Steel names are sprinting out of the gate after Donald Trump vowed late Friday to double Section 232 duties on foreign steel to 50 %, effective June 4.  The surprise hike instantly improves U.S. mills’ pricing power and set-off a reflex rally across the group.

• Tariff shock is the ignition: doubling the levy strips imported sheet of roughly $100/ton of price advantage, handing domestic producers a clear runway to raise offers.
• Share prices gap higher: Cleveland-Cliffs spikes 23 %, Nucor +10 %, Steel Dynamics +8 % as traders anticipate fatter margins and market-share gains once the new rate kicks in mid-week.
• Futures confirm the squeeze: Midwest hot-rolled-coil, already trending up this spring, surges from about $780 to $920 per ton in the first electronic prints after the headline.
• Momentum was building anyway: service-center inventories sit near four-year lows and mills have pushed through three $50/ton list hikes since March; the tariff simply accelerates a tightening tape.
• Macro & positioning tailwinds: Monday’s move forces short-covering in a sector that lagged the S&P by 15 pts YTD, while value-cyclical rotation funnels fresh capital into metal producers.
• Traders’ next checkpoints: June scrap-buy negotiations (later this week) will signal whether mills can lift coil while holding raw-material costs flat; watch for profit-taking 24-48 hours after Wednesday’s tariff start.

Taken together, the tariff news is the headline catalyst, but it lands on a market that was already tilting bullish on supply-demand tightening—amplifying both price and equity upside in today’s session.