X90管线钢的抗氢致开裂性能

目前有关X90管线钢抗H2S性能的研究报道较少.为此,采用NACE TM 0284-2003方法对X90和X80管线钢进行氢致开裂(HIC)试验以对比研究其抗HIC性能,论述了氢致开裂的机理,并分析了X90管线钢的微观组织和化学成分对氢致开裂的影响.结果表明:X90管线钢的抗HIC性能较X80管线钢差,X90钢的热影响区与焊缝区的抗HIC性能比母材好;X90钢易产生Mn的偏析,且C会加剧其偏析,同时Cr的碳化物析出使氢鼓泡易在此处产生,2种因素均导致X90钢的抗HIC性能降低;适当控制微观组织比例,降低C含量,在保证提高X90管线钢强度的同时,严格控制Mn和Cr的含量,可以提高其抗HIC性能.     

厚规格X80管线钢低温断裂行为研究EI北大核心CSCD

采用金相显微镜和扫描电子显微镜对厚规格X80管线钢微观组织和-25℃落锤撕裂试验断口形貌进行观察,研究了X80管线钢的断裂行为与组织之间的关系。研究发现,钢板从表面到厚度中心,针状铁素体体积分数逐渐降低,并出现较多的粒状贝氏体、多边形和准多边形铁素体。具有较高针状铁素体体积分数的钢板,其落锤撕裂剪切面积也越高,多边形和准多边形铁素体以及大尺寸MA岛的存在能够导致解理断裂的产生,不利于钢板的低温断裂韧性。在裂纹扩展的过程中,主裂纹附近组织出现变形,导致脆硬性的MA岛周围出现微孔,微孔与微孔之间随着组织变形相互连接而形成微裂纹。二次裂纹通常在针状铁素体周围出现转折或停滞,说明针状铁素体有利于阻碍裂纹的扩展,提高钢板的断裂韧性。     

厚规格X80管线钢低温断裂行为研究

采用金相显微镜和扫描电子显微镜对厚规格X80管线钢微观组织和-25℃落锤撕裂试验断口形貌进行观察,研究了X80管线钢的断裂行为与组织之间的关系。研究发现,钢板从表面到厚度中心,针状铁素体体积分数逐渐降低,并出现较多的粒状贝氏体、多边形和准多边形铁素体。具有较高针状铁素体体积分数的钢板,其落锤撕裂剪切面积也越高,多边形和准多边形铁素体以及大尺寸MA岛的存在能够导致解理断裂的产生,不利于钢板的低温断裂韧性。在裂纹扩展的过程中,主裂纹附近组织出现变形,导致脆硬性的MA岛周围出现微孔,微孔与微孔之间随着组织变形相互连接而形成微裂纹。二次裂纹通常在针状铁素体周围出现转折或停滞,说明针状铁素体有利于阻碍裂纹的扩展,提高钢板的断裂韧性。     

API X52管线钢在饱和硫化氢气田水溶液中的氢渗透与氢致开裂行为

天然气输送管道氢致开裂问题日益突出,而API X52管线钢在气田模拟水溶液中氢渗透和氢致开裂的研究较少。模拟了饱和硫化氢某气田水溶液,采用电化学和恒载荷拉伸试验方法,测定了API X52管线钢在不同充氢电流密度下的氢扩散系数、可扩散氢浓度(ω0)及管线钢氢致开裂临界可扩散氢浓度(ωHIC)。结果表明:API X52管线钢可扩散氢浓度(ω0)与充氢电流密度呈线性关系,即ω0=0.99+0.07J;其恒载荷下开裂临界可扩散氢浓度的对数值(lnωHIC)随拉应力(σ)呈线性下降,即σ=475-450lnωHIC。     

厚规格多相组织X80管线钢组织控制与断裂行为研究

目的 研究厚规格X80管线钢的力学性能及断裂行为与微观组织之间的关系。方法 通过硬度实验、拉伸实验、夏比冲击实验及落锤撕裂实验（DWTT）,研究X80管线钢力学性能,利用OM和SEM观察微观组织和断口形貌。结果 多边形铁素体（PF）、粒状贝氏体（GB）、准多边形铁素体（QPF）、针状铁素体（AF）和贝氏体铁素体（BF）多相组织的结合保证了钢板优异的强韧性。在落锤撕裂实验裂纹扩展过程中,裂纹扩展至QPF时呈平直扩展,裂纹扩展至GB时,较为曲折迂回,说明GB能有效阻碍裂纹扩展。细小的马氏体-奥氏体（M-A）组元和AF同样能够有效阻碍裂纹的扩展。结论 研究结果可为厚规格多相组织X80级管线钢的服役使用提供理论依据。     

