How can we delete materials permanently from Material master?

Use transaction MM70 - Material Master->Other->Reorganization->Material->Choose.
Build variant with selection range of material master records to be selected for deletion and maintain run parameters. Execute.
Use transaction MM71 - Material Master-> other-> Reorganization->Material->Reorganization
Build a second variant
Maintain run parameters and execute.
It is also important to remove the records manually from info record, POs, PRs, reservation etc for successful deletion of the material.