____<br/>is the isothermal heat treatment by which austenite transforms to<br/>bainite. A: Isothermal<br/>annealing B: Quenching C: Austempering D: Marquenching

In the as-quenched state, martensite is very hard and so brittle that a heat treatment known as_________must be accomplished sequently. A: normalizing B: annealing C: tempering D: austempering