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What’s up guys?!?! This is Michael with Michael Talks Metal back for another chat about metal. Do me a favor, if you are here, watching, and you haven’t subscribed, click that little button. It helps the channel out and we’d be grateful. For the last several weeks we have been talking about aircraft quality alloy steels.
The key qualification for aircraft quality is a very “clean” steel with testing by magnetic particle procedure AMS2301 to provide the pedigree.. Magnetic particle examination reveals the number and length of inclusions on or near the surface being examined.
Another quality category of alloy and stainless steels that requires a high degree of internal cleanliness is for bearings and related applications….”.BQ ” for bearing quality. BQ alloy production requires similar mill procedures during melting and refining, but are most commonly tested for inclusion content by a different method. Originally developed in Sweden by their “Jernkontoret”…. a national society of iron and steel producers, this method categorizes and measures by specific types of inclusions present.
Known as the “JK” rating system, inclusions in these steels are examined microscopically to identify both the type and size of the inclusions contained in the material. Samples are taken to represent the first, middle and last portion of the melt. Using very controlled procedures the prepared samples are scanned “visually” at high magnification and rated by comparison to a chart of standards or by a computer analysis of the scan.
Inclusion types are A thru D for sulfides, oxides, silicates and globular oxides. For each type of inclusion there is a rating for Thin or “T” and Heavy or “H” .Ratings are in increments of point 5 with 0 representing no inclusions of a rateable size.
Maximum allowable ratings are contained within the applicable material specification and may require data on all sampled locations or only the worst rating for each.
Another rating system; the “SAM” method ……rates inclusions on a different scale ( numerically expanded ) and uses only a single number to rate B and D inclusion types instead of a number for Thin and another for Heavy..
Details of the micro-inclusion rating methods are contained in ASTM E45.
Common Specifications for BQ alloy steels are:
ASTM A 534 for low carbon alloys for carburizing such as 8620 and 9310
ASTM 866 for medium carbon alloy steels like 4130 and 8640
ASTM A295 for high carbon alloy steels like 52100
ASTM A485 for high carbon high hardenability alloy steels ..modifications of 52100 .
ASTM A756 for 440C stainless steel.
AMS standards for bearing material also typically incorporate aircraft quality requirements as well. Those materials are both AQ and BQ and would have both magnetic particle and micro-inclusion JK ratings required.
For example AMS 6440 has both AQ and BQ requirements for alloy 52100
And like aircraft quality steel, bearing quality grades can also have a premium bearing quality that requires s second melt.
AMS 6447 is an example of premium BQ and AQ for 52100.
As we always say…. check the specs. That will wrap up another week of Michael Talks Metal. New here and made it this far? Well this is where I remind you gently to subscribe, here…missed previous videos, click here. Thanks for watching and this is Michael with Michael Talks Metals. Out.
