What is a grinding burn?
A grinding burn is a thermally induced surface defect that occurs during the grinding of hardened steel when excessive heat alters the material’s microstructure. It can reduce hardness, introduce tensile residual stresses, and significantly decrease the lifetime of parts.
These defects may cause premature cracking or rolling contact fatigue, even if no visual damage is visible.
What industries are most concerned by grinding burns?
Grinding burns are a major concern in industries that manufacture precision, heat-treated steel components where surface integrity affects fatigue life and reliability.
The most impacted sectors include:
Industry | Components Concerned by Grinding Burn Risk |
Aerospace | Landing gear components, transmission gears, turbine shafts, high-strength steel structural parts |
Automotive & Powertrain | Gearbox gears, crankshafts, camshafts, transmission shafts, differential gears |
Bearing Industry | Bearing rings, raceways, rolling elements, precision ground shafts |
Gear Manufacturing | Case-hardened gears, carburized gear teeth, precision ground gear flanks |
Energy (Oil & Gas, Power Generation) | Turbine shafts, compressor shafts, pump shafts, rotating equipment components |
Railway | Axles, gearbox gears, wheelset components, bearing assemblies |
Heavy Machinery & Industrial Equipment | Hardened shafts, machine tool spindles, high-load transmission components |
Defense | High-strength mechanical transmission parts, hardened steel drive components |
In general, any industry producing ground, hardened steel parts for high-load or safety-critical applications must control and detect grinding burns.
The critical importance of grinding burn detection is reflected in its formal inclusion within major international and aerospace standards such as SAE AMS 2649 (etch inspection of high-strength steel parts to detect overheating from machining or grinding), and SAE AIR6813 (aerospace technical report on grinding damage in high-strength steel landing gear), underscoring its direct impact on component safety, fatigue performance, and structural integrity.
Why is grinding burn detection challenging in industrial environments?
Grinding burn detection is difficult because many defects are shallow, invisible, and microstructural rather than geometric.
The main challenges are:
1. Chemical inspection limitations (Nital etching)
• Uses hazardous acids
• Operator-dependent
• Alters the surface
• Difficult to automate
2. Magnetic Barkhausen Noise (MBN) limitations
• Too sensitive to stress, grain size, and phase composition
• Requires extensive calibration that can drift along the production
• Difficult to isolate burn signature specifically
3. Weak burn invisibility
• Some burns (<100 µm deep) show no visible discoloration
• May not be reliably detected with standard temper etching
As a result, reliable, automated, non-destructive inspection remains a major challenge in quality control for heat-treated steels.
How does quantum NV-center magnetometry detect grinding burns?
Quantum NV-center magnetometry detects grinding burns by mapping microscopic magnetic fringe fields created by microstructural changes in heat-affected zones.
The technology uses Nitrogen-Vacancy (NV) centers in diamond, atomic-scale defects that act as ultra-sensitive magnetometers. Through Optically Detected Magnetic Resonance (ODMR), the system measures local magnetic field variations with micrometer-scale resolution.
When a steel component is magnetized, burned areas exhibit reduced magnetization compared to unaffected regions. This contrast generates magnetic fringe fields that the NV sensor maps precisely.
Furthermore, our Quantum NV Diamond solution can be combined with additional magnetic methods such as eddy current excitations, using the induced electromagnetic field to enhance the magnetic contrast in heat-affected zones. This hybrid approach makes the detection more robust, particularly on components with complex geometries or shallow burn depths where passive magnetization alone may yield lower signal contrast.
In summary: grinding burns become visible as magnetic field anomalies — and combining NV-center sensing with eddy current excitation can make that detection more reliable and repeatable across a wider range of industrial components.
How does NV magnetometry compare to Nital etching and Magnetic Barkhausen Noise?
