What is the difference between Monel alloy and stainless steel?
Monel 400 alloy (UNS N04400 or MCu-28-1.5-1.8 or Ni68Cu28Fe) is a nickel-based alloy material. It has excellent corrosion resistance in seawater, chemical solvents, ammonia sulfur chloride, hydrogen chloride, and acidic media such as sulfuric acid, hydrofluoric acid, hydrochloric acid, phosphoric acid, and organic acids, as well as alkaline media, salts, and molten salts. In addition, it has excellent mechanical properties, can be used in a wide range from low temperature to high temperature, and has good welding performance and medium to high strength.
Monel400 alloy is a solid solution strengthened alloy. Its alloy grade is UNS N04400, named according to the "ASTM-SAE Unified Number System". Compared with the common austenitic stainless steel 1Cr18Ni9Ti, Monel400 alloy has differences in physical and mechanical properties. The alloy has excellent electrical and thermal conductivity, its resistivity is about 70% of 1Cr18Ni9Ti, and its thermal conductivity is 36% higher than 1Cr18Ni9Ti.
Monel400 has good welding performance and can be used with arc welding (SMAW), argon arc welding (GTAW), inert gas shielded welding (GMAW) and other welding methods. Similar to austenitic stainless steel, no preheat treatment is required before welding, and no heat treatment is required after welding. Its welded joint form is similar to austenitic stainless steel, but it also has its own unique features.
Because the base metal has higher thermal conductivity and better heat dissipation performance, the molten pool generated during welding is smaller, and the penetration power and penetration depth of the welding arc are also lower than those of austenitic stainless steel, so special attention should be paid to the following two things. point:
① During the welding process, the heat input should be increased moderately, and too thick blunt edges should not be used. ②The angle of the welding groove should be appropriately increased to prevent poor fusion and avoid lack of fusion.
① The heat input should be appropriately increased during welding to avoid excessive thickness of the passivated edge; ② The welding groove angle should be appropriately increased to ensure the fusion quality and avoid non-fusion.
Physical properties: Density 8.80g/cm³
Monel400 alloy contains a high Ni content. In order to ensure welding quality, welding materials that match the chemical composition of the base metal should be used for deposition. Normally, we will use ERNiCu-7 as the welding wire, or ENiCu-7 as the welding rod.
processing
This alloy can be machined using conventional machining methods for iron-based materials. Water coolant is required during high-speed machining. This material will shrink during processing, so attention needs to be paid to processing shrinkage allowance to ensure dimensional accuracy. Monel400 is very sensitive to thermal cracks and is prone to cracks in arc craters. Especially after harmful impurities S and P are infiltrated, low-melting-point eutectic materials (such as Ni-S eutectic, Ni-P eutectic) are easy to aggregate at the grain boundaries. These low-melting-point eutectic materials have low strength and high brittleness. , easy to cause thermal cracks. The most important metallurgical factor in reducing weld solidification cracks is to strictly control the contents of S and P.
welding
Monel 400 has very good welding performance and can be welded using TIG and MIG methods. When welding, you can use Monel 400 body or EniCu-7 wire and electrode, and you can also use manual arc welding and submerged arc welding. Monel 400 can be welded with carbon and low alloy steels. Before welding, oil, lubricants, paint and other substances must be cleaned within 50 mm of the groove and both sides. For paint and other debris that are insoluble in degreasing agents, cleaning agents such as methyl chloride can be used to clean them. Marking ink can be removed using methanol. If there is any debris pressed into the surface of the weldment, it can be removed by grinding with a grinding wheel, and then rinsed with water. The material must be dry and the wire must be clean before welding. This prevents harmful impurities such as moisture, oil, sulfur and phosphorus from entering the welding pool.
