Effects of Deep Rolling on the Microstructure Modification and Fatigue Life of 35Cr2Ni4MoA Bolt Threads

Abstract

Stress concentration on a bolt thread, resulting from its own special shape, poses a threat to the fatigue strength of the bolt, which directly affects the safety and reliability of aircraft. In this paper, deep rolling was applied to a bolt thread to improve its fatigue resistance. The properties of the plastic deformation layer, including the surface morphology, microstructure, hardness, and residual stress, as well as the fatigue life of the bolt, were characterized by means of SEM, white light interferometer, EBSD, and fatigue tests. The results showed that the surface roughness of the bottom of the thread was reduced to 0.255 μm, and a plastic deformation layer of about 300 μm in depth was formed after rolling. A more compact streamlined fibrous microstructure, composed of refined grains, with increased dislocation density and hardness and decreased tensile residual stress, was formed in the plastic deformation layer. The fatigue life of the bolts after rolling increased by about 113%, evidencing the comprehensive result of these microstructure modifications.

Modification of the surface integrity of powder metallurgically produced S390 via deep rolling

“…The local forming of the surface-near edge zone leads to a smoothing of the roughness peaks, induction of residual compressive stresses and strain hardening. These edge zone properties have proven a positive effect on the fatigue strength of components [6].…”

Deep Rolling Techniques: A Comprehensive Review of Process Parameters and Impacts on the Material Properties of Commercial Steels

“…The bulk of the studies pertaining to DR were on standard test specimens or similar components because of the obvious limitations of tooling and experimentation for application prototypes. Nevertheless, there are satisfactory efforts available on DR of components such as turbine/compressor blades [104][105][106], aircraft structural components [8,21], axels [107][108][109], shafts [110,111], crankshafts [112][113][114], tension bolts [115], high-strength fasteners and threaded parts [116,117], connecting rod screws [118], torsion bars [119,120], gear tooth [83], roller and thrust bearing race/rings [78,96,121], welded joints [122][123][124][125][126], blanking punch fillets [22], hip implants [26,27], etc. When deep-rolled, all these applications exhibited significant improvement in fatigue performance, which was attributed to substantial strain hardening, higher magnitude and deeper penetration of CRS, tailored surface region microstructure, and increased boundary layer hardness along with an improved surface finish.…”

Optimization of Bolted Joints: A Literature Review

“…Furthermore, a deep rolling process can modify the microstructure at the thread interface, thus enhancing the fatigue life of a bolted joint (Figure 12). After rolling, the fatigue life of the fasteners increased by approximately 113%, demonstrating the comprehensive effect of these microstructure modifications [51]. Optimization of a thread root undercut in the roller of the planetary roller screw using FEM was performed.…”