×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Ferrite/Pearlite in Case Hardening steels

Ferrite/Pearlite in Case Hardening steels

Ferrite/Pearlite in Case Hardening steels

(OP)
How is a ferrite/[earlite structure achieved through heat treatment in a .15%carbon/3.5%nickel/.90%chromium steel
BS STD 655H13)?

RE: Ferrite/Pearlite in Case Hardening steels

A ferrite/pearlite microstructure can be obtained by heating the steel above the Ac3 temperature (often called the upper critical temperature) so that a uniform austenite is formed.  The steel is then cooled in a controlled manner so that ferrite + pearlite is formed, and not martensite or bainite.  Rapid cooling (quenching) produces martensite.  An extended dwell below the Ac1 (lower critical temperature) but above the Ms temperature (martensite start) can produce bainite.

So, for an alloy steel such as 655H13, the upper critical temperature will be ~ 800 C.  Full annealing or normalizing are two techniques that produce ferrite + pearlite structures.  Normalizing is usually performed by heating about 55 C above the Ac3 followed by air cooling.  Full annealing is typically performed just above the Ac3 temperature and then slow cooled (furnace cooled).  The slower cooling of annealing results in high temperature transformation to ferrite + pearlite and coarser microstructures than does normalizing.

Full anneal: 800-850 C then furnace cool
Normalize: 890-955 C then air cool

Keep in mind that a ferrite + pearlite microstructure can be produced by the steel mill after casting and during the rolling of this grade.  The transformation of austenite to ferrite + pearlite is controlled during the rolling process in order to obtain the desired properties (ferrite grain size, pearlite colony size, colony distribution, etc.).

RE: Ferrite/Pearlite in Case Hardening steels

(OP)
It is true to say that annealing/normalising will generally produce a ferrite/pearlite structure in most steels. However the high nickel and chromium content makes this difficult in this grade of steel. Isothermal treatments are more common provided the temperatures and times are selected carefully. Any thoughts?

RE: Ferrite/Pearlite in Case Hardening steels

I just found some time-temperature transformation curves for this grade (old designation of EN 36) in Atlas of Time-Temperature Diagrams for Irons and Steels from ASM.  I knew that the kinetics would be slow due to the high Ni content, but apparently the tranformation is EXCEEDINGLY slow.  90% transformation from an austenitizing temperature of 860 C requires something like 9 hours at 600 C, or 20-60 minutes at 440 C.  The Ms temperature is around 410 C so this complicates using the 440 C lower limit.

All of this explains why the normalizing temperature may be as high as 955 C for this alloy-- air cooling from this temperature should prevent martensite formation but allow enough dwell time to transform most of the austenite to ferrite + pearlite.  Isothermal transformation definitely looks like a good idea for this alloy, especially if the lower value of 440 C is to be used.  I hope this was helpful.  Feel free to post again if you want to discuss further.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close