Welding of Chrome Molly Plates

Date 01-03-2012 14:38

Hi Mark

There is not a single answer to this question. It depends on what the important design criterion are. (e.g. creep life, mechanical properties at elevated temperatures, mechanical properties at room temperature) Typically you need to decide on the limiting design condition, and find a filler metal that will meet those properties. Typically you will get it from a matching filler, but this is not always the case. You also need to decide if you can perform post weld heat treatment or not.

Hope this places you on the right direction to finding an answer.

Regards
Niekie

By js55

Date 01-04-2012 19:07

If the 13Cr Mo 4-5 is an ASME material what specification and classification is it?

By Mark Anthony Nofuente (*)

Date 01-06-2012 09:11

Thanks Nickie.

But seriously, this will be my first experience of handling a job with such specification and it will be for HRSG structures.

Hope by posting this topic, I could get more in depth details pertaining for welding of Chrome-Moly.

By js55

Date 01-06-2012 12:52

Not all "chrome moly's" are created equal. Give us more detail and you'll getmore detail.

By ozniek

Date 01-15-2012 06:57

Hi Mark

Your first post suggested that you are merely looking for a filler spec, while this last post suggest that you are looking for more general information on welding CrMo materials. I will give you some info, but I may still miss the point and not give you what you need. It is much better to give too much information rather than too little when asking a question.

CrMo materials are generally used in either elevated temperature (creep) duties (e.g. in boilers) or high strength ambient temperature (or at least not high enough temperatures for creep to be the failure mechanism) duties. (e.g. Structural frames for transport applications, crane booms etc. - Anywhere where strength is required while reducing weight.)

The general issue with welding CrMo materials are:

1) Hydrogen cracking. - So make sure that there are no sources of H present. Pre-heat will help, as will a post heat to reduce the H levels from the structure.
2) Brittle weld structures. - This can be dealt with on a number of different levels, including pre-heat, PWHT and the selection of filler metal. If you are not able to perform PWHT (which may be the case with your application?) then you need to select a filler material that will deliver a tough deposit without the PWHT, but then you need to ensure a high enough pre-heat to reduce the HAZ hardness. Typically the fillers that give matching strength properties without PWHT use low C content alloys. When using this filler, just check to see that the creep properties are acceptable at the temperature that you need, as the low C materials often have lesser creep properties. (I am assuming that HRSG means Heat Recovery Steam Generator, so your application is most likely in the creep range. I could be wrong, so CHECK THE DESIGN REQUIREMENTS.)
3) Temper embrittlement. - There was a good thread relating to the "X-Factor" that dealt with this, so have a look at that to deal with this issue. - Especially important if you are going to perform PWHT.

If the materials are very thick, then it is difficult to get away without doing PWHT. If PWHT just is not practical, then you can always go for the TTT welding method. In this case you perform a pre-heat that is high enough to hold the material above the martensite transformation temperature. (Typically 350°C does the job.) This temperature is then maintained constantly for a period long enough after welding has stopped to force a bainite transformation. (Typically 30 minutes will do.) It is important that the temperature does not drop below the Ms temperature at any time during this process, or you will get martensite formation. (The numbers above change, depending on the alloy, so check this also.)

This obviously just scratches the surface, but at least should help you understand why it is important to know what your design conditions and fabrication constraints are before tackling the job.

Regards
Niekie