δ铁素体含量对Fe-Cr-Ni-Mn-N系不锈钢氢脆敏感性的影响

采用高压气相充氢后进行缺口试样拉伸试验的方法,证实了δ铁素体含量的增加显著提高Fe-Cr-Ni-Mn-N系奥氏体不锈钢的氢脆敏感性.     

氢及形变对Fe-Cr-Ni-Mn-N系不锈钢组织和性能的影响

用金相显微镜、X射线衍射仪、透射电镜、磁强计等技术结合拉伸试验,研究了气相充氢与拉伸形变对三种奥氏体稳定性不同的Fe-Cr-Ni-Mn-N不锈钢马氏体转变和力学性能的影响,取得了一些定量的数据.结果表明,拉伸形变促进ε和α’马氏体在奥氏体不稳定的钢中的生成,而氢的存在能促进ε马氏体转变但抑制α’的产生.奥氏体不稳定的Fe-Cr-Ni-Mn-N钢比奥氏体稳定的同类钢抗氢脆能力差得多,这与ε马氏体的出现有关.     

EFFECTS OF MODIFICATION OF THE CARBIDE CHARACTERISTICS THROUGH GRAIN BOUNDARY SERRATION ON CREEP-FATIGUE LIFE IN AUSTENITIC STAINLESS STEELS

Modification of the carbide characteristics through the grain boundary serration is investigated, using an AISI 316 and 304 stainless steels. In both steels, triangular carbides were observed at straight grain boundaries while planar carbides were observed at the serrated grain boundaries. The serrated grain boundary energy is observed to be much lower than that of the straight one. Therefore, the carbide morphology is found to be changed from triangular to planar along the serrated boundary to reduce the interfacial energy between the carbide and the matrix. The creep-fatigue properties of these steels at 873K have been investigated. The creep-fatigue life of the sample with planar carbide at the serrated grain boundary was found to be much longer than that with triangular carbide at the straight one. These results imply that the planar carbides with lower interfacial energy have higher cavitation resistance, resulting in the retardation of cavity nucleation and growth to increase creep-fatigue life.     

EFFECT OF MICROSTRUCTURE ON HYDROGEN DAMAGE OFJBK-75 PRECIPITATE-STRENGTHENED AUSTENITIC STEEL

1.IntroductionHydrogenembrittlement(HE)0rhydr0gendamage(HD)ofall0ysisnotonlyrelatedt0chemicalc0mpositionsbutals0c10selyt0microstructures.Thereweres0merep0rts0ntheeffect0fmicr0structures0nHD0fsingle-phaseausteniticsteels[1-3].Themicrostructuralreas0nsofHD0fprecipitate-strengthenedausteniticsteels(PSAS),however,havereceivedlessattenti0n.Single-phaseausteniticsteelshaveproveninseveralinstancestohaveg00dresistancet0HD,butaretypicallynostr0ngerthan450MPainyieldstrength.Thus,anausteniticmatri…     

EFFECT OF ELECTRIC FIELD ON THE AUSTENIZATION OF A LOW CARBON STEEL

With an electric field during austenitizing, the martensite transformation of the low carbon steel was promoted, and more martensite were obtained. The electric field promotes the homogeneity of carbon, and reduces the free energy of austenite. The critical neuclus r^* and the critical driving force G^* responsible for the nucleation of proeutectoid ferrite were increased. As a result of which the diffusion controlled proeuctoid ferrite transformation was retarded and the hardenability was improved.     

EFFECT OF AGING ON HYDROGEN EMBRITTLEMENT SUSCEPTIBILITY OF STEEL Cr21Ni6Mn9N

Effects of 650℃ aging for 1—1000 h on structure and hydrogen embrittlement susceptibility(HES)of steel Cr21Ni6Mn9N have been investigated.The results show that M_(23)C_6 typecarbide precipitates at grain boundaries and Cr-depletive region appears beside them duringaging.The precipitates grow and connect each other as the aging time prolongs.Meanwhile,the degree of Cr-depletion aggravates first and then recovers gradually while the aging time isvery long,i.e.,1000 h.The HES of the steel increases with increasing aging time but does notreduce with the recovery of Cr content at the Cr-depletive region.That implies that the ex-isting of carbides at grain boundaries might be the main reason which promotes the HES ofsteel during aging.     

THE EFFECT OF PRIOR AUSTENITIC GRAIN BOUNDARIES ON NUCLEATION OF(225)_γ MARTENSITE IN STEELS

本文结果指出,T10A及GCr15两钢的单位体积内(225)_γ马氏体片数N_v与原始奥氏体晶粒平均直径D的关系为N_V=N_0(?)~(-1/2).用相变驱动力作用下的低温多晶范性形变的位错理论可推得此关系.据此认为(225)_γ马氏体形核是在相变驱动力作用下,开动位错源的结果.可见,没有预存的马氏体核胚,而只有预存的位错源.细化原始奥氏体晶粒是细化(225)_γ马氏体片的有效方法.     

