• High tensile and yield strength after tempering
• Strong elastic behaviour
• Good wear resistance
• Suitable fatigue performance for spring components

The same carbon level also reduces weldability and increases sensitivity to quench cracking, overheating and decarburisation.

Meaning of G, Г and Mn

The letters G, Г and Mn all refer to manganese in the context of these grade names.

• Г is the Russian Cyrillic designation for manganese.
• G is the Latin transliteration of Г.
• Mn is the international chemical symbol for manganese.

Manganese improves hardenability and helps the steel develop a more uniform hardened structure through a larger section than a comparable plain carbon steel.

The phrase “65G high manganese steel” should be used carefully. With approximately 0.90–1.20% manganese, 65G is more accurately described as a manganese spring steel or manganese-enhanced high-carbon steel. It is not comparable to austenitic high-manganese steels containing roughly 11–14% manganese.

Steel Classification

ST65G, 65G and 65Mn are classified as:

• High-carbon steels
• Manganese spring steels
• Structural spring steels
• Heat-treatable steels
• Wear-resistant carbon-alloy steels
• Non-stainless steels
• Ferromagnetic steels

65G is generally classified within the Russian рессорно-пружинная сталь category, meaning leaf-spring and spring steel.

65Mn is classified as a Chinese high-carbon manganese spring steel under the GB/T spring-steel system.

Spring Steel Category

Spring steels are designed to store mechanical energy through elastic deformation and return toward their original shape when the applied load is removed.

65G spring steel properties are particularly suitable for components exposed to:

• Repeated bending
• Cyclic compression
• Alternating tensile and compressive stress
• Sliding wear
• Repeated impact of controlled severity
• Elastic deflection within a designed stress range

The material must be correctly hardened and tempered to develop the required combination of elastic limit, strength and toughness. Untreated 65G or 65Mn does not provide the same spring performance as properly processed material.

Applicable Standards

The governing standard depends on grade designation, product form and production route.

A grade name alone does not define every dimensional, surface, testing or heat-treatment requirement. The complete designation must identify the applicable material and product standard.

GOST 14959-2016 Specification

GOST 14959-2016 covers hot-rolled and forged spring-steel products up to 270 mm in diameter or thickness. Products above 270 mm and up to 300 mm may be produced under separately defined conditions.

The standard also applies its chemical composition requirements to additional forms such as:

• Ingots
• Blooms
• Slabs
• Billets
• Forgings
• Stampings
• Sheet products

For 65Г steel, GOST 14959-2016 defines its chemical composition, delivery hardness and minimum mechanical properties obtained from specified heat-treated test samples.

The standard identifies spring-steel products intended for springs, leaf springs and machine components used in the hardened and tempered condition.

GB/T 1222 Specification

GB/T 1222-2016 defined Chinese spring-steel requirements including 65Mn steel. Its scope included:

• Round and square bars up to 120 mm nominal diameter or side length
• Flat spring steel up to 160 mm nominal width
• Flat spring steel up to 60 mm nominal thickness
• Coiled spring-steel rod up to 40 mm nominal diameter
• Chemical composition requirements applicable to billets and related products

GB/T 1222-2016 was superseded by GB/T 1222-2025, effective May 1, 2026. The term GB/T 1222-2016 65Mn steel remains useful when identifying legacy drawings, certificates, existing equipment specifications and historical material requirements.

New technical documentation should identify whether it requires the 2016 edition or the current GB/T 1222-2025 edition.

65G and 65Mn Standards Comparison

65G and 65Mn are close metallurgical counterparts. Their principal compositions overlap, but standard-specific residual-element limits and technical conditions remain different.

Chemical Composition Table

65G Steel Chemical Composition According to GOST 14959-2016

This 65G chemical composition develops high hardness and strength while retaining sufficient tempered toughness for spring and wear-loaded components.

65Mn Steel Chemical Composition Under GB/T 1222-2016

Requirements should be confirmed against the exact edition of GB/T 1222 stated in the technical documentation.

65G and 65Mn Chemical Composition Comparison

The close principal composition explains why 65Mn is frequently described as a Chinese equivalent of Russian 65G steel. However, equivalent chemistry does not eliminate differences in standard scope, tolerances, surface condition, testing or heat-treatment requirements.

Mechanical Properties Table

Mechanical properties vary with section size, processing route, test orientation and heat-treatment condition. The following values represent standard-based or commonly referenced conditions rather than universal values for every finished component.

