A Comparative Study On Wear Resistant Of NM450 And NM550 Martensitic Wear-resistant Steel

In this dissertation,two optimized composition wear-resistant steel substrates NM400/450 and NM500/550 were made as research objects.The effect of heat treatment on the microstructure and hardness of two kinds of wear resistant steel substrates was explored,and the optimized heat treatment process was formulated in accordance with the corresponding hardness grade(400 HB and 450 HB,500 HB and 550 HB),and two wear-resistant steel products with the hardness grade of 450 HB and 550 HB were prepared.The wear properties of two grade martensitic wear-resistant steel products were compared by different wear tests.The wear mechanism was analyzed,and the relationship between microstructure,hardness and wear resistance was discussed.The heat treatment optimization test showed that NM400/450 quenched at 910 ?and flowed by low temperature tempering at 200 ? could reach the hardness requirement of 450 HB grade wear-resistant steel,and tempering at 200 ? to 340 ? could reach the hardness requirement of 400 HB grade wear-resistant steel.NM500/550 quenched at 880 ? and flowed by low temperature tempering at 200 ? could reach the hardness requirement of 550 HB grade wear-resistant steel,and tempering within 290 ? could reach the hardness requirement of 500 HB grade wear-resistant steel.The prior austenite grains of 450 HB grade NM450 and 550 HB grade NM550 finished martensite wear-resistant steels produced by the optimized process were fine and uniform from the surface to the center,and the microstructures were all tempered martensite.The surface and center structures were uniform.The average hardness along the thickness direction of NM450 and NM550 plates reached 423 HB and 540 HB respectively.The wear tests showed that under the pin-on-disc sliding wear condition,the wear mechanism of two kinds of wear resistant steels under low load was mainly abrasive wear,NM450 also suffered adhesive wear in addition.Under high load,NM450 suffered serious oxidation delamination wear but there was only slight oxidation wear existed in NM550.Under the ring-on-block sliding wear condition,the wear mechanism of the two wear-resistant steels under low load was abrasive wear caused by plowing and accompanied by slight fatigue wear.Under high load,the degree of abrasive wear and fatigue wear was aggravated,deeper furrow was observed on the worn surface of NM450 and more spalling was observed on the worn surface of NM550.Under the condition of abrasive wear,the wear mechanism of the two wear resistant steels was micro-cutting mechanism.There were more transverse cutting grooves on the worn surface of NM450.Under the corrosive abrasive wear condition,the wearmorphology of the neutral medium was the characteristic of erosion wear.In the acid medium,there were obvious corrosion pits on the wear surfaces of the two wear resistant steels,and the wear mechanism was erosion and corrosion wear.The wear resistance of NM550 was significantly increased under the condition of high load pin-on-disk sliding wear with abrasive wear and slight oxidation wear as the dominant mechanism and abrasive wear under the dominant mechanism of micro-cutting,while the increase of wear resistance of NM550 under ring-on-block sliding wear condition and acid corrosion wear condition was smaller.