Gas Nitriding and Its Effects on Steel

30 April 2018

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.

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