Engineering Alloy Steels Sourced numerical data plus engineering analysis

Material / Grade

SAE 300M

300M (4340 modified) ultra-high-strength low-alloy steel for highly stressed aerospace and similar components; processing, heat treatment and hydrogen/finish control are critical.

Hardness potential46 / 100Comparison index

Toughness71 / 100Comparison index

Impact resistance70 / 100Comparison index

Bending resistance71 / 100Comparison index

Abrasive wear41 / 100Comparison index

Steel Overview

Complete introduction and metallurgical analysis

SAE 300M belongs to Engineering Alloy Steels and selection centres on a controlled balance of hardenability, strength, toughness and manufacturing response.

300M (4340 modified) ultra-high-strength low-alloy steel for highly stressed aerospace and similar components; processing, heat treatment and hydrogen/finish control are critical.

The expected microstructure is ferrite-pearlite, bainite or tempered martensite according to chemistry, section size and delivery condition; delivery condition, section size, melt quality and processing history can change that state.

Comparison indices are hardness 46/100, toughness 71/100, impact 70/100, wear 41/100 and bending 71/100. These are internal indices, not standard test results.

The screening temperature range is 180–350 °C; strength or hardness loss, oxidation, exposure time and creep must be assessed separately.

A representative process route is normalising, annealing or quenching and tempering as required by the applicable grade and product standard. Obtain actual temperatures, times and cooling media from the grade and product data sheet.

Manufacturing indices are weldability 27/100, machinability 68/100, corrosion resistance 18/100 and fatigue resistance 60/100; use them for screening only.

The principal risk is incorrect property assumptions when section size, heat treatment and delivery condition are not matched to the certified product. Evaluate geometry, surface condition, environment and the governing failure mechanism together.

A similar name or calculated relationship is not proof of interchangeability; match chemistry, specification, condition, heat treatment and MTC.

Engineering conclusion: SAE 300M is a rational candidate when adaptable mechanical performance across a wide range of engineering components matches the real load, environment and certified product condition.

Recorded standards:SAE/AISI designation — verify governing product specification

International Equivalents

International equivalents and designations

A close counterpart is not automatically interchangeable. Confirm chemistry, product standard, delivery condition, dimensions and heat treatment.

AISI / SAEOfficial designation for the same grade

SAE 300M

A registered identity within the same grade record.

PrimaryOfficial designation for the same grade

SAE 300M

A registered identity within the same grade record.

SAE shorthandOfficial designation for the same grade

300M

A registered identity within the same grade record.

UNSClose counterpart requiring verification

UNS K44220

Match chemistry, product standard, delivery condition, heat treatment and MTC before substitution.

BÖHLERClose counterpart requiring verification

BÖHLER V132

Match chemistry, product standard, delivery condition, heat treatment and MTC before substitution.

Chemical Composition

Chemical composition and the role of each element

The principal recorded elements are C≈0.405%, Si≈1.625%, Mn≈0.75%, P≈0.01%, S≈0.01%, Cr≈0.825%, Mo≈0.4%, Ni≈1.825%, V≈0.075%, Cu≈0.35%. Mid-range values support engineering interpretation and do not replace purchase limits. Composition is shown for screening and traceability. The current purchase standard and the heat-specific MTC remain authoritative.

Element	Weight-percent range	Metallurgical role and effect
C	0.38–0.43 %	Carbon raises hardness, strength and carbide potential; excessive carbon can reduce toughness and weldability.
Si	1.45–1.8 %	Silicon supports deoxidation and solid-solution strength and can influence tempering or oxidation response.
Mn	0.6–0.9 %	Manganese contributes to hardenability and sulfur control; its final effect depends on amount and processing.
P	≤ 0.01 %	Phosphorus is normally restricted because higher content can promote embrittlement and reduce toughness.
S	≤ 0.01 %	Sulfur may improve chip control in free-cutting grades but can reduce transverse toughness and weldability.
Cr	0.7–0.95 %	Chromium promotes hardenability and carbide formation and, at sufficient levels, corrosion or oxidation resistance.
Mo	0.3–0.5 %	Molybdenum improves hardenability and temper resistance and can support hot strength or pitting resistance.
Ni	1.65–2 %	Nickel generally improves toughness and through-section response and stabilises austenite in stainless systems.
V	0.05–0.1 %	Vanadium refines grain and forms stable carbides that support wear resistance and secondary hardening.
Cu	≤ 0.35 %	Copper can improve atmospheric corrosion resistance or precipitation response in selected alloy systems.

