Transcript Here:

What’s up guys? This is Michael with Michlin Metals back for another session of Michael Talks Metal. Like that name? Comment below and let me know what you think. So before we jump in, I just wanted to say, I was checking the channel stats the other day, turns out only 88% of you are not subscribed so let’s change that, click that little button and help me out! Thanks for watching, let’s get into it!

The last few weeks we have been talking about  aircraft quality alloy steels. In short, what makes a steel aircraft quality is the internal cleanliness of the steel and the testing required to assure it. (See previous weeks video here)

So what do we do if we need to have an alloy steel with even better performance from even fewer and smaller inclusions?  Premium aircraft quality, with a second melting under a vacuum or protective slag is the answer.

For the most critical applications, secondary or melting in a vacuum is used to further eliminate undesirable non-metallic components that can exist in the normal air melted and vacuum degassed aircraft quality alloys.  These alloys all have much lower Phosphorus and Sulfur contents than the same grade AQ alloy.  These alloys have improved toughness and fatigue resistance for the most highly stressed structural components like landing gear and engine mounts.

AMS 2300 magnetic particle cleanliness specification applies to all these alloys and has much stricter limits for the frequency and severity of any non-metallic inclusions than AMS 2301.

Most of these alloys have AQ equivalents that we discussed in the prior video so here we will focus on the specifications that apply to the premium quality grade. Two high strength alloys that did not have a popular AQ cousin are modified alloys of 4330 and 4340.

4330 Modified has increased Chromium at point 75 to point 95, Molybdenum point45 to point 50 and an addition of point 05 to point10 Vanadium as compared to 4330.  The increased alloy content provides additional toughness.

Specifications: AMS 6411, AMS 6427,and MIL- S- 8699

300M is a modified 4340 with higher Chromium at point 75 to point 95%, Molybdenum at point 35 to point 45%,  Vanadium at  point  05 to point 10%, and Silicon at 1.45 to 1.80%. These modifications provide increased toughness at high strength levels

Specifications: AMS 6417 and MIL-S-8844 are most common.

Additional alloys we talked about in their AQ versions have premium AQ versions as well:


Specification: AMS 6414


Specification: AMS 6276


Specifications: AMS 6265 and AMS 6267

Nitriding 135 Modified.

Specification AMS 6471


Specification AMS 6444

Melting and Remelting methods are often contained within these specifications for premium AQ alloys:

VIM is Vacuum Induction Melted. Induction coils provide the energy to melt the alloy within a vacuum chamber.

Multiple types of secondary melting are classified as Consumable Electrode Melted…..  “CEM”.

Two types melt an ingot electrode of the alloy progressively and allow it to re-solidify in the bottom of the unit.

“CEVM” >>> Consumable Electrode Vacuum Melted is a second  melt the electrode through the vacuum and then resolidify. “VAR” stands for Vacuum Arc Remelted  a more specific type

In Electro Slag Remelted>>>>>>” ESR ” for short, the melting is conducted within  a protective slag.

If you have not already guessed, the second melting required of premium aircraft alloys is very expensive.

In addition to details of melting, many other requirements are contained within the individual specifications and any applicable aircraft company standards.

So as we always say Check those Specs

Next week the topic will be other categories of cleanliness in alloy steels….so if you made it this far and are NOT subscribed, think again, no one makes it 6 mins into a video about metal and doesn’t really like what they see b/c most others have tuned out around 2 mins….if you missed any previous videos click here. Thanks for watching, this is Michael with Michael Talks Metal. Out!