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2023 Vol. 41 No. 4
Published: 2023-08-15
Test and Research
Measuring Technology
Defect Analysis
Subject Discussion
Test and Research
1
LIU Lu, GUO Jian, ZHAO Guang, LI Bo, ZHAO Jianglin, HAN Peng
Effect of microstructure on properties of roll surfacing
The service life of roll surfacing layer is closely related to the surface hardness and quality of surfacing alloy, while the surface hardness is closely related to the microstructure of the surfacing alloy. The surfacing alloy was prepared on 45 # steel substrate by the submerged arc surfacing technology using high-chromium molybdenum flux cored wire as the surfacing welding material. The alloy layer deposited by 420L welding wire had the dendritic structure composed of Fe-Cr solid solution and carbide, while the alloy layer deposited by YD255Mo-S welding wire was mainly composed of the mixture of black acicular martensite and residual austenite. The average microhardness HV0.2 of alloy layers deposited by two kinds of welding wires was 620 and 634.6, respectively. The maximum error was 11.9% and 9.1%, respectively. The overall average hardness value of alloy layer welded with YD255Mo-S wire was high with little fluctuation. The relationship between the microstructure characteristics of surfacing alloy formed under two grades of welding wire and the surface hardness of the alloy was studied.
2023 Vol. 41 (4): 1-4 [
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5
CAI Xinnan, ZHANG Hehe, LI Feng, TAN Tiantian, GUO Chunjiang, WAN Jie
Preparation and magnetic properties of Ni-Mn-Sn-Co porous microwires
Ni-Mn-Sn Heusler alloy has been widely studied as a potential magnetic refrigeration material. Ni-Mn-Sn alloy in the form of fiber or foam can improve the magnetic refrigeration efficiency. The ferromagnetic element Co was employed to replace a small amount of Ni in Ni-Mn-Sn alloy to enhance the magnetization intensity of the alloy. Ni-Mn-Sn-Co polycrystalline fibers were prepared by melt-extraction technique, and Ni-Mn Sn-Co porous fibers were prepared by corrosion method. The morphologies and properties of the Ni-Mn-Sn-Co fibers were characterized by means of scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and vibrating sample magnetometry (VSM) in a commercial physical property measurement system (PPMS). The results showed that the hysteresis loss of Ni-Mn-Sn-Co porous fibers was significantly reduced compared to the quenched fibers. The phase transition temperature slightly increased with the magnetic field shift, which was conducive to the improvement of the magnetic refrigeration efficiency.
2023 Vol. 41 (4): 5-10 [
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11
SHAN Xianfei, LEI Na, ZHAO Naisheng, YANG Yanlong, ZHANG Longhui
Drop hammer tear test and pendulum impact test of pipeline steel
The performance of drop hammer tear test and pendulum impact test of pipeline steel are two important parameters of materials, which can help determine the safety and reliability of materials or products. Two pipeline steel samples with different specifications and different properties were used to perform drop hammer tear test and Shaabi pendulum impact test at different temperatures. The impact shear section rate and the drop hammer shear area fraction in two test methods were compared. The difference and relationship were studied based on the test results. The results showed that the change laws of impact shear section rate and the drop hammer shear area fraction were basically consistent during the temperature variation for two pipeline steel samples with different specifications and different properties in drop hammer tear test and pendulum impact test.
2023 Vol. 41 (4): 11-14 [
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Measuring Technology
15
JIN Tao, SUN Fengyuan, WANG Haihua, ZHANG Jianfeng, ZHENG Xiaowei
Test method of austenite grain size of SiCr spring steel heat-treated wire
SiCr spring steel heat-treated wire was used as the sample. The austenite grain size was tested by direct hardening method and oxidation method. In the direct hardening method for the test of austenite grain size of SiCr spring steel heat-treated wire, the sample was etched with 4% nitric acid alcohol solution. The results showed that the appearance of martensite could not be restrained, leading to the unclear austenite grain boundary when observed under a microscope. As a result, the grade of austenite grain size could not be accurately determined. For the oxidation method, the austenite grain boundary of spring steel heat-treated wire was clear under the microscope. The heating temperature was adjusted by measuring the phase transition temperature and phase transition kinetic curve. The holding time of temperature was determined according to the sample size. The optimal heat treatment process for SiCr spring steel was heating at 810 ℃ for 30 min, and it could be close to the austenitic grain size in real spring steel heat-treated wire. This study could guide the technological breakthrough of heat treatment in spring wire drawing plant to improve the performance of spring steel wire.
