It has long been known that iron cannot be made strong until it is struck.
In earlier times, it was called Kaji(Smithery) or Hizukiri(Craft by Fire), and Tanzo(Forging) is originated from it.
Tanzo (Forging) literally means to strengthen and make. Strike the iron when it is still hot; this proverb is used in education for young people. You heat and strike iron, in order to form the iron into a required shape. When a heated solid metal blank is wrought, its crystal grains are made fine and its structure, improved. While the mechanical properties are improved, the solid metal blank can be formed into a required shape. Thus, some machining process can be skipped, and as a result, the machining hours can be reduced. This is what Tanzo is about.
Advantages of Forged Products
Processed steel products are made by machining rolled steel; therefore, the fabrication yield ratio is very low. As foundry pieces are made by pouring melted steel into molds, the compositions of the products vary and they are prone to incidental inclusions. It is another characteristic of foundry that the products cannot withstand a strong impact. On the other hand, forging is a technology to fabricate products of complicated shapes while increasing the strength of the products by the wrought steel.
* Metal flow
When steel is rolled, metal flow (flow of metallic grain) happens and affects the strength of the steel. It is same as strings of bamboo for instance. Because of the fibers, it is not easy to break bamboo crosswise but only lengthwise.
Processed Steel Product
※It is easily deformed, as the metal flow goes in one direction only.
Foundry Piece
※It cannot withstand a strong impact, as metal flow does not exist in it.
Forged Product
※It is not easily deformed, and it withstands a strong impact, as the metal flow goes along the product contour.
The increased strength is an advantage that forged products have over the steel products made by other technologies Utilizing the advantage, forged products ensure safe driving, turn and stop of vehicles.
