| Since the1960s, high strength steel with low crack susceptibity has been rapidly developed. Currently, the technology of advanced countries such as Japan and the United States have low welding crack sensitivity, and the strength of steel mature product level has formed series.Based on the continuous rolling technology and automation of state key laboratory of independent subject of high strength, low crack sensitivity steel, the goal for development and research to develop high strength steel production process and crack sensitive technology, and hope to make contributions to the national economy.This specimen of high strength steel of crack sensitive low alloy design using three kinds of alloy design scheme, one is in low carbon premise add B.One is not add B.A kind of Cu, Ni for not add elements, the main content of this article is divided into the following several aspects:.(1) The components of low crack sensitive steel, low carbon is the principle of alloying elements designis, reduce carbon equivalent, ensure the low crack sensitive coefficient of steel.(2) Utilizing single pass compression test, the influence of deformation temperature and deforming speed on stress has been researched, and the behavior of dynamic recrystallization has also been studied. The thermal behavior of high temperature deformation is carried out for tested steel. The results show that this kind of steel have high flow stress at high temperature, and its true stress-strain curve appear dynamic recrystallization only under the condition of very high temperature or low strain rate.(3) continuous cooling phase, the researchers found that not deformation condition and the cooling speed for0.6℃/s when microstructure for granular bainite (GB)+small poly (PF) ferrite, when the cooling speed to5℃°/s can be obtained the bainite ferritic (BF) tissue. With the increase of the deformation, upper and light CCT curve move and under the cooling speed up more polygons (PF), under high cooling speed ferrite bainite transition zone (BF) shrink, and acicular ferrite (AF) and granular bainite transition zone (GB). (4) in different tempering heat treatment temperature600MPa tensile strength of low grade steel welding crack sensitivity of mechanical properties and structure were studied through experiments, found after heat treatment,600℃tempering of strength to increase.The yield strength of steel with B and tensile strength than without B steel respectively150MPa105MPa and improved.But B elements damaged severely impact toughness of steel, steel shock absorption B significantly lower power without B steel.(5)By using two stages of steel rolling and cooling, fine rolling finishing temperature for800-840℃, cold temperature500-550℃, the cooling speed for20-25℃/s, can obtain satisfies the hot-rolled steel industry standard.(6)In order to determine reasonable welding parameters, and to estimate the service weldability and fabrication weldability, the tested steel was welded under different parameters using submerged-arc welding, Observed during welding thermal cycle changes in the microstructure The results proved that, The use of experimental steel has good welding performance, that is, the strength of welded joints of not less than the base metal. Tissue welding base material mainly acicular ferrite and bainite, the microstructure of weld zone to polygonal ferrite-based, and heat affected zone to granular bainite. |
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