This research work studies the influence of single microalloying elements (Nb and Mo) and the solidification route on the hot ductility behavior of a high-manganese austenitic Twinning Induced ...Plasticity (TWIP) steel. For this purpose uniaxial hot tensile tests in the temperature range of 700–1100°C under a constant true strain rate (10−3s−1) were carried out to evaluate the hot ductility as a function of reduction in area (%RA). In general, results revealed a beneficial influence of Nb and Mo additions to TWIP steels on the hot ductility behavior, particularly in the intermediate temperature range of 800–900°C, where the reduction of area (RA) value can be as high as 73%. The hot ductility behavior of the present TWIP steels is discussed in terms of solid-solution strengthening, solute drag phenomenon, dynamic recrystallization (DRX) and grain boundary precipitation. Ductile fracture type was recognized as the material failure surface containing many dimples in almost all the studied cases.
The effect of 2% V, 2% Nb plus 2% Ti added to a 17% Cr white iron was studied. The experimental alloys were made in an induction furnace by using high-purity raw materials. Alloying elements were ...added at the end of the ironmaking process before pouring. Thin bars of 25×15mm2 cross section and 250mm length were solidified into sand molds. Several bars of alloyed and unalloyed white irons were obtained for the present study. The as-cast microstructure consisted of eutectic M7C3 carbides in a matrix of austenite for the unalloyed iron, while for the alloyed iron the structure was composed of austenite, eutectic M7C3 carbides and MC primary carbides. The alloys were heat treated at 900°C to destabilize the austenitic matrix; a stronger mainly martensitic matrix reinforced with secondary carbides resulted from such treatment. The as-cast and heat treated alloys were tested under abrasive wear by using a rubber wheel testing machine and SiO2 as abrasive particles of 0.3mm diameter. The wear tests were undertaken by placing the rubbing surfaces against each other with loads of 25, 40 and 54N and pouring the abrasive SiO2 particles between the surfaces. The results indicate a considerable better wear resistance for the alloyed heat treated iron compared with those as-cast and unalloyed irons. The responsible for such better wear behavior is the strengthening of the matrix by the MC carbides plus the precipitation of secondary M7C3 carbides and the partial transformation of matrix from austenite to martensite after heat treatment. The strengthening of the matrix provides better support to the eutectic carbides against cracking which in turn prevents the surface destabilization.
In the present study, systematic additions of tungsten (up to 10.3wt%) and their effects on the microstructure, hardness, microhardness, and abrasive wear of 17%-Cr white iron was analyzed. Six ...high-chromium iron alloys with different tungsten additions were melted in an open induction furnace and cast into sand molds to obtain 50-mm×25-mm cross-sectional bars. The alloys were characterized by optical and electronic microscopy, energy dispersive spectroscopy, and X-ray diffraction. The bulk hardness and microhardness of the different phases of the microstructure (matrix and carbides) were measured in the as-cast conditions and after a destabilization heat treatment at 950°C for 45min. Abrasive wear resistance tests were undertaken for the different irons according to the ASTM G65 standard in both as-cast and heat-treated conditions. The results show that, when tungsten is added up to 4wt%, it partitions either to the matrix or to the M7C3 carbide, causing a moderate strengthening in both phases and contributing to an increase in the overall hardness of the alloys. When tungsten additions are higher than 4%, the presence of harder M2C and M6C carbides is prevalent in the microstructure and the bulk hardness of the alloys increased. The wear behavior was found to be consistent with the hardness values; an increase in the wear resistance occurred as the tungsten additions were increased. However, such an increase in the wear resistance is not considerable (just 13% higher for 10.3% tungsten addition to the iron). Tungsten was found not to have an important effect on the secondary carbide precipitation during heat treatment, and the wear behavior had the same trend as that in the as-cast alloys. The results are discussed in terms of the partition of tungsten to the carbide and matrix and on its tendency to form harder M6C-type carbides.
•Tungsten increased carbide volume fraction and for contents higher than 4% the W6C carbide was found.•Tungsten do not influence the secondary carbide precipitation process.•Hardness increases with tungsten content due to the increase in eutectic carbides volume.•Just a small increase in wear resistance (13%) was observed for tungsten additions of 10%.