HYDROGEN TRAPPING EFFECT OF SUBSTITUTIONAL ALLOYING ELEMENTS IN α-Fe

用电化学渗氢方法测定了氢在纯Fe和Fe-Cr,Mn,Co,Si,Mo的二元合金中的扩散系数。结果表明所研究的二元铁基合金中,随着合金元素浓度的增加,氢的扩散系数降低,氢的扩散激活能增加。根据Oriani模型计算了各种合金元素的氢陷阱参数,并获得了相应的氢与陷阱结合能。按陷阱结合能由小到大的顺序是:Si,Co,Ni,Mn,Cr和Mo。最后根据合金元素引起的晶格应变场与氢的弹性交互作用和合金元素与氢的电性交互作用对结合能的本质进行了分析。     

1Cr17Mn6Ni5N与Q235异种钢焊接接头组织分析

采用等离子弧对低碳钢Q235与奥氏体钢1Cr17Mn6Ni5N异种钢进行焊接,并对焊接工艺进行了优化.采用扫描电镜、光学显微镜、能谱仪对焊接接头的组织进行了分析,用显微硬度计对接头硬度进行了测试.结果表明:采用合适的工艺,可以实现高强度的连接,在焊缝区形成了板条马氏体组织,并在焊缝两侧产生了碳的迁移.     

EFFECT OF Mg AND δ-PHASE ON MECHANICAL PROPERTIES OF ALLOY GH169(INCONEL 718)

研究了微量元素Mg及δ相对GH169(INCONEL718)高温合金力学性能的影响结果表明,Mg含量从30ppm提高到70ppm,合金可以在保持高强度下进一步改善塑性,特别可提高在使用条件下的一些重要力学性能;δ相的数量、形态及分布明显影响合金的缺口周期持久寿命相应的组织观察表明,Mg在一定程度上也影响δ相的?些特性,因此通过控制Mg含量可控制δ相的数量,形态及分布特征,从而进一步提高GH169合金的力学性能     

EFFECT OF Mg AND δ-PHASE ON MECHANICAL PROPERTIES OF ALLOY GH169(INCONEL718)

Micro-alloying of Mg,ranged from 30 to 70 ppm,may improve the high temperatureductility,stress rupture,especially,certain important mechanical properties,such as cyclicstress rupture,creep/fatigue interaction and crack propagation rate.The quantity,morphology and distribution of δ-phase may obviously influence the notched cyclic stress rup-ture life.The relevant microstructure shows that the Mg may also influence to certain extenton the feature of δ-phase.Thus,to keep the Mg and δ-phase under control may further im-prove the mechanical properties of alloy GH169.     

EFFECT OF THERMOCHEMICAL PROCESSING WITH HYDROGEN ON MICROSTRUCTURE OF SUPER-α2 ALLOY

利用Ｘ射线定量相分析方法，研究加氢热化学处理对Ｓｕｐｅｒ－α２合金显微组织的影响。结果表明，合金组织由α２相，Ｂ２相以及Ｏ相组成，加氢处理可以有效地促进合金中Ｏ相的形成，且随合金中氢含量的增加，组织中Ｏ相的体积分数明显增大。针对加氢热化学处理对Ｓｕｐｅｒ－α２合金组织的影响机制进行了讨论。     

冷却速度对奥氏体不锈钢Cr15Mn9Cu2Ni1N组织与凝固模式的影响

利用控制冷却速度的凝固实验,研究连铸坯奥氏体不锈钢Cr15Mn9Cu2Ni1N不同冷却速度下的组织和凝固模式.结果表明,缓慢冷却时,显微组织为奥氏体基体上分布着蠕虫状残留铁素体;其凝固模式为全部液相先析出δ铁素体,随后通过固相转变形成奥氏体基体.较高冷却速度时,奥氏体组织有两种形态,一是分布着侧板条残留铁素体的奥氏体,二是圈状的分布在第一种奥氏体晶界的单相奥氏体.分析发现,冷却速度的增加使凝固模式发生如下变化:大部分液相先析出δ铁素体,随后固相转变为奥氏体;剩余液相直接转变为奥氏体.同时发现,氮含量的增加可以减小奥氏体晶粒尺寸.     

