I don't think that black metals are good for saving money in a long-term period. Their storage and security costs are too high to save near that value over time.
I think they are good materials only if you want use them in infrastructure, otherwise they will taking space in storeroom without point.
The best option for saving money for long term in my view is to invest in property, because property will never lose money and with the passage of time the value of your property will increase. If you put your money in bank, you will spend it after some time because of easy access. If you invest in crypto, it is also usable and not good for long term savings.