420 Stainless Steel: Properties, Hardness & Applications

What Is 420 Stainless Steel?

420 stainless steel is a martensitic stainless steel developed for applications that require significantly higher hardness and wear resistance than conventional austenitic stainless steels such as 304 or 316.

It is commonly designated:

UNS S42000

420 contains approximately 12–14% chromium and a higher carbon level than general-purpose austenitic stainless steels.

The combination of chromium and carbon allows the material to be:

Austenitized → Quenched → Tempered

to develop high hardness and mechanical strength.

Unlike 304 or 316L, 420 is magnetic and can be conventionally hardened by heat treatment.

Why Engineers Choose 420 Stainless Steel

420 is commonly selected when the application requires:

• High hardness

• Good wear resistance

• Heat-treatable strength

• Precision grinding capability

• Moderate corrosion resistance

• Magnetic behavior

• Better corrosion resistance than conventional non-stainless tool or carbon steels

It is particularly useful for mechanical components where wear performance is more important than maximum corrosion resistance or weldability.

420 Stainless Steel in One Sentence

420 is a heat-treatable martensitic stainless steel used for high-hardness and wear-resistant components that can be machined before hardening and finish ground after heat treatment.

Chemical Composition & Properties of 420 Stainless Steel

Chemical Composition

Representative UNS S42000 composition limits are shown below.

Actual composition requirements depend on the applicable product specification.

Role of the Main Alloying Elements

Chromium
Provides stainless-steel corrosion resistance and contributes to hardenability.

Carbon
Enables formation of a hard martensitic structure after quenching.

Higher carbon content generally supports higher achievable hardness, but can reduce toughness and corrosion performance if carbides consume too much chromium from the matrix.

Important Carbon-Level Note

“420 stainless steel” can cover materials with different carbon levels depending on product specification and regional designation.

This means that:

• Maximum achievable hardness

• Toughness

• Heat-treatment response

• Wear resistance

can vary substantially between products sold under the broader 420 family.

For controlled engineering purchases, the exact standard and chemical composition should be specified rather than relying on the grade name alone.

Mechanical Properties by Material Condition

Mechanical properties of 420 depend strongly on:

• Carbon content

• Austenitizing temperature

• Quench method

• Tempering temperature

• Section size

• Material condition

A single tensile or hardness value should therefore not be treated as representative of all 420 material.

Annealed Condition

Annealed 420 is softer and easier to machine than hardened material.

Representative values may fall approximately within:

These values are indicative only.

Exact requirements should be verified against the applicable product specification.

Hardened & Tempered Condition

After hardening and tempering, 420 can achieve substantially higher:

• Tensile strength

• Yield strength

• Hardness

• Wear resistance

Typical hardness depends strongly on carbon level and tempering condition.

For many commercial 420 grades, achievable hardness can extend into approximately:

40–50 HRC

Higher-carbon variants within the broader 420 family may achieve still higher hardness.

Engineering Note

Hardness should always be specified together with:

• Material standard

• Starting condition

• Heat-treatment procedure

• Required hardness range

For precision wear components, specifying only:

420 Stainless Steel

is often insufficient.

Typical Physical Properties

Physical properties are approximate and vary with temperature and material condition.

Lower Thermal Expansion Than Austenitic Stainless Steel

420 generally has a lower thermal-expansion coefficient than 304 or 316L.

This can be useful for precision mechanical components, although heat-treatment distortion must still be considered separately.

Corrosion Resistance & Environmental Performance

420 provides moderate stainless-steel corrosion resistance.

Its corrosion resistance is generally strongest when the material is:

• Properly hardened

• Properly tempered

• Clean

• Polished or finely finished

• Free from iron contamination

However, 420 does not provide the same corrosion margin as 304, 316 or 316L.

General Atmospheric Corrosion

420 can perform well in:

• Dry indoor environments

• Mild industrial environments

• Clean atmospheric exposure

• Light moisture exposure

It is commonly used where mechanical hardness is more important than maximum corrosion resistance.

Freshwater

420 can perform satisfactorily in selected freshwater applications.

Suitability depends on:

Chloride Content / Temperature / Surface Finish / Exposure Time / Crevice Geometry

For continuous wet service with significant chlorides, an austenitic or duplex stainless steel may be more appropriate.

