Welding and cutting of titanium plate is unavoidable work, but because of some of the characteristics of the titanium plate itself, when welding and cutting also has its specificity, more likely to occur in its welded joints and heat-affected zone (HAZ) a variety of shortcomings. We should pay special attention to the physical properties of titanium plates when welding. For example, the coefficient of thermal expansion of austenitic cutting titanium plate is 1.5 times that of low-carbon titanium plate and high-chromium cutting titanium plate; the coefficient of thermal conductivity is about 1/3 that of low-carbon titanium plate, while high-chromium cutting titanium plate's coefficient of thermal conductivity is about 1/2 that of low-carbon titanium plate; the specific electrical resistance is more than 4 times that of low-carbon titanium plate, while high-chromium cutting titanium plate is 3 times that of low-carbon titanium plate. These conditions, together with the density of the metal, surface tension, magnetism, and other conditions have an impact on the welding conditions.
Summarized, the welding function of titanium plate mainly reflects these aspects:
(1) high-temperature cracking: the high-temperature cracking mentioned here refers to the cracking related to welding. High-temperature cracks can be roughly divided into condensation cracks, microcracks, cracks in the HAZ (heat-affected zone), and reheating cracks.
(2) low-temperature cracks: low-temperature cracks sometimes occur in martensitic-cut titanium plates and some ferritic-cut titanium plates with martensitic arrangements. Because the primary cause of its onset is hydrogen dispersion, the degree of bonding of welded joints, and the hardening arrangement, the solution is to reduce the dispersion of hydrogen in the welding process, suitable for preheating and post-weld heat treatment and reduce the degree of bonding.
(3) resistance of welded joints: in austenitic cutting titanium plate to reduce the sensitivity to high-temperature cracking, in the composition depicted on the usual residual ferrite 5% -10%. However, the presence of these ferrites leads to a reduction in low-temperature resistance. In the duplex cut titanium plate for welding, welded joints in the area of the austenite amount of reduction and resistance to occur. In addition, with the addition of ferrite during the period, the resistance value tends to decrease significantly.
The reason why the resistance of welded joints of high-purity ferrite-type cut titanium plates decreases significantly is due to the mixing of carbon, nitrogen, and oxygen. During the period of some titanium plates in the welded joints of the oxygen content of the increase in the generation of oxide-type adulteration, these adulterants become a source of crack initiation or crack communication methods to reduce the resistance. some titanium plates are because in the maintenance gas mixed with air, during the nitrogen content increases in the matrix deconvolution surface {100} surface on the onset of slate Cr2N, the matrix hardens and makes the resistance.
(4) σ-phase embrittlement: austenitic cut titanium plate, ferritic cut titanium plate, and duplex titanium plate is prone to σ-phase embrittlement. Because the arrangement is divided into a few percent of the α phase, resistance is significantly reduced. The "phase" is usually separated in the range of 600-900℃, and is especially easy to be separated at about 75℃. As a preventive approach to avoid the onset of the "phase, austenitic cut titanium plate should minimize the content of ferrite.
(5) 475 ℃ embrittlement, in the vicinity of 475 ℃ (370-540 ℃) long time insulation, so that the Fe-Cr alloy decomposition into low chromium concentration of α solid solution and high chromium concentration of α 'solid solution. When the chromium concentration in the α' solid solution is greater than 75% deformation from slip deformation to twinning deformation, and then the onset of 475 ℃ embrittlement.
