Brittle stainless steel

I have a fair bit of stainless steel bars i acquired free some years ago from a friend. Large bars were tagged as 303 , and it machines and forges beautifully . There is also some 8mm bars ...

Now today i bending some tight radius bends on some black steel 8mm bars , heating a short area with a few seconds of carbon arc torch to yellow heat , and then bending . And then i ran out of 8mm black steel ! As its for a simple non stressed job , i thought i'd use a bar of the stainless .. I got it locally hot , bent it ..and it snapped like a bit of brass would ! I was surprised . Is it not 303 ?

The carbon arc was at least in part your down fall ! Noel.

Yeah ,I know they're dreadful things, but they do come in handy for rapid local heating !

I'm a Noel too . I was born on Xmas day

303 is not good for cold working but it should be better hot worked though you may not have got a uniform heat. Look at the properties on any website and that is what you will see. 316 is the one for bending.

This brings to mind when i was using a large stainless steel ladle for lead mealting, the bottom fell out of it on the fire!

The Austinetic stainless steels (3XX) are hot short. Meaning they fail when bent hot. The granular structure disintegrates, literally. These steels are best bent cold. They are readily annealed similar to copper but must not be quenched. If the severity of the bend is required then the area to be bent must be brought all the way up to forging temperature, way above the hot short zone. Don't put any bending stress on the steel in the transition zone next to the hot zone as this area is hot short!

Learned a few things professionally mashing metals around for these last 70 years. Many in error!

Cheers,

Pete

When I was still working the CNC and manual pipe bending machines were used to bend 321 and 316L stainless at room temperature and bends in the region of 2, 2D or 3D centreline bend radii (D is outside diameter, a 2D bend is centreline radius of twice the outside diameter). We had a purchase standard with a maximum hardness value as if the material was too hard the outside of the bend could rip open. When we got a batch of pipe that wouldn't bend we marked it up as use for straight lengths only and used a different batch for bending.

Martin C