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2015 Vol. 50 No. 8
Published: 2015-08-15
1
WANG Jing- zhong，LIU Zheng- dong，BAO Han- sheng，WANG Kuai- she
Study of steel and alloys for ultra- supercritical power plant in China
The present research in China of martensitic heat- resistant steel，austenitic heat- resistant steel and nickel base heat- resistant alloy used for boiler and ultra- supercritical thermal power unit was summarized. Compared with nickel base heat- resistant alloy，the research for martensitic and austenite heat resistant steels is relatively sufficient. The nationalization of martensitic heat- resistant T/P91，T/P92 steel and austenitic heat resistant steel S31042，S30432 and TP347HFG has been realized. Studies on the new 9%Cr martensitic steel were carried out. The investment and research for nickel base alloys is not enough and the research content is far from systematic，but the trend of study on nickel base alloys shows good momentum. Relatively comprehensive studies on Inconel 740，Alloy 617 and Alloy 263 have being researched by domestic scholars. Some recommendations were put forward for the research of key materials for ultra- supercritical thermal power units. Better future in China of research for heat resistant steels and alloys was prospected.
2015 Vol. 50 (8): 1-9 [
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ZHOU Mi,JIANG Tao, YANG Song- tao, WANG Yan- jun,ZHANG Li- heng,XUE Xiang- xin
Influence of the addition of ordinary ore on vanadium- titanium sinter properties
Vanadium- titanium (V- Ti) sinter，V- Ti sinter with YD ore，MF ore，ZF ore and mix ore (YD+MF+ZF) addition ,respectively，were produced by sinter pot. In addition，sintering rate，burning loss，yield(>5 mm),sinter strength (TI) ,RDI>3. 15 mm and softening properties were determined and analyzed. The results show that the quality of V- Ti sinter is poor，in particular RDI>3. 15 mm with a lower productivity. It is beneficial to improve quality and productivity by adding ordinary ores in V- Ti sinter mixture. The granulation properties and chemical composition，etc. should be considered together to ensure a certain content of SiO2，MgO and not too high- Al2O3 content with high permeability in sinter mixture. With YD,MF,ZF ,mix (YD+MF+ZF) ore addition，sintering rate and softening properties are all improved. V- Ti sinter with ZF addition has the highest TI (64. 25%)and a higher RDI>3. 15 mmbut a lower yield. V- Ti sinter with YD addition has a higher TI (64. 21%)and a higher yield but the lowest RDI>3. 15 mm. V- Ti sinter with MF addition improves TI and RDI>3. 15 mm with a higher burning loss and a lower- grate iron. The quality and productivity of V- Ti sinter with 13% (YD+MF+ZF) addition are better than that with 6. 5% (YD+MF+ZF) addition.
2015 Vol. 50 (8): 10-15 [
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16
CAI Hao- yu，QING Ge- le，ZHANG Wei- dong，LIU Hong- song,TIAN Yun- qing，MA Li
Influence of milling on property and ballability of iron concentrate
In order to research the influence of milling on property and ballability of iron concentrate，some kinds of iron concentrate were milled by ball mill in different degrees. And 11 kinds of samples were made by mixing the milled iron concentrate with different ratios. Then，some physical property tests and pelletizing on the samples were carried out. The result indicated that，as the time of milling increases，the appearance of particles after milled remained unchanged，the content of fine particle，the specific surface area and the content of capillary water all increased，but the content of molecular water did not change significantly. The specific surface area was mainly influenced by the content of fine particles (<10 μm).However，the strength of green pellets was mainly influenced by the specific surface area and particle size distribution. The content of >76. 33 μm fraction and <10 μm fraction should be controlled between 10%- 15% to make sure the pelletizing property and strength of green balls were better，when the specific surface area of iron concentrate lies between 1 500- 2 500 cm2/g.
