Posted by Stu Smalinskas on March 11, 2010 at 16:55:41:
In Reply to: Stringersin 316L Bar posted by HSheehan on February 24, 2010 at 11:43:45:
The BEST way is by using ultrasonic methods that are being developed by steel producers. It gives 100% inspection of inclusions in the volume scanned. But this is a rather expensive setup.
The next best are the conventional cut, mount, and polish to look for inclusions.
Another method is called a "blue fracture" test. This is where a longitudinal notch is cut into a section of bar, the bar is then austenitized and quenched. In the untempered condition, the bar is impact-fractured, aided by the notch, either by hammer or by wedge. The part is then tempered (300-350°C) in the furnace until the fracture surface develops a blue temper color. the fracture is then examined with at least 10X magnification. The inclusion stringers appear gray, contrasted against the blue fracture surface.