Compared to Nital Etching
NV magnetometry:
• Is completely chemical-free
• Does not alter the surface
• Can be automated and implemented in-line
• Is safer for operators
Nital etching:
• Uses corrosive acids, posing handling and safety risks
• Requires removal of protective coatings (e.g. oil films) prior to etching, creating corrosion risks such as pitting on exposed surfaces
• Time-consuming process, with inline production integration
• Requires highly trained inspectors for reliable interpretation of results
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Compared to Magnetic Barkhausen Noise (MBN)
NV magnetometry:
• Measures absolute magnetic field values
• Provides vectorial and quantitative mapping
• Offers spatial resolution below 100 µm
• Enables defect severity classification
• Miniaturized probe to access complex geometry
MBN:
• Is sensitive to multiple material variables
• Often requires calibration for each material batch
• Has lower spatial resolution
• Requires dedicated probes to be fit in all geometries
Is prior magnetization required before inspection?
Yes, controlled magnetization is required to maximize detection sensitivity.
At KWAN-TEK, we have established that as low as approximately 20 mT is typically sufficient to reveal even weak grinding burns. This is made possible by the exceptional sensitivity of our Quantum NV Diamond technology, which can detect the subtle magnetic field variations generated at such low magnetization levels — where conventional methods would struggle.
Operating at such low field strengths brings significant practical advantages: it makes the solution more portable, easier to deploy in industrial environments, and considerably less energy-consuming compared to inspection systems requiring high magnetization levels.
Magnetization aligns the material’s magnetic domains, creating contrast between burned and unaffected regions. Without controlled magnetization, residual magnetic history may mask defect signatures.
Why does magnetization direction matter?
Grinding burn detection is anisotropic, meaning detectability depends on the orientation of magnetization relative to the defect.
Burns are detectable when the magnetization contains a component perpendicular to their main axis. For complete inspection coverage, it is recommended to rotate the magnetization direction, apply it at approximately 45°, and perform multi-directional scans — ensuring both longitudinal and transverse defects are revealed.
What is the optimal lift-off distance between the sensor and the part?
For high-contrast, quantitative detection, a lift-off distance below 300 µm is recommended.
At this distance:
• Signal-to-noise ratio can exceed 50
• Defect quantification is reliable
• Spatial resolution remains high
Detection is still possible up to 500 µm, but signal amplitude decreases and spatial spreading reduces measurement precision.
This makes controlled lift-off important for inline industrial inspection.
Can NV magnetometry detect weak grinding burns?
Yes. NV technology can detect weak grinding burns with minimal microstructural alteration, including defects subsurface.
These shallow burns:
• May not show visible discoloration
• Are often difficult to detect using temper etching
• Can still reduce fatigue performance
High magnetic sensitivity enables reliable identification of these subtle heat-affected zones.
Can quantum magnetometry detect other defects in steel components?
Yes. NV magnetometry is a multi-modal magnetic sensing technique capable of detecting multiple defect types.
In addition to grinding burns, it can detect cracks, inclusions, and corrosion. It is also a promising tool for characterizing thermomechanical treatments, such as detecting residual white layers in nitriding or measuring the depth of case-hardening.
This makes it a versatile tool for non-destructive testing (NDT) in numerous industries such as aerospace, transportation and energy production, machining and manufacturing, nuclear.
Is NV magnetometry suitable for complex geometries?
Yes. Fibered endoscopic NV probes allow inspection of confined or complex geometries.
This enables access to:
• Gear tooth flanks
• Internal splines
• Turbine components
• Nuclear industry parts
Because the signal is transported optically through fiber, the system is immune to electromagnetic interference and suitable for harsh environments. Besides, the NV quantum works under high temperature or radiation.
Is NV magnetometry compatible with automated industrial inspection?
Yes. The method is:
• Contactless
• Chemical-free
• Non-destructive
• Quantitative
These characteristics make it suitable for integration into automated quality control systems and inline inspection workflows.
Unlike etching-based methods, it does not require surface preparation beyond controlled magnetization.
Is NV magnetometry compatible with artificial intelligence?
Yes, Quantum NV Diamond magnetometry and artificial intelligence are highly complementary technologies.
The NV sensor produces high-resolution, quantitative magnetic field maps with micrometer-scale precision. This structured, spatially rich data is ideally suited for AI-based analysis, particularly deep learning models trained to recognize the magnetic signatures of grinding burns and distinguish them from benign magnetic variations or noise. This combination of Quantum NV sensing and AI makes it possible to fully automate the entire detection and decision chain