Induction hardened Q+T piston rod billet in high frequency quenching equipment. In construction machinery, loaders and excavators hydraulic cylinder use a large number of transmission shaft, piston rod, cylinder bar and other shaft parts. Most parts are quenched tempered before processing.
The purpose of the quenching and tempering treatment is to make the piston rod have the comprehensive mechanical properties of strength, hardness, plasticity and toughness, and the internal structure is uniform and fine tempered sorbite, so as to prepare the organization for the subsequent surface quenching.
The length of the long cylinder piston rod is 3800-4200, and the diameter is Φ90-Φ110mm, so its heating equipment uses a 150KW well resistance furnace or 600KW suspension continuous resistance heating furnace, and the temperature is controlled by two areas. Hot process parameters: In the shaft furnace, 4 pieces are suspended in the air, the quenching heating temperature is 830±10℃, and after holding heat for 160min, it is divided into 2 times for quenching, and 2 pieces are quenched each time. The circulating cooling water is used for cooling, and the quenching and cooling swing up and down to ensure the maximum uniform cooling, and the water is cooled to about 100℃ (the rod steaming but not bubbling) into the shaft tempering furnace. Then 4 PCS were heated at 550±10℃ at a time, kept warm for 190min and cooled by water after tempering. After the above process tempering treatment, the performance is unstable, the hardness fluctuates between 210-255HBS, and the hardness of the same cylinder rod is also very different. And sometimes there are individual furnace hardness unqualified or low strength, need to be repaired.
The quenching deformation is relatively large, which increases the difficulty of subsequent straightening and machining. Due to the poor hardenability of 45 steel, metallograph observation of its internal organization is not a single uniform tempered sostenite, but there is a large free iron cable body in its heart, and individual parts also have a network iron cable body and Wei’s organization. In order to solve the above problems, we use a suspended continuous heat treatment tempering furnace for quenching heating, each hanging 2, heating and insulation after automatic quenching, each beat out a hang, to ensure uniform heating. Considering that the Ac3 temperature of 45 steel is 770-780℃, in order to refine the grain and reduce the deformation as much as possible, we use the subtemperature quenching process of 790±10℃ to refine the austenite grain, and obtain a fine and uniform slab martensite after quenching to improve the strength and toughness of the piston rod. In order to further reduce the deformation and improve the uniformity of quenching liquid cooling, we add 5%-10% quenching additives in tap water, and also use circulating water pump to force coolant circulation cooling. Tempering is still heated at 550±10℃, the beat is the same as the quenching beat, and the water is cooled after tempering to avoid the generation of the second type of tempering brittleness. After the improvement of the above process, the internal structure is uniform small tempered sorbite, the large block or network ferrite and Weil structure are removed, and the hardness and strength are uniform and stable.