Search

The IHTC (Interfacial-Heat-Transfer-Coefficient) between 22MnB5 and KDAHP1 hot work tool steel during the hot stamping process is an important thermal parameter to reflect the heat transfer efficie...

In this study, the microstructure and mechanical properties of martensitic hot-work tool steel AISI H13 produced by laser powder bed fusion (LPBF) under argon atmosphere in different LPBF process t...

While exposure to air contaminants from metal arc welding at workplaces has been intensively investigated over the last five decades, other hot work processes, such as flame and plasma cutting, air carbon arc gouging, and surface grinding have not received as much attention. Exposures to particulate matter (PM) during selected hot work processes, such as metal active gas (MAG) and manual metal arc (MMA) welding, flame and plasma cutting, air carbon arc gouging, and surface grinding were measured. Respirable, inhalable, and "total" fractions of the PM were collected with different air samplers in the workers' breathing zone. Concentrations of PM, chromium (Cr), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), copper (Cu), and lead (Pb) were determined in the samples by using gravimetric analysis and plasma-based analytical atomic spectrometry techniques. Bio-accessibility of the elements was investigated by using a synthetic lung lining fluid (Hatch´s solution) for the leaching of soluble metal compounds in the collected samples. Short term (15-75 min) workplace air concentrations of PM, Cr, Fe, Mn, Ni and Cu in the workers´ breathing zone during hot work processes were found to be high compared to the current 8-hr time-weighted average (TWA) exposure limit values (ELVs) in use in many countries. The short-term median concentrations of PM during the different hot work processes varied between 6.0 and 88.7 mg m

There are advantages to replacing weld joints with structural adhesive joints in shipbuilding, including reduction of labor associated with hot work and straightening work. However, the dimensional accuracy of the structural members must be the same for structural adhesive and welding, so the structural adhesive must fill gaps of the millimeter order. The lack of knowledge about the long-term reliability of thick adhesive layers is an obstacle to its practical use. Therefore, accelerated deterioration tests under high temperature and high humidity, recovery tests by drying after water absorption, xenon exposure weatherability tests, and salt water mist resistance tests were conducted to obtain relationships between each deterioration factor and decreasing time of strength retention rate. The durability evaluation was carried out for SGA structural adhesives from two different manufacturers. In this study, the substrate of the structural adhesives joint was A5052. It is assumed that the aluminum su...

The aim in this article is to evaluate microstructural changes, hardness variations, and wear behavior of H13 hot work tool steel as a function of austenitizing and tempering temperature us...

Decarburisation is found as an undesirable consequence of the heat treatment cycle in hot work tool steels. In this work, an increase in the decarburisation resistance of tool steel through...

Influence of cryogenic treatment on AISI H13 hot work die steels has been studied to correlate carbide density with surface roughness and dry sliding wear. This work includes hardening of AISI H13 ...

To investigate the evolution mechanism of Al2O3 inclusions after Mg treatment in H13 die steel, the determination of inclusions characteristics and thermodynamic calculation were carried out in the present study. The results showed that irregular and cluster Al2O3 inclusions in H13 die steel were modified to MgO·Al2O3 and MgO after Mg treatment. Two types of MgO·Al2O3 were detected after Mg treatment. The long-range gravity between the MgO-containing inclusions is weaker than that of the MgO-free inclusions. The long-range gravity between the inclusions decreases with the increasing of Mg content of the steel. The evolution mechanisms of inclusion in low Mg-containing and high Mg-containing H13 die steel were comprehensive discussed. The different reaction mechanisms result in the different of the core of the MgO·Al2O3 inclusion.

Mechanical components in tribological systems exposed to elevated temperatures are gaining increased attention since more and more systems are designed to operate under extreme conditions. In hot metal forming, the effect of temperature on friction and wear is especially important since it is directly related to process economy (tool wear) and quality of the produced parts (friction between tool and workpiece). This study is therefore focused on fundamental understanding pertaining to the tribological characteristics of prehardened hot work tool steel during sliding against 22MnB5 boron steel. The tribological tests were carried out using a high temperature reciprocating sliding friction and wear tester under a normal load of 31 N (corresponding to a contact pressure of 10 MPa), a sliding speed of 0·2 m s−1 and temperatures ranging from 40°C to 800°C. It was found that friction coefficient and specific wear rate decreased at elevated temperature because of formation of compacted wear debris layers...

