Why Hardness dropped after welding repair

[HF2085]

Hello Experts

we welded 4130 to 4130 material with suitable WPS with PWHT .
after welding, hardness in base metal was OK but we found crack on toe weld ,after repair and PWHT with same WPS that we used before for fabrication ,Hardness dropped on base metal ,

would you please tell what elements can make this problem ,or what is possibilities that can make this problem for us?

Thanks

 

[weldstan]

Continued time at PWHT/tempering temperature will reduce hardness in the base metal.

 

[HF2085]

Thanks weldstan ,would you please give me guide line to learn little bit more about it?

 

[metengr]

You can Google search tempering effects on low alloy steel. As mentioned by weldstan, further tempering will result in lower hardness/strength in heat treated steels, like 4130.

 

[HF2085]

Thanks metengr

 

[HF2085]

any other specific sources for that?

 

[metengr]

Yes, ASM Metals Handbook, Volume 4, Heat Treating
Look under Tempering/Tempering Time to better understand the relationship between tempering temperature and time as process variables.

 

[HF2085]

Thank you so much Metengr