Differential heat treatment method for forming roller

A differential heat treatment method for a forming roller, the differential heat treatment method comprising:

• an outer circumferential surface heat treatment step (S100) of heating an outer circumferential surface (21) of a roller unit (20) constituting a forming roller (10) such that a heat treatment is performed under a condition of a temperature of 1150 to 1200° C. for 25 to 35 minutes;
• a first natural cooling step (S200) of performing, after the outer circumferential surface heat treatment, natural cooling until a surface temperature reaches 100 to 150° C.;
• an inner circumferential surface heat treatment step (S300) of heating, after the natural cooling, an inner circumferential surface (22) of the roller unit (20) such that a heat treatment is performed under a condition of a temperature of 680 to 730° C. for 35 to 45 minutes;
• a second cooling step (S400) of performing, after the inner circumferential surface heat treatment, natural cooling until the roller unit reaches a room temperature state;
• and
• an inspection and release step (S500) of inspecting, after the second cooling, hardness of the outer circumferential surface and the inner circumferential surface to perform release when the hardness is within an error range.