What began as a simple labor of love years ago, namely to share what we’ve learned with the heat-treat industry, has reached an impressive milestone. This is the 100th column for “The Heat Treat Doctor”! So, how do we celebrate? By asking ourselves the most fundamental of questions: What is heat treating, and why do we do it? Let’s learn more.

Heat treating is a core manufacturing competency and can best be defined as “the controlled application of time, temperature and atmosphere to produce a predictable change in the internal structure (i.e. microstructure) of a material.” Thus, metallurgists are responsible to predict the microstructural changes that will occur in a component, while heat treaters are responsible for controlling the process and equipment variables so that the desired outcome will be achieved.

Heat treating allows us to vary the properties (mechanical, physical, metallurgical) of a given material to optimize its design performance. We heat treat, therefore, quite literally because we must. It is the most cost-effective way to achieve the desired outcome. One of the greatest challenges we face as heat treaters is that the same flexibility that allows us to manipulate the end result of a heat treatment, tests our ability to control and repeat our processes to achieve our customer’s desired product performance time after time.

Heat treating is a vital part of manufacturing. Thus, it is critical for any organization that relies on this technology to understand the relationship that exists between the variables that influence product response to heat treatment; namely material choice, properties, part design, manufacturing practices and heat-treating methods. This relationship is best illustrated by the Model of Material Science (Fig. 1).

The model is intended to help us understand the inter-relationship between each technology link. Just as a chain is only as strong as its weakest link, so too is the success of a heat-treatment operation dependent on proper execution of each phase of the model. The model explains how to achieve results using both the older philosophy (discovery-based methodology) and the newer approach (scientific-based) methodology.

The scientific- or engineering-based methodology (down arrow) starts by considering the needs of the end user, that is the performance demands of a specific product, which, in turn, requires the design engineer to select a material capable of achieving certain mechanical, physical and metallurgical properties. These properties can only be developed in the selected material by producing the correct microstructure that in turn dictates a particular heat-treatment process or series of processes be run in a specific piece of equipment.

The discovery or trial-and-error methodology (up arrow) begins with material selection. It involves using a specific piece of equipment to run a heat-treatment process or series of processes, thus producing a specific microstructure in the material, which, in turn, determines the mechanical, physical and metallurgical properties that the material will achieve and ultimately defines the end-use performance capability of the product.

While both methods can be employed with success, most heat-treatment operations today focus on the engineering methodology to more accurately predict and control the material (and hence product) response to heat treatment. Quality assurance and control is achieved by monitoring and checking each step along the way.

A good example of using this methodology is the range of products and services used in the most demanding service applications (Fig. 2). The Apache helicopter, for example, is a unique fighting platform, one that places the highest demand on each subsystem including the transmission, engines and weapons platform. The heat-treating challenges are obvious to ensure that each flight system is optimized. This type of challenge underscores the need to optimize our processes and to ensure that our equipment is under total control.

Many metalworking operations (e.g., grinding, stamping, rolling, forming, machining and plating) shape, size or produce finishes on metals, but only heat treating can significantly change the ultimate condition (physical, mechanical, metallurgical) of these shapes. Virtually all materials can have their properties enhanced by heat treatment.

Many heat-treating operations fall into two basic categories: softening (e.g., annealing, normalizing) and hardening (e.g., through hardening, case hardening). Softening removes stresses, refines grain structure and puts a material in a workable condition for subsequent operations. Hardening often improves surface hardness and wear resistance, increases toughness and improves resistance to impact so that the final product is a useful engineering material.

Heat-Treat Market Size

Heat treating in North America is conservatively estimated to be a $20-22.5 billion industry servicing more than 18,000 manufacturers. It can be further divided between captive shops (approximately 88-92%) and commercial (approximately 8-12%) shops. Further subdivisions are possible by process (Fig. 3 – online only, Table 1) and equipment (Fig. 4, Table 2).

Summing Up

For the heat-treatment industry to survive it must remain the most cost-effective solution to our customer’s needs. It is important, therefore, that we understand what makes it such a vital part of the success of today’s products and anticipate how it must evolve to stay the choice for tomorrow’s innovations. Threats abound, but so too do opportunities for growth and expansion in traditional and non-traditional markets. Heat treating has broken the stereotype of being a low-tech industry. Striving for continuous improvement and relying on sound scientific and engineering principles, with a dash of everyday common sense sprinkled in the mix, will ensure continued success. Rest assured, The Heat Treat Doctor and his column will be there to help! IH