Chromium Stainless Steel Research Articles

The effect of low pH in erosion-corrosion resistance of high chromium cast irons and stainless steels

Corrosive wear is a form of material degradation that is known to occur on equipment and components that handle suspended solids in aqueous solutions. This surface deterioration process is generally enhanced when the fluids contain chlorides that are acidic in nature. Such environments are encountered in many applications, one such example being the minerals processing industry.High chromium white cast irons are widely used in many engineering applications as they extend the service life beyond that of stainless steels. In this work, the corrosive wear of austenitic stainless steel UNS S31600 and martensitic stainless steel UNS S42000 are compared with high chromium white cast irons (27WCI and 37WCI) by using a submerged jet technique at perpendicular incidence. The testing medium consisted of 3.5% NaCl liquid solution (pH 7 and pH 3) with suspended silica sand particles. The post-test methodology characterised the material loss within the directly impinged zone and turbulent zone where abrasive damage is involved. In neutral conditions, the presence of chromium carbides in white cast irons provided benefits, whilst in the acidic conditions, the austenitic structured materials (for stainless steels and white cast irons) suffered lower overall material loss compared with the martensitic structured materials.

Simulation of casting process: case study on the gating and feeding design for outlet diaphragms of iron ore ball mill

In this paper, the sand casting process was evaluated using ProCAST simulating software and practical experience for manufacturing of the high chromium stainless steel outlet diaphragms used in iron ore ball mill. In the simulation practice, the effects of feeding and gating designs on the liquid flow, heat transfer and solidification phenomenon were evaluated to minimize the liquid surface turbulence during filling of the mold cavity and the shrinkage porosity formation during the liquid solidification in the mold. The effects of different gating ratios and number of feeders were numerically studied using different indicators in the software such as linear velocity, niyama criteria, fraction solid and shrinkage porosity. Further, the optimal design obtained by simulating process was empirically examined. The simulation results showed that the 1:3:4 gating ratio is the proper gating system that it obtains an unpressurized fluid flow without any surface turbulent of the liquid steel in the filling step. In addition, the simulation of solidification phenomenon was indicated that four feeders are required to eliminate of the shrinkage porosities. The empirical casting examination shown the optimal design by the simulation is proper for manufacturing of the steel part without critical defects.

Electronic properties and corrosion resistance of passive films on austenitic and duplex stainless steels

Passive films were grown at constant potential in acidic (pH∼2) and alkaline (pH∼13) solutions on chromium, AISI 304L, AISI 316L and Duplex stainless steels. Passive films on chromium grow following a high field mechanism considering the presence of dissolution phenomena. According to the photoelectrochemical characterization, passive films on Cr have a bandgap of 3.4 eV when formed in acidic solution, and of 2.4 eV when formed in alkaline solution due to the formation of Cr(OH)3. These films result to be poorly stable against anodic dissolution due to a very anodic flat band potential. Conversely, impedance and photoelectrochemical measurements proved that passive films on stainless steels are chromium rich oxide n-type semiconductors with a very high polarization resistance. Their band gap depends on the pH of the passivation solution and on the SS composition.

Changing nickel and chromium stainless steel markets - a review

Changing nickel and chromium stainless steel markets - a review

Rapid dendrite growth mechanism and solute distribution in liquid ternary Fe-Cr-Ni alloys

