8620 vs 4320 given case depth and cross section
8620 vs 4320 given case depth and cross section
(OP)
Hi. I'm looking for opinions for a material specification. We have a part that is likely to be manufactured out of 4320H, gas carburized. (8620H is only alternative available). The case depth (50 HRc) requirement is a minimum of .080". Yes, this part must be tough and able to withstand heavy loads and the occasional shock load. Here is my concern: A portion of the loaded section is to be .275" - .320" thick (cross section). If I am interpreting hardenability curves correctly (?), 4320 could have a core hardness well into the 40+ HRc range making the part much less tough and subject to fracture. Are my concerns valid? Would a change to 8260H be a solution? Are there any guidelines or "rules of thumb" for minimum core thickness when using 8620H and 4620H?
Thanks!
Thanks!





RE: 8620 vs 4320 given case depth and cross section
A couple of suggestions to consider if your application cannot tolerate this range but still desire 4320:
Use a medium-temperature quench oil, in the 200-225F range. This should keep the core in the low 40's on 4320 but still give the effective if you use 8620.
If the volume is sufficient, you can order a heat of material with a restricted jominy range. It may be tough to get a good fit from a bar warehouse but it is worth a shot also. For 4320 look for material with a low range hardness at the J4 jominy position, 33-37 HRC.