CREATE TABLE table_4520 ("Week" FLOAT, "Date" CLOB, "Opponent" CLOB, "Result" CLOB, "Attendance" FLOAT)

When did the Browns play the Pittsburgh Steelers?
SELECT "Date" FROM table_4520 WHERE "Opponent" = 'pittsburgh steelers'
SELECT "Date" FROM "table_4520" WHERE "Opponent" = 'pittsburgh steelers'