Thermomechanical stresses play an important role in defining the life of the work roll used in hot rolling process. In this research temperature dependent mechanical properties of cartridge brass are determined experimentally using high temperature compression tests at different temperatures and strain rates. Real life measurements are made from a brass rolling mill as input data for the simulation boundary conditions. Hot rolls are made of AISI H11 hot work tool steel. Temperature dependent mechanical properties of AISI H11 steel are used. Thermal and mechanical stresses produced in the work rolls during hot rolling process are predicted using a thermoplastic finite element approach in the ABAQUS Standard software. Hot rolling is compared with cold rolling to determine the effects produced on the work rolls. A criterion is introduced to compare the severity of stresses produced on the rolling surfaces in case of hot rolling and cold rolling based on the yield stress of the roller material for dif...

For comparing the enhancement degree of the thermal fatigue behaviour of different hot work tool steels processed by laser remelting, three kinds of hot work tool steels (HHD, H13 and HD steels) were selected to investigate the effect of biomimetic coupled laser remelting process on the thermal fatigue behaviour. The results showed that biomimetic non-smooth samples had better thermal fatigue behaviour compared to untreated samples, the biomimetic non-smooth sample of HHD had the optimum thermal fatigue behaviour. Moreover, before and after thermal fatigue testing, the microhardness and microstructure of biomimetic non-smooth units and parent materials have been investigated. The results showed that biomimetic non-smooth sample of HHD had the highest resistance of thermal cycles softening among the biomimetic non-smooth samples. The microstructures observation indicated that the microstructures of parent materials were a substantial amount of the carbides coarsening while the microstructures of bi...

This paper presents the results of laser re-melting and alloying parameters on the structure and properties of the surface layer of X40CrMoV5-1 hot work tool steels, using a high-power diode laser (HPDL). Investigation indicates the influence of the alloying carbides on the structure and properties of the surface layer of the steel, depending on the kind of alloying carbides and HPDL implemented. Laser alloying of the surface layer of the steel – without introducing alloying additions to the liquid molten metal pool and across the entire range of laser power used – causes a size reduction of the dendritic microstructure in the direction of crystallization, consistent with the direction the heat is being carried away from the laser beam's impact zone. Successful re-melting of the steel without introducing alloying additions into the liquid molten pool in the form of carbide powders causes a slight increase in the properties of the surface layer of the steel in comparison to analogical properties obtained t...

The surface of the hot work tool steel X37CrMoV5-1 (W300) was subjected to different thermochemical treatments in order to improve its mechanical properties, corrosion and wear resistance. Nitrocarburising with or without post-oxidation based on the TENIFER procedure and low temperature powder aluminising+nitrocarburising with or without post-oxidation were performed. Nitrocarburised and nitrocarburised+post-oxidised layers were characterised by testing their basic properties (compound layer thickness, nitrocarburising depth and microhardness) as well as their corrosion resistance. First, the microstructures of aluminised+nitrocarburised samples (with or without post-oxidation) were analysed by means of optical microscopy, and then the microhardness distribution across the surface layer. Finally, the corrosion resistance of aluminised+nitrocarburised samples (with or without post-oxidation) were examined. Glow discharge optical spectroscopy was employed to investigate the distribution of elements in the c...

Isothermal oxidation of plasma-nitrided tool steel at 750°C, typical of steel thixoforming process, was investigated. A multi-layered oxide forms on the surface of plasma nitrided X32CrMoV33 hot work tool steel when held at 750°C in an air furnace for 6 hours. The hematite layer at the surface is replaced by magnetite in the middle. The innermost layer is an iron –chromium spinel with approximately 4 at% Cr. These features are typical of oxidised low-Cr steels and suggest that nitriding does not affect the response to thermal exposure of hot work tool steels at elevated temperatures. It is thus concluded that hot-work tool steels are inadequate for tooling in the steel thixoforming process even when plasma-nitrided. The substrate tool material must contain higher levels of Cr to assure a slowly growing, adherent Cr2O3 layer to reduce the overall oxidation rate.

