The question is capability. They are quite able and smart. They do not have a lifestyle or technology which needs such skills. Say Noah and his sons took a iron saw with them. They can't make more because there are not enough people to support an iron making society.
Iron ages require agricultural ages.
The iron maker is a specialist who does not produce food. Only when there are enough people producing food can a certain number accept a lifestyle which is a drain on food resources. Frankly I don't think the post flood population was very significant for a long, long time. Even if he did, after he and 8 people survived, he would be too busy looking for tonight's dinner to do the work of mining the ore, hauling the ore, from hundreds of miles away, finding, mining and hauling the coal, and then tending the ovens. He would starve to death if he tried this.