Microstructure Evolution of a Cold-rolled 25Cr-7Ni-3Mo-0.2N Duplex Stainless Steel during Two-step Aging Treatments

A cold-rolled 25Cr-7Ni-3Mo-0.2N duplex stainless steel(DSS)has been aged in two steps.Firstly,the aging treatment at interval of 50℃ in a temperature range from 900 to 1050℃ was carried out in order to obtain fine grains.Secondly,another aging treatment at 850 ℃ was performed to reveal theσ-phase precipitation behavior.A detailed microstructure evolution during those two aging steps was observed by the optical microscope(OM),the scanning electron microscope(SEM),the electron backscatter difraction(EBSD)and the transmission electron microscope(TEM).The results revealed that the micro-duplex structure with grain size of lower than 10μm appeared after the first aging step.However,their grain size was rapidly increased with increasing aging temperature.Meanwhile,theδ→γand/orδ→γ+σtransformations took place in association with the occurrence of the extensive recovery or a little recrystallization inδ-grains.During the second aging treatment,σ-phase mainly nucleated atδ/γinterfaces and further grew along those interfaces into various morphologies(e.g.,butterfly and granule).A novel precipitation behavior was found in this study that theγ-grain boundaries bulged not only into theδ-grains as usual,but abnormally into theσ-phase precipitates without the prior precipitation of the isolated secondary austeniteγ2or another phases.     

电化学动电位再活化法评定不锈钢晶间腐蚀敏感性的研究

本文用电化学动电位再活化法(EPR法)研究了奥氏体不锈钢在H_2SO_4+Na_2S_4O_6溶液中钝化区回扫电位、扫描速度、溶液温度、溶液浓度等因素对测试灵敏度的影响,确定了AISI304、316系列奥氏体不锈钢在此溶液中的最佳实验条件。并进行了不同敏化状态的奥氏体不锈钢在此溶液中的EPR测试。研究结果表明:采用Na_2S_4O_6作为活化剂的EPR法同样是一种快速、定量、非破坏性的评价奥氏体不锈钢晶间腐蚀敏感性的方法。但在实际应用时,对于304系列不锈钢选用H_2SO_4+KSCN溶液比较灵敏,而对于316系列不锈钢则选用H_2SO_4+Na_2S_4O_6溶液更为灵敏。     

电化学动电位再活化法评定不锈钢晶间腐蚀敏感性的研究

本文用电化学动电位再活化法(EPR法)研究了奥氏体不锈钢在H_2SO_4+Na_2S_4O_6溶液中钝化区回扫电位、扫描速度、溶液温度、溶液浓度等因素对测试灵敏度的影响,确定了AISI304、316系列奥氏体不锈钢在此溶液中的最佳实验条件。并进行了不同敏化状态的奥氏体不锈钢在此溶液中的EPR测试。研究结果表明:采用Na_2S_4O_6作为活化剂的EPR法同样是一种快速、定量、非破坏性的评价奥氏体不锈钢晶间腐蚀敏感性的方法。但在实际应用时,对于304系列不锈钢选用H_2SO_4+KSCN溶液比较灵敏,而对于     

焊接及热处理工艺对0Cr18Ni9Ti不锈钢耐蚀性的影响

通过草酸电解结合组织观察、动电位扫描法和交流阻抗测试研究了直流焊、脉冲焊和固溶处理、稳定化处理对0Cr18Ni9Ti不锈钢的抗晶间腐蚀性和耐点蚀性的影响.结果表明,脉冲焊比直流焊对晶间腐蚀的不利影响更大;固溶处理可以明显改善焊后材料的耐晶间腐蚀以及耐点蚀性,并增大钝化膜的稳定性.     

Study on process of roll bonding stainless and carbon steel under non-vacuum condition

The non-vacuum roll bonding method of nickel plating on the base materials is put forward in accordance with the primary problems existed in the roll bonding of stainless/carbon steel. After nickel plating test on the base materials, the microstructure of nickel cladding is observed by scanning electron microscopy （SEM） at high, and room temperature, and the results show that the nickel cladding on base material can be protected from oxidation in the high temperature. Non-vacuum roll bonding tests of nickel plating on base materials are done by the roll bonding equipment, and the roll bonding plates of stainless/carbon steel are obtained. The microstructure and the elements distribution of non-vacuum roll bonding interface are analyzed by optical microscope （OM） and SEM. The results reflect that the nickel plating layer and the base materials bond well.     

