Significance of Normalizing Before Q&T for 300M VAR 7

[MechyMarco]

Hi all,

Designing some parts out of 300M VAR per AMS6417 and heat treating per AMS2759/2. I have some general metallurgy questions regarding normalizing and it's effect on the material's response to heat treating.

The raw stock is sent to us in the hot rolled normalized and tempered condition. Why would the mill temper after normalizing? Why not just normalize? I interpret AMS2759/2 to say that normalized stock must be preheated before hardening while AMS6417 makes no mention of that distinction. It just says to normalize and harden.

So my question is how/why does tempering after normalizing affect the outcome. Not a metallurgist but I am really curious about this. Seems like a redundant step as when you Q&T you're overwriting the previous microstructure with austenite anyway so it doesn't matter what it looked like before. Am I missing something here?

Any insight will be greatly appreciated!

Cheers.

 

[EdStainless]

N&T is used in high strength grades to deliver better ductility and machinability than often seen with just N.
I would hope that they used 1200F for the temper.
Many people will re-normalize, cool, then heat to austenitizing temp and oil quench, then double temper with air cool between.
On reason to N again is to assure uniform properties. We don't know what was done to it since you got it, how much stock was removed, or any cold work done. This is the safe path.

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P.E. Metallurgy, Plymouth Tube

 

[MechyMarco]

Right on. Thanks Ed. I'll go the safe path!

 

[metengr]

Normalization is a requirement for hardening this alloy.

 

[Maui]

The term temper as it is used in this context is a misnomer. It is more accurately called a subcritical isothermal anneal. So you are normalizing it and then annealing it afterwards.

Maui

 

[MagBen]

Double Maui, we call it subcritical anneal or over-temper, the temperature is higher than temper, normally 1150-1200F. Another purpose is to decrease cracking tendency

 

[MechyMarco]

Maui and MagBen. Thanks for the help. Makes a lot more sense now. My process sequence is going to be: rough machine, normalize, Q&DoubleT, finish machine (0.020'' shave) and maybe a stress relief 100F below temper. Not sure how much meat will have to come off at final machine so don't know how critical the final stress relief will be. Any thoughts on how critical it would be? My gut tells me to do it but don't know if it's really needed.

 

[WKTaylor]

MechyMarko...

300M per AMS6417... Are You using bars, hand-forged blocks or forging stock? In each case there is a specific condition it MUST be delivered in. Typical for thicker bars is as follow from AMS6417...

3.3.1.2 Bars Over 0.500 Inch (12.70 mm) in Nominal Diameter or Least Distance Between Parallel Sides
Hot finished, annealed, or normalized and tempered having hardness not higher than 311 HB, or equivalent

NOTE. Your contracting needs to be very explicit regarding HOW the raw stock should be processed for delivery... or at least make it crystal clear what you have during receiving evaluation!

NOTE. 300M at 311HB is relatively easy to machine a to a 'rough state', before final ['hard-as-the-hubs-of-h*ll'] HT to 270--290-KSI or 280-305-KSI [AMS2759/2]. In these UHS HT states, machining/grinding carefully with a lot of coolant and sharp tools is mandatory [see para 3].

However actual final heat treat process will depend on the state of the material, before Solution HT, this...

2. AMS2759/2...

TABLE 2A - ANNEALING, NORMALIZING, AND AUSTENITIZING TEMPERATURES AND QUENCHANTS, INCH/POUND UNITS

(2) All parts, except those made from H-11, 52100, or M-50 steels, shall be in one of the following conditions prior to
austenitizing: normalized, normalized and tempered, normalized and overaged, or hardened. If such parts have
been normalized only, without tempering or overaging, they shall be preheated within the range of 850 to 1250 °F
before exposure to the austenitizing temperature.

3. I found the following SAE document gives a very clear/stark discussion of processing 4340M and 300M into finished parts.

ARP1631 Manufacturing Sequence for Fabrication of High-Strength Steel Parts 300M or 4340 Modified Low-Alloy Steels 270,000 psi (1860 MPa) Tensile Strength and Higher

Processed correctly, 300M will serve capably and predictably at UH strength. However the process is EVERTHING: miss something, get something wrong, or miss-sequence the process and there could be 'hell-to-pay'.

Also I suggest serializing every part with a PERMANENT number so that it has INDIVIDUAL processing records. If something is amiss during a records review or interim/final QA eval, then at least You know which part(s) is(are) affected! This happened with one of my vendors: They failed to trace parts by explicit SN... and one set of records showed a process 'aw-sh*t' for [3] major parts after one HT operation. We had a hard time with the MRB disposition for these $150,000 parts!



Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[MechyMarco]

Hi all,

Just thought I'd give you some details on the actual part the material is for. It's a piston to be machined from 3-1/2'' bar stock. It's going to be loaded in pure compression (some areas in tension, like the port hole) around 100x with a lot of the loadings right on the edge of yield. Looking to do whatever it takes to maximize the strength. 300M seems like a good candidate. Other choice would be a 300 maraging steel.

WKTaylor,
Thanks for the heads up on ARP1631. The document does a great job of specifying the required processing sequence. I'll be sure to have a thorough discussion with our heat treater and machine shop about it. I'm out west and deal mainly with oil field shops so it may be difficult to get them on the same page regarding the strict adherence to the AMS standards.

Question for all. What would you say is easier to process/achieve? Max strength with 300M or a 300 maraging steel? I'm starting to lean towards the 300 maraging steel because it seems like less can wrong in the processing sequence. And it might even end up being cheaper. Thoughts?

Thanks in advance for all the input!

 

[EdStainless]

C300 does not have great toughness and fatigue. It doesn't like reversing loads.
If you are worried about 300M perhaps AirMet?