This research work studies the influence of microalloying elements (Ti and V) and the solidification route on the hot ductility behavior of high-manganese TWIP steels. Uniaxial hot tensile tests in ...the temperature range of 700–1100°C under a constant strain rate of 10−3s−1 were carried out. Hot ductility as a function of reduction of area (RA) showed a significant improvement in the V-microalloyed TWIP steel, when compared to a non-microalloyed TWIP steel with a similar composition, in the intermediate temperature range of 800–900°C. The highest value of 86% RA is attributed to the onset of dynamic recrystallization (DRX) near to the fracture tip. On the other hand, Ti addition to TWIP steel did not exhibit any improvement on the hot ductility, resulting in the worst hot ductility behavior, with a maximum value of 34% RA. The TWIP steels solidified in metallic ingot molds (MM) showed higher peak stress (σp) and ductility values than the sand mold (SM) cast ingots at low and intermediate temperatures, respectively, which is associated with the finer microstructure generated during solidification. Grain boundary sliding was recognized as the failure mechanism associated with second-phase particles precipitated at the grain boundaries, which play the role of nucleation and propagation sites of void-cracks.
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► Critical conditions for the DRX onset of boron microalloyed steels are determined. ►
σ
c and
ɛ
c tend to increase as strain rate increases and temperature decreases. ►
σ
c and
ɛ
c ...tend to decrease as boron content increases. ► Critical ratios
σ
c/
σ
p and
ɛ
c/
ɛ
p remain fairly constant (≈0.82 and ≈0.53). ► Boron additions promote solid solution softening and acceleration of the DRX onset.
From the present research, the critical conditions associated with the onset of dynamic recrystallization (DRX) of hot deformed boron microalloyed steels were precisely determined based on changes in the strain hardening rate (
θ) as a function of the flow stress. For this purpose, a low carbon steel microalloyed with four different amounts of boron (29, 49, 62 and 105
ppm) was deformed by uniaxial hot-compression tests at high temperature (950, 1000, 1050 and 1100
°C) and constant true strain rate (10
−3, 10
−2 and 10
−1
s
−1). Results indicate that the critical conditions for the initiation of dynamic recrystallization depend on the temperature and strain rate. In addition, both critical stress
σ
c, and critical strain
ɛ
c, were noticed to decrease as boron content increased. Such a behavior is attributed to a solute drag effect by boron atoms on the austenitic grain boundaries and also to a solid solution softening effect. The critical ratios
σ
c/
σ
p and
ɛ
c/
ɛ
p for all boron microalloyed steels remain fairly constant (≈0.82 and ≈0.53, respectively), such values are in agreement with those commonly reported for Al-killed, C–Mn, Nb, Nb–Ti, high carbon and stainless steels.
Cu–Ni alloys are thermally and chemically operationally stable alloys. Even though its wear resistance is superior to that of its pure metal components, the addition of reinforcing phases can further ...improve the wear behaviour of the alloys in an attempt to develop lighter materials resistant to degradation by corrosion and wear. The dry sliding wear behaviour of Cu10Ni matrix composites reinforced with 55 vol% TiC particles was investigated in an experimental pin-on-ring arrangement with a AISI M2 hardened steel ring as a counterpart at normal loads of 25 N, 52 N and 103 N, and sliding velocities of 0.3 m/s, 0.6 m/s and 0.8 m/s. The worn surfaces and wear debris were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (SEM-EDS) and x-ray diffraction (XRD) techniques. The infiltrated composites had less than 1.8% porosity. The Cu10Ni alloy exhibited significant material displacement towards the wear track margin and a highly deformed subsurface up to more than 200 μm deep. Despite the higher wear rate of the unreinforced alloy, the coefficient of friction (COF) of Cu10Ni was lower because of the hard-particles exposed in the surface of the composites. The dominant wear mechanism of the alloy was adhesive and oxidative wear. In the least case, the TiC/Cu10Ni composite has three times more wear resistance than the pure Cu10Ni matrix. The wear behaviour of the composite is characterized by a tribochemical reaction that involves oxidation of the matrix and transferred material forming protective tribolayers through an additional sliding process. The surface consists of numerous simple and mixed oxides of Fe, Cu and Ni. The highest rate of composite wear was achieved in the combination of maximum sliding velocity and higher applied load. The mechanism that governs the wear process in composites combines abrasive, adhesive and oxidative wear.
