Precipitation Of Fine Carbides Research Articles

スパッタエッチングによる薄鋼板および鋼線表面への微細突起物形成

Six kinds of steels with various thickness smaller than 3mm and SUS304 steel wires with 0.5 and 0.2 mm diameter were etched by argon ion sputtering at a radio frequency power of 100-350W for 0.9-19.8ks. Cone-shaped protrusions with various sizes smaller than 5μm were formed on the surface of SK120, SUS304 and SKD61 steel sheets. These protrusions were formed from the bottom of pillar-shaped carbides that precipitate perpendicular to the surface. When the sheet thickness is very small, the conical protrusions were not formed, but the column- or ringshaped protrusions with various sizes smaller than 1μm were formed on the surface of SUS304, SUS316, SUS316L and SKD61 steels. The reason will be that the precipitation of fine pillar-shaped carbides occurs densely due to a small temperature gradient in the thickness direction and the conical protrusions quickly decay to the column- or ring-shaped protrusions. Also for the SUS304 wire, the fine column- or ringshaped protrusions were formed over whole of the surface due to a roundabout of plasma. The sheets and wires with not only the cone-shaped protrusions but also the column- or ring-shaped ones will give wide and flexible applicability to machine parts and structures revealing many functions.

Fatigue Strength Degradation by Irreversible Hydrogen in Cold Drawn Eutectoid Steels

The fatigue tests were conducted for cold-drawn eutectoid steels having different activation energies and microstructures to investigate the mechanism of fatigue strength degradation by irreversible hydrogen. The fatigue strength of a sample with low activation energy was decreased by irreversible hydrogen, whereas the fatigue strength of a sample with high activation energy was not. When the activation energy for irreversible hydrogen becomes small, the desorption of irreversible hydrogen from its trap site is easily induced by cyclic loading, which results in a decrease in fatigue strength. When a sample having high activation energy was annealed at 473 K, the fatigue strength was decreased by irreversible hydrogen although the activation energy barely changed. This is because the precipitation of fine carbides due to annealing causes higher sensitivity to hydrogen embrittlement. High sensitivity to hydrogen embrittlement was concluded to induce the fatigue strength degradation by irreversible hydrogen. Therefore, the degradation of fatigue strength by irreversible hydrogen depends on the activation energy and sensitivity to hydrogen embrittlement.

Role of carbon in the chromium deposit electroplated from a trivalent chromium-based bath

Precipitation of fine chromium carbides have been considered to be the hardening mechanism of the anneal-hardened Cr–C deposit for a long time. However, according to this study, precipitation of carbon-based membranes may serve the hardening mechanism for annealed Cr–C deposit. The carbon-based membranes could be extracted from as-plated and annealed Cr–C deposits by etching in a solution of 33vol.% HNO3+67vol.% HCl. The structure of carbon-based membrane transforms from an amorphous carbon to a crystalline diamond-like structure with increasing the annealing temperatures. This leads to obvious increase in the hardness of annealed Cr–C deposits. Based on this mechanism, a hardened surface on Cr–C deposited steel specimens could be achieved by using reduction-flame heating for a short period (~1s).

Metallurgical principles of cryogenically treated tool steels—a review on the current state of science

The cryogenic treatment of tool steels has transformed over centuries from black art to science, but the metallurgical principles responsible for increase in wear resistance, tensile strength, toughness, and stability are still disputed. Metallurgists comprehend how tool steels respond to cryogenic treatment, but they also understand that for many years, the cryogenic treatment of tool steels had the reputation of being a quick fix for poor heat treatment practice. During the cryogenic treatment of tool steels, the process modifies the carbon present in the tool steels. However, cryogenic treatment has not been widely adopted by the cutting tools industry due to lack of understanding of the fundamental metallurgical mechanisms and due to the wide variation in reported research findings. In the present paper, an attempt has been made to review the literature on metallurgical changes that occurred during the cryogenic treatment of tool steels to benefit the cutting tools industry. The prominent reasons found to be responsible for improving the mechanical properties of tool steels are transformation of retained austenite to martensite and precipitation of fine carbides.

