Quench Cracking
Quench Cracking
(OP)
Can a decarburized layer reduce the tendency for quench cracking?
We have forged steel cylinders 14-ft long and 16-inch diameter. The entire length is hollow with a 2.25 inch wall thickness, except for 3 feet at one end which is solid. There are no sharp corners anywhere; just very large blend radii.
We are quenching in agitated water because we need a rapid rate to develop martensite in the thru section of the wall. No problem there, but in the section that is solid, we are sometimes getting circumferential and longitudinal cracks. We are now trying remedies, e.g., eliminating time delays, keeping warm before tempering.
I thought of eliminating the anti-carb coating thinking that a decarburizied layer would be ductile and not as prone to nucleating tensile cracks (even though its only ~.03 thick). Any thoughts or comments on that?
Thanks.
Additional info:
Heat treatment is to normalize, then austenitize, quench and temper.
Quenchant is natural lake water, Seasonal temperature is 50 – 75 deg F.
Steel alloy is experimental: 0.26 C; 0.65 Mn; 1.00 ea Si, Ni, W; 2.60 Cr and some Mo, V & Cu. (No actual TTT or CTT diagrams)
We have forged steel cylinders 14-ft long and 16-inch diameter. The entire length is hollow with a 2.25 inch wall thickness, except for 3 feet at one end which is solid. There are no sharp corners anywhere; just very large blend radii.
We are quenching in agitated water because we need a rapid rate to develop martensite in the thru section of the wall. No problem there, but in the section that is solid, we are sometimes getting circumferential and longitudinal cracks. We are now trying remedies, e.g., eliminating time delays, keeping warm before tempering.
I thought of eliminating the anti-carb coating thinking that a decarburizied layer would be ductile and not as prone to nucleating tensile cracks (even though its only ~.03 thick). Any thoughts or comments on that?
Thanks.
Additional info:
Heat treatment is to normalize, then austenitize, quench and temper.
Quenchant is natural lake water, Seasonal temperature is 50 – 75 deg F.
Steel alloy is experimental: 0.26 C; 0.65 Mn; 1.00 ea Si, Ni, W; 2.60 Cr and some Mo, V & Cu. (No actual TTT or CTT diagrams)





RE: Quench Cracking
Try pulling the material out of the quench at around 400-500F on the solid end and getting it into the temper before it falls below 300F. You should be below the M90 temperature and the cooling rate from 500 to 300F isn't going to make any difference in the transformation, but by slowing the cooling rate, you reduce the thermal gradient, so you reduce the tendency to crack.
Most quench cracks form below 400F.
rp
RE: Quench Cracking
Gold is for the mistress - silver for the maid
Copper for the craftsman cunning in his trade.
"Good!" said the Baron, sitting in his hall
But iron - cold iron is the master of them all.
Rudyard Kipling
RE: Quench Cracking
RE: Quench Cracking
I think Metalguy is identifying an area that won't form martensite - the 3 feet (1 m) length that is 16 inches (400 mm) in diameter. That area won't form martensite throughout.
RE: Quench Cracking
rp
RE: Quench Cracking
Here's the likely problem. You have a hard tempered martensite surface over a huge FCC austenitic core. As that core slowly transforms to BCC, it expands. The surface must also expand plastically, and that's not going to happen with untempered martensite, so it cracks--in all directions, as you've observed.
You solve the problem by using some kind of insulating sleeve around the solid end--even a thick ring of carbon steel should work. Try for a shrink fit before heating the barrel (large gun barrel?). The idea is to prevent the surface of the solid end from cooling fast enough to transform to anything but pearlite.
Then, as the interior transforms and expands, the relatively soft surface will plastically expand (stretch) w/o cracking.
Gold is for the mistress - silver for the maid
Copper for the craftsman cunning in his trade.
"Good!" said the Baron, sitting in his hall
But iron - cold iron is the master of them all.
Rudyard Kipling
RE: Quench Cracking
Gold is for the mistress - silver for the maid
Copper for the craftsman cunning in his trade.
"Good!" said the Baron, sitting in his hall
But iron - cold iron is the master of them all.
Rudyard Kipling
RE: Quench Cracking
In order to minimize the occurrence of quench cracks, heat should be drawn from the bar in as uniform a manner as possible during quenching. This is especially difficult to do properly when there are large changes in cross-section or relatively thin sections are adjacent to thick sections on the same part. Water quenching can aggravate the problem due to the formation of gas bubbles at the interface between the quenchant and the part. Agitation of the water helps to reduce this tendency, but does not eliminate it. Based on your description of the problem, the components have generous radii in all of the locations where changes in cross-sectional area occur, and the quench cracks probably result from a different issue.
I ran into a similar problem with cracks in oil quenched 422 stainless steel rounds. The standard practice was to austenitize the bars at 1925 F, oil quench until the bar temperature fell between 500 F and 900 F, and then air cool the rest of the way. After the bars air cooled below 200 F, they would go back into the furnace for a temper. We experienced sporadic cracking on several orders, and I was assigned the task of identifying the root cause and to determine the appropriate corrective action.
An experiment was conducted in the heat treat department to determine if the oil quenching practice that was used actually produced bar temperatures within the specified range. When the first 422 trial order was quenched the material was pulled from the quench tank after a 4 minute soak. The temperature of the steel had dropped to 300 F, which was far below the minimum specified temperature of 500 F. The other order was run with similar results. After a soak of 1 ½ minutes in much colder oil the steel temperature had dropped to 400 F. Apparently, the orders that experienced fallout had been left in the quench tank too long. They cooled too far below the aim temperature, and cracked.
You may be experiencing a similar issue. How long are you leaving the bars in the quench tank? Have you measured the temperature of the solid cross section of the bars as a function of time during quenching? Have you monitored the temperature of the water to determine if there is a relationship between the tendency to quench crack and the initial water temperature? These are some of the questions that you should be attempting to answer in order to identify the root cause of your problem.
Maui
RE: Quench Cracking
works with chrome moly steels
RE: Quench Cracking
If you think education is expensive, try Ignorance.
- Andy McIntyre
_____________________________________
RE: Quench Cracking
Thanks for the compliment. I was occupied with a number of projects and distractions that kept me from spending any significant time here. It's good to know that you noticed I was gone. And it's good to be back.
Maui