Thermal Fatigue Resistance Research Articles

Oxidation and Thermal Fatigue Behaviors of Two Type Hot Work Steels During Thermal Cycling

Thermal fatigue test has been carried out on widely used hot work steel 4Cr5MoSiVl and a low alloyed steel 3Cr3MoV in temperature range of 200 to 700 °C. Tempering resistance, as well as high temperature hardness/strength of steel specimens, works as a dominating material parameter on thermal fatigue resistance. During the heating period, high hardness can depress the inelastic deformation. This deformation is the origination of tensile stress, which acts as the driving force of heat checking during the cooling period. The cyclic strain-oxidation interaction can speed up the damage on surface defects, which plays an obvious role in initiation of thermal cracks. On 4Cr5MoSiVl steel specimens, borders between the matrix and inclusions such as titanium compounds, or lager carbides such as primary carbides, are focused by strain and attacked by oxidation, and are main initiating places of cracks. While on 3Cr3MoV steel specimens, larger strain causes plastic deformation concentrating around grain boundaries. Then the following oxidation accelerates this grain boundary damage and creates cracks.

Thermal fatigue resistance of hot work die steel repaired by partial laser surface remelting and alloying process

In this study, AISI H13 steel was processed using laser surface remelting and alloying with Co-based and iron-based powders for thermal fatigue resistance enhancement. The precracks were produced on the samples before laser treatment. The microstructures of laser treated zones were examined by scanning electron microscope. X-ray diffraction was used to describe the microstructure and identify the phases in molten/alloying zones. Microhardness was measured and the thermal fatigue resistance was investigated with self-controlled thermal fatigue test method. The results indicate that laser surface remelting and alloying can repair a large proportion of thermal cracks. Meanwhile, the strengthening network obtains ultrafine microstructure and super thermal fatigue resistance, which restrains the propagation of thermal cracks. Compared with samples treated with laser surface remelting and laser surface alloying with iron-base powder, samples treated with Co-based powder produce lower cracking susceptibility and higher thermal fatigue resistance.

The thermal fatigue resistance of H13 steel repaired by a biomimetic laser remelting process

In this study, the biomimetic laser remelting process was adopted to repair thermal fatigue cracks on an annealed hot work die AISI H13 steel. Several treated morphologies: spot, striation and lattice were processed by a pulsed Nd:YAG laser. The ultrafine microstructure within the unit was comprised of martensite, austenite and carbides. The average microhardness of the unit is much higher than that of the original surface, even after thermal cycles. Thermal fatigue results show that both crack density and crack length are reduced due to the blocking effect of strengthening units. And the partial laser surface remelting with lattice morphology is the most effective for repairing cracks and improving the thermal fatigue resistance of all.

Photocontrolled Intramolecular Charge/Energy Transfer and Fluorescence Switching of Tetraphenylethene‐Dithienylethene‐Perylenemonoimide Triad with Donor–Bridge–Acceptor Structure

Photochromic 1,2-dithienylethene (DTE) derivatives with a high thermal stability and fatigue resistance are appealing for optical switching of fluorescence. Here, we introduce a donor-photochromic bridge-acceptor tetraphenylethene-dithienylethene-perylenemonoimide (TPE-DTE-PMI) triad, in which TPE acts as the electron donor, PMI as the electron acceptor, and DTE as the photochromic bridge. In this system, the localized and intramolecular charge transfer emission of TPE-DTE-PMI with various Stokes shifts have been observed due to the photoinduced intramolecular charge transfer in different solvents. Upon UV irradiation, the fluorescence quenching resulting from photochromic fluorescence resonance energy transfer in TPE-DTE-PMI has been demonstrated in solution and in solid films. The fluorescence on/off switching ratio in polymethylacrylate film exceeds 100, a value much higher than in polymethylmethacrylate film, thus indicating that the fluorescence switching is dependent on matrices.

Impact on Performance, Emissions and Thermal Behavior of a New Integrated Exhaust Manifold Cylinder Head Euro 6 Diesel Engine