Stainless steels with excellent hardness and corrosion resistance performance have been widely used in industrial production. Ternary Fe-Cr-Ni alloys, as a model alloy of nickel chromium stainless steels, are of great importance in the fields of material science. Under non-equilibrium solidification condition, alloys may have new microstructure and improved performance. In this paper, two liquid ternary Fe-Cr-Ni alloys are deeply undercooled and rapidly solidified in a 3-m drop tube to investigate the microstructure evolution and solute distribution of alloy droplets with different sizes. In the drop tube experiments, the Fe-Cr-Ni alloy samples with a mass of 1.5 g are placed in a φ16 m mm×150 mm quartz tube with a 0.5-mm-diameter orifice at its bottom and heated by induction heating device in a high vacuum chamber. Then the samples are melted and overheated to 200 K above their liquidus temperatures for several seconds. The alloy melt is ejected out of the small orifice and dispersed into numerous droplets after adding high pressure helium gas flow. The alloy droplets with diameters ranging from 68 μm to 1124 μm are achieved. After experiments, the alloy droplets with different sizes are mounted respectively. Then they are polished and etched. The drop tube technique provides an efficient way to study the rapid solidification mechanism of alloys. Besides the experiments, the dendrite growth velocities of primary phase in two Fe-Cr-Ni alloys are calculated theoretically using the modified LKT/BCT model. As droplet size decreases, both cooling rate and undercooling increase exponentially and the morphologies of two alloys become well refined. Under the near-equilibrium solidification condition with a cooling rate of 10 K/min, both alloys consist of coarse lath-like α phase. After rapid solidification of Fe81.4Cr13.9Ni4.7 alloy droplets during free fall, the microstructure presents a lath-like α phase, resulting from the solid-solid phase transition. As undercooling increases, the primary δ phase is converted from the coarse dendrite with long trunk into equiaxed grain. For Fe81.4Cr4.7Ni13.9 alloy, the microstructure is composed of α phase grains. The transition of primary γ phase from coarse dendrite with long trunk to refined equiaxed grain occurs as the undercooling increases. Meanwhile, both dendrite trunk length and secondary dendrite arm spacing decrease drastically, suggesting that the rapid solidification is the main reason for grain refinement. Moreover, the relative segregation degree of solute Cr and Ni inside α phase grain also decreases obviously with the increase of undercooling, and the microsegregation of Ni is more remarkable than that of Cr. This suggests that the high cooling rate and undercooling cause the solute to be distributed evenly. Compared with that of γ phase, the dendrite growth velocity of δ phase is large and its dendrite tip radius is small. The two phase transform from solute diffusion controlled growth into thermal diffusion controlled growth as undercooling increases to 8 K. When undercooling is larger than 8 K and within the experimental undercooling range, the dendrite growth of both Fe-Cr-Ni alloys is controlled by thermal diffusion.

Experimental Study on the Behavior of TiN and Ti2O3 Inclusions in Contact with CaO-Al2O3-SiO2-MgO Slags.

TiN and Ti2O3 are the predominant inclusion types in Ti-alloyed ferritic chromium stainless steels. In order to ensure the required steel cleanness level, an effective removal of such inclusions in the slag during secondary metallurgy is essential. This inclusion removal predominantly takes place via dissolution of the inclusion in the slag. The dissolution behavior of TiN and Ti2O3 in CaO-SiO2-Al2O3-MgO slags as well as their agglomeration behavior in the liquid steel is investigated using High Temperature Laser Scanning Confocal Microscopy and Tammann Furnace experiments. Thermodynamic calculations are performed using FactSage 7.0. The behavior of TiN is observed to be completely different to that of oxides. Ti2O3 dissolves quickly in slags, and its dissolution behavior is comparable to that of other already well examined oxides. In contrast, TiN shows a very intense gas reaction which is attributed to the release of nitrogen during contact with slag. Slags with higher SiO2 content show a significantly higher ability for the dissolution of TiN as compared to Al2O3-rich slags. The gas reaction is found to also significantly influence the final steel cleanness. Despite the easy absorption of TiN in the slag, the formed nitrogen supports the formation of pinholes in the steel.

Effect of wire fretting on the corrosion resistance of common medical alloys.

Metallic medical devices such as intravascular stents can undergo fretting damage in vivo that might increase their susceptibility to pitting corrosion. As a result, the US Food and Drug Administration has recommended that such devices be evaluated for corrosion resistance after the devices have been fatigue tested in situations where significant micromotion can lead to fretting damage. Three common alloys that cardiovascular implants are made from [MP35N cobalt chromium (MP35N), electropolished nitinol (EP NiTi), and 316LVM stainless steel (316LVM)] were selected for this study. In order to evaluate the effect of wire fretting on the pitting corrosion susceptibility of these medical alloys, small and large fretting scar conditions of each alloy fretting against itself, and the other alloys in phosphate buffered saline (PBS) at 37°C were tested per ASTM F2129 and compared against as received or PBS immersed control specimens. Although the general trend observed was that fretting damage significantly lowered the rest potential (Er ) of these specimens (p < 0.01), fretting damage had no significant effect on the breakdown potential (Eb , p > 0.05) and hence did not affect the susceptibility to pitting corrosion. In summary, our results demonstrate that fretting damage in PBS alone is not sufficient to cause increased susceptibility to pitting corrosion in the three common alloys investigated. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2487-2494, 2017.

