Experimental materials and methods for heat treatment process of high strength and high toughness cast lock ring for dredger

The chemical composition of cast high strength and high toughness locking ring steel for dredger was studied. The lock ring is cast after batching and melting. The lock ring casting and auxiliary casting block are shown in Fig. 1. The complete austenitizing temperature of the test steel is determined by thermodynamic calculation with JMatPro software. The calculation results of equilibrium phase diagram of the test steel are shown in Fig. 2. It can be seen from the figure that A1 and A3 of the test steel are 682 ℃ and 810 ℃ respectively. The quenching temperature of general alloy steel is 80-100 ℃ above AC3, so the quenching temperature is 890 ℃ for heat treatment test.

The auxiliary ingot (Fig. 2) was cut from the casting lock ring as the test material. Firstly, it was quenched by water at 890 ℃ for 2 h, and then tempered at 450 ℃, 500 ℃, 550 ℃, 590 ℃, 620 ℃ and 650 ℃ respectively, and the heat preservation was conducted for 2 h and water cooling. After that, two standard u-notch impact specimens with dimensions of 55 mm × 10 mm × 10 mm and two standard tensile specimens with diameter of 5 mm and gauge length of 25 mm were cut from the heat-treated specimens. Optical microscope (ie200m) and scanning electron microscope (feiquanta250) were used to observe the microstructure and morphology; digital Rockwell hardness tester (200hrs-150) was used to test the hardness of samples; impact energy and tensile properties were tested by digital impact testing machine (jbs-300b) and tensile testing machine (CSS-3905), respectively. The average value of mechanical properties was taken as the test data.