It was a grand party – full of music, dancing and laughter. Even fireworks! The European operation of a major furnace company turned 25, and The Doctor was there amidst the festivities. Let’s learn more.

Technical Conference Highlights

In addition to joining in the fun, The Doctor was present, along with some 150 engineers from all over Europe, to give a talk on “Selecting the Best Quenching Method for Distortion Sensitive Gears” at SECO/WARWICK’s 19th Heat Treatment Technical Seminar on New Trends in Heat Treatment held at the Mierzecin Palace Resort in Mierzecin, Poland.      

The venue was spectacular, and the conference was even more so (leave it to a heat treater to find true beauty in the technical side of things). Of the 14 talks presented, several were especially noteworthy, including:

  • “Heat Treatment of Steels According to the Principle of Sufficient Hardenability” (J. Pacyna, AGH University of Science and Technology, Krakow)
  • “New Technology of Gas Nitriding – Zero Flow®. The Minimization of Process Media Consumption and the Reduction of Emissions of Process Gases” (T. Przygonski, SECO/WARWICK)
  • “PreNit® - The Economic Option for Vacuum Carburizing” (Professor P. Kula, Lodz University of Technology)
  • “Improved Efficiency and Productivity – The Achievements of Vacuum Carburizing Applications Based on Vector Vacuum Furnaces – CaseMaster® and UniCase Master®” (Dr. M. Korecki, SECO/WARWICK)
  • “Gear Distortion in the Processes of Bainite Nanostructurization” (S. Marciniak, Warsaw University of Technology)

While space prevents discussing all of these excellent talks, several will be highlighted here.

The Future of Gas Nitriding

ZeroFlow® technology uses only ammonia for nitriding and is designed to minimize ammonia consumption by optimizing the impact of process temperature, chemical composition of the atmosphere in the furnace retort (i.e., nitriding potential), nitrogen concentration in the surface layer and phase/zone microstructure at the near surface.

A rise in the process temperature increases ammonia consumption in a nonlinear relationship to the nitride layer formation. Higher nitriding potential of the atmosphere also increases gas consumption. Furthermore, the thicker the compound layer, the larger (and more dramatic) the increase in gas consumption (i.e., the concentration of nitrogen on the surface of the nitrided layer causes an increase in the consumption of ammonia). ZeroFlow technology reduces the consumption of ammonia by controlling precisely the growth kinetics of the nitrided layer. Case studies using ZeroFlow technology showed how to achieve the lowest overall consumption.

Advances in High-Temperature Processing

The control of grain growth is especially important in vacuum carburizing and is an active research area to shorten overall cycle time. Material with microalloying elements (e.g., Al, Nb, Ti) that pin the grain boundaries is one such approach.

Another technique involves the addition of nitrogen into the surface of the steel using a prenitriding step (PreNit®) added to the cycle as the work heats to carburizing temperature. The process involves the addition of ammonia to the vacuum furnace chamber during heating of the workload in the temperature interval from around 400-700˚C (750-1290˚F).

Nitrogen diffuses into the surface, forming precipitates that act to pin the grain boundaries and limit austenite grain growth before carbon diffusion takes over this function. The nitrogen then diffuses deeper into the case, which avoids higher retained-austenite levels. As a consequence, it has been reported that low-pressure carburizing temperature may be increased to as high as 1000°C (1850°F) without affecting the microstructure or mechanical properties (e.g., fatigue strength).

When compared to either atmosphere carburizing or low-pressure carburizing without prenitriding, this process controls grain size while case depth and hardness remain essentially the same – even when higher carburizing temperatures (for faster cycle times) are used. Economic comparison with atmosphere (endothermic gas) carburizing is favorable for case depths over 0.4 mm (0.016 inch) with reported savings up to around 60%.

The Future of Vacuum Hardening and Vacuum Carburizing

Of all the recent technological advances in the heat-treatment industry, the UniCase Master® is very intriguing. I am pleased to report that the concept exists in the real world – and in this writer’s opinion will allow our industry to achieve a competitive advantage over competing technologies by offering true one-piece flow, high productivity (one part every 30-60 seconds and up to 1 million gears or bearings a year), uniform and rapid part heating of one piece at a time and individual (contour) quenching in a compact footprint (15-20 seconds). The concept has been introduced previously (c.f., “Vacuum Equipment Innovations,” Industrial Heating, November 2015), but the big revelation was to both see the unit in productive operation in the R&D facility and to know that it has been working continuously over the last four months carburizing gears.

A Customer’s View

When our customers speak, I pay attention. Representatives from the aerospace industry talked about the advantages they have derived from using vacuum carburizing for aerospace engine components. Aerospace customers have demanding requirements, examples of which would be as follows:

  • Effective case depth: 0.5-1.1 mm (0.020-0.045 inches)
  • Surface hardness: 81-85 HRA
  • Core hardness: 35-48 HRC
  • Microstructure: Finely dispersed carbides in a matrix of tempered martensite
  • Retained austenite: 10% maximum
  • Case profile: Uniform distribution of carbon throughout the case and in particular in the transition (i.e., case/core interface) layer (i.e., no carbides in the grain boundaries and no carbide necklaces)
  • Residual subsurface compressive stress: 10 ksi maximum
  • Prior austenitic grain size: ASTM 5
  • IGO/IGA: ≤ 8 µm (0.003 inches)

The implementation of vacuum carburizing in the aerospace industry has resulted in the following advantages:

  • Surface activation (preoxidation, chemical treatment, blasting) not required
  • Shorter carburizing time (up to 30% less) in relation to the same carburizing temperature with conventional (atmosphere) carburizing
  • Savings in production costs (up to 15% less) by reducing the amount of carburizing gas
  • Reduced energy consumption (up to 15% less) by elimination of atmosphere generators and adaptation of modern technology solutions
  • No emissions (e.g., carbon dioxide); no open flames
  • Less distortion (up to 15% less) by controlling the speed of heating and cooling
  • Improved product quality (i.e., uniformity of properties, improved surface condition)
  • Extremely uniform case depth and better homogeneity of the carburized layer on internal and external surfaces
  • No internal oxidation
  • The ability to direct quench after carburizing
  • Elimination of copper plating layer prior to quenching
  • Reduction of product lead time (up to 30% less)
  • Reduce the post treatment time through a combination of high-pressure quenching and vacuum tempering

Summary

While not often called upon to do so, The Doctor enjoyed his role as a roving reporter. While this column is not intended to endorse the host company or their products, one could not help but be impressed by what was seen and heard.

Technological advances are not limited to any one company. It is exciting to know that innovation is alive and well.