Thermophysical properties of low cost lithium nitrate salts produced in northern Chile for thermal energy storage

In recent years, lithium containing salts have been studied for thermal energy storage (TES) applications because of their excellent thermophysical properties. In solar power plants, lithium is seen as a way to improve the properties of state-of-the art molten salts used today. Lithium nitrate is a good candidate for sensible heat storage, because of its ability to increase the salt mixture's working temperature range. In the present research, thermophysical properties characterization of lithium nitrate containing salts, produced in Chile, have been carried out. Corrosion evaluations at 390 ° and 565 °C for 1000 h were performed for low chromium steel T22 and stainless steels (AISI 430 and AISI 316), respectively. Chemical composition of the salts including identification of corrosion products and impurities was determined and an estimation of the Chilean production costs is reported. The study shows a loss of thermal properties after the corrosion tests. The heat capacity was reduced, possibly caused by the formation of oxides at high temperatures. The partial thermal decomposition of the salt was probably produced by the incorporation of corrosion products from the steel.

Single Point Incremental Forming to increase material knowledge and production flexibility

Nowadays, manufactured pieces can be divided into two groups: mass production and production of low volume number of parts. Within the second group (prototyping or small batch production), an emerging solution relies on Incremental Sheet Forming or ISF.ISF refers to processes where the plastic deformation occurs by repeated contact with a relatively small tool. More specifically, many publications over the past decade investigate Single Point Incremental Forming (SPIF) where the final shape is determined only by the tool movement. This manufacturing process is characterized by the forming of sheets by means of a CNC controlled generic tool stylus, with the sheets clamped by means of a non-workpiece-specific clamping system and in absence of a partial or a full die. The advantage is no tooling requirements and often enhanced formability, however it poses a challenge in term of process control and accuracy assurance. Note that the most commonly used materials in incremental forming are aluminum and steel alloys however other alloys are also used especially for medical industry applications, such as cobalt and chromium alloys, stainless steel and titanium alloys. Some scientists have applied incremental forming on PVC plates and other on sandwich panels composed of propylene with mild steel and aluminum metallic foams with aluminum sheet metal. Micro incremental forming of thin foils has also been developed.Starting from the scattering of the results of Finite Element (FE) simulations, when one tries to predict the tool force (see SPIF benchmark of 2014 Numisheet conference), we will see how SPIF and even micro SPIF (process applied on thin metallic sheet with a few grains within the thickness) allow investigating the material behavior. This lecture will focus on the identification of constitutive laws, on the SPIF forming mechanisms and formability as well as the failure mechanism. Different hypotheses have been proposed to explain SPIF formability, they will be listed however the lecture will be more focused on the use of SPIF to identify material parameters of well-chosen constitutive law. Results of FE simulations with damage models will be investigated to better understand the relation between the particular stress and strain states in the material during SPIF and the material degradation leading to localization or fracture.Last but not least, as industrial world does not wait that academic scientists provide a deep and total understanding on how it works, to use interesting processes, the lecture will review some applications. Examples in fields as different as automotive guard, engine heat shield, gas turbine, electronic sensor, shower basin, medical component (patient-fitted organic shapes) and architecture demonstrate that the integration of SPIF within the industry is more and more a reality.Note that this plenary lecture is the result of the research performed by the author in the University of Liege (Belgium) and in Aveiro (Portugal) with the team of R. de Souza during PhD theses of C. Henrard, J. Sena and C. Guzman and different research projects. It is also a synthesis of the knowledge gathered during her interactions with many research teams such as the ones of J.R. Duflou from KU Leuven in Belgium, J. Cao from Northwestern University in USA, M. Bambach in BTU Cottbus-Senftenberg in Germany, J. Jeswiet from Queen's University, Kingston, Canada who are currently working together on a state-of-the-art paper. The micro SPIF knowledge relies on contacts with S. Thibaud from the University of Franche Comte.

