Today, tool steel heat treatment is based on a simple premise, that to obtain the optimum performance from any given grade, every step of the heat treating process— including stress relief, preheating, austenitizing, quenching, deep freeze/cryogenic treatment and multiple tempers—must be done exactly correct. Absolute control of both process and equipment variability is one of many reasons why vacuum processing (Fig. 1) is popular in tool steel heat treatment ^[1].

The selection of any tool steel depends on a combination of factors including component design, application end use and performance expectation. For any given application (Fig. 2) the goal of heat-treating is to develop the ideal microstructure to help achieve the proper balance of desired properties (Table 1) namely hot (red) hardness, wear resistance, deep hardening and/or toughness. By Dan Herring

Argon is a favorite gas used in many vacuum brazing shops, since it is an inert gas that will not react with any of the metals being heat-treated or brazed in those vacuum furnaces. Thus, dry argon (as measured by a dewpoint meter right at the furnace) is often used for partial-pressure brazing applications, or for rapid-cooling needs, or merely as a gaseous atmosphere to allow better conduction of heat between components inside the furnace. But argon can also be dangerous, and even lethal!

Argon is an odorless, colorless, tasteless gas, and because it is heavier than air it will flow to the lowest spot in your shop floor, often down into holes or pits built into your shop floor. Many companies build those pits in their shop floors so that equipment can be lowered down into them, thus eliminating the need to add height to the ceilings of the buildings. By Dan Kay

If we are to see the true microstructure of steels, such as tool steels, we must properly prepare them. For years, the writer has often been told by people that “we just do not have the time to properly prepare the specimens – this is the best we can do.”

I would ask them how long it takes them to prepare a holder of 6 specimens. They would frequently give me times of one to two hours. They would look at me like I was crazy when I would say, “Let me show you how to prepare a holder in less than 30 minutes, and they will be perfect.” The “secret” to “perfect preparation” is first to section specimens while introducing as little damage as possible. Minimal damage takes a lot less time to remove than maximum damage! This paper presents guidelines and procedures for preparing tool steels – which can have a very wide range of hardness, and may be further complicated if the specimens are as-quenched (and, consequently, very prone to cutting and grinding damage). By George Vander Voort

Most of us are familiar with processing in the vacuum range up to around 1.33 x 10^-3 Pa (1 x 10^-5 torr) or slightly lower (Fig. 1). There are also lessons to be learned from understanding the demands of ultra-high vacuum applications (Fig. 2). Let’s explore what’s involved.

What is an Ultra-High Vacuum? Practical high vacuum levels (Table 1) range down to approximately 1.33 x 10-4 Pa (1 x 10-6 torr) while ultra-high vacuum (UHV) levels are in the vacuum range characterized by pressures of about 10-7 Pa (7.5 x 10-10 torr) and greater. These vacuum levels demand the use of special materials of construction and processing techniques such as preheating (i.e. bake-out) of the entire system for several hours prior to processing to remove water and other trace gases, which adsorb on the surfaces of the chamber. By Dan Herring

Joint clearances must be tight for effective Ni-brazing. 1. Nickel-based brazing filler metals (BFM) can leave a hard, non-ductile eutectic phase in the middle of a brazed joint.

The hard, non-ductile metallurgical phase-structures that form upon solidification of Ni-brazed joints must be carefully controlled, or else they can, and will, result in cracks inside the joint in stressful mechanical or thermal-cycling service. By Dan Kay

Experience has shown us that sensitive materials in the presence of minute quantities of unwanted gaseous contaminates can destroy the integrity and shorten the life expectance of components.

It is natural to ask ourselves what can be done to further protect the work in a vacuum environment after the pumps have done their part in reducing the chamber pressure to as low as is economically feasible in a production environment? This task falls to getter materials. By Dan Herring

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