Bright Annealing of 430F(R)
Bright Annealing of 430F(R)
(OP)
We have several components made from 430F & 430FR that require a bright anneal for both magnetic & assembly reasons. We have a local heat treater who does a great job for us but will not tell us his exact process. We subcontract the manufacture of some of these parts and the subcontractors are having trouble finding local heat treaters that can produce a consistently bright finish.
Here are some excerts from our bright annealing spec but it does not seem to be sufficient to get consistently bright parts. Times & temperatures are from Carpenter. I suspect the atmosphere is not adaquate. Any suggestions are welcome!
3.3.2 Annealing
Temperature, time, atmosphere and rate of cooling shall be as specified in Sections 3.3.2.1 through 3.3.2.3.
3.3.2.1 Annealing Temperature and Time
The parts shall be heated to the temperature range in
the chart below and held at the selected temperature
for 2 to 4 hours.
Silicon content Annealing Temperature
Less than 1% 788-843°C (1450-1550°F)
1% or more 843-1000°C (1550-1830°F)
Note: Furnace control thermocouple(s) may be used
for the temperature and time measurements provided
sufficient allowance is made to ensure all the parts in
the load reach the selected temperature for the
specified time.
3.3.2.2 Atmosphere
A dry hydrogen or vacuum atmosphere shall be used
during the heating and soaking periods of the cycle.
If a vacuum atmosphere is used, of 1X10-3 millimeters
(1 micron) of mercury or less shall be maintained
throughout the soaking period.
3.3.2.3 Cooling Rate
Furnace cool to 425°C (800°F) at a rate not
exceeding 56°C (100°F) per hour. Below 425°C
(800°F) cooling rate is optional. Nitrogen with a dew
point of -50°C (-60°F) or lower can be used to
assist cooling. Below 180°C (356°F) air cooling is
permissible.
3.5 Properties After Treatment
The characteristics and properties of the heat treated parts shall be in accordance with the requirements specified in Table 1, when tested in accordance with the applicable methods specified in Table 2. Unless otherwise specified herein, these properties apply to all portions of the part.
TABLE 1
REQUIREMENTS FOR HEAT TREATED PARTS
Hardness: 170 Max HV/10 kgf or 85 Max HRB
Surface Condition: Parts must be bright and clean. Discoloration in the form of an adherent oxide is not acceptable.
Dimensional Change and Distortion: Shall not exceed the limits necessary to meet finished part requirements.
Here are some excerts from our bright annealing spec but it does not seem to be sufficient to get consistently bright parts. Times & temperatures are from Carpenter. I suspect the atmosphere is not adaquate. Any suggestions are welcome!
3.3.2 Annealing
Temperature, time, atmosphere and rate of cooling shall be as specified in Sections 3.3.2.1 through 3.3.2.3.
3.3.2.1 Annealing Temperature and Time
The parts shall be heated to the temperature range in
the chart below and held at the selected temperature
for 2 to 4 hours.
Silicon content Annealing Temperature
Less than 1% 788-843°C (1450-1550°F)
1% or more 843-1000°C (1550-1830°F)
Note: Furnace control thermocouple(s) may be used
for the temperature and time measurements provided
sufficient allowance is made to ensure all the parts in
the load reach the selected temperature for the
specified time.
3.3.2.2 Atmosphere
A dry hydrogen or vacuum atmosphere shall be used
during the heating and soaking periods of the cycle.
If a vacuum atmosphere is used, of 1X10-3 millimeters
(1 micron) of mercury or less shall be maintained
throughout the soaking period.
3.3.2.3 Cooling Rate
Furnace cool to 425°C (800°F) at a rate not
exceeding 56°C (100°F) per hour. Below 425°C
(800°F) cooling rate is optional. Nitrogen with a dew
point of -50°C (-60°F) or lower can be used to
assist cooling. Below 180°C (356°F) air cooling is
permissible.
3.5 Properties After Treatment
The characteristics and properties of the heat treated parts shall be in accordance with the requirements specified in Table 1, when tested in accordance with the applicable methods specified in Table 2. Unless otherwise specified herein, these properties apply to all portions of the part.
TABLE 1
REQUIREMENTS FOR HEAT TREATED PARTS
Hardness: 170 Max HV/10 kgf or 85 Max HRB
Surface Condition: Parts must be bright and clean. Discoloration in the form of an adherent oxide is not acceptable.
Dimensional Change and Distortion: Shall not exceed the limits necessary to meet finished part requirements.