10Cr12Ni3Mo2VN马氏体耐热钢奥氏体晶粒长大行为

通过在不同加热温度和保温时间下等温奥氏体化,研究了10Cr12Ni3Mo2VN马氏体耐热钢奥氏体晶粒长大行为。结果表明:900~1150℃温度区间内,10Cr12Ni3Mo2VN马氏体耐热钢奥氏体晶粒尺寸随加热温度升高、保温时间延长而增大,且随保温时间延长,晶粒尺寸均匀性下降;由于碳氮化物在1100℃以上发生溶解,1100℃以上奥氏体晶粒发生粗化;1200~1280℃温度区间内,由于δ铁素体相的析出,10Cr12Ni3Mo2VN马氏体耐热钢奥氏体晶粒尺寸随加热温度升高而减小。拟合得到900~1150℃温度区间内10Cr12Ni3Mo2VN钢奥氏体晶粒生长模型为D=6.67×107×t0.303×exp(-1.81×105/RT)。     

EFFECT OF W CONTENT ON MECHANICAL PROPERTIES OF 12％Cr-W-V-Nb HEAT RESISTANT STEEL

本文报道了钨的含量对12％Cr-W-V-Nb耐热钢高温及室温力学性能的影响。试验结果表明:当钨的含量在2.2—3.0wt-％之间变化时,室温抗拉性能没有明显变化,但冲击韧性却随着钨量的增加而下降。另一方面,钨量的增加提高了短时间的持久强度,但对长时间的持久强度却没有改善作用。钨量的增加对析出行为有两方面的作用:促进Fe_2W型Laves相的形成并增加析出相总量;加速了回火后在高温加热过程中析出相的粗化。钨对高温力学性能的影响与析出特性有密切关系。在持久寿命较短时,析出相来不及粗化,析出量的增加造成了析出强化效果的加强,即钨量的增加提高了高温强度;而当长时间加热后,析出相发生了明显的粗化,降低了析出强化效果。     

氮含量对无镍含钼奥氏体不锈钢相变的影响

以Cr18 Mn14 Mo3无镍含钼不锈钢为基本成分,设计并冶炼了电渣重熔锭实测氮含量为0.008％～0.770％的4炉高氮CrMnMo奥氏体不锈钢(氮含量设计范围为0.004％～0.850％),对各试验钢的平衡相转变进行了热力学计算,对试验钢的显微组织形貌进行了观察.结果表明:试验钢的氮含量在0.40％到0.85％区...     

IN-SITU OBSERVATION OF δ→γ PHASE TRANSFORMATION OF AN AISI304 STAINLESS STEEL

利用共焦激光扫描显微镜原位观察了AISl304不锈钢冷却过程中高温铁素体(δ)→奥氏体(γ)相变的过程及其特征.结果表明,γ相优先在δ晶界处形成;冷却速率影响γ相的生长形态,典型形态分为块状、圆形、树枝状等;"游离"γ枝晶发生粗化,并和周围的γ枝晶聚合;相同冷却条件下,δ晶界处的γ枝晶聚合程度明显高于δ晶粒内部;二次枝晶在冷却过程中粗化,并竞争生长.利用ThermoCalc计算C元素在δ→γ相变过程中的偏析系数,以此求解δ→γ相变数学模型.     

0Cr16Ni5Mo马氏体不锈钢δ-铁素体含量及奥氏体晶粒度的控制

检验中发现0Cr16Ni5Mo钢的δ-铁素体含量超出技术协议规定值,为降低δ-铁素体的含量同时控制奥氏体晶粒度以满足材料使用要求,通过理论计算和热力学模拟分析δ-铁素体形成原因,后续采用不同温度的淬火和高温扩散对0Cr16Ni5Mo钢组织和δ-铁素体含量变化进行对比研究,另外采用两种循环热处理方式对奥氏体晶粒度进行控制。结果表明,随着淬火温度的提高,0Cr16Ni5Mo钢的奥氏体晶粒度不断增大,而对δ-铁素体含量的减少作用相对有限。高温扩散能使δ-铁素体明显减少,但当扩散温度大于奥氏体向δ-铁素体转变温度时,会相对延缓铁素体的溶解。进行1130 ℃的高温扩散后,可以采用850 ℃和830 ℃的变温循环相变热处理,消除马氏体组织遗传,均匀细化奥氏体晶粒。     

耐Pb-Bi腐蚀Si增强型铁素体/马氏体钢和奥氏体不锈钢的研究进展

结构材料是制约铅冷快堆建设的关键因素之一,原因是其组成元素在液态Pb-Bi共晶(LBE)中会发生不同程度的溶解,影响结构安全。候选结构材料铁素体/马氏体钢T91与不锈钢316在550℃饱和氧LBE环境中发生快速氧化腐蚀;溶解氧浓度降至1.26×10^-6%(质量分数)可减轻T91的液态LBE腐蚀,但低于1×10^-6%时,T91与316钢发生溶解腐蚀;T91液态LBE脆化敏感性高,导致其在350℃液态LBE中腐蚀疲劳寿命显著降低。与商用的(9%～12%)Cr铁素体/马氏体钢和316型奥氏体不锈钢相比,经微合金化的Si增强型铁素体/马氏体钢(9Cr-Si和12Cr-Si)和奥氏体不锈钢(ASS-Si),具有较好的组织稳定性和综合力学性能,且在液态LBE中形成的富Si氧化物提高了氧化膜的致密性,改善了其耐腐蚀性能,在550℃下静态饱和氧和动态控氧LBE环境中的溶解腐蚀受到抑制,有望满足铅冷快堆的设计需求。