Cryogenic

Cryogenic Music Wire (Cryowire)
© Brian Godden 1/1 /2003

What are the benefits of Cryogenically treated musical strings? In the case of steel, copper, brass, and their alloys, cryogenic treatment removes the built-in kinetic energy of atoms which is the energy of motion. There is a normal attraction between atoms that makes them want to get together. But their energy of motion keeps them apart unless that energy is removed by low temperature cooling. The treatment at temperatures of 88 degrees Kelvin (-300 degrees Fahrenheit) transforms soft austenite into hard martensite. This transformation closes the molecular surface, and re-aligns the internal crystalline structure. In musical wire, it improves intonation and harmonic content, and limits longitudinal stretching. The result is a longer lasting, more resonant, clearer sounding, stronger string.

Perfect Third Music manufactures and sells cryogenically treated steel, brass, and bronze strings, under our own brand name; “CRYOWIRE“.

For string prices see: Strings and Parts page

For the techno-buffs, see the graphs below.
Time-Temperature Paths on Isothermal Transformation Diagram.
Figure:1

a. Path 1 (Red line)
b. Path 2 (Green line)
c. Path 3 (Blue line)
d. Path 4 (Orange line)

a. (Red) The specimen is cooled rapidly to 433 K and left for 20 minutes. The cooling rate is too rapid for pearlite to form at higher temperatures; therefore, the steel remains in the austenitic phase until the Ms temperature is passed, where martensite begins to form. Since 433 K is the temperature at which half of the austenite transforms to martensite, the direct quench converts 50% of the structure to martensite. Holding at 433 K forms only a small quantity of additional martensite, so the structure can be assumed to be half martensite and half retained austenite.
b. (Green) The specimen is held at 523 K for 100 seconds, which is not long enough to form bainite. Therefore, the second quench from 523 K to room temperature develops a martensitic structure.
c. (Blue) An isothermal hold at 573 K for 500 seconds produces a half-bainite and half-austenite structure. Cooling quickly would result in a final structure of martensite and bainite.
d. (Orange) Austenite converts completely to fine pearlite after eight seconds at 873 K. This phase is stable and will not be changed on holding for 100,000 seconds at 873 K. The final structure, when cooled, is fine pearlite.
Below we have listed some simple examples at other temperatures that result in different phase transformations and hence different microstructures.

Examples of Iron-Iron Carbide Phase Transformations.
Figure 2.

The time-temperature transformation curves correspond to the start and finish of transformations which extend into the range of temperatures where austenite transforms to pearlite. Above 550 C, austenite transforms completely to pearlite. Below 550 C, both pearlite and bainite are formed and below 450 C, only bainite is formed. The horizontal line C-D that runs between the two curves marks the beginning and end of isothermal transformations. The dashed line that runs parallel to the solid line curves represents the time to transform half the austenite to pearlite.

Below are examples comparing electron microscopic photographs of cross sectioned steel music wire.

Before (austenite)
After (martinsite)

 

Conversion chart from Thousandths of an Inch to Millimeters.
Perfect Third carries gauges: 007" to .022" in Steel,
and .010" to .050' in Phosphor Bronze and Red Brass.

 

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