Abstract: Nitriding size change characteristics of the age-hardened steel were investigated and compared with the quenched and tempered steel. The results show that the nitriding size change of the age-hardened steel is slightly little bigger than that of the quenched and tempered steel which is related to the superposition effect of nitriding hardening and matrix age hardening of age hardening steel. Reasonable use of this superposition effect by pre-aging before nitriding can achieve nitriding layer strengthening while achieving control of the size change of nitriding parts. After pre-aging at 630-650 ℃ for 4 h and plasma nitriding at 520 ℃ for 40 h, the nitriding radial dimension increment of the 20CrNi3Mn2Al age-hardened steel gear sample is 0.056 mm and the deformation rate is 0.03%, which is similar to the quenched and tempered 42CrMo steel (radial size increment is 0.043 mm, deformation ratio is 0.021%).

Key words: age-hardening, age-hardened steel, size change, dimensional stability