AISI/SAE low alloy steels heat treatment

[FiLOM]

Hi all,

just trying to get into using AISI steels 4130, 4140, 4340, and eventually 1025 and its AMS specifications properly according to MMPDS. Kind of stuck on the "heat treatment" topic. These steals got their mechanical properties specified in MMPDS with a note under the line - "Minimum properties must be substantiated by tensile testing of production material after heat treatment..."
Does it mean that I have to do testing on specimens from the semi-finished product or the finished one?

What I am missing is some notes about machining. About changing the dimensions of material by machining, or about pre-machining and after-machining HT.
E.g. 4340 is supplied in Premium aircraft quality AMS 6414 with UTS 260ksi which is really hard to produce. And I want to machine it. It is machined in that HT260 treatment? What about the residual stresses after machining? Machining may be followed by normalizing, am I right? Than what? Quench and temper it again to HT260? BTW is it even machinable in HT260? Or there has to be pre-machining HT? In that case why even bother HT of semi-product?
And when do I have to do the testing? And from what material in which phase of production do I make the specimen?

 

[EdStainless]

You need mechanical testing after final heat treatment, whatever stage of production that is.
There are specification for the HT, for low alloy steels 6875 was the old one and I don't recall the new number.
For many alloys the rules about HT and testing change above 220ksi or so.
There are specs about residual stress control also.
I would never use 4340 at 260ksi, there are other options.
For very high strength steels it is common to rough machine as annealed, harden (Q&T), and then final hone or grind or lapp to the required finish dimensions. It isn't just size change but distortion as well that you need to consider.

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P.E. Metallurgy, consulting work welcomed

 

[SWComposites]

Does it mean that I have to do testing on specimens from the semi-finished product or the finished one? Yes.

 

[WKTaylor]

Fi...

You have asked a question that could take several years of study and experience 'to come-up-to-speed' about basic steel alloys, their heat treatments, fabrication, surface finishes, corrosion protective finishes, testing and qualification... etc... since everything put into making a high reliability aerospace steel part is interrelated. There are no easy answers... and the answers only get much harder when strengths levels jump from ~180-200-KSI to 260-to-300+-KSI.

I was going to try to provide an extensive list of specifications, processes, knowledge... and KISS... but the list GREW too long. Here is a sampling [no particular order].

MMPDS [MIL-HDBK-5] metallic materials performance, usage and allowables data
ASMH Aerospace Metals Handbooks [Carbon, alloy steels section]
MIL-HDBK-723 STEEL AND IRON WROUGHT PRODUCTS
[ASM steel handbook]
MIL-STD-866 Grinding of Chrome Plated Steel and Steel Parts Heat Treated to 180,000 PSI or Over
SAE ARP1110 Minimizing Stress Corrosion Cracking in Wrought Forms of Steels and Corrosion Resistant Steels and Alloys
SAE 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
SAE ARP1962 Training and Approval of Heat-Treating Personnel
SAE AMS2649 Etch Inspection of High Strength Steel Parts... and/or...
SAE ARP4462 Barkhausen Noise Inspection for Detecting Grinding Burns in High Strength Steel Parts
SAE AMS2759 Heat Treatment of Steel Parts General Requirements
SAE AMS2759/1 Heat Treatment of Carbon and Low-Alloy Steel Parts Minimum Tensile Strength Below 220 ksi (1517 MPa)
SAE AMS2759/2 Heat Treatment of Low-Alloy Steel Parts Minimum Tensile Strength 220 ksi (1517 MPa) and Higher
SAE AMS2759/9 Hydrogen Embrittlement Relief (Baking) of Steel Parts
SAE AMS2759/11 Stress Relief of Steel Parts
AMS-H-6875 Heat Treatment of Steel Raw Materials
SAE AMS2453 Low Stress Grinding of Steel Parts Heat Treated to 180 ksi or Over, and Low Stress Grinding of Chrome Plating Applied to Steel Parts Heat Treated to 180 ksi or Over
SAE HS-84 Manual on Shot Peening
NOTE1. Embedded in these data and spec are associated sub-processes, equipment requirements, etc... and mandatory testing... and certifications

My head hurts.

Regards, Wil Taylor
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