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2022 Vol. 40 No. 5
Published: 2022-10-15
1
MA Cong,WANG Yongguo,LIU Yang,WU Shengfu,GU Hairong,CUI Lei
Control and improvement of oxide scale on the surface of hotrolled highstrength steel
In the hot forming process, the iron oxide scale was not fully removed by shot blasting, resulting in a layer of black iron oxide scale on the surface after heating, which then affected the measurement and precise control of the heating temperature. The box heating furnace, field emission electron microscope and electron backscatter diffractometer were used to analyze the change rule of oxide scale thickness and structure of 460 MPa automobile axle housing steel under two different hot rolling process conditions. The studies showed that the oxide scale structure under the condition of Process II (shorttime steel burning at low temperature, high temperature final rolling, coiling process) was easier to be removed by shot blasting. After shot blasting and heating simulation experiments, there was no oxide scale covering on the surface, which could meet the requirements of temperature measurement.
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CHEN Wei,GUAN Jisheng,FU Yongtao,ZHU Congmao
Effect of cooling processes on coil oval deformation of ultrafine bainite 30MnTiB steel
The longitudinal and transverse coil diameter difference of ultrafine bainite 30MnTiB steel coil is too large after hot continuous rolling, resulting in many waste products. In order to solve this problem, four different cooling processes were designed. The microstructure, expansion amount and high temperature strength were measured by optical microscope (OM), thermal simulation test machine and high temperature tensile test machine. By combining with the degree of longitudinal and transverse coil diameter difference of 30MnTiB steel coil under four different cooling processes, the mechanism to cause diameter out of tolerance of 30MnTiB steel coil was analyzed. The results showed that the expansion of bainite transformation obtained after cooling was larger than that of pearlite and martensite transformation. The lower the transformation temperature, the greater the expansion, and the more serious the vertical and horizontal coil diameter deviation. During the cooling of steel coil in the range of bainite transition temperature, if the lower cooling rate was adopted for 30 m coil at beginning at lower temperature to increase the strength of inner ring, and then the higher cooling rate was used to reduce the expansion force of the coil, the problem of coil oval deformation of bainite 30MnTiB steel could be effectively solved.
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XU Jie,LI Lingxia,LI Jikang,CHEN Ying,WU Zhaobo
Effect of rare earths on inclusions in weathering resistant steel by electrolytic extraction
In order to investigate the modification effect of rare earth elements on inclusions in steel, two kinds of weathering steels, i.e., Q235 without rare earth elements and Q235BRE with rare earth elements, were studied. The inclusions in steels were extracted by nonaqueous electrolytic extraction and physical magnetic separation. Xray diffractometer, scanning electron microscope and energy dispersive spectrometer were used to analyze the types and threedimensional morphology of inclusions. The results showed that the inclusions in Q235 steel without addition of rare earth elements were mainly composed of manganese sulfide and mixed oxide inclusions of aluminum and silicon. The size was relatively large. Irregular polygonal inclusions of magnesium and aluminum oxide and oxygensulfur composite inclusions were up to 40 μm in size, and long strip manganese sulfide inclusions could be 50 μm in size. The inclusions in rare earth weathering steel Q235RE were mainly oxygensulfur rare earth composite inclusions, and the size was obviously smaller. The long strip sulfide was replaced by regular spherical rare earth sulfide and rare earth oxygensulfur complex inclusions. The size of irregular polygonal oxide inclusions was less than 15 μm, decreasing by about 60%.
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TONG Lulu,DU Lin,YAO Jian,TIAN Dongfang,LI Yankui,QIAN Yuan
Discussion on sampling and preparation methods of byproduct lowpressure coal gas in steel works
This paper provided a new method for sampling and sample preparation of byproduct lowpressure coal gas in steel works for detection. The sampling method without air interference and the sample preparation method of helium pressurization were combined, realizing the accurate detection of components in lowpressure coal gas. Through the samplingsample preparationdetection of gases (including N2, CO2, H2 and CO) existing in low pressure coal gas, the difference of detection data before and after pressurization was not significant. The relative standard deviation was below 4.93 % and the optimal mixing time in pressurization was 1 h, which indicated that this method was feasible. The proposed method was applied to the detection of components in actual lowpressure coal gas, and the found results exhibited high accuracy, simple operation, and high repeatability. This method provided technical support for the gas composition detection in blast furnace, converter, coke oven in steel industries.
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22
SHAN Xianfei,LEI Na,SHEN Jie
Analysis of influencing factors in hole expansion test of automobile plates by acid pickling
With the popularity of automobiles in life, people have higher and higher requirements in vehicle safety. The quality of automobile plate is an important indicator affecting the vehicle safety, and the hole expansion test is an important index to measure the quality of the automobile plate. The steel plate 1 and steel plate 2 were used for automobile parts such as suspension arm, beam, automobile chassis, suspension and surrounding parts. They had good raw material stamping forming and good extension flange performance. The tests were conducted in test rate, material specification, and whether the pore convex mode expansion top and the test surface was on a same plane. The test results showed that all these factors had great influence on the testing results.
