Meaning
Standardized Rockwell C indentation testing assesses thin film adhesion quality on hardened steel substrates through controlled mechanical deformation. Quality control technicians perform the vdi 3198 indentation test to verify physical vapor deposition film bonding before placing coated tooling into service. The test becomes inapplicable when substrate hardness falls below fifty-four Rockwell C due to excessive deformation of underlying steel.
Failure Class Evaluation
Applying a one hundred and fifty kilogram load creates a localized plastic impression that forces thin surface films to deform or fracture. Optical microscopy compares crack patterns and delamination zones surrounding the impression against standardized reference classes designated HF1 through HF6. Categories HF1 and HF2 represent acceptable adhesion with minor radial cracks, whereas categories HF3 through HF6 show severe delamination and film flaking.
Substrate Hardness Requirement
Substrates must provide sufficient mechanical backing to prevent deep plastic sinking that causes artificial coating failure. Insufficient core hardness permits excessive substrate displacement, producing shear stresses that delaminate even well-bonded surface layers. Proper vacuum heat treatment ensures the steel matrix supports thin nitride coatings under high indentation loads.
Quality Control Standard
Rapid visual assessment allows production facilities to verify coating quality on test coupons processed alongside tooling batches. Passing adhesion criteria ensures coated punches withstand high contact stresses during cell casing drawing.
