Investors are steering clear of corporate America’s most vulnerable borrowers, even as credit markets rally on bets that the worst of the global banking crisis may be over, Bloomberg News reported. The gap in spreads between the two weakest tiers of corporate debt typically issued — B and CCC — has widened dramatically since the end of February after three U.S. regional banks failed and Credit Suisse Group AG was hastily taken over. It now costs CCC issuers on average 531 basis points more than B rated issuers to sell bonds, according to data compiled by Bloomberg. The disparity comes as fixed-income traders allocate money into safer credits, such as investment-grade or U.S. government debt, amid concerns that borrowers in the lowest-rated rung of corporate debt are even more at risk of defaulting than usual as tumult in the banking sector, a potential recession and rising interest rates collide.