Background

3CR12 was originally developed in the late 1970’s as a low cost grade of stainless steel which possessed good fabrication properties. It was developed from grade 409 and has a chemistry which is controlled to ensure good weldability. Originally marketed to a mill specification as a proprietary brand, 3CR12 was developed in the mid nineties to ensure conformance to new international standards published both in Europe and the USA.

Through to mid 2004 3CR12, which is a registered trademark of Columbus Stainless (Pty) Ltd, was certified in accordance with EN 10088-2 1.4003, EN10028-7 1.4003 and ASTM A240 UNS S41003. As part of the continuous improvement of its products, Columbus Stainless (Pty) Ltd has further enhanced 3CR12 to improve its performance in more severe material handling applications. The product once again is a proprietary product meeting mill specifications rather than European and American standards. However, Columbus Stainless (Pty) Ltd continues to manufacture stainless steel conforming to the requirements of EN 10088-2 1.4003, EN10028-7 1.4003 and ASTM A240 UNS S41003.
Properties
Chemistry




C


Mn


Si


P


S


Cr


Ni


Ti

Min.


-


-


-


-


-


10.50


-


4(C+N)

Max.


0.030


2.00


1.00


0.040


0.030


12.50


1.50


0.60
Mechanical Properties

Properties, unless otherwise stated, are transverse at room temperature.

Gauge
(mm)


Tensile Str (MPa)


0.20% Proof Str (MPa)


Elong (%)


Impact Energy (J)


Hardness Brinell (HB)

<3


460 min


280 - 450


18


-


220 max

3 - 4.5


460 min


300 – 450


18


35 min


220 max

>4.5 – 12


460 min


300 - 450


20


35 min


220 max

>12


460 min


300 - 450


20


35 min


250 max
Physical Properties

At 20°C unless otherwise stated.

Property





Value

Density





7680 kg/m3

Modulus of elasticity in tension





200 GPa

Modulus of elasticity in torsion





77 GPa

Poisson’s ratio





0.32

Thermal conductivity


100°C


30.0 W/m.K




500°C


40.0 W/m.K

Electrical resistivity





678 nΩm

Co-efficient of thermal expansion


1-100°C


11.1 μm/mK




0-300°C


11.7 μm/mK




0-500°C


12.3 μm/mK

Melting range





1430-1510°C

Relative permeability





Ferromagnetic
Atmospheric Corrosion Resistance

Atmospheric corrosion will occur when metals are exposed to the environment. Atmospheric corrosion can be classified as dry, damp or wet corrosion. For the first of these, most dry metals corrode very slowly at ambient temperatures. It is the latter two cases, when the corrosive medium of water, in the form of rain or condensation, which combined with various salts and pollutants, can result in, that more severe corrosion taking place. Climate/geographical variations are therefore strong factors and the following atmospheres are generally distinguished; marine, industrial, rural and urban.

Atmospheric corrosion testing of 3CR12 has given corrosion rates as low as 0.00004 -0.00008” per year in certain marine environments, an improvement of 250 times the life of unpainted mild steel under the same conditions.

It should be noted that 3CR12 is not recommended for decorative purposes. In aggressive environments it will tend to form a light surface rust colored patina. However, this is superficial and does not affect the mechanical properties of the steel.

Should aesthetic qualities be of prime importance 3CR12 can be painted with a number of paint systems.

Long term atmospheric corrosion tests have been undertaken in several locations around the world. Tests in South Africa have lasted for up to twenty-six years. Samples were placed in a wide range of atmospheric conditions from rural through to severe marine and industrial environments. Corrosion rates are shown below at various time intervals for a representative range of test sites. Values for mild steel and zinc are given for comparison. The zinc value gives an indication of the performance of galvanized steel free from damage to the surface coating.
Fabrication
Cutting

· A number of processes both mechanical and thermal can be used.

· Mechanical methods include guillotining, sawing, blanking and piercing.

· Thermal cutting processes most commonly used are plasma and laser cutting.

· Other thermal and abrasive cutting methods may be used but can leave a rough and uneven cut edge, which requires dressing before welding or further use.

· Oxy acetylene cutting is not suitable for cutting stainless steels.
Forming

3CR12 can usually be formed on the same equipment, with the same tooling as for carbon steel.

The recommended inner bend radius is 2 x t for >6mm, 1 x t for ≤ 6mm. Reverse bending is not recommended. Bending should be carried out transverse to the rolling direction.

Stainless steels should not be contaminated with any mild or low alloy steel during handling, storage or fabrication.
Machining

3CR12 has machining characteristics similar to AISI 430 (i.e. a machinability rating of 60 compared to mild steel of 100). The reduced extent of work hardening compared to austenitic stainless steels eliminates the need for special cutting tools and lubricants. Slow speeds and heavy feed rates with sufficient emulsion lubricant will help prevent machining problems.
Weldability

3CR12 is metallurgically designed to give good weldability characteristics by a carefully designed, controlled and balanced chemical composition. It has high integrity weld zone mechanical properties in section thickness' up to 30mm. Welding processes that can be successfully used include: SMAW, GTAW, GMAW, FCAW, PAW, laser, resistance spot and seam welding.

It is recommend to use ER309L for GTAW and GMAW and E309L for SMAW.
Coating and Painting

Utility stainless steels may, under mildly corrosive conditions, develop a uniform rust colored patina. This does not affect the structural integrity of the steel, but for aesthetic reasons, painting may be required. Normal preparation is necessary, such as ensuring a clean, grease and contamination free surface. A primer coat is recommended for cold rolled material due to its smoother surface, but hot rolled, pickled steel may be suitably painted in a single coat.

Product Range

3CR12 is available in cold rolled (2B) and hot rolled (No 1). Black product is also available in some hot rolled gauges, specifically for non submerged material handling applications.
Applications

3CR12 has been used in a wide range of industries including:

· Mining

· Power Generation

· Sugar

· Bulk Handling

· Water

· Transport

· Telecommunications/Electrical

· Engineering

· Rail

· Agricultural

Typical applications are-

· Bulk wet materials handling

· Vehicle frame/chassis

· Rail car hoppers

· Sweeper/gritter vehicles

· Conveyors, chutes, screens, troughs

· Bunkers, hoppers

· Tanks and containers

· Chimneys, ducting

· Enclosures, cabinets

· Walkways, stairs, railings