Welding Cooling Rate (t8/5) Calculator
An advanced tool for welders and engineers to estimate the cooling time from 800°C to 500°C. This is critical for predicting the final properties of a weld and preventing defects like cold cracking.
The Metallurgy of a Weld: Why Cooling Rate Matters
When a weld is created, the metal is rapidly heated to a molten state and then begins to cool. This cooling process is not just about the metal getting cold; it's a critical phase where the final microstructure of the weld is determined. The rate at which the weld cools, particularly in the high-temperature range, dictates whether the final structure will be soft and ductile or hard and brittle. For high-strength steels, cooling too quickly can lead to the formation of Martensite, a very hard and brittle structure that is highly susceptible to hydrogen-induced cold cracking. Therefore, controlling the cooling rate is fundamental to ensuring a safe and durable weld.
What is t8/5 Time?
The "t8/5 time" (also written as Δt8/5) is a standardized parameter in welding metallurgy. It represents the time in seconds that it takes for the weld and the surrounding Heat-Affected Zone (HAZ) to cool from 800°C to 500°C. This specific temperature range is critical because it's where the austenite-to-ferrite phase transformation occurs in steel. A longer t8/5 time allows for the formation of softer, more ductile microstructures (like ferrite and pearlite), while a very short t8/5 time promotes the formation of hard structures like bainite and martensite.
This calculator uses a simplified version of the Uwer-Degen formula to provide an estimation of the t8/5 time. It considers three primary factors:
- Heat Input (Q): The amount of energy transferred to the weld per unit of length. Higher heat input slows down the cooling rate, increasing the t8/5 time.
- Plate Thickness (d): Thicker plates act as a larger heat sink, drawing heat away from the weld more quickly. This results in a faster cooling rate and a shorter t8/5 time.
- Preheat Temperature (T0): Preheating the base metal before welding reduces the thermal gradient, slowing down the cooling rate and thus increasing the t-8/5 time. This is a common strategy to prevent cracking.