Member since 1963
|Presented here is a listing of the many
processes we offer here at Edwards Heat Treating Service,
along with some general metal treating information. Using the navigation buttons on the
left, you can go directly to a specific topic of interest.
Edwards Heat Treating is on the
approved list for many companies, including United Technology, OEA Aerospace, Hughes
Helicopters, Lawrence Livermore National Laboratory, Sandia Lab, National Airmotive,
United Airlines and Alaska Airlines. We are certified to heat treat according to
Edwards is the most experienced heat treating company in Central and Northern California with over 200 years of collective heat treating experience. We specialize in fast turnaround, excellent quality control and customized work to suit customer applications.
Through Hardening - What Is It? - The object of through hardening is to harden
parts throughout their cross section. Not only is the surface resistant to wear, but the
entire part is more able to resist bending or twisting without failure. Steel producers
increase the carbon content of steel to obtain greater hardening ability. For example, low
carbon steel such as 1018, with .18% carbon, does not harden when quenched from its
critical temperature. A medium carbon steel such as 1045, with .45% carbon, will achieve a
hardness of, say, 35 on the Rockwell C scale. Carbon content near 1% and beyond will
provide a very hard part beyond Rc 60 in many cases. Unfortunately as hardness goes up,
the ability of the part to withstand shock and bending forces decreases. This latter
property is called "toughness."
Ask Edwards for comparisons of the various alloys and their heat
Water Hardening (W)
Parts may be designed with different hardness in certain areas of the part. Shafts may need to be hard in a bearing area but more ductile elsewhere to avoid breakage. Surfaces of gear teeth must be very hard to resist wear, but the core of the teeth or the gear body itself must be softer to resist cracking due to shock loads.
Induction hardening and carbon or nitrogen-added case hardening are two methods of selective heat treatment and are described later. Other techniques for selective hardening or softening of metals include:
Heating portions of parts using induction coils can soften previously hardened metal.
Induction hardening refers to the selective heating of steels using electric coils to rapidly heat one or more sections of a part to critical (austenitizing) temperature followed by quenching in water or oil.The non-heated area of the part remains unhardened. Induction hardening is specified when it is not advisable to harden certain areas of the part or when the desired hardened depth exceeds that which is possible when case hardened. It can also be specified as a surface treatment for alloys not suitable for carburizing.
| Typically, induction hardened parts are designed with high hardness to
resist abrasion or impacts in areas subjected to wear, such as in gear teeth or bearing
surfaces on shafts, while the balance of the part is tough and ductile to minimize
Induction Softening - Similarly, some parts may be selectively softened for machining or reworking. Material type and previous heat treatment will determine if this can be accomplished.
Edwards Heat Treating uses two induction heating units with the largest one offering rapid heating for thick sections. Many different coil sizes are in stock, meaning fast turnaround on a wide variety of shapes.
| In austempering, work heated to
its critical (austenitizing) temperature is quenched in a hot salt solution at 475 to 700F
and held at that temperature for a specified time, rather than oil or air quenching to a
lower temperature. Transformation is then complete and no tempering is necessary. With
certain alloys and hardness levels, the resulting bainite structure can be tougher than if
normally quenched and tempered.
Austempering is limited to fairly thin sections, about 1/8" in plain carbon steels and thinner in alloy steels, because the salt quench will not cool thicker sections fast enough.
Consider austempering for 1045, 1055, 1070 and 1095 sheet stampings, wire forms and thin bar sections.
Hardening just the surface layer of steels is called case
hardening. A very hard case,
or "skin" resists wear and is supported by a core of lower hardness, depending
on the type of steel, which is more tough and ductile, resisting breakage.
This is a form of case hardening in which the furnace atmosphere is adjusted to deposit
carbon into work when it is held at critical temperature. This layer of increased carbon
can then achieve very high hardness when quenched. Since the sub-surface area has a lower
carbon content, it does not harden as much or at all during this process. This leaves a
more tough, ductile core than a through-hardening alloy or tool steel with the same
surface hardness potential can offer.
| Similar to carburizing, this is a gaseous process for adding carbon and nitrogen to the
surface layer of steel during heating. Nitrides quickly form on the surface and are
inherently hard. Case depths are usually limited to .030". See the Carburizing section above for additional information.
Carbonitrided parts respond well to a CryoTune treatment for additional wear resistance.
If hard, clean parts with a light case depth are desired, carbonitriding is a cost-effective solution.
Annealing is a generic term denoting a softening treatment consisting of heating to and
holding at a suitable temperature, followed by cooling at a relatively slow rate. It can
improve machinability, cold working ability, mechanical or electrical properties and
increase dimensional stability.
| A type of softening, stress relieving involves heating to a suitable temperature below
the critical point, holding long enough to reduce residual stresses and then air cooling
to minimize the development of new residual stresses.
Notes About Residual Stress in Materials: Harmful internal stress may be developed in metals from cold working such as rolling, spinning, bending or drawing due to the disruptive effect on the crystalline structure. Residual stress may result from uneven cooling after welding due to the uneven expansion and contraction of the heated area adjacent to the unheated area. Shrinkage stress occurs in castings with sections of different thickness that cool at different rates. These stresses can be removed.
Parts that are highly stressed and/or must maintain dimensional accuracy for years must be stress-free before being put into service.
Residual stress often causes movement in the work during finish machining or grinding, negatively affecting the ability to hold tolerances. A stress relief step often minimizes finishing time, lowering the overall cost of the job.
Most steel parts are stress relieved in the range of 400F to 1250F. The strategy is to heat until the yield strength is lowered enough so stresses can expend themselves. In most steels, this is approximately 1200F.
Cryogenic, deep cold treatment (CryoTuning) also stabilizes most metals and some plastics. Consider it for parts or assemblies that should not receive an oven treatment for whatever reason.
|Normalizing is the process of heating steel just above the critical temperature and air
cooling to a temperature below the transformation range. It can help eliminate growth in
parts during subsequent hardening, thus minimizing finish grinding. It is especially
recommended for 8620 or 9310 parts that are to be carburized, such as gears. Usually a low
cost normalizing step prior to machining will result in a part that can be made closer to
size, saving time, aggravation and money.
If you have any questions, please call Edwards Heat
(510) 638-4140 or E-mail us at: email@example.com
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