difference in Hot Rolled and Cold Rolled material
difference in Hot Rolled and Cold Rolled material
(OP)
I know that the Cold Rolled material has a higher Yield Strength due to the work hardening during the forming process. However is that strength throughout the material or mostly around the surface area? And if so how deep would you expect the work hardening to effect? The question came up regarding 9" 1008-7 shafts that we purchase to make splined hubs from. We have specified the material as Cold Rolled however our vendor is having problems sourcing CR and would like to substitute HR instead. If 9" material is bored and splined for a 2" shaft does the work hardening of Cold Rolling even have an effect on the inner part of the material?





RE: difference in Hot Rolled and Cold Rolled material
-CRS yield strength is through the full depth, not just a surface layer
-CRS stock is much more dimensionally accurate, meaning that if you're making large quantities of parts there will be a difference in your cycle times and machining costs
RE: difference in Hot Rolled and Cold Rolled material
This is the thing I was most interested in knowing. I figured that the forming would give a work hardening the material down to X% of the thickness but didn't know if it would have an effect through the whole stick. Especially for a 9" shaft.
I was also aware of the looser tolerances of HRS but that is of secondary importance to strength.
Thank you for your answer.
Jim
RE: difference in Hot Rolled and Cold Rolled material
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: difference in Hot Rolled and Cold Rolled material
regardless of hot or cold working, for a 9'' bar, I would not expect an uniform deformation from the center to the surface. Even for an annealed 9'' bar, expect difference in microstructure/mechanics from center to surface.
RE: difference in Hot Rolled and Cold Rolled material
Attached is a catalog description of 1018 (rather than 1008) cold finished steel bar that discusses the difference in how small and large size materials are processed. Also note the difference in material properties at the bottom.
RE: difference in Hot Rolled and Cold Rolled material
However is that strength throughout the material or mostly around the surface area?
The deformation profile in rolled material is dependent on the size of the rod compared to the size of the rolls. When the size of the rod is large relative to the roller diameter more deformation is concentrated near the surface. So to answer your question it depends on your vendor's process. The same principle applies to hot rolling.
Hope this helps
Uconnmaterials
RE: difference in Hot Rolled and Cold Rolled material
paintballJim, when I read your initial post I failed at reading comprehension and thought you were talking about machining a splined shaft, 9" long, from 2" CR round bar. Now that I've read it again, that's a pretty blatant misread.
My first post in this thread would be correct if you were using 2" round bar, but at 9" diameter, everyone else that contradicted my post has it right.
RE: difference in Hot Rolled and Cold Rolled material
This caused quite a fuss about the relative strengths of HR and CR and should we select a different, stronger material. My position was that this material has been sufficient for several years so there is no need to run out and change it today because we found out we weren't getting what we thought. I also reasoned that cold working only affects the material to a certain depth (as UConnMaterials indicated) and by machining a hub out of the shaft we were probably beyond the affected zone where we needed the strength the most anyway.
Thank you again for your input.
RE: difference in Hot Rolled and Cold Rolled material
Good to hear the purchasing manager at your current vendor brought this situation to your attention before any of your products involved experienced a problem. Some vendors are reluctant to disclose these types of issues due to the potential financial liability involved with recalling/replacing a large number of non-conforming products. Hopefully this experience has shown you the importance of being very explicit with your purchase orders/specifications, and making sure there is a QA procedure to verify your vendor delivers exactly what you ordered.