Heat treated 4130 Color Result 1

[CR100]

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.

 

[CoryPad]

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.

 

[CR100]

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

 

[TVP]

Yes.

 

[deadrange]

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