BÖHLER V132 chemical composition referring to AMS 6417 / market grade 300M / UNS K44220 Sourced with conditions

Engineering Behaviour

Engineering behaviour and selection response

Hardness potential46 / 100

Hardness and hardenability are condition-dependent; numeric values require grade-specific heat-treatment context. Internal comparison index: 46/100.

Engineering analysis

Toughness71 / 100

Toughness has an internal index of 71/100 (high). Actual performance requires a documented product condition, heat treatment and test context.

Engineering analysis

Impact resistance70 / 100

Impact resistance has an internal index of 70/100 (high). Actual performance requires a documented product condition, heat treatment and test context.

Engineering analysis

Bending resistance71 / 100

Bending resistance has an internal index of 71/100 (high). Actual performance requires a documented product condition, heat treatment and test context.

Engineering analysis

Abrasive wear41 / 100

Wear resistance depends on hardness, microstructure/carbides and the wear mechanism. Internal comparison index: 41/100.

Engineering analysis

Corrosion resistance18 / 100

Not stainless; surface protection is generally required in corrosive service. Internal comparison index: 18/100.

Engineering analysis

Weldability27 / 100

Weldability has an internal index of 27/100 (low). Actual performance requires a documented product condition, heat treatment and test context.

Engineering analysis

Machinability68 / 100

Machinability has an internal index of 68/100 (high). Actual performance requires a documented product condition, heat treatment and test context.

Engineering analysis

High-temperature strength27 / 100

Temperature-dependent properties require grade-specific condition and test data. Internal comparison index: 27/100.

Engineering analysis

Creep resistance17 / 100

Creep resistance has an internal index of 17/100 (very low). Actual performance requires a documented product condition, heat treatment and test context.

Engineering analysis

Fatigue resistance60 / 100

Fatigue resistance has an internal index of 60/100 (moderate). Actual performance requires a documented product condition, heat treatment and test context.

Engineering analysis

Numerical scores are internal comparison indices. They are not standard test results, allowable design stresses or a manufacturer guarantee. Data Method

Hardness & Hardenability

Hardness and hardenability

Hardness and hardenability are condition-dependent; numeric values require grade-specific heat-treatment context. Internal screening index: 46/100 (moderate).

46/100

moderate

Comparison index

Governing factors

Chemistry and section size
Austenitising and quench severity
Tempering temperature and time
Test method and surface preparation

Data limits

Final acceptance requires the current standard, product form, dimensions, delivery condition and heat-specific MTC.

Impact & Toughness

Toughness, impact and fracture behaviour

Impact resistance is indexed at 70/100 and toughness at 71/100. These are not Charpy or Izod energy values; temperature, orientation, geometry and actual microstructure govern component behaviour.

70/100highComparison index

Microstructure, hardness and grain size influence impact tolerance.
Sharp radii, notches and surface defects reduce fracture resistance.
Test temperature, specimen direction and section must be identified.
For critical parts, accept impact energy only from a documented test of the same condition.

Temperature & Creep

Service temperature, thermal stability and creep

Temperature-dependent properties require grade-specific condition and test data. 180–350 °C is a screening range or sourced limit according to its evidence label. Check strength loss, oxidation, creep, exposure time and environment.

Continuous service

180–350 °CEngineering guidance

Review the limit against strength or hardness loss and exposure time.

Intermittent service

Do not assign an intermittent limit without product-specific source data.

Tempering and phase stability

Working and coating temperatures must remain compatible with the tempering condition and required microstructure.

Oxidation and environment

Oxidation or corrosion may become limiting before the strength criterion.

Relative creep resistance17/100Comparison index

The relative creep index is 17/100 (very low). It is not an allowable creep stress or rupture-life value.

Do not select this grade for long-term static high-temperature loading from the internal index alone.

Wear & Surface Behaviour

Wear resistance and surface behaviour

Abrasive wear

Wear resistance depends on hardness, microstructure/carbides and the wear mechanism. The abrasive-wear index is 41/100; final hardness, carbides, microstructure, contact mode and lubrication govern actual resistance.

Comparison index

Adhesive wear

Assess adhesive wear with the counterface material, lubrication, roughness, pressure and temperature.

Engineering analysis

Surface improvement

Evaluate surface treatment or coating only after confirming compatibility with chemistry, substrate and process temperature.

Engineering guidance

Mechanical & Physical Properties

Mechanical and physical properties

The record contains 5 sourced mechanical-property rows; each applies only to its stated condition, dimensions and test temperature.

