The Federal standard made for monel k500 wire represents only solution annealing. In the annealing process remained to the caution of heat treatment. The annealing temperature of alloy is between 1600oF to 1900oF. Therefore in alloy wire annealed solution of temperature 2050oF due to presence of titanium carbide, it should be immediately reduced in section thickness prior to final heat processing to meet the particular application criteria. The annealing temperature is reduced to 1600oF. Therefore the material solution annealing at temperature of 2050 oF can be aged without more reduction in section thickness and acceptable if it fulfills the special requirements like mechanical features.
To get an appropriate aging performance and tenderness, the sufficient water quenching from heating temperature should be done immediately without any delay. Late quenching or slow cooling results in half precipitation of age hardening phase and rapid impairment of aging. Including 2% alcohol to water reduces oxidation and increases pickling. The following age hardening processes are preferred to get the maximum characteristics.
The soft metal possessing 75-90 rc hardening is kept for 16 hours at temperatures to 1100oF to 1125oF then furnace quenching at the rate of 15oF to 25oF per hour to 900oF. The quenching at temperature of 900oF to room temperature is done by the furnace or air quenching without considering the rate of quenching.
This process is fit for forging and quenching or annealing or hot treated rods and wider cold treated rods and soften wire and strip. The medium cold treated material of 8-25 Rc is kept for 8 hours or more at temperature of 1100oF to 1125oF then quenching at 900oF at a rate more than 15oF to 25oF per hour. More hardness can be achieved by keeping the alloy for 16 ours at temperature especially if the wire us cold treated moderately. Following the general methods, the wire with previous hardness of 175 – 200 Brinell is kept for 16 hours.
The monel k-500 wire with 250 brinell hardness should get the complete hardness in eight hours. These methods are applied to the cold drawn rods, half-hard strip, cold-upset pieces and moderate-temper wire. The completely cold treated material with 25-35 Rc hardness is kept for 6 hours or more at temperature between 980 oF to 1000 oF then quenching up to 900oF at the rate lower than 15oF to 25oF per hour.
In few cases little more hardness can be achieved especially with the wire having lower edge of hardness by keeping for 8 to 10 hours at the above temperature. This process is best for spring temper strip, spring wire or massive cold treated pieces like small or cold treated balls. The quenching can be performed stepwise of 100oF keeping in the furnace for 4 to 6 hours at every step. The results of furnace quenching on yield strength of cold treated rod are shown in the following table:
|Diameter, in.||Tensile strength, ksi||Yield strength, ksi||Elongation %||Reduction area %||Hardness, Rc|