Investigation of Austempering Effect on Fatigue Crack Growth of AISI 4140 Steel

Defect and Diffusion Forum Pub Date : 2024-02-06 DOI:10.4028/p-5jjqqo

M. Badaruddin, Reza Annisa Ainnayah, Rizqy Nurully Wijaya, Slamet Sumardi

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Abstract

The compact tension (CT) and tensile specimens of the AISI 4140 steel in cold rolling condition (untreated steel) were austempered by immersing it into the salt bath at 362°C for 60 minutes. The tensile strength properties and the fatigue crack growth (FCG) resistance were performed to investigate the effect of the austempering process in AISI 4140 steel. A significant increase in the yield strength for austempered steel is about 8.7 % and the elastic strain energy increases by 55.7 %. Austempered steel's fatigue crack cycle is longer than that of untreated steel. Data of stress intensity factor range (ΔK, MPa.m1/2) and FCG rate (da/dN, m/cycle) was constructed in double log plot x-y axes for determining the materials constants m and C according to Paris’s law equation using a linear regression method. From the curve of ΔK versus da/dN, the constant m value for austempered steel (m = 3.45) shows better resistance than untreated steel (m = 3.77). On the other hand, the constant C value of 1.409×10-12 for austempered steel is one order magnitude higher than that of untreated steel (C = 4.151×10-13). The resistance of austempered steel against fatigue crack growth can be attributed to the formation of a bainite structure.

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奥氏体化对 AISI 4140 钢疲劳裂纹生长影响的研究

将冷轧状态下的 AISI 4140 钢（未处理钢）浸入 362°C 盐浴中 60 分钟，对其进行奥氏体化处理，以获得紧凑拉伸 (CT) 和拉伸试样。为了研究奥氏体化工艺对 AISI 4140 钢的影响，对其拉伸强度性能和抗疲劳裂纹生长（FCG）性能进行了测试。奥氏体回火钢的屈服强度大幅提高了约 8.7%，弹性应变能增加了 55.7%。奥氏体回火钢的疲劳开裂周期比未处理钢长。应力强度因子范围（ΔK，MPa.m1/2）和 FCG 率（da/dN，m/周期）的数据在双对数图 x-y 轴上构建，以便根据帕里斯定律方程，采用线性回归方法确定材料常数 m 和 C。从 ΔK 与 da/dN 的关系曲线来看，奥氏体回火钢的常数 m 值（m = 3.45）比未经处理的钢（m = 3.77）显示出更好的抗性。另一方面，奥氏体回火钢的常数 C 值为 1.409×10-12，比未经处理的钢（C = 4.151×10-13）高一个数量级。奥氏体回火钢对疲劳裂纹生长的抵抗力可归因于贝氏体结构的形成。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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Defect and Diffusion Forum

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