Quenched & Tempered Steels Official identity plus sourced composition

Material / Grade

SCM440

A JIS chromium-molybdenum machine structural steel commonly used after heat treatment for drive and mechanical components.

Hardness potential59 / 100Comparison index

Toughness68 / 100Comparison index

Impact resistance74 / 100Comparison index

Bending resistance78 / 100Comparison index

Abrasive wear54 / 100Comparison index

Steel Overview

Complete introduction and metallurgical analysis

SCM440 belongs to Quenched & Tempered Steels and selection centres on high strength with adjustable toughness after quenching and tempering.

A JIS chromium-molybdenum machine structural steel commonly used after heat treatment for drive and mechanical components.

The expected microstructure is tempered martensite or bainite, with the final balance governed by section size and tempering condition; delivery condition, section size, melt quality and processing history can change that state.

Comparison indices are hardness 59/100, toughness 68/100, impact 74/100, wear 54/100 and bending 78/100. These are internal indices, not standard test results.

The screening temperature range is 250–450 °C; strength or hardness loss, oxidation, exposure time and creep must be assessed separately.

A representative process route is controlled austenitising, quenching and tempering to the required strength-toughness condition. Obtain actual temperatures, times and cooling media from the grade and product data sheet.

Manufacturing indices are weldability 36/100, machinability 60/100, corrosion resistance 18/100 and fatigue resistance 64/100; use them for screening only.

The principal risk is quench cracking, distortion, temper embrittlement or an under-hardened core in excessive sections. 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: SCM440 is a rational candidate when strong and tough through-section performance for highly loaded components matches the real load, environment and certified product condition.

Recorded standards:JIS G 4053:2023

International Equivalents

International equivalents and designations

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

JISOfficial designation for the same grade

SCM440

A registered identity within the same grade record.

PrimaryOfficial designation for the same grade

SCM440

A registered identity within the same grade record.

EN / DIN / ISOConditional application alternative

42CrMo4

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

EN / DIN / ISOConditional application alternative

42CrMo

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≈0.25%, Mn≈0.75%, P≈0.015%, S≈0.015%, Cr≈1.05%, Mo≈0.225%, Ni≈0.125%, Cu≈0.15%. 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	0.15–0.35 %	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	0–0.03 %	Phosphorus is normally restricted because higher content can promote embrittlement and reduce toughness.
S	0–0.03 %	Sulfur may improve chip control in free-cutting grades but can reduce transverse toughness and weldability.
Cr	0.9–1.2 %	Chromium promotes hardenability and carbide formation and, at sufficient levels, corrosion or oxidation resistance.
Mo	0.15–0.3 %	Molybdenum improves hardenability and temper resistance and can support hot strength or pitting resistance.
Ni	0–0.25 %	Nickel generally improves toughness and through-section response and stabilises austenite in stainless systems.
Cu	0–0.3 %	Copper can improve atmospheric corrosion resistance or precipitation response in selected alloy systems.

SCM440 Sourced with conditions

Engineering Behaviour

Engineering behaviour and selection response

Hardness potential59 / 100

Hardenable; actual hardness depends on chemistry, section size, austenitizing, quench and tempering. Internal comparison index: 59/100.

Engineering analysis

Toughness68 / 100

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

Engineering analysis

Impact resistance74 / 100

Impact resistance has an internal index of 74/100 (high). Actual performance requires a documented product condition, heat treatment and test context.

Engineering analysis

Bending resistance78 / 100

Bending resistance has an internal index of 78/100 (high). Actual performance requires a documented product condition, heat treatment and test context.

Engineering analysis

Abrasive wear54 / 100

Wear resistance depends on final hardness, microstructure and wear mode; grade name alone is insufficient for substitution. Internal comparison index: 54/100.

Engineering analysis

Corrosion resistance18 / 100

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

Engineering analysis

Weldability36 / 100

Weldability has an internal index of 36/100 (low). Actual performance requires a documented product condition, heat treatment and test context.

Engineering analysis

Machinability60 / 100

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

Engineering analysis

High-temperature strength35 / 100

Temperature-dependent behavior varies with condition, exposure time, environment and product form; use sourced values for design. Internal comparison index: 35/100.

