Fracture Toughness Source

[nlj]

Does anyone know of a good resource for fracture toughness data for induction hardened material (in particular 52100 and 4140H)? All of the research I have conducted thus far had fracture toughness data for quench and temper material only.

Thank you!

 

[TVP]

Induction heating is just a method for changing the temperature in a metal, so that certain microstructures can be developed. If the final microstructure in 4140H is martensite that has been quenched after induction heating and then subsequently tempered at a low temperature, then find fracture toughness data for 4140H that has been quenched and tempered to a similar high hardness condition. Fracture toughness does not apply to an entire part, it applies to a microstructure, and therefore will be different if the case and core properties are different.

 

[nlj]

Thank you for the reply TVP.

I understand what induction hardening is and that the fracture toughness is dependent on the microstructure. My issue is that I haven't been finding fracture toughness data for the high surface hardness that our parts are specified to have (55 HRC). I'm not so concerned with the toughness at the core.

 

[Wrenchbender]

NLJ,

I’ve been told that the best source for fracture toughness and fatigue crack growth rate data is a series of papers by Michael Hudson, published by the Int’l Journal of Fracture:
Vol. 14, 1978, pp. R151 – R184.
Vol. 20, 1982, pp. R59 – R117.
Vol. 39, 1989, pp. R43 – R63.

I myself have also had trouble finding values for plain strain fx toughness (K_1c) to use in design work. Textbooks that I find useful are:
Dieter – Mechanical Metallurgy
Hertzberg – Deformation and Fx Mechanics
Nat’l Materials Advisory Board (NMAB), Report 328 (free on google books) Figure 1 shows ranges of K1c for various alloys in a lab environment (ambient temp, no corrosives).

To state the obvious in case you cannot find published values, a mechanical testing lab can run ASTM E399 for you. Valid plain strain results should be easy with such a high hardness.

As you probably know, for typical alloy steels
55 HRC = UTS apprx 300 ksi = pretty crappy K_1c

With hardness vs fx toughness it’s a case of not being able to have cake and eat it too, unless you go with a more expensive material, e.g. AF1410 or maraging steel.