Process control method in production of N80-1 non-tempered seamless casing

N80-1 non-tempered seamless casing is produced by hot rolling of medium carbon-manganese V steel, and controlled final rolling temperature > phase change point Ar3 is equivalent to normalizing treatment. The production method of N80-1 non-tempered seamless casing has the advantages of low cost, saving heat treatment resources and shortening the delivery period. However, the process control of N80-1 non-tempered seamless casing is very complicated (such as deformation, deformation rate, cooling rate and other performance factors can not be artificially controlled), coupled with the lack of effective process control technology, making the performance control of this product has been not stable, the performance is not stable in the range of 552-758MPa, and the impact toughness is often lower than the longitudinal 27J or the lateral 14J (API 5CT standard requirements), which seriously affects the material yield and use security. The development of N80-1 non-tempered seamless casing was developed in the mid-1990s and experienced the medium carbon-manganese Cr-Mo bainite non-tempered steel to medium carbon-manganese microalloyed ferrite. The development process of the body and pearlite type fine grain steel, due to the instability of performance, especially the abnormal impact toughness, the user has caused many major accidents during the use.

At present, medium carbon-manganese V steels are commonly used, such as domestically available 27Mn2V, 34Mn2V, 36Mn2V, 36Mn2VN, 35Mn2V and 40Mn2V. Although the development of steel grades is more comprehensive, steel grades are only one of the factors affecting performance, and the control of performance is more controlled by process parameters. At present, the research on the control method of N80-1 non-tempered seamless casing is less and scattered, and more mature or controlled steel and cold control technologies and theories such as plates and bars are used. This kind of controlled rolling and controlled cooling technology is mainly controlled by the deformation amount, deformation temperature and deformation rate of each pass in the rolling process to achieve the purpose of recrystallizing and refining grains of austenite, and then controlling Cooling, to change the tissue transformation process, and to control the termination temperature to evenly organize and eliminate residual stress to achieve the desired structure, and ultimately achieve the purpose of performance control. However, N80-1 non-tempered seamless casing, in addition to the deformation temperature can be artificially controlled, other parameters: deformation, deformation temperature, deformation rate, cooling rate can not be artificially controlled. Therefore, the traditional controlled rolling and controlled cooling technology can not be applied to the process control of N80-1 non-tempered seamless casing, which can only explain some phenomena qualitatively or optimize performance. The traditional control of rolling and controlled cooling technology, usually based on gleeble compressive stress thermal simulation test, through the hardness test and tissue observation, the process control of deformation, deformation temperature, deformation rate, cooling rate and termination temperature of each pass is obtained. parameter.

The application of such controlled rolling and controlled cooling technology and research method in N80-1 non-tempered seamless casing mainly has the following problems and shortcomings: 1. The traditional controlled rolling and cooling technology requires deformation amount, deformation temperature, deformation rate and cooling rate are controlled. However, for the N80-1 non-tempered seamless casing, the deformation, deformation temperature, deformation rate and cooling rate parameters are not artificially controlled, so the operability and practical significance are lost. 2, The traditional control of rolling and cooling technology is based on the study of hardness and microstructure, lacking quantitative relationship data of tensile properties and impact properties, while the two main performance indicators of N80-1 non-tempered seamless casing are respectively for tensile properties and impact toughness.