Development Of Q690D Plate High Strength Steel For Construction Machinery

High strength structural steel plates are widely used in infrastructure construction,engineering machinery and mining industry,etc.As construction and industrial machinery are developed towards greater size,lighter weight,and higher performance,the ordinary strength level of Q345B can not meet the requirements of manufacturing machinery industry.In recent years,steel for high strength construction machinery has become one of the hot spots in the field of iron and steel industry.Therefore,the development and implementation of stable mass production of high strength steel Q690D and above has been a goal of domestic iron and steel enterprises.In this paper,medium and low carbon components of Q690D high strength engineering machinery steel are designed.TMCP+tempering and TMCP+quenching+high temperature tempering are adopted.According to the chemical composition,rolling and heat treatment process preliminarily determined in lab,small batch debugging is carried out on the spot.After the field debugging performance is qualified,batch production is realized.The mechanical properties and shape of the plate meet the contract requirements.The main research contents and results are as follows:(1)The production of Q690D by TMCP+tempering process can reduce quenching process,reduce costs and improve production efficiency.The experimental results show that the performance of the steel is good and meets the requirements of the standard.(2)The production of Q690D by quenching +high temperature tempering process,the performance meets the standard requirements.After quenching at 840?900?,the grain size of the original austenite is 8?10 ?m,but higher than 930?,and the grain size of the austenite increases at 15?30 ?m.It can be seen that when quenching temperature is 900?930?,the austenite structure is completely austenitizing and the structure is fine.With the increase of tempering temperature 560?650?,the strength decreases and the impact toughness increases.According to the different thickness steel plate,the tempering temperature is different,and the tempered structure is tempered bainite.When the thickness of the steel plate t is less than or equal to 40mm,the optimum tempering temperature is 620?;when the thickness of the steel platet is 40 mm<t<80 mm,the optimum tempering temperature is 580?;when the thickness of the steel plate t 80 mm?t?120 mm,the optimum tempering temperature is 600?.(3)Based on the laboratory research and field test results of small batch,the chemical composition and rolling process for Q690D production has been determined,and to develop the heat treatment process for different composition and thickness of steel plate,the formation of "Q690D operation points" has been issued.The batch production is stable;the performance of the passing rate is 100%.