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Heat treated 4130 Color Result

Heat treated 4130 Color Result

Heat treated 4130 Color Result

(OP)

I have two different plates of 4130, both heat treated to a hardness of HRC 22, the but it looks like both plates are heat treated differently as the color of the finished plates is different.  Plate sample A is a dark gray to black while plate sample B is a light gray.

Is the finished color a result of the quench media?  For example one plate could be quenched with oil and the other water or brine?

Initially I though the tempering would effect the color, but given that they both have the same hardness value this maybe not the case.

RE: Heat treated 4130 Color Result

The finished color can depend upon several factors.  The type of quenchant can affect the final color.  In this particular case, I would speculate that the dark color is darkened/decomposed quenchant and/or scale from tempering.  The light gray color likely is the base metal color due to a descaling/cleaning operation after the tempering process.

RE: Heat treated 4130 Color Result

(OP)
Could it be that part was heat treated in a vacuum rather than atmosphere?  Would this have any effect on the color?

 

RE: Heat treated 4130 Color Result

Yes.

RE: Heat treated 4130 Color Result

Furnace atmosphere can play a large role in material surface color.

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