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Hardness and GMAW-Spray

Hardness and GMAW-Spray

(OP)
Looking for suggestions on how to reduce my weld and HAZ hardness readings when using GMAW Spray on carbon steel material. I often see readings well above 250 BHN on a wide range of thk.

Thanks,
Uglyspec

RE: Hardness and GMAW-Spray

Carbon steel covers a lot of materials and carbon contents, so the following is just a few thoughts on what might help. Can you perform a Post Weld heat treatment on these parts? That should bring it down some, preheating to 200f may also help. Also, what filler metal is being used? If it is an ER70S type, there should be very few problems with the deposit hardness. If Carbon content is over 0.30 it will require more controls.

RE: Hardness and GMAW-Spray

(OP)
Materials are typically SA-106B, SA-53B and SA-516 70 (sometimes normalized). We use ER70S-2 & ER70S-3.


Thanks,

RE: Hardness and GMAW-Spray

Increased preheat and higher interpass temps (500F-650F) will lower hardness. We just saw HAZ hardness in SA-516 Gr 70 HAZ up to 267 HV10 on 3/8" wall coupons with low preheat/interpass temps. Interpass temps between 130F and 250F. Highest hardness recorded on final root side after back grinding using 120 F preheat/interpass. Cap side, near surface, HAZ hardness values ranged from 209 to 219 HV10. The mid wall test locations were at 175 HV10 where the maximum interpass temp was recorded and the maximum tempering effect was achieved. Weld metal hardness readings were below 187 HV10.

Substantially greater hardness readings were recorded on root and cap side surfaces of 1 1/4" coupons where low interpass temps recorded - Cap pass interpass temp range from 260F to 350 F.

RE: Hardness and GMAW-Spray

A comment & q's;
with true spray transfer it does not seem that low heat input would be an issue unless you are traveling at a very high rate.
Have you seen much difference in weld hardness between 70S-2 and 3. I ask because in my experience using the GTAW process, we get much softer welds using S-3 filler.
Keep in mind that HAZ hardness will also be affected by the base metal chemistry. Have you looked at the CE for the material in question?

RE: Hardness and GMAW-Spray

The shielding gas mix can influence the hardness readings to a limited degree.

The use of a mix of Argon and Carbon Dioxide (SG-AC-12%) will ensure the deoxidizers are used for that purpose and do not increase the alloy content. Both Manganese and Silicon are used as deoxidizers in filler metals. If they are not utilized for deoxidizing the weld pool they become alloy constituents, thereby increasing the Manganese and Silicon content of the weld deposit and increasing the hardness values.

Slow cooling, high heat input, high preheat, high interpass temperatures will also reduce the hardness of the weld.

Best regards - Al

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