焊缝中氢的扩散行为及影响因素

 扩散氢会在焊缝中引起氢脆、延迟裂纹等,导致结构产生低应力断裂。为了研究氢的扩散行为,采用水银法和气相色谱法测定了逸出的扩散氢量,并采用真空抽取法测试了不同温度下残余氢的释放量。试验表明,扩散氢量不受焊道数量的影响,它的逸出时间随焊道数的增多而增长,逸出速度随合金含量的增多而降低。随着焊后冷速的降低,冷却过程中逸出的氢增多,测定出的扩散氢量减少;测氢试样在100~200℃保温时,逸出氢的总量变化不大,但逸出时间随温度的升高而明显缩短。残余氢量与扩散氢量的多少无关,它与焊缝的含氧量、组织和硬度等有关系。     

水银法测定焊缝扩散氢的影响因素

采用水银法研究了环境湿度、烘干温度、保护气体露点等测试条件对焊缝扩散氢含量的影响,分析了我国碳钢及低合金风焊条中的扩散氢含量,并且与国外焊条的扩散含量进行了对经     

金属中氢的分析技术进展

介绍了金属中氢的存在状态及其对材料的影响。总结了近年来金属中氢的检测方法及目前实验室常用的测氢设备以及分析方法。除常规取样、实验室检测方法外,由于工艺的要求,在线检测手段发展越来越快。钢液、铝液中氢的在线测量技术越来越多地应用到实际生产中,并已经研制出可在线同时检测钢液中氧、氮、氢3种气体元素的检测设备。熔敷金属中氢的检测已经逐渐由热导法替代了传统的水银法和甘油法。     

金属薄板的氢扩散试验

 金属板材氢扩散计算试验选用材料为40Cr及4Cr13轧制板材,运用电化学方法进行氢扩散试验。通过对薄板进行表面处理,且进行预镀镍及镀镍的处理,最终进行氢扩散系数的测定试验,并根据氢扩散试验得到的数据参数进行氢扩散系数的计算,最终得到两种钢的氢扩散系数。氢扩散计算试验适用于各种不同金属材料氢扩散系数的测定,为检测钢在使用过程中氢的积累提供基本参数及计算依据,且对于材料中氢的定量计算起到至关重要的作用。通过对两种材料成分及扩散系数的比较,进一步研究金属中合金元素质量分数对氢在金属中扩散的影响作用。     

钢中钛与氢的作用

利用电化学氢渗透技术研究了热轧碳钢和含钛钢的氢渗透,得出如下结论:①当少量钛在钢中以弥散TiC相分布时,氢陷阱能为20.0kJ/mol,远远大于碳钢的氢陷阱能;②当少量钛在碳钢中以弥散TiC形式存在时,能大大增加氢扩散激活能,因此氢扩散系数明显减小;③在某些应用领域,含TiC沉淀相的低合金钢是较好的抗氢材料。     

高强钢焊接氢致裂纹断口微观形貌的研究及模式化

采用插销实验和扫描电镜观察方法详细研究了焊缝扩散氢含量和非金属夹杂物对10Ni5CrMoV低碳中合金高强钢焊接热影响区氢致裂纹断口微观形貌的影响。结果得出,扩散氢含量是影响氢致裂纹断口微观形貌的主要因素,在插销净截面应力300～800MPa的范围内,加载应力对延迟扩展区断口形貌无明显影响。钢中硫化物夹杂的增加使扩展区形貌从IG_(HE)向MVC_(HE)转变,而含氧化物夹杂钢则转为QC_(HE)。作者提出了一个新的适于解释氢致裂纹扩展第Ⅱ阶段断口微观形貌的竞争开裂模式,从而从氢致裂纹本质机制上圆满说明了上述实验结果。     

利用HTDS对钢材料中氢扩散行为的分析研究

介绍了利用升温测氢装置(HTDS)进行的钢材料中扩散氢及非扩散氢定量区分与检测的方法,绘制出不同温度下氢扩散速率曲线图,找出最佳扩散温度区间。通过对管线钢服役中失效样品中扩散氢和不易扩散氢的测定,为失效分析提供有力判据。     

利用氢扩散诱导相变进行钛的低温精密焊接

正在钛制精密机械及装置的制造中,要求开发并建立一种无变形且尺寸精密的焊接技术。由于电弧焊、激光焊等焊接技术需要将钛熔融,很难用于精密焊接,而扩散焊等固相焊接是一种可望用于钛的精密焊接方法。这种固相焊接通常要在钛的β相变     

