Normalizing/Stress Relieving CroMo

[johnc]

According to the national standard ANSI/AWS D10.8-96, in the thickness ranges we typically see on automotive tubing and plate use (less then .125" thick) for ASME/ASTM Grade P11 or T11 (1 Cr-Mo or SAE4130) the recommendation is for no post weld heat treatment.

 

Typical racer practice is to evenly head up the weldment and the surrounding area (3 times the diameter of the tube) to 1,100 to 1,200F and maintain the temperature for 15 minutes. Then let the area air cool to room temperature.

 

I welded over 100 coupons of various 1 1/2" OD, .095" 4130 wall tubing joints (30, 45, 60, and 90 degrees) with no PWHT. This was part of the development of a certification program for automotive 4130 tube welding at Lincoln Electric. All 100 coupons were tested (along with another few hundred others from different welders) and all passed.

 

Personally I don't think PWHT is needed for 4130 tubing welding if the proper filler and gas shielding is used (including back purge). I think the FAA still requires it for their 4130 certification and I know a lot of fabricators (NHRA in particular) still normalize all their 4130 welds.

[260DET]

Whats a rough price in the US for a FIA type spec chromo Z cage in the US, John? Someone was saying in AU they are ~$10,000, thats ~$7500 in your money. May have to be Xrayed, I don't know.

[johnc]

Here in the US, there's not much demand for CroMo cages in the road racing world. Maybe the pro teams still build them but since SCCA stopped giving a wall thickness break for CroMo everyone builds their cages using DOM. In the past you could build a cage in an ITS 240Z using .095" wall CroMo instead of .120" wall DOM. Now you have to use either .120" CroMO or .120" DOM.

 

I don't have the FIA regulations handy so I don't know their welding and PWHT requirements for CroCmo. Assuming they require TIG welding and PWHT of all joints I guess a FIA CroMo spec cage in a 240Z would be about $3,500.