淬火温度对550MPa级厚钢板显微组织和力学性能的影响

EFFECT OF QUENCHING TEMPERATURE ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 550 MPa GRADE THICK STEEL PLATE

为了提高高强厚钢板低温韧性,对550 MPa级厚钢板进行了730—910℃淬火和600℃回火的热处理,研究不同淬火温度对其组织及力学性能的影响.实验结果表明:在亚温区淬火后回火,随淬火温度升高,试样强度和韧性均表现为先降低后升高,淬火温度升高到完全奥氏体区,试样强度进一步升高,但韧性降低.760℃亚温淬火后回火,试样组织为粗大的多边形铁素体,大量呈长条状、针状M/A组元断续分布在铁素体基体和晶界上,严重恶化韧性,力学性能最差.相比完全奥氏体化淬火后回火,850℃亚温淬火后回火,试样具有最佳强韧配合,这是由于组织细化,铁素体的出现增加了大角晶界比例,以及存在大量均匀位错胞状亚结构和稳定薄膜状残余奥氏体引起的.

The heat treatments of 730—910℃quenching and 600℃tempering were applied to enhance the low temperature toughness of 550 MPa grade thick steel plate.Moreover,the effect of quenching temperature on the microstructure and mechanical properties was studied.The results showed that strength and toughness of the specimen decreased at first and then increased as quenching temperature increased within intercritical region.When the quenching temperature was raised up to austenite region,the strength increased further,but the toughness decreased.Mechanical properties of the steel subjected to intercritical quenching at 760℃and tempering were the worst of all of the specimen, due to coarsened polygonal ferrite and the lath,acicular M/A constituent along grain boundaries and inside the grains,which deteriorated the toughness seriously.On the other hand,the steel treated by intercritical quenching at 850℃and tempering showed the optimum combination of strength and toughness compared with the steel treated by quenching after austenization and tempering.This is attributed to microstructure refinement,higher fraction of high angle grain boundaries caused by the formation of ferrite,abundant homogeneous dislocation cell substructure and stable thin film retained austenite.