Procedure for AISI 4350 welded to ASTM 572 Gr50

Date 11-13-2008 00:31

I would recommend a 120 KSI electrode. 650 F. Preheat and Interpass Temp. Do not go below 450F until set in the PWHT oven. I also recommend Normalizing at a temperature well over 1550 degrees F per hour per inch of thickness. Then cool to ambient in still air. Then stress relief at 1200 F for 1 hour per inch then cool to below 450 degrees F., 100 Degrees per hour per inch .

By DaveBoyer (*****)

Date 11-13-2008 04:14

With a post weld heat treat that Joe suggested, I think that You will have to re harden and re temper if You need to have 330 Brin. on the shaft.

I am NOT saying that Joe is wrong, just that it would negate the heat treatment that has been done to the shaft.

In any case, the heat treat of the shaft will be compromised in the HAZ, and there will probably be martinsite formation, so something must be done to temper it. Your suggestion of a post weld heat treatment at tempering temperature may be the best compromise if You need to maintain the 330 Brin.
If this is the rout You take, I would suggest holding the temperature for 1 1/2 hours after the shaft is at temperature.

By Joseph P. Kane (****)

Date 11-13-2008 12:49 Edited 11-13-2008 13:05

Dave

You may be correct. I didn't realize that he needed to maintain the 330 Bhn.

I based my reply on a technique I developed to weld with a 450 to 550 F preheat. All the literature and some experts told me that I would get no additional benefit by controlling the cooling below 600F. By experiment I found that I could get additional effects by slower cooling down to 450F. In the case where I used that sequence that I described, hardness was not affected, and the welds did not fail. When I etched the cross section, I was almost convinced that I had actually achieved some weld metal "diffusion" because of the length of time at temperature.

Things were desperate when I worked this out. It was amateur metallurgy, and the whole theory behind it might be metallurgical heresy. The reason I needed to develop this method was because 650F preheat and interpass temperature was too hot for the welders to handle physiologically. 450 to 500 they could do.

Still, I believe the correct electrode would not be an 80 strength class. Perhaps a braided heat band could be used to PWHT the weld zone alone, and not affect the rest of the 4150 shafting.

By Fredspoppy (**)

Date 11-13-2008 15:05

Gents,
I may be missing something, but I don't see a reason for the filler material being of higher strength than the weaker of the base materials. A sketch, or better description, of the configuration of what the parts look like, how they fit together and what the finished componet actually does, would be of benefit. As always with HSLA materials, proper preheat and PWHT is of great importance. The important part of this seems to be the HAZ of the 4350 shaft, and the proper care, post welding.

By DaveBoyer (*****)

Date 11-14-2008 03:57

Joe, He really didn't say that He needed to maintain the 330 Brin. hardness, I just guessed He needed to.

I don't have the specs at hand, but I think the post weld schedule You mentioned would leave the shaft pretty much softer.

A method of only heating the needed area would probably be a good choice if there is enough distance between the weld and where the shaft needs to be 330 Brin..

I don't know what the best electrode would be. As Fredspoppy points out little would be gained with a weld stronger than the Gr 50 plate, but the electrode must be compatible with both materials.

By Joseph P. Kane (****)

Date 11-14-2008 12:27 Edited 11-14-2008 12:39

Dave, Fredspoppy

I agree that from a structural strain standpoint the 80 class electrode is all that is necessary for the A-572 Gr.50.

I used 120 class electrode, because I know it is compatible metallurgically and heat treatment wise with the 4130, 4137, 4140 and 4150 material. I can tell you from experience and test, that the A-572 Gr-50 will not be affected if you use 120 series electrode with or without PWHT. So, while it is overkill to the A-572, it is not necessarily underkill to the 4150. Why take a chance?

Anyway, I admit I am not a Metallurgist, and I really screwed up by missing that 330hB requirement.

Joe Kane