AISI 410 SS lateral expansion

[curious_eng]

Greeting,

I’m currently working on the 410 stainless steel shaft (8.5” OD x 100” long with a 3.5”ID via deep hole drilling prior to heat treatment) and having trouble with longitudinal lateral expansion.
Longitudinal lateral expansion is conducted at 21 degree C and requirement is 25 mils.
Longitudinal charpy impact is conducted at 21 degree C and requirement is 30 Joules.
I’m getting longitudinal lateral expansion of 14 to 23 mils.

Typical composition: 0.12% C, 0.55% Mn, 0.10% P, 0.001% S, 11.90% Cr, 0.19% Si, 0.32% Ni, 0.018% V, .024% N.

This product is forged and heat treated to following conditions. Heat treatment:
Austenitize at 1725°F (I have tried austenitizing for 12 hours and 20 hours and results are same).
Oil quench
Temper at 1125°F for 10 hours.

We always get hardness of 229 BHN. Minimum requirement is 223 BHN.
Tensile requirement: 105 KSI and actual result 107 -109 KSI
Yield requirement: 85 KSI and actual result 87 - 91 KSI
Longitudinal charpy impact requirement: 30J and actual result 35 – 57J

I looked at the broken charpy sample structure and it looks brittle (shinny condition). I verified the raw material and it conforms to required chemistry and no cleanliness issue.
Does anyone has experience with this grade? I'm not sure if it is a heat treatment or forging issue. Some reason all my mechanical result are at the bottom end of the spec. Thanks in advance.

 

[metengr]

Have you evaluated the microstructure from a broken CVN specimen? This should be done before looking at options. For 410 SS, the austenitizing temperature should be 1800 to 1900 deg F, oil quench and temper at 1200 deg F min.

Also, I don't like the V present. Even at low level.

 

[curious_eng]

I reviewed the microstructure and it is brittle around broken area. Grain size is between 4 - 5. Structure is fully transformed to martensitic. Reason why I didn't choose higher austenitizing temperature:
1. Literature I found indicates austenitize between 1695F and 1850F and keep it at lower side for ductility. I'm getting lower charpy impact result, so I thought by going higher austenitizing temperature would make charpy result even lower. Correct if I am wrong.
2. I read in literature that Cr is sluggish, so it is harder to bring into solution. Therefore, I performed austenitizing at 12 hours and 24 hours, still similar result.
3. It is a long shaft and as per specification it can't be bend above 0.225".

 

[EdStainless]

If these are hollow, 8.5" OD x 3.5" ID then I don't see why you would need more than 5 hours for austenizing. I worry about grain growth in these alloys.
I also feel that your temp is a little low, but if it works then fine.
Have you looked at as quenched parts? Any RA?
Have you tried double tempering?

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

curious_eng
Based on your statements above, the tempering temperature is close to the threshold where embrittlement can ocurr - typically between 900 to 1100 deg F in 410. I would select 1150 to 1175 deg F, and significantly reduce your tempering time to 4 hours where you are on the slope toward increased notch toughness and still retain adequate strength.

 

[curious_eng]

I tried oil and water quench and quenched hardness is 388 BHN for both of them. I didn’t check for RA.
I attached micro photos of failed samples from different heat treat batch. I don’t have much experience with analyzing microstructure. Let me know if you guys notice anything different.

I have couple of questions:
1) Am I able to achieve my required mechanical properties by using 1725F austenitizing temperature? If not what is the recommended austenitizing temp. & time for this shaft?
2) Would double tempering lower tensile strength?
3) Currently all of the mechanical properties are closer to low end of the spec. which is very concerning. Anyway, I can increase tensile strength? Then I will temper the next batch at 1175F for short tempering cycle.

 

[metengr]

Based on what you reported your BHN for as-quenched condition is low. It should be about 425 BHN for 0.12% C. Look at your quench tank configuration and oil temperature, you may not be getting the quench rate you need to achieve the 425 BHN. This lower end hardness will also impact your lower end strength values your reporting.

 

[EdStainless]

Metengr, Thanks for the comment, that is part of what I was driving at but I didn't spell it out.
If you austenitizing temp is too low or the quench not aggressive enough you will not get good martensite.
The as-quenched hardness needs to be up there.
You will then likely need to use a higher temper temperature in order to get the strength back down where you want it.

