at what temperature does hydrogen become a liquid
Liquid hydrogen To exist as a liquid, H2 must be cooled below hydrogen's critical point of 33 K. However, for hydrogen to be in a fully liquid state without boiling at atmospheric pressure, it needs to be cooled to 20.28 K[3] (−423.17 °F/−252.87 °C).[4][5] One common method of obtaining liquid hydrogen involves a compressor resembling a jet engine in both appearance and principle. Liquid hydrogen is typically used as a concentrated form of hydrogen storage. As in any gas, storing it as liquid takes less space than storing it as a gas at normal temperature and pressure. However, the liquid density is very low compared to other common fuels. Once liquefied, it can be maintained as a liquid in pressurized and thermally insulated containers.
Blacksmith Iron is different from most other materials (including bronze), in that it does not immediately go from a solid to a liquid at its melting point. H2O is a solid (ice) at -1 C (31 F), and a liquid (water) at +1 C (33 F). Iron, by contrast, is definitely a solid at 800 °F (427 °C), but over the next 1,500 °F (820 °C) it becomes increasingly plastic and more "taffy-like" as its temperature increases. This extreme temperature range of variable solidity is the fundamental material property upon which blacksmithing practice depends.