Heat-resistant Stainless Steel Research Articles

Failure analysis of a heat-resistant stainless steel ring in a gas turbine burner

Hot gas path components in gas turbines are damaged by several mechanisms due to aggressive environments. In this research, the cracking of an insert ring, which is composed of Nb-stabilized heat-resistant stainless steel, after 8000 operation hours, is investigated. The microstructure of the ring is examined by optical and scanning electron microscopes equipped with energy-dispersive X-ray spectroscopy. The generated stress and strain within the ring during a complete operation cycle (startup to shutdown) of gas turbine are simulated by finite element simulation software. The microstructural investigations indicate the formation of some precipitates that mainly contain nitrogen atoms. The development of tensile loads within the ring during shutdown and brittle N-contained precipitates leads to cracking. The indicators of both types of hot corrosion are also observed.

Microstructural evolution and precipitation behavior of the 0.1C-18Cr-1Al-1Si ferritic heat-resistant stainless steel during hot deformation

The 0.1C-18Cr-1Al-1Si ferritic heat-resistant stainless steel has attracted considerable attention to high-temperature applications due to its favorable combination of creep and oxidation resistance. In this paper, the microstructural evolution and precipitation behavior of the 0.1C-18Cr-1Al-1Si ferritic heat-resistant stainless steel is studied from the compression deformation data in the temperature range of 850 °C–1050 °C and the strain rate range of 0.01–1 s−1. Experimental results demonstrate that higher temperatures and lower strain rates enhance the dynamic recrystallization (DRX) process with remarkable effectiveness. The main precipitates are proved as the AlN phases and the (Cr,Fe)23C6 carbides during hot deformation. With an increase in the deformation temperature, the size of (Cr,Fe)23C6 and AlN gradually increases, and volume fraction gradually decreases. When the strain rate decreases, the average size and volume fraction of (Cr,Fe)23C6 and AlN gradually increase. At the lower temperatures, the occurrence of dynamic recrystallization (DRX) is strongly influenced by (Cr,Fe)23C6 formed on the grain boundaries, mainly because it causes a pinning effect, which hinders the movement of dislocations and delays the occurrence of the DRX.

Damage characterization of heat resistant stainless steel grate plates in an iron ore pelletizing plant

Grate plate is one of the consumable components of chain grate in pelletizing plants, which is made up of heat resistant stainless steels. Service life of grate plates has major effect on productivity and quality of pellets. Objective of this work is to study the mechanism of intergranular cracking in heat-resistant stainless steel, one of the major degradation mechanisms of grate plates, in order to suggest preventive methods. To reach this goal, plant samples were provided from used and as-cast grate plates. The samples were studied using a scanning electron microscope (SEM) equipped with an energy dispersive x-ray spectroscopy (EDS) probe and metallography techniques. The results revealed that no Cr-depletion zone was formed during solidification and also during using of the grate plates at elevated temperatures. It was also revealed that formation of interdendritic Mn, S and/or C concentrated precipitates is the reason of the intergranular crack nucleation and propagation during the service time. As a solution to prevent that defect, it is suggested to reduce the distance between the liquid impenetrable temperature (LIT) and solidus temperature during solidification (for example with decreasing the concentration of S content).

Application of Cold Metal Transfer Welding for High Pressure Die Casting Mold Restoration

This paper presents results of the research focused on the possibility of the restoration of the shape parts of molds made of X15CrNiSi20-12 (EN 100 95) heat-resistant austenitic chromium-nickel stainless steel working in high-pressure die casting of aluminum alloys by clad welding. There were tested two welding wires—E Ni 6625 and E 18 8 Mn B 2 2—deposited on X15CrNiSi20-12 (EN 100 95) tool steel using cold metal transfer (CMT) welding in a protective atmosphere of Ar. The resistance of welds was tested against dissolution in molten aluminum alloy ENAC-AlSi9 and the testing procedure was designed. The resistance of welds against dissolution were assessed by exposition of welded clads in an aluminum melt for 120 and 300 min. The EDX semi-quantitative microanalyses of element distribution were performed at the welding–melt interface, and build-ups were also observed on the surface of welded clads.

