Iron is the last thing you want to make a sword out of.
It is a soft, maleable metal, that will rust like hell in any kind of atmospheric conditions. Depending on the composition of the bronze alloy, bronze might be far better than iron as far as corrosion and hardness is concerned. The "iron" swords that were better than bronze swords weren't iron at all, actually, they were eithe iron cast or steel swords, because of the fact that the melting process introduced carbon in the composition and, as a result poor quality steel, or some sort of iron cast [depending on the carbon percentage] were bourn. Steel though, should be faaaaar better than any metals or alloys mentioned above, and trust me, I know what I'm talking about since I'm a materials science engineer and I spent quite some time in front of microscopes and charts.
As far as silverweave weapons are concerned, I see it this way: The sword has a silver plating that should render it more resistant to corrosion, and in concordance, improve it's quality and slash because of the fact that the cuting edge, will stay sharp. And there might be some magic involved too. Let's not forget this is a game and normal RL rules don't apply.
Edit:
The availability of tin was a factor. Bronze weapons bend while iron ones break, which might mean something as well.
Iron bents like copper. The fact that the weapons you are talking about broke, suggests that the alloy they were made of was iron cast [more than 20% carbon]. That is a very fragile but also a very hard alloy.