Chloride Resistance

420 is not a chloride-resistant specialist grade.

Chlorides can increase the risk of:

• Pitting

• Crevice corrosion

• Surface staining

For:

Coastal Exposure / Salt Spray / Seawater / Chloride Process Fluids

consider 316L, 2205 or 2507 depending on the severity of the environment.

Marine & Seawater Environments

420 should not be positioned as a marine-grade stainless steel.

Direct seawater exposure is generally not a suitable primary application.

Where a high-strength component must also operate in seawater, the selection should consider corrosion-resistant alternatives rather than relying on hardness alone.

Chemical Resistance

420 provides resistance to selected mild chemicals but should not be positioned as a chemical-processing stainless steel.

For aggressive chemical exposure, consider:

316L / 904L / Higher-Alloy Stainless Steel

depending on the actual environment.

Effect of Heat Treatment on Corrosion Resistance

Heat treatment influences corrosion performance.

Improper heat treatment can cause chromium-rich carbides to form in ways that reduce chromium available in the surrounding matrix.

Proper hardening and tempering are therefore important not only for mechanical properties but also for maintaining useful corrosion resistance.

Environmental Suitability

Key Engineering Characteristics

High Hardness

Hardness is one of the defining properties of 420.

After appropriate hardening and tempering, 420 can achieve substantially higher hardness than:

304 / 304L / 316 / 316L

This makes it suitable for:

Wear Surfaces / Pins / Bushings / Valve Components / Cutting Components / Precision Mechanical Hardware

Good Wear Resistance

Higher hardness generally improves resistance to:

• Abrasive wear

• Sliding wear

• Surface deformation

• Mechanical contact damage

Actual wear performance still depends on:

Surface Finish / Lubrication / Contact Pressure / Counterface Material / Heat Treatment

Heat-Treatable Mechanical Properties

420 can be strengthened through conventional martensitic heat treatment.

This distinguishes it from austenitic grades such as 304 and 316L.

The final property balance can be adjusted through:

Austenitizing Temperature / Quenching / Tempering Temperature

Magnetic Behavior

420 is magnetic in both annealed and hardened conditions.

This is normal for martensitic stainless steel.

Moderate Corrosion Resistance

420 provides useful corrosion resistance for many mechanical applications, but corrosion resistance is not the main reason to select the grade.

If corrosion performance dominates the design requirement, another stainless steel family may be more appropriate.

Lower Formability

420 does not provide the ductility of 304 or 316L.

Forming should generally be completed in the annealed condition before final hardening.

Poor Weldability

The martensitic transformation and relatively high carbon content increase the risk of:

• Weld cracking

• High HAZ hardness

• Residual stress

• Reduced toughness

Welding should therefore be avoided where a more weldable stainless steel can meet the design requirements.

Manufacturing Compatibility of 420 Stainless Steel

420 is well suited to machining and grinding when the manufacturing sequence is planned around heat treatment.

CNC Machining

Compatibility: ✅ Good in Annealed Condition

420 can be:

Turned / Milled / Drilled / Threaded / Bored

before final hardening.

The annealed condition is normally preferred for extensive machining.

Machining After Hardening

Machining difficulty increases significantly after hardening.

High hardness increases:

• Cutting force

• Tool wear

• Heat generation

• Risk of poor tool life

After final heat treatment, grinding is often preferred for critical dimensions rather than extensive conventional machining.

Recommended Manufacturing Sequence

A common route for precision components is:

Annealed Material

↓

Rough Machining

↓

Semi-Finish Machining

↓

Hardening + Tempering

↓

Finish Grinding

↓

Polishing / Passivation if Required

This route allows most material removal to occur while the alloy is still machinable.

Drilling & Tapping

Compatibility: ✅ Good Before Hardening

Drilling and tapping should preferably be completed before final hardening where possible.

Hardened 420 can make:

Small Holes / Deep Holes / Internal Threads

considerably more difficult to produce.

Grinding

Compatibility: ✅ Excellent

Grinding is particularly important for hardened 420.

