This invention relates to a thermite welding process for joining sections of a railway line in situ, the process including the preliminary step of mounting a suitable welding mould about the aligned sections of railway line to be welded together and sealing the mould to prevent run out; mounting a vibration means on the railway line at a suitable distance from the mould and operating it at a suitable frequency; heating the sections of railway line to a desired temperature; igniting an ignitor means and allowing it to drop into the mould to react with molten steel in the mould and fill a weld area about and between the sections of railway line in the mould; and when solidified, to vibrate the railway line for a further period of time until stress relieving of the cast weld area has occurred.