AISI T1 Research Articles

Improving the Surface Performance of Discarded AISI T1 Steel by Cathodic Reduction and Thermal Diffusion-Based Boriding

Improving the Surface Performance of Discarded AISI T1 Steel by Cathodic Reduction and Thermal Diffusion-Based Boriding

Sulfonitrocarburizing of High-Speed Steel Cutting Tools: Kinetics and Performances.

The scholarly literature records information related to the performance increase of the cutting tools covered by the superficial layers formed “in situ” when applying thermochemical processing. In this context, information is frequently reported on the carbamide role in processes aiming carbon and nitrogen surface saturation. Sulfur, together with these elements adsorbed and diffused in the cutting tools superficial layers, undoubtedly ensures an increase of their operating sustainability. The present paper discusses the process of sulfonitrocarburizing in pulverulent solid media of high-speed tools steel (AISI T1, HS18-0-1) and its consequences. The peculiarity of the considered process is that the source of nitrogen and carbon is mainly carbamide (CON2H4), which is found in solid powdery mixtures together with components that do not lead to cyan complex formation (non-toxic media), and the sulfur source is native sulfur. The kinetics of the sulfonitrocarburizing process, depending on the carbamide proportion in the powdered solid mixture and the processing temperature, was studied. The consequences of the achieved sulfonitrocarburized layers on the cutting tools’ performance are expressed by the maximum permissible cutting speed and the maximum cut length. An interesting aspect is highlighted, namely the possibility of using chemically active mixtures. Their components, by initiation of the metallothermic reduction reaction, become able to provide both elements of interest and the amount of heat needed for the ultrafast saturation of the targeted metal surfaces.

Microstructure and mechanical properties of borided AISI T1 high-speed steel by dehydrated paste-pack boriding

Microstructure and mechanical properties of borided AISI T1 high-speed steel by dehydrated paste-pack boriding

Erosion of metals using angular silicon carbide particles

ABSTRACTIn this work, erosion tests conducted to evaluate the resistance of two materials, Metal Babbitt Grade 7 and AISI T1 against SiC particles. The erosion rates of these two metals compared with those obtained using AISI D2 steel in a previous work with similar testing conditions. Metal Babbitt and AISI T1 steel selected due to their high ductility and strength, respectively. A test rig similar to that shown in ASTM G76-95 standard used to perform the tests. Silicon carbide particles had a particle size between 350–450 µm. Tests carried out using different impact angles, 30°, 45°, 60° and 90° with a particle velocity of 24 ± 2 m/s and the abrasive flow rate was 0.7 ± 0.5 g/min. SEM photographs used to identify the wear mechanisms on the Babbitt and T1 steel and also obtained cross-section images of the wear scars on metal Babbitt to measure their depth.

Characterization and boriding kinetics of AISI T1 steel

The AISI T1 steel was hardened by the solid boriding process in the temperature range 1123–1273 K for a time duration of 2 to 8 h. A kinetic model, based on the integral method, was applied to the growth of a single boride layer (Fe2B) at the surface of AISI T1 steel. This diffusion model has been validated experimentally by considering two additional boriding conditions. A numerical solution was then obtained after solving the set of differential algebraic equations in order to compare the experimental thicknesses of Fe2B layers with the predicted values. The activation energy for boron diffusion in AISI T1 steel was estimated as 212.76 kJ mol−1and a comparison was made with other values available in the literature. The formed boride layers with a saw-tooth morphology were examined by scanning electron microscopy (SEM). X-ray diffraction confirmed that the borided layer was composed of only Fe2B. The Daimler-Benz Rockwell-C indentation technique was employed to assess the cohesion of Fe2B layers on AISI T1 steel. In addition, the pin-on-disc and wear scratch tests were carried out for investigating the wear behaviour of borided AISI T1 steel.

Study of tribofilms generation at different cutting speeds in dry machining hardened AISI T1 and AISI D2 steel

Hard dry machining of AISI T1 and AISI D2 steels at comparable hardness (around 59 HRC) were performed at 50 m/min, 80 m/min and 100 m/min cutting speeds separately with uncoated alumina ceramic tool inserts (Al2O3 + TiC), in order to study the effect of cutting conditions on the generation of tribofilms. Comprehensive assessment of uncoated ceramic inserts in machining of T1 and D2 at different cutting speeds was made by optical microscope, scanning electron microscope and X-ray photoelectron spectroscopy. It was shown that higher cutting speeds increased the formation of thermal protective and/or lubricating tribofilms. In machining D2 steel, more intensive formation of Cr-O tribo-oxides brought a lower wear rate; while in cutting T1 steel, a higher amount of W-O tribofilms generation provided better lubrication. At higher cutting speeds, wear/friction behaviour changes were attributed to differences in two factors: first, from a traditional micro-scale standpoint, the distribution of carbide within steels and the accumulation of thermal and mechanical damages during different cutting conditions; second, from a new nano-scale viewpoint, the generation of protective/lubricating tribofilms due to change of machining conditions.

