CR vs HR

[alphad]

I'm wondering about the structural performance. If you build a welded structure out of the same gauge Hot-rolled steel and obtained a certain performance level and then, replace the same structure with cold-rolled, commercial grade, same gauge material, then, it would perform better or worse under dynamic load?

 

[arunmrao]

Please come with more info on the grade of steel considered and the application details with loading conditions to get a more meaningful response.



Save water Drink Beer

 

[NickE]

If the strength of the two steels (I'm assuming low carbon, basic carbon steels) is the same there will be negligable differences in basic mechanical performance.

What is dynamic load to you?

 

[alphad]

Thanks NickE. I was looking for a general answer, and you provided me with that. Yes, the material of HR and CR,is commeral grade low carbon steel "sheet", 10GA -12GA range. The dynamic load is seismic. The structure is a simple two post rack, welded formed sheets together. Mechanical properties in sheet form of HR and CR seems very close to each other, it seems not to make any meaningful differences. I wanted to verify that thinking. And you just did it. Thank you very much.

 

[swall]

Alphad--be careful about this. While you can indeed obtain CRS with the same mech properties as HRS, it won't always be true. Many grades of cold rolled are given special annealing cycles, controlled cooling and a final roll pass. Each of these process steps can greatly change the mech properties even if the base chemistry is the same.

 

[GMIracing]

I was wondering if anyone else might have some further input in the difference between Cold Rolled and Hot Rolled sheet steel regarding other performance criteria.

Given you have two steels, same thickness, and same material properties requirements, I think that the resulting difference will be in the Grain Structure and the different chemical compositions needed to reach the required properties due to the cold vs hot working.

Only looking at a finer Grain Structure between CR and HR, how can this effect Formability, forming tolerances, distortion from welding, or strength in the HAZ from welding or Heat treating?

Maybe someone can point me in the direction of some references I can look into regarding this topic?

 

[swall]

GMIracing--I would suggest you take a look at ASTM A109, which covers cold rolled steel strip, max carbon .25. Table 3 will enlighten you as to the variety of mechanical properties that can be obtained with cold rolled low carbon steel with comparable chemistries. Intuitively, one tends to think of "cold rolled" as being stronger than hot rolled because of the work hardening from rolling. But as I mentioned in my previous post, cold rolled may be given various annealing and controlled cooling cycles to vary the mechanical properties of the final product.The main reason for being of cold rolled steel is superior surface finish. Then the thermal/mechanical processing is adjusted to give the formability and/or strength needed for the particular end use.

 

[GMIracing]

Thanks for the suggestion Swall, but I do not think that ASTM A109 will ever meet our product needs. The material properties are only approximate and the formability requirements are too vauge for what we require. Also, the chemical composition limits are nonexistent, which would cause variability in our processing steps of the raw material. This is not a specification I would consider.

I fear I was too general with my previous question, so I will try to further define it:

We use HSLA for most of our applications due to our criteria for applied stresses and formability. Currently, I would say our most commonly purchased is grade 340 or 410. So, with this in mind, we are mostly limited to ASTM A1008 (CR) or ASTM A1011 (HR) in the NAFTA production region.

Again, my question, when only looking at these two standards, what is the benifit of Cold Rolled vs the Hot Rolled equivilant (given the same grade 410 for both). Analysis of the two standards shows a 2% better min elongation percentage (18% for CR and 20% for HR), and both would meet our specficiations for forming. The chemcial composition limits are the same for both standards. Would one give better forming tolerances, fatigue stregth, tool wear rates, different weld HAZ properties, welding/brazing destortion rates, etc. Is the difference really only the superior surface finish properties with the Cold Rolled specification?

Again, I appreciate if anyone had some recommendation for references on sheet steels in machine design applications it would be a great help to me.

 

[swall]

GMIracing--suggest you start a new thread specific to your questions about HSLA sheet steels.