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

You will achieve higher strength with C300 in comparison to 300M. For your application, I would stick with 300M.

 

[WKTaylor]

MechyMark...

Be extremely cautious using 300M for engine parts! Due to extremely low tempering-temperature [550--600F], it does NOT tolerate high heat very well without changing the mechanical properties... dramatically. Above 600F, the 'blue-brittle' [temper embrittlement] phenomena can occur. In aerospace, 300M is considered a structural alloy... IE: highly stressed landing gear components and fitting attachments... that rarely see temperatures above 250F.

IF used in engines, You probably should consider 9Ni-4Co-0.20C or -0.30C [RT 220--240-KSI]. Per MMPDS-10, both alloys perform well-up-to ~900F.

For instance... these alloys [with nickel plating for corrosion protection] perform well as turbine-engine hot-section [750F] engine mounts and drag/thrust/sway-links.

2.4.2 9NI-4CO-0.20C
2.4.2.0 Comments and Properties — The 9Ni-4Co-0.20C alloy was developed specifically
to have excellent fracture toughness, excellent weldability, and high hardenability when heat-treated to 190
to 210 ksi ultimate tensile strength. The alloy can be readily welded in the heat-treated condition with preand
post-heat usually not required. The alloy is through hardening in section sizes up to at least 8 inches
thick. The alloy may be exposed to temperatures up to 900EF (approximately 100EF below typical tempering
temperature) without microstructural changes, which degrade room temperature strength.
... ...
2.4.3 9Ni-4Co-0.30C
2.4.3.0 Comments and Properties — The 9Ni-4Co-0.30C alloy was developed specifically
to have high hardenability and good fracture toughness when heat treated to 220 to 240 ksi ultimate tensile
strength. The alloy is through hardening in section sizes up to 4 inches thick. The alloy may be exposed to
temperatures up to 900EF (approximately 100EF below typical tempering temperature) without
microstructural changes which degrade room temperature strength. This grade must be formed and welded
in the annealed condition. Preheat and post-heat of the weldment is required. The steel is produced by
consumable electrode vacuum melting.





Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[MechyMarco]

WKTaylor,
Appreciate the concern. It's not for an engine. Going in a down hole environment where it'll see max 400F. I would never make the mistake of unintentionally tempering during use...at least not yet haha

Gonna go with 300M and see what happens. Appreciate the comments all.

Cheers.

 

[EdStainless]

When you go looking for other materials try here

http://www.questek.com/ferrium-m54.html

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P.E. Metallurgy, Plymouth Tube

 

[WKTaylor]

IF the environment is OK for 4330M then it might be OK for 300M

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[MechyMarco]

EdStainless,
Wow. I will definitely keep M54 in mind for future applications. The mechanical's are insane. Thanks.

WKTaylor,
We feel okay about 300M for the well bore environment despite the risk of SCC and hydrogen embrittlement from H2S. We have lots of parts made out of 4330V (lower quality air melt not the primo VAR) nitrided and they have stood up great. Will make a few prototypes and see how they perform before we splurg on any protective surface treatments. Likely go with electroless nickle plating if we do indeed need it.

 

[WKTaylor]

Good call Ed!!

Other Ferrium alloys...

https://www.cartech.com/en/product-solutions/

search 'Ferrium TDS'

Ferrium S53 has high mechanical strength/durability... and significantly improved corrosion resistance!

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[EdStainless]

I have worked with some of these alloys, they are pretty amazing (cough, expensive too)

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P.E. Metallurgy, Plymouth Tube

 

[tbuelna]

MechyMarco,

A couple comments in addition to the excellent advice provided by others.

If strength is a major concern, you might consider using AMS 6419 which should provide slightly better strength than AMS 6417. The two alloys have similar composition except for a slight difference in C content.

As WKTaylor noted, careful processing of parts made from this material is critical to ensure the finished product will perform as expected. For example, simply stating "heat treat per AMS2759/2" is probably not sufficient. The 3-1/2" diameter AMS 6417 raw material specified is hot rolled, and to obtain best results from heat treat a minimum amount of stock should be removed from all hot worked surfaces prior to heat treat. AS1182 provides guidance for stock removal allowance on premium aircraft quality steel bars. You also need to provide guidance to your heat treat vendor regarding part classification per AMS 2759/2 section 3.3.1. Based on your description, the part should be processed as type 1. This means at least .020" material will be removed from all part surfaces after heat treat.

 

[WKTaylor]

Tbuelna brought up an important point [machining surface layer to remove decarburization and otherwise disrupted/impure surfaces].

NOTE.
300M has one unique capability: very deep/thick section hardenability.

REF MMPDS-10...

Table 2.3.0.2. Maximum Round Diameters for Low-Alloy Steel Bars (Through Hardening to at Least 90 Percent Martensite at Center)
Maximum Diameter of Round or Equivalent Round, in


300M and D6AC [be careful with this alloy] are the only 'conventional' LA steels that can be quenched/tempered in section thicknesses up-to 5.0-Dia Round/Equivalent-round... see Figure 2.3.0.2

NOTE.
Allowable [recommended] LA steel section thickness for successful Q/T are in some cases shockingly low for many conventional steels.

Figure 2.3.0.2. Correlation between significant dimensions of common shapes
other than round and the diameters of round bars.

NOTE.

I personally wouldn't recommend relying on Q/T above 4.50"-section thickness, unless You have a REALLY savvy heat-treater, and/or You are boring-out the middle on the material. Even then, I would recommend metallurgical testing of fully tempered/machined parts to verify 'everything' [grain quality, grain-flow, mechanicals, toughness, etc...]

Also... 300M [and most VHS/UHS steels] can be very 'disagreeable' when it comes to forging parting-planes and the resulting grain-flow disruption.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]