Effects of Cl- and SO_4^(2-) Ions on Corrosion Behavior of X70 Steel

[ Manuscript received October 8, 2003, in revised form March 2, 2004]Corrosion behaviors of X70 steel were studied by means of electrochemical experiments and morphology observation. First, through potentiodynamic polarization in solution of various Cl- ions concentration, it was found that Epit began to appear in solution of Cl- concentration above 0.1 mol/L, and there was a critical point of Cl- concentration between 0.05 mol/L and 0.1 mol/L, below which the extent of pitting and general corrosion were trivial, while in solution of Cl- concentration above 0.1 mol/L, general and pitting corrosion became greater as the increasing of Cl- concentration. All of them were confirmed by the SEM observations after anodic polarization. Second, via the potentiodynamic polarization curves of X70 steel in 0.5 mol/L Cl- solution with 0, 0.05, 0.5 and 1 mol/L SO42-ions, it was found SO42- ions were able to inhibit corrosion aroused from Cl- ions, accordingly a model was set up to describe the process. In addition, to further explore the inhibited effect of SO42- ions, EIS was used in solutions of different Cl- and SO42- concentrations, the results revealed that the electrochemical resistance has a relation with the [SO42-]/[Cl-], that was, the bigger the value of [SO42-]/[CI-], the greater the electrochemical resistance.

国产SA516Gr.70(HIC)厚板容器筒节的成型技术

为研究应用于加氢装置的冷高压分离器等核心设备的国产SA516Gr.70(HIC)、厚度200 mm钢板的可焊性能和成型性能,对钢板化学成分、力学性能、硬度等进行分析,选用400℃时的屈服强度平均值进行筒节板料预弯受力计算,追踪580℃中温卷校成型工艺及筒节纵缝试板的化学成分、力学性能等。试验结果表明,国产SA516Gr.70(HIC)厚板在不同位置及方向各项力学性能均衡;中温校圆后筒节最大圆度4 mm、棱角度2 mm,成型尺寸合格;纵缝试板的力学性能满足技术文件要求。研究验证了国产SA516Gr.70(HIC)、厚度200 mm钢板的可焊性能和成型性能良好,其厚板容器筒节的成型技术达到国内较高的工艺水平。

Relationship between electrochemical characteristics and SCC of X70 pipeline steel in an acidic soil simulated solution

Stress corrosion cracking （SCC） of X70 pipeline steel in simulated solution of the acidic soil in Yingtan in China was investigated using slow strain rate test （SSRT）, SEM and potentiodynamic polarization technique. Experiment results indicate that X70 steel is highly susceptible to SCC as applied potential reduces, which is manifested in loss of toughness and brittle fracture. Constaat polarization current can detect the occurrence of SCC. The lower the polarization current is the sooner stress corrosion cracking occurs. The SCC mechanisms are different at varying potentials. When potential is higher than open circuit potential, anodic process controls SCC, whereas when potential is far lower than open circuit potential, cathodic process controls SCC, and between these two potential regions, a combined electrochemical process controls the SCC. Stress or strain has a synergistic effect with electrochemical reactions to accelerate the cathodic hydrogen evolution process, which makes the X70 pipeline steel to be more susceptible to SCC.

Research on anti-corrosion property of rare earth inhibitor for X70 steel

Three kinds of rare earth nitrates were adopted to sodium molybdate to get three kinds of LnN-M compounded inhibitors （La（NO3）3＋Na2MoOa（LaN-M）, Ce（NO3）3＋Na2MoOn（CeN-M）, Pr（NO3）3＋Na2MoO4（PrN-M））. The combination of weight-loss method and the electrochemical test, was used to evaluate and analyze the corrosion inhibition efficiency of these LnN-M inhibitors to make the research on their corrosion inhibition performance, and the sequential order of their performance was found as follows： CeN-M〉 LaN-M〉PrN-M, among which, the inhibition efficiency of CeN-M for the X70 steel could reach 98.21%. The synergism parameters were calculated by weight-loss method, these computational data indicated that the synergistic effect between rare earth nitrates and sodium molybdate was obvious and significant. Surface morphology, chemical composition and phase components of the precipitation films were tested for discussing the mechanism of LnN-M inhibitors. The outer electronic configuration of the lanthanide was found to have an important influence on the inhibition efficiency. The CeN-M inhibitor was discovered to have the best inhibition effect with the amorphous cerium oxides. The results of this research revealed that the precipitation films formed on the surface of the steel samples had a crucial influence on the inhibition efficiencies after adding LnN-M inhibitors.

