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Articles by Edward Rolinski
Intro to Heat Treatments for Steel
This article was updated April 26, 2023. It was originally published Oct. 12, 2018. Heat treatments let engineers and metallurgists tailor the properties of metal parts so that they are a better fit for specific applications. But to get the most out of these heat treatments, engineers should be familiar with their finer details. But there are many different heat treatments, including quenching, tempering, aging, stress relieving and case hardening.
Controlling nitrided layers and enhancing predictability of nitriding process with metallography
Nitriding is the thermochemical process for producing surface layers in ferrous alloys, such as steels and cast irons used for making various mechanical components and tools [1]. Ferritic nitrocarburizing (FNC) is a process of nitriding doped with a small amount of carbon [1]. Producing the best nitrided layers for the given application requires a good cooperation between designers of the product and the manufacturing companies making it.
How to Determine the Best Heat Treatment for Your Parts
Long before many of today’s technological advances, people have heat-treated metals to improve their physical and chemical properties for a given application. In the middle ages, blacksmiths forged and tempered metals (albeit in a relatively crude fashion) to create blades, tools, and goods for everyday life. Now, metallurgists and material engineers have a much broader array of specialized techniques and equipment to tailor materials to specific applications.
The Benefits of Nitriding and Nitrocarburizing
Nitriding (N) and nitrocarburizing (NC) are thermochemical treatments that diffuse nitrogen and carbon into the surface of metals. Nitriding is used on ferrous, titanium, aluminum, and molybdenum alloys, and most commonly on low-carbon, low-alloy steels. Nitrocarburizing is only used on ferrous alloys. They improve surface properties of metal components and tools such as scuff and corrosion resistance, and increase the fatigue strength.
Protect stamping dies with ion/plasma nitriding
It’s no secret that the demand for lighter yet safer vehicles has increased the demand for stronger steels in automotive bodies. Steels are significantly stronger than those that were used in older vehicle designs. New generations of advanced high-strength steels (AHSS) used in the auto industry create great challenges for stamping tools used in those applications.
Protect stamping dies with ion/plasma nitriding
New generations of advanced high-strength steels (AHSS) used in the auto industry create great challenges for stamping tools used in those applications because the stress required to induce sufficient plastic deformation in steel with tensile strengths as high as 1,800 MPa is as much as 400 megapascals. Chromium plating has been used successfully to protect stamping dies for many years. However, chromium plating’s limitations seem to be more pronounced as AHSS become harder.
Thermochemical Surface Technologies Applicable to Gears
Hardening of the gear surfaces has a profound effect on their performance. Reduction in friction, enhancing rolling contact fatigue resistance, and other tribological properties of the surface can be utilized by application of various surface techniques available to the manufacturing industry. For surfaces hardened by a diffusion process, what really matters is the depth of the hardened layer and its hardness and resulting tribological performance.
Distortion Engineering of Gears
The causes for distortion of gears are complex and the heat treatment process has been named as a main contributing factor [1]. However, the truth is, all the manufacturing steps prior to and after heat treating also make a contribution to distortion. Nevertheless, any thermal operations carried out on gears may trigger and reveal the hidden distortion potential induced by manufacturing.
Surface Properties
Proper selection of steel and its heat treatment is a fundamental challenge for gear designers and manufacturers. However, performance and endurance limits of the teeth depend strongly not only on the bulk mechanical properties of the steel used for the design but also on surface properties of the gear flank. The latter can be shaped by thermochemical as well as mechanical surface treatments. Wear and subsurface-initiated fatigue are the main failure modes of case-hardened gears [1].
Deep Nitriding for Gear Applications and Their Partial Treatments
Stress conditions inside gear teeth are complex and require a careful examination by the designer before any specific surface treatment of the gears should be recommended [1]. As a result of those examinations, nitriding applications, specifically plasma/ion nitriding, for the surface engineering of gears have been growing steady in recent years because of the many benefits offered by this technology.
Modern Nitriding Techniques for Gear Applications
Improving surface properties of gears can be extremely beneficial since many failures start at the surface in the contact area between the teeth [1]. Rolling contact fatigue properties of the gear surface are improved when a hard diffusion layer — with the compressive residual stresses built into it by the thermochemical surface engineering methods — are applied. Such a layer prevents or delays the formation of premature surface and subsurface cracks, core crashing, or subsurface fatigue.
Surface Engineering
Wear, corrosion, and fatigue failures are the most important mechanisms that lead to material degradation, which eventually causes failure of many gears. Those failures involve mechanical and/or chemical interaction of the material component considered with loads imposed by the environment. Hence, material performance and service life rely, to a high degree in many cases, on the properties of a material in its surface region.
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