In the previous article, we talked about the defects that may occur in the titanium-clad steel tube sheet, so how should such defects be repaired? So let's move on.
1. Introduction to the weldability of titanium steel materials
(1) Titanium and titanium alloys are easily polluted by impurities such as gases and cause embrittlement. The main elements that cause embrittlement of welded joints of titanium and titanium alloys are oxygen, nitrogen, hydrogen, carbon, etc. Titanium can interact with oxygen in the air at room temperature to form a dense oxide film, which starts to absorb hydrogen at 250 °C, oxygen at 400 °C, and nitrogen at 600 °C, and can react with hydrogen and oxygen. Violent reaction. Porosity is a common defect in titanium and titanium alloy welding. Oxygen, nitrogen, hydrogen, carbon dioxide, and water vapor can all cause stomata to form. However, hydrogen is the main gas that forms pores in titanium and titanium alloys, and most of the hydrogen pores are generated in the middle of the weld and the fusion line.
(2) Since titanium and titanium alloys contain fewer impurities such as sulfur, phosphorus, and carbon, few low-melting eutectic crystals are formed at the grain boundaries, the crystallization temperature range is very narrow, and the shrinkage of the weld is small when it solidifies. Low thermal crack susceptibility.
(3) When the amount of oxygen, nitrogen, and hydrogen in the weld is large, the properties of the weld and the heat-affected zone become brittle, and cold cracks are prone to occur under the action of large welding stress.
(4) The elastic modulus of titanium is about smaller than that of stainless steel. Under the same welding stress conditions, the welding deformation of titanium and titanium alloys is twice that of stainless steel. Therefore, a backing plate and a pressure plate should be used to press the workpiece to be welded during welding. to reduce welding distortion.
2. Since titanium is a material with good weldability but easily polluted, the temperature must be controlled during welding, and the heat input should be small, so electrode arc welding, carbon dioxide gas shielded welding, etc. are not suitable for titanium and titanium alloys. It is suitable to choose argon tungsten arc welding (GTAW) with better weld forming quality for repair welding of titanium layer;
Before welding, use acetone to clean the area to be welded, and send argon 3~5s in advance to replace the impurity gas in the welding area; short arc welding is used for welding, and the arc does not swing during the welding process; after welding, argon is delayed for 5~8s to protect the Welds are not contaminated. After the repair welding of the titanium layer is completed, a 100% coloring inspection is carried out on the welded seam, and there is no display; then the macroscopic inspection, hardness, and microstructure analysis of the welded joint are carried out.
(1) The titanium clad steel tube sheet with a damaged titanium layer will seriously affect the subsequent expansion and welded pipe work, reduce the quality of condenser products, and need to repair the titanium layer before use.
(2) The proposed welding process parameters meet the needs of the repair of the titanium layer, the microstructure of the welded joint is not very different, and the hardness value and corrosion resistance of the joint is in line with the performance of the titanium-steel composite tube sheet.
Baoji Taicheng Clad Metal Materials Co., Ltd, as a titanium-steel clad tube sheet supplier, can guarantee that every product we produce is strictly implemented in accordance with various national standards. High-quality products and high-quality after-sales service are our commitment to every cooperation. the commitment of the person. Welcome to consult and cooperate!