固态金属中质点扩散过程理论及方法

扩散是最重要的传质方式之一，扩散过程对于很多冶金或材料的制备过程有决定性作用。简述了固态金属中质点扩散过程中的宏观理论和微观机制，介绍了扩散过程的研究方法。     

Neutron imaging of hydrogen in iron and steel

Abstract

Neutron radiography and tomography have been used for a time resolved in situ analysis and a 3D mapping of hydrogen diffusion in iron and steel. Samples were electrochemically charged with hydrogen and afterwards neutron transmission images were taken. Hydrogen diffusion coefficients in duplex stainless steel were determined at 623 K by measuring and comparing the sample’s mean intensity with a hydrogen-free reference sample and subsequent normalisation to standards with known hydrogen content. In technical iron and in supermartensitic stainless steel the hydrogen distributions have been investigated. The radiographic images in iron show blisters, cracks and the distribution of molecular hydrogen inside cracks. The analysis of the diffusion behaviour of hydrogen out of a blister illustrates the capabilities of the method with respect to time and spatial resolution. The neutron tomography of supermartensitic tensile stressed samples illustrates the capability to visualise hydrogen distributions three-dimensionally.     

LF炉冶炼过程钢中w（H）控制的实践

在2008年重钢的探伤钢CDQ207生产中,钢中氢成为影响钢板探伤合格率的主要因素之一。通过加强合金烘烤、控制精炼环节原辅料水分等技术管理措施,强化LF过程w（H）控制,充分发挥LF精炼功能,确保了大部分炉次钢中w（H）控制在合理范围内。2009年1-10月探伤钢探伤综量合格率为95.93%,较好地完成了项目指标。     

Rate controlling processes for crack growth in hydrogen sulfide for an alsl 4340 steel

Parallel fracture mechanics and surface chemistry studies were carried out to develop further understanding of environment assisted subcritical crack growth in high strength steels. The kinetics of crack growth for an AISI 4340 steel (tempered at 477 K) in high purity hydrogen sulfide have been determined as a function of pressure at room temperature and as a function of temperature at hydrogen sulfide pressures of 0.133 and 2.66 kPa. The kinetics for the reactions of hydrogen sulfide with this steel and the extent of reactions were also determined. Two rate controlling processes have been identified. At the lower pressure, the rate of crack growth varies according to T^1/2 and is controlled by the rate of transport of hydrogen sulfide to the crack tip. At the higher pressure, crack growth is controlled by the rate of diffusion of hydrogen into the steel ahead of the crack tip and exhibits an apparent activation energy of about 5 kJ/mol. Embrittlement results from hydrogen that is produced by the reactions of hydrogen sulfide with the steel. These reactions are extremely rapid and are limited in extent, leading to the formation of one to two layers of “sulfide” on the fracture surfaces. The crack growth results are discussed in terms of measured reaction kinetics and published data on diffusion, and in relation to models for transport- and diffusion-controlled crack growth. Formerly with Lehigh University, Bethlehem, PA     

Continuous reduction of the oxide scale of hot-rolled steel strip in hydrogen

The continuous reduction in the oxide scale of hot-rolled steel strip in H₂–N₂ atmosphere was simulated in laboratory. Scale specimens were reduced in 20% H₂–N₂ or 50% H₂–N₂ atmosphere. The sample weight losses were measured after soaking at 550, 700 and 800°C. In both atmospheres, specimen reduced at 700°C showed the minimum weight loss after soaking for 240?s. At 700 and 800°C, higher hydrogen concentration accelerated the reaction in the beginning of soaking, but had little effect once the dense-reduced iron layer formed. While at 550°C, the reduced iron kept growing in porous structure and the weight loss rate increased significantly in higher H₂ concentration.     

Structure-property correlation of submerged-arc and gas-metal-arc weldments in HY-100 steel

Structure-property relationships of two HY-100 steel weldments prepared by submerged arc (SAW) and gas metal arc (GMAW) welding processes using identical heat input (2.2 kJ mm^-1) have been studied. It has been found that submerged arc welded (SAW) HY-100 steel weldments have a lower weld toughness than welds produced by the gas metal arc welding (GMAW) process. Optical, scanning, and transmission electron microscopy were used in conjunction with microhardness traverses to characterize and compare the various microconstituents that are present in the last weld pass of both weldments. TEM examination revealed the presence of coarse upper bainite, B-II bainite, and carbides in a highly dislocated ferrite matrix as well as in ferrite laths in the SAW weldment, while the GMAW weldment exhibited a typical fine low carbon lath martensite, autotempered martensite, and mixed B-II and B-III bainites which occasionally contained small regions of twinned martensite. The measured cooling rate in the SAW was found to be about 40 pct slower than that in GMAW. It was also found in the SAW that the weld metal inclusion number density was about 25 pct greater than that in GMAW. Micro-hardness traverses exhibited significantly lower hardness (about 50 HV) in the SAW weldment compared with GMAW, but the tempered weld metal microhardness in both the weldments was measured about the same, at 250 HV. The ductile-to-brittle transition temperature (DBTT) of both weldments was determined by Charpy impact test. Based on an average energy criterion, the DBTT of the SAW weldment was 323 K (50 °C) higher than that of the GMAW weldment. This difference in fracture resistance is due to the different weld metal microstructures. The different microstructures most probably result from differences in cooling rate subsequent to welding; however, the SAW weld also has a higher inclusion number density which could promote a higher transformation temperature for the austenite. Formerly Adjunct Research Professor with the Materials Engineering Group, Naval Postgraduate School Formerly Graduate Student at NPS     