The integration of the exhaust manifold in the engine cylinder head has received considerable attention in recent years for automotive gasoline engines, due to the proven benefits in: engine weight diminution, cost saving, reduced power enrichment, quicker engine and aftertreatment warm-up, improved packaging and simplification of the turbocharger installation. This design practice is still largely unknown in diesel engines because of the greater difficulties, caused by the more complex cylinder head layout, and the expected lower benefits, due to the absence of high-load enrichment. However, the need for improved engine thermomanagement and a quicker catalytic converter warm-up in efficient Euro 6 diesel engines is posing new challenges that an integrated exhaust manifold architecture could effectively address. A recently developed General Motors 1.6L Euro 6 diesel engine has been modified so that the intake and exhaust manifolds are integrated in the cylinder head. Extensive CAD/CAE/CAM analyses have been employed in order to guide the design of the overall surface and the water cooling jacket that surround the exhaust manifold of the new engine version, and thus to be able to improve the low-frequency thermal fatigue resistance of the head. The thus obtained prototype engine head has been tested on a highly-dynamic test bench at the Politecnico di Torino in order to characterize performance, emissions and thermal behavior in comparison to the baseline production engine. The results have generally been very promising and have shown the possibility of maintaining the same performance rating over the overall engine speed range as well as comparable emissions and brake specific fuel consumption in steady-state conditions. Furthermore, appreciably faster engine and aftertreatment warm-up have been recorded due to the higher heat fraction that is transferred to the coolant and to the more favorable exhaust gas enthalpy management. The latter benefit is in fact very interesting as far as the control of HC and CO emissions within the NEDC homologation is concerned

Experimental Investigation on Grinding Performance of Microcrystalline Alumina Abrasive Grinding Wheel for Superalloys

Superalloys are widely used in the aeronautic and astronautic industries owing to their excellent properties in aspects of high-temperature strength, heat stability and thermal fatigue resistance. However, the severe loading of grinding wheel and the poor integrity of grinding surface usually become the problem in grinding of superalloys with conventional grinding wheels. In this paper an experimental study was carried out to investigate the grinding characteristics of superalloys with microcrystalline alumina abrasive wheel. The roughness of grinding surface was tested, on which the effects of the grinding parameters were analyzed. Study results indicated that low loading of grinding wheel and high quality of grinding surface (Ra 0.2 μm) were obtained. The grinding parameters were optimized based on the experiment results.

Thermal Fatigue of the Selected Tool Steel Applied for Metal Moulds Elements in Die Casting of Metals

Abstract The work presents the results of research on thermal fatigue resistance of four steel grades used in the production of metal moulds for pressure diecasting. Thermal fatigue tests were performed on an original test bench using the L.F Coffin method - resistance heated samples. The steels additionally contained alloy additives in the following proportions: Cr = 5.0 ÷5.3%, Mo = 1.30 ÷3.0%, and V = 0.50 ÷1.0%. The thermal fatigue was analyzed using the temperature cycle: Tmin = 200°C; Tmax = 700 ÷750°C. The samples endured between few to few dozens of thousands of temperature cycles in the above temperature range. Steel with maximum vanadium content exhibited the highest level of resistance.

Study on the mechanical behaviors of grey iron mould by simulation and experiment

A three-dimensional finite element model (FEM) of 4.5ton ingot casting system including flow, heat and stress coupled calculation by ProCAST software has been developed. The temperature and stress distribution of grey cast iron mould dependence of solidification time has been revealed. The phase transformation stress has been also taken into account according to the thermal expansion coefficient measured from 293K to 1193K during the heating process. Based on the simulated temperature variation of the hot spot in the 4.5ton mould inner face, the thermal cycling experiment scheme is made. The tensile strength and thermal fatigue resistance of this grey cast iron at various temperatures against pretreatment cycles have been studied. The possibility and tendency of longitudinal cracks and map cracks in ingot mould under service conditions have been discussed.

The mechanical properties of H13 die steel repaired by a biomimetic laser technique

The H13 steel specimens with cracks were repaired by pulsed laser welding with filler wire and the laser parameters were analyzed to obtain the weld without defects. Strengthening units with different spacing were fabricated to improve the tensile strength and thermal fatigue resistance of the weld by laser technique on the surfaces of specimens, that is, PS-1, PS-2 and PS-3 for tensile specimens and PS for thermal fatigue specimen. The results indicated that the units have a beneficial effect on improving the tensile strength and thermal fatigue resistance of welded components of H13 steel. The improvement can be attributed to the microstructure characteristics within the units and the spacing of adjacent units is a key factor which affects the strength of weld by biomimetic treatment.

Effect of grain boundary orientation on radiation-induced segregation in a Fe–15.2 at.% Cr alloy

Ferritic chromium steels are important structural materials for future nuclear fission and fusion reactors due to their advantages over traditional austenitic steels, such as higher thermal fatigue resistance, lower thermal expansion coefficients and reduced swelling. However radiation-induced segregation or depletion (RIS/RID) of solute atoms at grain boundaries in these materials is a concern because these phenomena could adversely affect their mechanical properties. In an effort to develop a full mechanistic understanding of RIS/RID, a systematic approach combining orientation imaging, site-specific specimen preparation and three-dimensional atomic-scale analysis has been developed to characterize the behaviour of Cr and C at grain boundaries during irradiation. This methodology has been applied to a Fe–15.2at.% Cr alloy to investigate the effects of grain boundary misorientation, irradiation depth and impurities. Systematic differences in Cr segregation are reported as a function of grain boundary character and irradiation conditions. The similar properties demonstrated by grain boundaries of similar type means that it should be possible to apply relatively simple models to predict the long-term behaviour of these materials under irradiation conditions.