The effect of amorphous nanocrystalline inoculants on structures and properties of high speed steel

High speed steel (HSS) is widely used in the production of high-speed cutting tools and roll etc, and the modification method is an effective approach for improving the microstructure and properties of HSS. Fe–Al–Cr–Nb–C–N amorphous nanocrystalline inoculants were fabricated using the method of in situ reaction and rapid solidification. The phase compositions of Fe–Al–Cr–Nb–C–N inoculants were analyzed. And the effect of inoculants on structures and properties of AISI T1 HSS was studied. The results show that the inoculant is a mixture of amorphous and nanometer crystal, and Fe–Al(–Cr) intermetallic compounds are the matrix phases of inoculant, while particulate nitride, carbide and oxide are the important precipitation. After modification, the quenching and tempering microstructure of HSS has been refined significantly. The carbides contents increase and the sizes of carbides decrease in HSS. The hardness, red-hardness, wear resistance and impact toughness of T1 HSS were also improved obviously after modification.

Influence of Workpiece Material on Tool Wear Performance and Tribofilm Formation in Machining Hardened Steel

In addition to the bulk properties of a workpiece material, characteristics of the tribofilms formed as a result of workpiece material mass transfer to the friction surface play a significant role in friction control. This is especially true in cutting of hardened materials, where it is very difficult to use liquid based lubricants. To better understand wear performance and the formation of beneficial tribofilms, this study presents an assessment of uncoated mixed alumina ceramic tools (Al2O3+TiC) in the turning of two grades of steel, AISI T1 and AISI D2. Both workpiece materials were hardened to 59 HRC then machined under identical cutting conditions. Comprehensive characterization of the resulting wear patterns and the tribofilms formed at the tool/workpiece interface were made using X-ray Photoelectron Spectroscopy and Scanning Electron Microscopy. Metallographic studies on the workpiece material were performed before the machining process and the surface integrity of the machined part was investigated after machining. Tool life was 23% higher when turning D2 than T1. This improvement in cutting tool life and wear behaviour was attributed to a difference in: (1) tribofilm generation on the friction surface and (2) the amount and distribution of carbide phases in the workpiece materials. The results show that wear performance depends both on properties of the workpiece material and characteristics of the tribofilms formed on the friction surface.

Tool steel material selection using PROMETHEE II method

In the recent century, tools for machining, forming, or other types of metalworking industries have consumed several tons of steel materials. Although the earliest tool steels were plain carbon steels, the modern tools contain different alloying elements, like tungsten, vanadium, molybdenum, manganese, and chromium, to provide the properties desired for their wide applications. The presence of a large number of such tool steel materials is a result of the fact that no single material combines the maximum wear resistance, toughness, machinability, safety in hardening, and non-deformability properties. Each tool steel material has its own mechanical and physical characteristics that help it to be suited for a particular application. Also for a specific application, more than one alternative tool steel material may exist, which makes it essential to select the most appropriate tool steel material with the desired properties to meet the manufacturer’s requirements. This paper considers a list of ten tool steel materials whose performances are evaluated based on nine selection criteria. Preference ranking organization method for enrichment evaluation (PROMETHEE II) is then applied to solve this tool steel material selection problem to obtain the full ranking of the considered material alternatives. Molybdenum-type high-speed steel (AISI M2) and tungsten base high-speed tool steel (AISI T1) are the two best choices. Alloy steel (AISI 4140) is the worst preferred tool steel material.

Modification of high-speed steels by nitrogen compression plasma flow: Structure, element composition, tribological properties

The influence of the nitrogen compression plasma flow impact on the phase and element composition and tribological properties of AISI M2 and AISI T1 high-speed steels was investigated in this work. The bank capacitor initial voltage, the number of pulses and nitrogen pressure in the vacuum chamber varied during experiments, providing the change of energy deposited in the surface layer within the limits of 5–13 J/cm 2 per pulse. X-ray diffraction analysis, Auger electron spectroscopy, Rutherford backscattering analysis, scanning electron microscopy, optical microscopy, friction coefficient and microhardness measurements were used for the characterization of the treated samples. It was found that the treatment of both types of steel resulted in austenite formation in the surface layer and carbide partial dissolution. The growth of energy deposited in the surface layer leads to the increase of thickness of the affected by treatment layer up to 24 μm and to the decrease of MC and M 6C carbides volume fraction in the analyzed layer. Treatment leads to nitrogen penetration into the steel up to the depth of 400 nm and the redistribution of the alloying elements in the surface layer. The decrease of hardness due to dissolution of carbides was observed almost in all range of treatment parameters, thus making unsuitable the usage of the compression plasma flow treatment for high-speed steels tribological properties improvement as a stand-alone technique.

Structure-phase transformations in high-speed steel treated by compression plasma flow

The changes in the phase and element composition in the near-surface layer of high-speed AISI T1 steel after treatment with a nitrogen compression plasma flow are studied in this work. It was found that the treatment resulted in the partial dissolution of hardening carbides and the formation of γ -Fe phase. The nitrogen concentration is strongly dependent on the treatment parameters: the nitrogen pressure in the vacuum chamber and the number of impulses. The change in the phase composition led to a decrease in the friction coefficient and the microhardness.