Interkristalline Korrosionsrisse an einem Wellenkompensator aus nichtrostendem Stahl X6CrNiTi1810 bei Korrosionsbelastung durch Heißdampf/Dampfkondensat

Intergranular corrosion cracks of a X6CrNiTi1810 SS expansion bellow stressed in heated steam/steam condensate at elevated temperature Cracking of a single layer corrugated expansion bellow of titanium-stabilized austenitic chromium nickel stainless steel was caused by corrosion fatigue. The crack starts with an intergranular crack path, and the transgranular residual fracture shows striations. Similar manifestations of cracked surfaces of austenitic CrNi steel which were obtained under cyclic loading in MgCl₂ solution are described in the literature. There are, however, corrosion damages by intergranular crack formation in the non-sensitized microstructure of titanium-stabilized ferritic chromium and austenitic chromium-nickel stainless steels in water at elevated temperature, the causes of which have not been elucidated until now.     

Characterization of Microstructure,Strength, and Toughness of Dissimilar Weldments of Inconel 625 and Duplex Stainless Steel SAF 2205

The dissimilar combinations of Inconel 625 and duplex stainless steel SAF 2205 obtained from manual GTA welding process employing ER2209 and ERNi CrMo-3 filler metals have been investigated. Formation of secondary phases at the HAZ of Inconel 625 and grain coarsening at the HAZ of SAF 2205 were witnessed while using these filler wires. The average hardness of ER2209 weldments was found to be greater than ERNi CrMo-3 weld. Tensile fracture was observed at the weld zones for both the fillers. Impact test trials showed brittle mode of fracture on employing ER2209 filler and mixed(ductile–brittle) mode of fracture while using ERNi CrMo-3 filler. Further optical microscopy and SEM/EDS analysis were carried out across the weldments to investigate the structure–property relationships.     

Influence of sinter-cooling rate on intergranular corrosion of powder metallurgy superaustenitic stainless steel

Powder metallurgy superaustenitic stainless steel sintered in N₂–H₂ atmosphere (95%–5%) was obtained. Three different processes were applied by controlling the sinter-cooling rate (furnace, gas and water). Intergranular corrosion resistance was evaluated. Furthermore, microstructure, density, porosity, macro- and microhardness were investigated. Microstructures were characterised by optical microscopy and scanning electron microscopy with energy dispersive analysis of X-rays. Intergranular corrosion behaviour was evaluated by immersion and by single and double loop electrochemical potentio-kinetic reactivation tests. The superaustenitic steel after fast cooling by water quenching showed the best intergranular corrosion behaviour, the highest microhardness values and the most homogeneous microstructure.     

Z2CND18-12N.S阀门钢锻造工艺研究

奥氏体不锈钢在实际生产中,常出现晶间裂纹、表面横裂等缺陷,因此对生产实践数据的研究,就显得十分重要。本文阐述了核级阀门钢Z2CND18-12N.S的生产过程,通过对工艺路线设计、锻造温度范围、变形火次、变形量、每道次压下量等参数的确定,制定出锻造工艺,最终使产品通过各项检验,并为生产高级别的不锈钢产品积累了数据。     

铸造奥氏体不锈钢的铬镍当量比和相对磁导率

介绍了铸造奥氏体不锈钢中各元素的作用;通过铬当量和镍当量经验公式计算CrE/NiE。使用不锈钢的CrE/NiE(成分当量)图估算铸造奥氏体不锈钢中的铁素体含量;使用磁导率检测仪检测相应铸件的相对磁导率,从而验证了铬镍当量CrE/NiE、铁素体量与相对磁导率的非线性关系。     

Pulsed TIG welding-brazing butt joints of aluminum-stainless steel thin plates with different fillers

Aluminum and stainless steel plates with 1.5 mm thickness are joined by pulsed TIG welding-brazing process with ER1100, ER4043 and ER2319 fillers, separately. Good weld formation can be obtained by adjusting appropriate pulse parameters. The effects of the fillers on that the thickness of the intermetallic compound （ IMC ） and tensile strength of the joints are investigated. SEM results indicate layer with ER2319 filler is about 2 ~m, which is thinner than 2. 5 p~m of ER1100 filler and 3.5 txm of ER4043 filler. Moreover, the element distribution in both IMCs and welded seams with three fillers are different because of the different compositions of fillers. The results of mechanical property tests suggest that the joint strength with ER2319 filler is the highest, while the joint impact energy is the lowest. The joint with ERllOO filler exhibits the best comprehensive mechanical pet.formanee.     

