There is alarm signal in the ultrasonic flaw detection of PZ100 grade expansion pipe. The detected defects those trigger alarm signal are found through cutting open the area where there is alarm on pipe body. The defects of alarm of flaw detection are determined to be big inclusions of aluminium oxides with main components of O, Al, Mg and Ca through such methods as microstructure observation and scanning electron microscope energy spectrum analysis. The continuity of matrix for PZ100 grade expansion pipe is destroyed by cinder inclusions under surface of pipe and interlayer is formed, so cracks are formed under the action of rolling force so that flaw detector is alarmed. The product quality of PZ100 grade expansion pipe is ensured by strictly implementing technological operation regulation as well as strengthening macroscopic examination of steel billet and detection of inclusions of finished product.

The chemical compositions of X52QH seamless steel pipe for hydrogen compressed natural gas transportation are designed with microalloying design based on low carbon manganese steel. The results of laboratory studies and industrial trial productions showed that the pipe was with excellent low temperature toughness and strength, its microstructure was mainly bainite +ferrite, grain size of microstructure was grade 9.0 as well as low temperature impact energy at -90 ℃ of material was 200 J when the quenched-tempered heat treatment process of “910 ℃ quenching+640 ℃ tempering” was adopted. The CTOD (crack tip opening displacement) test (-10 ℃) results showed that crack tip opening displacement>0.9 mm (required to be≥0.254 mm). In the environments with and without hydrogen, the reduction of area and elongation of slow strain rate test materials are all over 90% so that they are with good crack extension resistance and hydrogen embrittlement resistance.

The composition and production process of hot rolled steel strip for CT70 grade corrosion resistant coiled tubing are independently designed and formulated as well as small batch industrial trial production is carried out. For the trial product, the yield strength is 520~522 MPa, tensile strength is 575~584 MPa, elongation is 33%~34%, microstructure is mainly ferrite +pearlite with a small quantity of bainite, banded structure is grade 1.0 and total of inclusions is grade 1.0 so that non-metallic inclusions are well controlled. The mechanical properties, resistance to hydrogen induced cracking (HIC) and welding performance indexes of steel strip for CT70 as well as the mechanical properties and hardness of coiled tubing manufactured with steel strip for CT70 could all meet the user requirements.

The causes on lower impact toughness of weld for 10 mm thick 700 MPa grade square and rectangular welded pipe welded with high frequency resistance are analyzed with such inspection and analytical equipment as metallographic microscope, impact testing machine, scanning electron microscope and energy dispersive spectrometer. The results showed that there were such endogenous inclusions as silicate and titanium nitride as well as foreign inclusion that is mainly manganese oxide at the weld, the combined effect of which causes impact absorbing energy at room temperature of weld to be less than 8 J. Subsequently, the weld quality of square and rectangular welded pipe is improved, impact absorbing energy of weld is increased to about 20 J by taking such measures as strengthening control level of steelmaking process and increasing upset force of high frequency resistance welding. In straightening and sizing process, cracking rate of square and rectangular welded pipe is decreased from 8% to 3%.

The defect with morphology of rolling skin is found on the internal surface of Φ406 mm×8.8 mm seamless tube for gas cylinder, but longitudinal ultrasonic testing does not give an alarm, so probe of transverse flaw detector is started to detect defects and the proportion of alarm is found to be higher. The cause of transverse defect on internal surface is that the lubrication effect in rolling process of continuous mill is not good through the macro analysis, chemical composition analysis, metallographic analysis and energy spectrum analysis of defective products as well as the improvement measures for rolling method of reducing arresting force are proposed.

The hardness of cross section and longitudinal section of rail head for 75 kg/m hot rolled bainite rail and heat treated bainite rail is tested as well as the reasons are analyzed combining with microstructure and energy dispersive spectrometer (EDS). The results showed that the change laws for hardness of cross section and longitudinal section of rail head were consistent from rail head to rail web for both states of rail. The hardness of rail head for hot rolled rail is decreased first and then increased from tread to rail web, hardness fluctuation is smaller from top surface of rail head to 13 mm below tread, microstructure is granular bainite+ lath bainite+ lath martensite as well as local hardness is abnormally high due to the existence of martensite segregation band or hard phase inclusions; the hardness of rail head for heat treated rail is decreased first and then increased from tread to rail web. The outliers of high hardness are because indentation contains hard phase inclusions and outliers of low hardness are because there is granular bainite structure in micro region. The rail is with more uniform duplex structure of bainite and martensite as well as both of them are existed in the form of lath so that segregation is significantly improved from the macroscopical view.