Typical applications include:

• Shaft diameters

• Bearing surfaces

• Valve components

• Wear surfaces

• Precision pins

• Tooling components

Grinding allowance should be planned before heat treatment.

Forging

Compatibility: ✅

420 can be hot forged using appropriate temperature control.

Forged components normally require controlled cooling and subsequent annealing or heat treatment before final use.

Forming

Compatibility: ⚠ Limited

Simple forming may be possible in the annealed condition.

420 is not recommended for:

Severe Deep Drawing / Complex Sheet Forming / High-Ductility Fabrication

Welding

Compatibility: ⚠ Poor / Not Preferred

Welding is technically possible but requires careful procedure control.

Where welding cannot be avoided, considerations may include:

• Preheating

• Controlled heat input

• Suitable filler selection

• Slow cooling

• Post-weld heat treatment

For welding-intensive assemblies, 304L or 316L is generally a more appropriate material.

Material Condition & Heat Treatment

Heat treatment is one of the most important parts of 420 stainless steel selection.

Annealing

Annealing is used to reduce hardness and improve machinability.

Typical annealing practice may involve heating to approximately:

840–900°C

followed by controlled slow cooling.

Exact treatment depends on product size, carbon level and applicable specification.

Austenitizing / Hardening

A typical hardening cycle involves heating approximately within:

980–1050°C

to form austenite and dissolve sufficient carbon and chromium into solution.

The component is then quenched using a suitable cooling medium.

Possible methods include:

• Oil quenching

• Air cooling for suitable section sizes

• Controlled gas quenching in vacuum heat treatment

Exact process parameters should follow the applicable heat-treatment specification.

Quenching

Quenching transforms the austenitic structure into martensite.

This produces high hardness but also increases:

• Residual stress

• Brittleness

• Distortion risk

Tempering is therefore required after hardening.

Tempering

Tempering adjusts the final balance of:

Hardness / Strength / Toughness / Residual Stress

Lower tempering temperatures generally preserve higher hardness.

Higher tempering temperatures generally reduce hardness while increasing toughness.

High-Hardness Tempering

Where maximum hardness and wear resistance are required, lower tempering temperatures are commonly used.

The exact range should be selected according to:

Required Hardness / Toughness / Section Size / Service Condition

Intermediate Tempering Range

Certain intermediate tempering temperatures can produce an unfavorable combination of:

• Reduced toughness

• Reduced corrosion resistance

• Temper embrittlement sensitivity

For this reason, generic heat-treatment temperatures should not be selected without reference to the applicable alloy specification and final property requirements.

Higher-Temperature Tempering

Higher-temperature tempering reduces hardness but can improve toughness.

This may be useful for:

• Mechanical shock

• Higher toughness requirements

• Components where maximum hardness is unnecessary

Heat-Treatment Distortion

Conventional martensitic hardening involves a phase transformation and quenching.

This can cause:

• Dimensional change

• Warpage

• Residual stress

Precision parts should therefore include:

Heat-Treatment Allowance / Grinding Allowance / Distortion Control / Final Inspection

420 vs 17-4 PH Heat Treatment

420 and 17-4 PH are both heat-treatable stainless steels, but the strengthening mechanism is different.

420

Austenitize → Quench → Temper

Primary goal:

High Hardness + Wear Resistance

17-4 PH

Solution Treat → Age

Primary goal:

High Strength + Controlled Toughness + Better Dimensional Stability

This distinction is important when choosing between the two grades.

Surface Finish Compatibility

Surface condition is particularly important for 420 because a smooth surface can improve both:

• Wear behavior

• Corrosion performance

Precision Grinding

Compatibility: ✅ Excellent

Precision grinding is one of the most important finishing methods for hardened 420 components.

Typical applications include:

Shafts / Pins / Valve Parts / Wear Surfaces / Precision Mechanical Features

Mechanical Polishing

Compatibility: ✅ Excellent

420 responds well to polishing.

A polished surface can:

• Reduce surface roughness

• Improve appearance

• Reduce sites for corrosion initiation

• Improve contact behavior

Passivation

Compatibility: ✅ Good

420 can be passivated after appropriate cleaning.

Passivation helps remove free iron and supports the stainless-steel passive surface.

It does not make 420 equivalent to 304 or 316L in aggressive environments.

