What are the differences between shot peening of austenitic stainless steel and ordinary shot peenin

What are the differences between shot peening of austenitic stainless steel and ordinary shot peening? 

The core difference between shot peening of austenitic stainless steel and ordinary shot peening

1. Material characteristic adaptation difference

Shot peening of austenitic stainless steel

Material microstructure characteristics: face-centered cubic structure (austenite), high work hardening rate (ΔHV ≥ 80)

Tempering temperature range: need to avoid 450-850℃ (to prevent intergranular corrosion), shot peening temperature ≤ 60℃

Passivation film characteristics: contains Cr₂O₃ passivation film, after shot peening, the passivation needs to be reformed (to enhance corrosion resistance) 

Common material shot peening (such as carbon steel, aluminum alloy)

Material microstructure characteristics: Body-centered cubic (for carbon steel) or close-packed hexagonal (for aluminum alloy), with a relatively low hardening rate

Annealing temperature range: No annealing risk, allows higher shot peening temperature (≤150℃)

Passivation film characteristics: No passivation film or only Fe₃O₄ oxide layer, no additional passivation required after shot peening 

II. Differences in Process Parameter Control

Selection of Projectile Material

Austenitic steel: Preferentially use stainless steel balls (HV300-400) or glass beads to avoid contamination by carbon steel balls (which can cause electrochemical corrosion).

Common materials: Carbon steel balls or cast iron balls can be used, with lower costs. 

Pressure and Coverage

Austenitic steel: Pressure 0.3 - 0.5 MPa, requires 100% coverage rate (to prevent local stress concentration), and the shot peening time is extended by 15% - 20%.

Common materials: Pressure 0.2 - 0.6 MPa, coverage rate ≥ 80% is sufficient, and the process tolerance is higher. 

Temperature control

Austenitic steel: The shot peening process requires water cooling for temperature reduction (≤ 60℃) to prevent excessive work hardening that leads to a decrease in plasticity (elongation needs to be ≥ 35%).

Common materials: Generally, temperature control is not required, and the temperature rise is allowed to be ≤ 100℃. 

III. Performance Enhancement Focus Differences

Austenitic Steel Shot Peening

Core Objective: Simultaneously enhance corrosion resistance (reconstruction of the passive film) and mechanical properties (compressive stress layer).

Typical Data: After shot peening of 316L, no pitting corrosion was observed in the salt spray test (5% NaCl) for 500 hours, and the fatigue strength increased by 40%. 

Common material shot peening

Core objective: Mainly for mechanical strengthening (for example, the fatigue limit of carbon steel increases by 20%-30% after shot peening), with insignificant improvement in corrosion resistance. 

IV. Post-treatment Process Differences

Austenitic Steel

Must undergo passivation treatment (such as nitric acid passivation), repair the passivation film damaged by shot blasting, and the Cr⁶⁺ content should be ≤ 0.1mg/L (in accordance with ASTM A967 standard).

Electrolytic polishing can be superimposed (Ra reduced to below 0.4μm), further enhancing the cleanliness (suitable for the pharmaceutical industry). 

Common materials

Generally, no passivation is required; only rust prevention treatment (such as oil coating) is needed, which is less costly. 

V. Application Differences

Application of Austenitic Shot Peening Tubes

Chemical Corrosion Prevention: Desalination pipelines, acid and alkali medium transportation

Food and Medicine: Sterile fluid pipelines (with Ra ≤ 0.8 μm)

High-end Equipment: Nuclear power steam generators, aviation fuel pipes 

Common shot peening material applications

Chemical corrosion prevention: Ordinary industrial pipelines, mechanical structural components

Food and medicine: Non-clean environment equipment

High-end equipment: Automotive chassis parts, ordinary pressure vessels 

Summary: Austenitic stainless steel shot peening is a special process that combines "corrosion resistance" and "mechanical strengthening". It requires targeted control in terms of material compatibility, process accuracy, and post-treatment. In contrast, ordinary shot peening focuses more on improving a single mechanical property and has a lower process threshold.