The Study On Heat-affected Zone Of X90 Welded Pipe Welding

By welding thermal simulation technique, modern physics testing technology, and plate butt welding test to analyzing the microstructure and properties of X90 pipeline steel HAZ proposed to optimize the production of welding technical advice. Respectively discusses the organization and performance in different areas of the welding heat affected zone(different peak temperature), different welding heat input(different cooling speed), secondary thermal cycle of X90 welding heat affected zone. And welding heat affected zone embrittlement mechanism and the changing rule of the softening mechanism. And welding control and prevention measures of local embrittlement and softening.Research shows that: When the welding thermal simulation peak temperature is 850-950 ℃, Although the temperature in the two phase temperature range(a +g), but there is no formation has a great influence on the material toughness organization, tenacity loss is not big; When the welding thermal simulation peak temperature is 1300 ℃, Coarse grain zone produce to local embrittlement, lead to toughness of materials drastically, and the region become the most weak of welding heat affected zone.With the increase of welding heat input, X90 pipeline steel welding heat affected zone coarse grain zone toughness of CGHAZ of a downward trend. Under the alloy composition of mucai1 steel weld CGHAZ under different welding heat input has a similar organization form, to determine the CGHAZ under different welding heat input with similar levels of toughness. Secondary peak temperature of 800 is ℃the critical zone temperature range(Ac1 ~ Ac3), this area critical coarse grain area(ICCGHAZ) in austenite grain boundary bulky M- A, and through a partially recrystallized grains have not been refined, Inherited genetic phenomenon of thick tissue organize a CGHAZ appear. Show the ICCGHAZ local coarsening, leading to a(ICCGHAZ) performance fell sharply; mucai1 steel weld CGHAZ once after 800 ℃after the second peak temperature of welding thermal cycle, microstructure and properties has not deteriorated sharply, the toughness remains at a good level. For this alloy composition and performance of weld tissue after secondary different peak temperature of thermal simulation, the performance of the regions were good.The first thermal simulation of X90 line pipe, austenitic grain grew up sharply in the welding thermal cycle caused the CGHAZ of coarse grain brittle; Secondary thermal simulation, due to the critical coarse grain zone formed A- M group distribution in austenite grain boundary and the "necklace" structure, and inherited a coarse grain zone of bulky organizations produce genetic phenomenon, caused the critical coarse crystal area local embrittlement(ICCGHAZ).In a peak temperature and the second peak temperature is above the tempering temperature, X90 pipeline steel softening phenomenon, and the softening phenomenon became more obvious with the increase of welding heat input. Reasonable pipeline steel alloy composition design, the pipeline steel welding heat input control in the reasonable range of heat input, after preheating before welding to change the cooling rate,according to the actual material reasonable heat treatment after welding,those can effectively prevent the local embrittlement phenomenon of pipeline steel welding heat affected zone.