Welding of Chromium Martensitic Stainless Steel
Chromium martensitic stainless steel is a type of stainless steel that often used in making high-strength parts and components, from high temperature construction and fabrication materials to ships, aircraft and automotive parts. It is well recognized for its strength, hardness and corrosion resistance. However, due to its high chromium content and hardening ability, chromium martensitic stainless steel is more challenging to weld than other stainless steels. In order to ensure a quality weld, it is important to utilize the right welding process and materials.
First and foremost, it is important to preheat and interpass the workpiece to prevent or limit stress and warping. The preheat temperature should be in the range of 250-340°C. Once the preheating and interpass have been done, the weld must begin with a stringer bead that is fed from one side and then the other. The lower limit for the welding amperage should be used for welding thick sections. The amperage should be within the ranges of 250 to 600 amperes (for 0.040 material) and 175 to 450 amperes (for 0.062 material). The next step is to fill the joint with alternating folded beads placed on either side. It is important to maintain the same heat flow along the entire joint while welding. When welding thin sections, a higher amperage can be used, but the arc should be shorter in order to minimize warping.
When welding chromium martensitic stainless steel, it is important to use an alloy filler metal that is compatible with the base material. The main options include ER312 and ER2209. ER312 is an 18 chromium, 9 nickel stainless steel filler metal that is used for welding thick sections of chromium martensitic stainless steel. It has a good general corrosion resistance and offers good low-temperature toughneess. ER2209 is an electrode that consists of 22 percent chromium and 9 percent nickel. It has better corrosion resistance and strength than ER312. It is also suitable for welding thick components at temperatures below -20°C. In addition, ER2209 electrodes may be used for DC welding, while ER312 is only suitable for AC welding.
Generally, a shielding gas should be used to protect the weld from oxidation. The most suitable shielding gas is a mixture of Argon (90%) and Helium (10%). A back purge is also recommended to ensure sound welds that are free from discoloration. When welding in a difficult position such as overhead, it may also be necessary to use a backing bar to maintain a root pass penetration and ensure good fusion.
In conclusion, welding chromium martensitic stainless steel requires a combination of special materials and processes. The right shielding gas and filler metal must be chosen in order to ensure the weld is strong and corrosion resistant. It is also important to preheat and interpass the workpiece, maintain the proper welding amperage, and use a backing bar if welding in difficult positions. Following these steps will help ensure a quality weld on chromium martensitic stainless steel.
