Flame hardening services selectively harden the surface of steel parts using a direct flame followed by rapid quench. It is the practical choice for large, heavy components — gear teeth, ways, rolls, and shafts — where you need a wear-resistant skin over a tough, shock-absorbing core. For buyers, flame hardening delivers localized hardness without treating the whole part.
What Is Flame Hardening?
A controlled oxy-fuel or gas flame heats the surface of the steel above its transformation temperature while the core stays cool. Immediately after, a water quench converts the heated skin to martensite. The result is a hard case over a soft, ductile interior — ideal for impact and wear.
The Process and Control
Flame hardening is a surface heat-treatment we run alongside our heat treatment operations. Pre- and post-machining on CNC turning and CNC milling set the geometry, and we finish ground surfaces on cylindrical grinding and surface grinding. Extruded bars from steel extrusion are common starting stock.
Materials and Compatibility
Flame hardening needs hardenable steel — medium-carbon and low-alloy grades respond best. It is a sibling of induction hardening services and part of our broader heat treatment services.
Applications and Depth
Gear teeth, spline shafts, slide ways, and crane wheels all benefit from a flame-hardened working face. Depth is tuned by flame dwell and quench timing. Shaft and gear work pairs naturally with our steel machining services and precision custom metal gears.
Quality Control and Tolerances
We measure case depth and surface hardness, and check for cracking. Because only the surface transforms, distortion is limited, but we verify critical dimensions after hardening. For deeper, uniform cases see our nitriding services.
Lead Times and How to Request a Quote
Flame hardening is fast for batches of large parts. Send the drawing with the hardened zone, target hardness, and material. We quote cycle and lot price, then process and return parts ready to use or finish-grind.
Frequently Asked Questions
Flame vs induction hardening?
Flame suits larger, irregular, or one-off parts; induction is better for consistent high-volume profiles.
What hardness can I expect?
Typically 50–60 HRC on the case for medium-carbon steels, depending on grade.
Will the part distort?
Less than through-hardening, since the core stays soft; we control quench to minimize movement.
Can you harden just one face?
Yes — localized heating is the whole point; only the flame-exposed zone hardens.
What steels work?
Medium-carbon and low-alloy steels; very low-carbon grades won’t harden enough.
Is post-machining needed?
Often a light grind restores size on the hardened zone; we quote that together.
Industries Served by Flame Hardening
Flame hardening is used on gears, machine ways, rolls, crane wheels, and agricultural and mining components that see sliding and impact. A hard face over a tough core is exactly what those parts need. It sits alongside our heat treatment work and with steel machining services that prepare the geometry.
Design and DFM Tips
Mark the hardened zone clearly and specify target hardness and case depth. Medium-carbon or low-alloy steel is required; very low carbon will not respond. Leave stock for any post-grind, since the quench can move the part slightly. Our induction hardening services are the alternative for consistent high-volume profiles.
Common Failure Modes to Avoid
Soft spots from uneven heating, cracking from over-aggressive quench, and distortion are the classic defects. They are controlled by flame pattern, dwell, and quench timing, plus fixturing. We check case depth and hardness and verify critical dimensions so the part is ready to run or finish-grind on receipt.
Specifying a Flame Hardening Quote
Mark the hardened zone on the drawing, give target surface hardness and case depth, and confirm the steel grade is hardenable. State whether post-grind stock is allowed so we can plan the quench distortion margin. We quote cycle time and lot price and verify case depth and hardness after processing, returning parts ready to run or to finish-grind to your final size.
Inspection and Documentation
Case depth is checked by cross-section or hardness traverse, surface hardness verified, and critical dimensions confirmed after quench. We retain cycle records so a repeat order is identical. That discipline is what makes flame hardening dependable for custom metal gears and other wear parts where a hard, well-controlled case is the whole point.
Why Buyers Choose a Single-Source Hardening Partner
Surface hardening should be specified with the machining that sets the geometry, not bolted on afterward. Planning flame hardening together with steel machining services and our induction hardening services avoids distortion surprises and keeps one quality system accountable for the finished, wear-resistant part you receive.
Quick Reference: Flame Hardening Spec Checklist
Mark the hardened zone, give target surface hardness and case depth, and confirm the steel is hardenable. State whether post-grind stock is allowed so we plan the distortion margin. We quote cycle time and lot price, verify case depth and hardness after processing, and return parts ready to run or to finish-grind to your final dimension.
For large or irregular steel parts that need a wear-resistant face, flame hardening delivers localized hardness with minimal distortion and a tough core underneath.
Ready to Start Your Flame Hardening Services Project?
Get a build-ready quote from Huaxiao’s engineering team. Share your drawing and we’ll return tolerances, lead time, and pricing.
