Someone else mentioned that prices in general would go up, this is correct but there is also another factor. Steel is the primary material used to build manufacturing equipment and there aren't any good replacements when you need something big, heavy and cheap enough to finance that can be used to mass produce other goods. This equipment has to be durable, have well known properties and you need to be able to make it using existing machine tools and processes. So if steel becomes much more expensive not only will everything become a lot more expensive, you will also negatively impact the creation of new businesses and innovation in manufacturing.

This is one of the major second order effects that always springs to mind when people just float the idea of increasing the cost of some material that produces CO2 as a byproduct as if just pulling a lever or adding a tax will solve the problem. The economy is a giant Jenga tower where all of the lower blocks are fossil fuel based processes. We sit way up on top where we can't see the bottom of the tower and we think "wow look at all this new stuff we've made, we sure are great! We should get rid of all that old junk so we can build more new stuff up here!" and maybe you can knock out a few of the pieces on the bottom without causing a disaster but eventually if you take out enough of them the whole thing will come crashing down.

If you want to build a carbon free economy then you need to start a new tower and you need to solve all of the fundamental problems in a new way with new technology that doesn't use fossil fuels and it needs to be as cheap or cheaper than what we can do now. That's a monumental task. And no, you can't knock over the first tower before starting the new one unless you want billions of people to die, most likely including you as well.