The downgrade of the Navratna PSU reflects slower-than -expected progress in leverage reduction, S&P said in a release.
"In our view, SAIL is highly unlikely to lower its ratio of debt (adjusted for retirement benefits and surplus cash) to EBTIDA below 3.5x by fiscal year-end 2015," the rating outfit said.
The state-owned firm could not be reached for comments.
SAIL's partly debt-funded capital expenditure programme has considerably increased its leverage but the investments made have not contributed to higher cash flows, according to S&P.
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"While we expect gradual improvement in SAIL's business performance beyond fiscal 2015, we cannot rule out delays to the roll-out of new capacity," S&P said.
It expects financial ratios to recover only marginally after increasing capacity.
The agency said it sees SAIL's liquidity as adequate, based on its external financial flexibility and funding availability due to its Government linkage.