What is peening and how does it improve fatigue resistance?

What is metal peening?

What is the purpose of metal peening? The peening definition is that it is a technique to introduce compressive stresses in the material’s surface. The peening process can be performed mechanically or by laser. These compressive stresses give a safety margin against cracks and corrosion when the steel is exposed to tensile loads or high cycle fatigue environments during operation. 

Where is peening used?

Surface peening is a common way to ensure a long and productive life for all kinds of steel components. Gears, screws, crankshafts, cams are some examples of applications that experience tensile stresses in operation and benefit from metal peening.

What peening process do you prefer?

Laser peening

Laser peening works by a laser pulse that creates a pressure wave which penetrates deep into the metal. This causes compressive residual stresses in the steel, counteracting tensile stresses that lead to corrosion, fatigue and cracking. Laser peening is a cold process which can penetrate the steel down to a depth of 10-12 mm. 

Shot peening

In shot peening, spherical metallic, glass, or ceramic particles are struck against the steel surface with enough energy to cause plastic deformation. The compressed surface of the peened metal improves fatigue resistance and reduces the risk for propagation of microcracks in the surface. 

Hammer peening

Hammer peening is similar to shot peening in the sense that it is a cold mechanical process that stretches the steel’s surface, thereby inducing residual compressive stresses. Hammer peening uses a ball-shaped punch which strikes the surface of the steel part at high frequency while being moved laterally. Every stroke creates a desired deformation, increasing the part’s resistance to corrosion and fatigue failure.

Other types of surface treatment

Surface etching

Chemical or photo etching are two terms used to describe the surface etching of metal. It is a kind of subtractive metal machining that changes the surface structure of a steel part using chemistry. One example of surface etching is when making steel molds for automobile interior panels.

Gas nitriding

Gas nitrided steel gets a harder surface and also usually becomes more resistant to corrosion. Gas nitriding is performed at a relatively low temperature, typically 520 °C. It works by diffusing nitrogen into the steel from a nitrogen-rich gas. The gas is usually ammonia (NH3). This method can also be called ammonia nitriding. 

Laser hardening

Laser hardening uses a laser beam to heat up the steel’s surface close to its melting point, typically 900-1400 °C. This changes the grain to an austenitic structure. Rapid cooling transforms the grain to a martensitic structure. The martensite zone can be as deep as 2 mm, improving the steel’s hardness and resistance to wear.

Toolox® is the right choice for peening

Toolox® is a prehardened and exceptionally clean tool steel with high fatigue resistance also in its original form. The peening process will improve the fatigue resistance even further. Toolox® is a highly versatile tool steel with excellent properties for high-performing machine components, molds, dies and stamping tools.