管线钢中的硫化夹杂物与氢致开裂

研究了5种材料在NACE溶液和人工海水溶液中的氢致开裂（Hydrogen-induced cracking,HIC）行为，结果表明：当材料中存在硫化夹杂物时，氢致开裂敏感性增大。为了提高材料的抗氢致开裂性能，应控制其含量与形态。对于更恶劣的腐蚀环境（酸性油气），管线钢抗HIC的评价应采用NACE标准进行氢致诱导开裂试验。     

X52管线钢抗氢致开裂试验裂纹成因分析

针对某段时期出现的X52管线钢产品经抗阶梯型破裂试验后,试样有明显阶梯裂纹,产品检验不合格的问题,对不合格批次的试样进行化学成分、炼钢工艺以及显微组织等方面的分析,分析了该抗硫化氢腐蚀X52管线钢氢致开裂的原因。结果表明:开裂批次试样的钙硫含量比值偏低,导致出现夹杂物偏聚和中心偏析,且夹杂物呈线状分布,是造成该管线钢产品抗氢致开裂试验开裂的主要原因。最后对X52管线钢的生产控制要点提出了相应建议,以提高其抗硫化氢腐蚀的能力。     

超快冷工艺对高铌X80管线钢抗腐蚀性能的影响

依据NACE标准,研究了采用新型超快速冷却工艺生产的X80管线钢抗硫化物应力腐蚀开裂(SSCC)、抗氢致开裂(HIC)和抗CO2等腐蚀的情况.SSCC腐蚀实验表明,产生开裂的临界应力值在65 ％σs (390MPa)左右,超过此临界值,试样的腐蚀敏感性较高,抗腐蚀能力较差,在95％σs加载水平下,应力敏感性极高.HIC腐蚀实验表明,裂纹敏感百分比、裂纹长度百分比和裂纹厚度百分比均为零.抗CO2腐蚀实验表明,在CO2压力为0.1MPa条件下,平均腐蚀速率为0.6843mm/a.研究表明采用新型超快冷工艺生产的X80管线钢具有优良的抗SSCC腐蚀性能、抗HIC腐蚀性能和抗CO2腐蚀性能.     

抗酸钢中产生氢致裂纹与氢鼓包的原因分析

将生产的抗酸管线钢按照NACE TM0284-2003标准进行硫化氢腐蚀试验,通过光学显微镜、扫描电镜对酸性腐蚀后试样中的氢致裂纹进行宏观与微观观察,发现氢致裂纹呈现多种形态,有阶梯状氢致裂纹、单个裂纹、Y字形裂纹等;对试样表面氢鼓包进行微观观察,发现鼓包心部实际也是氢致裂纹。观察发现:不论是氢致裂纹还是氢鼓包,裂纹均起源于偏析带状、氧化物夹杂以及粗大晶粒的晶界处。最终通过工艺控制,得到了良好的带状组织,保证了抗酸管线的批量生产。     

显微组织对贝氏体钢筋氢脆敏感性的影响

通过电化学充氢、慢拉伸实验并结合XRD、SEM、TEM和EBSD等显微组织表征方法,研究了显微组织对两种不同强度级别贝氏体钢筋氢脆敏感性的影响。结果表明:PSB1080钢筋强度高,但氢脆敏感性却低于PSB830钢;PSB830钢筋的组织分布不均匀,马氏体块尺寸差异较大,马氏体中高密度的位错为可逆氢陷阱,充氢之后氢分布不均匀,在拉伸的过程中,氢原子随位错迁移,扩散富集至裂纹尖端,裂纹在脆性大的马氏体和强度低的铁素体中扩展迅速,氢脆敏感性大。PSB1080钢筋板条间的残留奥氏体为不可逆氢陷阱,阻碍了氢原子的扩散富集,此外其组织的均匀性使钢中氢的分布也相对均匀,氢脆敏感性小。亚微米、纳米级的残留奥氏体同时具有良好的机械稳定性和化学稳定性,缓解了应力集中,阻碍了裂纹的扩展。     

