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SAE ARP4462 91st Edition, January 1, 1991
Barkhausen Noise Inspection for Detecting Grinding Burns in High Strength
Steel Parts
Description / Abstract:
Purpose:
This recommended practice covers the procedures and method for establishing acceptance criteria when performing Barkhausen noise testing of surface-hardened steel components to detect grinding burns (metallurg damage caused by over-heating) in bare or chromium-plated parts.
Application:
Primarily for nondestructive testing of heat treated, high strength low-alloy steel parts which have been ground, in accordance with MIL-STD-866 or commercial standard, before or after chromium plating. This test method may be used as an independent test or to confirm grinding damage detected in accordance with AMS-2440 or MIL-STD-867 in bare or chromium plated components.
This test method may be used to find grinding burns in finish ground parts, provided that the parts have no defects due to earlier manufacturing processes. If the parts have defects before grinding, this method will show the presence of these defects in addition to grinding burns, unless they are removed by grinding or other method. Such defects include soft spots and edges due to defective heat treatment, decarburization, stress variations due to cooling rate changes, etc.
This test method is not applicable for parts which have a plated metal, ferromagnetic deposit between the substrate and chromium plating.
Principle of Measurement:
The method used in this test is based on inductively detecting Barkhausen noise in ferromagnetic materials. The noise is generated by the abrupt movements of magnetic domain walls. The walls can be forced to move by application of an alternating magnetic field. When art alternating current coil is placed near the sample, the resulting change in magnetization will induce an electrical pulse in the coil. When the electrical pulses produced by all domain movements are added together in a bulk sample, a noise-like signal called Barkhausen noise is generated.
Two important material characteristics will affect the intensity of Barkhausen noise signal. One is the presence and distribution of elastic stresses. The other is metallurgical microstructure, often related hardness. A low intensity Barkhausen signal is generated in hard the materials and a high intensity signal in soft ones. In grinding burns, residual stress and microstructural changes are generally present. Grinding burns may result from retempering when the original tempered martensite has been exposed to further heat, resulting in a loss of hardness and compressive residual stress. Rehardening may occur due to transformation of ferrite to austenite from excessive local heating.
This recommended practice covers the procedures and method for establishing acceptance criteria when performing Barkhausen noise testing of surface-hardened steel components to detect grinding burns (metallurg damage caused by over-heating) in bare or chromium-plated parts.
Application:
Primarily for nondestructive testing of heat treated, high strength low-alloy steel parts which have been ground, in accordance with MIL-STD-866 or commercial standard, before or after chromium plating. This test method may be used as an independent test or to confirm grinding damage detected in accordance with AMS-2440 or MIL-STD-867 in bare or chromium plated components.
This test method may be used to find grinding burns in finish ground parts, provided that the parts have no defects due to earlier manufacturing processes. If the parts have defects before grinding, this method will show the presence of these defects in addition to grinding burns, unless they are removed by grinding or other method. Such defects include soft spots and edges due to defective heat treatment, decarburization, stress variations due to cooling rate changes, etc.
This test method is not applicable for parts which have a plated metal, ferromagnetic deposit between the substrate and chromium plating.
Principle of Measurement:
The method used in this test is based on inductively detecting Barkhausen noise in ferromagnetic materials. The noise is generated by the abrupt movements of magnetic domain walls. The walls can be forced to move by application of an alternating magnetic field. When art alternating current coil is placed near the sample, the resulting change in magnetization will induce an electrical pulse in the coil. When the electrical pulses produced by all domain movements are added together in a bulk sample, a noise-like signal called Barkhausen noise is generated.
Two important material characteristics will affect the intensity of Barkhausen noise signal. One is the presence and distribution of elastic stresses. The other is metallurgical microstructure, often related hardness. A low intensity Barkhausen signal is generated in hard the materials and a high intensity signal in soft ones. In grinding burns, residual stress and microstructural changes are generally present. Grinding burns may result from retempering when the original tempered martensite has been exposed to further heat, resulting in a loss of hardness and compressive residual stress. Rehardening may occur due to transformation of ferrite to austenite from excessive local heating.
SAE ARP4462 91st Edition, January 1, 1991
Barkhausen Noise Inspection for Detecting Grinding Burns in High Strength
Steel Parts