An apparatus for magnetic induction hardening of an annular workpiece, the apparatus comprising: a magnetic tool (14, 14', 14", 14"', 14"") having a body portion (54, 54', 54", 54"', 54"") formed of a generally non-magnetic material, the body portion (54, 54', 54", 54"', 54"") having a surface (58, 58', 58", 58"', 58"") configured to be positioned in close proximity to the annular workpiece being hardened, the surface (58, 58', 58", 58"', 58"") of the body portion (54, 54', 54", 54"', 54"") being a radially outwardly-facing circumferential surface configured for induction hardening an inner surface of the annular workpiece; and a magnetic arrangement (62, 62', 474) coupled to the body portion (54, 54', 54", 54"', 54"") at or adjacent the surface (58, 58', 58", 58"', 58"") of the body portion (54, 54', 54", 54"', 54"") and configured to provide regions of alternating polarity; a workpiece holder (18, 18') configured to support the annular workpiece in close proximity to the surface (58, 58', 58", 58"', 58"") of the magnetic tool (14, 14', 14", 14"', 14"") such that the radially outwardly-facing circumferential surface of the magnetic arrangement (62, 62') is adjacent the inner surface of the annular workpiece; a drive arrangement for rotating the magnetic tool (14, 14', 14", 14"', 14"") relative to the workpiece holder (18, 18') about an axis of rotation to induce heating of the annular workpiece to achieve a temperature in the austenitic range of the annular workpiece for hardening of the annular workpiece through a microstructural transformation. a magnetic tool (14, 14', 14", 14"', 14"") having a body portion (54, 54', 54", 54"', 54"") formed of a generally non-magnetic material, the body portion (54, 54', 54", 54"', 54"") having a surface (58, 58', 58", 58"', 58"") configured to be positioned in close proximity to the annular workpiece being hardened, the surface (58, 58', 58", 58"', 58"") of the body portion (54, 54', 54", 54"', 54"") being a radially outwardly-facing circumferential surface configured for induction hardening an inner surface of the annular workpiece; and a magnetic arrangement (62, 62', 474) coupled to the body portion (54, 54', 54", 54"', 54"") at or adjacent the surface (58, 58', 58", 58"', 58"") of the body portion (54, 54', 54", 54"', 54"") and configured to provide regions of alternating polarity; a body portion (54, 54', 54", 54"', 54"") formed of a generally non-magnetic material, the body portion (54, 54', 54", 54"', 54"") having a surface (58, 58', 58", 58"', 58"") configured to be positioned in close proximity to the annular workpiece being hardened, the surface (58, 58', 58", 58"', 58"") of the body portion (54, 54', 54", 54"', 54"") being a radially outwardly-facing circumferential surface configured for induction hardening an inner surface of the annular workpiece; and a magnetic arrangement (62, 62', 474) coupled to the body portion (54, 54', 54", 54"', 54"") at or adjacent the surface (58, 58', 58", 58"', 58"") of the body portion (54, 54', 54", 54"', 54"") and configured to provide regions of alternating polarity; a workpiece holder (18, 18') configured to support the annular workpiece in close proximity to the surface (58, 58', 58", 58"', 58"") of the magnetic tool (14, 14', 14", 14"', 14"") such that the radially outwardly-facing circumferential surface of the magnetic arrangement (62, 62') is adjacent the inner surface of the annular workpiece; a drive arrangement for rotating the magnetic tool (14, 14', 14", 14"', 14"") relative to the workpiece holder (18, 18') about an axis of rotation to induce heating of the annular workpiece to achieve a temperature in the austenitic range of the annular workpiece for hardening of the annular workpiece through a microstructural transformation.