Full Transcript:

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 shorthand 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 temperature .....typically 1900 degrees F....  assures that all the alloy elements needed for the hardening reaction are uniformly distributed within the metal structure. At these temperatures 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 chemical composition of the specific alloy, the resulting structure after the "solution treatment" is either 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. But things are stable enough that we can choose to fabricate components prior to a final heat treatment. This additional relatively low temperature heat treatment is  called "aging". The increased temperature and time allow the elements mobility to combine and form the "precipitates" (think particles) that then strengthen the structure.

Before we go further let's split the PH alloy types by the solution treated structure.......

First up are the Martensitic types. They form a low carbon somewhat 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 and corrosion performance.

The resulting heat-treated condition is designated 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 170,000 psi are achieved with this second simple heat treatment.

Conditions range from H900 thru to H1150, and even a Double H1150 (with two aging sessions at 1150 degrees F).  The higher the aging temperature 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.

Often, these types are solution treated by the producing steel mill and then the aging treatment is performed after additional fabrication to parts.

If already in the required aged condition, then no further heat treatment is required.  It’s all a matter of what provides the best manufacturing plan.

Common grades in this group include 17-4 (aka 630), 15-5, 13-8, 450, and 455

15-5 and 13-8 are examples of premium vacuum melted types .... 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.