How to flaten hardened and tempered steel strip?

Dear All,

I have a hardened and tempered steel strip of width 255 mm and 2600 mm long, thickness 2.1, 2.3 and 2.5 mm. It is having a flatness tolerance of +/- 0.2 mm but I need +0.05/0.05 mm . This sheet has a hardness of 45 to 48 HRC. Can any one guide me how to flaten this to get the required flatness. Please guide me the process which I need to adopt. In the process of flatening I should not loose thickness as well the hardness. Thanks in advance.