Interaction of 18Cr-10Ni stainless steel with liquid aluminium

The dissolution of an 18Cr-10Ni stainless steel in liquid aluminium at 700 to 850 ° C was found by the rotating disc technique to be non-selective and diffusion controlled. Experimentally determined values of the parameters characterizing the dissolution run are presented. In the case of saturated aluminium melts two intermetallic layers were found to form between the steel and the melt material at 700 °C. The compact layer adjacent to the steel surface is probably a solid solution based upon the Fe₂Al₅ compound. Its thickness,x, tends with increasing time to the limiting valuex _max = 10m. The porous layer adjacent to the melt material is probably a solid solution based upon the FeAl₃ compound. After a certain period of non-linear growth its thickness,Y, increases with time,t, according to the linear law:Y = 1 × 10^–8 t + 6 × 10^–6 m. The time dependence of the total thickness of both layers is well described in terms of the paralinear kinetics. In the case of undersaturated aluminium melts the formation of a single-phase intermetallic layer, 3 to 11 m thick, was observed at 700 ° C for 100 to 600 sec. The steel-to-aluminium transition joints with good mechanical properties were made by interaction of a solid steel material with liquid aluminium.     

Fe-17Mn-5Si-10Cr-5Ni形状记忆合金管接头性能分析

对 Fe- 17Mn- 5 Si- 10 Cr- 5 Ni合金管接头的形状记忆效应和连接性能进行了系统地分析 ,结果表明 :1形状恢复率随着预变形量的增加而降低 ;最大可恢复应变出现在 4%～ 6 %之间 ;预变形量为 4.5 %～ 8%时管接头的紧固力较大 ,耐压密封性较好。 2热—机械训练可显著提高管接头的形状记忆效应、连接的紧固力和耐压密封性。 3管接头的形状记忆效应随着其壁厚的增大而降低 ;管接头壁厚有一个合理的取值范围 ,可使其连接的紧固力较大、耐压密封性较好。 4管接头连接长度越长 ,管接头的紧固力越小而耐压密封性越好。5管接头结构对管接头连接的耐压密封性影响很大 ,随结构的不同耐压密封性可有几倍的差异     

Strain induced martensitic transformation of Fe-20Cr-5Mn-0.2Ni duplex stainless steel during cold rolling: Effects of nitrogen addition

The effects of nitrogen addition on the strain induced martensitic transformation (SIMT) behavior of duplex stainless steel (D-STS) with the low nickel content were examined in a wide range of strain by means of cold rolling. Nitrogen of 0.1, 0.2 and 0.3 wt.% was added into Fe-20Cr-5Mn-0.2Ni D-STS (in wt.%) and cold rolling was conducted up to the effective strain of ∼1.45 after annealing at 1000 °C for 30 min. In the as-annealed state, the austenite fraction increased with increasing the N content. Regardless of the N content, the ferrite grain size was coarser than that of austenite. The stacking fault energy of austenite of the present D-STSs inferred by the element partitioning analysis was low enough so that SIM transformation is available. Accordingly, during cold rolling, SIMT occurred in austenite with a sequential manner of austenite → ? martensite → α′ martensite with increasing strain. By contrast, the deformed microstructure of ferrite was dominated by dislocation cells. The SIM fraction, which was normalized with reference to the initial austenite fraction in order to eliminate its effect, increased with increasing the N content. Along with the present results, the factors influencing the SIMT kinetics in the present D-STSs with the different N content were discussed.     

The influence of non-metallic inclusion on the fracture behaviors of 25Mn-5Cr-1Ni austenitic steel

The influence of inclusion on fatigue life, threshold stress intensity factor, elasticplastic fracture toughness and Charpy absorbed energy of high manganese steel were studied for the temperature range of 298 ˜ 77 K. For this purpose, two series of steel, which contain different inclusion quantities, were used. Specimens are prepared to be S-L or S-T orientation with regard to the rolling direction. Experimental results showed that reduction in above strengths depend on both quantity and the orientation of inclusion. Crack growth behavior was discussed by taking into account the linkage of a main crack with a micro crack formed at the inclusion tip.     

Fe-15Mn-5Si-9Cr-5Ni形状记忆合金回复性能及微观结构演变

制备了含不同Al量的2种Fe-15Mn-5Si-9Cr-5Ni形状记忆合金,测定了多次训练之后的记忆效应,并用金相显微镜和透射电镜对材料的微观组织结构进行了观察,结果表明,训练之后的合金记忆效应明显提高,尤其是第二次训练会产生显著效果.含过量的铝对形状记忆效应不利.训练后的合金内存在宽大的层错,层错增多,有利于形状记忆效应的提高.     

