Fe, <0.3% C, 10.5-12.5% Cr, 0.3-1.0% Ni, <1.5% Mn, <1.0% Si, <0.4% P, <0.15% S, <0.03% N
Grade 3CR12 stainless steel is a low-cost grade chromium, containing stainless steel fabricated by modifying the properties of grade 409 steel. It resists mild corrosion and wet abrasion. It was originally developed by Columbus Stainless, which designated the registered trademark “3CR12”. Other designations of this grade include UNS S40977/S41003 and 1.4003.
Other designations that are equivalent to grade 3CR12 include ASME SA240 grades, ASTM A240/A240M grades and EN 10088.2. However, grade 1.4003 is also covered in EN 10028.7, which constitutes pressure-purpose stainless steels.
The following section will provide the key properties of grade 3CR12 stainless steel coil, sheet and plate, covered under Euronorm S41003, S40977, ASTM A240/A240M and EN 10088.2 1.4003.
The chemical compositions of various elements of grade 3CR12 stainless steels are tabulated below:
Table 1. Chemical composition of grade 3CR12 stainless steels
Given below are the mechanical properties of grade 3CR12 stainless steels:
Table 3. Mechanical properties of grade 3CR12 stainless steels
|Grade||Tensile Strength (MPa) min||Yield Strength 0.2% Proof Stress (MPa) min||Elongation (% in 50mm) min||Hardness|
|Rockwell (HR) max||Brinell (HB) max|
The following table outlines the physical properties of grade 3CR12 stainless steels:
Table 4. Physical properties of grade 3CR12 stainless steels
|Grade||Density (kg/m3)||Elastic Modulus (GPa)||Mean Coefficient of Thermal Expansion (µm/m/°C)||Thermal Conductivity (W/m.K)||
|Electrical Resistivity (nÙ.m)|
|0-100°C||0-300°C||0-700°C||at 100°C||at 500°C|
Grade Specification Comparison
Grade specifications for 3CR12 stainless steels are given in the following table:
Table 4. Grade comparisons for 3CR12 grade stainless steels
|Grade||UNS No||Old British||Euronorm||Swedish SS||Japanese JIS|
Given above are only approximate comparisons. The table is prepared to provide a comparison of materials that are functionally similar to each other, and the specifications are not legitimate. Original specifications can be verified if exact equivalents are required.
Possible Alternative Grades
Suitable alternatives to grade 3CR12 stainless steels are listed in the table below:
Table 5. Possible alternative grades to 3CR12 grade stainless steels
|Grade||Why it might be chosen instead of 3CR12|
|304||Excellent fabrication properties and corrosion resistance.|
|430||Excellent resistance to corrosion and good appearance. It does not require welding.|
|Galvanized steel||Inexpensive, fair corrosion resistance and fabrication properties.|
|Weathering steel||Inexpensive, acceptable fabrication properties and corrosion resistance.|
Grade 3CR12 stainless steels can be employed in applications for which aluminium, galvanized or carbon steels provide undesirable results, owing to its resistance to strong acids and alkalis, and cracking resulted from chloride stress corrosion. However, unlike grade 304, grade 3CR12 has minimal resistance to crevice and pitting corrosion in the presence of chloride.
Under ambient conditions, grade 3CR12 has improved resistance to water and chloride substances, as the corrosivity of chloride contents will be mitigated by the nitrate and sulphate ions. One of the major drawbacks of grade 3CR12 is that the surface of the material is subjected to mild corrosion when exposed to any type of environment. It is due to this reason the material is limited to decorative applications.
Grade 3CR12 stainless steels exhibit scaling resistance between 600 and 750°C in the presence of air, and between 450 and 600°C under stress environments. The material tends to become fragile upon prolonged exposure to temperatures between 450 and 550°C. However, the material does not lose its impact resistance at this temperature range.
Grade 3CR12 stainless steels are annealed at temperatures ranging from 700 to 750°C, divided into 25 mm section, and each section is soaked for 1½ h. The material is then allowed to cool. Care should be taken to prevent hardening during heat treatment. The mechanical properties and corrosion resistance characteristics of this grade can be affected by quenching treatments.
Once the material is annealed, processes such as pickling and passivating are performed.
Welding methods used for austenitic stainless steels can be applied to grade 3CR12 stainless steels. Low heat input techniques, such as GMAW (MIG) and GTAW (TIG), can be considered. During welding, grade 309 filler wire, pre-qualified by AS 1554.6, is preferred. However, grade 308L, 316L, 309Mo and 309L wires have also been employed in many cases. Any discoloration in the welded product can be removed using backing gases, or techniques such as purging and pickling.
Machinability of grade 3CR12 stainless steels is around 60% of that of mild steel. They have a work-hardening rate lesser than that of austenitic steels, and, hence, they do not require special machining methods.
Grade 3CR12 stainless steel plates can be obtained in standard, hot-rolled annealed and pickled (HRAP) finish, and coils are available in 2B or 2D finish. Black finish can also be produced by hot-rolling the material, leaving behind a dark oxidized surface on the steel. Grade 3CR12 with black finish has a good corrosion resistance and low friction and, hence, it is suitable for different wear applications.
Grade 3CR12 stainless steels find application in the following:
- Sugar processing industries
- Transport equipment, such as rail wagons carrying iron ores and coal
- Mining and mineral processing
- Oven and furnaces