ASTM B935-20

Standard Guide for Steam Treatment of Ferrous Powder Metallurgy (PM) Materials

SIGNIFICANCE AND USE
5.1 The performance and quality of steam-treated materials depends upon the surface cleanliness of the material prior to steam treatment and the adequacy of the processing. Steam treatment can be used as a decorative coating, producing a blue-gray to a blue-black appearance. It can reduce the susceptibility of ferrous PM materials to further oxidation and corrosion, thus providing better shelf life. More significantly, improvements in apparent hardness, compressive strength, wear characteristics, and some mechanical properties (see Appendix X1) can be observed due to steam treatment. The hardness of magnetite (Fe3O4) formed during steam treatment is typically equivalent to 50 HRC, and when present in sintered materials, their wear resistance can be improved significantly. Steam treatment is also used to seal parts or provide a base material for additional coatings. Steam treated ferrous PM materials are used in many industries, including automotive, marine, home appliances, and lawn and garden applications.
SCOPE
1.1 This guide is intended as an aid in establishing and maintaining a procedure for the steam treatment, also referred to as steam blackening, of sintered ferrous PM materials and the appropriate use and evaluation of these materials. Additional information concerning the effect of this process on ferrous PM material properties is contained in Appendix X1.  
1.2 Units—With the exception of the values for density and the mass used to determine density, for which the use of the gram per cubic centimetre (g/cm3) and gram (g) units is the longstanding industry practice, the values in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Sep-2020
• ICS: 77.160 - Powder metallurgy
• Technical Committee: B09 - Metal Powders and Metal Powder Products
• Drafting Committee: B09.05 - Structural Parts

Relations

• Refers: ASTM B243-18 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Oct-2018
• Refers: ASTM B243-16 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Jul-2016
• Refers: ASTM B243-13 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Nov-2013
• Refers: ASTM B243-12 - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Jul-2012
• Refers: ASTM B243-11 - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Nov-2011
• Refers: ASTM B243-10 - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Jan-2010
• Refers: ASTM B243-09a - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Dec-2009
• Refers: ASTM B243-09 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Jan-2009
• Refers: ASTM B243-08a - Standard Terminology of Powder Metallurgy
• Effective Date: 15-Mar-2008
• Refers: ASTM B243-08 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Feb-2008
• Refers: ASTM B243-06 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Nov-2006
• Refers: ASTM B243-05b - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Oct-2005
• Refers: ASTM B243-05a - Standard Terminology of Powder Metallurgy
• Effective Date: 31-Mar-2005
• Refers: ASTM B243-05 - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Feb-2005
• Refers: ASTM B243-04c - Standard Terminology of Powder Metallurgy
• Effective Date: 01-Dec-2004

Overview

ASTM B935-20: Standard Guide for Steam Treatment of Ferrous Powder Metallurgy (PM) Materials provides comprehensive guidance for the application, evaluation, and quality assurance of steam-treated sintered ferrous PM parts. Issued by ASTM International, this guide assists manufacturers and users in establishing effective steam treatment-often called steam blackening-to enhance surface properties, corrosion resistance, and mechanical performance of metal powder-based components. The document applies to both batch and continuous steam treatment processes and is widely referenced in industries reliant on durable, high-performance ferrous parts, such as automotive, marine, home appliance, and garden equipment manufacturing.

Key Topics

ASTM B935-20 covers the following essential aspects of steam treatment for ferrous PM materials:

• Significance of Steam Treatment:
  Steam treatment produces a magnetite (Fe3O4) coating, improving resistance to oxidation and corrosion and enhancing visual appearance (blue-gray or blue-black finish). This process extends shelf life and enhances part durability.

• Mechanical Improvements:
  Steam-treated PM components demonstrate better apparent hardness, increased compressive strength, and improved wear characteristics-vital for parts serving in demanding environments.

