Austempering

AUSTEMPERING IS A HARDENING PROCESS… for ferrous alloys in which the material being treated is quenched from the hardening temperature into a molten salt bath with precisely controlled temperatures. The material isothermally transforms to a structure known as bainite; this transformation takes place just above the temperature at which the hard and brittle phase occurs in conventional heat treatments. The material is quenched directly to the hardness desired by adjusting the temperature of the quench bath. Heating and salt quenching are the key process steps. Austempering will produce better mechanical properties, particularly higher ductility, resistance to shock, and fatigue stresses in ferrous alloys. Parts equal in ductility to conventionally quenched and tempered materials will run as much as 10 points harder on the Rockwell "C" hardness scale. The hot salt quench drastically reduces the likelihood of cracking and distortion. In addition, the slightly oxidizing quench salts provide a thin protective dark blue oxide film that is both protective and attractive, and which can be readily removed by a light pickle, leaving a base surface ideal for subsequent plating operations. The large salt quench tank at Heat Treat Specialists quenches parts continuously and rapidly from the high heat temperatures to the closely controlled salt bath temperatures, producing uniform hardness in piece part after piece part, and lot after lot. The advantages of austempering over conventional heat treat have long been recognized by metallurgical and material engineers since the invention of the process by research metallurgists at U.S. Steel Corporation some 30 years ago. However, the process was performed almost exclusively in batch type neutral salt furnaces for both heating and cooling operations. This method had disadvantages inasmuch as 1) a large labor input was required, 2) work fixtures lowered heating efficiency, and 3) high temperature heating salts transferred during the quench gradually dilute low temperature quench salts and cause non-uniform hardness. Recent engineering innovations have solved problems relating to the use of continuous atmosphere furnaces with hot salt quenches. HEAT TREAT SPECIALISTS has the most modern continuous equipment of this type available today – equipment that produces the highest quality heat treating available anywhere. The large production capability of this automated equipment provides all of the advantages of austempering at prices competitive with conventional heat treating.