Pickling

Compatibility: ✅ / Evaluate

Pickling can be used to remove oxide and heat-treatment scale.

Process chemistry and exposure time should be controlled to avoid excessive attack.

Bead Blasting

Compatibility: ✅ Good

Bead blasting can provide a uniform matte finish.

For corrosion-sensitive components, blasting media should be controlled to prevent iron contamination.

Laser Marking

Compatibility: ✅ Excellent

Suitable for:

Part Numbers / Serial Numbers / Material Identification / Traceability

Electropolishing

Compatibility: ⚠ Evaluate

420 can be electropolished, but this is not normally the primary finishing route for high-hardness martensitic components.

For sanitary or highly corrosion-sensitive electropolished applications, 316L is generally the more appropriate base material.

Common Finish Options

Precision Grinding ✅ / Mechanical Polishing ✅ / Passivation ✅ / Pickling ✅ / Bead Blasting ✅ / Laser Marking ✅ / Electropolishing ⚠

Surface Finish Selection Note

For hardened 420 components, the final finish should be considered together with the heat-treatment sequence.

A typical precision manufacturing route may be:

Machine → Harden → Temper → Finish Grind → Polish → Clean / Passivate

This allows final dimensions and functional surfaces to be controlled after heat-treatment distortion has occurred.

Typical Applications of 420 Stainless Steel

420 stainless steel is commonly used for components that require higher hardness, wear resistance and heat-treatable strength than standard austenitic stainless steels.

It is particularly suitable for precision mechanical parts that can be machined in the annealed condition, hardened and tempered, then finish ground or polished.

Shafts & Pins

Typical Applications:

Drive Shafts / Guide Pins / Pivot Pins / Precision Shafts / Locating Pins

420 can provide a useful combination of:

Hardness / Strength / Wear Resistance / Moderate Corrosion Resistance

For tightly controlled shaft diameters, finish grinding after heat treatment is often appropriate.

Valve & Pump Components

Typical Applications:

Valve Stems / Valve Components / Pump Shafts / Pump Hardware / Wear-Contact Components

420 is useful where moving components require higher hardness than 304 or 316L.

For aggressive chloride or chemical service, corrosion resistance should be reviewed separately.

Bushings & Wear Components

Typical Applications:

Bushings / Sleeves / Wear Plates / Guides / Contact Components / Retaining Elements

Hardened 420 can provide better resistance to surface deformation and sliding wear than common austenitic stainless steels.

Actual wear performance still depends on:

Counterface Material / Lubrication / Surface Finish / Contact Pressure / Heat Treatment

Precision Mechanical Components

Typical Applications:

Pins / Couplings / Mechanical Hardware / Precision Housings / Retainers / Small Load-Bearing Components

420 is a practical option where the part requires:

• CNC machining before hardening

• Controlled heat treatment

• Precision grinding

• High hardness

• Moderate corrosion resistance

Cutting & Tooling-Related Components

Typical Applications:

Industrial Blades / Cutting Components / Scrapers / Tooling Inserts / Mold-Related Components

420 is frequently considered where a stainless material requires higher hardness than general-purpose corrosion-resistant grades.

For maximum edge retention or very high hardness, 440C may be more suitable.

Fasteners & High-Hardness Hardware

Typical Applications:

Pins / Screws / Retaining Hardware / Mechanical Fasteners / Adjustment Components

420 can be used where hardware must resist mechanical deformation or wear.

Where corrosion resistance is more important than hardness, 304 or 316 may provide a better overall balance.

Mold & Die Components

Typical Applications:

Mold Inserts / Tooling Components / Precision Support Parts / Wear Inserts

420 can be useful where:

• Polishability

• Hardness

• Corrosion resistance

• Precision grinding

are required together.

The required hardness should be specified together with the heat-treatment condition.

When Should You Choose 420 Stainless Steel?

420 is a strong material choice when high hardness and wear resistance are more important than maximum corrosion resistance, welding performance or sheet-forming capability.

