When using the residual method of applying particles, which factor affects the residual magnetic field strength of the part?

The residual magnetic field strength of a part is primarily influenced by its retentivity, which is the ability of a material to retain magnetization after the external magnetic field is removed. In magnetic particle testing, particularly when using the residual method, the retentivity of the material determines how effectively it can hold onto the magnetic field created during the test.

Materials with high retentivity are particularly effective in retaining a strong residual magnetic field, which enhances the visibility and effectiveness of any surface or near-surface flaws detected using magnetic particles. Thus, when the magnetic field is applied to the part, a material with good retentivity will ensure that the magnetic field remains strong enough to attract the particles toward any defects present.

While factors such as the size of the part, environmental temperature, and application time can influence the overall effectiveness of the test, it is the intrinsic property of retentivity that directly affects the residual magnetic field strength after the magnetic field is applied.