Welding process of different metal materials

The welding properties of metal materials are closely related to factors such as material composition, welding methods, and usage requirements. The welding processes of different metal materials need to select appropriate welding methods and process parameters based on the physical and chemical properties of the material (such as melting point, thermal conductivity, thermal expansion coefficient, metallurgical compatibility, etc.), and pay special attention to material characteristics. Commonly used metal materials include non-alloy steel, alloy steel, stainless steel and non-ferrous metals. The following are common metal materials and their applicable welding processes:

According to the carbon content, non-alloy steel can be divided into low carbon steel, medium carbon steel and high carbon steel. From the perspective of material composition, carbon content will affect the plasticity of the material, thereby affecting weldability. The overall trend is that the higher the carbon content, the worse the weldability.

Low-carbon steel has good plasticity and good welding properties. Many welding methods can be applied, such as welding rod arc welding, submerged arc welding, argon arc welding, second-containment welding, plasma arc welding and brazing. The welding process parameters of low carbon steel are highly tolerant, so you need to pay attention to controlling the welding heat input to prevent deformation. Generally, no heat treatment is required after welding.

Medium carbon steel has average plasticity and medium welding properties. The most suitable welding method is welding rod arc welding. Preheating is required before welding to reduce the tendency of hardening and cracks. Small current, short arc and multi-layer multi-pass welding are used to maintain the preheating temperature between layers, and stress-removing annealing can be performed after welding.

High-carbon steel is characterized by high strength and high hardness, but low plasticity and poor welding. It needs to be preheated at high temperature before welding and strictly cleaned the bevel. It is preferred to use low-hydrogen welding rods or nickel-based welding rods. Small current, intermittent welding or segmented welding is used to reduce stress. After welding, it needs to be slow cooling and carried out.Annealing treatment above 650℃ to avoid cold cracks.

The content of carbon and alloy elements in alloy steel is low, and the weldability is good. Various welding methods can be selected for alloy steel, such as welding rod arc welding, submerged arc welding, melted electrode gas protection welding, electroslag welding and narrow gap submerged arc welding. In general, welding materials follow the principle of equal strength matching and choose welding materials with higher strength than the base material. When there are special performance requirements (such as corrosion resistance), the welding material should contain copper elements. During welding, two factors such as embrittlement and cold cracking of the heat-affected zone are taken into account, and the welding heat input amount needs to be controlled. Determine the preheating temperature according to actual conditions. For welding structures with relatively high requirements, high-temperature backtempering is required after welding.

Stainless steel has high corrosion resistance and is divided intoThere are two major categories: Cr and Cr-Ni systems. The former w(Cr)=12%~30%, and the basic type is Cr13 steel. The latter w(Cr)=12%~30%, w(Ni)=6%~12%, and the basic type is Cr18Ni9 steel.

All fusion welding methods can be used for austenitic stainless steel, such as tungsten argon arc welding, submerged arc welding and plasma arc welding. The welding material composition of austenitic stainless steel roughly matches the base material, and the carbon content should be less than the carbon content in the base material. In cases where corrosion resistance is required, you can choose to includeWelding materials for Ti, Nb and Mo elements. Preheating is hardly done before welding when welding austenitic stainless steel. The welding current is small to prevent the weld from overheating. After welding, pickling and passivation are carried out to maintain the corrosion resistance of stainless steel.

Martensite stainless steel has poor welding properties, and a suitable welding method is argon arc welding. When using welding rod arc welding, low-hydrogen type welding rods should be used. The welding material is used to choose welding materials that are close to the base material composition, and the carbon content in the weld metal is strictly controlled. When the welding structure is inconvenient to preheat or heat treatment, the welds are made of heteroweld-austeinic welding materials. Control heat input during welding to avoid intergranular corrosion; at the same time, the weld must be preheated before welding and heat treatment after welding, and the preheating temperature is150~400℃, high-temperature tempering is required after welding to prevent cracks.

Aluminum and aluminum alloys have good welding properties and can be welded by conventional welding methods. Commonly used welding methods include argon arc welding, plasma arc welding, electron beam welding, resistance welding and brazing. When choosing welding wires for aluminum and aluminum alloy welding, weld composition requirements, crack resistance, mechanical properties and corrosion resistance should be considered. When welding, pay attention to cleaning the oxide film and oil stains on the surface of the welded parts and wire before welding. Pay attention to the choice of protective gas when welding sheets of different thicknesses. Use pure argon as protective gas for thin and medium welds, and use argon as protective gas for thick and large welds.+Helium as protective gas.

The welding properties of copper and copper alloys are poor, and the thermal conductivity of copper is very strong. When welding, heat sources with high power and high energy density should be used. Common welding methods include argon arc welding, plasma arc welding, gas welding and submerged arc welding. Pure brass electrodes and brass electrodes are commonly used in welding materials, and mainly added to the welding wireAlloy elements such as Si, Mn, P, Al, Fe and Sn meet different materials and usage environments.Pure copper welding is prone to thermal cracks and needs strict controlImpurities such as S, Pb. The welded parts should be preheated before welding, and heat treatment or hot or cold hammered to reduce stress after welding.

Titanium and titanium alloys are active in chemical properties, and the commonly used welding methods areFor TIG welding and MIG welding, the protective gas is generally made of pure argon. The welding material is close to the base material and the strength can be slightly lower than that of the base material.Strictly clean the surface before welding (acetone cleaning); high-purity argon gas is required to protect the front and back of the weld to avoid oxidation, and the welding area needs to protect the inert gas hood; avoid high-temperature oxidation.

Nickel and nickel alloys have excellent corrosion resistance, high temperature strength and toughness, but due to their physical and chemical characteristics (such as high melting point, high thermal conductivity, easy oxidation, etc.), special attention should be paid to process parameters and operating points during welding. Nickel and nickel alloy welding materials with similar composition to the base material and higher purity are preferred when welding.TIG or MIG welding, when multi-layer weldingThe heat input needs to be controlled; the welds are cleaned after welding, and solid solution or stress-removing annealing treatment is carried out if necessary.

The level of welding technology has become one of the important symbols for measuring a country's industrial development. The use of materials in modern society is becoming increasingly novel. Only by mastering the welding process of various materials, continuously improving the level of welding intelligence, and carrying out automation technology innovation can we promote the rapid development of the country's economic transformation.