Choose 420 When You Need

• High hardness

• Good wear resistance

• Heat-treatable mechanical properties

• CNC machining before hardening

• Precision grinding after hardening

• Magnetic stainless steel

• Moderate corrosion resistance

• Better wear performance than 304 or 316

• A stainless alternative to some non-stainless hardened steels

420 Is Especially Suitable When

The Part Has Wear Surfaces

420 is useful for components exposed to:

Sliding Contact / Repeated Mechanical Contact / Surface Loading / Abrasive Wear

The Component Must Be Hardened After Machining

A common route is:

Annealed Material → CNC Machining → Hardening → Tempering → Finish Grinding

304 or 316 Is Too Soft

When austenitic stainless steels provide adequate corrosion resistance but insufficient hardness, 420 may offer a better mechanical solution.

Precision Grinding Is Part of the Manufacturing Route

420 works particularly well for shafts, pins and wear surfaces that require final grinding after heat treatment.

Selecting the Right 420 Heat-Treatment Condition

420 should not be selected using the grade name alone when final hardness is important.

The required heat-treatment condition should be matched to the application.

Annealed Condition

Selection Intent:
Machining / Limited Forming Before Final Hardening

Choose the annealed condition when substantial material removal is required.

High-Hardness Condition

Selection Intent:
Wear Resistance + Surface Hardness

Lower tempering temperatures generally preserve higher hardness after quenching.

Suitable where:

• Wear is important

• Surface deformation must be minimized

• Toughness requirements are moderate

Higher-Tempered Condition

Selection Intent:
Improved Toughness + Reduced Hardness

Higher tempering temperatures reduce hardness but can provide greater toughness and lower residual stress.

This may be appropriate for components exposed to:

• Mechanical shock

• Impact

• Cyclic loading

• Larger section sizes

Heat-Treatment Selection Note

The correct condition should be defined by:

Required Hardness / Toughness / Section Size / Wear Mechanism / Corrosion Environment / Distortion Allowance

Consider Another Grade When...

420 Stainless Steel vs Similar Grades

420 vs 410 Stainless Steel

Both 420 and 410 are martensitic stainless steels that can be hardened by heat treatment.

420 generally contains more carbon and can achieve higher hardness and wear resistance.

410 usually provides a better balance of toughness, machinability and general mechanical performance.

Choose 420 when:
Higher hardness and wear resistance are more important.

Choose 410 when:
A more general-purpose heat-treatable stainless steel is required.

CTA:
Compare 410 vs 420 Stainless Steel

420 vs 440C Stainless Steel

Both grades are heat-treatable martensitic stainless steels.

440C contains substantially more carbon and can achieve significantly higher hardness.

420 generally provides:

• Better toughness

• Easier machining before hardening

• More moderate heat-treatment response

440C is better suited to:

Bearings / High-Wear Precision Parts / Very High Hardness Applications

Choose 420 when:
High hardness is required but maximum hardness is unnecessary.

Choose 440C when:
Very high hardness and wear resistance dominate the design.

CTA:
Compare 420 vs 440C Stainless Steel

420 vs 17-4 PH Stainless Steel

420 and 17-4 PH are both heat-treatable stainless steels, but their strengthening mechanisms and selection priorities are different.

420 uses:

Austenitize → Quench → Temper

17-4 PH uses:

Solution Treat → Age

420 is primarily selected for hardness and wear resistance.

17-4 PH is primarily selected for high structural strength, toughness and dimensional control.

Choose 420 when:
Hardness and wear resistance are the main requirements.

Choose 17-4 PH when:
High yield strength and toughness are more important.

CTA:
Compare 420 vs 17-4 PH Stainless Steel

420 vs 304 Stainless Steel

420 can be hardened to much higher strength and hardness.

304 provides better corrosion resistance, formability and weldability.

Choose 420 when:
Wear resistance and heat-treatable hardness are required.

Choose 304 when:
General corrosion resistance and fabrication capability are more important.

420 vs 316L Stainless Steel

420 provides higher hardness and wear resistance.

316L provides substantially better chloride corrosion resistance and welding performance.

Choose 420 when:
The component is primarily a mechanical wear part.

Choose 316L when:
The component is exposed to chloride-containing, chemical or welded corrosion-sensitive service.

420 vs 416 Stainless Steel

Both grades are martensitic stainless steels and can be hardened.

416 is modified for better machinability.

