You can't combo into qcb+B if you just do the f+B, I believe. You can only combo it if you use f+B as part of a combo beforehand, it won't actually combo but it will let you combo after it.
One of his very good block strings is cr.B, cr.B, s.B, f+B, qcb+B
Even if the lights connect the f+B won't combo but it will let you cancel after it. On block the string does solid guard guage damage. If the opponent doesn't block the f+B in that string then qcb+B will combo.