Titleist AP1 iron is cast 17 4 stainless steel. This iron has a deep undercut so the club face is thinned out, because of this you get a better flex and more launch and ball speed. The AP1 has a very strong stainless steel body with 42.5 grams of tungsten near the toe, which allows for better MOI(motion on impact). This iron also has a nice wide flange, and the face is thin and flexes. Titleist calls this their longest and most forgiving iron that they have ever created. The leading edge is pre-worn, meaning that when there is turf interaction it won’t dig straight in.
Titleist 716 AP2 is crafted from forged 1-25 carbon steel. Modern forging allows for meticulous perimeter weighting. Tungsten is also a major part of this iron as well, allowing you to control where you put the weight of the club. Thus, in combination with the flange making it easier to get the ball airborne.