I can't figure out how to post in that bulletin board so I will post here. I have a lot of opinions about that failure.
First, hydrogen embrittlement is a well know phenomenon and used to be widely known in the hot rodding community. With the new generation of 'journalists' who are technically uneducated and practice their craft by reprinting manufacturer's installation brochures and pass that off as tech. The hydrogen atom is very small and passes easily through steel. A steel cylinder full of hydrogen will eventually empty itself due to this permeability. Hydrogen generated in the plating process will penetrate steel. If it is mild low carbon steel, there is no problem, the hydrogen will evolve out and there will be no cracks. However in high carbon, heat treated steel, the hydrogen is captured in the grain structure and causes a disruption in the chemistry that exhibits itself in brittleness and tendency to crack. The solution is to bake the parts for about 4 hours at 400F which 'boils' out the hydrogen molecules and restores the ductility of the steel.
That may or may not be a contributing factor to the failure in the steering arm in the picture. Another very likely possibility is inferior material. If those after market arms are cast, that is a huge problem. The steering arm is one of the most highly stressed pieces in the steering system and MUST be forged. That thing definitely looks cast. It broke at the thick section because that is where the stress is highest in the part. That is why they make it thicker! Regardless it needed a stress riser such as a hydrogen crack or a casting flaw to initiate the crack. If you look closely at the picture, the fracture face is white in the right-hand quadrant, showing that it had been cracked there for some time and water deposits had collected. Look more closely and there appears to be a pit on the surface of the rod in the middle of that white spot. If that is a casting pit, that would definitely initiate a crack. I can't believe they made that thing of cast iron, it must at least be cast steel. Regardless, should have been forged.
Finally this gives me a soap box to preach on my quest to get all rodders to beef up their steering systems. Just like MII front ends that are documented on this forum to be catastrophically failing due to bad engineering, this steering arm is obviously another example of the dangers of back-of-the-envelope engineering. The Speedway tech support guy was quoted as saying 'they have sold over 200 of them and never had a problem.' That is scary!! Engineers in Detroit are held to a standard of NO failures in 3 or 4 MILLION units!!!! 2 failures in 200 critical steering units would be a DISASTER in the auto industry. 200 units in a test is woefully inadequate. Be VERY careful in designing your steering system. ALWAY use strut rods in MII front ends, ALWAY use forged pieces where Detroit used forged pieces. If you weld anything in the system make sure you know what you are doing or have it done professionally.