化学蚀刻 304 不锈钢表面结构研究

目的研究化学蚀刻304不锈钢表面结构类型、形成过程及其应用。方法以304不锈钢为对象,以FeCl3系溶液为蚀刻剂,采用化学蚀刻的工艺,通过表面分析和SEM等手段,研究化学蚀刻的过程以及表面结构的类型。结果在40℃常压下,250 g/L FeCl3中使304不锈钢表面光滑的盐酸用量(y)与硝酸用量(x)满足一定的关系:y=19.37+0.13x±0.5,x≤120 m L/L;y=-8.67+0.62x±0.5,x≥130 ml/L。溶液中Cl-含量是影响蚀刻后不锈钢表面的平整度的主要因素。结论改变蚀刻溶液性质可以改变蚀刻后304不锈钢表面形成的结构。     

Microstructure and properties of SAF2507 superduplex stainless steel welded joints

SAF2507 plates （ 12 mm thickness ） were welded using shield metal arc welding （SMAW） process with E2594 electrode. The microstructure, o-phase, and impact fraetograph of the welded joints were analyzed using optical microscope and scanning electron mieroseope. The results show that the fusion zone consists of ferrite, chromium nitride, and secondary aastenite precipitation when welding is performed at low heat input （0. 5 kJ/mm）. However, the increase in heat input causes precipitation of brittle o＂ phase at the y/c~ interface in weld metal and heat-affected zone, as well as a brittle fracture along the grain boundary. Heat input in the range of O. 5 kJ/mm to 1.5 kJ/mm is suitable for joining SAF2507 plates.     

CORROSION FATIGUE CRACK INITIATION BEHAVIOR OF 316L STAINLESS STEEL IN HANK’S SOLUTION

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TIG welding-brazing joint of aluminum to stainless steel with hot wire

TIG welding-brazing process with high frequency induction hot wire technology was presented to create joints between 5A06 aluminum alloy and SUS32! stainless steel using ER1100 filler wire with different temperature. The joints were evaluated by mechanical test and microstructural analyses. The welding procedure using hot fiUer wire （400 ℃ ） significantly increases strength stability by 71% and average value of tensile strength by 30. 8 % of the joints, compared with cold wire. The research of microstructures in interfaces and welded seams reveals that using 400 ℃ hot filler wire can decrease the thickness of intermetallic compounds （ IMCs ） from 6 to 3.5 txm approximately, which is the main reason of mechanical property improvement.     

酸洗对薄壁0Cr18Ni9不锈钢腐蚀的试验研究

0Cr18Ni9不锈钢薄壁产品在酸洗过程中易发生过腐蚀。本研究采用0.1 mm厚度0Cr18Ni9不锈钢带,对酸洗的各影响因素进行试验研究,结果表明:材料状态不同,耐腐蚀能力不同,退火态更易出现过腐蚀;酸液温度、浓度及酸洗的时间均对不锈钢带腐蚀程度和力学性能有较大影响;在含HF的腐蚀剂中酸洗容易使薄壁不锈钢带力学性能降低,造成材料脆化,且HF含量越高对薄壁不锈钢力学性能影响越大。     

Lateral and radial corrosion propagation behavior of 9–21% Cr and 18% Cr + 2.8% Mo stainless steel reinforcing materials in simulated concrete environments