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

Not an ideal combination of Q&T. If your temper is low temp, your quench needs to high temp; when you temper temp is high, Quench low.

Avoid "impact trough", temper temperature range about 350-550C. when you temper temp is high (1125F), temper time matters, 10 hours is too long (impurities, mainly P, precipitate in grain boundaries).

When you get low impact, the corrosion resistance, especially scc, probably be sacrificed.

can you do 1800F quench + 500F temper?

Increasing temper temperature is a good idea to increase impact, but that could also decrease your tensile.

Also, did you cut specimens for testing from your big shaft. Or, you heat treated the small specimens with the shaft. This makes difference.

 

Ferrite phase is usually the bad actor for impact toughness in martensitic SSs, but I don't see much wrong structure-wise in the micrographs.
Is that 0.10% P a typo? Because that is extraordinarily high.
I think metengr is onto something: minor elements could be acting up after very long times at high temperature.

This looks like a job for F6NM (UNS S41500).

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[curious_eng]

It is a typo. P is 0.010%. As per customer specification, minimum tempering temperature is 1115F and minimum holding time is 6 hours.
Our oil quench tank has poor agitation. Unfortunately, I don't have much time to revamp the tank. Currently, we use overhead crane to move the shaft left and right inside the tank while quenching.

Quench oil temperature is typically set to 100F. I have heated the oil to 140F and it didn't make difference. Does it need to be increased?

My other concern is bending, currently shaft is bending between 0.075" and 0.205" at 1725F austenitizing temp. It varies for each time. If I go above 1800F would it make it even worse?
I'm going to perform another heat treat batch trial end of this week per suggestions. I will increase austenitizing temp to 1780F. Is 2 hours holding time at 1780F sufficient?

Thank you all for your feedback. I'll let you know as quenched hardness and other mechanical results.

 

[curious_eng]

I forgot to mentioned that we use prolongation for mechanical test. Prolongation is typically 6" long and I cut the sample 2" away from as quenched surface.

 

[EdStainless]

Typical soak time are 1hr plus 1hr per inch of thickness.
So if your part is 2.5" thick you are looking at 3-4 hours.
How are you supporting the part? is it bowing because of how it sits in the furnace, how you pick it up, or (more likely) uneven cooling?
If you get higher hardness as quenched, then you will likely need a slightly higher temper temperature.
Stick with 6 hr temper, longer doesn't help

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[MagBen]

One more thing: if you have to use the higher end of "Impact Trough" temper temperature, cooling rate matters too. Try to cool as fast as you can.

In looking at the title of your post, what do you mean by lateral expansion?
. do you mean the expansion was .025'' per 100''? what is the temperature range? Is 25 mils too high?

 

[mrfailure]

You may be at the bottom end of your spec ranges, but you do conform. Why would you want to change heat treatment properties from what is already successful?

 

[metengr]

mrfailure;
Because the poster indicates non-compliance buried in the post

Longitudinal lateral expansion is conducted at 21 degree C and requirement is 25 mils.

I’m getting longitudinal lateral expansion of 14 to 23 mils.

 

[curious_eng]

MagBen,
Lateral expansion is the increase in specimen width, measured in thousandths of an inch on the compression side (opposite of V-notch) using charpy sample. As per specification, testing temperature shall be 21degree C. To me, 25 mils spec. is above typical requirement.

Typically, we don’t normalize 410 SS. Anyone knows if normalize can help to improve grain orientation in this case?

 

[EdStainless]

Every time that you heat this material you will increase its grain size, don't heat it any more than you have to.
Isn't the material normalized to start with?

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

Anyone knows if normalize can help to improve grain orientation in this case?

No, it would not help.

 

[MagBen]

OK, so MIN 30J and MIN 25 mils are both specified?!
I found a relationship between energy and lateral expansion for ferritic stainless: L (mm) = E (J) /100 (per 10 mm specimen)
when E=30J, L = 0.3mm per 10 mm, this is equal to 30 mils per inch!

? you are not supposed to get elongated grians after HT.

If you got astm 1 or bigger, and wanted to refine grains, it maybe possible to normalize couple of times by carefully choosing temperatures. But it will be very difficult to refine astm 4 any further.