Effect of deteriorated microstructures on stress corrosion cracking of X70 pipeline steel in acidic soil environment

In order to investigate stress corrosion cracking （SCC） of X70 pipeline steel and its weld joint area in acidic soil environ- ment in China, two simulating methods were used： one was to obtain bad microstructures in heat affected zone by annealing at 1300 ℃ for 10 min and then, quenching in water; the other was to get different simulating solutions of acidic soil in Yingtan in south- east China. The SCC susceptibilities of X70 pipeline steel before and after quenching in the simulating solutions were analyzed using slow stain rate test （SSRT） and potentiodynamic polarization technique to investigate the SCC electrochemical mechanism of different microstructures further. The results show that SCC appears in the original microstructure and the quenched microstructure as the polarization potential decreases. Hydrogen revolution accelerates SCC of the two tested materials within the range of-850 mV to -1200 mV vs. SCE. Microstructural hardening and grain coarsening also increase SCC. The SCC mechanisms are different, anodic dissolution is the key of causing SCC as the polarization potential is higher than the null current potential, and hydrogen embrittlement will play a more important role to SCC as the polarization potential lower than the null current potential.

STUDY OF THE X70 PIPELINE STEEL CORRODING IN 3.0wt% NaCl SOLUTION USING ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY TECHNIQUE

The corrosion process of the X70 pipeline steel in 3.0wt% NaCl solution were studied using polarization method, and the chronological characteristics during the entire polarization plot were investigated in detail using EIS technique. In the active region of X70 steel, such as 20mV potential bias applied on open circuit potential (OCP), the impedance spectra was comprised of three parts: a high-frequency capacitive loop, a middle-frequency capacitive loop and a low-frequency inductive component. When positive polarization potential increased, the capacitive loops at high and middle frequency range merged, and the inductive component at low frequency shrunk. At high positive polarization potential bias (500-800mV vs. OCP), the high-frequency capacitive loop and the low-frequency inductive loop exhibited as disheveled points due to the synergism of the inhomogeneity of the corroding material and the localized corrosion. The results were fitted utilizing the equivalent circuits to simulate the impedance spectra and to interpret the electrochemical features shown during the experiments.

深拉钢丝用70钢盘条的研制与开发

新余钢铁集团有限公司(简称新钢,下同)为满足φ5.5 mm规格深拉钢丝用70钢盘条抗拉强度≥1 050 MPa的要求,优化设计了盘条成分,通过控制C元素含量,适当提高Si、Mn元素含量,降低S、P有害元素含量以增强盘条性能;优化了盘条生产过程中的控冷工艺,对比不同试验方案,得出较优控冷工艺参数为吐丝温度880~900℃,风机风量1#—4#设定为40 Hz,5#—8#设定为15 Hz,其余关闭,保温罩全开。生产的70-SL盘条抗拉强度平均值为1 100.5 MPa,均满足抗拉强度≥1 050 MPa的性能要求。通过盘条成分优化与工艺优化相结合的方法,成功研制出了抗拉强度满足要求的盘条产品,为开发其他系列高碳钢盘条提供参考。

DECREASING PITTING SUSCEPTIBILITY OF PASSIVE FILMS ON X70 PIPELINE STEEL IN NaCl SOLUTIONS BY ILLUMINATION

The influence of UV illumination on passivity and pitting susceptibility on X70 pipoeline steel in a borate buffer （pH=8.4 ） solution containing NaCl is described. It is observed that illumination of the sample leads to a decrease in its pitting susceptibility as indicated by pitting potential and incubation time measurements in chloride containing electrolytes. This effect is strongly dependent on the applied potential during passivation. The electronic properties of the passive films on X70 steel were studied by Mott-Schottky analysis and photocurrent transient measurements. The results indicated that illumination during passivation led to modifications in the electronic properties of the passive films, mainly to a decrease of the bulk doping and an increase in the surface state density. The cause for the decrease in the pitting susceptibility is preliminary explained in terms of such modifications of the passive flm.

