| The strengthening effect of Nb was found in 155-160 ksi grade perforating gun pipe.The paper focuses on the research and development of Q370qE-HPS for the new generation of high-performance bridge steel.The dissolution behavior of microalloy element Nb with heating temperature,the law of static recrystallization and continuous cooling of test steel,as well as the internal relations between ferrite-pearlite structure and strength,toughness and strength ratio were studied,and the welding application of test steel was completed in the factory of bridge.The results as followed:(1)Q370qE-HPS steel was designed with low C and micro Nb and Ti and control rolling and cooling process.With the increases of the heating temperature,the number of second phase particles decreases and the solid solution of Nb occurs.With the increases of the heating temperature from 1100 ℃ to 1200℃,the amount of dissolved Nb increased from 60% to 85%.At 1250℃,the quantity of dissolution of Nb increased to 90%.Q370qE-HPS steel billet heating process can be designed as follows: soaking temperature of 1200±10℃;heating section temperature less than 1250℃.Control the time in the furnace according to the thickness of the stock.(2)The parameters of Q370qE-HPS steel was designed as follows: the finishing rolling temperature of rough rolling of 1000℃,the finishing rolling temperature of precision rolling of 880 ~ 820℃,accelerated cooling of the start cooling temperature of 820~760℃,finish cooling temperature of 580℃(according to different thickness),cooling rate of 5℃/s.(3)As the grain size of ferrite decreases,the content of pearlite in Q370qE-HPS steel plate decreases accordingly,which significantly increases the yield strength,low temperature impact and the yield ratio.From the perspective of comprehensive regulation of mechanical properties,ferrite grain should be refined moderately,and the average grain size of ferrite should be controlled in the range of 6 ~ 10 μm,and the content of pearlite should be controlled in the range of 7 ~ 11%.(4)The welding hardening tendency of Q370qE-HPS steel plate,low crack sensitivity and good thermal correction performance.The mechanical properties of typical joints are in accordance with the specification for manufacture of railway steel Bridges by TB 10212-2009.Welding joint has low hardness,excellent low temperature impact performance,reasonable choice of welding materials and welding process parameters. |
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