What’s up guys?!?! Michael with Michael Talks Metal back for the 143 rd time in this video series ……today we’re dropping the first of two on the PH stainless steels. Buckle Up buttercup cause we’re goin for a ride!
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OK, back to today’s topic…. PH stainless steels.
High strength, excellent corrosion performance, and a simplified heat treatment are advantages of the PH types as compared to the conventional martensitic types we discussed in the last two videos.
PH is short for “Precipitation Hardening” which is a heat treatment that is a bit different from that of the conventional heat treatments. An initial “solution treatment” at high temp …..typically 1900 degrees Farenheight….that assures that all the alloy elements needed for the hardening reaction are uniformly distributed within the metal structure. At these temps the structure is austenitic. From this temperature, the alloy is cooled at a rate that retains the distribution of the hardening elements in solution.
Depending on the chemistry of the specific grade, the resulting structure after the “solution treatment” is martensitic, semi-austenitic, or austenitic. These structures contain more of the hardening elements than would be completely stable. So it’s just waiting for an additional heat treatment to cause things to happen within the structure. However, things are stable enough that we can choose to fabricate components prior to a final heat treatment. This additional relatively low temp heat treatment is called “aging”. The increased temp and time allow the elements mobility to combine and form the precipitates that then strengthen the structure.
Before we proceed, let’s break down the PH alloy types by the solution treated structure.
First up are the Martensitic alloys. They form a low carbon, relatively brittle martensite when solution treated. Alloys should not be used in the solution treated condition. When reheated to the aging temperatures the particles that form further strengthen the structure and also improve toughness & corrosion performance.
The resulting heat-treated condition is defined by the letter H followed by the aging temperature. For example: H900 indicates that it has been solution treated and then aged at 900 degrees F. Hardness increases and yield strength minimums of 170k psi are achieved with this secondary simple heat treatment.
Heat Treat conditions range from H900 thru to H1150, and even a Double HH1150. That just means there are two aging sessions at 1150 degrees F, thus “Double” H 1150. The higher the aging temp, the lower the strength but toughness is increased.
H1150M is an overaged condition producing the lowest hardness.
Solution treated, solution annealed, annealed, and Cond A are synonymous in these stainless steels. They mean the same thing.
Often, these types are solution treated by the producing steel mill and then the aging treatment is performed after additional fabrication to parts.
If the material is already in the required aged condition, then no further heat treatment is required. It’s all a matter of what works best for the application.
15-5 and 13-8 are examples of premium vac melt grades …. the additional melting under vacuum minimizes any harmful impurities for critical applications like highly stressed aerospace components
Specifications and part requirements are always critical, so for the 143 rd time we remind you to … CHECK THE SPECS!!!!!! TWICE
So this is Michael with Michael Talks Metal, thanks for watching. Make sure to check the website if you need more info www.michlinmetals.com and also if you are still here and haven’t subscibed please click here and consider doing so now. Missed last weeks’ video? Click here. Thanks for watching. I will see you next Thursday same time, same place – 10am YouTube. I’m out!