Will nickel in low alloy still cause quenching crack 2

Quench cracking is the result of high stresses due to the volume changes accompanying transformation from austenite to martensite. Nickel has a dramatic effect on hardenability, increasing it substantially when present in amounts greater than ~ 1%. Increasing hardenability produces greater amounts of martensite, and therefore can produce larger amounts of distortion and quench cracking.

The tendency for increasing amounts of cracking correlates well with decreasing M_s (martensite start) temperature and increasing carbon equivalent (C.E.). Increasing the amount of nickel decreases the M_s temperature and raises the C.E., so quench cracking is more likely in steel alloys with higher nickel levels.

But it is not just the nickel level! All alloying elements which can influence hardenability need to be considered, manganese, silicon, chromium, molybdenum, copper, vanadium and boron are powerful influences.
ASTM A 255 is a useful document to read to understand the influence of the different alloying elements on hardenability.

Nickel addition at higher levels imparts better mechanical properties. I would advise to continue maintain the same Ni content, but reduce the severity of quenching like polymer quenching and still obtain the properties minus the quench cracks and distortion. Please give this a try and let us know your observations. Happy quenching.