2015 Vol. 50 (8): 16-23 [
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YUAN Peng,,DENG Xiao- xuan,JIANG Min,WANG Xin- hua,JI Yun- qing
Investigation of subsurface hooks in continuous cast low carbon aluminum- killed steel slab
A distinctive microstructural feature called a “hook” is often observed on the subsurface of low carbon aluminum- killed steel slabs during continuous casting processes. Inclusions and bubbles are easy to be entrapped by the hooks，which makes Al2O3 cluster and “Ar+Al2O3” type inclusions gathered in subsurface layer of the slabs. A large number of samples were obtained from wide face，narrow face，and corner of the slab in this experiment. The characteristics of hooks in different positions of the slab were investigated. The results showed that in the wide face the center of hooks are deeper than others，in the narrow face the hook depth increase when close to the corner of slab，and hooks near the corners of the slab exhibited three- dimensional morphology. Furthermore，a mechanism of hooks entrapping alumina inclusions and argon bubbles was proposed，which suggested that marangoni force in the process of continuous casting plays an important role on the entrapment of alumina inclusions and argon bubbles. By investigating the behavior of inclusions and bubbles in solidification front of hooks，this mechanism explained the process of how hooks entrapping large side inclusions and bubbles well. From the result，the countermeasure of reduction of hooks and inclusions was proposed.
2015 Vol. 50 (8): 24-33 [
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34
PENG Qi- chun，QIU Lei，ZOU Jian，PENG Ming- yao，ZHANG Liang- zhou，ZHOU Jian- feng
Evolution of inclusions in non- oriented silicon steel W800 during production process
The cleanliness of steel and the amount，size distribution and morphology of inclusions in non- oriented silicon steel W800，which was produced by 210 t BOF- RH- CC，were studied by oxygen and nitrogen analyzer，scan electron microscopy(SEM)，image analytical，bulk sample electrolysis．The results show that w（T［O］） generally decreases， w（［N］） increases gradually in steel；the size of most inclusions in the steel is 0- 3 μm，the number of inclusions decreases ceaselessly during the smelting process. The inclusions during RH refining process are Al2O3 and a small amount of MgO- Al2O3. In tundish the number ofMgO- Al2O3 increases，individual inclusion of Al2O3 decreases. The main inclusions in casting slab are AlN，Al2O3 and MnS and the size is blow 10 μm，and individual Al2O3 is not be found，large inclusions mainly are Al2O3- SiO2，CaO- Al2O3- SiO2，CaO- MgO- Al2O3 formed with deoxidation products，slag and lining by the reaction．
2015 Vol. 50 (8): 34-38 [
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39
YANG Hao，CHEN Wen- man，HE Yu- ming，PAN Shi- song，PAN Yong- zhong，SU Gang
Analysis of surface micro- crack on thick plate of Q345A
Surface micro- crack on plate seriously deteriorates the product quality. After metallographic observ ation and EDS teste on slab and plate，the characteristics of the micro- crack and production parameters analyzed,the reason producing surface micro- crack on thick plate Q345A was that the falling coating of mold copper plate. For one hand，this situation caused copper element to infiltrate into the austenite grain boundary through slab surface which makes the crack along the grain boundary easy to happen. For the other hand，crack was also generated by thermal stress disproportionation after coating exfoliated，and the crack was more serious on slab containing Ti，which is sensitive to crack. Therefore，some control measurements were proposed. Firstly，the quality of mold copper plate is needed to be improved and avoiding copper wall be exposed. Secondly，the inspection of mold copper plate is enhanced before production and same measurements for the surface quality of slab after production. Finally，the protective casting is proposed to improve the steel cleanliness.
2015 Vol. 50 (8): 39-44 [
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45
GAO Hai，BAI Rui- guo，ZHU Rong，ZHANG Xing- li，TIAN Peng
Multistage and combined pretreatment of vanadium bearing hot metal
A hot metal tride pretreatment process combined with complex blowing predesulfurization for vanadium bearing hot metal，desilicon and detitanium during extracting vanadium，dephosphorization with dumping semi- steel was proposed. The complex blowing predesulfurization process was optimized by studying parameters of lance，blowing rate and desulfurizer ratio，and desilicon and detitanium in the Vanadium extraction process were realized. This study improved the oxidation rate and reduced the burden of converter through the dephosphorization technology research of semi- steel.
