Case-Hardening

Operation of giving to wrought iron a surface which will resist abrasion and wear as well as hardened steel. The article is heated to redne and immersed in powdered ferro-cyanide of potash, in which it is allowed to cool. Sometimes leather or horn is added to the mixture. The surface of the wrought iron undergoes a cementation and becomes highly carbonized on the surface. It has therefore the toughne to resist deflection which is given by the wrought iron center, and the hardne of steel to resist abrasion on the surface. The proce is applied to nuts, engine-guides, pins, etc. Animal and vegetable charcoal are also used.