SAE 9260 race car suspension spring heat treatment 2

[pardal]

Which the best suited heat treatmet to make on suspension spring for race car's.

They range from 11 mm [ 7/16"] to 16 mm [5/8"] wire diameter .
Up to 150 mm [6"] coil diameter .
Up to 600 mm [ 24"] length.
It is a guess 52 RC hardenes .

The furnace will be electric heat with controled atmosphere , it could be with a blend of Nitrogen and some hidrocarbon gas in a high press cylinder or a on furnace mix off the same gas .

I intend to heat in a small round hose furnace to handle only one spring by time.

The same furnace will be used to post quench treatment.
Thank in advance




Pardal

 

[TVP]

The following information should allow you to produce a suitable spring:

1. Austenitizing temperature to be 815-900 C.

2. Atmosphere control is very important-- this alloy is very sensitive to decarburization and intergranular oxidation. There should be no complete decarburization, and 0.15 mm maximum partial decarburization (SAE J419, Type 2).

3. The spring should be oil quenched. The transfer from the furnace to the quenchant should be as fast as possible. Agitate the spring while quenching. The as-quenched hardness should be at least 56 HRC (610 HV30 or ~ 580 HB).

4. Tempering temperature should be set so that the final hardness is 48-52 HRC (~361-514 HB). This will be somewhere around 360-440 C.

5. The spring should be shot-peened. A typical requirement is 0.30-0.45 mm A (SAE J442 & J443), with minimum coverage of 95%. This can be achieved by peening with cast steel shot S330-S390 (SAE J444) or cut-wire shot CW-41 or CW-47 (SAE J441).

6. After shot peening, the spring should be set (compressed to solid). If performed at ambient temperature (25 C), do this 3 times. You should also have a very good coating applied, typically zinc phosphate pre-treatment followed by a polyester powder coating, thickness = 40 micrometers minimum.

I hope this was helpful. Please post again if you have any other questions.

 

[pardal]

Hi TVP.

Your help could not be better.
What should be the atmosphere composition??
Could you give a stimated temp groving rate to reach the
815-900°C , and the time to be sustained.
The same for tempering.

Thanks againg.



Pardal

 

[TVP]

Pardal,

Hardening can be performed either in a Nitrogen-based neutral atmosphere (typically 97.1 N₂, 1.7 CO, 1.2 H₂) or in a hydrocarbon atmosphere (endothermic, exothermic, or a combination of the two). Catalysts are required for the hydrocarbon atmospheres, as well as precise control on the mixture, carbon potential, etc., so I would recommend the neutral hardening route. Make sure that the furnace atmosphere does not contain oxygen or water vapor from the surrounding environment.

The holding time during austenitizing is typically 1 hour minimum, or 15-20 minutes per 25 mm of maximum section thickness. The tempering operation should be performed as soon as possible after quenching. The holding time for tempering should probably be about 2 hours. Air cooling after tempering is ok.

 

[pardal]

TVP , thanks a lot for IT .
What should be the internal pressure inside the furnace??


Pardal

 

[TVP]

Pardal,

I do not know what the pressure inside your furnace should be. I would discuss it with your furnace manufacturer or someone who heat treats similar components.

 

[unclesyd]

Like TVP states consult the manufacturer if possible. If this is not possible I would run the furnace at slight positive pressure, 2" to 3" of water measured using a gauge on the inlet line. You should allow the furnace to vent so if you can put a flow meter in the atmosphere to the furnace box. On all our furnaces we turned the atmosphere over every minute. I would use a once every five minute turnover value to start with if the flow rate is not too high due to the tightness of the furnace. All this can be checked prior to the introduction of your parts or on a cold furnace.
The industrial gas companies used to supply atmosphere mixtures for you purpose.

 

[springmeister]

This wire size and OD are well within the range of modern cold coiling machines, which can coil and cut off up to 3/4" tempered 9254 alloys. Even if furnace atmospheres and temperatures are correct, a coil spring is flexible at red heat and will frequently distort in the furnace. It's easier to coil cold from pre-hardened wire.