Two Processes, One Medium, Different Goals

Both shot blasting and shot peening accelerate steel particles against a metal surface, but the engineering intent is different. Shot blasting aims at cleanliness — removing rust, mill scale and old coatings to ISO 8501 Sa2.5 or Sa3 — and creates an anchor profile of typically 40-75μm for coating adhesion. Shot peening, in contrast, is a cold-working process: its purpose is not cleaning but modifying the surface layer so that the part resists fatigue cracking, stress corrosion and wear.

How Shot Peening Improves Fatigue Life

When a spherical steel shot strikes the surface at 50-80 m/s, it creates a small indentation and plastically deforms the surface layer. The material beneath tries to restore the surface, generating compressive residual stress in a layer typically 0.1-0.8mm deep. Fatigue cracks almost always start at the surface, and compressive stress opposes crack opening — effectively delaying crack initiation and slowing propagation. With proper parameters, shot peening can substantially increase the fatigue strength of springs, gears, crankshafts and landing gear components.

Key Process Parameters

Shot peening quality is controlled and verified through measurable parameters:

- Intensity: measured with Almen test strips (A, N or C strip). Typical peening intensities range from 0.1 to 0.6 mmA depending on part size and material;

- Coverage: the percentage of the surface struck at least once — 100% is the minimum, and many specifications require 200% coverage for safety-critical parts;

- Shot size and hardness: fine shots (SAE S110-S170) for small fillet radii and high-strength steels, medium shots (S230-S330) for general components; peening media are usually at HRC 40-50;

- Exposure time and nozzle distance are adjusted to hold intensity and coverage within specification.

Choosing Steel Shot for Peening

Peening media must be as round as possible and free of sharp edges: angular or broken particles cut the surface instead of cold-working it, creating stress raisers rather than beneficial compression. Cast steel shot produced to SAE J827 is the standard choice for most industrial peening, while aerospace applications follow stricter specifications such as AMS 2431, which control microstructure, hardness uniformity and the maximum allowable content of broken particles. For peening stainless steel or aluminum parts, stainless steel shot avoids iron contamination that could later cause corrosion.

Typical Applications

- Automotive: gears, crankshafts, connecting rods, valve springs and stabilizer bars;

- Aerospace: landing gear, turbine discs and wing structural parts;

- Railway: axles, suspension components and springs;

- Oil and gas, power generation: drill pipes, turbine blades and high-strength fasteners.

Whether your goal is cleaning or strengthening, matching shot size, hardness and shape to the process is what separates a reliable result from costly rework.

Talk to Our Technical Team

We supply cast steel shot, alloy steel shot, stainless steel shot and cut wire shot for both blasting and peening applications, conforming to GB/T18838 and SAE specifications. Contact us for free samples and technical consultation on your peening parameters.