Full Transcript:

What’s up guys?!?! Michael with Michael Talks Metal back again for the 144th episode in our current video series; our second on PH stainless steels…  If you have not seen the first and would like to do so now . …. click here

Our next classification is called semi- austenitic. Chemical composition of these alloys lead to a different set of structures during the multiple steps in heat treatment.

Like all the PH stainless steels, the first step is a “solution treatment”that achieves a uniform distribution of elements in an austenitic structure. On cooling from the solution temperature, the structure of these alloys REMAINS austenitic at ambient temperature……….but only temporarily.

The relatively soft and ductile austenitic structure gives us an opportunity for much more extensive fabrication prior to hardening than in the martensitic types.

To enable the final hardening of the material, we need to  first make the austenitic structure transform to a martensitic structure.  Three methods can be used to trigger the formation of the martensite structure.


A subzero cooling to temperatures on the order of minus 100 degrees F and holding for up to 8 hrs.


Heating to about 1400 degrees F and holding up to 3 hours


cold work ( like cold rolling sheet )

Once we have produced the martensitic structure, our familiar aging treatments are able to do the final hardening.

The combined two step process of  hardening in these types is indicated by a letter prefix plus the H followed by the ageing temperature . The prefix indicates the method of forming martensite.

For example:

RH950  indicates a sub zero refrigeration ( hence the R) followed by ageing (the H) at 950 degrees F

TH1050 would indicate the Thermal  method followed by ageing at 1050 degrees F.

CH900 indicates Cold work followed by ageing at 900 degrees F.

Common examples of semi- austenitic grades are 17-7( AISI 631), 15-7 (632), AM-350 (633),and AM-355 (634).

Applications for these types often require the premium cleanliness of vacuum melting. Precise details of the required heat treatments vary by grade and specification.

Austenitic is our last classification of PH stainless steels. It is for those types that retain an austenitic structure from solution treatment through aging. Although much lower strength than the other two PH types, they are non-magnetic and have higher strength than the 300 series stainless steels.

Solution treatment is typically performed at higher temperatures than for the other types. Aging is performed at temperatures of 1300 deg F  and above. Most often only a single aging treatment applies to these alloys.  With their higher aging temperature, these alloys can be used at temperatures where the other PH types would lose strength.

An example of this type is grade A286…… used for aerospace engine or turbine applications.

Specifications and part requirements can change what we have shown here today …. so for the 144 th time


So this is Michael with Michael Talks Metal. Thanks for watching. More question about PH Stainless Steels? Check the website for more info www.michlinmetals.com. Still here and haven’t subscribed, click here. Missed last weeks’ video? Click here. Thanks for watching, see you same time, same place next week, Thursday, 10am, YouTube, I’m out!