1.Overview

What is INVAR Steel?

IINVAR is an acronym of invariable alloy and it was discovered by Guillanume of France in 1896. With over 36% nickel content, this Fe-Ni alloy steel does not experience any thermal expansion in the extremely low temperature environment (≤-163°C) or the above room temperature environment. In short, INVAR steel has a very low thermal expansion coefficient, which makes it appropriate for precision gauge, Bi metal, Tri metal and other high-tech electronic components. Riding the trend of bigger TV screens, the existing Al-killed steel is being replaced by INVAR steel for shadow mask. INVAR steel is also in high demand as an LNG ship material.

Material Characteristics

Chemical Composition (wt%) Classification C Si Mn Ni Fe Others For Bi-Metal,LNG 36% Ni ≤0.04 ≤0.25 0.2-0.4 36±0.5 B'ce B,Cu,Cr,Al, P,O,N For Lead Frame 42% Ni ≤0.04 ≤0.25 0.2-0.4 42±0.5 B'ce

A Comparison of Physical Properties with Stainless Steel Specific Gravity (g/cm³) Thermal Expansion Coefficient (10/°C) Young Rate (kgf/m²) Yield Strength (kgf/m²) Tensile Strength(kgf/m²) Elongation rate (%) Longitude (Hv) 36% NI INVAR Alloy 8.12 1.2 14700 30 31 35 135 STS304 7.93 18.8 19600 28 65 55 160 STS430 7.70 11.9 20300 32 50 28 150 * The thermal expansion coefficient of INVAR alloy is 1/10 that of STS and carbon steel (Al-Killed), and only 1/100 of pure steel.

General Properties

Low thermal expansion coefficient:1.5X10-6°C Highly clean steel: Less than 6µm­ of non-metallic inclusion Good etching capacity: Segregation, good structure Other: Weldability, skin stability

2. Usage

Shadow Mask

Shadow mask is a thin metal film with between 800,000 and 1.6 million tiny holes, which act to form images on TV and computer screens. It is one of three core components of the Braun monitor that determines the clarity of color monitors.
Shadow mask accurately guides the electro beams (red, green, blue) projected by the electric gun in color monitors of TVs and computers to the fluorescent surface inside the panel. It is also capable of color distinction so that monitors can display clearer color images.

Shadow Mask in Braun Tube 

Tri/Bi-Metal

	What is Tri-Metal ?	Tri-Metal is a precision material used in color monitors. It is made by continuously welding two steels of different chemical composition and mechanical and physical properties. Two types of materials, STS304 (high expansion) and INVAR (low expansion), are welded together to form one metal sheet.
	What is Bi-Metal?

Bi-Metal is a spring made by mold pressing the Tri-Metal Band into different sizes. It is mounted on four sides of shadow mask inside the color monitor and connects the shadow mask frame and stud pins. It also supports shadow mask frame, makes up for the deformity by thermal expansion, and create high resolution and colors.

Electro Gun electrode(G1,G2)

Use & Functions: It is one of the electric gun electrodes that shoots out electric beams out of a shadow mask hole. It also controls the thermal electron released from the cathode surface by outside signals.

Lead Frame

Lead Frame is a core component of semiconductor IC. It transmits electric signals between semiconductor chip and PCB substrate. It also protects the chip from outside moisture and impact, and serves as a support frame.

LNG Carrier

Natural gas with methane as its key element is frozen in -162℃ to make LNG (Liquefied Natural Gas). It is a colorless liquid that has 1/600 the volume of natural gas. The LNG carriers that transport LNG require the highest level of shipbuilding technology since the ships must be equipped with tanks that can withstand the extremely low temperature of -162℃ The materials used inside the LNG tanks on LNG carriers are aluminum, INVAR and stainless steel.