Effect of ageing on precipitation and impact energy of 2101 economical duplex stainless steel

The impact energy and microstructure of a thermally aged 2101 duplex stainless steel with composition of Fe–21.4Cr–1.2Ni–5.7Mn–0.23 N–0.31Mo were studied. The results showed that the room temperature impact energy of specimens decreased gradually with ageing temperature up to 700 °C and then increased with aging over 700 °C. The minimum value of impact energy was 37 J after 700 °C aging, which was only 34% of that for as-annealed specimens. For specimens aged at 700 °C, the room temperature impact energy decreased significantly after 3 min and was halved after 10 min. Fractographs showed that, with increasing aging time, the fracture morphology changed from fibrous fracture to transgranular and intragranular fracture. Scanning electron micrographs revealed that many precipitates were distributed along α/γ and α/α interfaces. The precipitates were extracted and confirmed by X-ray diffraction to be Cr₂N. Therefore, it can be concluded that precipitation of Cr₂N is the main reason for the decrease of impact energy in aged 2101 duplex stainless steel.     

23Cr-14Ni高氮奥氏体不锈钢σ相析出行为EI北大核心CSCD

采用经验公式、热力学计算方法、Gleeble热/力模拟实验技术,结合光学显微镜、扫描电镜及透射电镜分析,研究了23Cr-14Ni高氮奥氏体不锈钢中σ相的析出行为。结果表明,23Cr-14Ni高氮奥氏体不锈钢中σ相可在960~1030℃析出,高于1050℃溶解。σ相析出具有异常快速的动力学特征,在经过1030℃保温1 min固溶处理后,σ相可直接从奥氏体晶界快速析出,析出先于碳氮化物相。σ相析出动力学行为及相对碳氮化物的析出次序和传统奥氏体不锈钢显著不同。铬、锰、钼元素含量较高且钼元素在晶界处偏聚提高了σ相平衡析出温度,是加速σ相析出的主要原因。     

1Cr21Ni5Ti双相不锈钢马氏体相变及对韧性的影响

研究了1Cr21Ni5Ti双相不锈钢高温固溶后冷至室温～-50℃之间γ相内马氏体相变规律.结果表明:冷却到室温后γ相内形成少量密排六方ε马氏体.冷至0℃以下形成体心立方板条马氏体,板条马氏体具有自促发形成的特点,而群集在一起构成板条马氏体束,在γ相内呈不均匀分布;迹线分析表明,板条马氏体惯习面接近于{575}f;与冷却到室温的样品相比,降低固溶时的终冷温度对固溶态的冲击韧性影响不明显;经脆化处理后,终冷温度较低的样品冲击韧性较低.     

Microstructural modification during isothermal ageing of a low nickel duplex stainless steel

In order to reduce the cost of duplex stainless steel (DSS), the Ni could be partially substituted by Mn and N, to maintain the alpha/gamma microstructure, the corrosion resistance and mechanical strength similar to the common Ni–Cr–Mo DSS. In this paper the microstructure stability, impact strength and the general corrosion behaviour of a low Ni grade, 22Cr–4Mn–0,2N DSS, were examined. In the solution annealing condition the corrosion resistance is quite similar to the austenitic grade. A moderate precipitation of nitrides and carbides was evidenced after isothermal treatment in the range 600–900 °C, while no dangerous topologically close packed phases (TCP-phases) were detected. The precipitation affects the impact strength, which decreases to about 50 J, while the corrosion resistance is less markedly affected.     

Influence of thermal cycling on the martensitic transformation and shape memory effect of a Fe－16Mn－

ＩｎｆｌｕｅｎｃｅｏｆｔｈｅｒｍａｌｃｙｃｌｉｎｇｏｎｔｈｅｍａｒｔｅｎｓｉｔｉｃｔｒａｎｓｆｏｒｍａｔｉｏｎａｎｄｓｈａｐｅｍｅｍｏｒｙｅｆｆｅｃｔｏｆａＦｅ－１６Ｍｎ－５Ｓｉ－９Ｃｒ－４ＮｉｓｈａｐｅｍｅｍｏｒｙｓｔｅｅｌＱ．Ｇｕ，Ｊ．ＶａｎＨｕ...     

Corrosion of 15-5PH H1025 stainless steel due to environmental conditions

A simple corrosion experiment was conducted to simulate the effects of stray current and salt water environmental conditions of 15-5PH H1025 stainless steel, which is a common material used on aircraft. Pieces of non-corroded 15-5PH H1025 stainless steel were immersed in 71 °C tap water without current, 71 °C tap water with current, and deionized water with current. It was determined that with time, the condition of 71 °C tap water with current formed corrosion pits on this material. It is always important that during the materials selection design of a product, all aspects, including environmental conditions that may potentially surround the product, should be considered.     