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28
XU Qiaoping
A new method for measuring laser wavelength based on acousticoptic diffraction
This paper presented a new method for the measurement of laser wavelength. At room temperature, the ultrasonic wave was obtained using piezoelectric ceramic chip under the action of alternating electric field generated by high frequency signal source. Ultrasonic grating was formed using the propagation of ultrasonic wave in liquid. The spectrometer was replaced by a telescope system composed of a collimating lens and a micrometer eyepiece. The measurement of the spectral width of grating formed under the irradiation of sodium light with known wavelength and laser with unknown wavelength was completed. Combined with the grating equation, the wavelength of laser could be obtained. The principle of this method was simple, and the relative error between the measured result and the calibration value of laser wavelength was small. It could be used as an extended experiment of ultrasonic grating.
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32
ZHOU Yang，YANG E，ZHANG Jun，DONG Hao，LI Bo
Application of automatic grinding and polishing machine in metallographic sample preparation of iron and steel
The method of preparing steel metallographic samples by automatic grinding and polishing machine was mainly introduced. Combined with the actual effect of the prepared metallographic samples, the steps of grinding, ultrasonic cleaning, polishing, washing, and drying of the metallographic sample and how to adjust the operating parameters of the equipment during the use of the automatic grinding and polishing machine were explained, so that the automatic preparation of highquality metallographic samples in the whole process was realized. The results showed that the fullautomatic grinding and polishing machine could stably and automatically prepare highquality metallographic samples with appropriate operation steps and parameters, thus avoiding the false image caused by manual metallographic sample preparation, and improving the accuracy of subsequent test results.
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37
WANG Yanguo
Analysis and investigation on the reason for unqualified mechanical properties of Q345T steel sheet pile
Due to the great difference of mechanical properties between the preliminary and recheck tests of Q345T steel sheet pile, the reason was analyz by the means of chemical analysis, microstructure observation and mechanical performance test. The results show that the banded structure, Widmanstatten structure and banded inclusions are direct reasons for causing low tensile strength of steel. By tracing the whole production process of Q345T steel sheet pile, the inadequate removal of gas and inclusion, the aggregate segregation of impurities at late stage of slab casting, and the uneven heating temperature control are the root causes of unqualified microstructure and performances of the steel.
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41
TANG Pengjie,CAI Zhaolei,HAN Xu
Cause analysis on cracking of 20 steel superheater tube in waste heat boiler
Cracking and leakage of 20 steel superheat tube in a waste heat boiler occurred after service for less than one month. The reason for cracking was determined by macroscopic analysis, chemical composition test, mechanical property test, microstructure observation, microscopic analysis, and fracture analysis. The results show that the cracking of superheat tube belongs to brittle fracture. There are precipitated tertiary cementite and dispersed oxide inclusions along ferrite the grain boundaries of ferrite in microstructure, leading to grain boundary embrittlement and insufficient toughness of the material. During the process of cold bending, some cracks were initiated on the elbow surface. When the superheat tube with crack defects was used, the cracks expanded gradually with time under the action of high temperature and internal pressure of steam in the furnace, which finally resulted in cracking and leakage of the superheat tube.
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46
MIAO Tiejun,XU Yang
Analysis of early failure of train springs
One company purchased 52CrMoV4 materials to manufacture train suspension springs. During the maintenance process of the freight car after service for a period of time, the cracking of one suspension spring was observed. Therefore, this suspension of the train was disassembled for sampling. The failed spring was comprehensively analyzed by physical and chemical inspection, metallographic analysis, mechanical properties and fracture scanning. The results show that all technical indexes of the train spring can meet the design requirements. Finally, the fracture of spring was observed and analyzed by scanning electron microscope (SEM). It was found that the failure mechanism of the spring fracture belonged to fatigue fracture, and the fracture source was at the surface contact point of the spring. During the backandforth operation of spring, the contact wear point between two adjacent springs expanded and deteriorated gradually, thus eventually causing the fracture of spring.
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50
ZHANG Huan,ZHANG Yuanpu,WANG Xiaodong,YU Hongwei,ZHANG Kaiguang
EH36船板用钢探伤不合格原因分析
为找出EH36船板用钢探伤不合格的原因，将探伤不合格的钢板通过人工探伤缺陷定位取样，通过光谱仪、光学显微镜、电子探针等仪器，对试样的成分、组织进行分析，结果表明：EH36钢板基体组织为铁素体和珠光体，裂纹附近C、Mn、P元素偏析严重，且有大尺寸的MnS夹杂和高度富集的(Ti,Nb,V)化合物出现，裂纹开口处有马氏体和贝氏体异常组织形成。通过适当控制钢中S、P含量，优化精炼、连铸和加热工艺，可减轻铸坯中心偏析程度；采用细晶轧制和弱冷相结合，可抑制马氏体组织形成。综合以上措施可提高钢板探伤合格率。
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56
ZHANG Hailong，YUAN Xinglong
Defect analysis and prevention of cracking in 177.80 mm×10.36 mm P110 seamless pipe billet
Brand 30MnCr22 177.80 mm×10.36 mm steel tube blank was converted to P110 steel tube billet after upgrading by heat treatment. Some cracks were observed on the surface of tube billet in the subsequent nondestructive testing. The crack was sampled for macrofracture analysis, metallographic analysis, fracture scanning analysis and energy spectrum analysis. The property of cracks was determined. It was found that the raw materials of tube billet contained Ti, O, Si and Al. The smelting of steel billet was not pure enough. The stress in the quenching process of heat treatment was too large to induce the formation of quenching cracks. In the process of subsequent production, the formation of such crack defects could be avoided by optimizing the steel billet smelting, selection of quenching temperature in heat treatment as well as control of cooling temperature for steel tube. Therefore, the aims to optimize process and eliminate defect could be achieved.
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