Improving creep strength of the fine-grained heat-affected zone of novel 9Cr martensitic heat-resistant steel via modified thermo-mechanical treatment

The infamous type Ⅳ failure within the fine-grained heat-affected zone (FGHAZ) in G115 steel weldments seriously threatens the safe operation of ultra-supercritical (USC) power plants.In this work,the traditional thermo-mechanical treatment was modified via the replacement of hot-rolling with cold rolling,i.e.,normalizing,cold rolling,and tempering (NCT),which was developed to improve the creep strength of the FGHAZ in G115 steel weldments.The NCT treatment effectively promoted the dissolution of preformed M_(23)C_(6)particles and relieved the boundary segregation of C and Cr during welding thermal cycling,which accelerated the dispersed reprecipitation of M_(23)C_(6) particles within the fresh reaustenitized grains during post-weld heat treatment.In addition,the precipitation of Cu-rich phases and MX particles was promoted evidently due to the deformation-induced dislocations.As a result,the interacting actions between precipitates,dislocations,and boundaries during creep were reinforced considerably.Following this strategy,the creep rupture life of the FGHAZ in G115 steel weldments can be prolonged by 18.6%,which can further push the application of G115 steel in USC power plants.

Creep property research of new martensite heat-resistant steel G115

G115 steel was jointly developed by China Iron & Steel Research Institute Group Co.,Ltd.and Baosteel for usage in 600-650 ℃ ultrasupercritical boiler tubes.Using a hot extruded G115 tube,creep tests were conducted under a constant stress of 130 MPa and temperatures of 625,650 and 675 ℃.Comparing creep curves under different temperatures,it is observed that the creep performance of a G115 tube is more sensitive to temperature than stress.Steady-state creep rates of creep specimens are significantly increased by enhancing the temperature.A micro-structural analysis of ruptured creep specimens under a stress of 130 MPa and temperatures of 650 ℃ and 675 ℃ was performed;the fracture mechanism of creep specimens under these two temperatures mainly included the appearance of creep holes on the grain boundary and a decrease in the martensite lath density.

Effect of CO_2 on Atmospheric Corrosion of UNS G10190 Steel under Thin Electrolyte Film

The atmospheric corrosion of UNS G10190 steel under a thin electrolyte film in the atmosphere polluted by CO_2, has been studied in the lab using an atmospheric corrosion monitor (ACM) in combination with XRD and SEM observations of the surface of steel. The ACM study indicated that the corrosion rate of the steel increased with increasing carbon dioxide concentration. The XRD and SEM observations showed that no carbonate was found in the corrosion product on the steel surface. The corrosion product consisted of two layers, i. e., inner and outer layer. From the experimental results, it was concluded that CO_2 played an enhancing role in the atmospheric corrosion of UNS G10190 steel. The film of the corrosion product showed slight protection.

Electrolytic surface hardening of steel, cast iron and aluminium-bronze

Electrolytic hardening process was developed in USSR in the 1950s. The process was developed but was not commercially exploited. There is no evidence of work done on this process in India. The author has done this original work applied to different materials like steel, cast iron and aluminum-bronze. This paper gives details of microstructural transformations along with hardness value achieved. There is vital scope for this process to become viable for surface hardening and selective hardening of small components.

Relationship between the Brittlement Susceptibility and H Permeation Current for UNS G11180 Steel in 5% NaCl Solution with H_2S

Sulfide stress corrosion cracking (SSCC) behaviour of UNS G11180 steel in 5% NaCl solution with H2S was studied by slow strain rate tensile test (SSRT), SEM and electrochemical hydro gen permeation technique. The results reveal different cracking mechanism and H permeation current (IH) through UNS G11180 steel plate in different concentration of H2S solution. The susceptibility to SSCC of UNS G11180 Steel in 5% NaCl solution with H2S was evaluated by the permeation current(IH, μA), which depends on the concentration (c×10-6) of H2S by the equation:IH = 8.525 ×c0.7249. lt is proved that the electrochemical H permeation method is a practical way to assess the susceptibility to SSCC.

Effects of Strain Ratio on Fatigue Behavior of G20Mn5QT Cast Steel

Due to traffic and wave actions, cast steel joints are subjected to variable-amplitude fatigue loading, which may cause fatigue problems. The ratio of the minimum strain to the maximum strain(strain ratio)can be employed to analyze the influence of variable-amplitude fatigue both in the elastic and plastic ranges. To evaluate the effect of the strain ratio on G20Mn5 QT cast steel, the fatigue tests of smooth specimens were carried out at the strain ratio of 0.1. The cyclic deformation and the relationships between the strain amplitude, the stress amplitude, the Smith, Watson and Topper(SWT)parameter and fatigue life were studied and compared with those at the strain ratio of-1. Compared with other methods, Basquin formula and Solonberg formula provide reliable and appropriate ranges of S-N curve and fatigue limit at different strain ratios respectively. The SWT parameter can be used to predict the fatigue life at other strain ratios accurately.

