Carburizing & Carbonitriding
(SQF) in India
Precision gas carburizing, carbonitriding, and neutral hardening inside atmosphere-controlled sealed batch furnaces.
The Technology
What is Sealed Quench Carburizing?
Sealed Quench Furnace (SQF) carburizing is an advanced thermal case-hardening process that diffuses carbon into low-carbon steel components. The parts are heated to high temperature (900°C-930°C) under a controlled carbon-potential atmosphere. Liquid hydrocarbons (like propane) are introduced during the boost phase, and carbon atoms penetrate the steel's surface lattice.
Once the target case depth is reached, the batch is transferred to the furnace's integrated quench oil tank without leaving the protective atmosphere. This internal transfer prevents contact with ambient oxygen, completely eliminating scaling and surface decarburization. The result is a glass-hard, wear-resistant outer case supported by a highly ductile core.
Atmosphere-Sealed Carburizing Profile
Metallurgical Outcomes
Case Depth & Core Integrity
Sealed quenching achieves the dual mechanical profiles critical for high-wear, high-impact drive gears.
Controllable case depth
Uniform Case Profile
Precise control of carbon potential yields uniform case depth profiles, meeting tight microhardness specification ranges.
High surface hardness
Wear-Resistant Surface
Transforms low-carbon surfaces into high-carbon martensite (58-63 HRC), providing exceptional wear and galling resistance.
Impact toughness
Ductile Shockproof Core
The core remains low in carbon, maintaining its ductile ferrite-pearlite structure to absorb massive drive-line shock loads.
Protective atmosphere
Decarburization Control
Atmosphere isolation ensures that carbon is not depleted at the surface, ensuring the surface retains its wear resistance.
Reduced machining time
Scale-Free Finish
Components are quenched without exposing them to air, yielding clean surfaces that require minimal grinding or clean-up.
Enhanced fatigue limit
Compressive Surface Stress
Volumetric changes during martensitic case expansion introduce compressive stresses, significantly improving bending fatigue limits.
OUR PROCESS
How we execute Sealed Quench Carburizing
at Tapovan
Fixture Loading
Components are oriented on carbon fixtures to prevent shielding and ensure even gas circulation.
Controlled Heating
Charge heated in sealed chamber with protective gas. Carbon potential raised for boost diffusion.
Boost & Diffusion
Carbon absorbed in boost stage, then diffused in diffusion stage to achieve the target case depth.
Internal Quench
Temperature stabilized to 840°C, then batch drops into oil quench inside the sealed chamber.
Post-Quench Washing
Parts run through wash and rinse cycles to completely remove residual quench oil.
Tempering & QA
Parts tempered at 180°C. Case depth and surface hardness tested. Batch certified.
STANDARDS WE WORK TO
Applications in India
Specified Components
Extensively specified for automotive transmission gears, heavy-duty machinery gears, agricultural pinions, and high-impact wear components.
Transmission Gears
- Crown wheels & pinions
- Gearbox speed gears
- Helical input pinion shafts
- Synchronizer splines
Drivetrain Joints
- Spider cross-journals
- CV joint inner races
- Differential side gears
- Output flanges
Heavy Fasteners
- Socket head cap screws
- Heavy structural studs
- Anchor bolts
- Automotive wheel studs
Industrial Machinery
- Splined transmission shafts
- Excavator pivot pins
- Conveyor roller axles
- Cam followers
Frequently Asked
Common questions
Find technical answers about Sealed Quench carburizing and carbonitriding cycles.
A Sealed Quench Furnace (SQF) is an batch-type heat treatment system where the heating chamber, atmosphere control system, and quench tank are integrated into a single enclosed envelope. This configuration keeps the components under a protective atmosphere (such as nitrogen-methanol) during heating and transfer to the oil quench tank. This completely eliminates exposure to oxygen, preventing surface oxidation and decarburization.
The most common processes are Gas Carburizing (introducing carbon to low-carbon steels), Carbonitriding (introducing carbon and nitrogen to improve wear resistance in mild steels), Neutral Hardening (hardening alloy steels without altering surface chemistry), and carbon restoration.
SQF ensures high-quality surface integrity. Because the transition from the furnace chamber to the quench oil happens in a sealed chamber, components do not form heavy scale, surface decarburization is entirely prevented, and the parts emerge with a clean, semi-bright appearance, significantly reducing final grinding time.
Case depth refers to the thickness of the outer carburized layer that is high in carbon and hard (typically >58 HRC), while the core remains tough and ductile. We monitor this by placing carbon test coupons in every batch. We then evaluate the case depth on cross-section test specimens using micro-hardness testers in our metallurgical lab.
Low-carbon carburizing steels (carbon content of 0.15% to 0.25%) are ideal. Common grades include 20MnCr5, 16MnCr5, 8620, SAE 8620H, and EN351. These alloys permit carbon absorption at high temperatures, creating a hard surface case while maintaining core toughness.
Following the rapid oil quench, the components are washed to remove quench oil and then immediately tempered in a tempering furnace (usually between 150°C to 200°C for case-hardened parts). This relieves high stresses in the martensitic case, preventing cracking while maintaining surface hardness.
We supply digital process charts showing carbon potential, carburizing temperature, diffusion hold times, and oil quench temperatures, alongside microhardness case depth profile reports and certification.
Request a Quote
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We'll confirm the process.
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