Carbonates grades,

This product is mainly used within the ferroalloy plant as the reducing agent in a silicothermic process to produce the low carbon grade of refined ferromanganese. 

Refined Ferromanganese. Refined ferromanganese refers to alloys that are not carbon saturated and range from less than 0.10 to 1.50% maximum carbon. Medium carbon grades are used in special grades of steels where in final additions carbon control is important. The low carbon grades are used mainly in the production of certain grades of stainless steels. 

Martensitic Stainless Steels. The martensitic stainless steels have somewhat higher carbon contents than the ferritic grades for the equivalent chromium level and are therefore subject to the austenite—martensite transformation on heating and quenching. These steels can be hardened significantly. The higher carbon martensitic types, eg, 420 and 440, are typical cutiery compositions, whereas the lower carbon grades are used for special tools, dies, and machine parts and equipment subject to combined abrasion and mild corrosion. 

Specify low carbon grades of stainless steel. Since sensitization results from the formation of chromium carbides, one approach is to sufficiently reduce the level of carbon in the alloy. Reduction of the carbon level to 0.03% or less has been shown to be effective in preventing sensitization. The low carbon grade of 304 is designated 304L 316 is 316L. Note the cautions below. 

All lube piping should be stainless steel. The stainless steel should be one of the 300 series, preferably L or low carbon grade, such as type 304L. 

Type 316L-This is the low-carbon (0.03% max.) version of type 316 that should be used where the heat input during fabrication exceeds the incubation period of the 316 (0.08% carbon) grade. For example, it is used for welding plates thicker than 1 cm. 

The scope of the term stainless steel has not been precisely defined, but for general purposes it may be considered to include alloys whose main constituent is iron but which also contain not less than 10% Cr. As with low-alloy steels, a distinction between low or medium carbon grades and high carbon grades must also be drawn, the latter being more in the nature of alloy cast irons. These are used mainly for oxidation resistance at high temperatures and for applications where abrasion resistance allied to a certain amount of corrosion resistance is required, and will not be considered in this section. 

Selective corrosion in the heat-affected zone of a weld occurs most commonly when unstabilised stainless steels are used in certain environments. The obvious answer is to use an extra-low-carbon grade of stainless steel, e.g. types 304L, 316L or a stabilised grade of steel, e.g. types 321 and 347. Knifeline attack at the edge of a weld is not commonly encountered and is seldom predictable, and it must be hoped that it is revealed during preliminary corrosion testing. 

Brown has pointed out that Du Pont use evaluation tests for (a-) as-received unstabilised alloys containing more than 0-03% C to check the effectiveness of the final heat treatment and (b) stabilised or special low-carbon grades after a sensitising treatment (1 h at 677°C) to determine whether susceptibility might develop during a subsequent welding operation. 

The microporosity is often reported in recent research papers as nanoporosity. Commercial activated carbon grades have an internal surface area of 500 up to 1,500 mVg. Powdered activated carbon comes with particle size 1-150 tm. There are also granulated or extraded materials with granule size in the 0.5 -mm range. 

Prevention. In North America, susceptibility to intergranular corrosion and sensitization can be avoided generally by the use of low-carbon grades such as type 316L (0.03% C maximum) in place of sensitization-susceptible type 316 (0.08% C maximum). In Europe, it is more common to use 0.05% C (maximum) steels, which are still reasonably resistant to sensitization, particularly if they contain molybdenum and nitrogen these elements appear to raise the tolerable level of carbon and/or heat input. (Wahid)61, (Krysiak)14 However, this method is not effective for eliminating sensitization that would result from long-term service exposure at 425-815°C. 

Type 304 is listed because it Is the least costly of the acceptable materials. Other 300 series SS s may be needed for considerations other than low temperature. For example, low-carbon grades are desirable for seacoast environments to avoid intergranular stress corrosion cracking during the periods when the material is not at cryogenic temperature,... 

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