•TiC/Cu–10Ni composites are successfully prepared by capillary infiltration.•TiC/Cu–10Ni has three times better wear resistance than the pure Cu–10Ni matrix.•The lower rate of wear of TiC/Cu–10Ni is related to the formation of a tribolayer.•The dominant wear mechanism of Cu–10Ni alloy against M2 steel ring is adhesive.•The wear mechanism of TiC/Cu–10Ni combines abrasive, adhesive and oxidative wear.
From this study, titanium additions of 1, 3 and 5% were added to a 12%Cr–3%C white iron, and their effects on the microstructure, hardness and sliding wear were analyzed. The experimental irons were ...melted in a 10 kg capacity vacuum induction furnace and cast into wedge metallic molds to analyze different solidification thicknesses. The alloys were characterized by optical and electronic microscopy, and X-ray diffraction. Bulk hardness was measured in the as-cast conditions and after a destabilization heat treatment at 900 °C for 30 min. Sliding wear tests (block-on-ring) were undertaken for different thicknesses according to the ASTM G77 standard in both as-cast and heat-treated conditions under a load of 52 N. The results show that, high titanium additions caused a decrease in the carbon content in the alloy and that some carbon was also consumed to form primary TiC during solidification; this in turn decreased the eutectic M7C3 carbide volume fraction and promoted a more martensitic matrix. Bulk hardness changed from 53 HRC (as-cast) to 65 HRC (as-heat treated); however, the best wear behavior was observed for the 3%Ti iron. It was found that for such amount of titanium, a good combination of austenite/martensite matrix reinforced with primary TiC carbides was obtained. While for higher titanium amounts (5%) large agglomerates of TiC particles were segregated to the eutectic zone leaving the matrix unprotected; this phenomenon was particularly observed for thicker sections. After heat treatment, the precipitation of secondary carbides occurred within the matrix, which improved the wear resistance of most irons; however, the best behavior was observed again 3%Ti iron. These results are explained in terms of the obtained microstructure; particularly in the well distribution of primary TiC carbides within the matrix.
•High-Cr high-Ti irons were successfully melted under vacuum conditions.•The main wear mechanism was oxidative under dry sliding conditions.•The iron with 3%Ti showed the lowest wear rate due to the TiCs precipitated in matrix.•Destabilization heat treatments contributed to improve wear performance.•A linear relationship between wear rate and depth of carbide cracking was found.
The present study discuss the effects systematic additions of boron (up to 1.197 wt%) on the microstructure, bulk hardness and abrasive wear of a 17Cr– 3C–1Ni–1Mo white cast iron. The alloys were ...melted in an open induction furnace and cast into 25.4 mm × 12.5 mm cross-section bars. Characterization was carried out by optical and electronic microscopy, energy dispersive spectroscopy, and X-ray diffraction in the as-cast conditions and after a destabilization heat treatment. Hardness was also measured in both conditions. The results show that, boron addition produced a considerable increase of the carbide volume fraction from 27.1 to 53.84% (percentage by volume) and promotes the transition from the Cr rich M7C3 eutectic carbides to the lower C and Cr content M23(C,B)6carbide. However, the hardness values of the experimental alloys were not affected by this transition, and thus, the hardness values increased with the boron content due to a higher carbide volume fraction and the strengthening of the iron matrix reaching a maximum value of 767 HV for the higher B content. Likewise, a secondary hardening effect was produced by the destabilization heat treatment, increasing the hardness values of the different alloys. However, as the boron content increased, this hardening effect becomes less significant. Abrasive wear test were consistent with the hardness values in the as-cast condition by decreasing the wear losses with the increase in B for high and low loads. Similarly, for the destabilized irons, which exhibited higher harness values, a decrease in the wear volume losses were observed for B contents up to 0.598 wt% and the wear losses increased with the increase in applied load.