The effects of heat treatment process on the microstructure and properties of 60Cr2MnMoNi steel are studied as well as the changes of microstructure and properties of samples at different states are compared and analyzed with TV-4X metallographic microscope, R(D)-150A1 material hardness tester, N1500C material impact testing machine and INSTRON5989 electronic universal material testing machine. The results showed that the as-cast microstructure of 60Cr2MnMoNi steel was P+B+A(residual)+carbide, average hardness was 28.1 HRC, average impact toughness was 15.4 J/cm², tensile strength was 795.9 MPa, yield strength was 458.1 MPa, elongation was 2.6% and reduction of area was 1.1%; the annealed microstructure was F(a little)+P+carbide, average hardness was 24.5 HRC, average impact toughness was 193.4 J/cm², tensile strength was 846.6 MPa, yield strength was 443.1 MPa, elongation was 17.5% and reduction of area was 25.3%; the quenched microstructure was B+M+A(residual)+carbide, average hardness was 58.1 HRC, average impact toughness was 14.5 J/cm², tensile strength was 1 442.6 MPa, yield strength was 1 186.4 MPa, elongation was 2.7% and reduction of area was 1.8%; the tempered microstructure was S(temper)+B+carbide, average hardness was 45.1 HRC, average impact toughness was 64.9 J/cm², tensile strength was 1 389.5 MPa, yield strength was 1 004.4 MPa, elongation was 7.4% and reduction of area was 10.9%. The microstructure and properties of 60Cr2MnMoNi steel are changed through different heat treatment processes so that the performance requirements of spare parts for equipment in service under different operating conditions could be met.

In the paper, the study on influences of quenching temperature, holding time of quenching, tempering temperature and holding time of tempering on microstructure and properties of test steel is carried out by taking as-hot-rolled 10Cr5MoVRE seamless steel pipe as the object of study. The study results showed that the yield strength, tensile strength and hardness (HRC) of test steel were first increased and then decreased while elongation and impact energy were decreased with the increase of quenching temperature; yield strength, tensile strength and hardness (HRC) of test steel were decreased while elongation was increased as well as impact energy was first increased and then decreased with the extension of holding time of quenching; yield strength of test steel was increased by about 17.5%, tensile strength was increased by about 18.2% and impact energy was decreased by 8.1% with the increase of tempering temperature; strength and hardness of test steel were decreased while impact energy was gradually increased with the extension of holding time of tempering.

The spatial detection of rolling mill housing is the difficulty in rolling mill measurement. In the past, the measurement was with total station and inside micrometer, however, the measurement accuracy and technical indexes of this method could no longer meet the requirements of operating maintenance for rolling mill. In this paper, the method of measuring rolling mill housing with laser tracker is summarized. The centerline of rolling mill row is fitted according to the data of rolling mill housing collected by laser tracker as well as the coordinate system is established by taking the centerline of rolling mill row as the baseline so that such spatial position relationships as the centering size, window size and deflection of rolling mill housing could be obtained. The installation precision of rolling mill housing is recovered by adjusting the rolling mill housing based on the measurement data of laser tracker. This method is so reliable that it could be popularized.

For the laser cladding technology, metal powder is melted by high energy laser beam to form metallurgical bonding layer with base material, which could prepare functional coating. Its performances could be optimized through adjusting and controlling process parameters. In the iron and steel industry, the technology is applied for strengthening components and parts, corrosion prevention of equipment as well as repair of high value equipment. Such problems as peeling of cladding layer and cracks are solved by optimizing the pretreatment, process parameters and material adaptation as well as high-quality repair of complex components is realized combining the technology with such technologies as 3D scanning and robot, which could promote the intelligence of repair processes.