High-temperature hydrogen sulfide corrosion on the heat-affected zone of the AISI 444 stainless steel caused by Venezuelan heavy petroleum

The aim of this study was to evaluate the effect of welding on the corrosion resistance of the heat-affected zone (HAZ) of the AISI 444 ferritic stainless steel in medium containing Venezuelan heavy oil. AISI 444 steel plates were welded through the use of three levels of welding heat input (4, 6 and 8 kJ/cm). Samples were extracted from the welded plates and thermally treated in three different temperatures (200, 300 e 400 °C), while immerged in petroleum for a period of 4 h. Optical microscopy (OM), scanning electronic microscopy (SEM) and energy dispersive X-ray analysis (EDX) techniques were used for the analysis of the surface and transversal section of the joint. Electrochemical trials of cyclic potentiokinetic reactivation of double loop (EPR-DL) were also carried out. It has been concluded that the temperature of treatment has direct influence on the level of material corrosion and that the increase in the welding heat input contributes to a higher level of corrosion.     

Role of environmental variables on the stress corrosion cracking of sensitized AISI type 304 stainless steel (SS304) in thiosulfate solutions

The stress corrosion cracking (SCC) behavior of sensitized AISI type 304 stainless steel (SS304) has been studied in dilute thiosulfate solutions as a function of thiosulfate concentrations and applied potentials. The susceptibility to SCC was observed to increase with thiosulfate concentrations and applied potentials. The addition of boric acid produced the reverse effect. A critical potential was found to exist, below which no SCC took place. Potential fluctuations, as recorded in the tests under open circuit conditions, appeared to be correlated with crack initiation and propagation during SCC. Current fluctuations observed in the controlled potential tests also gave indications of crack nucleation; however, at higher applied potentials such fluctuations were absent. The formation and presence of martensite in the specimens seemed to have a minor role in the overall SCC process. The aggressiveness of the thiosulfate concentration was also an important factor in determining the degree of susceptibility to SCC. The results obtained in the slow strain rate tests under open circuit as well as under potential-controlled conditions suggested a film ruptureanodic dissolution type of mechanism operative during SCC of sensitized SS304 in thiosulfate solutions.     

Rolling contact fatigue and mechanical properties of titanium carbide film synthesized on bearing steel surface

The effect of plasma immersion ion implantation and deposition (PIII&D) titanium carbide (TiC) film on the rolling contact fatigue (RCF) life of coated on AISI52100 bearing steel surface is studied experimentally. Testing include plan-view optical microscopy (OM), X-ray diffraction (XRD), friction and wear behaviors, rolling contact fatigue life and nano-indentation measurements. XRD patterns show that titanium carbide phase is formed in the film, and the microhardness of treated samples is higher than that of substrate. Rolling contact fatigue failure tracks were observed using conventional light microscope. Surface wear and adhesive delamination existed. Results indicate that the maximum RCF life of the treated sample prolong by 6.5 times at a Hertzian stress level of 5.1 GPa and 90% confidence level, respectively. Comparison with the substrate, the maximum microhardness of treated specimen is increased by 28.4%. The friction coefficient decreased from 0.95 to 0.15 under identical wear conditions. This remarkable fatigue performance appears to be due to a combination of improved microstructure, adhesion, hardness and surface topography. Therefore, the PIII&D is regarded as one of the promising technologies for improving the RCF life of bearing.     

Investigations of yield stress,fracture toughness,and energy distribution in high speed orthogonal cutting

This paper presents a novel prediction method of the yield stress and fracture toughness for ductile metal materials through the metal cutting process based on Williams' Model [38]. The fracture toughness of the separation between the segments in serrated chips in high speed machining is then deduced. In addition, an energy conservation equation for high speed machining process, which considers the energy of new created workpiece surfaces, is established. The fracture energy of serrated chips is taken into the developed energy conservation equation. Five groups of experiments are carried out under the cutting speeds of 100, 200, 400, 800 and 1500 m/min. The cutting forces are measured using three-dimensional dynamometer and the relevant geometrical parameters of chips are measured with the aid of optical microscope. The experiment results show that the yield stress of machined ductile metal material presents an obviously increasing trend with the cutting speed increasing from 100 to 800 m/min while it decreases when the cutting speed increases to 1500 m/min further. Meanwhile, the fracture toughness between the chip and bulk material displays a slightly increasing tendency. In high speed machining, the fracture toughness of the separation between the segments in serrated chips also presents increasing trend with the increasing cutting speed, whose value is much greater than that between the chip and bulk material. In the end, the distribution of energy spent in cutting process is analyzed which mainly includes such four portions as plastic deformation, friction on the tool–chip interface, new generated surface and chip fracture. The results show that the proportion of plastic deformation is the largest one while it decreases with the cutting speed increasing. However, the proportions of energy spent on new created surface and chip fracture increase due to the increasing of both the chip's fracture area and the fracture toughness.     

