We founded that a layer of isometric nanocrystalline with a size of 50–300 nm has been formed on the surface of AISI 304 stainless steel subjected to multiple laser shock peening (LSP) impacts.
And we found that the deformation-induced martensite (DIM) is an important deformation mechanism for grain refinement in the top surface at ultra-high strain rates in AISI 304ss subjected to multiple LSP impacts.
The intersectional MTs and DIMs aligned in multiple directions plays an important role in the grain refinement of coarse grains in the surface layer of AISI 304ss.