Carbon content for heat treat

[Kinsrow]

Does .45-.50% carbon content on 420 SS produce the same tensile and yield strength as the .35-.40% carbon content on the same 420 SS when they get heat treat to 49-55 HRC?

In other word, would both type of SS with different carbon content produce the same mechanical property after the same heat treat ( assuming that both can reach the heat treat spec).

the design calls for .35-.40% carbon content 420 SS harden to 45-55 HRC, but I would like to prototype it using .45-.50% carbon 420 SS harden to 45-55 HRC

Thanks

 

[Metalmeister]

Kinsrow,

In answer to your first question - yes it would. Tensile strength correlates to hardness very well.

In answer to your second question - no it wouldn't. In general the high C content produces a higher hardness and higher strength for the same heat treatment. The depth that you would achieve that hardness would also be different.

The higher temperature properties and material response to heat treatment would be different as well. See my discussion of 5 minutes ago on the weld CVNs. Richer chemistry, in this case higher C, responds differently than a lean chemistry.

 

[Kinsrow]

But if they do reach the same hardness after heat treat, they should have the same mechanical property, no?

 

[TVP]

Kinsrow,

You need to be more specific than "same mechanical property". If heat treated to the same hardness, then the ultimate tensile strength will essentially be the same. Fracture strain (elongation) and fracture toughness (charpy impact or other test) likely will not be the same.

 

[Kinsrow]

I appologize for my laziness. I'm specifically interested on the yield and ultimate strength.

Thanks

 

[metengr]

Kinsrow;
Re; Strengthening Mechanisms

For martensitic stainless steels, conventional flow stress for plastic deformation and hardness and ultimate tensile strength are directly affected by carbon content (high carbon results in higher hardness, UTS and YS).

So, the short answer is heats of differing carbon content if heat treated to the same hardness would have similar UTS and YS values between them at RT. However, as TVP indicated their response to strain hardening, fracture strain and most certainly CVN impact energy would be different between the two heats. In this case, the higher carbon heat would have less strain to fracture and a higher CVN transition temperature.


Source; Handbook of Stainless Steels by Peckner and Bernstein