For that you need to inherit sale.order.line object and use
xpath to display in sale order form view. 

In PY:-

class SaleOrderLine(models.Model):

     _inherit = 'sale.order.line'



     x_field = fields.Char('X Field')



In Xml:-


    sale.order.view.inherit1
    sale.order
    
    
        
            
        
    




This fields shows after Description in the sale order line.



Hope it will helps you.

Thanks,