Heat Treating of 17.4PH Stainless 6

[StuartReid]

Hello, all,
I need help in working with a metal unfamiliar to me. I have a need to machine and heat treat 17.4PH stainless steel and I need to know temperatures, durations, atmospheric requirements. Does anyone have a reference, data tables, or the information off the top of their heads? Please help. Thanks Stuart

 

[TEV]

The professional society "American Society for Metals" now known as ASM Interantional, in Metals Park, OH 44073 publishes a book entitled "Heat Treater's Guide - Standard Practices and Procedures for Steel". 17-4PH has the Unified Numbering System designation UNS S17400, and is also known as Type 630 in ASTM Specification A 584.

The Heat Treater's Guide states that the most commonly used heat treating practice is (1) Solution heat treat at 1875 to 1925F, oil quench to room temperature; (2) Age at 900F for 1 hour and air cool. This is known as condition H900. A hardness of approximately 42 to 44 HRC should result.

You will probably receive the metal in the solution treated and quenched condition (i.e. - the first heat treatment above has already been done), but you need to confirm this from the supplier's material certification. It can be machined in this condition. Do the aging treatment after machining.

 

[TVP]

H900 is one of several heat treating options. Some sources for additional information are the following:

MIL-H-6875H Process for Heat Treatment of Steel

http://assist2.daps.dla.mil/quicksearch/

Alloy Data Sheet for Carpenter Stainless 17Cr-4Ni

http://www.cartech.com/

(click on Technical Information, then Alloy Category, then Stainless Steels, then Precipitation Hardenable Stainless Steels)

The MIL standard has now been superceded by an SAE AMS spec, but the content is the same, so this is an excellent reference. The Carpenter website is probably the best repository of free technical information on metals on the internet. In addition, they are an excellent vendor with which to work.

 

[kenvlach]

TEV & TVP gave you good advice & info sources.

I suggest making every effort to avoid the formation of the very tenacious heat treat scale that forms in air. Three methods are inert gas furnace, vacuum furnace & wrapping tightly in SS foil. See details in thread 330-40071 below: "Heat Treating 17-4PH No Discoloration Allowed!" and "REMOVAL OF HEAT TREAT SCALE FROM STAINLESS STEEL" at

http://www.finishing.com/50/89.html

We passivate PH SS for customers & thus sometimes have to descale parts in a nitric acid-fluoride solution.
We have successfully persuaded customers to use one of the methods mentioned (switch to a heat treater with a better furnace or use SS foil) and they & we have been pleased with the better finish & less use of nasty chemicals.

 

[bruv]

There is also an ASTM standard for cast 17/4PH alloys, ASTM A747, which gives details of the precipitation hardening treatments for all conditions. Grades covered are CB7Cu-1 and CB7Cu-2.

Bruv

 

[Metalguy]

You should be aware that the H900 HT condition of 17-4 PH can be quite susceptible to hydrogen cracking-depending on stresses and the environment.

There are quite a few other 4 hr HTs at higher temps. that are much better in this regard, although you will have to give up some strength and have a worse discoloration problem.

 

[Metalguy]

>"I have been intrigued by the cracking of 17-4 at HT."<

I will assume you mean HT=heat treatment rather than during heat treating or HT=high temp.

If so, there should be many sources of the hyd. cracking problems in the H900 condition--do a Google, etc. I believe the US Navy prohibited its use way back in the late 1950's. I have personally been involved in quite a few H900 cracking failures. The problem is greatly reduced by using 4 hr. @1075 deg F, but even better is 4 hr. @1100. If you can use the lower strength, the best HT is 4 hr. @1150.

If you need high strength, 17-7PH is more resistant, especially in the H900 cond. You can get Rc47 with that.

17-4PH (H900) can crack even in relatively pure water.

 

[WKTaylor]

Guys...

SAE AMS2759, AMS2759/3D, AMS2759/9 and amd2759/11 provide excellent information on heat treatement on PH CRES.

AMS-H-6875 is now primarily for wrought materials [billet, plate, raw forgings or forging stock, etc]. AMS2759(*) is (are) specific, and VERY complete, for heat-treatment of aerospace steel parts [all strength levels of LAS & CRES]. Spec includes H2 embrittlement relief (/9) and stress relief treatments (/11).

Next best are the AMS material specs or the ASTM Material specs... though critical heat treat details are often left out.

Boeing Spec BAC5619 is also very good for CRES [BAC5617 for LAS].

NOTE: MIL-HDBK-1587 expresses positive restictions [NO] on temper conditions H900 & H925. I have used these conditions successfully... but ALWAYS include a post machining stress relief ... and H2 embrittlement relief [as needed]. Still dicy, tho...

Regards, Wil Taylor