Effect Of Heat Treatment On Microstructure And Property Of High Strength Wear-Resistant Steel NM400

Based on the developing of high strength low alloy wear resistant steel plate,the steel should have high strength and good wear resistance to service in production and life.Moreover,the cost of steel production and the shortage of energy should also be considered.Thus the test steel should have good mechanical performance,save scarce resources to reduce costs to achieve a fine steel with excellent performance and good economic benefits.In this paper,the production process of NM400 is explored.The chemical composition designing,the continuous cooling transforming(CCT),rolling and heat treatment process parameters were studied.The mechanical properties of the steel and tissue in different conditions were compared with the laboratory testing equipment,the effect of heat treatment process parameters on the microstructure and properties of tested steel were obtained.The results are as follows:(1)High strength low alloy abrasion-resistant steel NM400 with high strength and good toughness has successfully developed by adding a certain amount of Cr,B,Mo and other alloying elements in the ordinary C-Mn steel,and applying reasonable hot rolling process and heat treatment process to satisfy the required of low-cost and high-performance.(2)The steel plates with 10mm and 25mm had been got in RAL laboratory.After hot rolling,tensile strength of 10mm steel plate was 830?916MPa,impact energy was13?71J;the tensile strength of 25mm steel was 726?1057 MPa and impact energy was 16?77J.(3)The static CCT curve in non-deformation conditions were obtained by means of thermal dilation.The hardenability of tested steel is excellent.When cooling rate is 0.5?/s?1?/s,the main tissue is F+B+P.When cooling rate is 2?/s,the tissue is all bainite.When the cooling rate is 5?/s,martensite transformation began and the tissue is B+M.When the cooling rate greater than 20?/s,tissue is substantially martensite.(4)The dynamic CCT curve in deformation conditions were obtained by thermal simulation machine MMS-200.After making deformation,the ferrite region was expanded,and the temperatures of transformation start and end are increased,the speed of the phase transformation is accelerated.(5)After quenching and low temperature(150?250?)tempered,the matrix structure of tested steel is tempered martensite.Fine carbides and precipitates containing Mo,Ti,Nb distributed on the matrix.The quenched martensite contains a high density of dislocations,the precipitates nucleation on dislocations,pinning dislocations after tempered,increase the dislocation strengthening to the resistance to interface motion.Tensile strength of tested steel is 1314?1359MPa,impact energy is 96?137J.