65G Mechanical Properties at Approximately 20°C

65Mn Mechanical Properties in Referenced GB/T 1222-2016 Condition

Finished springs may require different strength and hardness levels according to component geometry and service load.

Physical Properties Table

The following physical values are representative of 65G steel and vary with temperature, composition and metallurgical condition.

These values are appropriate for engineering reference and thermal-process planning. Final design calculations should use properties confirmed for the specified material condition.

Density and Elastic Modulus

The commonly used density for 65G and 65Mn steel is approximately:

• Density: 7.85 g/cm³
• Density: 7850 kg/m³
• Elastic modulus at room temperature: approximately 200–215 GPa
• Poisson’s ratio: commonly estimated around 0.27–0.30 for engineering calculations

Density is useful for component mass calculations. Elastic modulus determines the relationship between stress and elastic strain but does not directly indicate the steel’s maximum spring load.

Heat treatment substantially changes strength and hardness but causes relatively little change in room-temperature elastic modulus.

Tensile Strength

The referenced minimum tensile strength for heat-treated 65G and 65Mn test samples is approximately 980 MPa.

Actual 65G tensile strength can vary significantly according to:

• Tempering temperature
• Section thickness
• Quenching effectiveness
• Surface decarburisation
• Cold-working level
• Product form
• Test orientation
• Final hardness

Lower tempering temperatures normally produce higher hardness and tensile strength but lower toughness. Higher tempering temperatures reduce strength while improving ductility and resistance to brittle failure.

Yield Strength and Elongation

The referenced minimum yield strength for quenched and tempered 65G is approximately 785 MPa, with minimum elongation of about 8% under the specified GOST test condition.

A similar 785 MPa minimum yield value is commonly associated with 65Mn under the referenced GB/T 1222-2016 condition.

The yield strength is critical for spring design because permanent deformation begins when the operational stress exceeds the material’s elastic capability.

A spring component must therefore be designed with consideration for:

• Static stress
• Alternating stress
• Stress concentration
• Surface condition
• Residual stress
• Operating temperature
• Required service life
• Safety factor

Fatigue Strength

There is no single universal 65G fatigue-strength value that applies to every spring, sheet, strip or bar.

Fatigue strength depends strongly on:

• Surface finish
• Decarburised-layer depth
• Inclusion cleanliness
• Grain size
• Heat-treatment uniformity
• Shot peening
• Residual stress
• Edge quality
• Component geometry
• Mean stress
• Stress amplitude
• Number of load cycles

65G steel fatigue strength and 65Mn fatigue strength can be significantly reduced by scratches, sharp corners, scale pits, grinding burns and partial decarburisation.

For critical springs, fatigue performance must be determined from the finished component geometry and its actual production route rather than from tensile strength alone.

Hardness Details

65G steel hardness is controlled through annealing, cold working, quenching and tempering.

Hardness values should not be transferred between product standards without confirming the delivery condition and test method.

Annealed Hardness

Annealing reduces 65G and 65Mn hardness to improve:

• Machinability
• Cutting
• Drilling
• Punching
• Bending
• Cold forming
• Preparation for final hardening

A controlled annealed condition may fall around 200–241 HB, depending on the exact product specification and annealing cycle. Some sheet references specify approximately 229 HB maximum.

For precision forming, a spheroidised carbide structure is often preferable because it reduces forming load and improves machinability before final heat treatment.

Hardened and Tempered Hardness

Directly after quenching, 65G and 65Mn can develop a high-martensitic hardness, often in the range of approximately 58–62 HRC when the section is fully hardened.

The as-quenched condition is normally too brittle for most spring applications. Tempering is required to:

• Reduce internal stress
• Improve toughness
• Stabilise dimensions
• Adjust hardness
• Improve resistance to crack initiation
• Establish the required spring performance

A finished spring condition may commonly be selected in the approximate 40–50 HRC range. The correct target must be determined from the component design, section size and loading mode.

Heat Treatment Process

The typical 65G spring steel heat-treatment process includes:

1. Controlled preheating where required
2. Austenitising at the specified hardening temperature
3. Oil quenching
4. Immediate tempering
5. Controlled cooling
6. Hardness verification
7. Dimensional inspection
8. Surface and decarburisation inspection where required

The heat-treatment process must produce a uniform structure without excessive distortion, cracking, overheating or surface carbon loss.

Reference Critical Transformation Temperatures for 65G

Critical temperatures can shift according to composition, heating rate, prior structure and measurement method.

Annealing Temperature

A 65G annealing temperature must be selected according to whether the objective is full annealing, soft annealing, spheroidising or stress relief.

