Today, the titanium alloy welding industry is more and more common in daily life, and with the Titanium alloy welding With the continuous development of the industry, stainless steel welding has gradually sprouted. So what is the weldability of titanium alloy and stainless steel? What's the difference between the two? Next, let's discuss in detail: the performance difference between titanium alloy welding and stainless steel.

First of all, titanium, the main component of titanium alloy, and iron, the main component of stainless steel, are both high-melting-point materials. If the fusion welding method is used to connect the two, the heating temperature will be very high, and a large amount of welding will occur in the process of welding heating and cooling. stress. In addition, the melting point of the two differs by 140°C. When the material with the low melting point reaches the melting state during the welding process, the material with the high melting point is still in a solid state. The loss of melting point material, the burning or evaporation of alloying elements, makes the welding joint difficult to weld.

The second is the problem of intermetallic compounds between the two. Because of the active metallicity of titanium, it will form a brittle phase at the interface when it is connected with most metals. There are also problems of intermetallic compounds and material oxidation when connecting titanium alloys with stainless steels. Iron and titanium are easy to form intermetallic compounds, such as TiFe, TiFe2, Ti2Fe, etc. Because the intermetallic compounds have greater brittleness, the joints are embrittled, and under the action of welding stress, it is easy to cause cracks or even cracks in the weld, resulting in joints. The plasticity and high temperature function of the two parts deteriorate, and the welding quality decreases, which brings great difficulties to the welding between the two. Titanium undergoes phase transformation at a temperature of 1155K, exists in the form of body-centered cubic lattice β-Ti at high temperature, and is α-Ti with close-packed cubic lattice at lower temperature. The solid solubility of iron in α-Ti is very small, only 0.05%~0.1% at room temperature, and does not exceed 0.5% at the eutectoid temperature. Iron is a stable element of β-Ti, and its solid solubility in β-Ti is larger than that in α-Ti. When the eutectic temperature is 1355K, the solid solubility of iron in β-Ti reaches a maximum of 25%. After iron is dissolved in β-Ti, the temperature of the phase transition point can be lowered. When the iron content in β-Ti reaches a certain value, β-Ti will be stored at room temperature, and with the further increase of iron content in β-Ti , in the cooling process, it will form the supersaturation of iron in titanium, and then exceed its solid solubility in titanium to form an intermetallic compound.

Then the alloying elements chromium and nickel in stainless steel can also form brittle intermetallic compounds with titanium, while titanium is still a strong carbide constituent element, and it will combine with carbon in steel to form brittle TiC. Multiple complex brittle intermetallic compounds may also be formed between titanium, iron, chromium and nickel, which further embrittles the weld and further reduces the joint performance.

The last is the difference in thermal conductivity and specific heat capacity between the two. The thermal conductivity and specific heat capacity of the material will deteriorate the crystallization conditions of the weld metal, severely coarsen the grains, and affect the wet performance of the refractory metal. The difference between the two coefficients of linear expansion. The coefficient of linear expansion of iron is about 1.5 times that of titanium. The larger the coefficient of linear expansion, the greater the coefficient of thermal expansion and the greater the shrinkage during cooling, while the welds of dissimilar materials with different coefficients of linear expansion will generate a large welding stress when they crystallize. This welding stress is not easy to eliminate, and often leads to large welding deformation. Because the stress conditions of the materials on both sides of the weld are different, it is easy to cause cracks in the weld and the heat-affected zone, resulting in the peeling of the weld metal and the base metal. Oxidation products also significantly reduce the strength and ductility of the weld metal. Titanium and stainless steel are more prone to oxidation at high temperatures, which then degrades the quality of the joint. Titanium tends to react with hydrogen, oxygen and nitrogen in the air at high temperatures. Titanium begins to absorb hydrogen above 250°C, oxygen above 400°C, and nitrogen from 600°C. Oxidation of the welding material will cause the welding area to be contaminated by these gases and embrittle, and even cause pores. The dissimilar metal connection structure has the general functional advantages of the component metals. However, due to the huge differences in physical, chemical and mechanical properties between the dissimilar metals, the conventional welding method is prone to the problem of metallurgical incompatibility, and a brittle compound phase is formed at the interface. , and the problems that seriously affect the welding quality and performance such as residual stress due to the mismatch of thermophysical properties, thus greatly restricting the industrial use of dissimilar metal welded structures.

After looking at the above performance differences between titanium alloy welding and stainless steel, we should understand: when we are welding titanium alloy and stainless steel, the key to dealing with the above problems is to study the variety, quantity and distribution shape of the brittle phase, and to adjust it. Manipulation and improvement to increase the plasticity and resistance of the joint. At the same time, appropriate welding methods and welding process parameters should be selected to reduce welding stress, reduce the volume fraction of intermetallic compounds at the interface, and select effective protective measures to avoid oxidation and inhalation of the welded material during welding. High-quality connection between the two.