Microstructure, hardness, and thermal fatigue behavior of H21 steel processed by laser surface remelting

We investigate the effects of laser surface remelting on the resistance to thermal fatigue of a hot working die steel H21 in this work. Laser treatment was engineered to process samples with several treated morphologies. A dominantly martensitic microstructure, nano-sized carbide and high dislocation density in the treated area, were resulted. The average microhardness of the treated area is ~780 HV. The thermal fatigue resistance of laser-treated samples is notably higher than their as-received counterpart. As the thermal fatigue cycle increases, the microhardness of treated area is reduced and then flatted. Crack initiation and propagation both are hampered by it.

Thermal fatigue resistance of H13 steel treated by selective laser surface melting and CrNi alloying

In this study, the selective laser surface melting and laser surface alloying technologies were adopted to improve the thermal fatigue resistance of medium carbon hot-work die steel (H13) by a CO2 laser. Two kinds of mixed chromium (Cr) and nickel (Ni) powders were used as the laser alloying materials, and the effects of the mixing ratio on the thermal fatigue resistance were investigated thoroughly. Some important results such as cross-sectional morphology, phases, hardness and thermal fatigue behavior were analyzed and evaluated. It indicates that the laser surface alloying technique using mixed powder with ratio of 75%Cr–25%Ni can considerably enhance the thermal fatigue resistance of the H13 steel. The laser alloyed zone has excellent properties such as preventing crack initiation and oxidation corrosion compared with original H13. Thermal cracking and oxidation corrosion that occurred at substrate surface can be surrounded and intercepted by a gridded laser strengthened structure. Therefore, the naturally developed cracks could be effectively prevented. Theses results and analysis show that laser surface technique can be positively used to improve surface mechanical properties of H13 dies.

Effect of thermal fatigue on the wear resistance of graphite cast iron with bionic units processed by laser cladding WC

Thermal fatigue and wear exist simultaneously during the service life of brake discs. Previous researchers only studied thermal fatigue resistance or abrasion resistance of compact graphite cast iron (CGI), rather than combining them together. In this paper, wear resistance after thermal fatigue of CGI was investigated basing on the principle of bionics, which was close to actual service condition of the brake discs. In the meanwhile, the effect of thermal fatigue on wear resistance was also discussed. Non-smooth bionic units were fabricated by laser cladding WC powder with different proportions (50wt.%, 60wt.%, 70wt.%). Microstructure and microhardness of the units were investigated, and wear mass losses of the samples were also compared. The results indicate that thermal fatigue has a negative effect on the wear resistance. After the same thermal fatigue cycles times, the wear resistance of laser cladding WC samples is superior to that of laser remelting ones and their wear resistance enhances with the increase of WC content.

Thermal Fatigue Behavior of Nitrocarburized and Low Pressure Nitrided Modified JIS SKD61 Hot Work Mold Steel

A novel method using induction heating equipment was employed to investigate the thermal fatigue behaviors of two hot-work steels, JIS SKD61 and modified JIS SKD61, vacuum hardened treated to 45 HRC. Selected specimens, austenitized at 1298K for 25min, gas quenched to room temperature and tempered at 873K, were salt bath nitrocarburized at 843K for 80min and low pressure nitrided at 813K for 6h, respectively. Microstructure, microhardness, X-ray diffraction and thermal fatigue tests were conducted. The results show that the thermal fatigue properties of the 898K tempered specimen were better than those of other treated specimens. The reason is that the hardened processes would give high tensile strength, which improved the tool material thermal fatigue resistance. The thermal fatigue properties of modified JIS SKD61 specimen, including mean crack length and crack distribution density, were better than those of JIS SKD61 specimen. Low pressure nitriding treatment with a homogeneous nitrided layer could better maintain thermal fatigue resistance than the nitrocarburized steel.