A typical soft-annealing or spheroidising approach may use:

• Heating near approximately 720–760°C
• Adequate soaking for section equalisation
• Slow controlled furnace cooling
• Continued cooling through the transformation range
• Air cooling after reaching a suitable lower temperature

Higher-temperature industrial cycles may also be used for specific starting structures. Excessive heating can produce coarse grains and increase the risk of distortion during subsequent hardening.

The final annealing process should be qualified against the required hardness and microstructure.

Normalising Temperature

A representative 65G or 65Mn normalising temperature is approximately 830–860°C, followed by air cooling.

Normalising may be used to:

• Refine an irregular prior structure
• Improve structural uniformity
• Prepare forged material for machining
• Reduce the effect of previous thermal cycles
• Establish a controlled structure before final hardening

Normalising is not normally the final process for a high-performance spring. Final spring properties are usually developed through quenching and tempering.

Hardening Temperature

The recommended GOST 14959-2016 test-sample hardening temperature for 65G is:

• Hardening temperature: 830°C
• Permitted process variation in the referenced standard: approximately ±15°C
• Quenching medium: oil

A commonly referenced 65Mn hardening temperature is:

• Hardening temperature: approximately 830°C
• Typical range: 810–850°C
• Quenching medium: oil

Overheating can cause coarse austenite grains, increased brittleness and reduced fatigue performance. Insufficient heating can result in incomplete transformation and non-uniform hardness.

Quenching Medium

Oil is the principal quenching medium for 65G and 65Mn because it provides a lower cooling severity than water.

Oil quenching helps reduce:

• Cracking risk
• Excessive distortion
• Residual stress
• Uneven transformation
• Edge damage in thin sections

The result depends on:

• Oil temperature
• Oil condition
• Agitation
• Component geometry
• Load arrangement
• Transfer time
• Section thickness
• Surface scale

Water quenching can be too severe for many 65G components and should not be substituted without a qualified process.

Tempering Temperature

The GOST reference heat-treatment condition for 65G test samples uses:

• Tempering temperature: 470°C
• Cooling medium after tempering: air
• Referenced tensile strength: minimum 980 MPa
• Referenced yield strength: minimum 785 MPa

A commonly referenced GB/T 1222-2016 condition for 65Mn uses a tempering temperature around 540°C following oil quenching.

Tempering temperature must be selected according to the required balance of:

• Hardness
• Elastic limit
• Tensile strength
• Toughness
• Fatigue resistance
• Dimensional stability

The same tempering temperature should not be applied automatically to every spring geometry.

Recommended Heat-Treatment Cycle

Representative 65G Heat-Treatment Cycle

Representative 65Mn Heat-Treatment Cycle

These cycles are engineering references. Furnace type, section size, loading density and component geometry require process-specific qualification.

Effect of Tempering Temperature on Hardness

Tempering temperature directly affects 65G steel hardness and final spring behaviour.

65G and 65Mn may show sensitivity to temper brittleness under unsuitable conditions. Process control and cooling practice must therefore be consistent.

Microstructure and Hardenability

After correct quenching, 65G and 65Mn develop a predominantly martensitic structure in sufficiently hardened sections.

After tempering, the structure becomes tempered martensite with carbides distributed according to the selected thermal cycle.

Manganese improves hardenability compared with plain carbon steels containing less manganese. This means a greater section depth can transform during oil quenching.

Important metallurgical risks include:

• Coarse grains from overheating
• Retained non-martensitic regions from inadequate quenching
• Surface decarburisation
• Quench cracks
• Temper brittleness
• Non-uniform hardness
• Excessive retained stress

65G hardenability remains lower than that of alloy spring steels such as 60Si2Mn or 50CrV4. Larger or highly stressed sections may require a more strongly alloyed grade.

Elasticity and Spring Performance

65G elasticity results from its high yield strength after suitable heat treatment rather than from an unusually high elastic modulus.

Its spring performance depends on:

• High elastic limit
• Correct tempered hardness
• Uniform cross-section
• Clean surface condition
• Controlled residual stress
• Suitable component geometry
• Absence of decarburised edges
• Proper load distribution

65G steel for springs and leaf springs performs effectively when stresses remain inside the qualified operating range.

The steel is not automatically suitable for every spring design. Large sections, extreme fatigue requirements or high-temperature service may require silicon-manganese, chromium-vanadium or other alloy spring steels.

Fatigue Resistance

65G fatigue resistance is one of its key advantages when the material is correctly processed.

