HEAT TREAT DIST. AND STOCK SIZE

[gearHTr]

I would love some confirmation if I am on right track or way off here. We make a landing gear axle out of 4340 steel that always moves a bit at heat treat-we roll quench after heating to 1500 for 2 hrs.70% of length is solid 2" diameter, ends are tapered and hollowed out, min wall thickness approx 3/16"
So - this time around there is more movement than normal, coinciding with a raw material change from 2 1/2 diameter CF round bar to 2 1/2 diameter cores that had been removed from 7" diameter round bar.

Could this be a contributing factor? we do a harden and temper before turning for machinability, but it may not be taking all the movement out.
thanks

 

[dbooker630]

I believe it is possible. The new material is taken from 7" bar which may have a much lower reduction ratio than the original 2.5" bar, especially if it's continuous cast steel. The grain structure and 'soundness' is different.

 

[Goahead]

I would be concerned with impact properties, for a landing gear axle. If the product is for aerospace I doubt that this change in material form can be accepted without substantiating all design properties.

http://www.welding-advisers.com/

 

[EdStainless]

If there are any centerline casting defects you have them all. I don't like trepaned bar, it isn't the same as a bar finished to size. This piece was in a much different heat treat condition than you 2 1/2" bar. It had to have cooled much slower.

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[TVP]

I agree with the others-- this is a substantial change in manufacturing process, and will result in a substantial change in microstructure, properties, etc. Distortion is very much controlled by initial casting shape and subsequent rolling schedule, so the only surprise to me is that you describe the difference as "more movement than normal" rather than "twice as much movement" or "three times as much movement", etc.

 

[gearHTr]

thanks for the help, gentlemen. Confirms what I thought was happening