• Processing Considerations:

  • The effectiveness relies heavily on pre-treatment surface cleanliness.
  • Both batch and continuous furnaces are addressed, with critical temperature management and atmospheric controls.
  • The procedure includes preheating, steam introduction, maintaining specific temperatures, and cooling.
  • The presence of contaminants, such as oils, lubricants, and rust, can significantly hinder steam treatment effectiveness.

• Evaluation and Testing:

  • Visual inspections suffice for decorative purposes.
  • Enhanced properties may require tests for hardness, density, and metallographic evaluation to assess oxide layer thickness and uniformity.

Applications

Steam-treated ferrous PM parts are prevalent wherever robust performance and longevity are priorities. Key application areas include:

• Automotive components:
  Gears, bushings, and structural parts benefit from improved wear resistance and corrosion protection.
• Marine hardware:
  Enhanced resistance to corrosive environments extends the service life of components exposed to water.
• Home appliances:
  Steam-treated parts ensure reliability and durability in high-use household devices.
• Lawn and garden equipment:
  Parts subjected to outdoor conditions gain from added protection and visual appeal.
• Base for Secondary Coatings:
  Steam treatment can act as a primer layer for subsequent coatings like paint or plating, improving adhesion and performance.

Related Standards

For organizations implementing or auditing steam treatment of ferrous PM materials, the following ASTM standards are commonly referenced alongside ASTM B935-20:

• ASTM B243 - Terminology of Powder Metallurgy
• Standards covering material specifications and testing methods for PM components.

Alignment with ASTM B935-20 ensures products meet industry expectations for quality, durability, and corrosion resistance, supporting consistent manufacturing outcomes and reliable performance in service.

Practical Value

Adherence to ASTM B935-20 provides clear, industry-accepted procedures for steam blackening of ferrous powder metallurgy materials. Key benefits include:

• Increased part life due to improved surface protection
• Enhanced mechanical properties suitable for critical applications
• Reduction in post-sintering oxidation and corrosion risk
• Confidence during audits and product qualification through recognized international standards

