Gas Nitriding
in India (Planned)
Advanced gas diffusion processing yielding ultra-high surface hardness, superior wear resistance, and absolute minimum distortion.
The Metallurgy
What is Gas Nitriding Heat Treatment?
Gas Nitriding is a thermochemical surface treatment that diffuses atomic nitrogen into low-alloy, tool, and carbon steels to create a hard, wear-resistant surface. The furnace charge is heated to sub-critical temperatures (500°C-530°C) in a sealed chamber. Ammonia gas is introduced; as it makes contact with the heated metal, it dissociates into nitrogen and hydrogen.
The nascent nitrogen atoms diffuse into the steel, reacting with alloying elements (such as chromium, molybdenum, and aluminium) to form microscopic nitride precipitates. Because the process is completed entirely below the critical temperature, no liquid quench is required. This avoids thermal shocks and phase transformations, yielding parts with zero dimensional distortion.
Gas Nitriding Time-Temperature Path
Metallurgical Outcomes
Surface Nitrides & Dimensional Control
Nitriding delivers maximum surface protection with minimal dimensional displacement.
Vickers hardness up to 1000 HV
Ultra-High Surface Hardness
Chromium and aluminium alloys react to form exceptionally hard nitride networks, exceeding carburized hardness levels.
Zero quench distortion
Dimensional Stability
Operating below Ac1 prevents structural transformations, maintaining absolute dimensional integrity in gears and spindles.
Reduced surface friction
Anti-Galling Properties
The compound white layer structure prevents adhesion and metal-to-metal galling under heavy load conditions.
High fatigue strength
Compressive Surface Stresses
Interstitial nitrogen atoms introduce deep compressive stresses, improving resistance to rotational fatigue failure.
Oxidation barrier
Corrosion Protection
The monophase compound case prevents rust and moisture penetration, eliminating the need for chrome coatings.
Thermal stability
Heat Softening Resistance
Unlike standard carbon-hardened steels, nitrided steel surfaces retain their hardness at operating temperatures up to 450°C.
OUR PROCESS
How we execute Gas Nitriding
at Tapovan
Degreasing & Prep
Surface completely cleaned of oils and rust. Pre-nitrided finishes activated for nitrogen absorption.
Masking & Loading
Masking paste applied to areas that must remain soft. Racked uniformly in retorts.
Purging & Heating
Oxygen purged with nitrogen gas, then furnace heated slowly to nitriding temp (500-530°C).
Ammonia Nitriding
Ammonia introduced and dissociation rates controlled for 12-60 hours to form diffusion case.
Slow Gas Cooling
Charge cooled slowly inside retort under protective gas atmosphere to prevent surface scaling.
Hardness Verification
Surface Vickers hardness and compound layer thickness verified in lab before tagging and dispatch.
STANDARDS WE WORK TO
Applications in India
Specified Components
Critical for high-wear parts where dimensional distortion cannot be tolerated, including hydraulic shafts, extruder screws, and motor gears.
Precision Shafting
- Hydraulic piston rods
- Steering gear racks
- Long motor armature shafts
- High-speed rotor spindles
Extrusion Tooling
- Plastic extruder screws
- Extrusion barrel liners
- Injection moulding tie bars
- Mould cavities
Valving Systems
- Engine valves (stem hardened)
- Control valve spindles
- High-pressure seat rings
- Gate valves
Gears & Splines
- Slender internal gears
- Splined gear couplings
- Timing gears
- Worm screw shafts
Frequently Asked
Common questions
Find technical answers about nitrogen diffusion cycles.
Gas Nitriding is a thermochemical surface-hardening process where nitrogen is diffused into the surface of solid steel. The process is conducted at sub-critical temperatures (500°C-530°C) in an ammonia (NH3) gas atmosphere. The ammonia gas dissociates at the steel surface, releasing nascent nitrogen that diffuses into the metal to form hard iron/alloy nitrides. Because it is a sub-critical diffusion process, no rapid liquid quench is required, eliminating quench-related distortion.
A nitrided case typically consists of two zones: an outer 'compound layer' (or white layer) made of iron-nitrogen compounds which is exceptionally hard and corrosion-resistant, and a deeper 'diffusion zone' containing alloy nitrides (chromium, molybdenum, aluminium nitrides) that provides fatigue resistance and support for the compound layer. Surface hardnesses of 700 to over 1000 Vickers (HV) can be achieved depending on the steel grade.
Medium-carbon alloy steels containing nitride-forming elements like chromium, molybdenum, vanadium, and aluminium respond exceptionally well. Common grades include EN19, EN24, EN31, EN41B (specifically designed nitriding steel containing aluminium), H13 hot-work tool steel, and D2 cold-work tool steel.
Standard hardening processes require rapid oil or water quenching, which induces thermal stresses and phase transformations that distort critical geometry. Gas Nitriding operates below the steel's critical temperature (Ac1), meaning the crystal lattice does not undergo phase changes, and parts are cooled slowly. This results in virtually zero dimensional distortion, making it perfect for long, slender shafts and gears.
Nitriding case depths are shallow, typically ranging from 0.1mm to 0.6mm. Because nitrogen diffusion is slow at sub-critical temperatures, cycles are long — a 0.2mm case depth may take 12 to 24 hours, while a deeper 0.5mm case depth can require 48 to 60 hours of soaking.
Yes. The compound layer formed on the surface significantly increases resistance to atmospheric corrosion, mild acids, and oxidation. For many B2B engineering applications, this eliminates the need for post-treatment chrome plating or blackening.
We provide furnace cycle records detailing temperature, ammonia flow, and dissociation rates, along with surface hardness reports and micro-examination depth assessments.
Request a Quote
Send your drawing.
We'll confirm the process.
Share your material grade (e.g. EN41B, EN19), required nitrided case depth, drawing highlights, and quantities. We respond with a plan within 24 hours.
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