Investigation on hot deformation behavior of AISI T1 high-speed steel

The hot deformation behavior of AISI T1 (18W–4Cr–1V) high-speed steel has been investigated in the temperature range 950–1150°C at strain rates of 0.001–10 s −1 and true strains of 0–0.6. The results show that the activation energy for deformation, Q, decreases with the increase of strain below 1000°C, and it changes slightly with the strain above 1000°C. Metallography shows that there are fine carbide particles precipitated in the grains, and that these lead to dispersion hardening and an increase in the value of Q. There are fewer of these particles above 1000°C than below it. The Zener–Hollomon parameter and the hyperbolic sine function are used to predict the flow stress as influenced by temperature and strain rate for different strain levels.

Influence of Carbide Size, Hardness and Temperature on Sliding Friction and Wear of a Boundary Lubricated High-Speed Steel and Si3N4 Ceramics©

In this study, the authors investigated the friction and wear performance of a high-speed steel (AISI T1 grade) and an Si3N4 ceramic under boundary lubricated sliding conditions. Moreover, the effects of hardness, carbide size, and temperature on friction and wear were investigated. Tribological tests were performed with pairs of T1 steel and Si3N4 ceramic at temperatures ranging from 22° to 150°C. The steel samples contained hard carbide particles ranging in size from 2 to 8 μm and exhibited hardness values ranging from 730 to 934 kg/mm2. The specific wear rates of pins were deduced from height displacement and from wear scar diameter, while the wear of disks was calculated from profilometry traces across the wear grooves. The results of wear tests showed that the combination of a Si3N4 ball on a T1 steel disc resulted in the lowest pin wear rate of 10−15 mm3/N. mm. The variation of hardness and carbide size in T1 steel had negligible effects on wear. The increase test temperature caused an increase in wear. Finally, under conditions of boundary lubrication, the tribological characteristics of Si3N4 and T1 high-speed steel were remarkably similar to one another.

The role of voltage pulse off-time in the electrodischarge machined AISI T1 high-speed steel

A transistorized pulse generator has been used to study the effect of changing the voltage pulse off-time, at constant values of pulse on-time, on the machining characteristics of electrodischarge machined AISI T1 high-speed steel. A copper electrode with positive polarity, kerosene dielectric, side flushing and a current setting of 31.2 A were used throughout all of the experiments. The results have shown that the metal removal rates are not very sensitive to off-time changes at a low pulse on-time corresponding to finish machining and show a higher sensitivity to these changes at higher on-times corresponding to intermediate and rough machining. Volumetric electrode wear has been found to be less with shorter off-times when finish machining but independent of the off-time when intermediate or rough machining. The values of the surface roughness of the machined specimens have been found to be independent of the off-time and direction of flushing, for all machining conditions.

Thermodynamische Berechnung der Phasengleichgewichte für Schnellarbeitsstähle

This paper reports Thermo-Calc computations of phase equilibria in the six-component system Fe-Cr-Mo-W-V-C which provide a quantitative understanding of the microstructures of three important high speed steels, AISI T1, M2 and M7. Compositions and volume fractions of the phases in equilibrium during austenitization are reproduced with good accuracy, and so are the temperatures of the liquidus line and the peritectic reaction. The influence of the individual alloying elements such as Mo, W, V and C is presented. Since the volume fractions and compositions of the matrix and of the blocky carbides MC and MaC do not change during quenching and tempering, the Thermo-Calc computations provide exact predictions of all the coarse components of the microstrncture, allowing computertailoring of microstructures

Microstructural changes during overtempering of high-speed steels

To elucidate the mechanisms determining the creep resistance of high-speed steels during tool service, overtempering at 600°C has been investigated for two alloys modeling the matrix compositions of AISI M2 and T1. Composition changes and coarsening of the secondary hardening precipitates were studied by transmission electron microscopy and field-ion microscopy with atom probe analysis. Strengthening in the peak-hardened state is due to coherent precipitates of types M2C and MC. During overtempering, M2C coarsens too rapidly to be of importance for the sustained strength of the material. The MC precipitates, on the other hand, are fairly stable. Some coarsening does occur, but the MC population is replenished by a second wave of precipitation which makes use of the roughly 50 pct of carbide-forming elements, carbon, and nitrogen, which remained in solid solution after tempering to the peak-hardened state. This precipitation reaction continues for times of the order of the tool life.

Laser melt injection of BN powders on tool steels I:Microhardness and structure

A 5 kW continuous wave CO 2 gas laser, operating in an oscillating square beam mode, was utilized to melt inject hexagonal BN powders into the surfaces of AISI T1 and M 2 tool steels. Optical metallography, scanning electron microscopy, Auger spectroscopy and Vickers' microhardness tests were employed to characterize the melt layers. Both the hardness and the BN concentration of laser-processed layers were increased with an increase in the number of superimposing laser passes. A Vickers hardness of 2150 HV (maximum) was obtained in the specimen that was BN injected ten times. Microstructural features included fine cellular-dendritic structures and complex precipitates of metal boronitrides. The melt layers were nearly free from cracks and pores.