Relationship between microstructure and hydrogen induced cracking behavior in a low alloy pipeline steel

Hydrogen induced cracking(HIC) behaviors of a high strength pipeline steel with three different microstructures, granular bainite lath bainite(GB + LB), granular bainite acicular ferrite(GB + AF), and quasi-polygonal ferrite(QF), were studied by using corrosion experiment based on standard NACE TM0284. The HIC experiment was conducted in hydrogen sulfide(H_2S)-saturated solution. The experimental results show that the steel with GB + AF and QF microstructure present excellent corrosion resistance to HIC, whereas the phases of bainite lath and martensite/austenite in LB + GB microstructure are responsible for poor corrosion resistance. Compared with ferrite phase, the bainite microstructure exhibits higher strength and crack susceptibility of HIC. The AF + GB microstructure is believed to have the best combination of mechanical properties and resistance to HIC among the designed steels.     

Hydrogen-induced cracking susceptibility and hydrogen trapping efficiency of different microstructure X80 pipeline steel

The hydrogen-induced cracking (HIC) susceptibility of the X80 steel in H₂S environment and its heated-treatment microstructure was evaluated. The field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM) and energy dispersive spectroscopy (EDS) were employed to study the morphology and chemical composition of the inclusions, precipitates and HIC cracks in the X80 steel. The hydrogen trapping efficiency was investigated by measuring the permeability (J _∞L) and the apparent diffusivity (D _app). The results showed that heat-treated specimens had lower trapping efficiency, but were more susceptible to HIC. Most of the HIC cracks initiated from the inclusions rich in Mn, Al, Ca, and Ti, and propagated transgranularly in the original and air cooled specimens, but mainly intergranularly in water quenched specimens.     

Effect of bainitic microstructure on the susceptibility of pipeline steels to hydrogen induced cracking

Hydrogen induced cracking (HIC) of API X80 and API X100 pipeline steels have been investigated in high pH carbonate-bicarbonate environment using slow strain rate testing (SSRT) method. It has been found that while both steels are highly susceptible to HIC, and diffusible hydrogen content is higher in API X80 than in API X100, the later steel is more vulnerable than the former at high (more negative) cathodic potential. This higher susceptibility can be primarily attributed to the combined effect of (1) separation of bainitic lath boundaries due to hydrogen trapping in these locations, (2) mobile hydrogen, and (3) stress. The charging-discharging experiments followed by SSRT experiments in air suggest that, the cracks that appeared due to lath boundary separation did not cause the reduction of ductility by themselves, rather it was the diffusible hydrogen that forced these cracks to propagate and, ruptured the steel with very low percent reduction of area (%RA). Despite the fact that the mobile hydrogen content plays a key role in causing the embrittlement, the large number of cracks in API X100 steel, resulting from the bainitic lath boundary separation at high cathodic potential, superseded the effect of higher diffusible hydrogen content in API X80 steel. The general conclusion is that bainitic lath type microstructure is more vulnerable to HIC at high cathodic potential than the ferritic/granular bainitic ones. It has been also found that applying cathodic protection can lead to excessive hydrogen embrittlement in both of the abovementioned steels in high pH carbonate-bicarbonate environment and, therefore, efforts need to be invested in developing nobler (more positive corrosion potential) and better HIC resistant steels.     

管线用钢显微组织对氢致裂纹影响的研究

选用了四种不同显微组织的国产同牌号管线用钢,根据美国腐蚀工程师协会标准NACETM0284-2003,对其进行氢致开裂实验,并用光学显微镜和扫描电镜对其断面组织进行了观察,分析其显微组织对抗氢致裂纹性能的影响。认为,带状组织以及组织不均匀性是引起材料抗氢致裂纹性能下降的主要因素,但这两种因素引起开裂的方式和机理不同。同时发现晶粒度大小对该材料抗氢致裂纹性能没有明显影响。     

TEM研究氢对双相组织的影响

用电镜观察了充氢后双相钢的亚结构,探讨了氢致双相钢机械性能下降的原因。观察表明:充氢后,F相中位错增殖,最后形成胞状亚结构;M相中位错组态变化不明显,但随充氢量增加,裂纹将在M板条界萌生和扩展,有时也横穿M板条;F/M相界充氢后出现宽化现象,并向F相一侧增殖位错,进而界面起裂。M量越多,则此现象越明显。M相与F/M相界起裂对充氢电流密度比充氢时间更为敏感。M相及F/M相界充氢后损伤严重,导致双相钢塑性下降,成为宏观拉伸时易于裂纹萌生和扩展的薄弱部位。     

