Hardness and microstructure testing are very important to verify the process. The industry has moved more toward controlling key process variables to reduce the amount of cut product or coupons. Of course, dimensional control is vital, and statistically based testing is a must. Special attributes are typically verified, and critical applications get a lot of attention.
Nondestructive evaluation (NDE/NDT) is a significant part of the modern bearing process. NDE includes eddy current for cracks, microstructure, case depth, and hardness; ultrasonic testing (UT) on key applications for inclusions, porosity and internal cracking; magnetic particle testing (MPI) for surface and near-surface cracks; automated case-depth verification; grinding-injury detection; and vision systems. These are just some examples of tools in use.
Traceability is extremely important to bearings, especially for those in key applications like aerospace, high-speed trains and automotive. Traceability is very important for expensive applications such as wind or large, hard-to-replace gearboxes. It is in the best interest of a heat treater to maintain good traceability and records because exposure is minimized if there is an issue or question about a batch. Take photos of loading techniques and final loads. Many bearings are serialized at the end of the process by chemical etching or laser marking, and heat-treat records become part of the batch traceability information for reference.