The group said it now expected the Chinese market to contract by up to 1 percent, having previously guided for growth of between 0.5 to 1 percent.
While ArcelorMittal does not have much direct exposure to China, the world's largest consumer of steel is an important driver of the global market.
Core profit in the second quarter fell 20 percent compared to the same period last year to $1.40 billion, just above the $1.38 million expected in a Reuters poll of 12 analysts.
ArcelorMittal, which produces 6 to 7 percent of the world's steel, repeated its 2015 guidance that core profit would come in at between $6 and $7 billion.
The group said core profit at its mining business fell 70 percent compared to the same period last year, because of a decline in iron ore prices which was only partially absorbed by lower costs.
Net debt stood at $16.6 billion, unchanged from the end of the first quarter. The group had reached a record low of $15.8 billion at the end of 2014.