Ultra-low　carbon　steel　(ferritic　steel),　commercial　purity　aluminum　and　high　purity　copper　were　heavily　deformed　by　the　accumulative　roll　bonding　(ARB)　process,　and　the　microstructural　evolution　during　the　ARB　was　analyzed.　Significant　grain　refinement　by　grain　subdivision　mechanism　was　confirmed　in　all　three　kinds　of　materials.　On　the　other　hand,　microstructure　refinement　slowed　down　with　increasing　strain　and　the　grain　size　stayed　in　nearly　a　constant　value　in　the　ultrahigh　strain　region.　The　mechanism　of　the　grain　size　saturation　was　discussed.