Grain Refiners & Carbon Getters for Steel Brazement

[DebbieAliya]

Hello Everyone.
I am new to this forum.
I am working on a steel assembly that is made by brazing low carbon steel (call it 1005 for now) with a more or less pure copper braze filler at 2000 degrees F or about 1095C.

The material is experiencing some erratic grain coarsening, especially in cold worked areas. In addition, the material does not appear to contain any of the standard grain refiners (or at least not in sufficient quantity to have an effect). It also has an upper lower yield phenomenon that I don't like.

The problem I see is that the grain refiners are mainly made for formability purposes in stamping operations or for minimizing damaging affects of welding in Heat Affected Zones. None of these processes go up to such high temperatures as this brazing operation.

Any ideas for what microalloys could be used to maintain steel strength after brazing? Any ideas on why the braze operation would make the upper lower yield point so much more prominent than in the cold rolled steel? (I don't have microstructure info on the cold rolled steel, ie don't know if it is annealed or temper rolled or what...)

 

[metengr]

No surprise observing grain growth with the 1005 carbon steel that was cold worked. For elevated temperature grain refinement you need to investigate micro alloys that contain vanadium and niobium additions, and are deep draw quality. Do a web search or review ASTM Standards for high strength micro alloy steels that are deep draw quality. The vanadium and niobium alloy additions form carbides that are even stable at high temperatures for short duration, like your application. The carbides help to pin the austenite grain boundaries.

 

[DebbieAliya]

Thank you,
I know it is not a surprise.
High strength steel won't work with the tooling that has been made. It may be possible to specify a Nb or V fine grained material, but some info I have indicates that it will also dissolve at 2000F. Also, I want to get rid of the upper lower yield point phenomena, and since there is supposedly no nitrogen in the material, I don't know what is causing this phenomena.

 

[metengr]

The dissolution of carbides is a function of time at temperature and the carbide chemical composition. For your brazing application, which I would consider relatively short duration versus a solution anneal, you might be surprised that it could require more time to dissolve the Nb or V carbides.

 

[DebbieAliya]

You are telling me what I want to hear. But I haven't found anything in writing yet that indicates it will prevent the yield point elongation.