Heat treatment homemade anvil top plate

[caotropheus]

Greetings

During my journey on ways to "homemade" an anvil, this is my third construction. This time I  decide to try to weld a top plate of hardenable steel. The main body of the anvil is mild steel, the top plate has its origin in a plough share.

Before welding the top plate, I tested the reaction of the plough share steel to 7018 welding. So, I took my stereoscopic microscopic and made some pictures. Everything seemed to be O.K, no cracks or separation between welding and steel. 

So I built the anvil you see above. The top plate covers only the main body and the angular horn (or tail, as you prefer)

Now I am about to heat threat the top plate. The resources I have is a garden hose and 10 buckets 20 litre water each for quenching. 

Before I jump "head first" quenching, I decided to take a piece of the plough share steel and weld (with 7018 rods) it to mild steel round stock. The mild steel stock was 20 mm diameter, 60 mm long. I had to forge to shape (60 mm long X 20 mm width X 15 mm high) the plough steel to weld it to the  round stock.  I brought sample to non magnetic and quenched under a water shower (to simulate anvil's top plate quench). I took a slice of this sample, etched and looked under the microscope...and it does not look good! you can see small cracks not visible to the naked eye. 

I have been thinking about the cause and solutions for this, probably I warmed up the sample too much before quenching?...probably I can quench with water but slower with a mist, not a shower?...

Please people, help me here thinking about the correct way of heat treating this steel,  I would like for my little experimentation to yield a "anvil with a harden top plate firmly attached". I would hate to remove the top plate and lay instead hard facing rod. 

Thanks