Property	Value	Condition	Dimension	Test temperature
Hardness	≤ 311 HB	AMS 6417 bar, normalized/tempered supply condition	According to the product data sheet	20 °C
Tensile strength	≥ 270 ksi	Hardened and tempered as cited	According to the product data sheet	20 °C
Yield strength Rp0.2	≥ 220 ksi	Hardened and tempered as cited	According to the product data sheet	20 °C
Elongation	≥ 8 %	Hardened and tempered as cited	According to the product data sheet	20 °C
Reduction of area	≥ 30 %	Hardened and tempered as cited	According to the product data sheet	20 °C

Sourced with conditions

Physical properties

Density, elastic modulus, expansion and conductivity depend on family, temperature and product condition. Use grade- and product-specific values for precise calculations.

Obtain density and expansion data from the product data sheet for dimensional calculations.
Elastic modulus and conductivity vary with temperature.

Engineering analysis

Heat Treatment

Heat-treatment stages and process controls

The representative family route is normalising, annealing or quenching and tempering as required by the applicable grade and product standard. Numerical temperatures are shown only when supported by the record.

Heat-treatment stage

Engineering guidance

Confirm every numerical parameter from the current product and process specification.

Cooling: As specified by process sheet

Preheating and austenitising

Engineering guidance

Set preheat steps and austenitising parameters from the grade/product data sheet and actual section size.

Cooling: Oil quench

Tempering / property adjustment

Engineering guidance

Set tempering or ageing to the required hardness, toughness and service-temperature balance.

Cooling: Air between cycles

Annealing / stress relief

Engineering guidance

Assess the supply condition, residual stress, section size and prior machining before selecting time and temperature.

Cooling: Grade- and process-specific cooling

Preheating and austenitising

Engineering guidance

Set preheat steps and austenitising parameters from the grade/product data sheet and actual section size.

Cooling: Grade- and process-specific cooling

Quenching / controlled cooling

Engineering guidance

Choose the quench medium and cooling severity against hardenability, geometry, distortion and crack risk.

Cooling: Grade- and process-specific cooling

Tempering / property adjustment

Engineering guidance

Set tempering or ageing to the required hardness, toughness and service-temperature balance.

Cooling: Grade- and process-specific cooling

Tempering / property adjustment

Engineering guidance

Set tempering or ageing to the required hardness, toughness and service-temperature balance.

Cooling: Grade- and process-specific cooling

Process control: Review delivery condition, actual section, equipment capability, crack and distortion risk and target hardness before approving the cycle.

Engineering Charts

Hardness, toughness, impact, temperature and process charts

Chemistry data retain their evidence label; 0–100 charts are internal indices and stages without temperature are process sequences.

Multi-axis engineering profile

Comparison index

Chemical composition

Derived from source data

Hardness–toughness balance

Comparison index

Toughness, impact and fatigue

Comparison index

Wear and surface response

Comparison index

Mechanical properties or comparison indices

Sourced with conditions

Service temperature

Engineering guidance

Heat treatment

Engineering guidance

Related-grade similarity

Comparison index

All comparison indices

Comparison index

Failure Modes & Selection

Potential failure modes and selection guidance

Potential failure mechanisms

incorrect property assumptions when section size, heat treatment and delivery condition are not matched to the certified product.
Fatigue initiation from surface defects, section transitions or stress concentration.
Property loss after unsuitable heat treatment, cooling or finishing.
Corrosion, oxidation or environmental attack when protection is inadequate.

Selection and design notes

Match designation, material number, product standard and supply form before purchase.
Compare the governing failure mechanism with hardness 46, toughness 71, impact 70 and wear 41 indices out of 100.
Use mechanical values only within their cited condition, dimensions and test temperature.
Confirm the heat-treatment route and target hardness with the processor before final machining.
Review the heat number, MTC and required test results before release.

Derived calculations

Carbon equivalent CE(IIW)0.931 Calculated

Calculated from recorded inputs; apply only within the stated formula scope and limitations.

Advantages & Limitations

Advantages, limitations and unsuitable applications

Advantages

adaptable mechanical performance across a wide range of engineering components.
A clearly labelled engineering profile supports comparison with related grades.
Grade identity, chemistry, counterparts and references remain traceable in one dossier.

Limitations and weaknesses

incorrect property assumptions when section size, heat treatment and delivery condition are not matched to the certified product.
A 0–100 index cannot be converted into design stress, impact energy or creep life.
Hardness and toughness depend on section, delivery condition and actual processing.
Do not approve a substitute before checking the product standard and heat-specific MTC.