The influence of metallurgical factors on corrosion fatigue strength of stainless steels

Corrosion fatigue strength of stainless steels is controlled by tangled interaction among environmental, mechanical and metallurgical factors. In order to estimate corrosion fatigue strength it is indispensable to understand the role of an each influencing factor. The aim of this paper is to present briefly surveyed results on metallurgical factors on corrosion fatigue strength of stainless steels such as austenitic, martensitic and duplex stainless steels mainly based upon author’s experimental results. The targeted dominant metallurgical factors focussed upon are chemical compositions, heat treatment, manufacturing process and microstructures.The emphasis is placed upon effect of Molybdenum content on corrosion fatigue strength of austenitic stainless steels in 3%NaCl aqueous solution, tempering temperature on corrosion fatigue strength of 13% Chromium stainless steel in 3%NaCl aqueous solution and volume percent ferrite on corrosion fatigue strength of duplex stainless steel in potassium alum aqueous solution. The surface and fracture surface observation by optical and scanning electron microscopy revealed that corrosion pit formed at corrosion fatigue crack initiation area. In light of relatively smaller effect of corrosive environment on corrosion fatigue crack propagation rate it can be surmised that corrosion fatigue strength of stainless steels is governed by crack initiation process. It can be concluded that corrosion fatigue strength of stainless steels is strongly influenced by metallurgical factors such as chemical compositions, heat treatment, manufacturing process and microstructures.The information obtained in this survey directly lead to prevention of corrosion fatigue failure in stainless steels made components, selection of stainless steels in corrosive environments and development of corrosion resistant stainless steels.

Methodology for Assessment of Surface Defects in Undermatched Pipeline Girth Welds

The demand for subsea transport of highly corrosive constituents has noticeably increased in recent years. This has driven the requirement for high strength pipelines with enhanced corrosion resistance such as chromium stainless steel or bimetal pipes. The latter are carbon steel pipes with a corrosion resistant alloy lining. Reeling is a cost effective installation method for small to medium size subsea pipelines, up to 457.2 mm (18 in.) in diameter. However, plastic straining associated with reeling has an effect on weld defect acceptance criteria. The maximum acceptable defect sizes are typically developed using engineering critical assessment (ECA), based on the reference stress method, which requires that the weld metal is equal to or stronger than the parent metal in terms of the stress–strain curve. However, evenmatch/overmatch cannot always be achieved in the case of subsea stainless or bimetal pipelines. In this work, a parametric finite-element (FE) study was performed to assess the effect of weld metal undermatch on the crack driving force, expressed in terms of the crack tip opening displacement (CTOD). Subsequently, the fracture assessment methodology for reeled pipes was proposed, where the ECA as per BS7910 is first carried out. These acceptable defect sizes are then reduced, using an analytical formula developed in this work, to account for weld undermatch.

(Invited) Baseplate Materials for Securing Reliability of Wide Band Gap Power Semiconductor Module Operating at High Temperatures

