The evidence shows three overlapping clusters: heat-treatment-based methods (C21D, 20.2% of the 4,174 records in scope) are the largest, followed by welding and peening-related methods (B23K, 11.3%) and coating deposition itself (C23C, 9.5%). Measurement and verification methods (G01L, 7.0%) support both of the larger routes but are rarely claimed alone. In practice this means most patented residual stress control happens through a post-deposition or joining step rather than through the spray process itself, so freedom-to-operate work should check heat-treatment and welding claims even when the underlying question is about a coating.

The ranked leaders include major Japanese industrial and steel manufacturers among the top filers, with the leading assignee holding 125 records and the fifth-ranked holding 74. The top five combined account for 12.1% of the 4,174 records in scope, and the top ten combined account for 19.8% — a moderate concentration rather than dominance by one or two firms. This is a ranking of the 100 companies the data endpoint returns, not a definitive top-100 or top-50 list, and a long tail of smaller filers holds the remaining share.

Filing activity peaked in 2018 at 141 records and has generally declined since, sitting at 115 by the 2022 midpoint and falling further toward the most recent, still-partial year. This pattern points to a mature field rather than one attracting a fresh wave of entrants. Because publication typically lags filing by around 18 months, the last one or two years in any dataset understate real activity, but the multi-year trend before that lag window is consistently flat-to-declining, not growing.

US20230207147A1, assigned to Kanadevia Corporation and published 2023-06-29, claims a method of applying compressive stress to a canister holding fuel assemblies while it sits submerged in fill water inside a cask body, using the water to shield radioactive rays during the stress treatment. Its scope is specific to nuclear fuel canister handling and the fill-water shielding combination, not to compressive stress application generally. Work outside spent-fuel canister or radioactive-environment pressure vessels is unlikely to be blocked by this particular claim, though the general compressive-stress concept sits inside a densely populated prior art field that predates it.

The thinnest claim density relative to volume sits in general metal-working (B23P, 6.1% of the 4,174 records in scope) and alloy composition (C22C, 6.6%), both well behind the dominant heat-treatment and welding classes. A first claim combining a specific alloy composition with an in-process compressive stress target during a named forming step would sit outside the densest existing claim clusters. Recent-year momentum data also shows several established filers slowing or stopping activity, which is a further signal that adjacent branches are not being actively defended.