Ferrite or austenite grains: which is required for this application? 1

[coreman73]

I am trying to determine which type of grain structure (either ferritic fine as rolled grain or austenitic fine grain by application of correct steel making composition) needs to be included in a specification for AISI 1045. This steel will be used to make hand tools, which will be formed using a progressive die/stamping operation.

We normally always specify ferritic fine as rolled grains but the steel provider is asking if they should supply the steel in the austenitic grain form. I don't have the knowledge to answer this and would appreciate some help. We are working off of ASTM A29 for the material.

 

[redpicker]

Your supplier is referring to the prior austenitic grain size. 1045 would have a pearlitic/ferric microstructure in the as-rolled condition. Usually, when someone referrs to a "fine-grained steel", they are referring to the prior austenitic grain size, or the grain size you would expect when given a "typical" austenitizing cycle. In the as-rolled condition, you could have some fairly large ferritic/pearlitic grains even if you are buying a "fine-grained" steel. To insure a fine peralitic/ferritic grain size in a hot-rolled bar, you would probably have to normalize the material, an extra heat treating step, which is why your vendor is making the request; he is trying to avoid the extra cost if it isn't necessary.

If you are going to heat the material above 1500F, you probably will want a fine austenitic grain size (typically 5 or finer and is also typically only insured by chemistry control and not usually tested for at the mill). This means you shold have a fine-grained structure after your heat treating. If you have always used a steel with a fine-grained microstructure as your raw material, however, you may want to research the reasons the requirement was added to your purchasing requirements.

rp

 

[Guest102023]

I would presume that fine (ferrite/pearlite) grain size is specified for reasons of material formability.

 

[coreman73]

rp,

Thank you for yet another excellent response. It was very helpful to have it explained that way. I'm jealous of your knowledge.

brimstoner,

Thank you. That makes sense that we'd need fine grains to improve formability.