The hardening mechanism of a chromium–carbon deposit electroplated from a trivalent chromium-based bath

It has been shown by several researchers that the hardness of a Cr–C deposit obtained from a trivalent Cr-based bath can be tremendously increased to be 1600 Hv after annealing at 600 °C for 1 h. Presently the precipitation of fine chromium carbides in the annealed Cr–C deposit is considered to be the hardening mechanism. However, based on our experimental data, we find that precipitation of a nanosized diamond-structured membrane could be the main hardening mechanism. According to this alternative hardening mechanism, hardening of a Cr–C deposited steel can be accomplished with induction- and flame-heating within a 1 s time period.

Characterization of precipitates in a 7.9Cr–1.65Mo–1.25Si–1.2V steel during tempering

In this paper, the precipitates formed during the tempering after quenching from temperature 1150 °C for 7.90Cr–1.65Mo–1.25Si–1.2V steels are investigated using an analytical transmission electron microscope (A-TEM).The study of this tempering is carried out in isothermal and anisothermal conditions, by comparing the results given by dilatometry and hot hardness. Tempering is performed in the range of 300–700 °C. Coarse primary carbides retained after heat treatment are V-rich MC and Cr–Mo-rich M 7C 3 types. In turn, it gives a significant influence on the precipitation of fine secondary carbides, that is, secondary hardening during tempering. The major secondary carbides are Cr–Mo–V-rich M′C (and/or) Cr–Mo-rich M 2C type. The peak hardness is observed in the tempering range of 450–500 °C. In the end, we observe between 600 and 700 °C, that this impoverished changes the phase. At these high temperatures of tempering, we observe that there is a carbide formation of the types M 6C developing at the expense of the fine M 7C 3 carbides previously formed.

Effect of cooling rate on microstructural formation and hardness of 30CrNi3Mo steel

The variation of microstructural formation and the hardness of the 30CrNi3Mo steel were systematically explored as a function of applied cooling rates in the range of 1–500°C/min. According to the measured Rockwell hardness results, four characteristic stages could be separated as different ranges of cooling rates, which corresponds well with the microstructural evolution observed. With the applied cooling rate increasing, the transformed structure evolves from granular bainite, lower bainite, self-tempered martensite, to finally martensite without self-tempering. Among them, the self-tempered martensite, obtained in the transformed specimens cooled with rates of 25–80°C/min, exhibits the highest hardness values due to the precipitation of fine carbides within it.

W-Cr 工具鋼のスパッタエッチングによって形成した微細円錐状突起物層のナノインデンテーション特性

The sputter-etching was carried out on a W-Cr tool steel specimen quenched at 1373 K using argon plasma to form conical or ring-shaped carbide protrusions on the surface. Nano-indentation tests were used to investigate deformation characteristics of the protrusions from load P vs. displacement h curves at maximum loads of 10, 50 and 245 mN. For the surface layer with conical protrusions, the P-h curve at the maximum load of 245 mN is almost similar to that of the specimen without sputter-etching. The reason is explained by a balance of two factors, i.e. the hard carbide layer decreases the deformation during the indentation, while the soft region formed by the depletion of carbide-forming elements under the carbide layer increases the deformation especially after the carbide layer is cracked by the indentation. When the maximum indentation load is 10 mN, the scatter of P-h curves appears reflecting different indentation positions such as the top or side of the protrusions. For a mixture of the thick block-like layers with ring-shaped protrusions and the matrix areas surrounded by them, the maximum displacement and recovery after unloading are both large when the maximum load is 245 mN. The reason will be that the elastic deformation of the thick block-like layers supports the indentation load decreasing the plastic deformation of the soft region under the layers. When the indentation load is 10 mN, the scatter of displacement is very large depending on the indentation either to the protrusions or to the soft matrix region. Tempering after the sputter-etching increases the deformation resistance of the whole layer perhaps due to the precipitation of fine carbides in the soft region under the carbide layer.

Improvement in the mechanical strength of magnetostrictive (Fe–Ga–Al)–X–C (X = Zr, Nb and Mo) alloys by carbide precipitation

(Fe 0.80 Ga 0.15 Al 0.05 ) 99 X 0.5 C 0.5 (X = Zr, Nb and Mo) alloys with high strength (>800 MPa) and high magnetostriction (>100 ppm) were developed by means of the formation of fine carbide precipitation of intermetallic compound, as well as grain refining by carbide phases, XC, which have an inhibitory effect on crystal grain growth. The fracture mode differed from that in binary FeGa alloy as a result of the presence of a transgranular phase caused by the XC.

