Review slewing bearing raceway induction hardening through material, surface hardness, effective case depth, soft-zone control and traceable inspection.
Slewing bearing raceways need a hard wear-resistant contact layer supported by a tougher ring core. Induction hardening creates that combination by heating and quenching a controlled path around the raceway. Quality cannot be represented by one surface hardness reading because depth, pattern, transition zones, material condition and tempering all affect performance.
An engineering drawing should define the applicable material and heat-treatment requirements, while the inspection plan explains how production evidence is collected. This guide describes the records buyers and engineers should review without prescribing one hardness range for every bearing design.
Start with material and pre-heat-treatment condition
The ring material must provide chemical composition, cleanliness and hardenability suitable for the required raceway section. Review the material grade, delivery condition, heat number and mechanical properties against the approved specification. Traceability should connect the finished serial number to the original heat and any intermediate heat-treatment batch.
Ring forging, rolling, normalizing or quench-and-temper history influences the core that supports the hardened layer. Material substitution cannot be approved from a similar carbon percentage alone. Section size, alloy content, impact requirements, welding restrictions and later machining all belong in the review.
Surface hardness is only the first measurement
Surface readings confirm that the raceway reached and retained the specified hardness at defined locations. The report should identify the instrument, method, calibration, measurement positions and acceptance range. Readings taken on an unprepared curved surface or at undocumented points are difficult to compare.
A high reading does not prove adequate depth, and excessive hardness may reduce toughness or increase cracking risk. Tempering and residual-stress control must match the manufacturing procedure. Review abnormal scatter around the circumference rather than accepting an average that hides a local low or high sector.
Effective case depth supports the contact stress field
Effective case depth is determined using the threshold and test method defined by the drawing or applicable specification. A cut section or qualified process evidence is generally required because portable surface testing cannot reveal the subsurface profile. The sample location should represent the raceway and include enough information to relate it to the induction path.
Depth must be evaluated together with roller or ball size, raceway geometry and load. A shallow hard layer can place maximum shear stress in softer material, while an unnecessarily deep layer increases manufacturing risk and cost. Engineering defines the target; production qualification demonstrates the process can achieve it consistently.
Control the induction start-stop and soft zone
A circular scanning process has a start-stop transition where the hardened path overlaps or terminates. The approved design controls this region and often marks its position so it can be placed away from the principal load zone when required. The location, width and hardness transition should be documented rather than hidden by an average report.
Inspect for grinding burn, surface cracks, decarburization and geometry change after heat treatment. Magnetic particle or another specified nondestructive test may be part of the control plan. Raceway finish and profile inspection follow final grinding because correct metallurgy with incorrect geometry still produces poor load distribution.
- Material certificate linked to ring heat and serial number.
- Surface hardness map with positions and calibrated method.
- Effective case-depth evidence and qualified sampling plan.
- Soft-zone or transition-zone location and acceptance.
- Crack inspection, final raceway geometry and process release.
How to review a supplier report
Compare every result with the drawing revision and inspection plan, not with an undocumented shop standard. Confirm units, acceptance range, sample identity, date and responsible inspector. The broader inspection report guide shows how hardness records fit with dimensional, gear and assembly evidence.
If field damage is under review, do not treat hardness alone as root-cause proof. Correlate metallurgy with load, lubrication, contamination and mounting evidence described in the raceway spalling analysis guide.
FAQ
Is one hardness reading enough?
No. Position, circumferential consistency, case depth, transition zones and core support also matter.
Can case depth be measured with a portable hardness tester?
Surface testing alone cannot establish the subsurface hardness profile. Use the specified qualified method.
Does compliant hardness prove the bearing cannot spall?
No. Load, lubrication, contamination and mounting conditions remain essential.
Engineering references
For a drawing-based review, send MERYDOM the application, load cases, dimensions and required documentation. Final selection and service instructions must follow the approved drawing and equipment manufacturer requirements.