Oblique Y-groove cracking test of the welding cold cracking susceptibility of domestic X-70 pipeline steel

Gas Transmitting From West to East Project' is significant. It should ensure the welding quality and safety of pipeline. The task is very arduous to guarantee the quality of the project in the condition of long line, complex weather and geology features. In this paper, the welding cold cracking susceptibility of domestic X 70 pipeline steel adopted by the project, which is one of the most interesting questions of welding quality about petrol pipeline, was studied by means of oblique Y groove cracking test. The crack ratio of surface and section was tested under the conditions of different welding materials and preheat temperature .The thickness of plate steel was 14.7 mm and 10.3 mm . The results reveal that X 70 pipeline steel has good crack resistance. The research has important value for the construction of large scale pipeline engineering and the application of domestic X 70 pipeline steel.

Study on the microstructure and hardness of in-service welded joint of X70 pipeline steel

Hydrogen induced cracking （HIC） is one of the main problems of in-service welding onto active pipeline. Microstructure and hardness of welded joint have a vital effect on hydrogen induced cracking. The microstructure and hardness of welded joint of XTO pipeline steel were studied using simulation in-service welding device. The results show that the main microstructures of in-service welded seam are grain boundary ferrite , intracrystalline acicular ferrite , as well as small amount of widmanztatten structure. The main microstructures of coarse grain heat-affected zone （CGHAZ） are coarse granular bainite, lath ferrite and martensite. Metastable phases such as martensite and lath ferrite are found in CGHAZ because of the too quick cooling velocity a＇nd the hardness of the CGHAZ is high.

Study on M/A islands in pipeline steel X70

The fine structure of M/A islands in pipeline steel X70 has been studied by transmission electron microscope (TEM). It is shown that the M/A islands are about 1-2 μm in size and distribute at the grain boundary of irregular massive ferrite or acicular ferrite in the microstructure of the steel undergoing TMCP (thermo-mechanical controlled processing). The analysis of diffraction contrast shows that the M/A islands consist of retained austenite and some martensite lamellae different in size and orientation. The microt winning and midrib exist in the lamella of lenticular martensite, which exhibit the typical character of high-carbon martensite. The influences of TMCP parameters on M/A islands have been studied carefully. With the increase of the cooling speed, the amount of M/A islands decrease slightly and the morphology of M/A islands changes to thin dispersive short bars from thick irregular long strips.

Influence of cooling conditions on X70 pipeline steel in-service welding HAZ

The chamber device was designed and set up to simulate the in-service welding. The results show ： the t8/5 , t8/3 and inner wall peak temperature Tp decrease with the cooling rate increases. The welding energy is carried off by flowing medium, the cooling rate increases, and many unbalanced microstructures such as granular bainite, martensite and M-A generate ; it worsens the properties of HAZ. Under air-cooling, the cooling rate is slow, the austenite grain grows obviously, the lath ferrite crosses the whole austenite, and it causes the hardness value is also big. The change of HAZ width is not obvious with the increase of cooling rate; and burn-through is not susceptible to the cooling rate. The quench microstructures increase and the hydrogen does not outflow from the HAZ easily when increase the cooling rate, so the susceptibility of hydrogen cracking increases.

Study of microstructures and properties for girth weldingof domestic X70 pipeline steels

With the development of domestic pipeline steels, it is necessary to develop suitable welding technology which can improve the properties of the welded pipeline. In this paper, the microstructures and mechanical properties of domestic XTO pipeline steels and welded joints are discussed. The welding consumables of BOHLER E6010 and HOBART 81N1 are matched for girth welding. The following characteristics in heat-affected zone（ HAZ） are indicated that microstructures of intercritical HAZ（ ICHAZ） is finer and more uniform, the grain sizes of fine-grain HAZ （ FGHAZ） and subcritical HAZ （ SCHAZ） are smaller than that of coarse-grain HAZ（ CGHAZ）. The hardness, tensile strength and toughness of welded joints come up to the standard. The micrographs of impact specimens in welded joints are cleavage, quasi-cleavage and dimple which shows there is typical ductile rupture.