<> Wide Band Gap (WBG) power semiconductors such as SiC and GaN are currently in the spotlight for realizing high power density converters. To derive their characteristics, one of the important issues of power module technology is high temperature operation. It is well known that a power module equipped with the WBG power semiconductors can operate in high Tj (Junction Temperature) as over 200 degrees C. This device feature can achieve great improvements for downsizing of cooling system of converter compared with the conventional Si power device. However the conventional power module technologies are designed to be reliable up to Tj=175 degrees C. Therefore, it is important to develop high temperature capable power module technologies which can operate in Tj=250 degrees C. At this temperature, there are no standard assembly parts as solder, seal resin and ceramic. In addition, high temperature makes assembly process harder because of huge thermal stress. Furthermore, high temperature operation induces large thermal resistance failure after long-term thermal cycle test. Regarding this background, this study aims to investigate the coefficient of thermal expansion (CTE) mismatch behavior between the baseplate and the ceramic substrate at Tj=250 degrees C. CTE mismatch causes thermal cycle reliability failure at the soldered joint between the baseplate and the ceramic substrate. Therefore, it is important to observe soldered joint condition during thermal cycle test. In particular, we conduct a series of verification tests in order to investigate the soldered joint crack propagation caused by CTE mismatch. In this test, the samples are shown in Fig. 1. The Cu-metalized Si3N4 ceramic substrates are attached to the baseplates with Au–Ge solder. As the baseplate material, Al (pure aluminum) and Cu (oxygen-free copper) are selected which are used for the conventional power modules, in addition, SUS410 (chromium stainless steel) and W-Cu (89W–11Cu) that CTEs are similar to those of the Cu-metalized Si3N4 ceramic substrate are selected. The samples undergo the thermal cycle load of –40 to 250 degrees C and the crack propagation of the soldered joint areas are observed by Scanning Acoustic Tomography (SAT). Fig. 2 shows SAT images of the joint areas and Fig. 3 shows the remaining joint area rate (= remaining joint area / initial joint area) as a function of the number of thermal cycles. Consequently, the smaller mismatch of CTE between the baseplate and the ceramic substrate contribute to less crack propagation of joint area in the case of Cu, SUS410, and W–Cu samples. On the other hand, the crack propagation of Al samples is unexpectedly small in spite of the largest CTE mismatch. The discussion of the result is as follows. It is well known that the dominant factor of the plastic deformation mechanism is grain boundary sliding not dislocation in the uniform temperature, TH = T/Tm (absolute melting temperature), exceeds 0.4. Therefore, creep deformation easily occurs in the case. While Al’s 0.4 Tm is 100 degrees C, the other materials' are higher than 250 degrees C. Therefore, in particular, plastic deformation easily occurs for Al, compared with the other three materials in –40 to 250 degrees C. This implies that the Al baseplate plastic deformation caused by thermal stress of CTE mismatch ends up with the stress relief of the soldered joint. At the result of the thermal cycle load, the existence of a fine wavy deformation trace on the rear of the Al baseplate is observed as shown in Fig. 4. That should almost be equal in area to the soldered joint of the baseplate. This physical change implies that repetition plastic deformation should occur to the Al baseplate because the wavy trace is not shaped on the baseplates of the other three materials. In conclusion, we verify the effects of CTE mismatch between the baseplate and the ceramic substrate of the soldered joint in –40 to 250 degrees C. As the result, it is clarified that similar CTE between the baseplate and the ceramic substrate is important in order to realize long-term reliability. On the other hand, it is also clarified that the baseplate plastic deformation contributes to better thermal cycle capability even if the CTE mismatch is large. This study will contribute to realizing the power module which is able to operate in Tj=250 degrees C. <Acknowledgement> This study was supported by the Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “Next-generation power electronics/Consistent R&D of next-generation SiC power electronics” and “the Novel Semiconductor Power Electronics Project Realizing Low Carbon Emission Society” (funding agency: NEDO) Figure 1

Influence of PWHT on Toughness of High Chromium and Nickel Containing Martensitic Stainless Steel Weld Metals

Commonly used 12.5Cr-5Ni consumable specified for welding of martensitic stainless steels is compared with newly designed 14.5Cr-5Ni consumable in terms of their suitability for repair welding of 410 and 414 stainless steels by gas tungsten arc welding process. Changes in microstructure and austenite evolution were investigated using optical, scanning electron microscopy, X-ray diffraction techniques and Thermo-Calc studies. Microstructure of as-welded 12.5Cr-5Ni weld metal revealed only lath martensite, whereas as-welded 14.5Cr-5Ni weld metal revealed delta-ferrite, retained austenite, and lath martensite. Toughness value of as-welded 12.5Cr-5Ni weld metal is found to be significantly higher (216 J) than that of the 14.5Cr-5Ni weld metal (15 J). The welds were subjected to different PWHTs: one at 923 K (650 °C) for 1, 2, 4 hours (single-stage PWHT) and another one at 923 K (650 °C)/4 h followed by 873 K (600 °C)/2 h or 873 K (600 °C)/4 h (two-stage heat treatment). Hardness and impact toughness of the weld metals were measured for these weld metals and correlated with the microstructure. The study demonstrates the importance of avoiding formation of delta-ferrite in the weld metal.

Influence of Solid-Liquid Composite Casting on Interface and Microstructure of High Chromium Cast Iron

High chromium cast iron and stainless steel bimetal were fabricated by liquid-solid composite casting .The interface diffusion behavior and microstructure evolution of high chromium cast iron were studied. The results indicated that interface element diffusion behavior between stainless steel and high chromium cast iron was obviously existed. Under experimental conditions, there were many refined grainy-shaped carbides precipitation in stainless steel near interface, located at austenite grain boundary and intragranular austenite. As for high chromium cast iron, the morphology of the carbides varied from the interface to the specimen edge. The rod shaped carbides approached to composite interface were finer and become coarser rod-like or blade-like with increased distance from the composite interface. The reasons for elements diffusion and microstructure change were associated with alloys contents and temperature field.