420 is generally selected for higher hardness and wear performance.

Choose 420 when:
Hardness and wear resistance are more important.

Choose 416 when:
Machining productivity is more important.

Standards, Specifications & Material Forms of 420 Stainless Steel

420 is supplied under different product standards depending on whether the material is purchased as bar, plate, sheet or another form.

Common Material Designations

Important Equivalence Note:
420 is a broad martensitic stainless family, and international designations are not always exact one-to-one equivalents.

Carbon ranges can differ substantially.

For controlled engineering work, the actual specification and chemistry should be checked before treating grades as interchangeable.

Common ASTM Specifications

ASTM A276 / A276M

Commonly applies to:

Bars / Shapes

Relevant for machined shafts, pins and other bar-stock components.

ASTM A479 / A479M

May apply to:

Bars and Shapes for Boiler and Pressure-Vessel Applications

where Type 420 is included by the applicable specification.

ASTM A240 / A240M

Depending on product and specification scope, 420 may be available in flat-product forms such as:

Plate / Sheet / Strip

The exact grade and mechanical requirements should be verified for the required product form.

Common European Product Forms

Depending on exact EN grade and specification, related martensitic stainless steels may be supplied under EN 10088 product standards.

Because carbon content and heat-treatment requirements matter significantly for 420-type stainless steels, the EN grade should be specified explicitly rather than simply converted from “420.”

Common Material Forms

420 is commonly available as:

Round Bar / Flat Bar / Plate / Sheet / Strip / Forged Stock / Billet / Precision Ground Bar

Round Bar

Commonly used for:

Shafts / Pins / Bushings / Valve Components / Precision Turned Parts

Flat Bar & Plate

Commonly used for:

Wear Components / Tooling Parts / Mold Components / Milled Mechanical Parts

Sheet & Strip

Used in selected applications where thin martensitic stainless product is required.

420 should not be treated as a general sheet-metal fabrication grade.

Common Material Conditions

420 may be supplied in conditions such as:

Annealed / Soft Annealed / Hardened / Hardened & Tempered / Ground

For CNC machining projects, annealed material is usually the most practical starting condition.

For final parts, the required hardness or heat-treatment condition should be defined explicitly.

Surface Conditions

Depending on product form, 420 may be supplied as:

Hot Rolled / Cold Drawn / Peeled / Turned / Ground / Polished / Annealed Surface

Precision ground bar can be particularly useful for shafts and cylindrical components.

Purchasing Specification Note

“420 stainless steel” alone may not provide enough information for a controlled engineering purchase.

This is especially important because carbon content and final hardness can vary.

Where mechanical properties matter, the drawing or purchase specification should identify:

• Grade

• UNS designation

• Applicable ASTM / EN specification

• Product form

• Dimensions

• Starting condition

• Required hardness

• Hardening requirement

• Tempering requirement

• Surface condition

• Grinding allowance

• Material certification

• Heat / lot traceability

• Heat-treatment certification

A clearer specification might look like:

420 / UNS S42000 / ASTM A276 / Annealed / Final Hardness XX–XX HRC

where the hardness range is selected by the design engineer according to the actual application.

420 Stainless Steel Selection Summary

Choose 420 For

Wear-Resistant Shafts / Pins / Bushings / Valve Components / Pump Components / Precision Mechanical Parts / Industrial Blades / Tooling Components / High-Hardness Hardware

Choose 410 When

A lower-carbon martensitic grade with a broader toughness-oriented mechanical balance is preferred.

Choose 440C When

Maximum hardness and wear resistance are required.

Choose 17-4 PH When

High structural strength and toughness are more important than maximum hardness.

Choose 304 When

Corrosion resistance, formability and welding are more important.

Choose 316L When

Chloride resistance and welded corrosion-sensitive service are the main requirements.

Choose 416 When

Free-machining behavior and heat-treatable mechanical properties are more important than maximum hardness.

Material Selection & Engineering Support

Selecting 420 stainless steel requires more than confirming the alloy grade. Final hardness, heat-treatment condition, machining sequence, dimensional tolerance and corrosion environment should all be considered before production.

420 is most suitable when hardness and wear resistance are primary requirements and moderate corrosion resistance is sufficient.

