problem in heat treating low alloy steels of various sizes and sections
is the development of quench cracks, distortion and dimensional changes.
Interrupted quenching in a salt bath can eliminate these undesirable by-products.
Thermal and transformational stresses in heat treating are illustrated by Time-Temperature-Transformation data,commonly referred to as TTT Curves or "S" Curves.
By controlling quenching severity, austempering and martempering provide a cooling rate ahead of the nose of the S-curve so that the work reaches the optimum isothermal quench temperature without undesirable higher temperature transformation properties.
manufacturing costs and improve metallurgical results with Salt Baths designed
four primary factors when designing quench furnaces for batch and in-line
1. Bath Temperature Uniformity - This
is essential for consistant metallurgical properties. Heavy duty or light
duty, gas or electric, AJAX furnaces provide temperature control
Austempering, austenitic steel is cooled at a sufficient rate to avoid
the nose of the S-curve, and held just above the start of martensitic transformation
(Ms point) for complete transformation to a bainitic structure while the
temperature remains constant - thus alleviating thermal and transformational
stresses that could cause cracking or distortion.
Austempering involves less heat treatment time and is preferred when fast turnaround is a prime consideration.
Martempering, austenitic steel is also cooled at a sufficient rate to avoid
the nose of the S-curve, preventing the start of pearlitic or bainitic
transformation. The Martempering temperature is selected just above the
Ms point. When the temperature is uniform throughout the steel, it is cooled
in air to room temperature. During cooling martensite forms. Thermal and
transformational stresses are lowest.
Martempering produces a minimum of strain on heavy sections.
AJAX Electric Company
60 Tomlinson Road
Huntingdon Valley, PA. 19006 U.S.A.
Phone: (215) 947-8500 • (800) 516-9916 • Fax: (215) 947-6757
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