KUBOTA CA-6NM

Abstract Kubota CA-6NM is a hardenable Fe-Cr-Ni-Mo alloy based on the 13% chromium stainless steel alloy CA-15. Ductility, impact properties, and resistance to salt water corrosion are raised by the addition of nickel and molybdenum. Castability in thick or intricate sections is better than that of the 13% chromium alloy. Similarly, the alloy is more readily welded and requires lower preheat temperatures. The alloy is most generally used in the normalized and tempered condition, but variations in heat treatment are used to enhance specific properties. This datasheet provides information on composition, physical properties, hardness, and tensile properties as well as fracture toughness and creep. It also includes information on low and high temperature performance, and corrosion resistance as well as casting, heat treating, and joining. Filing Code: SS-1196. Producer or source: Kubota Metal Corporation, Fahramet Division.

Post-operation state and extension of service life of compressor blades of the gas-turbine power plant GTE-45-3

Gas turbine engine compressor blades are the most essential parts among all the units of gas turbine power plants. They are made of chromium stainless steels. Erosive and corrosive wear of working surfaces as well as thermal stress fatigue are the main types of damage of compressor blades after long-term use. The aim of this work was to develop methods of recovering the serviceability of the material of the power plant ГТЭ-45-3 compressor blades with a view to extending their service life. To examine the post-operation state of compressor blades and the material serviceability the compressor blades of the gas turbine engine power plant ГТЭ-45-3 made of corrosion-resistant steels ЭИ961 (13Х11Н2В2МФ) and 12Х13 were investigated after their service life expired with the total engine hours equal to 50000. To evaluate the serviceability of the blade material an unconventional approach and know-how were used. The results of analysis of the microstructure of corrosion-resistant steels as well as their physical and mechanical properties are presented in the paper. A process of material serviceability recovery is developed with a view to extending the service life of compressor blades. The process includes the following sequence of operations: machining aimed at removing corrosion and mechanical defects, argon-arc welding that restores the geometry of the rotor blades, thermal tempering for removing residual stress.

Capability of mechanical alloying and SPS technique to develop nanostructured high Cr, Al alloyed ODS steels

Oxide dispersion strengthened (ODS) Fe alloys were produced by mechanical alloying (MA) with the aim of developing a nanostructured powder. The milled powders were consolidated by spark plasma sintering (SPS). Two prealloyed high chromium stainless steels (Fe–14Cr–5Al–3W) and (Fe–20Cr–5Al+3W) with additions of Y2O3 and Ti powders are densified to evaluate the influence of the powder composition on mechanical properties. The microstructure was characterised by scanning electron microscope (SEM) and electron backscattering diffraction (EBSD) was used to analyse grain orientation, grain boundary geometries and distribution grain size. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) equipped with energy dispersive X-ray spectrometer (EDX) were used to observe the nanostructure of ODS alloys and especially to observe and analyse the nanoprecipitates. Vickers microhardness and tensile tests (in situ and ex situ) have been performed on the ODS alloys developed in this work.

