1. Overview
Stainless steel grade 444 (00Cr18Mo2) is ferritic stainless steel with ultra-low carbon-nitrogen, 18% chromium, and 2% molybdenum, and high corrosion resistance. This steel is generally stabilized with niobium or titanium, which can avoid intergranular corrosion after welding.
Compared with austenitic stainless steels such as SUS304 and SUS316L, the biggest advantage of this steel is its excellent resistance to chloride-ion stress corrosion cracking, and its resistance to chloride ion pitting corrosion is better than SUS304, which is equivalent to SUS316L. Therefore, this steel grade is particularly suitable for various water treatment devices.
444 stainless steel is an ultra-low carbon-nitrogen, highly corrosion-resistant ferritic stainless steel containing 18% chromium and 2% molybdenum. Its yield strength is equivalent to 1.5 times that of carbon steel and 6 times that of fiberglass. It has outstanding properties in terms of earthquake resistance, snow resistance, wind pressure resistance, and impact resistance.
444 stainless steel is generally stabilized with niobium (Nb) or titanium (Ti) to avoid intergranular corrosion after welding. It is particularly suitable for various water treatment devices. (Such as food processing equipment, heat exchangers, water storage tanks, solar energy collection panels, etc.)
444 stainless steel has high thermal conductivity and is suitable for heat exchange purposes. The thermal expansion coefficient is small, suitable for thermal expansion and contraction, and used under conditions of thermal cycles.
444 stainless steel is also relatively excellent in corrosion resistance. In chloride media with high concentrations, chloride stress corrosion cracking is generally not produced.
444 stainless steel has good resistance to pitting, crevice corrosion, stress corrosion, good resistance to intergranular corrosion, and high-temperature oxidation.
Therefore, 444 stainless steel has the same corrosion resistance as 316L stainless steel due to its high chromium and nickel content. It can replace 316L stainless steel in many applications. The absence of nickel makes its cost lower. The addition of stabilizing elements titanium and niobium enhances its resistance to intergranular corrosion and high-temperature oxidation.
However, the main limitation is that 444 stainless steel is magnetic, while 316L stainless steel is non-magnetic. Therefore, the corrosion resistance, heat resistance, and welding performance of 316L stainless steel occupy an important position in the fields of petrochemicals, natural gas pipelines, food, and medical treatment.
2. Chemical Composition
|
Standard |
Grade | C% | N% | Cr% | Ni% | Mo% | Other |
| JIS G4305 |
SUS444 |
0.025 | 0.025 | 17.00~20.00 | — | 1.75~2.50 | Nb or Ti or Zr： 8′(C%+N%)~0.80 |
| SUS304 | 0.08 | — | 18.00~20.00 | 8.00~10.50 | — |
— |
|
| SUS316L | 0.030 | — | 16.00~18.00 | 12.00~15.00 |
2.00~3.00 |
— |
SUS444 has ultra-low carbon and nitrogen impurity elements
SUS444 is added with molybdenum to improve pitting resistance
SUS444 is added with stabilizing niobium or titanium element
|
Grade |
Yield Strength N/mm2 |
Tensile Strength N/mm2 |
Elongation % |
Victorinox hardness |
Cold bending 180°, d=2a |
|
SUS444 Typical |
310 | 480 | 30 | 160 | Qualified |
|
SUS444 Standard |
≥245 | ≥410 | ≥20 | ≤230 |
Qualified |
| SUS304 Standard | ≥205 | ≥520 | ≥40 | ≤200 |
— |
| SUS316L Standard | ≥175 | ≥480 | ≥40 | ≤200 |
— |
3. Mechanical Behavior
|
Grade |
Density g/cm3 |
Magnetic | Thermal conductivity, 100°C,W/m*K |
Thermal expansion coefficient 0~100°C,mm/m*K |
|
SUS444 |
7.75 | Have | 26.8 | 11.0′10-6 |
| SUS304 | 8.03 | No | 16.2 |
16.9′10-6 |
| SUS316L | 7.99 | No | 16.2 |
16.0′10-6 |
The density of SUS444 is low and the usable area increases
SUS444 has good thermal conductivity and easy heat dissipation
SUS444 has low thermal expansion and welding distortion
4. Corrosion Resistance
4.1 Resistance to chloride ion stress corrosion cracking
Using laboratory accelerated corrosion test method, test standard: GB/T 17898-1999 “Test Method for Stress Corrosion of Stainless Steel in Boiling Magnesium Chloride Solution”.
