Australian Stainless Steel Development Association (ASSDA) has outlined new and emerging stainless steel grades, which may be considered as alternatives to the traditional and widely known varieties. Users are seeking cost effective alternatives to both chromium and molybdenum austenitic 300 series grades. Austenitic 200 series, duplex stainless steels and ferritic grades can all be used instead of 304 and 316, if they are selected, designed, fabricated and used appropriately. The alloying elements in stainless steel contributing to corrosion resistance are chromium and molybdenum. Within each of the alternative groups there are grades with different corrosion resistance resulting from the chromium and molybdenum contents. The well-known austenitic 300 series grades contain the highest levels of nickel. According to ASSDA, these grades are austenitic despite their lower nickel because they have more manganese. Manganese is about half as effective in forming austenite as nickel, so for every 1% of nickel left out, about 2% of manganese has to be added at the same level of chromium, which suppresses the formation of austenite. Half the nickel in these grades has been replaced by manganese and the price of manganese is also rising strongly. The lower chromium 200 series grades are generally suitable for use with mild acids and alkalis including most foods (pH not less than 3). They are satisfactory with 20C potable water and are suitable for indoor exposure. They are used extensively for cookware and serving bowls applications where the corrosion conditions are not severe since the utensils are washed and dried. The formability and deep draw ability of the 200 series are especially useful for these applications.
Hi, You are correct, Minimum refers to the one cycle for which this part will expose until final work shop PWHT. hence mill test certificate shall include this. Max. SPWHT, refers to additional cycles of heat treatment that are reserved for future repairs during equipment lifetime. Again, these simulated no. Of cycles shall be specified in MTC. The idea is we need to make sure that steel mechanical properties are not compromised upon exposure to multiple repairs (i e 4 cycles in your case). One could say, if steel is subjected to 4 cycles and is ok, then it should by defacto be good for one cycle, yet, this is wrong assumption cause mechanical problems and microstructure of materials varies accordingly based on no. Of cycles for which material will expose. This is apparent in alloy steel and especially for impact test values as an example. In your case, this forged CS with properties before PWHT can be understood to be " as forged" condition (i.e. Wit...
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