Reading a furnace chart in five minutes

Every heat-treated batch leaves our furnaces with a chart: temperature against time, one line per thermocouple. It is the only record of what the parts actually saw.

Three things to check

• The soak starts when the slowest thermocouple reaches temperature, not the furnace setpoint
• Soak time matches the section thickness on the drawing
• The cooling rate matches the procedure: quench, air or furnace cool

Our furnaces are surveyed to AMS 2750, so the thermocouples on the chart are themselves checked against a reference every quarter.