Summary for 4130 annealing Discussion
Basic annealing of 4130 question: Mike Klos asked why MIG welds on 4130 tubing turn much darker than the surrounding metal after Parkerizing, and whether annealing would prevent the color mismatch. The answer explains that surface appearance after finishing depends on the substrate’s chemistry and microstructure, and weld metal will usually differ from the base alloy steel in both. To homogenize the microstructure, the part would need to be heated to about 1600 °F and furnace cooled, but even that may not eliminate the color difference if the weld filler has a different composition. The reply also warns that annealing will alter the steel’s mechanical properties. A better approach, according to the answerer, may be to duplicate the original heat treatment of the 4130, likely normalizing or quenching and tempering, rather than relying on annealing alone.
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
2000
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
Minneapolis, Minnesota
2000
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?
JOHN MCGHEE
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