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Basic annealing of 4130 question

Q. I need to Parkerize some parts that I have welded on (mig) and after parkerizing, the welds show as very dark in color compared to the rest of the surface.

I have been told that if I anneal them, it will not show. How is this done? The metal is 4130 tubing and there are spot/fill welds. Please be specific and technical. Any info will be helpful. Thanks, Mike

Mike Klos
- Wentzville, Missouri

A. The surface appearance after surface treatment is affected by the chemical composition and/or microstructure of the substrate. The weld will certainly have a different structure than the alloy steel and probably a different composition. Annealing to homogenize the microstructure would involve heating the entire part to a temperature of about 1600 °F, then furnace cooling. This heat treatment may not change the final surface appearance if the weld metal has a different composition than the base metal.

Also remember that the heat treatment will change the mechanical properties of the alloy steel. A better alternative may be to duplicate the original heat treatment - probably either normalized or quenched and tempered.

larry hanke
Larry Hanke
Minneapolis, Minnesota

Does stripping powder coating at 800 °F weaken 4130 steel?

Q. I am using 4130 normalized on a recent project. In some cases my powder coater has to repaint due to coverage or other issues. He puts the powder coated parts in an oven at 800 °F to strip the old powder. Does the 800 °F "tempering" reduce the ultimate strength of 4130?

product designer - Parkdale Oregon USA
July 20, 2016

A. It would depend on the hardness requirement of the final product and the final tempering temperature. Normally one wants to stay around 50 °F below the final tempering temperature to avoid any affect to the final hardness.

Donna Warner
- New Century Kansas USA
September 20, 2016

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