When we deal with applications where strength-to-weight ratio is a critical consideration, we often turn to solutions involving the so-called “light metals.” Aluminum, magnesium, titanium and in some cases beryllium enhance engineering performance while minimizing the weight of components and structures. Most of us involved in heat treating these materials know how we do it, but it is equally important to understand why we do it. By Daniel H. Herring

Stainless steels are widely used in the chemical, petrochemical and food-processing industries due to their favorable corrosion properties. The industrial world would not exist without this class of material.[1] They exhibit generally poor tribological properties, however, which limit their applications to use in tribocorrosive environments. By Luiz Carlos Casteletti, Amadeu Lombardi Neto, G.E. Totten

When we talk in terms of heat treating in vacuum, most people think we do so in a space entirely devoid of matter. In reality, this isn’t true. In practical terms then, a vacuum is a space with a highly reduced gas density. Just how many gas molecules are still present and how they react inside the vacuum furnace is something we should better understand. By Daniel H. Herring

While the end-use application of a component dictates its heat treatment, as heat treaters we know that we must achieve a delicate balance between the properties of strength and ductility. Nowhere is this fine line more evident than in the tempering process where precise control of time and temperature are critical to help produce a part with optimized microstructure and mechanical properties. Essentially, tempering is the modification of this newly formed microstructure toward equilibrium. Almost all steels that are subjected to any type of hardening process are tempered. A temper is a subcritical heat treatment that alters the microstructure and properties. In general, tempering lowers strength and hardness while improving ductility and toughness of the as-quenched martensite. However, this is not always the case. By Daniel H. Herring

Heat treating of stainless steels depends to a great extent on the type (wrought or cast) and grade of stainless steel, as well as the reason for the treatment, most often to ensure that the properties altered during fabrication are restored (e.g. corrosion resistance, ductility, or hardness) so that the stainless steel component can perform in its intended service environment. There are quite a variety of different heat treatments available. By Daniel H. Herring

Martempering and marquenching are terms often associated with hot oil quenching. Formally, martempering (full martempering, true martempering) is a term applied when an austenitized work piece is quenched into a medium whose temperature is essentially maintained in a bath just above the martensite start (Ms) temperature of the steel and held in that medium until its temperature is uniform throughout – but not long enough to permit bainite (or pearlite) formation – and then allowed to cool in air (Fig 1a). When the martempering process is applied to carburized material, the controlling martensite start temperature is that of the case and as such this process variation is called marquenching.[1]

A modified form of these processes is called hot oil quenching (modified marquenching) and takes place just below the martensite start temperature (Fig. 1b). In many steels the required critical cooling rate is such that faster quenching than that possible by marquenching or martempering is necessary to obtain full hardness. It has also been found effective in reducing quench stresses and improving part dimensional stability. But how is hot oil quenching best accomplished in the real world? By Daniel H. Herring