Welding 1.5" thick 4140, preheat and other issues
Welding 1.5" thick 4140, preheat and other issues
(OP)
We are currently welding 1.5" 4140 material together with a preheat of only 150F. The part is stress relieved (often not until the next day or even longer). Then the inside diameter is slightly machined and the unit is sent to NDT (Mag Particle). We were having failures of roughly 1 out of 11 at NDT where we simply machined out the bad area and repeated the welding procedure. Well, most recently we had a batch sit after the weld for over a week before it was stress relieved and we experienced a 90% failure rate without changing any other variables as far as we can tell. Can snyone tell us if the amount of time before stress relief and after weld is a factor? What other variables are key factors? What are other things to consider in this application? Are we preheating enough?
Thanks!
Thanks!





RE: Welding 1.5" thick 4140, preheat and other issues
RE: Welding 1.5" thick 4140, preheat and other issues
RE: Welding 1.5" thick 4140, preheat and other issues
Overkill for 1 CR don't you think?
RE: Welding 1.5" thick 4140, preheat and other issues
RE: Welding 1.5" thick 4140, preheat and other issues
RE: Welding 1.5" thick 4140, preheat and other issues
But allowing the welded steel to cool down between welding and PWHT means that the accumulated stresses from are immediately applied to the two welded sections. And prevention of problems from internal stressses is is the "hole" reason why PWHT is all that it is cracked up to be on even relatively thin (1-1/2") sections. 8<)
RE: Welding 1.5" thick 4140, preheat and other issues
Also I would hate to know what the HAZ would punch with a 150F preheat and cool down before PWHT.
RE: Welding 1.5" thick 4140, preheat and other issues
preheated 300*F slow cool down after welding (insulation)
welded w/ e8018 B2 LA 92 wire 888 flux
2 months between welding and PWHT
100% rt after pwht
100% mt after pwht
100% ut corner joints after ut
200-210 bhn in HAZ
190-200 bhn in weld
(krautkramer mic 10)
67/40 ft/lbs @ -20*F lcvn in weld
94/112 ft lbs @ -20*f lcvn in haz
and no cracks
RE: Welding 1.5" thick 4140, preheat and other issues
RE: Welding 1.5" thick 4140, preheat and other issues
What??? Haven't you ever heard of portable weld rod heaters?
Incorrect statement. Hydrogen diffuses at 450 deg F and increases in diffusivity as temperature increases up to a maximum. Post weld bakes can be effective at 500 deg F, and do not require 700 deg F.
RE: Welding 1.5" thick 4140, preheat and other issues
Sorry but I still disagree with the 500F @ 2hr "Intermediate Stress Relief" to completely defuse hydrogen even at 1.5". I have spent allot years testing PWHT in labs. All times and all temps and have the reports to prove that not everything you read in the books and codes about PWHT is true.
RE: Welding 1.5" thick 4140, preheat and other issues
I've even seen them plugged in, and some are even kept at the right temperature even. 8<)
I've also seen them not used, seen rods dropped on the floor and dropped in water, rods rained on, rods kept in unplugged heaters, rods not kept in ovens back at the tool room at the shop, ......
RE: Welding 1.5" thick 4140, preheat and other issues
My only final comment is that the post weld bake is NOT a stress relief, period. The post weld bake is only intended to assure diffusivity of entrapped hydrogen after a weld is completed.
PWHT is a completely different thermal treatment at higher temperature that provides two benefits - reduction in residual stress from welding and tempering of hardened weld metal and base metal in the heat affected zone of the weld.