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-- Invar steel:
(Invar) nickel iron alloy (nickel 36%, iron 63.8%, carbon 0.2%)
invar has a very low coefficient of thermal expansion (between - 20 ℃ and 20 ℃, with an average value of about 1.6 × 10-6/℃), known as the king of metals, is an indispensable structural material for precision instruments and equipment.
-- Source:
In 1896, the Swiss French physicist C.E. Guilme found that the alloy with this composition has this characteristic: it shows a very small coefficient of thermal expansion at room temperature (- 80~230 ℃). Guilaume also won the Nobel Prize in 1920 for his discovery, making him the second physicist to receive this honor after German physicist Wilhelm. Conrad. Roentgen and the first scientist in the metallurgical field to do so.
-- Nominate:
Due to differences between different languages and other reasons, Invar has many names, but the commonly used names are classified as follows:
1. United States and UK: Invariable Alloy, in addition to Invar36, Invar35, Ni36Fe, Fe Ni36, NiInvar, Unispan36, Ni1036, etc.
2. Japan: unchanging steel.
3. Germany: Vacodil36, in addition to Ni1036 and others.
4. China: Low expansion alloy, in addition to invar alloy, invar steel, invar steel, non expansion steel, indium steel, invar, 4J36, non expansion alloy, etc.
The commonly used and standardized way of writing is Invar.
--Characteristic:
1. The coefficient of thermal expansion is small, and the average expansion coefficient at room temperature is 1.6 × 10-6/℃, and relatively stable at room temperature -80 ℃~230 ℃.
2. The strength and hardness are not high. The tensile strength is about 590Mpa, the yield strength is about 410Mpa, and the Brinell hardness hardness is about 141HBS.
3. The thermal conductivity is low, at 10W/m.K, which is only about 1/4 of the thermal conductivity of 45 steel.
4. Plasticity, toughness, elongation, reduction of area, and impact toughness are all very high, with elongation δ= 30-45%, shrinkage rate δ= 50~70%。 impact toughness α K=130-310 J/cm2。
Invar cannot be strengthened by heat treatment, and its characteristics are similar to austenitic stainless steel, but it is even more difficult to machine than austenitic stainless steel. The main manifestations in cutting processing are high cutting force and high cutting temperature. In the processing process, it also has soft and viscous properties and great plasticity, which is not easy to break chips, exacerbates tool wear, and reduces the machining accuracy of the workpiece. Therefore, high-performance tools must be used.
--Development and application:
The discovery of Invar has attracted the attention of scientists from various countries, resulting in significant improvements in both the variety, performance, and application of Invar. Its development process:
In 1927, Japan developed the Fe Ni Co series Superinvar with increased production costs;
In 1931, a Fe Ni Cr stainless Invar was developed to increase production costs;
In 1937, German A. Kussmann discovered the Fe Pt and Fe Pd metallurgical series Invar;
In 1964, Invar began mass production according to industrial standards and became a commercial alloy material;
In the 1970s, Inco Corporation in the United States developed Incoloy903 alloy, which led to the entry of low expansion alloys into high-temperature applications;
In the late 1980s, a modern low expansion superalloy series was formed based on the Invar series of alloys.
As a low expansion alloy, structural stability is required, and FeNi36 type Invar can maintain a stable austenite state near -273 ℃, thus obtaining the widest application. The expansion of its application field has also undergone a relatively long process:
In the early days, it was mainly used for manufacturing precision instruments and meters, swing rods for standard clocks, swing wheels, and hairsprings for clocks and watches;
In the 1920s, Invar was used instead of platinum as a guide wire for glass sealing, significantly reducing costs;
In the 1950s and 1960s, it was mainly used for electronic tubes, thermal bimetallic sheets for temperature control, length rulers, geodetic baseline rulers, etc;
By the 1980's and 1990's, it was widely used in microwave technology, liquefied gas containers, shadow masks for color TV sets, overhead cable cores, resonant cavities, laser collimator cavities, main substrates for lithography machines, etc;
After entering the 21st century, with the rapid development of space technology, its applications have expanded to aerospace remote sensors, precision laser equipment, optical measurement systems and waveguide structures, various microscopes, support systems for large lenses in astronomical telescopes, and various scientific instruments that need to install lenses;