Precipitation of secondary carbides in hot work tool steels during tempering heat treatments has been investigated using simulations based on a thermodynamic description coupled with kinetic parameters through multicomponent nucleation and growth models. The simulations reproduce the measured effects of steel composition on the precipitation of secondary carbides. Both Si and V increase the volume fraction of fine secondary carbides precipitated during tempering provided that the austenitising temperature is adjusted to give the same fraction of retained primary carbides. The most important effect of Si in 5%Cr steels is its influence on the primary carbide stability at austenitisation temperatures, but increasing the V contents has a strong effect on the fraction of secondary carbides, without increasing the size, and can thus improve the yield strength. The most critical input to the calculations is the thermodynamic description of the individual phases.

The present paper reports the influence of hot working conditions on the microstructure of Ti2AlNb/TC11 dissimilar joint. Linear friction welding technique was used to fabricate the joints. The microhardness and tensile properties of the joints have been tested. It was found that the fine structure of linear friction welds underwent abnormal grain growth and abnormal grain boundary phase growth in the post-weld solution heat treated condition. This phenomenon significantly deteriorated the ductility of the joint. After appropriate hot work, abnormal big grains/phases disappeared, and the joint exhibited good tensile properties due to its fine structures.

Following the coverage of cold work tool steels (see Part 1, IHTSE, 2010, 4, 138–144), the present contribution reviews the possibilities, requirements and optimum heat treatment parameters of new hot work tool steels and plastic mould steels. The focus is laid on low Si grades of hot work tools steels and their heat treatment and nitriding behaviour, paying special attention to the NADCA recommendations. With respect to plastic mould steels, corrosion resistant grades and their property dependence on heat treatment parameters are especially emphasised.

Several new tool steel grades as well as optimised modifications of standard grades have been developed by special steel producers during the last one to two decades. These steels offer the potential for better properties and tool performance, but only if the heat treatment is performed with an optimum combination of parameters. The achievement of this potential is supported by advanced heat treatment equipment and processes. This paper gives an overview of the possibilities, requirements and optimum heat treatment parameters of these new tool steels based on the examples of cold work tool steels. Thereby special attention is paid to 8%Cr steels, spray formed steels, powder metallurgy steels as well as surface hardening and cryogenic treatment. A second part will be published successively, with examples on hot work tool steels and tool steels for plastic moulding.

The principal failure mechanism of steel thixoforming dies is thermal fatigue owing to forging pressures much lower than those encountered in conventional forging. This makes a properly designed thermal fatigue test the best method to identify suitable tooling materials for the steel thixoforming environment. Samples of X32CrMoV33 hot work tool steel and CrNiCo alloy were cycled thermally between 450 and 750 degrees C, every 60 s for a total of 1500 cycles. While the thermal stresses generated at the surfaces of the two materials were very similar, their responses to thermal cycling were markedly different. The X32CrMoV33 steel was softened by nearly 40% after only 400 cycles, raising serious concerns over its temper resistance under steel thixoforming conditions. The extensive oxidation and subsequent spalling of oxide scales suffered by the X32CrMoV33 hot work tool steel is also a major shortcoming. The performance of the CrNiCo alloy, on the other hand, was judged to be satisfactory with a much thinner heat affected zone and a much better oxidation resistance. Lack of evidence for heat checking in this alloy after 1500 cycles is an encouraging sign.

A review of the principal results obtained in the laboratory of metallurgy of the University of Trento is presented in this article. The correlations between heat treatment, surface engineering, microstructure, and properties of hot work and high speed steels in a wide range of applications were evaluated. The basic damage mechanisms of tools and dies were illustrated. The thermal cracking (heat checking) occurring in hot work tool steels for casting/forging dies and in high speed steel work rolls was studied by means of a customary thermal fatigue test. The corrosion by molten metal in die casting dies has been studied by immersion in liquid aluminium. The tribological properties of dies during aluminium hot extrusion were analyzed using a specific simulation test.

A tribological test aimed at the simulation of aluminium hot extrusion was performed. A 6082-Al disc, induction heated up to a maximum surface temperature of 350°C, is allowed to rotate against a conformal hot work steel block, simulating the extrusion die. The test simulates the wear mechanism observed under in service conditions. After an initial period, the hot plasticised Al progressively adheres to the steel counterpart thus allowing direct Al–Al contact. The high shear stresses given by the strong adhesion produce the nucleation of deep cracks which strongly deteriorate the surface of the steel by delamination. Hot work tool steel (AISI H11) is employed as extrusion dies. Salt bath nitriding (Tenifer) is usually carried out to improve wear resistance. The possible application of PVD (CrN, TiAlN) and CVD (TiC + TiN) hard coatings, exhibiting lower compatibility versus Al, has been evaluated in the present work. The occurrence of two distinct damage regimes was detected. Regime 1 shows minor e...

