the only steel 37 i know of is the former denomination of todays S235 steel series as per Eurpean standards. But, tensile str. as per spec. would be max. 470 MPa which could be translated to around 140 HV. HV = 220 seems far off?! However, this might be a property that was set when the sheet was rolled (thermomechanical rolling process), but then you could have a more serious issue with the material as the strength properties of the material might be compromised (prone to brittle failure, nonsufficient capacity to take on deformation) and when annealing, the mech. properties might change to anything.
So, perhaps you could give more input on your base steel: denomination, stand. mech. properties, previous heat treatment etc., or finally get to the supplier and request for support?
Regards
