ER70S-3 deposited hardness and machinability.

[Tmoose]

A foundry is proposing repairing small defects in 3000 lb steel rough machined castings with ER70S-3 TIG welding rod.
The castings are ASTM A27 Gr 60-30. Normalized at 870°C. Actual 529 MPA (76 ksi) tensile strength. Probably ~ 39 HRC .
Way "better" than the ASTM A27 Gr 60-30 60 ksi/415 MPa (~ HRC 31) minimum specification.

We reportedly have had problems in the past when finish machining similar parts with weld repairs.
So we are forbidding weld repairs on surfaces requiring accurate finish machining.

Per Lincoln their LNT25 ER70S-3 rod typical "as welded" tensile strength is 560 MPa / ~ 81 ksi.
In one common chart that equates to ~ HRC 41.
39 (actual casting) and 41 HRC (typical weld) don't sound that far apart to me. Elongations are 35% ( casting ) and 22% ( typical weld)

I'm thinking those troublesome castings //may// have been closer to the ASTM Minimums, so the 10 pts difference in hardness may have been the issue in days of yore.

Comments?

thanks,

Dan T

 

41 HRC is high for UTS of 81 ksi, I found a table saying it is equivalent to 85 HRB.

That your 60-30 casting strength exceeds the minimum by so much is not unusual. Weld hardness in steel is typically higher than surrounding base metal (as well as undiluted weld metal that is the basis of filler metal MTRs) due to higher carbon base metal mixing in to the weld pool.

I don't feel that weld deposit hardness is the problem here, rather I suspect that machining may be uneven because of high residual stress fields around the weld deposit.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[weldstan]

I don't know where you got your hardness vs tensile properties but they are quite wrong. ironic's estimates are much closer to reality. Both strength levels indicate hardness in the Rb85 to Rb90 range. With GMAW welding, hardness of ER70S-3 can approach Rc 20 in the as welded condition.

 

[CWEng]

Is the casting heat treated after welding? Stress relief PWHT will reduce the property differences, and normalizing PWHT will make the weld softer than the casting. In the as-welded condition, you will have the biggest property differences and machining issues. Do you know the heat treat condition of the castings with machining problems?

 

[M.CH]

Hi Tmoose ,

Increasing of the tensile strength of material and welding consumable may be increase the hardness but this is not general rule and tensile is not the only parameter.

there is several material with different chemical composition with same Yield strength range. tensile/hardness may be got by chemical composition/heat treatment/pricipitation hardening,work hardening, etc.
for instance I got 20 HRC on X80 material (Yield=80MPa).

Acc to my experience:
hardness of deposited weld by 70s-3 on is around 200~230 HV10 (approximately 200~240) and it can not got 39 or 41 HRC even if weld diluted by base material.
&
in other hand weld repair length/volume, pre heat, heat input, welding speed, weld width,... affect on hardness.

I suppose that ,practically, increasing of hardness from 39 to 41 HRC has not important effect ,especially ASTM A27 used in general application & refer to ASTM A781 FOR Chemical composition, which title of ASTM A781 is "... General Industrial Use".

Best Regards,

 

[mfgenggear]

Tmoose

We reportedly have had problems in the past when finish machining similar parts with weld repairs.
So we are forbidding weld repairs on surfaces requiring accurate finish machining.

what was the issue?