Engineering analysis

Creep resistance23 / 100

Creep resistance has an internal index of 23/100 (very low). Actual performance requires a documented product condition, heat treatment and test context.

Engineering analysis

Fatigue resistance64 / 100

Fatigue resistance has an internal index of 64/100 (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

Hardenable; actual hardness depends on chemistry, section size, austenitizing, quench and tempering. Internal screening index: 59/100 (moderate).

59/100

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 74/100 and toughness at 68/100. These are not Charpy or Izod energy values; temperature, orientation, geometry and actual microstructure govern component behaviour.

74/100highComparison 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 behavior varies with condition, exposure time, environment and product form; use sourced values for design. 250–450 °C is a screening range or sourced limit according to its evidence label. Check strength loss, oxidation, creep, exposure time and environment.

Continuous service

250–450 °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 resistance23/100Comparison index

The relative creep index is 23/100 (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 final hardness, microstructure and wear mode; grade name alone is insufficient for substitution. The abrasive-wear index is 54/100; 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

No complete sourced numerical mechanical set is stored for this condition; labelled comparison indices are shown instead of invented test values.

Comparative property	Internal index	Information type
Hardness potential	59 / 100	Comparison index
Toughness	68 / 100	Comparison index
Impact resistance	74 / 100	Comparison index
Bending resistance	78 / 100	Comparison index
Abrasive wear	54 / 100	Comparison index
Corrosion resistance	18 / 100	Comparison index
Weldability	36 / 100	Comparison index
Machinability	60 / 100	Comparison index
High-temperature strength	35 / 100	Comparison index
Creep resistance	23 / 100	Comparison index
Fatigue resistance	64 / 100	Comparison index

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 controlled austenitising, quenching and tempering to the required strength-toughness condition. Numerical temperatures are shown only when supported by the record.

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

Comparison index

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

quench cracking, distortion, temper embrittlement or an under-hardened core in excessive sections.
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 59, toughness 68, impact 74 and wear 54 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)0.803 Calculated

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

Advantages & Limitations

Advantages, limitations and unsuitable applications

Advantages

strong and tough through-section performance for highly loaded 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

quench cracking, distortion, temper embrittlement or an under-hardened core in excessive sections.
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 dataquench cracking, distortion, temper embrittlement or an under-hardened core in excessive sections

Applications & Processing

Industrial applications and processing

Typical applications

Gears and power-transmission components
Shafts, axles and rotating machine components
High-strength fasteners and mechanical connections
Highly loaded heavy-machinery components
Components under fatigue, torsion or cyclic loading
General engineered and machine components
highly loaded shafts and axles
bolts, rods and fasteners

Manufacture, welding and surface engineering

Weldability has an internal index of 36/100 (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

SCM440 is worth evaluating when the principal need is strong and tough through-section performance for highly loaded components. Internal indices of hardness 59/100, toughness 68/100, impact 74/100 and wear 54/100 must be aligned with the real failure mechanism. The leading risk is quench cracking, distortion, temper embrittlement or an under-hardened core in excessive sections. 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 SCM440 steel?

A JIS chromium-molybdenum machine structural steel commonly used after heat treatment for drive and mechanical components.

What are the main applications of SCM440?

Application contexts include Gears and power-transmission components, Shafts, axles and rotating machine components, High-strength fasteners and mechanical connections and Highly loaded heavy-machinery components, subject to the product standard and actual condition.

How hard can SCM440 be?

Hardenable; actual hardness depends on chemistry, section size, austenitizing, quench and tempering. Internal screening index: 59/100 (moderate).

Is SCM440 suitable for impact loading?

Impact resistance is indexed at 74/100 and toughness at 68/100. These are not Charpy or Izod energy values; temperature, orientation, geometry and actual microstructure govern component behaviour.

What is the service-temperature limit of SCM440?

Can SCM440 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.

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Current gradeSCM440Quenched & Tempered Steels

Selected gradeA30422 / 42CrMoQuenched & Tempered 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

BÖHLER V320 technical dataManufacturer data sheet · Tier A

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

View source

Special Steel Strip — SCM series chemical compositionManufacturer catalog · Tier A

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

View source

JIS G 4053:2023 — Low-alloyed steels for machine structural use (preview)Official Standard Metadata · Tier A

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

View source