What’s up guys? Michael with Michael Talks Metal back for the 148th time to do what I do best…. talk about metals.
A customer of ours received two bundles of the same item of the same heat number. He got two test reports with the same chemistry but hardness and tensile properties were different. Within spec of course, just a bit different.
What’s up with that?
Apparently each bundle was a different mill shipment and mill production lot. If both bundles had been part of the same shipment from the mill, the one mill cert would have had the values from the two lots on one document. So what is a “Lot” in the world of metals?
The most universal and simple definition is that a lot is composed of material of the same chemical composition, shape, condition, and nominal cross section dimensions processed together or sequentially.
Inspections, tests, and certifications draw on the details of the production lot for requirements.
Let’s look at a couple of examples to illustrate.
A steel mill produces a heat of a martensitic steel and hot rolls it all to 1-1/2″ bar at the same time. So far we have produced a single lot for chemical composition, shape, size, and condition.
If we take some of the bars and anneal them sequentially, the heat treatment creates a new “lot” for purposes of testing any properties affected by this processing. Condition is different than our original lot.
Later we take some additional bars and heat treat them to a 30 Rc hardness. Again we have a different condition and thus another new lot for testing.
A month later, we take more bars and repeat the heat treating process to the 30 Rc hardness. Again we have a new lot that must be tested since we have gone beyond the applicable rules about being processed together or sequentially.
Testing requirements and the frequency of test are often dependent on lot and amount of material within the lot.
Of course there are more to the rules that affect the definition of lot than the simplified version we shared with you today. Type of metal and ordered specifications are all important.
So for the 148th time, we remind you to…CHECK THE SPECS!!!! Twice
So this is Michael with Michael Talks Metals. Thank you so much for watching. Looking to learn more about what “lot” means in metal? Check the website www.michlinmetals.com for more info. Missed last weeks, click here. Still here and not subscribed, click here. Thanks for watching, see you next week, same time, same place. YouTube, 10am. I’m out.