IWPDF2023

Effect of Static Strain Aging of AISI 4140 steel after Flow Forming

T. Özbay 1 , ∗ , A. Karakaş 1 , T. Yalçinkaya 2

1 Repkon Machine and Tool Industry and Trade Inc., 34980 Şile, Istanbul, Türkiye 2 Department of Aerospace Engineering, Middle East Technical University Ankara 06800, Türkiye

∗ talha.ozbay@repkon.com.tr

Keywords: AISI 4140, static strain aging, flowforming

The phenomenon of static strain aging can be described as a process where materials, after being pre-deformed, exhibit a new yield point when held at room temperature or higher temperatures. This process, resulting from the restriction of dislocation movements by solute atoms, can alter the mechanical properties of the material. The efficiency of the aging process is directly related to temperature and time. Adequate time and temperature are required for adequate aging. In this study, the changes in the mechanical properties of AISI 4140 steel due to the mechanism of static strain aging were investigated and analyzed. The AISI 4140 parts were first reduced by 50% using the flowforming process then were aged at 200 ° C, 250 ° C, and 300 ° C for 2 and 4 hours each, respectively. The yield strength of the pre-deformed material before aging is 1200Mpa and the elongation is around 7%. Tensile tests were conducted on the aged specimens to examine their mechanical properties. The yield strengths at 200 ° C, 250 ° C and 300 ° C were measured around 1250 Mpa, 1350 Mpa and 1400 Mpa, and the elongation values were measured as 6.7%, 6.5% and 5.5%, respectively. According to the results, it was observed that yield strengths of aged specimens at which 250 and 300C temperatures increased, but as for aged specimens at which 250C, it did not exhibit yield strength increasing, because of insufficient temperature for activation energy of interstitial atoms which block dislocation motions. References [1] Mojtaba, M. A. (2015). Static strain aging in low carbon ferrite-pearlite steel: forward and reverse loading (Doctoral dissertation, University of British Columbia). [2] Baird, J.D., Strain Ageing of Steel-a Critical review. Iron and Steel, (36), pp.186–192, 1963

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