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 Half the nickel in these grades has been replaced by manganese and the price of manganese is also rising strongly.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.