Development of S11306+SA516Gr70 roll-bonded clad steel plate for pressure vessels

To meet the demand of the pressure vessel industry, Baosteel has developed an S11306 ＋ SA516Gr70 roll-bonded clad steel plate. Comprehensive inspections of the composition, microstructure, and properties are performed to systematically evaluate the steel plate in normalized state and normalized ＋ stress relieved state. The results show the cladding interface of the Sl1306 ＋ SA516Gr70 roll-bonded clad steel plate has high shear strength, and the base metal has good mechanical properties. The performance is fully consistent with the technical requirements of the roll-bonded clad steel plate for pressure vessels.

不同模拟焊后热处理制度对SA-516Gr.70钢组织及力学性能的影响

分析了不同模拟焊后热处理制度对SA-516Gr.70钢的显微组织和力学性能的影响。结果表明,保温时间相同,随着模拟焊后热处理温度提高,SA-516Gr.70钢强度降低30~40 MPa,-15℃下冲击吸收能量降低100 J以上,主要原因在于,随着模拟焊后热处理温度的升高,钢中晶粒尺寸长大、个别第二相粒子粗化。

铅浴淬火工艺对70钢丝组织和性能的影响

研究了900℃均热+500℃铅浴54 s空冷处理对70钢(0.67%～0.75%C)Φ5.5 mm热轧钢丝经38.9%压缩率拉拔的冷拔钢丝组织和性能的影响。结果表明,500℃铅浴等温处理,该钢过冷奥氏体转变的孕育和转变时间最短,该钢丝抗拉强度提高了21.4%,伸长率提高9.5%,为随后通过细拉工艺进一步提高钢丝的综合力学性能建立了基础。

SCC of X70 and Its Deteriorated Microstructure in Simulated Acid Soil Environment

In order to study the stress corrosion cracking （SCC） of X70 pipeline steel and its weld joint in acid soil environment of southeast of China, two simulating methods were used here. The one was to obtain the bad microstructures in heat affected zone by annealing at 1300℃ for 10 min and air cooling to room temperature, the other was to get a series of simulating solutions of the acid soil environment. SCC susceptibilities of X70 pipeline steels＇before and after being normalized in the simulated solutions were studied by slow strain rate test （SSRT） and microstructural observation of fracture areas. Potentiodynamic polarization curves were used to study the electrochemical behaviour of different microstructures. SCC does occur to both the as-received material and normalized microstructure after heat treatment as the polarization potential decreased. Hydrogen embrittlement （HE） is indicated occurring to all tested materials at -850 mV （vs SCE） and -1200 mV（vs SCE）. The SCC mechanisms are different within varying potential range. Anodic dissolution is the key cause as polarization potential higher than null current potential, and HE will play a more important role as polarization potential lower than the null current potential.

高碳硬线70钢的生产实践

介绍了武钢集团昆明钢铁股份有限公司开发生产高碳硬线70钢热轧盘条的工艺,分析了其组织、成分、性能,总结了工艺操作要点,为开发高碳钢提供了依据。

HG70高强度钢与HS-70焊丝的焊接分析

研究了HG70钢与HS-70焊丝焊接后焊缝的焊接结合性能和使用性能,在拘束焊接条件下,采用HS-70型焊丝,试验钢板的焊接接头的拉伸、硬度和冲击韧性试验结果表明:HG70钢和HS-70焊丝的焊接接头具有较低的裂纹敏感性,结合性能良好,其焊接接头具有优良的力学性能,具有了优良的焊接匹配性。

70钢扁丝真空球化退火工艺研究

本文研究了70钢扁丝球化退火的一种新工艺——真空球化退火,介绍了真空球化退火的设备及其特性,分析和讨论了扁丝退火质量的影响因素,并得出了最佳工艺参数。