What’s up guys!? This is Michael with Michlin Metals back for video 2 of the New Year! New Year and new types of metals to talk about. Before that, how about you help me out and subscribe. Just click this little button here. If not, drop a like, it helps the channel out!  For the next several weeks the topic will be alloy steels.  Aircraft Quality alloy steels to be precise. So what makes an alloy steel “Aircraft Quality” aka “AQ” as compared to commercial quality aka “CQ” in alloys such as 4130, 4140, 4340, 8620, 9310, and 52100?

First, some of the things we know about aircraft.  Weight is important so parts need to be made as light as possible and as a result they tend to be highly stressed. Also they operate in temperatures well below zero at altitude and can be subjected to impact loads or cyclic loads that can cause metal fatigue. Failures are at a minimum very very costly to repair or catastrophic beyond all repair and people get hurt or worse. when I say, check the spec, I mean it.

Key to the performance of these critical parts is the micro cleanliness. That, is the elimination of microscopic flaws that then allow us to safely use the steel at high and cyclic stress levels. Specifications require confirmation that the cleanliness has been achieved.

So, for an example, let’s look at the differences in production and requirements between a commercial quality ( CQ)  alloy steel and an aircraft quality (AQ)  alloy steel.  It all starts in the melt shop of the  producing mill. Chemical analysis of an AQ alloy restricts the Phosphorus and Sulfur to a maximum of .point  025 % each. The CQ alloy maximum is point 035 max for Phosphorus and point 040 for Sulfur. Reducing these elements reduces the formation of non-metallic “inclusions” in the steel. Inclusions are blemishes or marks that are usually unwanted.

Vacuum degassing takes out dissolved gas like oxygen in our AQ alloy to further reduce any inclusions formed from the melt during solidification.  CQ alloys would not require vacuum degassing.

AQ alloys require additional tests performed at various stages of mill production. Tests are conducted on samples that represent the first,  middle, and last portion of each heat cast to verify physical soundness and to verify the microcleanliness.

A macroetch aka “Macro”  test to look for physical flaws like cracks and voids on samples of the full cross section.

Machined samples are used to verify the micro cleanliness of the steel using AMS 2301 magnetic particle inspection. Inclusions are limited to a maximum frequency (how many) and severity (how large)  permitted. This inspection at the mill confirms the capability of the heat lot to meet requirements of final inspection conducted after manufacture of finished parts.

Additional requirements and types of tests and inspections are  contained in the various AQ specifications. Aerospace Material Specifications “AMS”, MIL, and various aerospace companies like Boeing, Pratt and Whitney, General Electric, etc so as we always say   “Check the Specs”.

Thanks for watching, if you made it this far, first off THANK YOU! Guess what I know? I KNOW you like metal….so click here to subscribe! If you have missed any of the previous videos, click here. Thanks for tuning in, this is Michael with Michlin Metals, I’m out!