Heat Treatment And Mechanical Properties Of The Steel Used For Track Plants Of Heavy Duty Crawler Crane

Crawler crane is one of the most important construction machinery in modern engineering. The track plants are the key components of the crawler crane. In this paper, a systematic study was conducted about the relationship between the heat treatment process and the microstructure as well as the properties of the steel used for track plants.The NiCrMo steel with the excellent hardenability and toughness is one of the most common steel used as heavy duty track plants material. Track plants with casting technique has the microstructure of sorbite after quenched and tempered. The NiCrMo steel meets the application requirements of the large track plants.The effect of heat treatment on the microstructure and mechanical properties of NiCrMo medium carbon low alloy steel used in the heavy duty track shoe was investigated by optical microscopy, scanning electronic microscopy(SEM), electron probe micro-analyzer (EPMA) and the tensile and impact tests at room temperature. The results demonstrated that an homogenization for8hours at1000℃diminished significantly the dendritic segregation of carbon in the as-cast microstructure. The tensile strength increased roughly linearly with the increase in the carbon concentration, whereas the toughness decreased dramatically. When quenching from above910℃, the grain coarsening would lead to the inferior of the strength and hardness and with further increasing the quenching temperature to over970℃the abnormal grain growth occurred. Tempered sorbite was obtained at450～550℃tempering. With increasing the tempering temperature the strength of the steel with a carbon content of0.32%reduced from1340MPa to1220MPa,but the impact toughness increased from40J·cm-2to65J·cm-2.The wear test results showed that:the wear rate changed in three distinct regions with increase in applied load. The oxidative wear at low values of load, severe metallic and delamination wear at middle level load, and oxidative wear with a decreasing wear rate. The wear rate curve went up first and then decreased at the third regions with the load increasing.Under low stress, the deformation and distortion of oxide layers on the surface lead to mild oxidative wear. The occurrence of abrasion and delamination lead to severe wear at middle loads. Formation of oxides, along with straining of the subsurface at higher loads, resulted in oxidative wear with decreasing wear rate.