30万—60万千瓦汽轮机叶片用钢AISI403（1Cr12Mo）的研制

叙述了３０万～６０万千瓦汽轮机叶片用钢ＡＩＳＩ４０３（１Ｃｒ１２Ｍｏ）的生产工艺以及Ｎｉ、Ｍｏ和热处理工艺对钢的机械性能的影响。当Ｎｉ、Ｍｏ含量分别不小于０．３％时，钢的机械性能满足ＰＤＳ技术条件的要求。     

How surface damage removal affects fatigue life

The effect of the removal of work hardened surface layers from specimens of 2024-T4 aluminum alloy and AISI-4130 steel on their fatigue lives has been investigated. Specimens were fatigued at selected stress levels for a given number of cycles and the surface layer was removed followed by subsequent fatigue cycling. Results confirm that when a material is subjected to fatigue loading, damage accumulates in the surface layers in the form of work hardening. Removal of the surface layer brings the specimen back to its pre-fatigued condition.     

Impact of TiO2 nanoparticles and nanowires on corrosion protection performance of chemically bonded phosphate ceramic coatings

The impact of the addition of TiO₂ nanoparticles and nanowires on the morphology, phase characteristics, contact angle, and electrochemical performance of chemically bonded phosphate ceramic coatings (CBPCs) was investigated. The chemical composition and surface morphology of the TiO₂ nanoparticle and nanowire modified with and without (heptadecafluoro-1,1,2,2-tetradecyl) trimethoxysilane were characterized. Results indicated that the hydrophobic –CF₂– and –CF₃ groups were successfully introduced into the TiO₂ nanoparticles and nanowires after modification. Corrosion resistance of CBPCs with TiO₂ was evidently improved compared with that without TiO₂. Such improvement was mainly due to the combined effects of low surface energy materials and micro/nano structures. In addition, CBPCs with TiO₂ nanowires exhibited higher hydrophobicity and corrosion resistance than those with TiO₂ nanoparticles because of the special columnar structure of the nanowires.     

Investigation on material mixing during FSW of AA7475 to AISI304

AA7xxx and AISI304 stainless steel (SS) are employed in promising applications. Al alloy-to-SS dissimilar joining is difficult and challenging. Major challenge in the joining of these alloys is the difficulty in mixing of these materials which possess exotic and widely distant properties. AA7475-T761 is a high strength aluminum alloy which is used in key aircraft components. Maiden AA7475-T761 and AISI304 dissimilar joints were fabricated using friction stir welding. Welding was performed with tool having pin diameter of 4 mm and offset of 1.25 mm on Aluminum side. Tool rotational speed, traverse speed and shoulder diameter were varied in the range of 450–560 rpm, 50–63 mm/min, and 12–14 mm, respectively. Mechanical tests showed that joint formed with 14 mm diameter, 560 rpm and 50 mm/min gave the best joint efficiency of 71% of Al-alloy at 7.31% elongation. The materials mixing issues during processing were analyzed with SEM mircrostructure and fractography. Metallography also revealed that offset is critical to the success of joint as it controlled effective mixing of SS and Al in 15 and 85 vol.%, respectively. SS fragments from thermo-mechanically affected zone of SS were found to be partially sheared forming layer of thickness equal to tool traverse/revolution ratio.     

铁素体渗氮工艺模拟

纯铁的莱勒图被广泛用于选择合金钢的渗氮工艺。本文首次采用计算热力学来确定AISI 4140钢的莱勒图。研究表明，AISI 4140钢的莱勒图与纯铁的存在明显差异。对AISI 4140钢进行了渗氮试验，目的是验证计算热力学的预测结果。扫描电镜结果显示化合物层中存在两种相，利用透射电镜对化合物层与扩散层界面的研究结果证实了γ′-Fe4N和ε-Fe2－3（C，N）相的共存。这些试验结果与用计算热力学建立的AISI 4140钢莱勒图高度吻合。