Hi Jeff, During my years as a landscape gardener here in Cornwall, obviously we moved alot of big shrubs and dug out alot of old big plants. I got my local blacksmith the weld a steel scaffold pole (as a handle) onto a very nice 'old type' Spear and Jackson stainless steel spade head. It was incredibly heavy but that assisted the cutting of roots etc. The most important thing was to keep the blade as sharp as possible using a file. Eventually, after many years use the head got shorter until time came to replace it. The first 'new' stainless steel head i had welded on was totally useless as it bent under minimum pressure !!. (and seemed very soft when it was being sharpened) The second (and third) snapped as yours did very quickly due to I think the poor quality of the steel !!! So eventually after scouring car boot sales, I found another 'old style' head similar in quality to the original which i now treasure. So I think there are stainless steel heads of either bad temper (which snap) and some which are very soft (which bend). Another thing that Ive noticed is the good types have a much more concave shape to the head thus giving them the extra strength when under extreme pressure. The softer and poorer types tend to be 'flatter', which is why I think they bend !!
Regards, Lannerman.