Experimental Research On Microstructure And Properties Of 42CrMo Steel After Casting-rolling Compound Forming And Heat Treatment

The hot ring rolling forming process is an advanced manufacturing method to produce seamless ring such as flange and bearing ring. It has been widely used in the equipment manufacturing and other industries. Compared to the traditional ring rolling process, the short casting-rolling compound forming process has many advantages such as saving energy and materials, and increasing efficiency. In this study, theoretical analysis, thermal simulation test and rolling experiment were combined to research the new forming process based on previous studies.Hot deformation behavior and microstructure evolution of casting billet was researched by using Gleeble-3500 thermal-mechanical simulator. Hot ring rolling of centrifugal casting and sand casting 42 CrMo blanks were performed on vertical ring rolling machine D51-350. The influence of the feed speed on deformation and microstructure evolution were studied. Heat treatment was used to improve the performance of the rolled parts. The microstructure and mechanical properties were studied also. The conclusions are as follows:(1) The flow stress behavior of 42 CrMo centrifugal casting steel is similar to the sand casting one. With the increase of the compression pass, the cumulative stain and the flow stress increase. In the interval, the flow stress decrease with the materials being softened and the stress being released. Deformation temperature, interval time and strain rate have significant effects on the grain size and distribution. High temperature, slow compression speed and long interval are good for the grain growth. The grain distribution of the centrifugal casting ring is more uniform.(2) All rolled ring blanks got enough strength and hardness, while their plasticity and toughness are poor, especially when deformation temperature is 1100 ℃ and feed rate is 4-3-2 mm/s. The ring blank rolled at the feed rate of 3-2-1.5 mm/s have a better performance.(3) After tempering at 590 ℃, more carbide particles were observed and distribution is more uniform. At the same time, dimples are bigger and deeper. Carbide particles of the sand casting ring are larger and even more than centrifugal casting ring at the same tempering temperature. To obtain better performance where strength and hardness match well with plasticity and toughness, sand casting ring should be tempered at 530 ℃ while centrifugal casting ring should be tempered at 590 ℃.