The life of a concrete structure exposed to deicing compounds or seawater is often been limited by chloride induced corrosion of the steel reinforcement. A complete assessment of the potential benefits afforded by new candidate rebar alloys must address both the lateral and radial corrosion propagation behavior in comparison to conventional steel as well as other factors that might affect the risk of corrosion‐induced concrete cracking. The radial (depth) and lateral (length) corrosion propagation behavior of 18% Cr + 2.8% Mo (S31653) stainless steel, 21% Cr (S32101) duplex stainless steel, and 9% Cr steel compared to plain ASTM A615 carbon steel were characterized in saturated Ca(OH)₂ solution. Radial pit growth was found to be Ohmically controlled for all materials but repassivation occurred more readily at high applied potentials for 18% Cr + 2.8% Mo and 21% Cr stainless steels. Conversely, pit growth on plain steel propagated at all applied anodic potentials and did not repassivate until deactivation by cathodic polarization. Stainless steel also showed the highest resistance to lateral corrosion propagation from an active site during microelectrode array testing. 21% Cr duplex stainless and 9% Cr steel showed similar radial propagation behavior and corrosion morphology, which was intermediate to that of plain steel and S31653 stainless steel. Based on an existing concrete cracking model, it is expected that 9–21% Cr and 18% Cr + 2.8% Mo corrosion resistant rebar materials would require a greater depth of corrosion attack than carbon steel before damaging concrete via corrosion product formation.     

Intergranular precipitation and corrosion in weld of low Cr ferritic stainless steel

In the present research, intergranular precipitation and corrosion in the weld of low Cr ferritic stainless steel was investigated. Free-exposure and double loop electrochemical potentiokinetic reactivation corrosion test results revealed that IGC occurred in both the weld metal and heat-affected zone of the welds aged for more than 1 h at 500 °C. Intergranular Cr segregation was observed around the TiC precipitation of the weld in which IGC developed during the corrosion tests. This observation is subsequently discussed in the experimental results.     

Corrosion Behavior of 5A05 Aluminum Alloy in NaCl Solution

The corrosion behavior of 5A05 aluminum alloy in 3.5 wt.%NaCl solution was investigated by scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),Fourier transform-infrared(FT-IR)spectroscopy and electrochemical impedance spectroscopy(EIS)test,and the corrosion mechanism was also discussed.The results showed that the corrosion rates of the 5A05 alloy were low and decreased with the increase in immersion time.Under the conditions of exposure studied,this alloy sufered from pitting corrosion that took place from or around the intermetallic particles existing in the alloy.The number and size of the hemispherical corrosion pits on the sample surfaces increased with the increase of the test time.The dark-grey layer of corrosion products formed on 5A05 aluminum alloy in 3.5%NaCl solution contained many microcracks.Furthermore,XPS and FT-IR analysis proved that the corrosion products were mainly composed of Al2O3,Al(OH)3 and AlCl3.     

不锈钢等离子渗铪并固体渗碳后的高温摩擦性能

目的提高0Cr18Ni9Ti奥氏体不锈钢的抗高温摩擦性能。方法利用等离子渗金属技术在不锈钢表面等离子渗铪,之后进行固体渗碳,在HT-500型球-盘磨损试验机上进行高温摩擦磨损实验,分析其高温摩擦性能及摩擦机制,并与不锈钢基体试样及不锈钢渗铪试样进行对比。结果渗铪试样的渗层厚度约为45μm,渗铪+渗碳试样的渗层厚度达100μm。渗铪+渗碳层弥散分布着许多粒状和短棒状碳化物颗粒,碳化物类型主要为MC型、M7C3型和M23C6型。基材的摩擦曲线波动起伏大;渗铪试样的摩擦系数较大,但磨损微观表现平稳;渗铪+渗碳试样的摩擦系数最小。磨损失重由大到小依次为:基材渗铪试样渗铪+渗碳试样。在300,500℃下,渗铪试样的耐磨性相对基材分别提高至1.47倍和1.94倍,渗铪+渗碳试样分别提高至2.13和2.28倍。基材划痕尺寸宽且较深;渗铪试样的表面硬度提高,且摩擦磨损过程中出现了合金氧化物;渗铪+渗碳试样的表面硬度高,基体韧性好,仅出现了很浅且窄的磨痕。结论通过等离子渗铪及离子渗铪+固体渗碳,均能提高不锈钢表面的抗高温摩擦性能,相比之下,离子渗铪+固体渗碳的效果更好。