Thermocracks®, a Specific Testing Machine for Evaluation of the Thermal Fatigue Resistance of Materials

Cracking by thermal fatigue is one of the major problems encountered during the operation of numerous parts such as exhaust manifolds or brake discs. One way to improve their lifespan is to develop new materials solutions. Estimating thermo-mechanical fatigue resistance of new materials can be performed with a specific test machine developed by CTIF, associating a multi-position wheel, an induction heating and a cooling by air blowing. Test consists in measuring the number of thermal cycles corresponding to the first crack appearance and to the complete failure of a specific versatile sample.Two examples of studies performed with this machine are shown hereafter.First tests were performed to compare the thermo-mechanical fatigue resistance of different grades of ferritic spheroidal graphite cast iron. These materials are an interesting alternative to alloyed steels or nickel-alloyed cast irons, for the constitution of exhaust manifolds and turbine housings working in the upper-middle temperatures (up to 950°C). The compared materials are SG irons alloyed with silicon (with or without molybdenum), and aluminium.Truck brakes dissipate several megajoules of energy every few seconds, which leads to high thermal stresses in the rubbing discs. Therefore, truck brake discs are mainly damaged by thermal fatigue cracking. One improvement way is to evolve disc material with the aim of increasing their thermal fatigue resistance while keeping the braking performance. For the thermal fatigue tests being as close as possible to real brake conditions, a specific geometry of sample and inductor was developed, to reproduce the thermal gradients observed during tests on real brake discs. The test parameters were then chosen after a coupled numerical-experimental study on full-scale braking. Behaviour of different materials under cycling loading (microstructural changes and cracking) is compared with regard to the results obtained during braking tests.

Nickel-Base Alloy Solutions for Ultrasupercritical Steam Power Plants

Abstract Significant research efforts are being performed in Europe, Japan and the U.S. to develop the technology to increase the steam temperature in fossil power plants in order to achieve greater efficiency and reduce the amount of greenhouse gases emitted. The realization of these advanced steam power plants will require the use of nickel-based superalloys having the required combination of high temperature creep strength, oxidation resistance, thermal fatigue resistance, thermal stability and fabricability. HAYNES® 230® and 282® alloys are two alloys that meet all of these criteria. The metallurgical characteristics of each alloy are described in detail, and the relevant high temperature properties are presented and discussed in terms of potential use in advanced steam power plants.

LSS H13

Abstract LSS H13 is a hot work tool steel with versatility. It has hot strength, toughness, and thermal fatigue resistance. This datasheet supersedes Alloy Digest TS-688, April 2010. This datasheet provides information on composition, physical properties, hardness, and elasticity. It also includes information on forming, heat treating, and machining. Filing Code: TS-708. Producer or source: Latrobe Specialty Steel Company.

New thermally stable photochromic di(het)arylethenes of the cyclopentenone series

Oxidation of 2,3-diarylcyclopent-2-en-1-ones with m-chloroperoxybenzoic acid gave new thermally stable sulfone derivatives of photochromic diarylethenes. The spectral properties of the compounds obtained (the wavelengths of the maxima of the absorption bands of their initial and cyclic forms, the quantum yields of photocyclization and photobleaching reactions) as well as their thermal stability and fatigue resistance were examined. The relationship between the structures of the synthesized compounds and their photochromic properties was determined. The energy differences between the ground-state molecules of the starting and photoinduced isomers of 2,3-diarylcyclopent-2-en-1-ones were calculated by the DFT/B3LYP1 method with the 6-31G(d) basis set. The calculated energy differences can be used to predict and explain such spectral characteristics of photochromic diarylethenes as the thermal stability of photoinduced isomers and the quantum yields of cycloreversion reactions.

Study on the Thermal Fatigue and Anti-Melting Loss Properties of the H13 Steels with Surface Vapor Oxidation

H13 steel specimens with vapor oxidation surface treatment and without surface treatment, were carried out by thermal fatigue test and melting-loss test to research the effect of vapor oxidation surface treatment in the aluminum alloy die casting. The results show that the vapor-oxidized specimens have better erosion resistance and similar thermal fatigue resistance to those without surface treatment. Compound layer and compact layer form in melting-loss test are mainly Fe2Si2Al8 and Fe2Al5, respectively.

Thermal fatigue properties of differently constructed functionally graded materials aimed for refurbishing of pressure-die-casting dies

Different surface layers, constructed on the basis of functionally graded materials using a laser cladding technique, were designed to study the possibility of using them in applications subjected to thermal fatigue. Three different filler materials, varying in terms of the concentrations of alloying elements were used. A graded chemical composition was achieved, varying the concentration of silicon from 0.1wt.% at surface layer to 1wt.% in the base material. A specially designed thermal fatigue test was utilized for the assessment of the thermal fatigue resistance of designed surface layers and compared with base tool steel AISI H13. The results of thermal fatigue testing showed that the different concentrations of alloying elements in the surface layers resulted in different thermal fatigue resistances. The thermal fatigue resistance was observed to be approximately 27times higher in specimens with lower silicon content compared to base material. This was found to be closely correlated with the microhardness and the resistance to softening during annealing.