Comparative Study on Microstructures of Zincalume Steel(G550)Welded Joint Between Metal Inert Gas and Laser Beam Welding

Zincalume steel(G550)is commonly used in various construction fields because of its high corrosion resistance and good mechanical properties.In recent years,a number of steel companies have massively produced zincalume steel(G550)with large volumes of waste.For the reduction of massive industrial wastes,the zincalume steel(G550)was welded in the lap joint configuration using different welding parameters in the metal inert gas(MIG)welding and laser beam welding(LBW)process in this study.The MIG welding and LBW are more welcomed welding methods due to their high efficiency and low cost.However,they are different as the LBW offers welding speed three to five times faster than MIG welding,while LBW’s heat transfer to workpieces is much less than MIG welding,which can avoid some distortions.The microstructure of zincalume steel(G550)was investigated using scanning electron microscopy(SEM)and the microstructure characterizations of welded specimens were analyzed.The experiment found the columnar dendrites extended under the heat flow direction during the MIG welding and LBW process.Thus,the columnar grains were formed in between the equiaxed zone and fusion zone(FZ)at high heat input and slow cooling rate.Moreover,the grain size of FZ was comparatively smaller than heat affected zone(HAZ)and base metal(BM).

焊接用钢ER70S-G小方坯连铸水口堵塞分析及其控制

w(Ti)为0.12%~0.25%的焊接用钢ER70S-G,采用小方坯连铸生产工艺易发生浸入式水口结瘤问题,水口结瘤物的主要成分是Al_(2)O_(3)、Al_(2)O_(3)·MgO以及TiO_(2)。对冶炼、连铸过程钢水中夹杂物数量、尺寸和成分进行分析,发现精炼后期和中包浇注过程中小尺寸夹杂物的比例较高,说明夹杂物去除和钢水保护浇注效果差。通过采取提高转炉终点C含量、减少铝铁加入量、改变钛合金化方式、密封中间包和水口吹氩等措施,减少钢水中夹杂物,解决了ER70S-G小方坯连铸水口结瘤问题,铸坯质量完全满足下一步轧钢工序的要求。

高钛焊丝钢ER70S-G冶炼工艺优化实践

高钛焊丝钢ER70S-G研发时经常出现水口结瘤、结晶器“结鱼”、铸坯夹渣等问题,尤其是铸坯夹渣导致轧制后盘条表面出现连续性锯齿状结疤缺陷,严重影响盘条表面质量。引起水口结瘤、结晶器“结鱼”的主要原因是存在TiO_(x)、TiN等高熔点非金属夹杂物。通过控制钢水中氧氮含量、使用纯净合金、降低渣中SiO_(2)活度、调整钛合金化时机及温度等手段,解决了水口结瘤、结晶器“结鱼”、铸坯夹渣等问题,将高钛焊丝钢ER70S-G连浇炉数提高至10炉,盘条成材率提高至97%,优化效果显著。

Seismic responses of the steel-strip reinforced soil retaining wall with full-height rigid facing from shaking table test

To investigate the seismic response of the steel-strip reinforced soil retaining wall with fullheight rigid facing in terms of the acceleration in the backfill, dynamic earth pressure in the backfill, the displacements on the facing and the dynamic reinforcement strain distribution under different peak acceleration, a large 1-g shaking table test was performed on a reduced-scale reinforced-earth retaining wall model. It was observed that the acceleration response in non-strip region is greater than that in potential fracture region which is similar with the stability region under small earthquake,while the acceleration response in potential fracture region is greater than that in stability region in middle-upper of the wall under moderately strong earthquakes. The potential failure model of the rigid wall is rotating around the wall toe. It also was discovered that the Fourier spectra produced by the inputting white noises after seismic wave presents double peaks, rather than original single peak, and the frequency of the second peak trends to increase with increasing the PGA(peak ground amplitude) of the excitation which is greater than 0.4 g. Additionally,the non-liner distribution of strip strain along the strips was observed, and the distribution trend was not constant in different row. Soil pressure peak value in stability region is larger than that in potential fracture region. The wall was effective under 0.1 g-0.3 g seismic wave according to the analyses of the facing displacement and relative density. Also, it was discovered that the potential failure surface is corresponds to that in design code, but the area is larger. The results from the study can provide guidance for a more rational design of reinforced earth retaining walls with full-height rigid facing in the earthquake zone.

20g钢高温高压水蒸汽氧化行为研究

通过20 g钢在360℃,18.67 MPa水蒸汽条件下的氧化试验,用静态增重法测定了20 g钢的氧化动力学曲线,其氧化动力学遵循抛物线规律;对氧化膜进行扫描电镜、X射线衍射和能谱分析,结果表明,氧化膜的氧化物类型为Fe3O4,呈颗粒状,而且,Fe3O4中富Fe;氧化物晶粒是通过形核和长大形成的;氧化初期,氧化速度较快,且随后的氧化反应一直在氧化膜的外表层进行,即发生外氧化.

