Flame Hardening

What does flame hardening mean?

Flame hardening is a surface hardening method in which a metal is heated to a high temperature with a flame and then quenched at Medium carbon steels, heat treatable or alloy steels or cast irons to create a hard, wear resistant surface. Flame hardening uses the direct impact of an oxygen gas flame on a defined surface.

The result of the hardening process is determined by four factors:

Combustion head design
Heating time
Target temperature to be reached
Composition of the metal to be treated

Typical flame hardening applications include:

blades
gears
rollers
Cams
Automotive components

Flame tempering

Flame tempering is performed on parts made of mild steel, alloy steel, medium-hard steel carbon and cast iron. As the name suggests, flame hardening uses the direct heat of oxyfuel flames. Metals are heated to temperatures up to their austenitization temperature, changing the surface while the core remains unaltered and smooth. If the steel surface reaches the austenitizing temperature, it must be quenched immediately. As the material then rapidly cools, it develops a harder surface that is less susceptible to wear and corrosion.
The surface of the steel, which often consists of austenites and/or ferrites before hardening, forms martensite.
Flame hardening can be applied differently or on the entire surface of a Workpiece. The result of flame hardening is determined by the heat of the flame, the heating time and rate, the temperature of the cooling process, and the elemental composition of the target material.
The flame is based on gases that allow her to reach
high and stable temperatures. In the most common cases, these are oxygen and acetylene, sometimes also propane.

Types of flame hardening:

Basically, two types of flame hardening techniques are used, namely centrifugal hardening and gearing process at the same time. Spin hardening is best for gears with sufficient mass to absorb the excessive heat applied in this process without excessive distortion.
Some common types of hardening include work hardening, solid solution hardening, precipitation hardening, and quenching and tempering.

Advantages of flame-hardened steels include:

Improved wear resistance
Short processing time (compared to other carburizing processes such as nitriding and case hardening)
Inexpensive
Less distortion
Few processing steps
Higher hardness

What steels can be flame hardened?

Flame hardening is a surface hardening process used on medium carbon or alloy steels (such as 1045, 4140, 4340) or cast iron to create a wear resistant surface (shell) on the part.