2023 Vol. 41 (4): 15-19 [
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20
YANG Xiao, PAN Hengpei, WANG Shining, LI Xuefeng, ZHANG Xinyao, GAO Lingqing
Test and analysis of needle-like metallographic sample in micro-nano scale
In the process of metallographic analysis, the insetting of needle-like sample in micro-nano scale will easily cause the capillary phenomenon, which leads to the limited resolution of metallographic structure. As a result, it is difficult to accurately evaluate the micro structure. The needle-like sample in micro-nano scale were treated by grinding and polishing, and then eroded with the chemical reagents. After that, the sample was placed in ethanol and acetone solution for ultrasonic treatment followed by drying with a hair dryer. The results showed that due to the low melting point and high volatility of acetone solution, the addition of ultrasonic treatment in acetone solution in the process of conventional micro-nano metallographic sample could effectively remove the residual solution between the mosaic material and the sample. The occurrence of capillary phenomenon was reduced, which could ensure the clear observation of metallographic sample as well as the effective characterization of microstructure.
2023 Vol. 41 (4): 20-23 [
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Defect Analysis
24
LIU Guijiang, TENG Zhengde, SHAN Mingyan, YANG Yongfeng, LU Wei, WANG Junmin
Cracking analysis of 42CrMoA roller shaft end
The macroscopic examination, chemical composition and micro failure analysis were conducted for the cracking defect of the end of 42CrMoA roller shaft. The failure analysis showed that the cracking source of the roller shaft was the original end crack of the raw material. The process investigation and discussion analysis confirmed that the original end crack of raw materials was the sawing crack formed in the cold cutting process of grinding wheel saw. The main cause of sawing cracks was the combined effect of steel cooling stress and sawing thermal stress. The occurrence of sawing cracks could be prevented by annealing the steel and cooling slowly in pits.
2023 Vol. 41 (4): 24-26 [
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27
HAN Qibiao, GAO Longyong, CHE Jinfeng
Production practice of inclusion control in 9Ni steel for LNG storage tank
During the production of 9Ni steel medium-thick plates 06Ni9DR, many batches were unqualified in ultrasonic flaw detection. The defective parts of the samples were inspected and analyzed using the metallographic microscope and scanning electron microscope. The results showed that there were a large number of CaO-Al
2
O
3
inclusions (in length of 61-167 μm) accompanied by a small amount of MgO and sulfide in the steel, which was main reason for the unqualified flaw detection. Due to insufficient addition of aluminum in LF deoxidation, the burning loss of aluminum during refining led to further reduction of aluminum content. Aluminum was added in the later stage of LF treatment or in the process of RH treatment, thus a large number of such inclusions were generated. After taking some measures such as controlling the end-point carbon and oxygen content of the converter, extending the RH vacuum treatment time and soft blowing time, and ensuring sufficient liquid steel sedation time, the quantity of inclusions in the steel plate had been significantly reduced. Meanwhile, the proportion of unqualified ultrasonic flaw detection decreased from 8.11% to 0.2%.
2023 Vol. 41 (4): 27-30 [
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31
GUO Lei, WANG Shaocan, LIU Yan, CONG Baoyi
Cause analysis of cracking of 304 stainless steel adapter strip
As the transportation equipment of the large marine ship, cracks were found on the adapter strip of one transfer vehicle during use. The material of the adapter strip was 304 stainless steel. In order to find out the causes for the cracking of the adapter strip, the macro analysis, micro analysis, chemical composition, mechanical properties and metallographic analysis of the adapter strip were carried out by scanning electron microscope, direct reading spectrum, energy spectrometer, metallographic microscope, universal material testing machine and Brinell hardness tester. Through the stress corrosion test, the causes for the crackng of the adapter strip were verified. The results showed that the unqualified material of the adapter strip of the transport vehicle was the main reason for the cracking, and the intergranular corrosion and stress corrosion in the marine environment were the inducing factor for the craking of the adapter strip. Through the vibration aging treatment of the frame and the use of 316L stainless steel with better corrosion resistance, the occurrence of similar incidents could be effectively avoided.
2023 Vol. 41 (4): 31-35 [
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36
ZHANG Demei
Cause analysis of fracture of stop valve
The fracture of stop valves was observed in batches after use for one year. The fractured stop valves were comprehensively analyzed by means of chemical composition, hardness, microstructure and fracture appearance. The results showed that the chemical composition of the stop valves could meet the requirements of national standards (the mass fraction of Zn exceeds 38% of the total mass fraction). There was no abnormality for the hardness and microstructure. The fracture appearance indicated that the stress corrosion was the main reason to cause the failure of stop valves. The combined effect of three factors, i.e., no stress relief annealing was conducted for this batch of stop valves, the tightening force was larger, and the environment humidity was high, caused stress corrosion of stop valves which had strong tendency to stress corrosion. As a result, the early fracture occurred.
