Making Sugar on Stainless

[pontiac]

Yes another newbie question..

I've heard a couple people refer to making sugar when welding stainless..

As far as I can tell making sugar ruins the corrosion resistance of the stainless steel..

What causes it and what does it look like when I do it?

Thanks!

[Sberry]

I think they are refering to carbide precipitation,,, we will get an alloy specialist here I am sure.

[Dan]

Re: Making Sugar on Stainless

Originally posted by pontiac
Yes another newbie question..

I've heard a couple people refer to making sugar when welding stainless..

As far as I can tell making sugar ruins the corrosion resistance of the stainless steel..

What causes it and what does it look like when I do it?

Thanks!

Scott

I ll try to make you a sample piece at work tonight. Then I will post a picture of this sample and try to explain to you what cause this.

[Seldom]

Nope, it’s not carbide precipitation, that’s when an austenitic SS weld is held at an elevated interpass temperature too long say between 800F & 1500F. While carbide precipitation certainly affects corrosion resistance and there are several other even more detrimental effects related to that condition.

Sugaring is simply oxidization of the SS weld pool at temperatures above 500 degrees F when it’s not shielded by an inert gas usually occurring on the backside of a weld. This oxidation is detrimental in corrosive environments because the oxide layer may/will reduce the corrosion resistance and facilitate preferential corrosion. In addition, while the heated SS is exposed to air it’s picking up other reactive elements that have a negative impact on the weld’s mechanical properties. Also, the gross lack of “wetting” and fusion at the edges of the oxidized sites and not always evident but always present are notches or cracks at the weld/base metal interface. These can propagate in service and cause failure.

If the oxidized (sugared) site is accessible the sugar can be ground off but this is a “catch 22” because when this is done, the passive oxide layer (what makes SS corrosive resistant) is also removed. It’s far better to prevent sugaring then react to it after you have it!

[Sberry]

Well I learn something new again!

[Dan]

Cool, Seldom gave such a great explaination that all I need to do is post my picture.

This is the back side of the weld joint. I ran weld extremely hot so the sugar would definately show up in the picture for you.

[pontiac]

Thanks Seldom and Dan!..

Just the answer I was looking for