Bright Tempering: Achieving High-Quality Appearance During Tempering
By Aymeric Goldsteinas and Craig Moller
Cleanliness and efficiency are of the utmost importance when tempering. So what can be done to prevent discoloration? Through customer collaboration, we have evaluated tempering concerns and gathered data resulting in innovative software and equipment improvements that expand industry capabilities.
This paper analyzes what matters most when putting materials through the tempering process. Authors describe how to reduce cycle time while increasing uniformity through the use of both vacuum and convection heating. This paper will also present data collected from tests run on the bright tempering of sensitive alloys such as PH 17-4 (X5CrNiCuNb 16-4), Inconel 718 and 420 stainless steel (X42Cr13) that yielded bright, clean and uniform parts.
Imagine trying to temper your materials above a charcoal or coal forge, or even by fire. From the oldest known example of tempered martensite in 1200 B.C., the process of tempering has remained relatively unchanged over the ages. However, all that is changing. The TITAN® T brings tempering technology into a new age, moving thermal processing forward.
The TITAN T excels in workpiece uniformity and process performance efficiency. Through true vacuum tempering, the furnace provides brighter and cleaner parts. Tempering furnaces are coming out of the dark ages and into a bright future with Ipsen's TITAN T. The increasingly well-known TITAN platform is built using an innovative, flow‐production process that integrates premium components, all developed with the customer in mind. Endurance testing combined with ongoing user feedback allow the TITAN product line to remain agile while setting a standard of excellence. Our controls system is continuously enhanced for usability and precision.
TITAN T Design and Processing
The development of the TITAN T vacuum temper furnace stemmed from the desire to dedicate batch furnaces to low-temperature heat treatment process applications, such as aging, annealing, stress relieving and tempering.
The TITAN T is a true vacuum temper that produces clean parts through the use of both vacuum and convection heating. The use of convection allows for the reduction of cycle times by one hour and 35 minutes (at 500 °F or 260 °C), as demonstrated in Fig. 1.
Figure 1: A comparison has been achieved between convection heating and vacuum heating rates with the standard load. The slowest TC reaches set point temperature within ±10 °F (±5 °C).
Its innovative design, integrating premium components, was developed with the customer in mind. In addition, endurance testing combined with ongoing user feedback allow the TITAN product line to remain agile, while setting a standard of excellence.
The TITAN T vacuum temper furnace has a large work zone size that accommodates greater load capacities with faster cycle times and improved uniformity. As part of the TITAN platform, the TITAN T has the same quick delivery and start‐up to minimize customer downtime. Multiple processes can be accomplished with this furnace, including tempering, age hardening and stress relieving.
TITAN T Testing and Results
The TITAN T vacuum temper furnace, including controls, is compact using minimal floor space and includes the technical features outlined in Table 1.
|Work Zone Size||36" x 36" x 48" (900 mm x 900 mm x 1,200 mm)|
|Number of Trim Zones||3 (front, middle and rear)|
|Heating Element Material||Graphite|
|Heat Shields||Stainless steel shields|
|Maximum Load Weight||6,000 lbs. (2,700 kg)|
|Operating Temperature Range||300 °F - 1,450 °F (150 ° - 787 °C)|
|Clean-Up Temperature||1,500 °F (815 °C)|
|Rate Power of VRT||240 kVA|
|Convection Capability||Up to 2 bar|
|Maximum Quench Pressure||Up to 2 bar|
|Partial Pressure Capability||100 micron - 1,000 micron (13 Pa - 133 Pa)|
|Gas Quench Direction||Front to rear|
Table 1: Technical features of the TITAN T vacuum temper furnace.
Our new, inspired VacuProf® software offers touch screen controls that are continuously enhanced for usability and precision. The VacuProf software gives customers direct access to recipe management, work TCs, maintenance, alarms and process trends. It also monitors temperature, vacuum and pressure levels.
PH 17‐4 stainless steel cylinders were run through an H900 conditioned heat treatment cycle for one hour, as shown in Fig. 2. The parts were heated from room temperature to 900 °F (480 °C) then cooled with nitrogen at 2-bar pressure. As demonstrated in Fig. 3, parts came out bright and clean and the test yielded uniform results.
Figure 2: PH-17-4 H900 heat treatment cycle.
Figure 3: PH 17‐4 stainless steel cylinder after one-hour aging cycle.
During the development and testing of the TITAN T vacuum temper furnace, it was gleaned that discoloration on sensitive material is due to the remaining ppm of oxygen and that a vacuum level of 10-4 - 10-5 Torr is required during evacuation and heating-up. Discoloration occurs in the temperature range of 400 °F - 500 °F (204 °C - 260 °C); therefore, the burnout cycle improves parts' brightness by cleaning up gathered material on the stainless steel shield.
It was also determined that medium vacuum is suitable for most of the steel grades, including tool steel. Additionally, testing a high-vacuum option proved that it will provide a reliable process independent of humidity concentration in the atmosphere, furnace cleanliness and part outgassing.