Companies seeking to optimize their use of steam-treated PM materials will find ASTM B935-20 an essential reference for process validation, quality control, and product development.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B935 − 20
Standard Guide for
Steam Treatment of Ferrous Powder Metallurgy (PM)
Materials
This standard is issued under the fixed designation B935; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* atmosphere;(3)heattheloadtotheprocessingtemperatureand
maintain the temperature for the duration of the processing
1.1 This guide is intended as an aid in establishing and
cycle; and (4) cool the load to a temperature suitable for
maintaining a procedure for the steam treatment, also referred
handling. This process will produce a layer of black iron oxide
to as steam blackening, of sintered ferrous PM materials and
(magnetite) on the surface of the parts and on the surfaces of
the appropriate use and evaluation of these materials. Addi-
the interconnected porosity by the reaction.
tional information concerning the effect of this process on
ferrous PM material properties is contained in Appendix X1. 3Fe14H O ~gas!↔Fe O 14H ~gas!
2 3 4 2
1.2 Units—With the exception of the values for density and 3.2 For continuous steam treatment, parts are transported
through the furnace on a continuous mesh belt, and the thermal
the mass used to determine density, for which the use of the
gram per cubic centimetre (g/cm ) and gram (g) units is the profileofthefurnace(temperaturesettingsofthevariouszones
and the speed of the mesh belt) is set to ensure that parts are
longstanding industry practice, the values in inch-pound units
are to be regarded as standard. The values given in parentheses clean and at the appropriate temperature before they are
exposed to the superheated steam.
are mathematical conversions to SI units that are provided for
information only and are not considered standard.
4. Terminology
1.3 This standard does not purport to address all of the
4.1 Definitions of powder metallurgy (PM) terms can be
safety concerns, if any, associated with its use. It is the
found in Terminology B243.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
5. Significance and Use
mine the applicability of regulatory limitations prior to use.
5.1 The performance and quality of steam-treated materials
1.4 This international standard was developed in accor-
depends upon the surface cleanliness of the material prior to
dance with internationally recognized principles on standard-
steam treatment and the adequacy of the processing. Steam
ization established in the Decision on Principles for the
treatment can be used as a decorative coating, producing a
Development of International Standards, Guides and Recom-
blue-gray to a blue-black appearance. It can reduce the
mendations issued by the World Trade Organization Technical
susceptibility of ferrous PM materials to further oxidation and
Barriers to Trade (TBT) Committee.
corrosion, thus providing better shelf life. More significantly,
2. Referenced Documents
improvements in apparent hardness, compressive strength,
wear characteristics, and some mechanical properties (see
2.1 ASTM Standards:
B243 Terminology of Powder Metallurgy Appendix X1) can be observed due to steam treatment. The
hardness of magnetite (Fe O ) formed during steam treatment
3 4
3. Summary of Guide
is typically equivalent to 50 HRC, and when present in sintered
3.1 A normal sequence of steps for batch processing is: (1) materials, their wear resistance can be improved significantly.
preheat the load; (2) introduce a superheated steam-rich
Steam treatment is also used to seal parts or provide a base
material for additional coatings. Steam treated ferrous PM
This guide is under the jurisdiction of ASTM Committee B09 on Metal materials are used in many industries, including automotive,
Powders and Metal Powder Products and is the direct responsibility of Subcom-
marine, home appliances, and lawn and garden applications.
mittee B09.05 on Structural Parts.
Current edition approved Oct. 1, 2020. Published November 2020. Originally
6. Apparatus
approved in 2005. Last previous edition approved in 2016 as B935 – 16. DOI:
10.1520/B0935-20.
6.1 The material can be processed in either a batch-type
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
furnace or a continuous belt-type furnace. The furnace must be
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
capable of heating the load, maintaining it at the processing
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. temperature, and maintaining a steam atmosphere free of air
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B935 − 20
leaks. Both batch type and continuous furnaces shall meet the to a temperature of 840 to 930 ºF (450 to 500 ºC). Exothermic
same criteria described in the following procedure section. gas burners are suitable for the pre-heat zone.
While comparable performance may be obtained from batch 7.2.2 The temperature in the steam zone of the furnace is
and continuous furnaces, the process conditions used may not generally set to a temperature of 800 to 1100 ºF (430 to
be exactly the same. 590 ºC). A typical process temperature is 1000 ºF (540 ºC).
7.2.3 The actual process temperature and the time at tem-
perature depend on the desired properties of the steam-treated
7. Procedure
