PWHT for ss & cs

Date 08-25-2008 16:21

The carbon steel would generally be the requirement followed since seldom is stress relief used for austenitics. Heat treats for austenitics is most often solution anneals, though even then seldom used for welded assemblies.

By qaqcmpm (*)

Date 08-27-2008 07:36

IF I DO BUTTERING OF CS WITH 309L AND PWHT THE CS. AFTER THAT I WELD CS & SS. IS IT ACCEPTABLE AS PER B31.3

By js55

Date 08-27-2008 13:29

There's not much point in buttering if your using SS filler, although the thermal expansion can be accomodated better with nothing on the other side, especially if its a large assembly with considerable constraint on the joint. The idea of buttering is primarily to eliminate HT of SS. If you weld with a nickel alloy it makes sense. But direct SS to CS welds with 309 are done everyday.
You should consult engineering to determine if a direct weld is acceptable in your case. In most cases it is.
Another thing, some believe that 309 eliminates the possibility of martensite formation-a hard brittle microstructural constituent. This is not the case. Martensite is always formed. Its a question of how you minimize the martensitic zone. The less dilution the thinner the zone the better the remaining microstrucutre can accomodate any stress.

By qaqcmpm (*)

Date 08-28-2008 04:49

what about the PWHT? when to do?

By Nanjing Date 09-23-2008 06:40

I beleive you do not have to do PWHT if you use an austenitic filler wire.

By vittorio (*)

Date 09-24-2008 09:18

in my opinion you shloud do the buttering with a 309 electrodes then do the PWHT and then complete the welding process. this is the usual approach to a dissimilar welgin between SS and CS.
look also at this publication sfrom NIDI where it's explained the procedure.

http://www.nickelinstitute.org/index.cfm/ci_id/3293/la_id/1/document/1/re_id/0

page 35.

http://www.corrosionist.com/Materials_Stainless_Steel_Welding.htm

hope this help

V.

By bjayapal 2 Date 10-11-2008 07:20

Please check the operating temperature. If you are using E-309Mo the temperature shall not be more than 700 F

Jayapal

By gwg

Date 10-21-2008 02:50

......and the reason for not using 309 stainless steel filler metal in a dissimilar metal weld (DMW) joint above 750 deg F is a damage mechanism known as "carbon migration". This damage mechanism is common for cs or low alloy steel to ss dissimilar metal weld joints that are exposed to service temperatures above 750 deg F. The carbon in the cs or low alloy steel wants to combine with the chromium in the stainless steel filler metal resulting in a very narrow band along the fusion zone of the weld that essentially becomes decarburized over time. Carbon is what promotes creep strength in cs and low alloy steels. The DMW failures from carbon migration are rather distinct and look like welds that never fused with the base metal. The decarbrized zones actually follow the weld bead profile of the DMW thus giving the appearance of welds that never fused.

Inco A or other nickel-base filler metal should be used to join carbon or low alloy steel to austenitic stainless steel if the weld joint is exposed to service temperatures at or above 750 deg F. The nickel content is high enough where it reduces the diffusivity of carbon, thus reducing susceptibility to carbon migration and prolonging the creep life of DMW joints.

I would butter the cs base metal using Inconel and PWHT per B31. After this operation is completed, you can complete the weld joint using either austenitic stainless steel or Inconel.