Flame hardening

The flame-hardening process is used for a wide variety of applications. These include (1) parts that are so large that conventional furnace treatments are impractical or uneconomical, (2) prevention of detrimental treatment of the entire component when only small segments of die part require heat treatment, and (3) use of less costly material to obtain the desired surface properties where alloyed steels would be normally applied. Flame hardening is limited to hardenable steels (wrought or cast) and cast iron. Typical hardnesses obtained for the flame-hardened grades depend on the quench media (Table 1). The practical level of minimum surface hardness attainable with water quenching for various carbon contents is shown in Fig. 1. 

Induction hardening is a versatile heating method that involves placing a steel part in the magnetic field generated by high-fi equency alternating 

1 Relationship of carbon content to minimum surface hardness attain-able by flame or induction heating and water quenching. Practical minimum carbon content can be determined from this curve. Source Ref 1 

Thin sections are susceptible to cracking when quenched with oil or water, (c) Hardness is slightly lower for material heated by spin-  

Equipment Oxyfuel torch, special head quench system Power supply, inductor, quench system 

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Fig. 3. Flame hardening (a) tempeiatuie—time heating curves of a 25 x 50 x 100 mm specimen at a feed of 75 mm /min and burner distance of 8 mm showing temperatures of A, surface B, 2 mm below surface and C, 10 mm below surface (b) hardness—depth curves for a 0.50% C steel 25 X 75 X 100 mm specimen at a feed of 50 mm /min, temperatures ia °C measured 10 mm below the surface, and burner distances ia mm, respectively, of A, 530 and 50 B, 540 and 12 C, 545 and 10 D, 550 and 8 and E, 565 and 6. Flame heating followed by water spray quenching. HV = Vickers hardness.

PISTON RINGS are normally cast-iron of the single-piece snap-ring type, although other materials may be used when conditions require. PISTON ROD is carbon-steel, flame-hardened over packing travel area. 

PISTON ROD is carbon-steel, flame-hardened over packing travel area unless otherwise specified. 

Flame hardened Heavy case depths with good capacity for contact loads, good bending fatigue resistance and fair dimensional control... 

The dies themselves are generally constructed of medium carbon alloy steels, with flame-hardened lips and chrome or nickel plating on the flow surfaces. Insulation of the die body Is common to prevent temperature variations that could result from air drafts. Dies can be electrically heated, or steam or oil heat can be used. Cooling is usually provided by natural convection, though forced air can also be used. 

Surface hardenability - laser hardening, flame hardening or inductive hardening,... 

FIGURE 4.90 Cracking during flame hardening due to excessively abrupt cooling conditions... 

Figure 4.90 shows an example of a plastic compression mold made of the prehardened plastic mold steel 1.2738 (40CrMnNiMo8-6-4). Cracking occurred during flame hardening of the parting lines due to the absence of pre-heating. 

FIGURE 4.91 Flame hardening a mold surface in a wear area... 

Selective hardening treatments, for example, flame hardening... 

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