|
Experiment material |
SUS304 | SUS316L | SUS444 |
|
Crack occurrence time, h |
2.5 | 9.8 |
48h no cracks |
| Crack penetration time, h | 2.5 | 11.8 |
48h no cracks |
|
Surface morphology of the sample after the test |
 |
 |
 |
SUS444 has excellent resistance to chloride ion stress corrosion cracking
4.2 Resistance to chloride ion pitting corrosion
Using laboratory accelerated corrosion test method, test standard: GB/T17897-1999 “Stainless steel ferric chloride pitting corrosion test method”, test time: 48 hours.
SUS444 has better resistance to chloride ion pitting corrosion than SUS304
The pitting corrosion resistance of SUS444 is equivalent to that of SUS316L
4.3 Resistance to intergranular corrosion
The laboratory accelerated corrosion test method is used for TIG welded joints, the test standard: is GB/T 4334.5-2000 “Sulfuric acid-copper sulfate corrosion test method for stainless steel”, test time: 16 hours. Test results: After the test, two samples on the front and back surfaces were bent 180¡ã. Observed with a magnifying glass 10 times, no intergranular corrosion cracks were found. The surface morphology of the sample bend is shown in the figure below.
No intergranular corrosion tendency after 444 welding
5. Welding Characteristics
|
Recommend R |
Avoid Q | |
| Welding method | TIG welding, plasma welding, MIG welding and laser welding (Preferential use of pulse function) |
Gas welding, such as oxyacetylene |
| Welding materials | SUS444 base metal cutting strip or ER316L; keep the welding material clean |
Non-ultra-low carbon welding consumables, such as ER308 |
|
Welding shielding gas |
Ar or Ar+He mixture; use back protection gas |
Nitrogen and hydrogen |
| Welding heat input | Minimal welding heat input, such as low welding current, low welding voltage, etc. |
Weaving bead; too high welding voltage |
| Welded structure | Arrange the welding sequence reasonably to reduce welding constraints |
Excessive welding groove assembly gap |
| Other | Clean the welding groove with acetone before welding; pickling passivation treatment on the weld after welding |
Preheat before welding; heat treatment after welding |
Please note: When SUS444 and non-ultra-low carbon nitrogen stainless steel (such as SUS304) TIG or plasma self-fusion welding, the corrosion performance of the weld will be reduced.
6. Forming Characteristics
| Drawing performance | Bulging performance |
Notes on bending |
| SUS444 is equivalent to SUS304 | SUS444 is lower than SUS304 |
The minimum diameter of the bending indenter is recommended to be greater than 1*a (a is the plate thickness) |
7. Available Product Specifications
| Surface condition | Thickness (mm) | Width (mm) | Form |
| 2B or 2D | 0.7~3 | 1000~1219 | Rolls |
8. Main Purpose
SUS444 is the most heat-resistant steel grade among ferritic steels. It has excellent high-temperature oxidation resistance within 1000℃. On the contrary, 304 is most likely to be corroded when the water temperature reaches 50-90℃. Compared with 304, stainless steel grade 444 has high chlorine resistance, excellent stress corrosion resistance, pitting corrosion resistance, etc., and it is not easy to scale and has a strong heat absorption effect. Its corrosion resistance is similar to SUS316 steel.
Based on the characteristics of the stainless steel grade 444, it is mainly used to manufacture water storage tanks, solar water heaters, heat exchangers, video machinery, printing, and dyeing machinery, stress corrosion resistance equipment, and automobile engine exhaust pipes.