you have to do this one

add a boolean field in your model like

_columns = {
        'is_created' : fields.boolean('Created')
    }

and in xml add attribute for the field to be made readonly, like,

<field name="your field name" position="attributes">
        <attribute name="attrs">{'readonly': [('is_created','=',True)]}</attribute>
</field>

and override create function in your model, like

def create(self, cr, uid, vals, context=None):
        vals['is_created'] = True
        lot = super(stock_production_lot, self).create(cr, uid, vals, context=context)
        return lot