Cooling Time
Cooling time is the time it takes for the weld metal to cool from a high temperature (e.g., 800 °C) to a lower one (e.g., 500 °C). It influences hardness formation and the phase structure of the steel.
Physical-Chemical Mechanism
Cooling time refers to the period during which the weld metal drops from a high temperature. This process affects the atomic structure of the material and can lead to different phases like martensite or austenite.
Metallurgical Relevance & Risks in Welding
Too fast cooling (short cooling time) can lead to a hard, crack-sensitive structure (martensite). This increases tensile strength and raises the risk of cracks and hot cracks. Too slow cooling (long cooling time) can lead to a soft, ductile structure (austenite), which reduces toughness and strength.
Workshop Practice & Instructions
To ensure optimal cooling time, cool the weld metal in a controlled environment. This can be achieved using cooling water or special cooling dies. For steels with high carbon content, a cooling time of 5 to 10 seconds (t8/5) is recommended to achieve a balance of hardness and toughness.