Characteristic 3Cr12

3Cr12 plate is a weldable chromium containing utility stainless steel, with a fine grained duplex ferritic-martensitic microstructure. Originally 3CR12 was not included in any international specifications.
3Cr12 stainless plate was designed as a corrosion resisting steel and will exhibit staining when exposed to aggressive atmospheric conditions. 3Cr12 was not designed as a high temperature steel, does have useful mechanical properties at temperatures where mild or carbon manganese steels would be unsuitable.

Equivalent 3Cr12

3CR12 has been designated DIN grade 1,4003 and ASTM/ASME 41003. EN 10088.2, ASTM A240/ A240M grades UNS S40977 and S41003 and ASME SA240 grades UNS S40977 and S41003. 1.4003 is also included in EN 10028.7

Like other chromium stainless steel, 3CR12 stainless has useful strength at temperature about 600oC. This ele vated temperature strength is significantly higher than that of plain-carbon steels. Hot working can be carried out at 700ºC - 800ºC without significantly affecting subsequent mechanical properties. Above 850ºC, 3CR12 behaves superplastically due to the fine grained duplex microstructure.

Grade	Why it might be chosen instead of 3CR12
304	Better corrosion resistance and fabrication properties are required.
430	Better corrosion resistance and appearance is required. Weldability not needed.
Galvanised steel	A lower cost is required, and the reduced corrosion resistance and fabrication characteristics of galvanised steel are acceptable.
Weathering steel	A lower cost is required, and the reduced corrosion resistance and fabrication characteristics of weathering steel are acceptable.

Stainless 3CR12 is effective in many applications where carbon steel, galvanised, aluminised or painted steel or aluminium give unsatisfactory life. It is not attacked by strong alkalies, and often gives adequate resistance in acidic conditions.

Stainless 3CR12 strongly resists chloride stress corrosion cracking, but is less resistant than 304 to pitting and crevice corrosion in chloride environments. 3CR12 is likely to resist water with chloride contents of up to 150 to 200 mg/L at ambient temperatures. The presence of sulphate or nitrate ions will reduce the corrosivity of chlorides. Light surface rust can form in many atmospheres, making the material unsuitable for decorative applications.

Heat Resistance

In air 3CR12 offers scaling resistance to 600°C continuous or 750°C intermittent, but if under stress the temperature should be limited to 450°C continuous or 600°C intermittent. 3CR12 suffers negligible embrittlement after extended exposure at temperatures of 450-550°C; it can be used safely at these temperatures without loss of room temperature impact resistance.

Heat Treatment

Annealing - heat to 700-750°C, soak for 1½ hours per 25mm section. Air cool. The maximum temperature of 750°C should not be exceeded. Annealing should usually be followed by pickling and passivating.

This grade should not be hardened by heat treatment; quenching treatments may reduce the corrosion resistance and mechanical properties.

Cutting
The most effective cutting methods are:

Cutter	Remarks
Abrasive Disc	use dedicated discs
	Avoid overheating
	Vitrified or resinoid aluminium oxide discs recommended
Plasma	Oxygen-free nitrogen is the most economical primary cutting gas.(Other gasses can be used)
	Heat discolouration must be removed prior to use in a corrosive environment
Guillotine	Use well sharpened and correctly alligned and set blades to avoid sheared breaks and rollover.
	Capacity of guillotine (rated in terms of mild steel thickness) must be downrated by 40% of 3CR12.

Plat 3CR12 stainless can be readily welded using similar techniques to austenitic stainless steels. Low heat input processes are preferred - particularly GTAW (TIG) and GMAW (MIG). Filler wire pre-qualified by AS 1554.6 (3CR12 referred to as "4003") is grade 309, but 309L, 309Mo, 316L and 308L have been successfully used. Argon plus 1-2% oxygen shielding gases are recommended. Discolouration of the weld should be removed by pickling, except possibly in wear applications; effective purging and use of backing gases is often a better option.

Machining Plate 3Cr12

3CR12 has a machinability similar to that of grade 430, ie about 60% of that of mild steel. The work hardening rate is lower than that of austenitic stainless steels, so reducing the need for special machining techniques.

Finishes

3CR12 is available in standard HRAP (Hot Rolled Annealed and Pickled) finish in plate, and 2B or 2D in coil. This is hot rolled and with the high temperature scale left on the steel. The resulting dark oxidised surface has good low friction characteristics and a corrosion resistance that is useful for many wear applications, even although slightly less resistant than the "white" pickled finish.

What is Plate 3Cr12 Application

Storage tanks, dryers, walkways, fluid lines and pulp handling, frames, chassis, steps, wheel arches, handrails, firewalls, containers, tanks, frames, battery boxes, hoppers, sweepers, Deck plates, conveyor pans, idler rollers, air doors, mine car hoppers, shaft ranges, skip liners, breakers, hoppers, chutes, hot gas ducting, pump covers, oil tank roofs, turbine exhaust, nuclear power stillages, cooling stacks, high-voltage capacitor boxes, shelters, flood gates, power plant hoppers and conveyors, weir plates, cable trays, water and sewage treatment equipment, tile curing racks, spray booths, dust control, handrails,

Referensi:
www.azom.com
http://askzn.co.za/stainless-steel/tech-grade-3cr12.htm
www.sassda.co.za