Step 2 of 4
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Nitriding, deeper: why this course exists
The four levers that make one nitriding job different from another, and what a complete nitriding certificate documents that an incomplete one leaves out.
Step 2 of 4Temperature
The ferritic nitriding window is roughly 350-590°C. Cycle temperature sets the diffusion rate, determines which iron-nitride phases form in the compound layer, and bounds the risk of over-tempering the substrate. A 30°C move changes case depth measurably on the same steel. Running above 590°C pushes the iron-nitrogen system into the γ (austenite) field and the compound-layer chemistry collapses. Running below the substrate's tempering temperature minus 30°C softens the core. The usable window for tool steels in practice is 480-560°C.
Quick check
A vendor offers to run an H13 die at 600°C to shorten the cycle. The substrate was tempered at 595°C. Why is this a wrong recipe regardless of what the certificate says about surface hardness?