Talk To Other Members
RE: Bright Annealing of 430F(R)
The atmosphere should have a dew point no higher than -40C or 0.1 torr partial pressure of water. The cool down should be rapid because the atmosphere is less reducing at lower temperatures.
RE: Bright Annealing of 430F(R)
The cool down rate is limited because we need near optimum magnetic properties. The .1 torr H2O partial pressure would be for the atmosphere in the furnace prior to pump down (760 torr absolute pressure), is that correct? As we are specifying a vacuum of .001 torr, it would not make sense to have .1 torr H2O partial pressure under vacuum.
RE: Bright Annealing of 430F(R)
Bright annealing isn't real hard to do well. I have not heard the same said of vacuum annealing.
RE: Bright Annealing of 430F(R)
RE: Bright Annealing of 430F(R)
RE: Bright Annealing of 430F(R)
I put the vacuum anneal option in the spec initially because I didn't want to restrict the heat treater unnecessarily. IF the part comes out bright & has the magnetic properties, I don't really care how it is accomplished. It looks like a lot of heat treaters only read the time/temperature part of the spec.
RE: Bright Annealing of 430F(R)
Is there a good way to remove the oxides? Citric passivation and electropolishing do not seem to be effective and I am concerned about size change, particularly on the press fit diameters (+/-.0004").
RE: Bright Annealing of 430F(R)
Is this scale all the way to black? I'm concerned that you say it has significnt thickness. This just doesn't seem right. I wouldn't expect more than a light straw-colored tint from casual oxide formation.
RE: Bright Annealing of 430F(R)
The thickness problem is that when the plater is using chemical etching to remove the scale before passivation the process is not exact and close control is not possible. I had once very accurate parts to 0.01 mm tolerance aged in air furnace. When the scale was removes the parts were within -0.05 mm. Then another batch was aged in vaccum furnace with very light almost un-noticeable colloring result. Chemical etching to remove this scale resulted in the same -0.05 mm instead in less than 0.01.
RE: Bright Annealing of 430F(R)
Immerse the part in a solution of 10% NaOH(W) + 3% KMnO4(W) at 80°C to 95°C for 30 minutes. Rinse well. The solution will turn green after a short time and become less effective.
A quick (10 seconds) immersion in 20% HNO3(V)+ 2% HF at room temperature. Rinse quickly with running water and the oxide should be loose but may have to scrubbed off. You may have to adjust the composition of the pickling solution and time of the immersion. Watch the time, keep it as short as possible. Dip twice in the pickling solution if needed .
I've used this procedure in cleaning 430 extrusion nozzles with over 1000, 0.0120" dia holes and still maintained the edge of the hole with no discernible radius at 100X .
Do this procedure in a lab with a shower and fume hoods if possible.
The appropriate PPG is required.
There is still a little art in cleaning scale as each condition is different
.
We purposely forced an oxide on our 430 SS components for enhanced corrosion resistance.
RE: Bright Annealing of 430F(R)
RE: Bright Annealing of 430F(R)
Yes this is true to a "degree." Brightness is relative unless you specify the degree. To some customers a vacuum anneal would qualify as bright anneal but not in your case. You definitley need H2 atmosphere with low dewpoint as suggested for reducing oxides.
Also to corroborate the comment about prefinish condition before annealing. You need to alert your subcontractors to this fact and that they make sure the parts are properly degreased prior to annealing.
RE: Bright Annealing of 430F(R)
You need to require annealing in a reducing atmosphere. Hydrogen with at least a -40 DP
My hunch is that some oxide is present on the surface to start with. It may be shiney, but it is there. No vacuum or inert gas can remove existing oxides.
You can try to clean the parts afterward with nitric acid. Be carefull though, you can get rapid attack.
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm
RE: Bright Annealing of 430F(R)
I will remove the vacuum option, add the -40 dew point requirement and specify that the parts must be clean and free of oils prior to the anneal.
Thanks for all the responses, you have been a big help.
RE: Bright Annealing of 430F(R)
Any contacts in Chicago area will be a great help.
RE: Bright Annealing of 430F(R)
You may not be able to get it done.
Vac anneal and chemical clean my be your best bet.
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm
RE: Bright Annealing of 430F(R)
I just tried out a new source and the samples came back today, they look great. The surface is shiny, bright and silver.
The recepie used was Vaccum annealing (Nitrogen) at 1550 - 1850°F and the parts were ultrasonic cleaned at our facility before sending to Heat Treat.
Seeing different results produced by different sources on the same material, I am led to believe that the condition / Maintanence of the Furnace is also very important.
RE: Bright Annealing of 430F(R)