Hot work tool steels contain several strong nitride forming elements such as Cr, V and Si that affect the nitriding of steels for many applications. The present paper presents the effects of different alloy compositions of hot work tool steels, including standard grades, new vacuum remelted high performance grades and some model alloys, on the hardness profile after nitriding. The effect of the content of different elements (Cr, Mo, V, Si and Al) on the maximum hardness level and the nitriding depth were investigated. Reducing the silicon content enhances the nitriding performance, resulting in a higher nitriding depth or shorter nitriding duration. Aluminium reduces the nitriding depth slightly but leads to a strong increase in the surface hardness. Furthermore, aluminium significantly improves the thermal stability of the nitrided layer under operating conditions. The results can be used to aid the selection of hot work tool steels and appropriate nitriding parameters.

Linear elastic fracture mechanics was used to optimize the vacuum heat-treatment procedures for conventional hot-work AISI H11 tool steel. The fracture toughness was determined with non-standard, circumferentially notched and fatigue-precracked tensile-test specimens. The fracture-testing method is sensitive to changes caused by variations in the microstructure resulting from the austenitizing and tempering temperatures as well as the homogeneity of the material itself. The combined tempering diagram– Rockwell-C hardness, Fracture toughness KIc, Tempering temperature was used for the choice of the vacuum heat-treatment parameters necessary to obtain the best properties for a given application with respect to the investigated steel.

The present paper presents the results of metallographical investigation and wear tests of tool steel grades: hot work steels 4H5W2FS, AMS 6437E and cold work steels ASTM A681, Ch12FS. All surfaces were hardened by the Carbo process (carburising) and by the NiCar process (nitrocarburising). The thermochemical treatment was conducted in powder pack for durations of 6 h (carburising) and of 4 h in the case of nitrocarburising. Wear tests were conducted by the three cylinder cone method. Wear velocity was 0·58 m s−1, unit loads were 50 and 400 MPa, wear path was 3470 m. Oil SAE30 was applied at the rate of 30 drops/min−1. Factors investigated were: morphology, depth and microhardness of the cases obtained, their microstructure, as well as phase composition.

This study is part of a bigger picture on investigating three main cutter path strategies—raster, single-direction raster, and offset—in order to evaluate the feasibility of employing high axial depths of cut (10 mm ≤ A d ≤ 20 mm) when high-speed rough milling hardened AISI H13 hot work tool steel with the aim of achieving high volume of metal removed with short machining time. Here, comparative studies were made of the surface topography maps induced at various axial depths of cut in order to gain an in-depth understanding of their effects on the surface texture obtained via the parametric study of alternative cutter path strategies. Previous work has shown that the use of an offset cutter path strategy when high-speed rough milling hardened steel using an axial depth of 15 mm resulted in the lowest tool life, as compared with the use of raster and single-direction raster strategies.[1]This article also describes a novel approach on improving the offset cutter path strategy by selecting the pro...

Duplex treatments are becoming increasingly interesting in several technological applications through which complex forms of stresses act during service. In pressure die casting, for example, corrosion and erosion by molten metal and oxidation contribute, together with thermal fatigue, to excessive degradation of the dies and inserts. While the benefits introduced by combining nitriding and PVD coating have been assessed in counteracting soldering and wear problems, the resistance of such duplex systems with respect to thermal fatigue has not yet been established.In this work, the role of plasma nitriding, PVD coating (CrN, ZrN), and duplex treatment in counteracting thermal cracking, i.e. heat checking, of hot work tool steel is considered. Thermal fatigue tests carried out on a laboratory scale, highlight the negative role of coatings, although this result has to be partially ascribed to an unsuitable prenitriding treatment and heavy oxidation.

Boriding has been employed with some success to increase the service life of commercial forging dies fabricated from the hot work steel AISI H13. This steel is poorly suited to the treatment, however, since an undesirable intermediate layer is formed between the hard boride coating and the core. In practice, a boride coating thickness well below that required for the application has been imposed by the need to minimise the thickness of this layer. An experimental study was undertaken with the aim of improving the effectiveness of a boriding treatment by engineering the subsurface of AISI H 13 steel. It was established that a carburising pretreatment markedly improved the microstructural features of the steel subsurface. The formation of the undesirable layer was completely inhibited within the range of boride thicknesses employed in commercial practice and severely limited at the higher thicknesses better suited to forging applications.

