1 Products Description
SS316 Stainless Steel Clad Steel Plates are an important part of the new material field, with strong design ability, high specific strength and modulus.
A series of superior properties , such as good fatigue fracture resistance, strong corrosion resistance, and integration of structure and function, are difficult to replace with other materials as functional and structural materials, indispensable basic materials for the development of modern industry, national defense, science and technology, and important material basis for the development of new technological revolution. Metal composites have become one of the research hotspots in materials science.
2 What is explosive recombination method
The schematic diagram of explosive recombination is shown in Figure 1-2. With the help of high-speed detonation and impact of explosives, this method can generate instantaneous high pressure and high strain rate near the impact point between the clad plate and the substrate in microseconds, so that the oxide film at the composite interface is damaged and exposed to the fresh metal surface. In addition, a thin transition zone is formed on the exposed fresh metal surface, and there is plastic deformation, melting Diffusion and waveform characteristics, so as to realize the strong and solid connection between the clad plate and the substrate. By converting the chemical energy of explosives into mechanical energy, the explosive recombination method realizes the metal material welding which integrates pressure welding, fusion welding and diffusion welding.
Explosive compounding method is a relatively mature production technology, which is simple in process and equipment, low in cost and rich in energy; It has a wide range of applications, and can realize the metallurgical combination of alloys and metals with great physical properties; It is flexible and can realize the combination of special-shaped parts; The bonding strength is high, and the composition and thickness ratio of component materials will not change. Explosion recombination also has disadvantages: noise and environmental pollution caused by production process; It is dangerous; The composite ratio is low and the composite interface quality is poor; The thickness is limited, so it is not suitable for the production of thick and thin plates, and the production efficiency is low. Under the strategic planning of high efficiency, environmental protection and energy conservation, explosive compound method is doomed not to be the mainstream production technology.
3Selection of materials and welding methods
The base material specification of SS316 Stainless Steel Clad Steel Plate is 55mm thick, the material is Q235B, the composite layer is 5mm thick, and the material is TP316L austenitic stainless steel plate. See Table 1 for its chemical composition. The microstructure of base material Q235B is ferrite and pearlite, and its metallographic structure is shown in Fig. 1a; The microstructure of composite layer TP316L is typical austenite, and its metallographic structure is shown in Fig. 1b.
In view of the thick thickness of the stainless steel composite plate in this project and the relatively large welding workload, CO2 gas shielded welding is used at the base layer side to 2~3cm away from the stainless steel side, and then flux cored wire arc welding is used. The advantages of CO2 gas shielded welding for base course are various, mainly including high production efficiency, excellent weld quality, beautiful surface formation, good working conditions, saving welding materials and better control of welding deformation. The transition layer and composite layer are welded by stainless steel flux cored wire arc welding to ensure a smooth transition of alloy composition and avoid component segregation.
Chemical composition of plate (mass fraction) %
a) Q235B microstructure
b) TP316L microstructure
4 Groove form
The thickness of the stainless steel composite plate used in the project is 55mm. In order to prevent the defects such as cracks and air holes caused by poor welding fusion and increased welding stress, the double U-shaped groove (see Figure 2) is used. The groove form can ensure the welding quality, with less filler metal and a small fusion ratio, which is convenient for operation. The groove of stainless steel composite plate is generally made by mechanical means. If the groove is processed by plasma cutting, gas cutting and other methods, the oxide layer on the stainless steel side surface must be removed. After processing, the groove shall be visually inspected, and there shall be no cracks and delamination.
Figure 2 Groove form
5 Welding implementation
3.1 Cleaning before welding
Clean up the oil stain, rust, metal chips, oxide film and other dirt within 50mm of the groove and its two sides, and apply anti splash materials within 100mm of the composite layer from the groove.
3.2 Welding sequence
(1) Welding and welding of the base course The weld bead of the base course shall not touch and melt the stainless steel of the composite layer. When welding the base material first, the root or surface of the weld bead shall be 2~3mm away from the interface of the composite layer. Weld reinforcement shall comply with relevant standards.
(2) The welding of the transition layer of stainless steel clad plate is very important, but the selection of the welding materials for the transition layer is also very important. The purpose of welding the transition layer is to compensate for the reduction of alloy elements (such as Cr, Ni, etc.) caused by dilution, so as to keep the alloy composition of the clad weld at the proper level. When the transition layer is welded, the local melting of the base structural steel will dilute the alloy composition of the stainless steel weld. At the same time, there is also the burning loss of Cr and Ni alloy elements. In this way, the content of Cr and Ni alloy elements in stainless steel welds will be reduced, and the carbon content in stainless steel welds will be increased, so that hard and brittle martensite structure is easily formed in stainless steel welds, and the plasticity, toughness and corrosion resistance of welded joints will be reduced. Therefore, in the actual welding production, in order to compensate for the loss of these alloy elements and keep the alloy properties of the transition layer at the proper level, welding materials with high content of Cr, Ni and other alloy elements and low carbon content should be selected, but the crack resistance should also be considered to control the weld seam.
In this way, the weld with duplex structure can be obtained under normal welding parameters, and a large number of martensite structures and welding cold cracks can be avoided. In the welding of transition layer of stainless steel clad plate, there are not only dilution and burning loss of alloy elements, but also changes in structure and properties. At the same time, after welding, the hardening phenomenon caused to the surface, matrix and overall material of clad steel plate is also very different from the physical properties of the two steels. The thermal conductivity of the stainless steel layer is lower than that of the base layer, and the linear expansion coefficient and resistivity are also much higher than that of the base layer. Therefore, when welding the transition layer, it will cause greater welding stress and deformation. In addition, the non-uniformity of the fusion zone at the junction between the weld and the base metal, the combination and superposition of these phenomena will easily lead to the generation of welding cracks. Therefore, the key to prevent the transition layer from cracking due to its fragility is to ensure that the transition layer has excellent plasticity and toughness, reduce the welding stress, and control and adjust the uneven structure of dissimilar steel joints. Therefore, in order to ensure the uniform transition of alloy composition, stainless steel E316LT0-4 welding wire is used when it is 2~3cm away from the stainless steel side to form a good transition layer between the carbon steel base layer and the stainless steel composite layer, so as to ensure the
Smooth transition without segregation of structural components, control the heterogeneity of structural components of dissimilar steels, and prevent welding cracks arising therefrom.
(3) Welding of composite layer When welding the composite layer, pay attention to protecting the surface of the composite layer, prevent the surface of the composite layer from being damaged by welding spatter, and do not strike an arc on the surface of the composite layer, weld kalan and temporary support at will. The surface of the composite layer shall be as flat and smooth as possible with the weld surface. Weld reinforcement after welding ≤ 1.5mm.
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