Cases requiring caution or an alternative material

Critical design without condition- and section-specific test dataDirect substitution based only on name or similarity scoreLong-term creep service without sourced time–stress–temperature dataincorrect property assumptions when section size, heat treatment and delivery condition are not matched to the certified product

Applications & Processing

Industrial applications and processing

Typical applications

Shafts, axles and rotating machine components
High-strength fasteners and mechanical connections
Structures, bridges, profiles and transmission components
Aerospace, landing-gear and high-integrity rotating components
General engineered and machine components
shafts, pins and machine components
gears and transmission parts where the grade is qualified
forgings and heat-treated sections

Manufacture, welding and surface engineering

Weldability has an internal index of 27/100 (low). Actual performance requires a documented product condition, heat treatment and test context.

Forming and forging depend on steel family, delivery condition and the grade-specific qualified temperature range.

Select nitriding, induction hardening or coating against chemistry, substrate hardness and application.
Keep coating-deposition temperature compatible with the tempering condition and substrate.
Control hydrogen embrittlement, residual stress and distortion in high-strength components.

Engineering Conclusion

Engineering conclusion and selection recommendation

SAE 300M is worth evaluating when the principal need is adaptable mechanical performance across a wide range of engineering components. Internal indices of hardness 46/100, toughness 71/100, impact 70/100 and wear 41/100 must be aligned with the real failure mechanism. The leading risk is incorrect property assumptions when section size, heat treatment and delivery condition are not matched to the certified product. Final approval requires the current standard, product form, dimensions, delivery condition, heat treatment and heat-specific MTC.

Engineering analysis

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Frequently Asked Questions

Frequently asked questions

What is SAE 300M steel?

300M (4340 modified) ultra-high-strength low-alloy steel for highly stressed aerospace and similar components; processing, heat treatment and hydrogen/finish control are critical.

What are the main applications of SAE 300M?

Application contexts include Shafts, axles and rotating machine components, High-strength fasteners and mechanical connections, Structures, bridges, profiles and transmission components and Aerospace, landing-gear and high-integrity rotating components, subject to the product standard and actual condition.

How hard can SAE 300M be?

Hardness and hardenability are condition-dependent; numeric values require grade-specific heat-treatment context. Internal screening index: 46/100 (moderate).

Is SAE 300M suitable for impact loading?

Impact resistance is indexed at 70/100 and toughness at 71/100. These are not Charpy or Izod energy values; temperature, orientation, geometry and actual microstructure govern component behaviour.

What is the service-temperature limit of SAE 300M?

Can SAE 300M be replaced by a close grade?

Approve substitution only after matching chemistry, specification, product form, condition, heat treatment and MTC.

Steel Comparison

Engineering steel comparison

Compare this grade with any other dossier. Scores from 0 to 100 are internal screening indices, not laboratory values or allowable design stresses.

Close suggestions:

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Current gradeSAE 300MEngineering Alloy Steels

Selected gradeSAE 4337Engineering Alloy Steels

Current-grade chemistry

Second-grade chemistry

Current-grade heat treatment

Second-grade heat treatment

Current-grade applications

Limitations

Second-grade applications

Limitations

Select a second grade to update the comparison.

Sources & Evidence

Sources, methodology and evidence

Sources support grade identity, recorded values or the engineering method. General guidance does not replace product-specific certification.

Grade-specific sources

Ovako Heat Treatment Guide — International grade listIdentity And Heat Treatment Model Reference · Tier A

Reference supporting grade identity or recorded values; interpret it within the cited product and condition context. Role: identity and heat treatment model reference.

View source

Laxcon alloy steel family/open datasetFamily Context · Tier A-open-data

Reference supporting grade identity or recorded values; interpret it within the cited product and condition context. Role: family context.

View source

Grade-specific published composition sourceGrade Composition · Tier A/B-reference

Reference supporting grade identity or recorded values; interpret it within the cited product and condition context. Role: grade composition.

View source

SAE ARP1631A — 300M / 4340 Modified high-strength partsCurrent Sae Process Standard · Tier A

Reference supporting grade identity or recorded values; interpret it within the cited product and condition context. Role: current sae process standard.

View source

Aircraft Materials — 300M / E4340 Mod AMS 6417/6419Mechanical Heat Treatment · Tier B-manufacturer-distributor

Reference supporting grade identity or recorded values; interpret it within the cited product and condition context. Role: mechanical heat treatment.

View source