Thermal creep properties of alloy D9 stainless steel and 316 stainless steel fuel clad tubes

Uniaxial thermal creep rupture properties of 20% cold worked alloy D9 stainless steel (alloy D9 SS) fuel clad tubes for fast breeder reactors have been evaluated at 973 K in the stress range 125–250 MPa. The rupture lives were in the range 90–8100 h. The results are compared with the properties of 20% cold worked type 316 stainless steel (316 SS) clad tubes. Alloy D9 SS were found to have higher creep rupture strengths, lower creep rates and lower rupture ductility than 316 SS. The deformation and damage processes were related through Monkman Grant relationship and modified Monkman Grant relationship. The creep damage tolerance parameter indicates that creep fracture takes place by intergranular cavitation. Precipitation of titanium carbides in the matrix and chromium carbides on the grain boundaries, dislocation substructure and twins were observed in transmission electron microscopic investigations of alloy D9 SS. The improvement in strength is attributed to the precipitation of fine titanium carbides in the matrix which prevents the recovery and recrystallisation of the cold worked microstructure.

Effect of cryogenic treatment on distribution of residual stress in case carburized En 353 steel

The effect of cryogenic treatment on the distribution of residual stress in the case carburized steel (En 353) was studied using X-ray diffraction technique. Two types of cryogenic treatment: shallow cryogenic treatment (193 K) and deep cryogenic treatment (77 K) were adopted, as a supplement to conventional heat treatment. The amount of retained austenite in conventionally heat-treated, shallow cryogenically treated and deep cryogenically treated samples was found to be 28%, 22% and 14%, respectively. The conventionally heat-treated, shallow cryogenically treated and deep cryogenically treated samples in untempered condition had a surface residual stress of −125 MPa, −115 MPa and −235 MPa, respectively. After tempering the conventionally heat-treated, shallow cryogenically treated and deep cryogenically treated samples had a surface residual stress of −150 MPa, −80 MPa and −80 MPa, respectively. A comparative study of the three treatments revealed that there was an increase in the compressive residual stress in steel that was subjected to cryogenic treatment prior to tempering. The experimental investigation revealed that deep cryogenically treated steel when subjected to tempering has undergone a reduction in compressive residual stress. Such stress relieving behaviour was mainly due to the increased precipitation of fine carbides in specimens subjected to DCT with tempering.

English

Four high-strength low-alloy (HSLA) steels with varying chemical compositions were forgedin two different temperature ranges followed by cooling in various media. Microstructures andmechanical properties of the steels were evaluated. The microstructures obtained in water–quenchedlow-carbon HSLA steels were lath martensite packet within the pancaked grains. On air or sandcooling predominantly bainitic ferrite or granular bainite structure forms. The strength propertiesof these steels decreased with decrease in cooling rate and is accompanied by an increase inelongation and impact toughness values. The ductile-to-brittle transition temperature of HSLA-100grade steel was found to be – 40 oC. The impact fracture surface of air cooled HSLA-100 steel showedductile failure with formation of dimples at 20 oC and at – 20 oC. The fracture mode changed to brittlefailure with formation of cleavage and river pattern at – 40 oC and at – 60 oC. The microstructuresof the ultra-low carbon HSLA steel show lath ferrite or granular ferrite in water-quenched condition.With slower cooling rate, the volume fraction of lath ferrite decreased with an increase in formationof polygonal ferrite. The maximum strength value obtained in air-cooled condition is achieved dueto precipitation of fine microalloying carbides and carbonitrides. Slower cooling rate increases thevolume fraction of polygonal ferrite which increases the toughness value.

Influences of Co addition and austenitizing temperature on secondary hardening and impact fracture behavior in P/M high speed steels of W–Mo–Cr–V(–Co) system