Effect of cracking feedstock on carburization mechanism of cracking furnace tubes

In the present research, one of the primary problems which often arises in cracking furnaces of ethylene plants was pioneered. This problem is associated with high failure rate of heat resistant cast stainless steel tubes used in pyrolysis furnaces. The interaction between feed types and tubes which is accompanied by carburization is considered as the main origin of such a high failure rate. Hence, in this study three samples of tube (a heat resistant alloy of HP40 + Nb) involving as-cast sample (without exposure to feed), the sample exposed to liquid feed and the sample exposed to gaseous feed were studied. In this respect, two types of feed including liquid phase (i.e., naphtha), and gas phase (ethane) were selected to be compered in terms of their influence on the tube structure. In order to evaluate the interaction between the feed type and the tube destruction, microstructural changes were studied using SEM, EDS and microhardness analyses. The results revealed that higher values of hardness were obtained for the gas feedstock tubes compared to the liquid feedstock ones and as-cast sample. This can be attributed to easier carbon diffusion and more sever growth of carbide in the tube structure that makes it more brittle. Moreover, in inner surfaces of tubes, spalling of oxide layers in addition to reformation of chromium oxide on the surface cause chromium to diffuse into the metal surface, leading to reduction of the chromium content to 5 wt%. The results showed that generally the gas feedstock caused more microstructural changes and damages on the tube structure compared with the liquid feedstock with identical life services.

Comparative Study on the Oxidation Behavior of Austenitic and Ferritic Heat-Resistant Stainless Steels at High Temperatures

A comparative study of the high-temperature oxidation behavior and mechanism of 0Cr25Ni20 austenitic heat-resistant stainless steel (AHSS) and 0Cr18AlSi ferritic heat-resistant stainless steel (FHSS) at 800°C, 900°C, and 1000°C in air up to 140 h was performed using isothermal oxidation tests. The oxidation kinetics of 0Cr25Ni20 AHSS and 0Cr18AlSi FHSS followed the parabolic law. The oxide films on 0Cr25Ni20 AHSS were composed of continuous and dense Cr2O3, MnCr2O4, and a small amount of NiMn2O4, whereas silicon exhibited internal oxidation and deteriorated the adhesion between the oxide film and substrate. Nickel-free 0Cr18AlSi FHSS exhibited good oxidation resistance at 800°C and 900°C due to dense, continuous, and well-adhered multicomponent oxide films containing Al2O3, Cr2O3, MnCr2O4, and a small amount of MnFe2O4. The oxidation resistance of 0Cr18AlSi FHSS declined at 1000°C, mainly due to the formation of nonprotective Fe2O3 and severe internal oxidation of aluminum.

Influence of solidification induced composition gradients on carbide precipitation in FeNiCr heat resistant steels

Secondary precipitation of Cr-rich carbides in heat resistant austenitic stainless steels has been investigated both experimentally and using finite element simulations. The microstructural evolutions in two commercial grades were characterized using electron microscopy. A special emphasis was given on the peculiar spatial distribution of M23C6 secondary carbides exhibiting precipitate free zones surrounding primary carbides, and high density precipitate zones extending with longer aging times. Solidification induced chemical composition gradients were clearly exhibited in the as-cast alloys with significant chromium depletion in the vicinity of primary M7C3 carbides. It is then proposed that these gradients play a major role in the secondary precipitation mechanism. Classical nucleation and growth theories have been adapted to account for (i) the flux of solutes with large difference in diffusion coefficients, (ii) the initial composition gradients in the matrix and, (iii) the chemical driving force for nucleation and growth of M23C6 carbides. Within this framework, the whole kinetics has been reproduced. It clearly shows that the spatial distribution of secondary carbides that play a key role in the creep resistance of these alloys is the result of a complex interaction between initial composition gradients in as-cast alloys and solute flux resulting from phase transformation during aging.

Precipitate Evolution in a Modified 25Cr-20Ni Austenitic Heat Resistant Stainless Steel During CreepRupture Test at 750 ℃

Precipitate Evolution in a Modified 25Cr-20Ni Austenitic Heat Resistant Stainless Steel During CreepRupture Test at 750 ℃

Analyze the effect of Molybdenum on Heat Resistance Stainless Steel Casting SCH 22

There was SCH 22 component named hanger that is produced by casting, where it is one of the components applied at 1100°C work temperature. Problems on the product is the occurrence of scaling, causing the the function failure and shortening its lifetime. Generally, this scaling occurs when the material is exposed to high temperature, then kinds of iron oxide layers are arisen such as FeO, Fe3O4, and others. Based on the literature, Molybdenum can be added to the SCH 22 with maximum limit of 0.5%. The purpose of this study is to know the influence of Molybdenum to the mechanical properties and analyze the phenomenon of scaling on Heat Resistant Stainless steel Casting (SCH 22). It is expected that molybdenum could increase the scaling resistance in the high temperature. The method is making specimens through metal casting process where the molybdenum content are made to 0.3%, 0.7%, 1.1%. Each specimen should be heated at 1150°C and held for 4 hours. Then the mechanical strength and micro structure are observed to see the effect such molybdenum addition. The result is obtained that the 0.7% addition of molybdenum element can reduce the degradation due to scaling on Heat Resistance Stainless Steel Casting SCH 22.

