What effects does shot peening have on the properties of austenitic stainless steel

What effects does shot peening have on the properties of austenitic stainless steel? 

The influence of shot peening strengthening on the properties of austenitic stainless steel mainly manifests in multiple dimensions such as mechanics, surface and corrosion resistance. The details are as follows:

1. Mechanical performance optimization

Significant improvement in fatigue strength: Residual compressive stress of -800 to -1200 MPa is introduced on the surface, which inhibits the initiation of fatigue cracks. The fatigue life of 304 stainless steel can be extended by 2 times, and the fatigue strength can be increased by 30% to 50%.

Hardness and wear resistance are enhanced: The hardness of the surface increases from HV200 to HV300 to 400 due to work hardening, and the wear resistance is improved by 1 to 3 times, suitable for wear-resistant parts such as pump shafts and valves. 

II. Surface Performance Improvement

Controllable surface roughness adjustment: By controlling the particle size (0.1 - 2.0mm) of the projectiles, the surface roughness Ra can be adjusted within the range of 0.5 - 5.0μm, balancing the requirements for friction reduction and anti-adhesion wear (for example, when Ra = 1.0μm, the friction coefficient decreases by 20%).

Enhanced passivation film performance: The induced lattice distortion by shot peening promotes the diffusion of Cr elements, resulting in an increase of 30% in the thickness of the passivation film and an increase of more than 500 hours in the corrosion resistance time of the neutral salt spray test. 

III. Corrosion Resistance and Stress Corrosion Prevention

Stress Corrosion Cracking (SCC) inhibition: In an environment with Cl⁻, compressive stress can counteract 60% to 80% of tensile stress, reducing the risk of SCC. For example, the service life of seawater heat exchanger tubes has been extended by 3 times.

Electrochemical corrosion resistance improvement: The density of the passivation film increases, and the corrosion potential of 316L stainless steel in acidic medium shifts positively by 100 to 200 mV, and the corrosion current density decreases by 40%. 

IV. Process Compatibility and Function Expansion

Non-thermal processing advantages: Room temperature treatment does not alter the matrix structure, avoiding deformation during heat treatment (deformation of thin-walled parts <0.05mm), suitable for precision parts.

Enhanced coating adhesion: Rough surfaces provide mechanical anchoring for PVD/CVD coatings, the adhesion of TiN coatings increases from 50N to 120N, improving the composite protection performance. 

Typical data comparison (taking 304 stainless steel as an example)

Fatigue strength (MPa)

Untreated: 200

After shot peening treatment: 280 - 300

Improvement rate: 40% - 50% 

Surface hardness (HV)

Untreated: 200

After shot peening treatment: 320 - 350

Improvement rate: 60% - 75% 

Salt spray test (h)

Untreated: 500

After shot peening treatment: >1000

Increase rate: >100% 

Coefficient of friction

Untreated: 0.6

After shot peening treatment: 0.48

Improvement percentage: 20% 

In conclusion, shot peening strengthening achieves the synergistic improvement of multiple properties of austenitic stainless steel through physical metallurgical methods, significantly expanding its service range in fields such as aerospace and petrochemicals.