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)?
BS STD 655H13)?
RE: Ferrite/Pearlite in Case Hardening steels
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
RE: Ferrite/Pearlite in Case Hardening steels
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.