20G钢焊缝区碱脆开裂及Ni-Cr-Fe涂层的防护特性

用四点弯曲恒定载荷法结合慢应变速率拉伸试验，研究了由热浓碱液引起的２０Ｇ钢板焊缝区应力腐蚀开裂行为及Ｎｉ－Ｃｒ－Ｆｅ涂层防护效果和耐蚀特性．结果表明，碱脆最严重的区域发生在焊接接头的近缝区，增加恒定载荷，延长腐蚀时间，都使应力腐蚀拉伸强度σｂｓｃ下降；用应力腐蚀临界时间可衡量材料的应力腐蚀敏感性，据此评价了涂层的防护效果．

20g钢高温裂纹扩展控制参量

在 2 0 g钢高温裂纹扩展实验基础上 ,将裂纹扩展速率da/dt分别与断裂参量静截面应力σnet、应力强度因子K和C 积分相关联 ,以寻求非稳态蠕变扩展阶段 ,高温裂纹扩展速率的恰当控制参量·研究结果表明 :断裂参量静截面应力、应力强度因子与裂纹扩展速率之间的关系受到加载速率和温度影响·在 4 0 0℃和 5 0 0℃下 ,C 积分与裂纹扩展速率均存在着惟一的关系·用C 积分控制 2 0 g钢高温裂纹扩展速率da/dt较合适 ,并建立了 2 0

经长时运行的T91与G102异种钢焊接接头组织与性能分析

对运行了78000h的T91与G102(12Cr2MoWVTiB)异种钢焊接接头进行了组织和性能分析。结果表明,T91母材的显微组织未发生明显变化,G102母材的显微组织发生了回复和再结晶;焊接接头的向火侧抗拉强度及高温短时力学性能均低于母材标准要求值;G102侧及T91侧熔合线冲击值较低;该异种钢焊接接头(低匹配)的薄弱环节在G102及T91侧熔合线以及G102侧热影响区正火区处。

20G和2．25Cr—1Mo钢氢蚀后的疲劳性能

对２０Ｇ和２．２５Ｃｒ－１Ｍｏ钢经不同程度氢蚀后的常规力学性能与疲劳裂纹扩展行为进行了对比研究。并对氢蚀组织变化与裂纹扩展路径进行了显微观察。结果表明，氢蚀使２０Ｇ钢的疲劳裂纹扩展速率明显增大；扩展门槛值在氢蚀起始阶段显著降低，随后又呈增加趋势，对２．２５Ｃｒ－１Ｍｏ钢，由于元素Ｃｒ，Ｍｏ的作用，其氢蚀程度远低于２０Ｇ钢，从而未造成疲劳裂纹扩展速率的明显改变，分析表明，氢蚀后疲劳裂纹扩展门槛值的上升可以归因于曲折开裂路径造成裂纹闭合效应的增加。

G105钻具材料的渗氢行为研究

采用电化学渗氢和硫化物应力腐蚀开裂实验方法,研究了G105钢的钻杆、方钻杆、转换接头的渗氢性能,以及在应力渗氢环境下的断裂行为。结果表明,不同构件G105材料的渗氢电流和氢的渗透通量有明显区别。随充氢电流增大,试样的渗氢电流和氢的渗透通量增大。在不同应力条件下,3种部件的渗氢实验表明,其断裂时间随应力的增大而缩短。

铸钢件缩孔缩松判据G/T^(1/2)临界值的实验研究

对广泛用于铸钢件缩孔、缩松预测判据Ｇ／Ｔ临界值进行了实验研究。在本实验条件下，发现对碳素钢及合金钢试验铸件，Ｇ／Ｔ的临界值基本为一常数，受原始合金成分的影响较小，对铸件形状及浇注温度的影响不敏感。

20g高压锅炉用无缝管的质量控制

简要介绍了 2 0 g高压锅炉用无缝钢管的生产工艺流程 ;对 2 0 g钢成分控制、脱氧控制 ,以及成品管热处理工艺控制进行了分析 ,进而采取了合理的工艺措施 ,从而保证了钢管质量。

热处理对G—X22CrMoV121钢组织和硬度的影响

本文研究了热处理工艺对G-X22CrMoV121耐热钢组织和硬度的影响。结果表明:经1000℃～1050℃淬火空冷即可得到板条马氏体,其硬度随回火温度升高下降缓慢,具有良好的抗回火稳定性。经750℃4h+680℃4h二次回火,布氏硬度HB250左右,可达到较好的机械加工性能和综合机械性能的配合。

管线钢用BGSJ101-G烧结焊剂的研制

从渣系选择、焊剂碱度、焊接热输入、水玻璃模数、Mn/Si及MnO的含量等方面阐述了对焊剂工艺性能及焊缝冲击韧性的影响。研制出的管线钢用BGSJ101-G烧结焊剂为氟碱型渣系。应用表明,该焊剂匹配的H08C焊丝完全满足X70及其以下钢级管线钢的焊接性能要求,并成功投入多条油气长输管线钢管的生产之中。