Heat affected zone in 4130

By Bobby Passmore Date 04-15-2002 15:51

I need to qualify a procedure on 4130 base marerial using the GTAW process and using AK10 wire or another wire that will give me 95K yield. My problem is that we have tried this in the past and have had a hard time keeping the heat affected zone hardness below a 22 max. Rc. We have tried preheating up to 500 degrees and we always stress relieve but we cannot stress over 1190 degrees. If anyone has any suggestions I would greatly appreciate it.

Thanks,
bp

By GRoberts (***)

Date 04-15-2002 17:06

We have similar hardness requirement (23 HRc max) for CA6NM castings (martensitic stainless). What is common practice on those is to PWHT at 1225-1275F, and then cool to room temperature, and then PWHT again at 1050-1150F. The reason this is done is because after the first PWHT, some retained austenite transforms to martensite during cooling. The second PWHT tempers this newly formed martensite. Of course on 4130, the temperatures are different. (for instance, a middle of the road 4130 steel has a 326F Martensite finish temperature, and CA6NM has a Martensite finish temperature of 100F) But the double tempering concept is still the same.

Also, how long are you holding at temperature. Usually, if you cannot temper as high as desired, a longer time at a lower temperature can achieve the same results.

G Roberts