Cobalt chromium stents versus stainless steel stents in diabetic patients

The clinical outcome in diabetic patients undergoing percutaneous coronary intervention (PCI) is inferior to that in non-diabetic patients. Several aspects of diabetic coronary artery disease appear to be responsible for this observation. In comparison with stainless steel stent, cobalt chromium stent has a higher radial strength and radio-opacity for similar electronegativity, this allow for the production of thinner struts with a similar radiological visibility. Therefore we studied and compared six-months prognosis of cobalt chromium stent versus stainless steel Bare metal stents in diabetic patients undergoing PCI. Our study included seventy diabetic patients with Ischemic heart disease amendable to percutaneous stenting with stents ⩾3 mm in diameter and ⩽25 mm length. They were randomly assigned to cobalt chromium stents (Group I) or stainless steel stents (Group II). PCI was done with initial success and we excluded patients with unsuccessful PCI or complications during intervention, using stainless steel stent and chromium stent in the same lesion, left main stem lesions, osteal and bifurcational lesions. Our primary end point was Major adverse cardiac events (death, Myocardial infarction, unstable angina, emergency CABG or target lesion revascularization); over period of 6 months and our secondary end point was in-stent restenosis assessed by coronary angiography at 6 months in the follow up period. Total MACE in group (I) was 9 patients, coronary angiography was done for those patients after the cardiac event, that showed 7 patients with ISR and 2 of them showed patent stents. Patients without MACE whom undergone follow up coronary angiography after 6 months, revealed 6 patients suffered ISR out of 23 patients. While total MACE in group (II) was 5 patients, coronary angiography for those patients showed 4 patients with ISR and 1 of them showed patent stent. Patients without MACE whom undergone follow up coronary angiography after 6 months revealed 10 patients suffered ISR out of 28 patients. So as a result for all patients included in our study, 13 patients from group (I) suffered ISR in the period of 6 months follow up period, they represented 40% of the group, while 14 patients in group (II) with a percentage of 42.4% of the group suffered ISR at 6 months. There was no statistically significant difference between the two groups as regard the incidence of ISR at follow up. ( P > 0.05). We concluded that no significant statistical difference was found between the two stents (cobalt-chromium alloy bare metal stent versus conventional bare metal stainless steel stent) in diabetic patients regarding (initial procedural success, in-hospital complications, the incidence of ISR at follow up, event-free survival at follow up).

Bacterial and osteoblast behavior on titanium, cobalt–chromium alloy and stainless steel treated with alkali and heat: A comparative study for potential orthopedic applications

HypothesisAnatase-modified titanium (Ti) substrates have been found to possess antibacterial properties in the absence of ultraviolet irradiation, but the mechanism is not known. We hypothesize that this is due to the bactericidal effects of reactive oxygen species (ROS) generated by the surface anatase. ExperimentsAlkali and heat treatment was used to form anatase on Ti surface. The generation of ROS, and the behavior of bacteria and osteoblasts on the anatase-modified Ti were investigated. Cobalt–chrome (Co–Cr) alloys and stainless steel (SS) were similarly treated with alkali and heat, and their surface properties and effects on bacteria and osteoblasts were compared with the results obtained with Ti. FindingsThe anatase-functionalized Ti substrates demonstrated significant bactericidal effects and promoted apoptosis in osteoblasts, likely a result of ROS generated by the anatase. The alkali and heat-treated Co–Cr and SS substrates also reduced bacterial adhesion but were not bactericidal. This effect is likely due to an increase in hydrophilicity of the surfaces, and no significant ROS were generated by the alkali and heat-treated Co–Cr and SS substrates. The treated Co–Cr and SS substrates did not induce significant apoptosis in osteoblasts, and thus with these properties, they may be promising for orthopedic applications.

A new resource-saving, low chromium and low nickel duplex stainless steel 15Cr–xAl–2Ni–yMn

A new family of resource-saving, low Cr and low Ni duplex stainless steels, with compositions of 15Cr–xAl–2Ni–yMn (x=1.2–2.8, y=8–12, wt.%) has been developed by examining the effect of Al and Mn on microstructure, mechanical property and corrosion property. The results show that 15Cr–1.2Al–2.0Ni–8Mn and 15Cr–2.0Al–2.0Ni–10Mn alloys have a balanced ferrite–austenite relation and that 15Cr–2.8Al–2.0Ni–12Mn alloy has a primary ferrite phase structure. The ferrite volume fraction increases with the solution treatment temperature and Al content while decreases with Mn content. No precipitate was found after solution-treated at 750°C for 30min. 15Cr–1.2Al–2.0Ni–8Mn alloy has a strong strain hardening effect, and 15Cr–2.0Al–2.0Ni–10Mn alloy has a good TRIP effect. Both of the 15Cr–1.2Al–2.0Ni–8Mn and 15Cr–2.0Al–2.0Ni–10Mn alloys have excellent impact toughness at low temperature with the impact energy higher than 125J at −40°C. The pitting corrosions always occur in austenite phase. Among the designed alloys, 15Cr–1.2Al–2.0Ni–8Mn and 15Cr–2.0Al–2.0Ni–10Mn are found to be excellent alloys with a proper phase proportion and a better combination of superior mechanical property and good pitting corrosion resistance.