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In metallurgy, peening is the process of working a metal's surface to improve its material properties, usually by mechanical means, such as hammer blows, by blasting with shot (shot peening), focusing light (laser peening), or in recent years, with water column impacts (water jet peening) and cavitation jets (cavitation peening). [1]
The thermal method involves changing the temperature of the entire part uniformly, either through heating or cooling. When parts are heated for stress relief, the process may also be known as stress relief bake. [13] Cooling parts for stress relief is known as cryogenic stress relief and is relatively uncommon. [citation needed]
This technique is part of the High Frequency Mechanical Impact (HFMI) processes. Other acronyms are also equivalent: Ultrasonic Needle Peening (UNP), Ultrasonic Peening (UP). Ultrasonic impact treatment can result in controlled residual compressive stress, grain refinement and grain size reduction.
The stress relief treatment resulted in 47% growth of the original, large peak, while it shifted to the left 28-RPM (less than 0.75%). Figure 5: Vibratory Stress Relief was performed on this mild steel weldment weighing almost 12 tons. Overall size was 17' × 15' × 2' (≈ 5.2 × 5.6 × 0.6 meters).
Shot peening is a cold working process used to produce a compressive residual stress layer and modify the mechanical properties of metals and composites. It entails striking a surface with shot (round metallic, glass, or ceramic particles) with force sufficient to create plastic deformation .
Laser peening (LP), or laser shock peening (LSP), is a surface engineering process used to impart beneficial residual stresses in materials. The deep, high-magnitude compressive residual stresses induced by laser peening increase the resistance of materials to surface-related failures, such as fatigue, fretting fatigue, and stress corrosion cracking.
The need for PWHT is mostly due to the residual stresses and micro-structural changes that occur after welding has been completed. [2] During the welding process, a high temperature gradient is experienced between the weld metal and the parent material. As the weld cools, residual stress is formed. [2]
Hot pressure welding: HPW Metals are pressed together at elevated temperatures below the melting point in vacuum or an inert gas atmosphere Aerospace components Hot isostatic pressure welding: 47: HPW A hot inert gas applies the pressure inside a pressure vessel, i.e. an autoclave: Aerospace components Roll welding: ROW