Precaution:
1.Adjust the chemical composition of the weld, and add stabilizing elements to reduce the possibility of forming chromium carbide, such as adding titanium or niobium.
2. Reducing the carbon content in the weld can reduce and avoid the formation of chromium carbides, thereby reducing the tendency to form grain boundary corrosion. The carbon content is below 0.04%, which is called "ultra-low carbon" stainless steel. Chromium carbide formation can be avoided.
3. Control the residence time in the dangerous temperature area to prevent overheating, fast welding and fast cooling, so that the carbon cannot be precipitated in time.
Austenitic stainless steel welding structure prevention methods:
①Use low carbon grades 00Cr19Ni10 (304L) or 00Cr17Ni14Mo2 (316L), or stable grades 0Cr18Ni10Ti (321, more common in Europe) or 0Cr18Ni11Nb (347, more common in the United States). The use of these grades of stainless steel can prevent carbide precipitation during welding. number of harmful effects.
②If the structural parts are small and can be heat treated in a furnace, heat treatment can be performed at 1040-1150 ° C to dissolve chromium carbide, and rapid cooling at 425-815 ° C to prevent carbon precipitation.
Welded ferritic stainless steels may also exhibit intergranular corrosion in certain media. This is caused by the precipitation of carbides or oxides and the strain of the metal lattice when the steel is rapidly cooled from above 925°C. Stress relief heat treatment after welding can relieve stress and restore corrosion resistance. Adding titanium with more than 8 times carbon content to 1Cr17 stainless steel can usually reduce the intergranular corrosion of welded steel structures in some media. However, the addition of titanium is not effective in concentrated nitric acid.
Precautions in alloy applications:
a. Use alloys that resist intergranular corrosion;
b. Select the appropriate heat treatment process, such as aluminum alloy over-aging treatment;
c. Determine the welding process, aluminum alloy bonding and milling process, and avoid processing at temperatures that are prone to intergranular corrosion.
