Robert,
as you have mentioned the designation "1045" please let me ask if you mean an SAE 1045?
This material - as far as you meant this - is according to the German standard "EN 10083-1 (10/1996)" which is the replacement for the old DIN 17201 a/o DIN 17204.
It is a quenched and tempered construction steel and standardized as "C45E" (old designation: Ck 45).
The material has mechanical properties as follows:
Tensile Strength: 700... 850 MPa
0.2 Yield Strength: 370... 490 MPa
Elongation (A5): 14... 17 %
For the welding procedure (SMAW presumed) please find attached some information in terms of preheating and welding (WeldingProcess.pdf) as well as the appropriate continuous TTT-diagram for your kind information.
I hope this helps a bit and my assumptions with respect to the material grade were correct.
Best regards,
Stephan