The clad steel plate is a bimetallic plate made of stainless steel, nickel-based alloy, copper-based alloy or titanium plate as the clad layer, and pearlitic steel as the base layer, which is made by explosive welding, clad rolling, surfacing and other methods. The base layer of stainless steel clad steel plate should meet the requirements of joint strength and stiffness, and the cladding layer should meet the requirements of corrosion resistance. In order to ensure that the composite steel plate does not lose its original comprehensive properties, the base layer and the cladding layer must be welded separately.

Usually the welding at the junction of the base layer and the cladding belongs to dissimilar steel welding, and its weldability mainly depends on the physical properties, chemical composition, joint form and filler metal composition of the base layer and the cladding. At present, the clad steel plate with austenitic stainless steel as the clad layer and pearlite as the base layer is the most widely used, followed by the clad steel plate with ferritic steel as the clad layer and pearlite as the base layer.

Titanium steel composite plate

1)  Welding points

1. Welding method

When welding clad steel plates, welding methods such as electrode arc welding, submerged arc welding, argon tungsten arc welding, CO2 gas shielded welding and plasma arc welding are usually used. At present, the cladding is usually welded by argon tungsten arc welding or electrode arc welding, and the base layer is welded by submerged arc welding or electrode arc welding.

2. Groove form

The butt joint groove form can be V-shaped, X-shaped, V and U combined groove. The backside of the joint can also be machined at a short interval to remove the cladding metal to ensure that the base weld bead is not welded to the cladding when welding the base bead. Generally, X-shaped groove double-sided welding is used as much as possible, first welding the base layer, then welding the transition layer, and finally welding the cladding layer to ensure that the welded joint has good corrosion resistance.

At the same time, the welding characteristics of the transition layer should also be considered, and the welding workload on one side of the cladding layer should be minimized. Whether the cladding is on the inside or the outside, the base layer is welded first. When the cladding is on the inner side, the base welding root shall be cleaned from the inner side before welding the cladding. When the cladding is on the outside, the last weld bead of the base layer shall be polished. When welding the cladding, first weld the transition layer, and then weld the cladding.

3. Filler metal selection

In most cases, a suitable intermediate filler metal is selected as the transition layer of the steel, so as to control the iron content of the final weld bead of the cladding metal, avoid embrittlement and cracks in the weld bead at the cladding and the base layer, and ensure the cladding welding. Corrosion resistance, wear resistance and other special properties.

4. Welding sequence and selection of welding materials

① Usually the base layer is welded first, and the weld of the first base layer (carbon steel, low alloy steel) should not penetrate into the cladding metal to prevent embrittlement or cracking of the weld metal.

② When welding (surfacing) the clad side, the effect of dilution must be considered. Therefore, when welding the cladding of the clad plate, a suitable filler metal should be selected to weld one or more transition layers first, and then weld the cladding. The filler metal of the transition layer must be able to tolerate dilution of the base steel.

③ The roots can be cleaned by carbon arc gouging, shovel or grinding. Any residue in the root groove must be removed prior to overlaying the transition layer.

④ Post-weld heat treatment is required to eliminate welding residual stress. When selecting the heat treatment temperature, consideration should be given to: the difference in the heat treatment specifications of the base layer and the clad layer; the influence on the corrosion resistance of the clad layer; whether the diffusion of elements at the interface between the base layer and the clad layer will produce brittle phases. , resulting in the deterioration of the performance of the steel plate; due to the difference in the physical properties of the base layer and the cladding, the cladding has stress corrosion cracking and so on.

5. Post-weld heat treatment

The stress relief heat treatment can be carried out after welding the base layer, then welding the transition layer, and then welding the cladding layer. Take the lower limit of heat treatment temperature and prolong the holding time.

2) Welding difficulties and solutions

1. When welding the base layer, due to the large thickness of the plate, the welded joint is subject to a large restraint stress; under the action of the welding thermal cycle, the heat-affected zone is prone to produce martensite hardened structure, which increases the hardness and brittleness of the welded joint. Toughness and plasticity are significantly reduced. These factors can lead to welding cracks. In order to effectively prevent the occurrence of welding cracks, the measures that can be taken are: choose low-hydrogen electrode; dry the electrode as required before use; carefully clean the groove surface of water, oil, rust and other impurities; choose reasonable welding process parameters, such as Preheating before welding, slow cooling after welding, adopting multi-layer multi-pass welding, controlling the temperature between layers, etc.; choose the appropriate welding sequence to reduce welding stress, etc.

2. When welding the cladding with stainless steel electrode (A002), it is easy to melt the base layer and dilute the metal composition of the weld, thereby reducing the plasticity and corrosion resistance of the weld metal, and the brittleness of the fusion zone is significantly increased. Therefore, when welding cladding, the welding line energy must be controlled, and multi-layer multi-pass welding is used to reduce the welding penetration.

3. When the transition layer is welded with austenitic steel electrode (A302), the weld is prone to hot cracks. At the same time, the carbon migration process occurs in the transition zone: that is, carbon transfers from the low-chromium base layer to the high-chromium stainless steel deposited metal. Therefore, a high-hardness carburization layer and a low-hardness decarburization are formed at the junction of the base layer and the cladding layer. layer, causing embrittlement (or softening) of the fusion zone, reducing the lasting strength and prone to fatigue cracks. It is advisable to use small-diameter electrodes and fast multi-pass welding. If necessary, cold water can be used to accelerate cooling, prevent the formation of decarburized layers, and make the welded joints have high strength and toughness.