Cracking problems in Heat treating 4340
Cracking problems in Heat treating 4340
(OP)
I have some critical service pivot pins in a heavily loaded piece of plant equipment for which I am having spare pins manufactured.
My original equipment supplier furnished details of the pins and associated parts at time of order placement several years ago. The drawings include the required material, heat treating specification, finish dimensions and plating.
One of the pins cracked during flame hardening, and the heat treater says the specification is at fault. The original equipment supplier says the specification is without fault.
I am looking for some informed opinions from experienced Metallurgists.
The specifications are as follows:
Material: AISI 4340, 12" diameter x 34" long (approx.)
Through harden to a mid-radius yield strength of 148,000 psi yield strength and flame harden to a surface hardness of 45-50 Rockwell C.
Finish diameter is 300mm j6 at 32 micro-inch average roughness after plating.
Plating is to be Nedox FM-5 by Magnaplate.
Constructive comments are requested and will be very welcome.
My original equipment supplier furnished details of the pins and associated parts at time of order placement several years ago. The drawings include the required material, heat treating specification, finish dimensions and plating.
One of the pins cracked during flame hardening, and the heat treater says the specification is at fault. The original equipment supplier says the specification is without fault.
I am looking for some informed opinions from experienced Metallurgists.
The specifications are as follows:
Material: AISI 4340, 12" diameter x 34" long (approx.)
Through harden to a mid-radius yield strength of 148,000 psi yield strength and flame harden to a surface hardness of 45-50 Rockwell C.
Finish diameter is 300mm j6 at 32 micro-inch average roughness after plating.
Plating is to be Nedox FM-5 by Magnaplate.
Constructive comments are requested and will be very welcome.





RE: Cracking problems in Heat treating 4340
RE: Cracking problems in Heat treating 4340
RE: Cracking problems in Heat treating 4340
How is the material purchased, peeled bar, forging,etc?
Does the bar have any NDT checks prior to heat treating?
Can you post your flame hardening procedure?
RE: Cracking problems in Heat treating 4340
It would be easier to answer your question if you provided more details regarding the heat treatments performed. For initial heat treating to obtain 148 KSI Y.S in the center of the 12" diameter bar, what were austenitizing temperature, quench media and tempering temperature. What was the "flame hardening" process methods and quench media and its application methods.
RE: Cracking problems in Heat treating 4340
Another point of clarification is in order -- What was the nature of the crack? Was this classical quench cracking, or was the crack a linear line, perhaps indicative of a seam or near surface inclusion band? Did the cracking occur in the vicinity of one or more stress raisers or geometry changes, such as a hole, retaining ring groove or step change in diameter? I'd also like to know what aspect of the specification the heat treater blames. Is he scrambling to avoid blame or does he have an intelligent and legitimate complaint. And perhaps the most important question is, "If he had fault with the drawing, why didn't he raise the issue prior to performing the work?"
RE: Cracking problems in Heat treating 4340
1. My original post of July 29 included all of the information on the drawing. Quench medium, draw temperature, etc. were not specified on the drawing (or on the purchase order & attachments).
2. I will attempt to make a photograph of the crack available, as it is most descriptive. This will be addressed in a subsequent post.
3. I will list the detailed steps that were used in the heat treatment processes in a later post. I am in process of gathering this detailed information and do not yet have all of the information.
RE: Cracking problems in Heat treating 4340
Ricko,
The drawing calls out a final surface hardness which dictates the draw temperature depending on as quenched hardness after flame and quench.
Jesus is THE life,
Leonard