Welding AISI 4140 Pins to A572 Grd 50

[maxxpower]

Hi all,

I know there is a considerable amount of knowledge within this forum and I would like to get your opinions regarding this material combination.

Background;

Large frame weldment comprised of A572 Grd 50 material. There are several locations where welding 1.5" and 3" pins to the A572 are required.

The location where the 3" pin is located is a box beam type design where the pin passes through both walls and will be fillet welded in 4 locations.

The location of the 1.5" pin is a little more troubling as it is butted up against a 1" plate and has a gusset butted up against the side of it. There would be a fillet weld at the base and a flare bevel groove weld along the gusset.

There is no code requirement for this weldment but I would still like to do a procedure qualifiaction with this material combination.

I plan on using filler material matched to the A572 Grd 50 with a relatively high preheat. Both of the sub-assemblies are small enough for stress releving
but I would prefer to avoid it if possible, however I know it would be the surest way to avoid cracking.

I am pushing for this to be welded in the annealed condition but the designer has not weighed in on the heat treat condition of the 4140 yet.

I will lay out the 2 plans I am considering and hope to get some feedback. Both plans are assuming the annealed condition.

Plan 1.
600F Degree Preheat and Interpass
GMAW ER80S-D2 95%Argon 5%Oxygen
Immediate stress relief at 1100F for an hour per inch of thickness.

Plan 2.
600F Degree Preheat and Interpass
ER70S-2 90% Argon 10% Co2
Short Postheat
Insullation Blanket Slow Cooling

I know some have had success with 309 SS wire so I am open to any criticism or reccomendations. I would also like some reccomendations on a PQR method.
I would like to qualify this to AWS D1.1 but am unsure that I could acheive the required bend radius even with the longitudal dissimilar metal bend specimen.

I do not have much experience with with this 4140 material so I am certainly open to suggestions from people who know this material better than I do!

Thanks in Advance!

 

[metengr]

Why are you using 4140 alloy steel for this application? ASTM A 572 specification provides material in various shapes, including bar. Why not fabricate the pins out of A 572 bar? For field welding, I would use material with a lower carbon content, like A 572 to avoid cracking associated with hydrogen.

 

[stanweld]

Agree with metengr or is the 4140 pin hardened to some requirement which you do not indicate.

Plan 1: Why use ER80S-D2. With dilution this will produce a highly hardened deposited weld metal before PWHT which is more crack prone.

Plan 2: What is "short" PWHT? A dehydrogenation treatment or what? I also would not recommend ER70S-2 for spray arc transfer - prefer ER70S-3 or -6.

Why use GMAW? For this weld you have picked the process which will provide the highest hardness vs GTAW, FCAW or SMAW. For a multipass weld, why is preheat and maximum interpass temp the same? This would seem to be contaproductive when you are using GMAW, apparently to reduce welding costs.

 

[steakman911]

E8018-B2L would be my preffered filler metal and process, if indeed you require a 4140 material for the pins. Some kind of earth moving equipment maybe - rotating/connection pins of some kind..?? Other wise the question as to why said chemistry is definitely valid. welding in the Annealed condition is recommended.

 

[Guest102023]

There is no universal requirement for weld metal must be matching, but there is an unwritten law that says you may grossly overmatch on strength if you select an alloy filler metal when joining low alloy steels. There are different aspects to 'matching' that depend on the application and environment.

Second, isn't A572 an HSLA steel and should therefore never be PWHT?

We first need to know the technical requirements for the weldment.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[stanweld]

A-572 Gr 50 is essentially low carbon steel microalloyed with V and or Nb to assure the 50 KSI SMYS. Some toughness may be lost if post weld heat treated at 1100 F due to formation of secondary carbide or carbo-nitride precipitates. It is not like HSLA, T-1 type structural steel. I have made similar welds in the past by first buttering the 4140 alloy pin with E7018-HR4 electrodes using 450F minimum preheat, immediately folowed by a 600F dehydrogenation heat treatment and subsequently welding the buttered area to the Gr 50 structural steel with E7018.

 

[maxxpower]

Thanks for the replies,

The materials have been specified by the design engineers of the weldment. We are doing a contract fabrication of the prototype so I

have no control of the material specifications. I am not entirely convinced that the designers have completely thought out their

reasoning for specifying the 4140 material in this application. I also requested that the pins be made from a lower carbon material

such as 1018, however I was told that the designers really wanted the 4140 material as the protruding portion of the pin will be a

pivot point for a braking mechanism that will be under severe tension.

As some have asked, this will be a piece of earth moving equipment.

The designers have agreed that the pin can be in the annealed condition. I selected the filler materials and preheat temperatures

based on research from multiple sources like the ASM Metals Handbook, as well as some Lincoln Electric publications.

I would also prefer to use the SMAW process but we have limited personnel available for this. I chose the GMAW process for its ease of

use and the fact that most of my research states that you want to avoid excessive penetration when welding high carbon steel.

If the general consensus is to weld with the FCAW or SMAW process I would have no problems with FCAW as the rest of the frame will be

welded with this process. I would also prefer to avoid PWHT if possible, which is why the higher preheat temperatures sounded like the

right idea.

Now that we know that 4140 is the requirement and that it will be in the annealed condition what would some opinions be for preheat,

filler metal for the GMAW or FCAW process, and post weld heat treatment (if any)?

I really appreciate your input! Thanks in advance!

 

[stanweld]

My concerns with GMAW have been given. I would recommend FCAW with E71T-1M or equivalent, 75 to 80% Ar - 20 to 25% CO2 shielding. Buttering with FCAW and preheat/interpass followed by dehydrogenation as previously recommended.