NAITE TECH can review the material specification together with the drawing, required hardness and manufacturing route before production.

Material Grade Review

420 can be reviewed against application requirements such as:

• Required final hardness

• Wear resistance

• Mechanical strength

• Toughness

• Corrosion environment

• CNC machining requirements

• Heat-treatment requirements

• Grinding requirements

• Dimensional tolerance

• Surface finish

• Product form

• Applicable ASTM / EN specification

• Certification and traceability requirements

Where another stainless steel grade provides a better fit, typical alternatives include:

General Martensitic Mechanical Performance → 410

Higher Maximum Hardness → 440C

High Structural Strength + Better Toughness → 17-4 PH

Higher Machining Productivity → 416

Better General Corrosion Resistance → 304

Higher Chloride Resistance → 316 / 316L

Hardness Requirement Review

Hardness is one of the most important specification items for 420 stainless steel.

The grade designation alone does not define final hardness.

Final properties depend on:

• Carbon content

• Starting material condition

• Austenitizing temperature

• Holding time

• Quench method

• Tempering temperature

• Section size

• Final grinding or finishing

For controlled engineering components, the required hardness range should be stated on the drawing or purchase specification.

A requirement such as:

420 / UNS S42000 / ASTM A276 / Final Hardness XX–XX HRC

is more useful for production than simply:

420 Stainless Steel

Heat-Treatment Review

420 develops its useful high-hardness properties through conventional martensitic heat treatment.

A typical manufacturing sequence may include:

Annealed Material

↓

Rough Machining

↓

Semi-Finish Machining

↓

Austenitizing

↓

Quenching

↓

Tempering

↓

Finish Grinding

↓

Polishing / Passivation if Required

Heat treatment should be selected according to the required balance of:

Hardness / Strength / Toughness / Wear Resistance / Distortion

The highest achievable hardness is not automatically the correct condition for every component.

Machining & Grinding Review

420 is generally easier to machine before final hardening.

Important manufacturing considerations include:

Annealed Machining
Most turning, milling, drilling and threading should normally be completed before final hardening.

Heat-Treatment Allowance
Precision features may require additional material allowance before heat treatment.

Distortion Control
Quenching can introduce dimensional change or warpage.

Finish Grinding
Critical shaft diameters, bearing surfaces and wear features may require grinding after heat treatment.

Threaded Features
Threads should generally be completed before hardening where practical, unless the design requires a specific post-treatment process.

Corrosion Environment Review

420 provides moderate corrosion resistance, but it should not be selected primarily for severe corrosion service.

Important factors include:

• Chloride concentration

• Moisture exposure

• Operating temperature

• Surface finish

• Crevice geometry

• Deposits

• Cleaning chemicals

• Heat-treatment condition

Where corrosion resistance dominates the application, another grade may be more appropriate.

Typical alternatives include:

Better General Corrosion Resistance → 304

Higher Chloride Resistance → 316L

High Strength + Better Chloride Resistance → 2205 Duplex

Severe Chloride Service → 2507 Super Duplex

Specification Review

For controlled projects, material and production requirements can be reviewed together with:

• 420 / UNS S42000

• Applicable ASTM / EN specification

• Product form

• Material dimensions

• Starting condition

• Final hardness requirement

• Heat-treatment requirement

• Grinding allowance

• Surface finish

• Certification requirements

• Heat / lot traceability

• Heat-treatment documentation

The engineering drawing and purchase specification should take precedence over general website reference data.

Material Quality & Traceability for 420 Stainless Steel

For heat-treated 420 components, both material identity and final heat-treatment condition may need to be controlled.

Material Grade Verification

The specified material can be checked against the drawing and purchasing requirements before production.

Typical identification may include:

420 / UNS S42000

Where an EN or other international designation is specified, the actual chemistry and product specification should also be confirmed rather than relying only on a nominal grade conversion.

Starting Material Condition

Incoming material condition can affect both machining and final heat-treatment response.

Typical starting conditions may include:

• Annealed

• Soft annealed

• Cold finished

• Ground

• Other specified supply conditions

For machining-intensive components, annealed material is generally the preferred starting condition.

Mill Test Reports

Mill Test Reports can be supplied for applicable materials and projects where material certification is required.

