This is to report about a welding experiment perform cd in joining heat treated rails with the hardness of 308-390 Hv and high abraision resitance.
The following are the results summarized with some comments : -
1) In joining heat treated rails by manual arc welding, satisfactory joint strength can be obtained, when the bottom and web are welded with low hydrogen type electrodes, following 90% of the top part welding by means of the same type electrodes, and then the head surface is built up about 10 mm deep with the intention of hardfacing. The joining strength does not change by hard surfacing.
2) For padding the employment of Mn Austenite type or Martensite type electrodes cannot be recommended, because of the cracks occurring at the fusion line between padding and base metals. We advise the use of low Cr steel type electrodes whose welding hardness is compatible with that of rail head and the welded metal is difficult to cause cracking.
3) By welding, the surface hardness of rail head is softened over the range of about 10 mm from the fusion line. Rails post heated for 30 min. at 600°C immediately after welding tend to be softened down to about 250-280 Hv. over the heating zone, but the micro-structure of the point 50mm apart from the fusion line is not remarkably changed, compared with the base metal structure.
4) As the result of passing trains for 80 days, it is recognized that the hardness of welding metal and softening zone of wheel side is inclined to increase by the cold working (train pass load ; 38, 000 ton/day) up to 2 mm depth under the head surface.
5) The abraision loss of the base metal, the post heated softening zone and the deposit metal are almost equivalent 2 1/4 years after construction (train pass load 8, 200, 000 ton/year, gradient ; 15/1000, straight track of 348m), and the local abraision can't be observed.
It is therefore considered that this weldng procedure can be used practically.
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