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Guaranteed load soak 2

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COKA

Materials
Apr 22, 2003
108
Can anybody explain to me where the guaranteed load soak should be used and where it should not be used? I know that the guaranteed load soak means that the part being annealed (or brazed or heat treated) has to get up to temperature even though the furnace is already at temperature. Also, if a part is supposed to be annealed for say 30 minutes at 1850F, but with guaranteed soak it may end up staying in for 45 minutes at that temperature because the part was not there yet. How will the extra 15 minutes affect the annealed part? And another problem, what if you're supposed to braze an already brazed part (with the same braze paste) for 5 minutes at temperature, and you end up leaving the part for 10 or 15 minutes in guaranteed load soak.... the previous braze will brobably run.

Thanks!

Confused

Coka
 
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Coka;
For brazing purposes, the time required at temperature is to achieve melting of the braze metal to provide for adequate flow and wetting. Since there is no melting of base metal, extra time is not required. From my experience with aluminium brazing, there was no soak or hold time once the melting temperature of the braze metal was reached.

The load soak time for heat treatment (such as annealing, solution treatment or austenitizing) must be specified for two reasons;

1. you need adequate time for the component temperature to reach equilibrium with the furnace temperature (no shadowing affects when viewed in the furnace), and

2. time at temperature to achieve complete phase transformation of the original microstructure to austenite, and to dissolve precipitates or carbides, as well.

Extra time at temperature during annealing generally promotes grain growth. However, extra time at temperature also helps to dissolve carbides in certain alloys.
 
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COKA,
metengr's comment about brazing also applies to Iron base and other alloys. We used to specify 1-2 minutes at temperature. If held for extended time at braze temperature, excessive flashing could result causing braze metal/alloy to flow into unwanted areas and the braze fillet will diminish.

What metengr said about soak time is true. However extending soak time from 30 minutes to 45 minutes will have little effect unless the temperature is higher than recommended for the process as temperature affects grain growth much more than time affects grain growth.

Guaranteed soak time should commence from the time the surface of the part reaches soak temperature. Tests have shown the following when a thermocouple is buried deep inside the part and compared to readings from t/c's on the surface of the part: Although the core temperature of the part lags the surface temperature as the part is coming up to heat, as the part nears soak temperature, the core temperature catches-up with the surface temperature. Reference: Carpenter Steel Co. "Tool Steels Simplified."


Jesus is THE life,
Leonard
 
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what about aging processes. IE: H900 for 17-7ph stainless. 60min+10-0 at 900F+-10. Would the surface temperature be used (part on the outside of the basket) or would the internal temp of the parts basket?

This is a precip process, and is the lowest temp/time of the different choices for PH stainless. (smallest most coherent precipitates.) If after 1hr the internal temp is only 850F then has the required temperature for activation of the Rx been reached? Or should the internal temp be stabilized? How much precipitate growth occurs in the extra 1/2hr wait for the internal to catch up with the external? Slightly over aged is not really much of a problem with the part, but we do need the highest strength possible.

nick
 
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NickE,
Very good point. In that instance, I would specifiy several t/c's to monitor the extreme limits of the load and the interior of the charge. All zones of a furnace are not necessarily heated equally.

Jesus is THE life,
Leonard
 
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