Structure-property correlation of submerged-arc and gas-metal-arc weldments in HY-100 steel

Metallurgical and Materials Transactions A - Structure-property relationships of two HY-100 steel weldments prepared by submerged arc (SAW) and gas metal arc (GMAW) welding processes using...     

Structure-property correlation of submerged-arc and gas-metal-arc weldments in HY-100 steel

Structure-property relationships of two HY-100 steel weldments prepared by submerged arc (SAW) and gas metal arc (GMAW) welding processes using identical heat input (2.2 kJ mm^-1) have been studied. It has been found that submerged arc welded (SAW) HY-100 steel weldments have a lower weld toughness than welds produced by the gas metal arc welding (GMAW) process. Optical, scanning, and transmission electron microscopy were used in conjunction with microhardness traverses to characterize and compare the various microconstituents that are present in the last weld pass of both weldments. TEM examination revealed the presence of coarse upper bainite, B-II bainite, and carbides in a highly dislocated ferrite matrix as well as in ferrite laths in the SAW weldment, while the GMAW weldment exhibited a typical fine low carbon lath martensite, autotempered martensite, and mixed B-II and B-III bainites which occasionally contained small regions of twinned martensite. The measured cooling rate in the SAW was found to be about 40 pct slower than that in GMAW. It was also found in the SAW that the weld metal inclusion number density was about 25 pct greater than that in GMAW. Micro-hardness traverses exhibited significantly lower hardness (about 50 HV) in the SAW weldment compared with GMAW, but the tempered weld metal microhardness in both the weldments was measured about the same, at 250 HV. The ductile-to-brittle transition temperature (DBTT) of both weldments was determined by Charpy impact test. Based on an average energy criterion, the DBTT of the SAW weldment was 323 K (50 °C) higher than that of the GMAW weldment. This difference in fracture resistance is due to the different weld metal microstructures. The different microstructures most probably result from differences in cooling rate subsequent to welding; however, the SAW weld also has a higher inclusion number density which could promote a higher transformation temperature for the austenite.     

Relevance of high-temperature oxidation in life assessment and microstructural degradation of Cr-Mo steel weldments

Measurement of the thickness of oxide scales that develop over high-temperature components has found an innovative application in life assessment of steam generation and handling systems. The present study is an investigation of the high-temperature corrosion and scale thickness across the weldments of a “chromium-molybdenum” steel, and reviews its possible relevance to the life assessment of the welded high-temperature components by scale thickness measurement. Results are presented of the recent investigations on the combined roles of the oxidizing environment and secondary carbide precipitation on the extent of void formation in the microstructurally different regions of weldments of the chromium-molybdenum steel. Specimens of the weld metal, heat-affected zone (HAZ), and base metal of a 2.25Cr-1Mo steel weldment were oxidized in steam. Extensive internal oxidation and oxidation-induced void formation (with a much greater intensity in the case of the HAZ) is discussed. The greater intensity of oxidation-induced void formation in the HAZ may facilitate preferential cracking in this region of the weldments and, hence, is proposed to be an important parameter in the context of the recently developed codes for life assessment of aging high-temperature components.     

Model for controlling processes in the ladle treatment of steel

In Russia, the Bardin Central Research Institute of Metallurgy (TsNIIchermet) has used results obtained from many years of basic research to construct physicochemical models of the processes of deoxidizing, desulfurizing, alloying, and finishing steel in out-of-furnace treatments in accordance with the main chemical reactions that take place. Construction of the models has in turn made it possible to develop a series of software applications designed to solve practical problems that arise in controlling the processes which occur in ladle metallurgy.     

A model for calculating solubility of hydrogen in steel

Abstract

A model has been developed for calculating the hydrogen solubility in steel on the basis of composition (S, Ti, B) and grain size, with the objective of improving the control of hydrogen content in steel products. The effects of sulphur are in agreement with previous experience, but complex effects have been observed with variations in titanium and boron contents. The model defines trap sites in crystallographic terms for the various phases and features of interest. Segregation effects have been studied using laboratory casts and with composites using continuously cast slab from which the natural segregation has been removed. Segregated regions absorb large amounts of hydrogen, but the crack threshold is reduced such that the composites have much lower safe hydrogen levels than unsegregated material. The effects of assumptions in the model on number of traps and binding energies are considered.