Depending on the material source and specification, an MTR may include:

• Material grade

• Heat number

• Chemical composition

• Mechanical properties

• Product specification

• Material condition

• Product dimensions

Heat-Treatment Certification

Where final hardness depends on controlled heat treatment, heat-treatment records may be required.

Depending on the project, documentation may include:

• Heat-treatment process

• Austenitizing temperature

• Quench method

• Tempering temperature

• Holding time

• Furnace or batch identification

• Treatment date

• Final hardness results

Required documentation should be agreed before production.

Hardness Verification

Hardness testing can be used to verify the final heat-treated condition.

Depending on the drawing or inspection plan, verification may specify:

• Hardness scale

• Required hardness range

• Test location

• Number of test points

• Acceptance criteria

For precision wear components, final hardness should be evaluated together with dimensional and surface requirements.

Heat & Lot Traceability

Heat, lot or batch information can be maintained where traceability requirements apply.

This may be particularly relevant for:

• Heat-treated precision components

• Valve and pump components

• Wear-resistant parts

• Repeat production

• Controlled material specifications

• Customer-approved material sources

Incoming Material Inspection

Incoming 420 material can be checked for:

• Material identification

• Product form

• Dimensions

• Surface condition

• Visible defects

• Material documentation

• Starting condition where specified

For precision heat-treated components, the starting material condition should be confirmed before the manufacturing sequence is finalized.

PMI & Additional Material Verification

Where additional alloy verification is required, Positive Material Identification or another agreed material-verification method may be considered.

The method, acceptance criteria and documentation should be agreed before production.

Important:
PMI can help verify alloy chemistry but does not confirm final hardness, tempering condition or complete mechanical performance.

Final Dimensional Inspection

Because 420 normally undergoes quenching and tempering, heat-treatment distortion should be considered for tight-tolerance components.

Final inspection may include:

• Critical dimensions

• Shaft diameters

• Flatness

• Straightness

• Roundness

• Concentricity

• Thread features

• Ground surfaces

Where required, final grinding can be performed before dimensional acceptance.

Documentation Support

Depending on project requirements, supporting documentation may include:

Material Certificate / MTR / CoC / Heat-Treatment Certificate / Hardness Report / Heat or Lot Records / Incoming Inspection Records / Dimensional Inspection Reports / Additional Agreed Quality Documentation

Quality & Traceability Note

For 420 stainless steel components, material certification and heat-treatment verification may need to be treated as separate controls.

The material certificate identifies the supplied alloy.

The heat-treatment and hardness records verify the process used to develop the final mechanical condition.

If a project requires a specific hardness range, heat-treatment certificate, material standard or heat-number traceability, these requirements should be identified during quotation.

Technical References

The technical information on this page is intended for engineering reference and preliminary material selection.

Final material, heat-treatment and mechanical-property requirements should be verified against the applicable product specification.

ASTM International

ASTM A276 / A276M
Stainless steel bars and shapes.

Relevant for many 420 bar-stock components used for CNC machining.

ASTM A479 / A479M
Stainless steel bars and shapes for boiler and pressure-vessel applications where the applicable grade and requirements are specified.

ASTM A240 / A240M
Stainless steel plate, sheet and strip where the required Type 420 flat product is covered by the applicable specification.

European Standards

Related martensitic stainless steels may be specified under applicable EN 10088 product standards.

Because 420-type grades can vary in carbon content, the exact EN designation should be verified rather than assumed to be a direct one-to-one conversion.

Material Designations

AISI / ASTM Type: 420

UNS: S42000

Common EN Comparable Grade: 1.4021*

Common EN Designation: X20Cr13*

JIS Family: SUS 420J1 / SUS 420J2*

*International designations may differ in carbon range and specification requirements. Confirm actual equivalence before controlled purchasing.

Additional Technical References

Material and heat-treatment information may also be reviewed against technical data published by:

• ASTM International

• British Stainless Steel Association

• World Stainless

• Major stainless steel producers

• Applicable heat-treatment specifications

• Customer or industry standards

Technical Note

General website data should not replace application-specific engineering assessment where hardness, wear, fatigue, fracture, corrosion or safety requirements are critical.