What are the requirements for industrial lead blocks for lead quenching (lead bath)?

You mean the lead bath furnace, right? Ordinary lead ingots are fine, because the purity of ordinary lead ingots can reach more than 98%. Moreover, if you take a lead bath, you need to add a protective agent or something, and the lead liquid will be oxidized, and the purity is definitely not that high.

Lead bath furnace has great environmental pollution and occupational hazards. In 2005, the National Development and Reform Commission explicitly eliminated the equipment, and the relevant technical documents were few, and the industrial furnace manufacturers did not provide technical research and development support, so it is not recommended to use it.