Comparison of mechanical properties between sucker rod normalizing and medium frequency induction penetration heating normalizing

The heat treatment method of the sucker rod is normalizing + high temperature tempering (quenching and tempering treatment). The heat treatment equipment usually used is medium frequency induction heating equipment, water spray quenching or air cooling.

In order to improve the corrosion fatigue resistance of the sucker rod, plasma spraying can be performed on Class C and K grades, which can significantly increase the service life. In addition, heat treatment + shot peening are used, and finally a layer of zinc is sprayed to improve the corrosion fatigue strength of the sucker rod. More than 3 times.

After a sucker rod is used for a certain period, its remaining fatigue working life becomes shorter and shorter, and its reliability decreases, thus causing accidents of its breakage. By testing the old sucker rods, we can classify those that can still be used. Repair is an important cost-saving measure for oil fields. During the repair process, heat treatment (heat treatment and surface strengthening treatment, etc.) is used to restore the fatigue strength of the old sucker rod. The odd heat treatment is consistent with the above process.

The repair process includes cleaning, testing, sorting, minor repair, overhaul, etc. The minor repair of the sucker rod includes: cleaning, flaw detection, shot blasting, stress dispersion, and heat treatment. Thread inspection, thread renewal, anti-corrosion, packaging, etc. The specific process of repairing the pump is: recovery of the sucker rod → visual inspection → cleaning → material inspection → straightness inspection → flaw detection → rod head processing → shot blasting → heat treatment → flaw detection → assembly → protective wire → anti-corrosion → packaging, etc. .

Analysis and implementation key points of sucker rod heat treatment process.

1. From the perspective of the service conditions and technical requirements of the sucker rod, it should have high comprehensive mechanical properties. Therefore, low-alloy structural steel can be satisfied through appropriate heat treatment. The heat treatment method is based on the properties of its own material. for sure.

2. It should be noted that the basic principles for determining the heat treatment process parameters are: first, it must be fully austenitized, with an appropriate amount of carbide dissolution and homogenization of components; secondly, the grain size should be controlled above level 6, and so on. To determine the heating time and holding time, this can be completed by conducting a series of public welfare tests. At the same time, the performance and atmosphere of the heat treatment equipment must be integrated to adopt the optimized heat treatment process parameters.

3. Mechanical performance indicators are hard indicators for sucker rods. Only by strictly implementing the heat treatment process can the design requirements be met. The implementation has proved that when surface decarburization or carbon depletion occurs during the heating process, it will directly affect the hardness and mechanics after heat treatment. performance, and may even crack. Therefore, metallographic inspection of raw materials and parts should be strengthened to prevent the production of substandard products. The controlled atmosphere is mostly a mixture of nitrogen and cracked gas of methanol or ethanol. Quality defects on the surface can be avoided by controlling the carbon potential.

4. Uniform absolute heat and cooling of the sucker rod is the prerequisite to ensure that its mechanical properties are guaranteed. The cooling accumulation and the inability of the cooling medium to circulate during production are very fatal links, especially during the normalizing process of 45 steel. is obvious, so in the actual operation process, there should be entanglements and preventive measures to reduce the influence of human factors.

5. After the sucker rod is normally normalized, it is prone to oxidation and decarburization, which will reduce its fatigue life.

6. Judging from the mechanical properties of the sucker rod's medium-frequency induction heating through normalizing heating and tempering, it is better than ordinary normalizing. The main reason is that the structural refinement of the parts has unique advantages. , on the one hand, it improves the strength and toughness of the sucker rod, on the other hand, it significantly improves the fatigue strength. The grain size of medium frequency induction, that is, thermal penetration normalizing, can be refined to 11-2 levels, and its structure is Xilizhuang ferrite evenly distributed on pearlite, while the strength after normalizing in an electric furnace is 6-7 levels, so medium frequency is used Induction heating penetration normalizing is the development direction of process progress.

7. Due to improper or out-of-control welding and post-weld heat treatment, it is easy to cause a sucker rod fracture accident, excessive load on the welding seam and heat shadow fracture. The local modulation treatment after welding will produce a new heat treatment affected area, which can easily lead to softening and strength reduction of the joint. Therefore, local medium-frequency induction heating and tempering heat treatment of the weld joint should be carried out, and the temperature should not exceed the quenching and tempering of the base metal before welding. The processing temperature is correct to ensure that the strength and humanity of the joint meet the requirements.