17-7PH OR (9ru10)
17-7PH OR (9ru10)
(OP)
First the process flow as designed.
condition C -> Condition A -> blank/form -> Harden to RH950
(The reason we had to start with Cond. C is cause thats all that our supplier could deliver right now. so we Vacuum annealed the material to make prototypes. Production will use actual mill annealed coil.)
The dimensional test pieces came back from the heat treaters (VacMet, Warren, MI) today and the rockwell is roughly 10pts (HRc) under the expected (35 vs 44). I've checked the material cert from Sandvik and the chemistry is correct for 9RU10 (which has the same nominals as 17-7PH). Haven't mounted and polished a specimen yet (since we dont have a met lab at my location. I reviewed the furnace charts and all them temps and times were correct. No scale or other staining of the steel so I'm sure that there was no de-carb or carb going on.
What happened?
As an extra note: I did an air furnace anneal and treat of the same steel (from the same dang piece) last year and for condiiton TH1050 got HRc or ~42. I am completely lost as to why this happened.
nick
condition C -> Condition A -> blank/form -> Harden to RH950
(The reason we had to start with Cond. C is cause thats all that our supplier could deliver right now. so we Vacuum annealed the material to make prototypes. Production will use actual mill annealed coil.)
The dimensional test pieces came back from the heat treaters (VacMet, Warren, MI) today and the rockwell is roughly 10pts (HRc) under the expected (35 vs 44). I've checked the material cert from Sandvik and the chemistry is correct for 9RU10 (which has the same nominals as 17-7PH). Haven't mounted and polished a specimen yet (since we dont have a met lab at my location. I reviewed the furnace charts and all them temps and times were correct. No scale or other staining of the steel so I'm sure that there was no de-carb or carb going on.
What happened?
As an extra note: I did an air furnace anneal and treat of the same steel (from the same dang piece) last year and for condiiton TH1050 got HRc or ~42. I am completely lost as to why this happened.
nick





RE: 17-7PH OR (9ru10)
AK-Steel (pg 4)
http://www.aksteel.com/pdf/markets_products/stainl...
AL (pg 4)
http://www.alleghenytechnologies.com/Ludlum/Docume...
)
hmmm Underaged?
nick
RE: 17-7PH OR (9ru10)
Re-age one of already aged pieces and see if it gets harder.
You know that without an anneal after forming your finished hardens will vary based on the amount of local cold worked. Heavily strained areas could end up much harder than the nominal.
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm
RE: 17-7PH OR (9ru10)
I'm going to re-age one of the test pieces as soon as my little prototype furnace gets back up and running, Right now it just got moved badk here form the tool shop and needs some wiring to make it work.
nick
RE: 17-7PH OR (9ru10)
If you require to have a strict hardness (and not strength) than you will have to change/adjust the heat treatment temperature to get the hardness but with every new batch of material you will have to do tests to find the correct temperatures. However, be carefull not to loose toughness and elongation properties.
RE: 17-7PH OR (9ru10)
What's a good way to get an assured strength, The hardness is not very importat this part operates against Al. But a strength and EL of a hardened SS is important. (quickly >200ksi UTS) We cant really use cond C (1t 90degree bent tab). I figure that the bend is going to be worked just enough to give a higher strength and prevent the tab from deforming.
I really think that the parts will work, just that I need to be able to have the assurance of a known strength level.
nick
Nick
I love materials science!
RE: 17-7PH OR (9ru10)
RE: 17-7PH OR (9ru10)
It lists the aging time as 1 hr (-0 minutes; +30 minutes) and includes a note that "An additional 1 to 1 1/2 hours at the specified temperature or an additional 10 to 20 F (6 to 11 C) degrees for an additional 1 to 1-1/2 hours after aging may be used to lower the hardness or other engineering property."
It also lists minimum tensile strengths (in "Tensile Strength Conversion to Condition" tables for this heat treat condition for various 17-7PH product forms as follows:
Sheet and Strip: 210 ksi
Plate: 200 ksi
Bar: 180 ksi
RE: 17-7PH OR (9ru10)
nick
RE: 17-7PH OR (9ru10)
(addtl. ageing : 1hr at load temp of 950+/-10F)
I think that the slight dropping is due to coarsening of the Ni3Al.
Any other ideas.. (Im gonna go over to the met lab next week and mount an polish an etch and see if Ive got RA, bunches of ferrite, or other things, (any hints), I may try to look at the precipitate if I can resolve it, and I can find out some info about th size to expect for them. Unless of course the size is only resolvable in the TEM, If a slightly used decent older JEOL (6300) can get an image i will. (I can also check chemistry, however since TH1050 worked I dont think it will be too far off.)
nick
RE: 17-7PH OR (9ru10)
I am confused, I understand that you want high strength of >200 ksi. Therefore, why do you keep with the hardness? Isn't it better to do a tensile test of the same material with the different heat treatments if you suspect something is wrong with the material or the heat treatment?
At TH1050 the minimum ultimate tensile strength is only 177Ksi according to MIL-HDBK-5J.
What is the calculated stress at the part?
When you sayed before "...prevent the tab from deforming.." did you mean permanent deformation or an elastic deformation?
If it is a permanent deformation, then your stresses are too high and the difference between H950 and H1050 may not be enough to give you a reasonable factor of safety.
If it is an elastic deformation then no matter what strength the metal will have it will not change the deformation. The elastic deformation is only the function of the material modulus of elasticity and the dimensions i.e. width and thickness of the tab, especially the 1 mm thickness.
RE: 17-7PH OR (9ru10)
You're right about TH1050. The FEA work Ive done on this design gives stresses ~60-80ksi (Tensile -the other side of the beam is in approximately the same magnitude just compressive) After some number of cycles (<10^7) the last run of prototypes failed. (Air furnace TH1050) We were unsure as to wether the Use of the air furnace and the fine scale that cracked. or if there were small cracks because the air solution anneal did not produce a soft enough material to take the bend.
So we went to vacuum/inert gas processing to rule out scale. and used a reputable accredited heat treater to rule out the effect of my 1965 Lucifer Over/Under heat treating furnace. (with furnace controllers that are almost as old.)
Then I looked over AK's data book and they give In Table 3 (pg5) the following as properties acceptable for Materials Specification:(all values in appropriate american units)
RH950
UTS : 210min
.2%YS: 190min
Elon.: 5%min
HRc: 44min
I figured that the extra strength wouldnt hurt so I told the project Eng. to get quotes for RH950 as opposed to any of the T treatments.
There are two needs of High UTS. 1) high endurance Limit (EL)
2) prevent plastic deformation (IE higher UTS means Higher yield)
RE: 17-7PH OR (9ru10)