In the case of the heat treated 1.197 wt% B added iron, the wear losses were significantly affected by the applied load during the wear tests. For this alloy, a volume lost of 0.639 mm3 was observed for the test with 54 N a load, which corresponds to the lower value obtained for any B content and experimental condition, while in the case of the test performed with 130 N a relatively high volume lost of 1.319 mm3 was measured which is considerably higher compared with the lower boron alloys in the same condition. This behavior was attributed to the massive carbide cracking observed after heat treatment promoting the carbide detachment during the test with 130 N of load.
From the author's review of the literature, the effect of such a high boron addition on the microstructure and wear behavior have never been performed or published for high chromium white cast irons. And the based in the experimental results of the present study, the addition up to 1.197%wt boron in the as cast condition represents an effective way to increase the hardness and wear resistance of these kind of alloys in the as-cast condition suppressing the destabilization heat treatment.
•Hardness values are increased with boron addition.•A secondary hardening effect is produced by destabilization heat treatment.•Boron addition in the as-cast condition considerably reduces the wear losses•Destabilized irons exhibit higher harness values and lower wear losses•High B alloying is suitable for low-impact applications and high wear resistance
Nickel-Titanium carbide composites are promising candidates for abrasive applications where high electrical and thermal conductivity and good wear resistance are needed. This paper describes the dry ...sliding wear behavior of a Ni/TiC composite material. The composite with 60 vol% reinforcement was prepared by a liquid infiltration technique, obtaining a continuous matrix material and homogeneous distribution of the reinforcement. The wear behavior of the composite with residual porosity of 1.4% and hardness 49 HRC was investigated under two-body abrasion conditions using a pin-on-ring device with a counterpart ring made of M2 hard steel. An increase in the wear rate was observed when increasing the applied load and the sliding distance, while decreasing at a higher sliding speed. The first part of the wear process is characterized by a tribochemical reaction mechanism by oxidation of the matrix.
At higher speed the increase in temperature between the surfaces favors the formation of stable and adherent oxides of the type NiO and likely TiO2 that act as lubricants. Iron oxide is also likely to form due to wear of M2 ring, most likely Fe3O4. The characteristics of the worn surfaces at higher load and lower speed suggest a dominant mechanism of adhesion wear, showing a significant amount of material displaced plastically towards the margin of the wear track. The TiC particles exposed on the composite surface reduce the load to the matrix, decreasing the wear rate of the ductile material.
•TiC reinforcements reduce the dry wear rate of nickel based composites.•High wettability of Ni-TiC system allows liquid infiltration of Ni/TiC composites.•Dry wear of Ni/TiC with M2 steel counterpart is controlled by tribochemical reaction.•High loads limit the Ni matrix to provide mechanical support for TiC reinforcement.•The wear resistance of Ni/TiC is high enough to act as a counterpart for M2 steel.
•Magnetic properties of Si-Al and Si-Al-Sb electrical steels.•Si + Al and Si + Al + Sb electrical steels processed by alternative route.•In-situ phase transformation analysis by dilatometry.•Columnar ...grain growth in Si + Al and Si + Al + Sb electrical steels.
It has been recently reported that the magnetic behavior of electrical steels containing Si + Al, can be improved by an alternative processing route, which involves the intercritical annealing of the hot-rolled bands before cold-rolling. The effects of such processing route has not been investigated in steels containing Si-Al-Sb. It has been reported that Sb can enhance the magnetic behavior of these steels. The present work reports the microstructure and magnetic properties of Si-Al-Sb electrical steels processed by the alternative processing route. Results were compared with those of Si-Al electrical steel sheets processed both by the conventional and the alternative route. Microstructural characteristics of hot-rolled electrical steel samples were modified by an intercritical annealing conducted at 850 °C from 30 min to 720 min. After this, samples were cold rolled using thickness reductions of 80 % and 90 %, and annealed at 750 °C, 850 °C and 950 °C for 8 min. Characterization of the samples included: spark optical emission spectrometry, dilatometry, optical microscopy and scanning electron microscopy, while magnetic properties were determined in a silicon steel sheet iron loss tester. Results demonstrate that, Si-Al-Sb steels processed by the alternative route exhibit better performance (higher permeability, lower coercivity, lower core loss), than Si + Al steels processed either by the conventional or the alternative route.
