Corporate bond returns worldwide have turned positive for the year, recouping January losses as the manager of the world’s biggest fixed-income mutual fund warns credit is "somewhat exuberantly and irrationally priced."

Bonds have gained 0.73 percent in February, pushing returns this year to 0.31 percent following a 0.42 percent loss in January, according to the Bank of America Merrill Lynch Global Corporate & High Yield index. Average yields have dropped 11 basis points this month, leaving borrowing costs for the riskiest to the most-creditworthy borrowers within 5.6 basis points of the record-low 3.24 percent reached Dec. 28.