Experimental Investigation on the Performance of Armour Grade Q&T Steel Joints Fabricated by Flux Cored Arc Welding with Low Hydrogen Ferritic Consumables

Quenched and Tempered(Q&T)steels are widely used in the construction of military vehicles due to its high strength to weight ratio and high hardness.These steels are prone to hydrogen induced cracking(HIC) and softening in the heat affected zone(HAZ)after welding.The use of austenitic stainless steel(ASS) consumables to weld the above steel was the only available remedy to avoid HIC because of higher solubility for hydrogen in austenitic phase.Recent studies revealed that low hydrogen ferritic(LHF)steel con...     

A focus on different factors affecting hydrogen induced cracking in oil and natural gas pipeline steel

In this research, hydrogen induced cracking (HIC) behavior of an API X70 pipeline steel has been studied. In order to create HIC cracks, an electrochemical hydrogen charging experiment was carried out on X70 steel by using 0.2 M sulfuric acid and 3 g/l ammonium thiocyanate for 8 h. Moreover, SEM, EDS and EBSD techniques were used to characterize the as-received (AR) steel and investigate the different aspects of HIC phenomenon as well. The results showed that the inclusions and precipitates which play a key role in HIC phenomenon have been distributed randomly through the cross-section of tested steel. However, the concentration of them was higher at the center of cross-section than other areas. All HIC cracks initiated and propagated through the center of thickness where center segregation of elements has occurred. It is also observed that HIC cracks were initiated from several special types of inclusions and precipitates such as manganese sulphide and carbonitride precipitates. EBSD results showed that the dominant local texture of center of thickness in RD-TD plane was {001}//ND and {111}//ND. Moreover, HIC cracks propagate through differently oriented grains where the local texture is random.     

Effects of acicular ferrite on charpy impact properties in heat affected zones of oxide-containing API X80 linepipe steels

This study was concerned with effects of acicular ferrite on Charpy impact properties in heat affected zones (HAZs) of two API X80 linepipe steels containing oxides. In the one steel, Mg and O₂ were additionally added to form a larger amount of oxides than the other steel, which was a conventional X80 steel containing a considerable amount of Al and Ti. Various HAZ microstructures were obtained by conducting HAZ simulation tests under different heat inputs of 35 kJ cm⁻¹ and 60 kJ cm⁻¹. Oxides present in the API X80 linepipe steels were complex oxides whose average size was 1-2 μm, and the number of oxides increased with increasing amount of Mg and O₂. The volume fraction of acicular ferrite present in the steel HAZs increased with increasing number of oxides, and decreased with increasing heat input. When the volume fraction of acicular in the HAZ was higher than 20%, Charpy impact energy at −20 °C was higher than 100 J as the ductile fracture mode was dominant. Particularly in the steel HAZs having a larger amount of oxides, Charpy impact properties were excellent because oxides worked as nucleation sites of acicular ferrite during welding. Charpy impact properties of the HAZs could be well correlated with the volume fraction of acicular ferrite and number of oxides under different heat input conditions.     

应力三轴度对淬火态硼钢氢脆敏感性的影响

对硼钢进行电化学充氢和低应变率拉伸,分别画出了纯剪切、单向拉伸及近似平面应变状态下淬火态硼钢充氢前后的应力-应变曲线,并基于等效塑性应变量化了硼钢的氢脆敏感性,研究了应力三轴度对淬火态硼钢的力学性能和氢脆敏感性的影响。用SEM及EBSD表征试样断口的微观组织,根据淬火态硼钢充氢前后断裂模式的变化分析了硼钢在不同应力状态下的氢脆机理。结果表明,淬火态硼钢在剪应力状态下的氢脆机理与拉伸应力状态显著不同,使其氢脆敏感性比拉伸应力状态显著降低。     

马钢X80管线钢的开发

本文对马钢生产的XSO管线钢的力学性能和显微组织进行了研究。通过对X80管线钢试样进行了力学性能测试和显微组织观察。结果表明,马钢生产的X80管线钢显微组织为针状铁素体为主,力学性能优良、均匀,屈服和抗拉强度分别在565MPa和660MPa以上;低温冲击韧性优异,满足了西气东输二线标准对X80管线钢的质量要求。