Tempering to reduce eliminate Martensite on Rail
Tempering to reduce eliminate Martensite on Rail
(OP)
We apply electrical wire by thermite weld to subway rail.
The thermite weld creates a btittle martensite area which has been known to crack.
I was wondering if I can temper the metal on site (at the subway track). Is this possible and if so how?
Thanks in advance
The thermite weld creates a btittle martensite area which has been known to crack.
I was wondering if I can temper the metal on site (at the subway track). Is this possible and if so how?
Thanks in advance





RE: Tempering to reduce eliminate Martensite on Rail
If this is a small "tack weld" by the thermite process to attach wires, you can try to locally post weld heat treat this weld and rail base metal in the field using a neutral flame gas torch with Tempstiks to verify your PWHT (or tempering) temperature. This local PWHT method is conducive to field application. The duration of heat could be as little as 15 minutes at PWHT temperature, while carefully monitoring the metal temperature of the rail and weld using Tempstiks so the region is not overheated.
The temperature for local PWHT is selected based on the chemical composition of the rail steel and the original heat treatment specification. If the rail was supplied in a tempered condition, you need to remain below this original tempering temperature. For a gas torch application of PWHT, I would remain 100 deg F below the original tempering temperature for the rail.
RE: Tempering to reduce eliminate Martensite on Rail
If the track is true manganese steel, no PWHT is required. If you are getting cracking at your thermite welds, I'm willing to bet you have high carbon steel track and will require a PWHT.
RE: Tempering to reduce eliminate Martensite on Rail
Carbon 0.74 - 0.84
Maganese 0.80 - 1.1
Phosphorus 0.035
Sulfur 0.037
Silicon 0.01 - 0.060
Nickel 0.25 (max)
Chromium 0.25 - 0.50
Molybdenum 0.10 (max)
Vanadium 0.03 - 0.05
How do I find the PWHT for this rail?
RE: Tempering to reduce eliminate Martensite on Rail
You need to locate the specification for this rail. I have seen AAR rail specifications that in addition to rail steel composition, the specification provides information regarding heat treatment. This is the information you need to know to optimize your PWHT temperature to avoid affecting the bulk properties of the rail upon exposure to local PWHT temperature.