Seamless stainless steel tubes for structure
Seamless stainless steel tubes for structure
Geological pipes are used for geological drilling. They are used by construction teams for geological drilling. They can be divided into geological drill pipes, core pipes, casing pipes and sedimentation pipes according to their uses.
Standard: GB/T 14975-2012
Common materials/steel grades: DZ40, DZ50, DZ60, R780, etc.
Seamless stainless steel tubes for structure are used for geological drilling. With the development of industrial production in my country, the demand for geological drilling pipes is increasing. DZ60 grade geological drilling pipes have been made of 45MnMoB steel in the past. According to the development of the market, in order to seize the opportunity, the 42MnMo7 geological drilling pipe will be formed as soon as possible. Production capacity to meet market demand, relying on its own technical strength to develop the production process of 42MnMo7.
With the development of industrial production in my country, the demand for geological drilling pipes is increasing. DZ60 grade geological drilling pipes have been made of 45MnMoB steel in the past. According to the development of the market, in order to seize the opportunity, the 42MnMo7 geological drilling pipe will be formed as soon as possible. Production capacity to meet market demand, relying on its own technical strength to develop the production process of 42MnMo7.
Steel characteristics analysis
42MnMo7 steel is a steel grade developed by German Mannesmann Company according to the American Petroleum Institute standard API. It is mainly used to produce N80 tubing and casing. The steel grade is bainitic steel, Ac1 is 720-730℃, Ac3 is 770-780 ℃, high strength, low plasticity, high brittleness, poor cold working performance. The data shows that the ways to improve the ductility and toughness of 42MnMo7 steel are as follows:
1. Obtain fine grains, because the effective grain size of bainite steel has a closer relationship with austenite grain size than ferrite + pearlite steel. Therefore, the austenite grain size is minimized before the bainite transformation, so as to obtain fine grains to improve the toughness of the steel. Adding grain refinement elements and reasonable heat treatment are effective measures for grain refinement.
2. Reduce the content of P, S, N, H, O and other harmful elements in steel, reduce non-metallic inclusions in steel and appropriately reduce the carbon content in steel. Reducing the content of harmful elements in steel can reduce their segregation in grain boundaries, greatly reducing the sensitivity to delayed damage and environmental embrittlement; non-metallic inclusions are the source of cracks, and reducing non-metallic inclusions reduces cracks Probability of generation: C has a high strengthening effect, but it significantly reduces the toughness. It is beneficial to improve the toughness by appropriately reducing the content of C within the standard requirements.
3. Eliminate internal stress to the greatest extent. The internal stress of the steel pipe is mainly caused by a large number of dislocations in the metal during the cold and hot deformation process, and the accumulation and mutual interference of dislocations prevent further slippage. The existence of internal stress makes the steel pipe poor plasticity and high brittleness. Only when the internal stress is eliminated to the maximum extent can the plasticity and toughness of the steel pipe be significantly improved.
4. Reduce surface oxidation, decarburization and hydrogen absorption. Bainitic steel has high strength and poor plasticity, and slight defects on the surface may cause cracks and brittle fractures in the steel pipe. Therefore, it is necessary to strictly control the heating of steel billets, heat treatment and pickling of steel pipes.
Main process flow
Electric arc furnace preliminary refining-refining outside the furnace-billet continuous casting-tube billet rolling-tube billet perforation-waste tube heat treatment-steel pipe cold drawing-finished product heat treatment-steel pipe correction-acceptance-packaging Warehousing
Main process characteristics
42MnMo7 Steelmaking Process
The key to 42MnMo7 smelting is composition control. Reducing harmful impurities and gas content is to avoid segregation in the slab. Therefore, the smelting process has the following requirements:
a. Pay attention to the intensity of oxygen blowing during the melting process to ensure that the melting carbon is greater than 0.50%, and the end carbon is greater than 0.20%;
b. Due to the large amount of ferromanganese added, in order to prevent the increase of P in ferromanganese from causing P to exceed the standard, the steel release P of the primary furnace is ≤0.10%, and the steel release temperature is greater than 1640℃;
c. Add ferroniobium with steel flow at a recovery rate of 95%;
d. Hanging bag temperature: 1580-1590℃ for the first package, 1560-1570℃ for the renewal package.
Tube billet rolling
42MnMo7 is a medium carbon bainite series steel with a certain amount of Nb added. The addition of Nb can prevent the austenite primary grains from growing during the heating process of the billet. Considering the solid solution of Nb into austenite and ensuring rolling in the recrystallized region, the heating temperature is set to 1180-1220°C. The purpose of controlling the finishing rolling temperature is to refine the grains and prevent the plastic deterioration of the tube blank. A large number of studies have shown that: by rolling near the critical temperature of austenite, due to the reduction of the deformation temperature, the austenite recrystallization ability is weak, and the austenite crystal It is rolled and elongated, and defects such as dislocations generated during the deformation process are not easy to disappear, so a large number of nucleation sites are provided, the nucleation rate is high, and the grain refinement steel has good toughness. In the rolling process control, the final rolling temperature is determined to be Ar3+ (50-100) ℃ about 820-870 ℃.
Tube perforation
Blank inspection—cutting and blanking—inclined-hearth furnace heating—two-roll cross-rolling piercing
The tube billet is heated at a low temperature and slow speed, the heating temperature is controlled at 1220-1240℃, the heating time is 50-60min, the rolling rhythm is controlled at 3 pcs/min, and the number of cloth in the furnace is kept above 150.
Cold drawn
The waste tube is subjected to internal stress annealing, pickling, and lubrication, and then placed for 2-3 days to eliminate hydrogen embrittlement, and then the finished product is drawn on a 75t chain cold drawing machine.
Sum up
After controlling smelting, rolling, and adopting reasonable heat treatment process of waste pipe, the cold drawing process of steel pipe is very smooth, there are no cracks, cracks, pullout and other phenomena, die consumption is stable at a reasonable level, and the yield rate is 80% the above. The finished steel pipe has good plasticity and high strength after heat treatment, which can meet the requirements of users.
