T91 steel containing trace amounts of nitrogen Shanghai t91 alloy tube, the role of nitrogen in two aspects. When soldering heat: on the one hand from the solid solution strengthening effect, room temperature solubility of nitrogen in the steel is very small, T91 steel after welding the weld heat affected zone heating and post-weld heat treatment process, the process has appeared in the solution and precipitation of VN austenite heat affected zone has formed due to VN of dissolved nitrogen content increases, the degree of supersaturation at room temperature after which the tissue to improve, there is a small VN precipitates in the subsequent post-weld heat treatment, which increases the structural stability improve the enduring strength values ??of the heat affected zone. On the other hand, T91 steel also contains a small amount of A1, with the formation of nitrogen can A1N, A1N in a lot more than 1 100 ℃ was dissolved in the matrix, again precipitated at lower temperatures, can play a better dispersion strengthening effect. As can be seen, T91 low critical cooling rate of imports t91 alloy pipe, large austenite stability, less prone to the normal cooling pearlite transformation, which occurs when cooled to a lower temperature martensitic transformation. Because of this t91, T91 hardened and cold cracking tendency great. Since the heat-affected zone of a variety of tissues have different densities, different expansion coefficients and lattice forms Tianjin t91 alloy pipe, the heating and cooling process is bound with different volumetric expansion and contraction; on the other hand, since the welding heat uneven and has the characteristics of high temperature, and therefore a lot of internal stress of welded joints T91. For T91, very stable austenite, to cool to a lower temperature (about 400 ℃) to become martensite. Coarse martensite brittle and hard, but in the joints under complex stress state. At the same time, the hydrogen cooling process to weld seam zone near the weld diffusion, the presence of hydrogen embrittlement prompted the martensite, the result of their combined effects, it is prone to cold cracking in the hardened area. t91 alloy tube 51X3.5, Jinnan District t91, Katherine source of steel provided by source Pipe Co., Ltd. Liaocheng trillion. Liaocheng Katherine source Pipe Co., Ltd. (www.lczygg.com) strong, credible, Liaocheng in Shandong steel industry has accumulated a large number of loyal customers. The company better work attitude and constantly improving Katherine source of innovative ideas will lead pipe and you work into the brilliant, for a better future!