Burlington, Ontario, August 17, 2015 - A new column, written by vacuum heat treating expert Dan Herring “The Heat Treat Doctor”® in collaboration with Edwards Vacuum will be published monthly and offer helpful tips and techniques on vacuum pumping systems to a worldwide audience of individuals using all types of vacuum equipment. The first article will appear in the September 15th “What’s Hot!”. This Vac-Aero exclusive publication launched back in September 2007 and contains hundreds of archived articles can now be found in the “Resources” section of the VAC AERO website where anyone can sign up for the monthly newsletter. Keeping pace with the development of new vacuum processing technologies is the reason VAC AERO takes pride in its continued support of the metal treating community by helping to promote, collaborate and assist others in their search for solutions on important issues in the practice and application of vacuum processing.
When performing any type of vacuum heat treatment it is always important to be aware of the possibility of evaporation and/or sublimation of elements, which can be present in the material being processed, introduced into the vacuum system with the workload, inherent in the equipment design or introduced during maintenance, repair or rebuilds. In cases where evaporation may be a concern, the vaporization rate is of prime importance and is directly related to the furnace pressure (the higher the pressure, the more frequent the collision of gas molecules and correspondingly, the few metal atoms leave the metal's surface). What is Evaporation? Vaporization is the process that occurs when a chemical or element is converted from a liquid (or a solid) to a gas. When a liquid is converted to a gas, the process is called evaporation or boiling; when a solid is converted to a gas, the process is called sublimation.
Stainless steels are essentially iron-based alloys with at least 10.5% (or more) chromium added to it. There are many different types of stainless steels available to designers to consider, and austenitic stainless steels, which contain nickel as well as chromium, have been quite popular over the years for use in a wide range of brazement-designs due to their inherent corrosion resistance, brazeability, as well as the fact that they are often non-magnetic and do not need subsequent heat-treatment. These Fe/Ni/Cr alloys, designated as the 300-series of stainless steels, can be hardened by cold-working, but due to the temperatures involved in most brazing processes, are primarily used in the “annealed” (soft) condition in end-use service.
For many years, ASTM E384 has stated that test forces from 1 to 1000 gf can be used to determine the Vickers or Knoop micro-indentation hardness. But, is it realistic to consider using very low test forces when the indents are measured with a light optical microscope? ASTM E92 is being resurrected and changed to cover all test loads, micro- and macro-loads, from 1 gf to 120,000 gf. Most micro-indentation hardness testers manufactured over the last 50 years or more have provided the user with a 10X objective used to find the area of interest for testing and one measurement objective, 40X magnification being the most common. A few testers have offered 50X or 60X objectives to measure the indents. It is rare to find a tester with a multiple objective (and indenter) turret, such as the DuraScan system which has ports for 2 indenters and 4 objectives.
To successfully process component parts in a vacuum furnace, we need to create and control the “atmosphere” surrounding the work. In general, applications run in vacuum furnaces can be broken down into five main (5) categories: Processes that can be done in no other way than in vacuum; processes that can be done better in vacuum from a metallurgical standpoint; processes that can be done better in vacuum from an economic viewpoint; processes that can be done better in vacuum from a surface finish perspective and process that can be done better in vacuum from an environmental perspective. A principal difference between vacuum heat treatment and all other forms of thermal processing is the absence of, or perhaps better stated, the precise control of surface reactions.
Constructed of the finest materials and craftsmanship, VAC AERO’s high performance vacuum furnaces are operator friendly and designed to minimize maintenance and downtime to deliver outstanding quality and value to commercial and in-house heat treaters alike. VAC AERO’s vacuum furnaces are designed for rapid heating rates to very uniform temperatures at high vacuum levels and can be customized to suit unique applications such as high pressure gas quenching, high temperature heat treating, ultra-clean processing and more. VAC AERO’s high efficiency hot zones are designed for easy maintenance and reduced energy consumption. Our external quench system allows for easy maintenance of the heat exchanger and quench motor. A high efficiency blower and motor combine fast cycle times and quenching speeds to provide uniform gas distribution and superior cooling performance from processing temperatures at pressures of up to 10 bar.