By Aatreyee Dasgupta

(Reuters) -Top U.S. steelmakers' second-quarter fortunes are likely to be a mixed bag, caught between a fillip from higher steel prices and uneven demand amid uncertainty over U.S. President Donald Trump's tariffs.

In its mid-quarter update, Nucor forecast second-quarter profit ahead of analysts' estimates compiled by LSEG, citing higher average selling prices across its steelmaking segments, especially sheet and plate mills that produce flat-rolled products used in construction, automotive, manufacturing, agriculture and energy sectors.

Nucor's higher shipments and steady pricing could be attributed to a "more diverse footprint," J.P. Morgan analysts said in a note.

Steel Dynamics, meanwhile, projected its profit below analysts' estimates on lower flat-rolled volumes due to an inventory overhang. It also forecast lower earnings from its fabrications business on higher input costs.

After an initial spike in steel prices as buyers stocked up after Trump on February 2 first floated steel tariffs, constant flip-flops eventually slowed demand.

The increase was moderate due to growing domestic supply, while demand has weakened due to seasonality and tariff uncertainty, BMO Equity Research said in a note.

Trump's plans to double tariffs on U.S. steel and aluminum imports to 50% from the current 25% have hiked costs for buyers and hit manufacturing.

Further, the impact of higher prices may not immediately figure in companies' earnings, since producers operate under fixed price contracts spanning months, and analysts expect benefits may show during the third quarter. 

"While tariffs may push spot prices higher, those increases are slow to flow through to earnings," said Raul Munoz, managing director at insurance broker Marsh.

Analysts expect spot prices to remain range-bound over the summer.

"We believe some of the recent resilience in steel prices will lead to higher 3Q earnings revisions due to the prolonged impact of import tariffs," Jefferies said.

Steel Dynamics will report results on July 21 and Nucor on July 28.