Shop Demonstration on the effects of Preheat

By Welducator Date 01-17-2012 17:24

I'm trying to create a shop demonstration on the effects of preheat on weld properties. Ideally, I'd like to make a small weld on some type of carbon steel material without preheat and then with preheat. I'd then like to do some sort of test such as a bend test and have the non-preheated weld break open while the preheated weld bends without breaking. This would clearly demonstrate the formation of a hard brittle microstructure cause by rapid cooling of the weld from a high temperature. I have tried this approach on several types of Cr-Mo steels, but have not been able to get the straps to break open on a reliable basis.

Are there any educators out there who may have tried something like this? Do you have a type of steel you can recommend? Is there some other approach that someone can suggest to clearly demonstrate the effects of preheat on weld properties?

Thanks for your reply

By pipewelder_1999 (****)

Date 01-20-2012 20:09

A fillet weld break on a piece of 1" thick aisi 1045 should do it. I will try it myself.

Gerald

By Lawrence (*****)

Date 01-21-2012 04:02

If your strictly looking for pointing out the effects of rapid cooling you can simply prepare a piece of plain A36 in the shape of a bend strap and apply an arc strike in the bend area,, Blend flush and bend. You will have breaks and cracks.

This will not demonstrate preheat value, but will open the door to the concept.

By jwright650 (*****)

Date 01-21-2012 12:13

>the effects of rapid cooling you can simply prepare a piece of plain A36 in the shape of a bend strap and apply an arc strike

I can help with that....I have a few pics of arc strikes on A36 flatbar, and bent in my coupon bender.

As a control piece, the A36 flatbar bent "without" any arc strikes is to the far left in the picture. The other 4 were laid on a table side by side and a welder took a E7018 and drug it quickly across the four pieces, then ground them down to his satisfaction, the samples were bent in a coupon bender set up for A36/V50 using the correct bend radius and bent. As shown in the pic, every where there was a droplet of weld metal that melted and rapidly cooled....initiated a crack.

By jwright650 (*****)

Date 01-21-2012 12:18

close up...sorry about the quality of the pic. Our shop camera in 2006 wasn't the best with macro shots.

By Lawrence (*****)

Date 01-21-2012 16:29

Super good illustration John.

It makes believers right now when they see this happen in a matter of minutes right in front of the eyes.