Weldability of this type of steel 1

[seahawks]

1.What is the weldability of the material? I am not sure of what it is, but I have its properties. C-0.25-0.3%, Mn-1.2-1.3%, Si-0.5-0.6%, Cr-1.2-1.5%, Mo-0.3%. oil quenched and tempered to 38-40RC hardness. I have to weld a 3"x6"x6" plate of 4140 to a 3" round x24"of the parent material in question. This is for a excavator mounted hydraulic hammer, so the weld material would have to be impact resistant.
2.Would I have to have it annealed before welding?
3.What GTAW electrode and gas should be used?
4. Is there a preheat temp before welding?

 

[metengr]

seahawks;
The weldability of the parent steel composition you stated is acceptable under controlled preheat requirements and with post weld heat treatment (if you do not intend to anneal it before welding). You don't mention what type of weld joint - full, or partial penetration groove weld, external fillet weld, continuous or stitch welds???

Annealing before welding would certainly help to reduce cracking in the parent material, but would require a complete re-heat treatment after welding. Can you re-heat treat after welding and risk distortion? In addition, the 4140 plate would be heat treated to the same hardness as the parent material - 38-40 HRc. You need to answer these questions before welding w/wo re-heat treatment.

 

[seahawks]

thanks metengr, I was thinking that both parts should be annealed before welding and machining. I have to pollish the part prior to heat treating and tempering.
Could you tell me the series of alloy steel this is? I have been searching, but cant find a real answer. If you know of a web address i can look it up myself.