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Steel grades that belong to martensitic stainless steels include 1Cr13, 2Cr13, 3Cr13, 4Cr13, 3Cr13Mo, 1Cr17Ni2, 2Cr13Ni2, 9Cr18, 9Cr18MoV, etc. ⑴Weldability: It has a strong tendency to suffer from cold cracking. Both the weld area and the heat-affected zone develop a hard and brittle martensitic structure after welding. The higher the carbon content in the steel, the greater this tendency to cold cracking is. During welding, in the heat-affected zone where the temperature exceeds 1150°C, the grain size increases significantly. Cooling that is too fast or too slow can both cause brittleness in the joints. For example, when the cooling rate after welding of 1Cr13 steel is less than 10°C/s, a coarse ferrite and carbide structure forms in the heat-affected zone, resulting in a significant reduction in plasticity ； When the cooling rate exceeds 40°C/s, a coarse martensitic structure is formed, which also reduces plasticity. Martensitic stainless steels have very little tendency to intergranular corrosion. ⑵Welding process 1) Preheating before welding Preheating before welding is the main process measure to prevent the formation of cold cracks. When the mass fraction of C is 0.1%–0.2%, the preheating temperature is 200–260°C; for highly rigid welded parts, it can be raised to 400–450°C. 2) Post-weld cooling: The welded joint should not be heated directly from the welding temperature for tempering, as the austenite may not have fully transformed during welding. If heating for tempering is carried out immediately after welding, carbides will precipitate along the austenite grain boundaries and austenite will transform into pearlite, resulting in a coarse-grained structure that significantly reduces toughness. Therefore, the welded part should be cooled before tempering, so that the austenite in the weld and heat-affected zone is essentially completely transformed. For weldments with low stiffness, they can be cooled to room temperature before tempering ； For weldments with large thicknesses, more complex processes are required ； After welding, cool to 100–150°C and hold for 0.5–1 hour, then heat to the tempering temperature. 3) Post-weld heat treatment aims to reduce the hardness of the weld and heat-affected zone, improve plasticity and toughness, and simultaneously reduce welding residual stresses. Post-weld heat treatment includes tempering and full annealing. The tempering temperature is 650–750°C; hold for 1 hour, then cool in air ； If the welded part requires machining after welding, to achieve the lowest hardness, full annealing can be employed: the annealing temperature is 830–880°C, with a holding time of 2 hours; after that, the part is cooled in the furnace to 595°C and then cooled in air. 4) Selection of welding electrodes: Welding electrodes for welding martensitic stainless steels are divided into two main categories: chromium stainless steel electrodes and chromium-nickel austenitic stainless steel electrodes. Common chromium stainless steel welding electrodes include E1-13-16 (G202) and E1-13-15 (G207) ； Common chromium-nickel austenitic stainless steel welding electrodes include E0-19-10-16 (A102), E0-19-10-15 (A107), E0-18-12Mo2-16 (A202), E0-18-12Mo2-15 (A207), etc.