Evolution of crystallographic orientation during thermomechanical fatigue of heat-resistant stainless steel

We present the evolution of crystallographic orientation and microstructure during thermomechanical fatigue (TMF) of heat-resistant cast austenitic stainless steel at peak temperatures reaching 950 °C using the electron backscatter diffraction (EBSD) method. Higher restraints or peak temperatures induced larger crystal misorientation by geometrically necessary dislocations (GNDs), forming dislocation walls or subgrains in the grains. Networked carbide clusters in the microstructure locally amplified the misorientation in the adjacent matrix and initiated fatigue cracks. The mean value of cumulative misorientations over a specific distance in the matrix was linearly proportional to the cyclic plastic strain.

A study of microstructural evolution of Fe-18Cr-8Ni, Fe-17Cr-12Ni, and Fe-20Cr-25Ni stainless steels after mechanical alloying and annealing

In this study, high-energy mechanical alloying technique was used to produce nanocrystalline stainless steels of three different compositions from elemental powders. The microstructural evolution (grain growth and phase transformation) as a function of alloy compositions and annealing temperatures were investigated by room and high temperature x-ray diffraction experiments, transmission electron microscopy and focused ion beam microscopy. The results revealed that stainless steels with low nickel content (i.e., Fe-18Cr-8Ni) underwent a deformation-induced martensitic transformation during room temperature mechanical alloying. Deformation-induced martensitic transformation with increasing nickel content (i.e., Fe-17Cr-12Ni and Fe-20Cr-25Ni) would not be possible by room temperature milling but was created by high strain rate cryogenic processing, the degree to which was compositional dependent. Post process annealing induced the reverse transformation from martensite-to-austenite the ratio of which was found to be a factor of alloy composition and annealing temperature. The real time in-situ x-ray studies showed that the martensite-to-austenite reverse transformation was completed at around 600 °C and 800 °C for Fe-18Cr-8Ni and Fe-20Cr-25Ni steels, respectively. Microscopy studies revealed a significant enhancement in the resistance to grain growth for Fe-17Cr-12Ni steel over other compositions at elevated temperatures as high as 1200 °C. As such, cryogenic processing following by reverse martensitic transformation of high Ni containing alloys provides a pathway for developing higher heat resistant stainless steel alloys.

Mechanical study in drilling of heat resistant austenitic stainless steel

Machining of difficult-to-cut-materials like heat resistant stainless steels leads to the rapid tool wear and tool failure. The analysis of drilling process of these steels is even more difficult as it is not easy to investigate the cutting process at the drill tip. Therefore for this critical operation, modelling of cutting forces is very important. The study of the mechanical loading is based on the cutting tool geometry variation along the cutting edge. This study aims to investigate the drilling of heat resistant stainless steels with two geometries of twist drills, by analyzing specific cutting energy and forces at a global and a local scale.

Fracture and Damage Behavior in an Advanced Heat Resistant Austenitic Stainless Steel During LCF, TMF and CF

Future advanced ultra-supercritical power plant will be run at higher temperature and pressure. New materials will be used to meet the requirements. However, the structure integrity of these materials needs to be evaluated. Sanicro 25 is a newly developed advanced austenitic heat resistant stainless steel with the aim to be used in future 700 °C or 650 °C power plants to replace part of Ni based alloys. This paper provides an overview on the fracture and damage behavior in this material during LCF, TMF and CF. The cyclic hardening and fatigue life during LCF, TMF and CF will be discussed. The influence of prolonged service degradation has been analyzed by the use of pre-aged material for TMF and CF loading conditions.