Steel matrix composites bring new possibilities in the production of inexpensive wear resistant materials for the chemical and process industries. Hot isostatic pressed composites consisting of a hot work tool steel matrix reinforced with different ceramic particles have been examined. The processing parameters used (1100°C temperature, 100 MPa pressure, and 3 h holding time) resulted in almost fully densified materials and an optimum metal–ceramic bonding. The introduction of ceramic particles caused grain size refinement in the iron alloy. The composites possessed excellent wear resistance and a much greater hardness than the unreinforced alloy; their toughness, however, was reduced. PM/0727

Influence of dielectric and temperature in electrical discharge machining of hot work tool steel

Many work environments expose workers to extremely hot and humid conditions. The most vivid example of this is the firefighter, who inevitably must tolerate heat stress as part of the risks inherent to his or her job. Whereas the worker is expected to report imminent heat exhaustion before catastrophe occurs, ultimately the employer is held liable by the Occupational Safety and Health Administration (OSHA) for providing a safe work environment for its workers. Therefore, it is incumbent upon employers to screen workers for susceptibility and to rotate workers in and out of a hot work environment so as to prevent deleterious health outcomes, even fatalities. Heat-related illness is a problem for many types of workers: metal smelters, outdoor construction and law enforcement workers, plastics manufacturing workers, landscaping and recreation maintenance personnel, staff in warehouses without air conditioning, cooks and kitchen workers, and athletes. A number of human factors contribute to a worker's susceptibility to heat stress, such as medical conditions, increasing age, overall level of fitness, presence of other metabolically stressful illnesses, the use of certain medications, dehydration, alcohol intake, and individual ability to acclimatize to extreme temperatures. Environmental factors that can contribute to heat stress besides high ambient temperature are low convection currents, high humidity, low evaporative loss, and high insulation levels around the body. Acclimatization is defined as the time needed for physiological adaptation to extreme temperature changes. An average individual takes about 1 to 2 weeks to adapt to extreme cold or hot temperatures. Successful acclimatization occurs if the physiologic mechanisms of the cardiovascular, pulmonary, and renal systems interrelate effectively to adjust the body's core temperature by using evaporative heat loss or conservation. The process of acclimatization requires intact and responsive cardiovascular and renal systems. The National Institute of Occupational Safety and Health has recommended that post-offer and surveillance examinations for heat stress include a complete history and physical examination to screen for relative or absolute contraindications to hot environments (1). These recommendations were made with the intent to screen workers who are more susceptible to heat stress before a catastrophic event occurs in the workplace. No specific examination exists to screen workers' susceptibility to hot environments. However, specific questions directed at screening for risk factors for heat stress can be included in the medical history to identify susceptible individuals. These questions should highlight factors that are relative or absolute contraindications to prolonged exposure to hot environments. Factors that may contribute to the tendency to develop heatrelated illnesses are considered relative contraindications to heat stress exposure (Table ​(Table11). Absolute contraindications are factors that are definitely known to contribute to heat-related illnesses (Table ​(Table22). Table 1 Relative contraindications to heat stress exposure* Table 2 Absolute contraindications to heat stress exposure* Relative contraindications to hot environments need to be assessed on a case-by-case basis, based on severity and lability of the worker's condition. For example, a severely hypertensive worker is more at risk than a moderately hypertensive worker. The person with severe hypertension is more likely to decompensate sooner than one with moderate hypertension. Besides evaluating a worker with a complete history and physical examination, environmental monitoring with a wet bulb globe thermometer is recommended. This instrument measures ambient humidity, which has additive heat stress effects on human physiology. Recommended ambient temperature limits vary, as the ambient humidity and convection factors vary. That is to say, as the humidity increases, the recommended temperature limits decrease. As the convection factors decrease, the recommended temperature limits decrease. Human factors such as an excessively rapid pulse (>90 beats per minute) with slow recovery time after exercise (more than 3 minutes) and/or an elevated baseline core temperature (>100.4°F) indicate a need for a rest period to allow for recovery to baseline before re-entry into the hot work area. Baseline measurements and exercise recovery time can serve as indicators whether or not a worker is fit to enter a hot environment at the beginning of the workday. Recommended alert limits and recommended exposure limit guidelines are encouraged by OSHA. When workers are exposed to heat stress, biological monitoring with the 3-minute pulse test recovery is recommended during the hottest time of the day or the hottest workplace location. Absolute contraindications should be adhered to in workplaces. Workers with these risk factors or conditions should not be exposed to hot environments. If these risk factors are not identified, poor or fatal health outcomes may not be avoidable. Exposure to a hot work environment requires that workers be continuously hydrated. Fluid loss through perspiration is genetically predetermined and proportional to the number of sweat glands per square inch of skin. Drinking water needs to be readily available to workers exposed to a hot work environment. Water misters are available that cool the skin continuously when workers voluntarily walk by. Construction crews at an outdoor worksite often use these. In conclusion, the next time a company calls your office about a worker who has been overcome in a hot work environment, the patient history and environmental factors may be useful in helping you determine an etiology and whether that worker can return safety to that environment in the near or distant future, or maybe not at all.