Fatigue performance can be improved through:

• Fine and uniform microstructure
• Correct tempering
• Smooth edges
• Controlled grinding
• Removal of surface defects
• Shot peening where appropriate
• Avoidance of sharp section transitions
• Control of tensile residual stress
• Protection from corrosion
• Prevention of surface decarburisation

Corrosion pits and surface scratches can act as fatigue-crack initiation points. Surface protection is therefore important even where general atmospheric corrosion is not the primary design concern.

Wear Resistance

65G and 65Mn provide good wear resistance after hardening and tempering.

Their carbon content allows the formation of a hard martensitic structure, while manganese contributes to effective hardening.

Typical wear-related applications include:

• Wear plates of moderate thickness
• Scraper elements
• Agricultural machine parts
• Cutting edges
• Friction components
• Resilient washers
• Saw-related components
• Hardened strips
• Wear-loaded machine parts

65G wear resistance is higher than that of many low-carbon structural steels. It does not, however, replace specialised tool steels, abrasion-resistant alloy plates or carbide materials in extremely severe wear conditions.

Toughness and Impact Resistance

65G toughness depends strongly on tempering temperature and section size.

The material offers a practical strength-to-toughness balance after correct tempering, but it is not considered a highly impact-tough steel.

Important limitations include:

• Reduced toughness at excessive hardness
• Increased cracking risk at sharp corners
• Sensitivity to quench stress
• Reduced reliability where deep surface defects are present
• Limited suitability for severe repeated impact
• Potential temper-brittleness sensitivity

Components combining high impact loading with large section thickness may require a lower-carbon or more strongly alloyed spring steel.

Machinability

65G machinability is most favourable in the annealed or spheroidised condition.

Recommended machining considerations include:

• Machine before final hardening where possible
• Use rigid workholding
• Avoid local overheating
• Control cutting-tool wear
• Use appropriate coolant
• Remove sharp machining marks from fatigue-critical surfaces
• Provide suitable finishing allowance
• Avoid grinding burns after heat treatment

Machining hardened 65G requires suitable abrasive or hard-cutting processes. Poor surface finishing can reduce the fatigue life of the final component.

Cold and Hot Formability

Annealed 65G strip, sheet and wire can be formed into springs and resilient components before final heat treatment.

Cold-forming capability depends on:

• Annealed hardness
• Carbide distribution
• Strip thickness
• Bend radius
• Edge quality
• Rolling direction
• Surface condition
• Tool geometry

Tight bends in a hard or heavily cold-worked condition can produce edge cracking.

Hot forming is used for larger spring components and forged parts. Heating temperature must be controlled to prevent:

• Grain coarsening
• Scale formation
• Decarburisation
• Uneven deformation
• Surface cracking

Final quenching and tempering are generally required after hot forming.

Weldability

65G and 65Mn weldability is poor because their high carbon content and manganese-assisted hardenability promote the formation of hard, brittle heat-affected zones.

Welding is generally not recommended for critical spring components.

Where welding is unavoidable, the procedure may require:

• Controlled preheating
• Low-hydrogen consumables
• Restricted heat input
• Slow cooling
• Post-weld heat treatment
• Hardness inspection
• Crack examination
• Engineering qualification

A welded joint can have significantly different fatigue performance from the unaffected spring steel. Welding should never be treated as a routine fabrication method for highly stressed 65G springs.

Corrosion-Resistance Limitations

65G and 65Mn are not stainless steels. Their atmospheric corrosion resistance is limited.

Unprotected material can rust when exposed to:

• Moisture
• Condensation
• Salts
• Acids
• Industrial contamination
• Outdoor weather
• Humid storage
• Marine environments

Protective systems may include:

• Oil films
• Phosphate coatings
• Paint systems
• Black oxide
• Controlled plating processes
• Mechanical barriers
• Corrosion-inhibiting packaging

Coating processes must be selected carefully for high-strength spring components. Some chemical and electroplating operations can introduce hydrogen and increase the risk of delayed cracking.

Key Advantages and Limitations

Main Advantages

• High strength after quenching and tempering
• Strong elastic response
• Good fatigue resistance under controlled conditions
• Good wear resistance
• Better hardenability than lower-manganese plain carbon steel
• Suitable for spring strip, sheet, bar, wire and forged forms
• Useful for agricultural and mechanical wear parts
• Close Russian and Chinese grade relationship
• Established heat-treatment routes
• Effective combination of hardness and tempered strength

Main Limitations

• Poor weldability
• Limited corrosion resistance
• Sensitive to surface decarburisation
• Sensitive to overheating
• Risk of distortion and cracking during quenching
• Lower hardenability than highly alloyed spring steels
• Reduced toughness at excessive hardness
• Fatigue life strongly affected by surface defects
• Standard-specific differences between 65G and 65Mn
• Not suitable for automatic substitution without technical review

Applications and Uses

65G steel applications and 65Mn steel applications include components that require elasticity, repeated deflection, hardness and wear resistance.

