Tempering - 20 C

[ibf]

Dear All ;

I need to prove to my customer that :

(Tempering temperature - 20 C) , is an acceptable temperature to be used on stress relieving cycles for weld repairs in castings. Would you please reference a literature for that , so I can substantiate my statement ?

Thank you again !

 

[metengr]

ibf;
What is the material of the castings? Also, are you referring to cryogenic treatment after tempering?

 

[ibf]

Hi metengr !

ASTM A 27 GRADE 70/40 Normalized and tempered on a furnace car , and stress relieved after welding repair via SMAW or FCAW.

 

[metengr]

ibf;
Ok, one of those not quite Sr moments again. Could you describe your entire sequence for weld repairing these carbon steel castings?

Preheat
Filler metal
Casting thickness
stress relieving temperature
NDT

 

[ibf]

Pre heat - 120 / 150 C

Filler metal - AWS E7018

Casting thickness - it varies from 2 up to 4 inches

S.R temperature 550 C ( TEMPERED AT 570 C ).

NDT - WELDMENTS ARE M.T`d before and after S.R / after S.R weldments are randomly selected for traverse HB via EQUOTIP to make sure that the H.A.Z is not creating a "metallurgical notch".

We consider a metallurgical notch when the gradient in HB between the H.A.Z and base metal is equal to , or higher than 40 HB points.

 

[redpicker]

I was confused by your original post. I thought you were trying to stress relief at either 20 C or minus 20C, neither one would do much good on carbon or low-alloy steel castings.

But using the tempering temperature minus 20C is acceptable practice.

rp

 

[ibf]

Correct.

It is tempering "minus" 20 C. In that case : 570 - 20 = 550 C.

Now , back to my question :

Are you aware of any literature where such rule can be found in writing.

We successfully use it for years ; however , I need to convince him that such a practice is reliable.

 

[metengr]

ibf;
Typically, PWHT temperature is never performed at or above the original tempering temperature (if specified in the original heat treatment) because you will adversely affect the mechanical properties that were required by the original heat treatment. I normally specify the PWHT temperature to be 50 deg F below the original temping temperature just to be sure that I don't exceed it after welding.

Your justification is any steel heat treatment book (like ASM Handbooks, Volumes 1 and 4) that will show the application of thermal treatment above the original tempering temperature will result in lower stregnth properties (it is as though you tempered again at a higher temperature).

 

[metengr]

ibf;
One last thought to leave you with - have you considered using a temper bead weld repair method on these carbon steel castings to avoid stress relief (PWHT) altogether? Given the thicknesses you reported and the chemical composition of the castings, temper bead may be worthwhile.

 

[ibf]

Thanks for the tip "metengr" , and by the way , I found the statement I was looking for on ASM - Handbook - vol. 15 (Castings) - PAGE 714 (9TH EDITION).