The main disadvantages of ASTM A240 430 ferritic stainless steel are low toughness, high brittleness, high brittle transition temperature, high sensitivity to notches, and the causes of brittleness are as follows.
1.High Cr steel [w(Cr) greater than 15%] stays in the range of 400~525 degrees Celsius, which will cause the brittleness of ASTM A240 430 ferritic stainless steel, called 475 degrees Celsius brittleness. This brittleness is related to the steady phase along the grain boundary. It can be removed by heating to above 475 degrees Celsius and then quickly cooling.
2. When heated for a long time at 550 to 820 degrees Celsius, the σ phase will be precipitated. The σ phase is an intermetallic compound Fe Cr having a high hardness (above 68 HRC) and brittleness. There is still a large volume effect during precipitation, often along the grain boundary
Out. Its precipitation makes ASTM A240 430 ferritic stainless steel brittle and promotes corrosion between grades and reduces corrosion resistance of steel. The phase a is dissolved by heating above 820 C to eliminate the brittleness of the sigma phase.
3.ASTM A240 430 ferritic stainless steel has a coarse as-cast microstructure and does not undergo phase change during heating and cooling. Therefore, in the hot working process such as casting, forging, welding, rolling, etc., the grain growth occurs, and it cannot be refined by heat treatment, so that the room temperature is improved.
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