Let’s discover new tricks and old tips on how to best heat treat, whatever your application.
In this Technical Tuesday, originally published in the March/April 2024 Aerospace Heat Treat print edition, Heat Treat Today compiled top tips from experts around the industry to get the best results in your heat treat furnace by optimizing fixtures and fabrications.
#1 Welding Fabrications with Nickel Alloy
“Heat resistant alloys used for heat treating fixtures, muffles, retorts, radiant tubes, and other parts are typically stainless steel or nickel-based austenitic alloys.
“Good welding practices for nickel alloys are centered on the need to remove heat as quickly as possible in order to minimize the time spent in the hot tearing range. The first consideration is to keep the heat input as low as possible to still get a full penetration weld. The actual input in kJ is dependent on the alloy being welded.”
Source: “Marc Glasser on the Tools and Trade Secrets of Heat Resistant Alloy Welding,” reprinted in Heat Treat Today, 2020.
#hottearingrange #austeniticalloys
#2 Consider Corrugated Inner Covers
Inner covers are a component of the batch annealing process in the steel industry. If your inner covers are vertically corrugated, consider horizontally corrugated inner covers instead. Horizontally corrugated inner covers are repairable and, for this reason, offer longer overall life and better value.
Source: Alloy Fabrications
#batchannealing #innercovers #maintenance
#3 Countermeasure To Combat CFC Failure
“It is important to consider the specific process conditions in advance so that unwanted reactions — from carburization to catastrophic melting of the workpieces — can be avoided. Effective countermeasures can be taken.”
Dr. Demmel gives the following countermeasures:
- Ceramic oxide coatings such as aluminum oxide (Al2O3) or
zirconium oxide (ZrO2) layers placed onto the CFC - Hybrid CFC fixtures having ceramics in key areas to avoid direct
contact with metal workpieces - Alumina composite sheets
- Boron nitride sprays
- Special fixtures made of oxide ceramics
Source: Dr. Jorg Demmel, “CFC Fixture Advantages and Challenges, Part 2,” Aerospace Heat Treating (Heat Treat Today, March 2023).
#CFC #fixtures
#4 Allow for Thermal Expansion
When bringing furnaces to operating temperature, always be aware of thermal expansion of your alloy components. Muffles, retorts, and radiant tubes all expand with heat input. These components must be free to expand within the furnace or early failure may result.
Source: Alloy Fabrications
#thermalexpansion #heattreatfailure
#5 Batch Rotary Retorts — Stay Put and Stay Clean
Batch rotary retorts are positioned on furnace rollers at the front of the furnace. In time, these retorts expand until they no longer track on the rollers. Extend the life of your batch rotary retorts by using adjustable roller brackets (available from Alloy Engineering). And to keep the outlet tubes clean, use Alloy Engineering pigtails and augers to self-clean batch rotary retort outlet tubes.
Source: Alloy Fabrications
#thermalexpansion #heattreatfailure
#6 Corrosion at Every Corner
“[All] materials are chemically unstable in some environments and corrosive attacks will occur. It can often be predicted or modeled. . . In the real world, however, it is important to recognize the various forms of corrosion, namely:
- Uniform (or general) attack
- Intergranular attack
- Galvanic (or two metal) action
- Erosion
- Dezincifi cation (or parting)
- Pitting
- Stress corrosion
- Electrolytic (or concentration) cells
Source: Dan Herring, The Heat Treat Doctor©, Atmosphere Heat Treatment, vol. II, 2015, pp. 621.
corrosion #heattreatmaterials
Article provided by Heat Treat Today Editorial Team
