High strength steel
The residual compressive stress introduced by the shot blasting / shot peening is a percentage of the ultimate tensile stress, which increases as the strength / hardness of the part material itself increases. High strength / hardness metals are more brittle and more sensitive to surface defects. For its shot blasting / shot peening, allowing these high-strength metals can be used in the prone to fatigue under the working conditions. The aircraft landing gear is usually designed with a fatigue strength of 300 ksi (2068 MPa) combined with shot blasting / shot peening.
The steel parts that have not been shot / shot peened are machined to have the best fatigue properties of about 30 HRC. If the material strength / hardness exceeds this level, the fatigue strength will be reduced due to the increase in the sensitivity and brittleness of the surface gap. By the introduction of the compressive stress, the fatigue strength is increased in proportion to the increased strength / hardness. When the material hardness of 52 HRC, after strengthening the fatigue strength of up to 144 ksi (993 MPa), than did not strengthen the same material anti-fatigue strength increased more than 2 times.
Typical applications for the use of shot blasting / shot peening to improve high strength / hardness parts include wrenches and impact tools. In addition, the shallow scratches on the surface have little effect on the fatigue strength of the high strength steels subjected to shot blasting / shot peening, and are highly destructive to those that have not been strengthened.