Heat treating steel is a controlled process where altering even the smallest details can significantly impact the final outcome. For many, the go-to reference is the Aerospace Materials Specification AMS 2759, with its associated "slash” specs (i.e. 2759/5 for stainless steels or 2759/7 for carburizing grades). They provide comprehensive guidelines for hardening various grades of steel. However, translating those standards into a clear, step-by-step procedure isn’t always straightforward.
As Todd Chavanne from Sullivan’s Business Development team explains, “The AMS covers a wide range of steels—including the grades we offer at Sullivan—but it doesn’t easily spell out the heat treatment process for each one. For example, you can’t just look up XD15NW or 440C and find a separately listed, ready-made recipe. The grades are individually listed but grouped together in tables with footnotes making it difficult to find all the necessary details.”
At Sullivan, our deep expertise with high-performance bearing grade steels means we understand how each material responds during heat treatment. In this post, Todd shares practical advice for customers who are case hardening steel grades for the first time—making the process simpler and more successful.
Unlike through hardening—which hardens the entire part or piece of steel—case hardening produces a harder, wear-resistant outer layer (the case) while preserving a softer, ductile core.
“A bearing steel is not very ductile to begin with, and when we’re case hardening, we’re trying to make the center as tough or ductile as possible by not fully hardening it, ideally only making a section of that part hard because it’s what’s going to be exposed to the wear. You’re working to get the best of both worlds out of a singular piece of steel.” In many cases, this allows you to avoid needing a coating.
There are several case hardening methods, with carburizing, nitriding, and induction scanning being the most common for Sullivan’s aerospace grades. Each technique has its advantages and disadvantages and requires a unique heat treatment procedure in order to be successful. See our related post, Hardening Options for Steel.
Sullivan offers expert guidance and an initial heat treatment recommendation for customers new to a specific steel grade. By leveraging our close relationships with mills and our extensive experience collaborating with heat treaters, we provide practical, actionable advice tailored to your needs.
Responding to comments like, “I want to get a little more hardness” or “I want to preserve a little bit of toughness; how do I do that?” is part of our service. We’re available to make heat treatment as straightforward as possible.
To help customers get started, Todd often translates the AMS specifications into clear, practical instructions—outlining recommended temperatures, times, pressures, and other key settings.
“What makes Sullivan’s stand out, particularly from other distributors, is that we don’t just hand you a material spec sheet and a heat treat spec and say, ‘Go; you’re on your own.’ Which is how it happens a lot of times.”
When our experts understand a part’s intended application and required properties, they can quickly determine the optimal heat treatment approach. We’re committed to sharing that expertise with our customers, ensuring they have the knowledge and confidence to achieve the best results.
Sullivan can recommend experienced heat-treaters for the steel we carry but strongly recommends conducting a trial run when case hardening a bearing grade that’s either new to you or to your heat treater. We’re as invested in the outcome as you are, since each trial helps us further refine our expertise with these specialty grades.
“Do the heat treatment our recommended way first, so it proves out the promised properties of the steel. This step is especially important when dealing with a third-party heat treater, who may not be familiar with the grade.”
Following the appropriate AMS 2759 “slash spec” procedure for your initial trial is wise, as this establishes a reliable baseline for performance. Once you have those first results, you can then consider fine-tuning the process to optimize or tailor outcomes for your part or application.
When working with a steel grade you haven’t used before, it’s often unlikely that the case hardening will deliver the exact properties you desire on the first attempt—but there’s always a reason behind the results.
“I ask for the printouts of what was done, the temperatures, pressures, timing between processes, all that. We review it for gaps in the process or steps that weren’t followed. Most customers are happy after one or two attempts. Typically, there are only a few trial iterations. After the second, one more tweak and we’re there.”
After analyzing the heat treat results and reviewing all documentation, Todd explains that a second trial with minor adjustments usually brings performance to about 90% of the customer’s target. In most cases, a third iteration is all it takes to achieve the desired outcome. “And once your heat treatment is figured out, you can do it over and over again, no problem,” says Todd.
We stock a range of specialized, high-performance steels designed for the most demanding applications. Our selection of case-hardening grades includes:
At Sullivan, we dedicate time, expertise, and resources to help you achieve the performance you need. Supporting your heat treatment process for case hardening is just one of the ways we add value. If a part doesn’t meet your expectations, we work with you to identify the cause and guide you toward a solution.
Looking for a harder case or a tougher case-hardened part? Ask about your options, start a Live Chat, or contact us today to get started.