2023 Vol. 41 (4): 36-39 [
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40
DONG Juan, CAI Fengwei, CHEN Yongxiang
Cause analysis of abnormal etching test of 18CrNiMo7-6 wind power planet wheel forgings
The chemical composition, gas content, hardness and non-metallic inclusions of 18CrNiMo7-6 wind power planet wheel forgings were tested to find out the reasons for the abnormal etching test. The results showed that 18CrNiMo7-6 molten steel was not completely deoxidized or it contacted with the air due to the imperfect protective measures during pouring. Al in the steel was oxidized to Al
2
O
3
, which was eventually remained and dispersed in the wind power planet wheel forgings, resulting in unqualified forgings etching detection. The forging samples were reanalyzed by etching test. The macroscopic examination on any cross section showed that the same black etching points could be found, which verified the analysis conclusion.
2023 Vol. 41 (4): 40-44 [
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45
CHEN Rong, LIU Xibin, SHI Mingcan
Cause analysis on fracture of windlass steel wire rope for aerial work
In order find out the causes of fracture in the service process of wire rope for aerial work, the fracture surface and microstructure of the defective part were analyzed by means of stereo microscope, optical microscope and scanning electron microscope. Meanwhile, the mechanical properties of the normal samples were analyzed using tensile testing machine. The results showed that the white layer microstructure and friction extrusion trace were formed due to the repetitive extrusion and friction between steel wire rope and reserved hole of fixed pully during use. The shear fracture of steel wire rope with damaged surface occurred in repetitive lifting of diagonal tension. The integrity of remaining steel wire rope was destroyed. The fracture of whole steel wire rope was caused when the load-bearing capacity was greater than the ultimate load.
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49
WANG Zhijun, QI Jiangtao
Cracking failure analysis of low-chromium ultrapure ferritic stainless steel for flange
Low-chromium ultrapure ferritic stainless steel is one of the main products of flange steel.Some irregular crack defects were observed in the end of the stamped flange during inspection. The cracks occurred at the end face or single face in the thickness direction. A sample with dimension of 20 mm×20 mm was sampled from the cracking part of flange, and the chemical composition was determined by X-ray fluorescence spectrometer. The section perpendicular to the rolling direction of the sample was polished and etched by FeCl
3
+HCl mixed acid solution. The microstructure and morphology were observed by optical microscope (OM), and the precipitated phases of sample were analyzed by scanning electron microscope (SEM). The analysis showed that the annealing time at high temperature was too long, resulting in the precipitation of a large number of hard and brittle granular intermetallic compounds (Fe
2
Ti and Fe
3
P) in the crystal and grain boundary of the low-chromium ultrapure ferritic stainless-steel matrix. These precipitated phases were irregularly distributed in the form of strips along the thickness direction. The precipitation of these intermetallic compounds, especially the cold brittleness effect of P element, caused the increase of local stress concentration, leading to local cracking during cold working of flanges.
2023 Vol. 41 (4): 49-52 [
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Subject Discussion
53
YU Jianxin, CUI Xiping, WANG Xiaopeng
Uncertainty analysis of measuring elastic modulus by static method and resonance method
The elastic modulus of metal materials was measured by the static method and the resonance method, respectively. In the static method, an electronic universal testing machine and extensometer were used for the tensile test of dumbbell-shaped bar samples, and the slope of the elastic section of the engineering stress-engineering strain curve was used to calculate the elastic modulus. In the resonance method, the bending resonance test of rectangular free beam sample was carried out by using dynamic elastic modulus and damping analyzer, and the elastic modulus was indirectly measured according to the relationship between the elastic modulus and the fundamental bending frequency. According to the standard for evaluation and expression of uncertainty in measurement, the measurement uncertainty of elastic modulus by static method and resonance method was compared using 7075 aviation aluminum alloy as an example. The results showed that the maximum uncertainty of static method was the deformation error measured by extensometer, and the maximum uncertainty of resonance method was the thickness measurement error. The measurement results by resonance method were better than those by static method. The measurement uncertainty analysis could provide reference for the selection of measurement methods and evaluation of results of elastic modulus.
2023 Vol. 41 (4): 53-59 [
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