Welding dissimilar metals

Date 03-24-2017 16:59

I have a job that came into our shop to weld 21-6-9 to 17-4. Looking at the CTEs, there is a huge difference. 21-6-9 is approximately 16-19 um / m C while 17-4 is approximately 6-7 um / m C. Is this going to cause a problem in welding? Would love any advice you've got on making a good weld. This is a machined overlap butt tube weld, 1/2" OD, .035 wall. 17-4 has the overlapping feature. Fore reference, weld spec is BAC5974.

P.S. I know this may be somewhere in the forums already, but I could only get the search function to work to look for users, not text within posts, so I'm sorry for any redundancy.

By 803056

Date 03-24-2017 23:42

Yes. Cracking can occur during the welding cycle and thermal fatigue if there is thermal cycling during its service life.

Al

By Vasant315 Date 05-09-2017 08:18

Hello everyone, I have a question: Job type : Ship - Chemical Tanker
Is there any problem, if we weld Mild steel stiffeners (235Mpa) on stainless steel (UNS S31803 - 450Mpa), yield strength is almost double the stiffener does it really cause any problem?
Cargo tank is made up of stainless steel plates and mild steel stiffeners. Stainless steel plate is used to protect from corrosion caused by the chemical that is to be carried, and the stiffeners are to be welded other side of the plate.

By 803056

Date 05-09-2017 12:03

The primary concern would be low cycle thermal fatigue due to changes in temperature. In your case, changes in temperature will be minimal or at least the temperature change will be relatively slow.

Consider the coefficient of thermal expansion for the two metals, i.e., carbon steel stiffeners versus the stainless steel tank shell. The difference will produce high stresses as the temperature changes over time. It will be noticeable as buckling in the areas where the welds are located. Eventually, there will be cracks in the thinner member. The initiation of cracking will be dependent on the temperature swings and whether there is a temperature differential between the stiffeners and the tank shell. The greater the temperature differential, the greater the buckling and the sooner cracking will occur. If the stiffeners are attached with intermittent fillet welds, expect cracks at the ends of the fillet welds.

Best regards - Al

By Lawrence (*****)

Date 05-09-2017 12:29

Welcome to the forum Vasant.

That's a good question, but I think that your issue is of such complexity that an engineer from the shipbuilder who has a grasp of all the conditions of stress and metallurgy should take this situation in hand.

By Faza73 Date 06-09-2017 09:48

Hello Everyone
I'm mechanical engineer student, and my project is designing a prototype that use welding as the joint between two metal. the problem is one metal is JIS SC450(cast steel) wich is astm a27 gr65-35 equivalent and the other one is JIS SS400 wich is astm a36 equivalent, I'm confused since AWS D1.1 table of matching base metal, it did not mention cast steel and non cast steel joint.
are those two material weldable or it isn't?

thx for the answer before.

By 803056

Date 06-10-2017 03:24

The short answer is maybe.

ASTM A27 has several grades that vary in strength and chemistry and possibly heat treatment. Some grades have no mechanical requirements, only chemistry requirements. That being the case, the casting may be easily welded or it may need to be annealed before welding. Some grades will require higher preheat than other grades. As a result, some grades may be more easily welded than other grades.

Best regards - Al