The Effects Of Three Surface Modification Technologies On The Properties Of 4145H Steel Were Studied

Oil,as a strategic material,plays a decisive role in China's national economic development,but China's oil resources are scarce.In order to ensure the national energy security,the difficulty of oil exploration and development is increasing and the number of complex structure wells such as deep wells,ultra-deep wells and highly inclined and displacement wells is multiplied,and the drilling tool failure accidents occur from time to time,which seriously affects the drilling safety and economic benefits.Based on a large number of researches on documentation of the failure analysis and prevention of drilling tools,this paper systematically studies the material properties of 4145h steel of downhole tools,integrating failures of drilling tools on the drilling site.For the downhole tools faced with complicated working conditions,such as alternating stress,friction and wear,corrosion environment and so on,this paper explores the effects of three kinds of surface modification treatment technologies on the material properties of downhole tools.The following researches have been conducted in this paper:(1)The process parameters of three kinds of surface modification treatment technologies of CVD vapor deposition,laser quenching and QPQ salt bath multiplex heat treatment,are determined by literature investigation related to three kinds of surface modification treatment technologies.4145h steel is prepared and processed in accordance with national standard HB5287-96 "Metal Materials Axial Loading Fatigue Test Method".The original samples are subjected to surface modification treatment according to the determined process parameters of the three treatments.(2)The fatigue resistance of 4145h steel after three kinds of surface treatment technologies under normal temperature and pressure is studied.Rotating bending fatigue tests are carried out on samples with different surface modification treatments and original samples.In the medium-short life region,the statistical analysis of the experimental data is conducted with the method of grouping.In the long life region,S-N curves of four kinds of samples are obtained with up and down method.The experimental results are analyzed to obtain the difference between fatigue S-N curve of the three different surface modification treatments and the original samples.The fracture of fatigue samples is analyzed by scanning electron microscopy(SEM)to study its forming and expanding.The differences between fatigue crack source region,propagation region and transient crack region of different process samples have been obtained.(3)The wear resistance of 4145h steel after three kinds of surface treatment technologies under normal temperature and pressure is studied.Four kinds of samples are tested for wear resistance respectively to get the relationship curves between three kinds of abrasion loss and time.The effects of three kinds of surface treatment technologies on the wear resistance of the samples are analyzed.It can be found from the experimental that CVD treatment technology improved the wear resistance of the samples in the process of short-term wear more than other.The relationship curve between hardness value and depth from the center to edge of sample is obtained by using a micro-hardness instrument.(4)The corrosion resistance of 4145h steel after three kinds of surface treatment technologies under normal temperature and pressure is studied.The corrosion test of four kinds of samples are conducted in the saturated CO2 solution,and the corrosion rates of the four samples within different soaking time are calculated by formulas.The relationship curves between corrosion rate and time of samples with the three kinds of surface treatments and the original samples are compared to anlyze the effects of three kinds of surface treatment technologies on the corrosion resistance of the material.The sample fracture and corrosion surface morphology are observed and analyzed by scanning electron microscopy(SEM).