Possible defects and preventive measures caused by heat treatment of ferritic stainless steel

Possible defects and preventive measures caused by heat treatment of ferritic stainless steel

1. Sensitization tendency of intergranular corrosion For general ferritic stainless steel with a carbon content greater than 0.01%, the annealing temperature exceeds 850°C, which will increase intergranular corrosion due to the generation of grain boundary precipitates. sensitivity. In actual production, sometimes in order to improve the annealing production schedule or consider equipment utilization, iron may be mixed with other materials for heat treatment. The particularity of solid stainless steel increases the annealing temperature, resulting in reduced heat treatment effect of the steel. Therefore, annealing of ferritic stainless steel should be strictly implemented Process, control heating temperature. 2. Brittleness Ferritic stainless steel will produce high-temperature brittleness when heated at higher temperatures. Insulation or slow cooling at 600~400℃ may cause O-phase brittleness and 475℃ brittleness. sex. Therefore, attention should be paid to controlling the heating temperature not to be too high, and to avoid staying in the brittle zone. It is better to air-cool below 600°C.

 3. The grain size becomes larger

The grain size of ferritic stainless steel also tends to increase with increasing heating temperature, which is detrimental to the plasticity of the steel. From this perspective, ferrite does not When heat treating stainless steel, lower temperatures should also be used as much as possible to prevent overheating.

4. Surface is poor in chromium In an oxidizing atmosphere, ferritic stainless steel is heated to high temperatures and for a short time, causing chromium on the steel surface to be preferentially oxidized and chromium deficient. Some studies have proven that it contains 18% chromium When ferritic stainless steel is heated at 788°C for 5 minutes, the chromium content in the oxide film on the steel surface reaches 21.5%, indicating that preferential oxidation of chromium occurs. This will inevitably reduce the amount of chromium on the surface of the steel and reduce corrosion resistance. If heated for a long time, the oxide film will thicken to a certain extent, preventing further oxygen invasion. Enter, giving the chromium in the matrix a chance to diffuse to the chromium-poor layer, and the chromium-poor layer will be eliminated.