4130 cracking at LOW temperatures
4130 cracking at LOW temperatures
(OP)
We have machined parts made from 4130, austenized and quenched and tempered to Rc 28-32.
They were put in service in 1977 in Alaska. Although we tested them at -50 F , these parts have developed cracks.
Would treating these parts with cryognics (liquid nitrogen) have helped avoid these cracks?
These parts could have been exposed to a shock load but doubtful.
Parts are 1.25" thick and used in shear.
Thanks,
awol
They were put in service in 1977 in Alaska. Although we tested them at -50 F , these parts have developed cracks.
Would treating these parts with cryognics (liquid nitrogen) have helped avoid these cracks?
These parts could have been exposed to a shock load but doubtful.
Parts are 1.25" thick and used in shear.
Thanks,
awol





RE: 4130 cracking at LOW temperatures
RE: 4130 cracking at LOW temperatures
function: The 4130 parts hold a large metal plug in a pipeline. Pipeline pressure (crude oil) is trying to push the plug out.
forces/moments : No moments. Pure (as can be) shear. We estimate 40,000 psi shear if only half of these items take the load. This is conservative.
Temperature fluctuations: In Alaska; Frozen tundra, some above ground.
corrosive environment: Chlorine? no H2S? no
plated or coated? no, oil dipped and lubricated
Were they welded? no
fabrication method: machined from bar
These didn't crack all the way thru. Just cracks were noticed during disassembly and cleaning. Disassembly and cleaning is done only when they are being cut from a pipeline for reuse elsewhere. Cleaning and disassembly not a normal process. Now you have me wandering what they used to clean these with. Maybe something harsh. I will ask.
Thanks, Awol
RE: 4130 cracking at LOW temperatures
RE: 4130 cracking at LOW temperatures
RE: 4130 cracking at LOW temperatures
RE: 4130 cracking at LOW temperatures
Material is bought hot rolled plate.
we have a vendor heat treat it to Rc 28/32 (we don't specify the temper or quench media; is that important?)
We do impact testing on test coupon at low temp.
No coating. Just a dry film spray (aerisol).
No welding. Just milling and drilling. No tapped threads.
Thanks for the help!
-awol
RE: 4130 cracking at LOW temperatures
1. Is corrosion protection (zinc plating, organic coating, etc.) necessary?
2. Is hydrogen embrittlement causing the cracking? Failure analysis using a Scanning Electron Microscope can detect whether or not this was a brittle failure (intergranular/cleavage fracture instead of ductile failure by microvoid coalescence).
3. What processes contributed to the hydrogen environment? Or is the hydrogen from an external source once the component is in use. If it is the latter, see point number 1.
RE: 4130 cracking at LOW temperatures
If part was pickled to remove heat treatment scale then back comes the hydrogen although i'm not sure how significant hydrogen will be in a part with hardness 28 to 32 and service life approaching 25 years.
Off hand I do not know the Mf temperature for 4130 but if its well below room temperature and your part working conditions are well below that temperature, I would have insisted on a cryogenic heat treatment operation to ensure all austenite has transformed to martensite during quenching. Then tempering can proceed without the risk of untempered martensite forming from any retained austenite remaining in the microstructure after quenching.
As part was installed in 1977 it is difficult to check heat treatment records, however if you are replacing the part, seriously consider your heat treatment tecnique.
RE: 4130 cracking at LOW temperatures
If it was brittle delayed failure was caused environmentally, then corrosion must be present for SCC to ahve occurred. In which case, coatings, etc., will help.
Absent corrosion, brittle delayed failure comes only from hydrogen embrittlment due to initial processing sources.
If failure analysis can show fatigue or shock loading or some other failure mode due to external forces, then toughness enhancement from cryogenic treatment may have helped delay or prevent failure.