This post will address the gas nitriding process and its effects on steel. Essentially, we’ll be looking at a heat treatment technique that addresses alloy hardening concerns and the need for a process that attenuates the corrosion rate of this ferrous-heavy metal. But first, considering the importance of this subject, just why is gas nitriding such a vital part of any thermal treatment arsenal?

Armoured Against Industrial Pressures

All kinds of forces try their best to undermine steel components. High pressures push alloy panels until they bulge. Meanwhile, a process-essential steel component is rusting or experiencing wear. Gas nitriding work case hardens steel. To be specific, this is a heat treatment technique that’s designed to enhance the surface properties of those steel parts. It does this by thermochemically depositing a coating of hard nitride precipitates all around the component.

Gas Nitriding: The Effects on Steel

Now that the process recap is out of the way, just how does this heat treatment technique impact steel parts? Well, inside our gas nitriding furnace, the temperature is about to hit the 525°C mark. The ammonia gas is reacting, soaking into the surface of the hot steel. After forty-five to sixty minutes, the nitrogen in that gaseous compound penetrates the alloy surface and case hardens the component. For this example, we’re using a steel shaft, a part that’s expected to endure when great pressures are applied. It’s operating in a hot and humid factory, and previous shafts have experienced corrosive pitting. Now, thanks to this gaseous heat treatment process, the shaft no longer suffers from pitting, even when the humidity level peaks.

Controlling the Operation

Pure ammonia is the best choice here, especially when an absolutely corrosion proof steel workpiece is the goal. The next controllable element is the time the part spends inside the furnace. A temperature above 500°C is preferred, and 525°C seems to be a sweet spot for the process. Returning to the timeline, a thirty-minute minimum treatment time can be extended to cover a period of two hours, which is when maximum case hardening depth is achieved. Of course, as with any other thermally active processing station, the ratios of iron and carbon, plus any other exotic additives, will impact the final results.

The disassociated nitrogen bonds with the surface steel to produce a corrosion resistant alloy. Granted, there are steel alloys that exhibit similar properties, but the gas nitriding process introduces this feature without incurring the additional expenses we associate with those alloys. Lastly, that newly nitride-coated part is fatigue resistant and hard. Think of it, a heat treatment procedure that gifts steel with these essential features, and no parts-deforming super-high temperatures were needed.

Process economy is an ideal we chase in heat treatment technology. Masses of fuel and heat are devoured during a hard day’s work inside this manufacturing environment. How does the work retain a cost-efficient edge? Particularly in flame hardening, how do we surface harden a large workpiece while we’re also worrying about an economical processing approach? Well, flame hardening is selective, which means there’s already a frugal system in action.

Flame Hardened Frugality

Talk of affordability occupies the mind of a processing engineer. Certainly, there’s no shortage of techniques. Carburizing processes cook away inside some manufacturing facilities. Meanwhile, another factory has chosen a carbonitriding method. Both techniques have a common factor, the inclusion of a chemical alteration system. The chemicals are diffused, with the metal surface then altering as the furnace fills with gas. Feed systems and gases, they’re efficient but expensive. On the other hand, the flame hardening process doesn’t use chemicals. Mounted on a scanner mechanism, the focused heat source selectively hardens targeted workpiece sections. Gear teeth, for instance, only require hardening on their outer edges, not their entire form.

Dance of the Flame

Most of these facts have been covered in other articles. Flame hardened parts receive focused treatment, and that treatment further reduces costs by reducing post-treatment grinding and finishing. Furthermore, the treated parts don’t experience process distortion, not to the degree found in other surface hardening techniques. Beyond those cost-cutting benefits, there’s the manner in which the flame head discharges its thermal load. Scanning heads move in closely compressed scan lines across large surfaces. Elsewhere, a wheel or vehicle axle is spinning in a special mechanism. The flame is fixed, but the cylindrical piece is rotating at a carefully calculated velocity. In a truly advanced heat treatment station, both methods operate concurrently. The progressive scan is in motion, the part is rotating, and a quench operation immediately follows each stage.

Providing superior wear surfaces, the secret to economical case hardening lays in that three-dimensional control system. The gas and flame head is discharging a measured thermal envelope, one that’s sharply focused. It’s now up to the progressive scan velocity and rotating equipment to regulate the heat. When that head, or parts-moving mechanism, is properly regulated, travel speed combines with output temperature and flame shape to ensure calculated surface hardened depth. More cost-effective than chemical diffusion technology, flame hardened parts come in many shapes and sizes. As long as that selective treatment mechanism can get into the geometry of a workpiece, this is a supremely economical heat treatment solution.