2015 Vol. 50 (8): 45-50 [
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51
YU Yang，WANG Lin，ZHANG Xi- bang，WANG Chang，CHEN Jin，JIAO Hui- li
Generation mechanism and control strategy of equally- spaced longitudinal stripes on the surface of hot- rolled plate
Equally- spaced longitudinal stripes introduced in hot rolling process couldn’t be completely eliminated after pickling，cold rolling and continuous annealing，which seriously affect the quality of finished product. Defect evolution research during the whole process and technological experiment have been carried out，which confirmed that the translations of grinding spiral lines，closely related to the roll grinding process and CVC roll profile curvature，from the finishing work roll surface in last pass to the steel strip surface，was the main cause. Grinding spiral lines on roll surface and the resulting equally- spaced longitudinal strips in hot- rolled sheet surface were caused by the mismatch of grinding wheel surface and the roll surface curve，and could be completely eliminated by optimizing CVC profile of finishing work roll and roll grinding parameters.
2015 Vol. 50 (8): 51-57 [
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58
ZHAO Xin- qiu，，MENG Qing- gang，YANG Jing- ming，，CHE Hai- jun，
Optimization of rolling schedule based on improve immune clone multi- objective algorithm
Rolling schedule is set by the model of optimize first and then choice to solve the difficult problem of select weight，because there is coupling and restrict each other between objective functions. In order to improve the efficiency of mill，improve the plate shape and surface quality，selecting the power distribution，excellent flatness and the slip rate as objective functions，The rolling schedule of steel cold rolling mill in Tangshan is optimized by Improve Immune Clone Multi- objective Algorithm（IICMA）. The experiment results show that IICMA can guarantee convergence and improve the distribution degree of the population at the same time；and the optimized different preferences rolling schedules can meet the requirements of different choices. Compared with the original procedures，the use of the mill is more reasonable，flatness is better and the slip rate reduces to an acceptable level.
2015 Vol. 50 (8): 58-64 [
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SUN Jian- liang,ZHANG Yong- zhen,PENG Yan,QI Xiang- dong,HAO Lu- han
Step type critical region normalizing heat treatment process of heavy cylinder
The step type critical region normalizing (STCRN) heat treatment process (HTP) was put forward as the center part of heavy cylinder was prone to mixed grain and crystal grain structure，long period of heat treatment，large energy consumption after the isotherm type austenite region normalizing (ITARN) process. The microstructure and mechanical properties after the proposed HTP methods were verified，and the two times STCRN was the best HTP. The results show that: First，the two- time STCRN on eliminating mixed grain and crystal grain is better than that with ITARN method，and the average grain size is 18um after the heat treatment. Also，the cementite spheroidization and homogenization inside the grain is more effective. Besides，the yield strength，tensile strength and the-30 ℃ charpy impact energy of the heavy cylinder material are 681 MPa，768 MPa and 181 J,respectively after two- time STCRN HTP，and the comprehensive mechanical properties are better than that with the ITARN method. Furthermore，the -30 ℃ impact fracture after the two- time STCRN is quasi- cleavage fracture，with significantly more plastic ridge and larger low temperature impact absorbing energy than that with ITARN. Finally，compared with the ITARN，the holding time of two- time STCRN can be shortened by 30% and the normalizing temperature is also decreased，which greatly reduces the energy consumption.
2015 Vol. 50 (8): 65-70 [
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71
HUANG Zhen- yi,XIAO Ya,HOU Qing- yu,WANG Ping,ZHANG Xiao- feng
Effect of temper temperature and cooling rate on the microstructure and properties of T91 alloy steel
Based on the actual situation ，in order to improve the structure property of T91，be benefit for later processing，the effects of temper temperature within the range of 300- 780 ℃ and cooling rate on the microstructural evolution and hardness change of T91 steel have been analyzed and compared by means of metallographic analysis，scanning electron microscopy and hardness measurement，and to provide some practical reference significance. The results show low degree of tempering to reply at 300- 400 ℃，hardness is difficult to be reduced. Under the condition of tempering at 500- 600 ℃，large amount of fine dispersed granular carbides precipitate in the matrix microstructure of T91 steel，and the Vicker hardness remains high. As the temperature increases at 600- 780 ℃，carbides precipitate along the grain boundary adequately，hardness decreases obviously. With the increase of tempering cooling speed，hardness gradually decreases. A large number of carbides precipitate at the sensitive range from 500 to 600 ℃ under the condition of furnace cooling (5 ℃/min)，and the hardness of T91 steel is high. In the way of tempering at 780 ℃ and cooling rate(50 ℃/min)，getting through the sensitive interval quickly，the carbides precipitate less in the matrix，and the hardness decreases obviously，comprehensive properties meet the processing requirement.