Thermal-fatigue properties have been investigated and compared in five standard hot-work tool-steel grades and one newly developed grade. The results demonstrate that heat-checking resistance, hot yield strength, and temper resistance can differ considerably between different martensitic hot-work grades of rather similar alloy type. The very best resistance against thermal fatigue is obtained with alloys having the highest hot yield strength and temper resistance. The new grade, which is based on a carefully balanced alloy composition, is found to offer superior properties in these respects. The findings stress further the importance of selecting a proper tool material when dealing with high-temperature hot-working applications in which the tool is subjected to large thermal fluctuations.

The tensile, impact, and fatigue properties of a range of powder-forged steels have been examined. A relationship has been found between the content of non-metallic inclusions and the fatigue performance. The properties of powder-forged steels at 900 N/mm2 strength were compared with those of En16 wrought steel at the same level. The properties of wrought steel are demonstrably extremely variable, depending on the degree of hot work imparted during processing and on the relationship of the test-piece axis to the principal direction of working. The properties of powder-forged steel lie between the highest and lowest that can be expected in wrought steel; comparisons between the two types of material can be made only after careful consideration of their specific characteristics. Powder-forged steels were shown to be capable of developing useful properties over wide ranges of composition.

An AISI H13 hot-work die steel was subjected to combined thermal and mechanical treatments, namely ausextrusion followed by dynamic strain aging. Process variables investigated include ausextrusion temperature, austenitizing temperature, amount of prestrain, straining temperature, and strain rate. The effect of variables on mechanical properties and microstructure was determined. After optimization of the process variables the steel had a 0·2% proof stress value of over 2700 MN/m2, an increase of some 80% over that of conventionally heat-treated material. Mechanical instability was observed above the 0·2% proof stress level.

Five different martensitic hot-work tool-steel alloys, two new alloys and three already established ones, have been investigated and compared with respect to decisive material properties. It is the...

A wear-test programme carried out using a newly developed hot-work tool-wear simulation technique is described. Recently developed cast die steels containing coarse carbide dispersions have been assessed by comparison with orthodox hotwork steels. The new materials showed favourable wear properties under hotworking conditions. The relative wear resistances obtained for the materials Show good agreement with the results of previous hot-forging wear tests. Qualitative results from associated wear-surface observations and tool-workpiece compatibility studies are discussed to highlight the role of the technique in the overall assessment of a new tool material.

Temperature, humidity and radiant heat in an environmental test room were varied over wide limits while five heat stress indices were measured simultaneously: Effective Temperature, Effective Temperature Corrected for Radiation, Wet Bulb Globe Temperature, Heat Stress Index, and Wet Globe Temperature. Regression equations based on 34 tests for the five indices showed them to be interrelated at probabilities exceeding 99%. Similar tabulations were prepared from published data for other indices. An evaluation of the indices revealed that Wet Bulb Globe Temperature and Wet Globe Temperature are best suited to hot work situations where radiant energy is present. For hot, moist conditions, the Effective Temperature is the preferred index.

Etude de la teneur en vanadium de l'acier H-13 et proposition d'une nouvelle conception d'alliage dans laquelle le niobium est partiellement utilise a la place du vanadium