Has anyone had problems with quench cracking of alloy cold finish bars

[consultmet]

Recently we have had problems with quench cracking of cold finish 4140 bar. The heat treater claims there are tiny surface fold conditions present from the cold finish process that cause the quench crack. Metallographic examination so no surface conditions associated with the crack initiation. Further the cold finishing process includes an annealing process at the mill to remove residual stress.

Has anyone experienced the same problem quenching and tempering cold finish bars?

 

[redpicker]

Quench cracking 4140 bar is common. 4140 is very quench crack susceptable, so, depending on conditions, cracking is likely.

What size bar?
What kind of heat treatment, quench?
What is the nature of the cracking?

There are certianly going be "tiny surface fold conditions" on cold finished bar. Emphisis should be made on "tiny". One of the reasons for cold finishing is to improve the surface finish over hot-rolled product. You may still get some shallow imperfections with cold finishing, but they should be rather shallow.

rp

 

[swall]

I frequently see seams in 5160 bars (1" diameter or so)that have been either peeled or centerless ground. The surface enhancement is not always deep enough to remove all imperfections. If bar is merely cold drawn through a die without either of the above steps, any thing on the hot rolled bar will carry through on the cold drawn bar, except that seams and other imperfections will be smeared over. And yes, seams and other imperfections will open up during heat treat.