Suitable for End-Use
First, the material that you select must be suitable for the end use, so determining the appropriate chemical resistance needed for the application is your first ‘screen.’ I like to use the Corrosion Resistance Tables provided by Carpenter to make sure that I get this right.
Required Mechanical Properties
Next, in addition to the appropriate chemical resistance for the application, the material that you select must have the mechanical properties necessary for the application. High temperatures, low temperatures, thermal cycling, impact or tensile loads, magnetic response or electrical properties ( think solenoid applications) -what are the mechanical properties required?
Ability to be Fabricated
Now we need to look at your list of candidate grades to determine their ability to be fabricated into the geometry needed for your part. Is machinability going to be an issue here? How about cold work, or work-hardening? Which grade will assure that the parts produced will have necessary features, fit, and finish, without requiring additional (expen$ive) processing.
Determine Commercial Availability
Now from the much shorter list of candidate materials, it is time to determine if the grade you want is ‘commercially available.’ While the grade you prefer may indeed be listed in somebody’s catalog, the fact is that there may be a minimum order quantity, lead time, or freight expense that makes your choice commercially impossible. Not to mention that the grade you select may be available only in a different form- like flat roll rather than bar stock. In this case, you consider the second best choice, then the third, until you get to material that is actually commercially and practically available.
Consider Costs- and Benefits
Finally, you can look at the cost per pound/kilo to rank the grades available. Here is where you need to be very careful, as savings in cost per pound can be easily lost if the grade you choose is too expensive to fabricate due to lower speeds and feeds required to get features and finish compared to alternatives that may be slightly more expensive per pound. Or your lower cost material may require an additional thermal processing step that the others do not. Perhaps you need special straightness or a special end treatment, that is a benefit that might justify the additional expense, and that is only available in certain grades from certain suppliers- we’ll address that next.
Final Criteria, Supplier and Agency Acceptability
Lastly, now that you are ready to place the order, it is time for one last contract review to assure that the material supplier is accredited and on your customer’s approved supplier, approved process, certified quality system lists, as well as an acceptable country of origin. Also that they are agency approved if there are agency requirements cited in the specification. And that if the grade you chose has ‘conflict minerals’ in it, that your customer signs off on that, or is willing to pay whatever up-charge you may find necessary to cover your costs of conflict mineral compliance and reporting. If you or your customer is sensitive to preferred suppliers- often the case due to their special means of provisioning- special straightness, packaging, end geometries available, tighter tolerances, etc. etc., now is the time to consider that as well.
That’s the way I do it. Order of operations is a hierarchy of suitabilities.
If you follow my methodology of suitability- in order-chemical compatibility for end-use, properties, then processing availability, costs and supplier status- you will avoid a lot of extra work and wasted time.
Have and follow a process.