Modeling of deleterious phase precipitation during isothermal treatments in superduplex stainless steel

The deleterious constituents σ, χ, and eutectoid γ₂ can precipitate during hot forming and welding operations in superduplex stainless steels. In this study the precipitation of these phases in superduplex UNS S32750 was investigated. Two materials with similar composition and quite different grain sizes were used in the study. Specimens were subjected to isothermal treatments in the 800–950 °C temperature range for time periods up to 240 min. Under these conditions, quantifications of deleterious phases by light optical microscopy were carried out in order to model the precipitation kinetics of these deleterious constituents. A sigmoidal equation, similar to the one developed by Johnson–Mehl–Avrami was fitted to all the analyzed temperatures. Precipitation velocity was evaluated so as to compare the kinetics of deleterious phases in the two materials. The activation energies for precipitation were calculated based on Arrhenius equation.     

Observation of hydrogen effects on fatigue crack growth behaviour in an 18Cr-8Ni austenitic stainless steel

The hydrogen effect on crack growth behaviour in a type 304 austenitic stainless steel was investigated and the following results were obtained. The crack growth rate in hydrogen gas is accelerated compared with that in air. In order to clarify the mechanism of the acceleration, the growth behaviours of a crack propagating in a grain and propagating along the boundary to be a fracture facet were investigated. Slip behaviour, opening displacement and fractography showed that the slip-off mechanism in fatigue crack growth is valid even in hydrogen gas. Hydrogen mainly affects slip behaviour such that slip bands concentrate at a crack tip and result in acceleration of the growth rate. The facets are not significantly responsible for the acceleration. The ratio of facets to the entire area is low, and a crack nearly compensates for the temporary acceleration by the facets with subsequent deceleration.     

Creep behaviour of a 25wt % Cr-20wt % Ni austenitic stainless steel doped with antimony

The effect of antimony on the steady state creep rates, , of a 25 wt% Cr-20wt% Ni austenitic stainless steel with 0.005 wt % C is studied. The effect on vacancy viscous creep (Coble creep) is shown to be different to that on dislocation creep (power law creep). The effect on Coble creep is particularly striking. The threshold stress is significantly increased by antimony additions.     

The influence of antimony-additions on the creep behaviour of a 25wt% Cr-20wt% Ni austenitic stainless steel

The effect of antimony on the creep behaviour (dislocation creep) of a 25 wt% Cr-20 wt% Ni stainless steel with ~ 0.005 wt% C was studied with a view to assessing the segregation effect. The antimony content of the steel was varied up to 4000 ppm. The test temperature range was 1153 to 1193 K, the stress range, 9.8 to 49.0 MPa, and the grain-size range, 40 to 600m. The steady state creep rate, , decreases with increasing antimony content, especially in the range of intermediate grain sizes (100 to 300m). Stress drop tests were performed in the secondary creep stages and the results indicate that antimony causes dislocations in the substructure to be immobile, probably by segregating to them, reducing the driving stress for creep.Nomenclature _a Creep stress in a constant load creep test without stress-drop - _A Initial applied stress in stress-drop tests - Stress decrement - ( _A-) Applied stress after a stress decrement, - t _i Incubation time after stress drop (by the positive creep) - _C Strain-arrest stress - _i Internal stress - _{s s}-component (= _i- _c) - Steady state creep rate (average value) in a constant load creep test - Strain rate at time,t, in a constant load creep test - New steady state creep rate (average value) after stress drop from _A to ( _A-) - Strain rate at time,t, after stress drop.     

Cracking due to Cu and Ni segregation in a 17-4 PH stainless steel piston rod

The 17-4 PH stainless steel is employed to produce piston rods in industry due to the high strength and toughness, good workability and nice corrosion resistance. In the present failure analysis, obvious long cracks were observed along the longitudinal direction on the surface of the commercial 17-4 PH stainless steel piston rod after heat treatment. The cracks were carefully looked into by observing the crack tip and characterizing the microstructure along the cracks. The results showed that the cracks were mostly initiated from the surface of the rod and propagated along the phase boundary between martensite and δ ferrite. The EDXA showed that the segregation of Cu and Ni should be responsible for the cracking after heat treatment. In order to define when the crack was coming into being, oxidation film along the crack was considered as a clue. The scrutiny of the oxidation film on the crack edge illustrated that the crack should be formed right in the heat treatment of aging.     

Hot workability of 00Cr13Ni5Mo2 supermartensitic stainless steel

The hot workability of 00Cr13Ni5Mo2 supermartensitic stainless steel was investigated by hot compression and hot tension tests conducted over the temperature range of 950–1200 °C and strain rates varying between 0.1 and 50 s^?1. The processing map technique was applied on the basis of dynamic materials model and Prasad instability criterion. Microstructure evolutions, Zener–Hollomon parameter as well as hot tensile ductility were examined. The results show that, as for the hot working of 00Cr13Ni5Mo2 supermartensitic stainless steel in the industrial production, the large strain deformation should be carried out in the temperature range 1140–1200 °C and strain rate range 0.1–50 s^?1, where the corresponding Zener–Hollomon parameters exhibit low values. Moreover, when deformed under high strain rate range (above 15 s^?1), the deformation temperature can be reduced reasonably.