3CR12 is a weldable, structural, corrosion resistant steel containing a nominal 12% Chromium. 3CR12 was originally developed as an alternative material of construction to materials such as mild steel, galvanised and alurninised steel, where the mechanical properties and corrosion resistance of these materials was unsuitable.
With an average life expectancy of 5 to 10 times that of mild steel and at considerably less cost than higher grades of stainless steel, 3CR12 is recognised as an extremely effective alternative to coated mild steel, resulting in minimum capital cost increases and significant maintenance cost savings.
3CR12 has been in use in the sugar industry, locally and world-wide, since 1980 and has become an accepted material in many applications ranging from the cane yard to the final product.
3CR12 exhibits excellent properties in wet sliding abrasion applications by resisting corrosive attack, therefore improving flow and reliability. This allows widespread use of 3CR12 in cane sugar and beet handling applications, where abrasion is aggravated by the moisture and solids present in the cane and beet being processed.
All metals react with oxygen and water in he air to form a surface layer of oxide. That formed on carbon steel is soft, friable, hydrated iron oxide rust. The process of rust degeneration is greatly accelerated by surface abrasion or scouring.
3CR12 with a nominal 12% Chromium content, has an inert tough surface layer of iron-chromium oxide. This passive layer is invisible to the naked eye, allowing the natural brightness of the metal to be seen. If scratched, the film has the ability to reform instantaneously, thus maintaining protection.
With mild steel, abrasion removes the corroded layer and exposes fresh reactive surfaces for further corrosion to take place.
3CR12's excellent wet sliding abrasion properties are derived from its superior corrosion resistance and slideability. Under dry conditions, 3CR12 offers only marginal improvement over mild steel, but under wet or damp conditions (eg. over 4% moisture), the corrosion vector is underestimated. Dry conditions are seldom encountered in the cane sugar and beet sugar industry.
When the cost per unit loss by corrosion abrasion is taken into account, 3CR12 is superior to other grades tested. (See histogram below).
The sugar industry is characterised by high maintenance costs due to the replacement and repair of equipment due to corrosion and corrosion abrasion.
Sugar cane is not washed prior to cutting and crushing in the mills and the presence of sand and stone contribute to the abrasive conditions that already exist.
3CR12 with its excellent wet sliding properties improves the flow of materials and has gained rapid acceptance in cane handling and bagasse applications. It has also gained acceptance in most other areas within the sugar mills due to its corrosion resistance and superior mechanical properties.
Examples of the many applications where 3CR12 has been used in the processing of sugar cane are listed below
Maidstone Sugar Mill have installed their second diffuser which was comissioned in the 1995 season. The diffuser is 70 metres long, 10 metres wide and capable of processing 300 tonnes of sugar cane per hour The roof, side wall internals, perforated floor sections and lifting screws have been fabricated from 3CR12.
3CR12 is proving its worth in corrosion abrasion applications as liners on cane carriers and deck plates on intercarriers and ash disposal carriers. The photograph on the left is of the Felixton sugar mill ash seffler deck plates which were installed in 1992 and are still in excellent condition. The carrier disposes wet ash originating from bagasse burnt in the boilers.
Transvaal Sugar's (T.S.B.) new Komati mill in Komatipoort started production in March 1994, processing 225 tonnes of cane per hour which has doubled over the past five years.
3CR12 is being used in areas where corrosion and corrosion abrasion present high maintenance demands.
The Komati mill has installed 3CR12 in its conveyor systems, cane carrying, diffuser feed slat and sample system conveyors. In the juice extraction area where the acidic nature of the product can rapidly degrade mild steels, 3CR12 has been used for the diffuser side walls, roof and some juice piping. Chutes and intercarriers in this area have also been fabricated in 3CR12.
Downstream production machinery fabricated using 3CR12 includes the clarifier launders and root mud mixers, filter frame, agitator, trough and hood filtration piping. The evaporator tubes and fourth effect condenser, pan tubes and condensation pipes have also been fabricated from 3CR12. Further into the mill, 3CR12 has also been used to build the centrifugal monitor casings, sugar screw conveyors and sugar scales.
In total, over 450 tonnes of 3CR12 has been used in the Komati mill, demonstrating the versatility of the 3CR12 applications throughout the factory.
| C | Ni | Mn | Si | P | S | Cr | Ti |
|---|---|---|---|---|---|---|---|
| 0.03% | 1.5% | 1.5% | 1% | 0.03% | 0.03% | 11% to 12% | 0.6% |
| Ultimate Tensile Strength | 460 | MPa | min | |
| Proof Strength (0.2% offset) | 280 | MPa | min | |
| Elongation (in 50mm) | t < 4.5 mm | 18 | % | min |
| t > 4.5 mm | 20 | % | min | |
| Hardness | t < 12 mm | 220 | BHN | max |
| t>12 mm | 250 | BHN | max | |
| Charpy Impact (20°C) | 35 | J/cm3 | min | |
| Density | 7860 | kg/m3 | |
| Modulus of Elasticity (tension) | 200 | GPa | |
| Specific Heat Capacity | 460 | J/kgK | |
| Thermal Conductivity | at 100°C | 23 | W/mK |
| at 500°C | 25 | W/mK | |
| Electrical Resistivity | at 25°C | 660 | |
| Coefficient of thermal expansion | 0-100°C | 10.8 | μ/m°C |
| 0-300°C | 11.3 | μ/m°C | |
| 0-700°C | 12.5 | μ/m°C | |
| Melting Range | 1430-1510 | °C | |
| German Werkstoff Equivalent | 1.4003 | ||
| American Equivalent | ASTM A240 410S | ||