Common uses include:

• Coil springs
• Flat springs
• Leaf springs
• Spring rings
• Retaining elements
• Thrust washers
• Resilient washers
• Brake bands
• Clutch components
• Friction discs
• Collets
• Feed collets
• Gears of suitable loading
• Bearing-related components
• Agricultural machine parts
• Scrapers
• Cutting components
• Hardened strips
• Saw-related parts
• Wear-loaded machine elements

Application suitability must be evaluated using the finished component condition rather than the grade name alone.

Spring, Automotive and Agricultural Applications

Spring Applications

65G steel for springs and leaf springs is used in:

• Flat springs
• Round springs
• Compression springs
• Extension springs
• Torsional spring elements
• Spring clips
• Retaining rings
• Resilient washers
• Clutch springs
• Brake springs
• Valve-related springs of suitable dimensions

Automotive Applications

Possible automotive and transport applications include:

• Leaf-spring components
• Brake bands
• Clutch-related resilient parts
• Retaining elements
• Spring washers
• Elastic fastening parts
• Wear-loaded linkages

Agricultural Applications

65G steel for agricultural machine parts may be used for:

• Scraper elements
• Flexible tines
• Resilient holders
• Cutting and wear parts
• Harvester components
• Soil-contact components of suitable design
• Spring-loaded machine mechanisms

Agricultural components must balance hardness with sufficient toughness to avoid brittle fracture during impact.

Blade, Cutting and Wear-Part Applications

65Mn blade steel and 65Mn knife steel are common descriptive phrases because the material can develop high hardness and wear resistance.

Potential applications include:

• Industrial cutting strips
• Utility blades
• Agricultural cutting elements
• Saw components
• Scrapers
• Machete-style blades
• Hardened wear strips
• Resilient cutting components

65Mn steel for blades and cutting tools should not be confused with corrosion-resistant knife steels. It requires surface maintenance and corrosion protection.

Compared with specialised tool steels, 65Mn offers a simpler composition and effective toughness when correctly tempered, but its edge retention, corrosion behaviour and high-temperature stability remain application-dependent.

Available Product Forms and Delivery Conditions

ST65G, 65G and 65Mn can be processed in multiple product forms.

Russian Metals presents the grade in relation to its required chemical composition, processing condition and final mechanical performance rather than treating every form as technically identical.

Available Sizes, Dimensions and Tolerances

Dimensions and tolerances depend on the applicable product standard.

65G Scope Under GOST 14959-2016

65Mn Scope Under GB/T 1222-2016

Published dimensions should match the actual product programme and applicable tolerance standard. Unsupported stock-size claims should not be added to technical content.

Equivalent Grades and International Comparison

Equivalent grades must be treated as exact, close or nearest comparisons.

Equivalent tables do not override the original standard. Chemical composition, cleanliness, dimensions, hardness and test requirements must be compared before substitution.

65G vs 65Mn, AISI 1065, 1075 and 60Si2Mn

Grade Comparison Table

Are 65G and 65Mn the Same Steel?

They are close counterpart grades but not literally the same standard designation. Their principal chemical composition ranges are highly similar, which makes them reasonable comparison grades. Substitution still requires confirmation of:

• Standard edition
• Product form
• Dimensions
• Delivery condition
• Surface quality
• Hardness
• Heat treatment
• Mechanical testing
• Decarburisation limits
• Final application

Is 65G Equivalent to AISI 1065?

AISI 1065 is a useful nearest comparison based on carbon content, but it generally contains less manganese than 65G. SAE/AISI 1566 or German 66Mn4 can provide a closer manganese-based comparison in some contexts.

65Mn vs 1075 Steel

65Mn normally contains 0.62–0.70% carbon, while 1075 is generally positioned around 0.70–0.80% carbon. 1075 can develop higher hardness, while 65Mn uses greater manganese to improve hardenability.

65Mn vs 1095 Steel

1095 contains substantially more carbon than 65Mn. It can achieve high hardness and edge retention but normally has lower toughness and greater sensitivity to cracking. 65Mn generally provides a more forgiving balance for resilient cutting and spring components.