parts. Times at temperature in the superheated steam are
7.1 Batch Processing
typically from 45 min to 1 ⁄2 h.
7.1.1 Place the load in the furnace and preheat in air until
the temperature of the entire load is above 212 °F (100 °C) but
8. Interferences
not in excess of 800 °F (430 °C). A temperature of 600 ºF
8.1 Thesurfaceofthematerialtobesteam-treatedshouldbe
(315 ºC) is typically used.
free of contaminants, including red rust, soot, and dirt. Steam
7.1.2 Once the load is preheated, introduce superheated
treatment cannot reduce existing rust. Soot and dirt attract
steam into the furnace until all of the air is purged from the
moisture, which causes rust to form during steam treatment.
furnace or processing zone. This steam atmosphere shall be
The soot and dirt will remain as surface blemishes after steam
maintained until the processing cycle is complete.
treatment.
NOTE 1—The temperature of the parts shall be in excess of 212 °F
8.2 Since steam treatment builds an iron oxide layer on the
(100 °C) before the superheated steam is introduced. If it is not, water will
condense on the parts and rust spots will form. The temperature shall not pore surfaces, it tends to restrict access to the non-oxidized
exceed 800 °F (430 °C) before all of the air has been purged from the
interior iron, causing the reaction to slow until further treat-
system by the superheated steam or the parts will be covered with a
ment has little effect on the thickness of the oxide layer.
smooth even coating of rust caused by air in the furnace atmosphere.
7.1.3 Raise the temperature of the furnace to the processing 9. Hazards
temperature of between 800 °F (430 °C) and 1100 °F (590 °C)
9.1 Hydrogen is generated as a by-product of the steam
while maintaining the atmosphere of superheated steam. A
treatment process. This hydrogen must be flushed from the
typical processing temperature is 1000 °F (540 °C).
furnace and air ingress must be prevented. Prior to opening a
batch-type furnace, the furnace should be flushed with nitrogen
NOTE 2—The processing temperature depends on the desired proper-
ties. Lower temperatures result in deeper oxide penetration, while higher
or an inert gas unless the parts and furnace are cooled to below
temperatures produce a thicker surface oxide layer.
the auto ignition point of hydrogen while still in the steam
NOTE 3—Processes that decrease the amount or the size of the
atmosphere.
surface-connected porosity such as copper infiltration, grinding, vibratory
finishing, sizing, machining, burnishing, shot peening, or polishing will
9.2 Warning—Foreign material can interfere with steam
reduce the effectiveness of the steam treatment by limiting the ability of
treatment and possibly pose a serious health threat. Some
steam to penetrate the part
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: B935 − 16 B935 − 20
Standard Guide for
Steam Treatment of Ferrous Powder Metallurgy (PM)
Materials
This standard is issued under the fixed designation B935; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This guide is intended as an aid in establishing and maintaining a procedure for the steam treatment, also referred to as steam
blackening, of sintered ferrous PM materials and the appropriate use and evaluation of these materials. Additional information
concerning the effect of this process on ferrous PM material properties is contained in Appendix X1.
1.2 Units—With the exception of the values for density and the mass used to determine density, for which the use of the gram per
cubic centimetre (g/cm ) and gram (g) units is the longstanding industry practice, the values in inch-pound units are to be regarded
as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and
are not considered standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
B243 Terminology of Powder Metallurgy
3. Summary of Guide
3.1 A normal sequence of steps for batch processing is: (1) preheat the load; (2) introduce a superheated steam-rich atmosphere;
(3) heat the load to the processing temperature and maintain the temperature for the duration of the processing cycle; and (4) cool
the load to a temperature suitable for handling. This process will produce a layer of black iron oxide (magnetite) on the surface
of the parts and on the surfaces of the interconnected porosity by the reaction.
3Fe14H O ~gas!↔Fe O 14H ~gas!
2 3 4 2
3.2 For continuous steam treatment, parts are transported through the furnace on a continuous mesh belt, and the thermal profile
This guide is under the jurisdiction of ASTM Committee B09 on Metal Powders and Metal Powder Products and is the direct responsibility of Subcommittee B09.05
on Structural Parts.
Current edition approved Oct. 1, 2016Oct. 1, 2020. Published October 2016November 2020. Originally approved in 2005. Last previous edition approved in 20092016
ɛ1
as B935 – 05B935 – 16.(2009) . DOI: 10.1520/B0935-16.10.1520/B0935-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B935 − 20
of the furnace (temperature settings of the various zones and the speed of the mesh belt) is set to ensure that parts are clean and
at the appropriate temperature before they are exposed to the superheated steam.
4. Terminology
4.1 Definitions of powder metallurgy (PM) terms can be found in Terminology B243.
5. Significance and Use
5.1 The performance and quality of steam-treated materials depends upon the surface cleanliness of the material prior to steam
