Grinding burns alter the hardness and mechanical properties of steel components and can result in cracks or failure. Nital etching is widely used in the industry to detect grinding burns, but it poses environmental and safety risks and requires visual detection. Alternative techniques such as magnetic Barkhausen noise inspection have been developed, but automation is hindered by calibration drifts and by the sensor dimensions. Here, we introduce a novel non-destructive approach based on nitrogen-vacancy center in diamond to detect leakage magnetic field from grinding burns. This technology enables quantitative vector magnetic field measurement, is contactless and does not require calibration. Grinding burns with different sizes were successfully detected with a high spatial resolution and sensitivity.