Analysis of oxidative decarburization defects in sucker rod heat treatment and new medium frequency induction penetration heating normalizing process

The sucker rod is a key equipment part for oil extraction. Its material is made of special steel YG42D. Its chemical composition (mass fraction, %) is: 0.43C, 1.00CR, 0.19MO, 0.80Mn, 0.25Si, 0.028S, 0.03P. During work, the sucker rod reciprocates up and down in the oil pipe, bears cyclic loads, and is immersed in the produced crude oil liquid. It is corrosive by the medium H2S, CO2 and salt water in the liquid. The failure of the sucker rod is mostly due to fatigue failure. The traditional heat treatment process of sucker rods uses electric furnace heating and normalizing, and high temperatures will affect the process. During production, it was found that workpieces using the traditional normalizing process are prone to oxidation and decarburization defects, which reduces the fatigue life of the sucker rod and increases the machining allowance. Moreover, the original process cycle is long and energy consumption is low, which reduces the fatigue life of the sucker rod. . From the aspects of improving workpiece product quality, improving production efficiency, and reducing costs, it is required to improve the original heat treatment process of the sucker rod. To this end, after production testing and verification, a new medium-frequency induction penetration heating normalizing process for sucker rods was proposed, and good results were achieved.

The purpose of normalizing the workpiece is to improve the structural defects caused by sucker rod rolling and upsetting processing, so as to refine the grains and improve its mechanical properties; the function of high-temperature tempering is to eliminate the internal stress generated during normalizing and stabilize the structure. . Medium frequency induction penetration heating normalizing process parameters; heating temperature is 890°C, workpiece moving speed is 40mm/s, voltage is 750V, current is 190-210A, power is 120-140KW, power factor is 0.9, inductor size is 80 diameter -Diameter 1200. Test results on the mechanical properties of the sucker rod after heat treatment using conventional normalizing and medium frequency induction penetrating heating normalizing processes. It can be seen that after the sucker rod is heat treated with medium frequency induction penetrating heating normalizing, its mechanical properties are significantly better than processed by conventional processes.

Analysis suggests that the superior performance of the sucker rod after medium-frequency induction penetration heating and normalizing is the result of tissue refinement. As we all know, the refinement of the workpiece structure has unique advantages. On the one hand, it can improve the strength and toughness of the sucker rod; at the same time, the grain refinement can significantly improve the fatigue strength of the workpiece. After the sucker rod is normalized by medium-frequency induction penetration heating, the grain size is refined to level 11-12, and fine-grained ferrite is evenly distributed on the pearlite of its structure. After normalizing in the electric furnace, the grain size is obviously coarser, only grade 6-7, and the structure is composed of coarser large blocks of ferrite and pearlite. The depth of the other decarburization layer is 0.20-0.25mm, while the depth of the decarburization layer of the medium-frequency induction penetrating heating workpiece is less than 0.05mm. Therefore, the mechanical properties of the sucker rod in the later period of normalizing using medium-frequency induction penetrating heating are significantly better than those of traditional circuit normalizing process.

After adopting improved medium-frequency induction penetration heating and normalizing, the energy consumption in sucker rod production has been greatly reduced, and the production cost has been reduced. It has been calculated that the use of the new process can save 600,000 KW of electricity per month, with significant economic benefits. At the same time, the cost and maintenance costs of the new process are lower than those of resistance heating furnaces. Therefore, the cost-upgrading technology and economic benefits of the new process have obvious advantages, and the prospects for promotion and application are promising.