That temperature range isn't  going to do much to tungsten, unless it has a specially developed oxide film or passivated surface that could have been damaged by the scratching.

There is a paper on tungsten corrosion by Cifuentes et al.:

Corros. Sci. 33(10), 1581-1592 (1992).

It may give you some pointers.

Good luck

Luis

Three points to note are:

[I] Normally [W] remains unreactive towards O2 but when heated in O2 (especially at low atmospheric pressure), there are fair chances that[ W ]may form a protective layer of its NONCONDUCTING oxide[WO3] with no free electrons [W^+6; 5d^0.7s^0].On the other hand , in the [W] sheet , there are present loosely held six electrons[ 5d^5 7s^1]/ W atom. As the free electrons are the carriers of electricity, the oxidized sheet , with no free electrons , is not expected to show any electrical conductivity .

[II] No doubt, not whole of [W] is changed to its nonconducting oxide,yet the conductivity of [W] still left unoxidized at 140C will still decrease largely as follows:

At room temperature/ low temperatures, the KERNELS [the W ions at lattice sites] remain in their fixed positions and the electrons carry the current. But at 100-140C, the KERNELS LEAVE THEIR ALLOTTED POSITIONS AND OBSTRUT THE FREE MOTION OF ELECTONS By COMING IN THEIR WAY and DECREASE ELECTRICAL CONDUCTIVITY.

[III] When scratched, the NONCONDUCTING WO3 OXIDE LAYER IS PEALED OFF. BELOW THIS OXIDE LAYER, THERE COMES THE UNOXIDIZED [W ]METAL WHICH CAN CONDUCT THE ELECTRICITY .

Thanks a million all. @Manohar any reference on this. I am looking for an explanation on what is the oxidation rate of commercial W wires at low temperatures.

The word tungsten comes from the Swedish tung sten, which means heavy stone. It also has the highest melting point of all the elements, at 3,422°C.

http://www.iom3.org/materials-world-magazine/news/2015/feb/01/elements-risk-tungsten