Effect of Peening Treatment on Grain Refinement and Fatigue Strength Improvement of Aged Steel

Why It Matters

The findings prove that legacy steel structures can be rejuvenated with surface engineering, offering a cost‑effective path to extend bridge service life and reduce replacement demand.

Key Takeaways

• Peening refines grains up to compressive stress depth
• Refinement depth varies with original grain size
• Surface hardness rises after peening aged steel
• Fatigue strength matches that of conventional steel
• Excessive peening intensity can over‑soften aged steel

Pulse Analysis

Aging infrastructure, particularly historic bridges, presents a mounting challenge for owners seeking to balance safety with budget constraints. Peening—a mechanical surface‑treatment that imparts compressive residual stress—has long been used on new steel to improve fatigue resistance, but its applicability to century‑old alloys remained uncertain. By extracting steel plates from demolished bridges and applying controlled peening, researchers could directly assess how decades‑old microstructures respond to modern retrofitting techniques.

The study’s metallographic analysis showed that grain refinement progresses alongside the compressive stress front, yet the extent of refinement is tightly linked to the steel’s original grain size. Near‑surface Vickers hardness measurements confirmed a measurable increase, indicating that the treated layer becomes more resistant to deformation. Fatigue testing under a low stress ratio (R≈0.1) revealed that the aged steels achieved fatigue life improvements on par with contemporary grades, validating peening’s efficacy even after a century of service. However, fracture‑surface examinations warned that the peening intensity calibrated for fresh steel can be too aggressive for older alloys, potentially causing grain loosening and diminished performance.

For engineers and asset managers, these insights translate into actionable guidance: peening can be incorporated into bridge rehabilitation programs, but intensity parameters must be recalibrated for legacy materials. Tailoring the treatment reduces the risk of over‑softening while still delivering the desired fatigue gains. As infrastructure renewal budgets tighten, such nuanced application of proven technologies offers a pragmatic route to extend the lifespan of existing steel structures, supporting both safety objectives and fiscal responsibility.