UPDATE 2-Steel Dynamics Q3 profit beats Street; shares rise

* Q3 EPS $0.30 vs est of $0.23

* Q3 rev $1.17 bln vs est of $1.06 bln

* Q3 boosted by flat-rolled segment sales

* Sees Q4 earnings slightly lower than Q3

* Shares up 3 pct in after-market trade (Adds analyst comments, details)

Oct 19 (Reuters) - Steel Dynamics Inc (STLD.O) posted third-quarter earnings that beat market estimates, as a spike in automobile production boosted demand for the steelmaker's flat-rolled products.

In the latest quarter ended Sept. 30, the company posted a net profit of $69 million, or 30 cents a share, compared with $193 million, or 98 cents a share, a year ago.

Revenue for the quarter more than halved to $1.17 billion from the year-ago period, when steel prices were at their peak.

Analysts, on average, were looking for earnings 23 cents a share, before items, on revenue of $1.06 billion, according to Thomson Reuters I/B/E/S.

"Improved flat-rolled shipments were likely due to the cash-for-clunkers program related auto production and share gains from integrated steel producers who had capacity offline throughout the quarter," analyst Luke Folta of Longbow Research said.

The $500 billion steel industry witnessed a slow recovery from one of the worst downturns ever, as spending was boosted by a government-sponsored discount scheme for new motor vehicle purchases, dubbed "cash for clunkers," which ended in August.

Shipments at the company's flat-rolled steel segment, used by vehicle manufacturers, accounted for about 73 percent of the total shipments at its steel operations.

However, the sixth-largest steelmaker in the U.S., expects fourth-quarter results to be impacted by lower flat-roll steel shipments, hurt by seasonality and slowing market momentum, and lower margins in its metals recycling due to lower scrap prices.

"Our outlook for the fourth quarter anticipates a slight easing in current operating rates, which could result in somewhat lower earnings than the third quarter," Chief Executive Keith Busse said.

Steel Dynamics expects increased expenses related to the anticipated start-up of its Mesabi nugget plant, and said it may end 2009 with a "small profit."

Shares of the company rose 3 percent to $15.72 in trading after the bell. They closed at $15.39 Monday on Nasdaq. (Reporting by Antonita Madonna Devotta in Bangalore; Editing by Pradeep Kurup)