I have an old induction melting furnace manufactured by EMA (german
make), the furnace stopped working and I have traced it to a shorted
thyristor.

It is a hockey puk package type thyristor and the casing says it's a
siemens BSTN 4760

What I need is a datasheet for the thyristor and an equivalent replacement

Hi,

I have some information for you,
It seems to be an inverter grade (high speed) high voltage SCR. 
I don't have the detailed info on it, suggest you talk to these guys,
who will cross-reference it and get a replacement part for you: 

http://www.superiorinduction.com/Components/Components-main.htm


Siemens Semiconductor became Infineon Technology back in 1999 
http://www.infineon.com/ 

What package is the device in? I've seen some huge 2400V go for over $300 

and i have some data,
BSTN47C60 
--------- 
Fast Switching SCR 
------------------ 
VRRM = 900V 
IT(avg) = 425A 
VT @ IT = 18uS 
dV/dt = 500V/uS 
Tj(Max) = 125C

hope this helps. ;-)