The secondary hardening and fracture behavior in P/M high speed steels of W–Mo–Cr–V(–Co) system has been investigated in terms of Co addition and austenitizing temperature. Austenitizing was conducted at 1100 and 1175 °C of relatively low and high temperatures, respectively. Tempering was performed in the range of 500–600 °C. Coarse primary carbides retained after heat treatment were V-rich MC and W–Mo-rich M 6C types. Since the dissolution of W–Mo-rich M 6C with relatively low stability was more promoted with increasing austenitizing temperature, the alloy content of the W and Mo in the matrix was enhanced. In turn, it gives a significant influence on the precipitation of fine secondary alloy carbides, that is, secondary hardening during tempering. The major secondary carbides were W–Mo–Cr-rich M 2C type. The peak hardness was observed in the tempering range of 500–540 °C, depending on Co addition and austenitizing temperature. With an increase in austenitizing temperature, the aging deceleration was observed. This phenomenon may be attributed to the increased content of W and Mo in the matrix, both diffusing slowly in the matrix and inhibiting growth of M 2C carbide, as compared to Cr. In addition, the aging acceleration occurred in the Co bearing alloy, promoting the precipitation of M 2C carbides, as well as the overall increase in hardness. In general, the impact toughness was decreased with an increase in hardness. In addition, the impact toughness to hardness balance was lowered in the Co bearing alloy.

Effect of Deep Cryogenic Treatment on Carbide Precipitation and Mechanical Properties of Tool Steel

It is well known that the durability of tool steel could be improved by deep cryogenic treatment. It has been assumed that the increase of service life of tool steel caused by decrease of retained austenite and/or by formation of nano-scale fine η-carbide. But the principles of deep cryogenic treatment remain unclear yet. In this research, to manifest the effect of deep cryogenic treatment on wear resistance, the specimen was emerged in liquid nitrogen for 20 hours for deep cryogenic treatment after austenitizing and the following tempering temperature was varied. The microstructure of specimens was observed using TEM and the mechanical properties and wear resistance were examined. As the tempering temperature increased, the carbides became larger and fine carbides were formed above certain temperature. In the case of deep cryogenic treated specimen, the number of carbides increased while the carbides size was decreased, furthermore, the fine carbide forming temperature was lowered also. It was considered that the deep cryogenic treatment increased the driving force for the nucleation of carbides. As tempering temperature increased, hardness decreased while wear resistance and impact energy increased. The deep cryogenic treated specimens showed this tendency more clearly. It was considered that the wear resistance is affected not only to the hardness but also to the precipitation of fine carbides, and this carbide evolution can be optimized through the deep cryogenic treatment.

Intergranular cracking of Hastelloy C-276 in the socket welded assemblies

The cause of thermal cracking about a socket welded tube was investigated by stress simulation and its comparison to hardness distribution of welding seam, HAZ and matrix of the tube. In the condition of heat-input in melting range of 1349°C, the stress was concentrated in HAZ at the opposite side of welding area by ANSYS program, which corresponded to the distribution of real hardness values of the tube. The high stress concentration in HAZ might be induced from fine carbide precipitation which formed during welding process. It could cause, therefore, tube cracking in operating condition simultaneously followed by bulging inside of the welded tube. In the crack propagation through all the tube originated from inside HAZ, it might be accelerated by thermal fatigue, and propagated along grain boundaries accompanied by the metal dust formation.

Influence of Hot Rolling and Post-Tempering on the Mechanical Properties of Duplex Stainless Steel Containing Martensite and Ferrite

In this research, SUS 403 duplex stainless steel containing martensite and ferrite was processed with hot rolling at a range of reductions (15–50%) and post-tempering at a range of temperatures (473–873 K) to investigate microstructural change during tempering and mechanical properties as a function of tempering temperature and ferrite grain size. The results indicate that Cr-rich carbides precipitate when tempering at the range of 473–773 K. The precipitation of fine carbides increases the carbide-ferrite phase boundary area. Again, the hard carbides reinforce the ferrite matrix along the boundaries and, consequently, results in enhancing mechanical properties. A secondary strengthening phenomenon in stress and hardness occurs at 773 K tempered. The ferrite grain size decreases with increasing reduction. Fine grain structure leads to an increase in grain boundaries and homogeneous dispersion of carbides, which provides a dominant action against crack propagation and improves the mechanical properties. Except the hardness, the maximum mechanical properties of each rolling reduction are better than that of the specimens quenched and tempered without hot rolling. [doi:10.2320/matertrans.47.2779]

The precipitation and transformation of secondary carbides in a high chromium cast iron

The precipitation and transformation of secondary carbides in a newly developed 16Cr–1Mo–1Cu cast iron subjected to a destabilization heat treatment was investigated. The results showed that the initial fine secondary carbide precipitation from the austenite matrix consist of (Fe,Cr) 23C 6. Two kinds of (Fe,Cr) 23C 6 carbides initially precipitated: one is cubic with a cube–cube orientation relationship with the austenite matrix, and the other is grainy with no orientation relationship with the matrix. The latter carbide may be precipitated in the cooling process after a destabilization treatment. With prolonged holding time, the fine (Fe,Cr) 23C 6 carbides have transformed into M 7C 3 rods with an orientation of [100] (Fe,Cr)23C6 [100] (Fe,Cr)7C3 and (01¯5) (Fe,Cr)23C6 (010) (Fe,Cr)7C3 between the M 23C 6 and M 7C 3 carbides.

