Constructional steels and spring steels are hardened by heating to austenitising temperatures under a protective (endothermic) atmosphere and then oil quenched in sealed quench furnaces. Parts are then washed and tempered to achieve the specified hardness (mechanical properties).Common steels processed:1040/1045, 1340, 4140, 4340, 5140, EN25, EN26, 300M (S155), Arne/01/Silver steel, K245, CK1055, 9258, 5160, SUP9n.