treatment and the adequacy of the processing. Steam treatment can be used as a decorative coating, producing a blue-gray to a
blue-black appearance. It can reduce the susceptibility of ferrous PM materials to further oxidation and corrosion, thus providing
better shelf life. More significantly, improvements in apparent hardness, compressive strength, wear characteristics, and some
mechanical properties (see Appendix X1) can be observed due to steam treatment. The hardness of magnetite (Fe O ) formed
3 4
during steam treatment is typically equivalent to 50 HRC, and when present in sintered materials, their wear resistance can be
improved significantly. Steam treatment is also used to seal parts or provide a base material for additional coatings. Steam treated
ferrous PM materials are used in many industries, including automotive, marine, home appliances, and lawn and garden
applications.
6. Apparatus
6.1 The material can be processed in either a batch-type furnace or a continuous belt-type furnace. The furnace must be capable
of heating the load, maintaining it at the processing temperature, and maintaining a steam atmosphere free of air leaks. Both batch
type and continuous furnaces shall meet the same criteria described in the following procedure section. While comparable
performance may be obtained from batch and continuous furnaces, the process conditions used may not be exactly the same.
7. Procedure
7.1 Batch Processing
7.1.1 Place the load in the furnace and preheat in air until the temperature of the entire load is above 212 °F (100 °C) but not in
excess of 800 °F (430 °C). A temperature of 600 ºF (315 ºC) is typically used.
7.1.2 Once the load is preheated, introduce superheated steam into the furnace until all of the air is purged from the furnace or
processing zone. This steam atmosphere shall be maintained until the processing cycle is complete.
NOTE 1—The temperature of the parts shall be in excess of 212 °F (100 °C) before the superheated steam is introduced. If it is not, water will condense
on the parts and rust spots will form. The temperature shall not exceed 800 °F (430 °C) before all of the air has been purged from the system by the
superheated steam or the parts will be covered with a smooth even coating of rust caused by air in the furnace atmosphere.
7.1.3 Raise the temperature of the furnace to the processing temperature of between 800 °F (430 °C) and 1100 °F (590 °C) while
maintaining the atmosphere of superheated steam. A typical processing temperature is 1000 °F (540 °C).
NOTE 2—The processing temperature depends on the desired properties. Lower temperatures result in deeper oxide penetration, while higher temperatures
produce a thicker surface oxide layer.
NOTE 3—Processes that decrease the amount or the size of the surface-connected porosity such as copper infiltration, grinding, vibratory finishing, sizing,
machining, burnishing, shot peening, or polishing will reduce the effectiveness of the steam treatment by limiting the ability of steam to penetrate the
part. Increasing the density reduces the pore size, which reduces penetration unless sufficiently large porosity is available to maintain a pathway for the
steam. Copper infiltration also coats the surface of iron particles with copper, which prevents steam from reacting with the iron and decreases the
effectiveness of steam treatment as a surface treatment.
7.1.4 Hold the load at the processing temperature for 30 to 120 min, depending on the desired properties. Steam treatment builds
an oxide layer on pore surfaces and gradually restricts the access of the steam to the interior of the part. Higher temperature causes
the metal to be more reactive, producing a thicker surface layer and limiting the penetration of the oxide into the part. Lower
temperature produces deeper penetration with a thinner surface layer.
NOTE 4—A discussion of sealing method is recommended for parts requiring additional surface treatments (plating, painting, and so forth).
B935 − 20
7.1.5 The oxide produced by steam treatment is slightly porous, which can allow corrosive material to penetrate to non-oxidized
iron. While the oxide provides improved shelf and handling life by itself, oil impregnation, an oil dip, or rust preventatives are
recommended for applications requiring additional corrosion protection.
7.2 Continuous Processing
7.2.1 A pre-heat zone is used to bring the parts up to temperature, while at the same time burning out any residual oil or fluid and
cleaning the parts. The pre-heat is typically set to a temperature of 840 to 930 ºF (450 to 500 ºC). Exothermic gas burners are
suitable for the pre-heat zone.
7.2.2 The temperature in the steam zone of the furnace is generally set to a temperature of 800 to 1100 ºF (430 to 590 ºC). A
typical process temperature is 1000 ºF (540 ºC).
7.2.3 The actual process temperature and the time at temperature depend on the desired properties of the steam-treated parts. Times
at temperature in the superheated steam are typically from 45 minutesmin to 1 ⁄2 h.
8. Interferences
8.1 The surface of the material to be steam-treated should be free of contaminants, including red rust, soot, and dirt. Steam
treatment cannot reduce existing rust. Soot and dirt attract moisture, which causes rust to form during steam treatment. The soot
and dirt will rem
...