Precipitation in V bearing microalloyed steel containing low concentrations of Ti and Nb

The paper describes the precipitation behaviour in a thermomechanically processed V bearing microalloyed steel containing small additions of Ti and Nb (0·007–0·008 wt-%) using analytical transmission electron microscopy. An intriguing aspect is the significant precipitation of titanium and niobium at these low concentrations, contributing to strength. A high density of multimicroalloyed precipitates of (V, Nb, Ti)(C, N) are observed instead of simple TiN, TiC, and NbC precipitates. They are characterised as cuboidal (45–70 nm), spherical (20–45 nm), irregular (20–45 nm), and fine (10–20 nm). Estimation of solubility products of carbides and nitrides of V, Nb, and Ti implies that the precipitation of titanium occurs primarily in austenite. Interphase precipitation of niobium occurs during austenite to ferrite transformation, while complete precipitation of vanadium takes place in the austenite–ferrite region close to completion of transformation. Substoichiometric concentrations of Ti and Nb, the presence of nitrogen, and the mutual extensive solubility of microalloying carbonitrides explains the formation of core shell (triplex/duplex) precipitates with highly stable nitrides ((Ti, Nb, V)N) in the core and carbides ((Ti, Nb, V)C) in the shell. The qualitative stochiometric ratios of triplex and duplex carbonitrides were Ti0·53Nb0·35V0·12 and Ti0·6V0·4, Nb0·51V0·49 and Ti0·64Nb0·36. Extensive precipitation of fine carbides on dislocation substructures, and sub-boundaries occurred. They were generally characterised as vanadium carbide precipitates with ordered cubic L12 structure and exhibited a Baker–Nutting orientation relationship with the ferrite matrix. M4C3 types of carbides were also observed similar to the steel, having high concentrations of Ti and Nb.

Composition, microstructure, hardness, and wear properties of high-speed steel rolls

The effects of alloying elements on the microstructural factors, hardness, and wear properties of four high-speed steel (HSS) rolls fabricated by centrifugal casting were investigated. A hot-rolling simulation test was carried out using a high-temperature wear tester capable of controlling speed, load, and temperature. The test results revealed that the HSS roll containing a larger amount of vanadium showed the best wear resistance because it contained a number of hard MC-type carbides. However, it showed a very rough roll surface because of cracking along cell boundaries, the preferential removal of the matrix, and the sticking of the rolled material onto the roll surface during the wear process, thereby leading to an increase in the friction coefficient and rolling force. In order to improve wear resistance with consideration to surface roughness, it is suggested that a reduction in the vanadium content, an increase in solid-solution hardening by adding alloying elements, an increase in secondary hardening by precipitation of fine carbides in the matrix, and formation of refined prior austenite grains by preaustenitization treatment be employed to strengthen the matrix, which can hold hard carbides in it.

The effect of double austenitization on the microstructure and fracture toughness of AISI M2 high speed steel

In this study, the effect of double austenitization on microstructure and toughness of AISI M2 high speed steel was investigated. For double austenitization treatment, the specimens, which are hardened initially at 1220°C and quenched in air, were hardened for a second time in the temperature range 1150 – 1050°C. For comparison purposes, another set of specimens is austenitized singly in the temperature range 1150 – 1050°C. Tempering process was carried out between 500 – 640°C. A double austenitization causes a fine carbide precipitation in the matrix, having sizes in the range of 0.10 ± 0.05 μm and volume fractions of between 1 and 6%. It is shown that a double austenitization treatment causes a decrease in fracture toughness (KIc), when compared with single austenitized ones. The reason for the lower KIc values of double austenitized specimens are attributed to these fine carbide precipitates: It is suggested that they limit the plastic deformation capability of the matrix and yield lower fracture toughness values.