Development of Heat-resistant Ferritic Stainless Steels “NSSC<sup>®</sup>429NF” and “NSSC<sup>®</sup>448EM” Utilized Dynamic Precipitation Hardening for Automotive Exhaust Systems

Development of Heat-resistant Ferritic Stainless Steels “NSSC<sup>®</sup>429NF” and “NSSC<sup>®</sup>448EM” Utilized Dynamic Precipitation Hardening for Automotive Exhaust Systems

Effect of Plastic Strain and Recovery Rate on Thermal Fatigue Behavior in High Heat-resistant Ferritic Stainless Steel SUS444

Effect of Plastic Strain and Recovery Rate on Thermal Fatigue Behavior in High Heat-resistant Ferritic Stainless Steel SUS444

Characteristic of Warm Laser Shock Peening of ЭП866 Heat Resistant Martensite Stainless Steel

Characteristic of Warm Laser Shock Peening of ЭП866 Heat Resistant Martensite Stainless Steel

High temperature oxidation behavior of a high Al-containing ferritic heat-resistant stainless steel

The high temperature oxidation behavior of a high Al-containing ferritic heat-resistant stainless steel at temperatures of 800, 900, and 1000°C in air were studied in isothermal oxidation tests. The results showed that the isothermal oxidation kinetic curves obtained at different temperatures followed the parabolic law, and the weight gain per unit at 1000°C was significantly higher than that at 800 and 900°C. The oxidation rate at 1000°C was about three times faster than that at 800 and 900°C. Continuous and compact multicomponent oxide films mainly composed of Cr2O3, Al2O3, spinel MnFe2O4, and MnCr2O4 were obtained at 800 and 900°C. The oxide film started delaminating at 1000°C; the outer layer was composed of Cr2O3, spinel MnCr2O4, and MnFe2O4, the middle layer was composed of Fe2O3 and Fe-Cr matrix, and the inner layer was composed of Al2O3 and SiO2. Oxidation resistance at 1000°C was reduced mainly because of porous Fe2O3 and inner oxidation of Al and Si. In addition, the oxidation mechanism was discussed based on kinetic and morphological observations.

Effects of Cryogenic Treatment on the Strength Properties of Heat Resistant Stainless Steel (07X16H6)

Cryogenic treatment on metals is a well known technology where the materials are exposed to cryogenic temperature for prolonged time duration. The process involves three stages viz. slow cooling, holding at cryogenic temperature and warming to room temperature. During this process, hard and micro sized carbide particles are released within the steel material. In addition, soft and unconverted austenite of steel changes to strong martensite structure. These combined effects increase the strength and hardness of the cryotreated steel. In this experimental study, the effects of cryogenic treatment, austenitising and tempering on the mechanical properties of stainless steel (07X16H6) have been carried. After determining the strength properties of the original material, the specimens were cryotreated at 98K for 24 hours in a specially developed cryotreatment system. The effects of austenitising prior to cryogenic treatment and tempering post cryotreatment on the mechanical properties of steel samples have been experimentally determined and analysed.

Effects of interface thermal resistance on surface morphology evolution in precision glass molding for microlens array.

To study the effects of the interface thermal resistance on surface morphology evolution in precision glass molding (PGM) for microlens array with different mold materials, including Tungsten carbide and heat-resistant stainless steel, the glass-mold interface thermal resistance is calculated, and heat-transfer simulation of PGM based on an interface thermal resistance model at the heating stage is conducted correspondingly. The effect of flattening behavior on the glass-mold interface is explained. Then, experiments evaluating the relationship between heating time and glass surface roughness are carried out, and the glass adhesion phenomenon appearing on the heat-resistant stainless steel mold is observed and analyzed. Finally, the microlens array is fabricated on the nickel phosphorous plating layer on the heat-resistant stainless steel substrate by diamond-ball nose-end milling, and experiments of PGM for the microlens array are carried out to verify the interface thermal resistance model. The result shows that a high-quality surface can be obtained by the combination of a smooth mold and rough glass. Compared with the microlens array fabricated with the rough glass preform, using the smooth glass preform achieves higher form accuracy without defects or blurs.

Research on machining quality control in micro milling of low-rigidity characteristics

Micro cutting is widely used in the machining of micro components and micro features of conventional size components. During the micro cutting process, the manufactured components and characteristics usually belong to mesoscale, and the final geometric accuracy and surface quality are affected by many factors. In this paper, a series of micro milling tests based on heat-resistant stainless steel (12Cr18Ni9) are carried out to figure out the influence of different factors on machining quality of mesoscale low-rigidity characteristics. During the study, the small displacement torsors (SDT) theory are employed to characterize the perpendicularity tolerance of mesoscale surface. Optical microscopic measurement method is used to obtain SDT parameters, then the width of the tolerance zone is obtained; based on which, the effect of different factors on machining quality is systematically studied. In addition, the surface roughness and micro topography of the machined surface are also analyzed, and the phenomenon of surface deterioration caused by high-temperature chip is effectively controlled. Finally, a general method for ensuring the processing quality of mesoscale low-rigidity characteristics is proposed.