2015 Vol. 50 (8): 71-76 [
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CHEN Si- lian，HUI Wei- jun，SHAO Cheng- wei，ZHAO Xiao- li，DONG Han
Effect of controlled cooling on microstructure and properties of medium- carbon high- vanadium microalloyed steel
The effect of post- forging controlled cooling on the microstructure and hardness of a kind of medium- carbon high- vanadium microalloyed steel (37MnSiVS) for fracture splitting connecting rod was investigated by Gleeble- 3800 thermal simulator. The results showed that the cooling rate had a significant influence on the microstructure and properties of sample. Both the pearlite content and hardness of tested steel gradually increased with the increase of cooling rate. As the cooling rate was higher than 1. 5 °C/s，the bainite was observed in microstructure and the hardness did not increase any more. The forging deformation is advantageous to the formation of fine microstructure and higher content of ferrite. However，the hardness of steel decreased. The fast cooling to about 600 °C followed by proper isothermal treatment significantly promoted strength of tested steel due to the precipitation strengthening effect of many fine and dispersed V(C,N) particles. The results indicated that the differentiation control of forging hardness (strength) could be realized by adjusting post- forging cooling method，which could control the microstructure and precipitation of V(C,N) particles.
2015 Vol. 50 (8): 77-82 [
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CHENG Bing- gui,WU Feng- juan,LIU Dong- sheng
Microstructure and mechanical properties of low carbon copper- containing steel plate for shipbuilding with yield strength of 785 MPa
The continuous cooling transformation (CCT) behavior of an advanced steel used as offshore structure and shipbuilding with yield strength greater than 785 MPa was studied. A novel process route consisting of controlled- rolling and direct quenching followed by tempering (DQ- T) was used to process the tested steel. The microstructure and mechanical properties of DQ- T treated plates were studied. The as- quenched plate consists of refined lathlike martensite (LM) with high- density dislocations，which act as preferred precipitation sites for ε- Cu and/or NbC particles during tempering. These precipitates improve the tempering resistance of the steel. Peak strength associated with the lowest impact toughness is achieved in the steel tempered at 500 ℃. The microstructure of the plate tempered at 710 ℃ (in two- phase region) for 1 h consists of secondary lathlike martensite (SLM) and ferrite ，resulting in best combination of strength and toughness，i. e. ，yield strength (Re) of 810 MPa，ultimate tensile strength (Rm) of 1 066 MPa，Charpy V- notch toughness(KV2)of 97 J even at- 80 ℃.
2015 Vol. 50 (8): 83-88 [
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behavior of X80 pipeline and its weld joint XIE Fei，XU Chang- hao，WANG Dan，WU Ming,WANG Hai- yan，XIE Hong- yu
Influence of temperature on electrochemical corrosion
Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) technology were used to study the effect of temperature on electrochemical corrosion behavior of X80 pipeline steel and its weld joint in simulated Ku’erle soil solution. The results showed that the corrosion current density of X80 steel first increased and then decreased with the increase of temperature. Moreover，the increase of the amplitude gradually narrowed. When the temperature was 80 ℃，there was a peak value on charge transfer resistance，and the corrosion behavior of the metal was the most intense at this time. When the temperature was 90 ℃，electrode corrosion reaction was restrained，the corrosion rate decreased observably. The corrosion of weld joint part was more than other part of the steel at the same temperature.
2015 Vol. 50 (8): 89-94 [
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YANG Zhao- hui，，LI Jian，HUANG Tao，YU Hong- jiang，WANG Liang，，LI Xiang- yang
Galvanic anode protection techniques for steel tanks used in the overseas oilfields
Through electrochemical test and morphology analysis of the dissolved anode，the component content of the galvanic anode had been optimized. Al- 4. 5%Zn- 0. 025%In- 1. 5%Mg- 0. 05%Ti- 0. 015%Ga was the best component content in the oversea oilfield water with high concentration of salinity and chloride. The influence and mechanism of the alloy elements，which affected the current efficiency of galvanic anode，had been analyzed. Simulation and field experiment both indicated that optimal galvanic anode worked well in the oilfield water with high concentration of salinity and chloride.
2015 Vol. 50 (8): 95-99 [
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