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1.
Hongsug Oh Sunghak Lee Jaeyoung Jung Sangho Ahn 《Metallurgical and Materials Transactions A》2001,32(3):515-524
The objective of this study is to investigate the correlation of microstructure with wear resistance and fracture toughness
in duocast materials that consisted of a high-chromium white cast iron and a low-chromium steel as the wear-resistant and
ductile parts, respectively. Different shapes, sizes, volume fractions, and distributions of M7C3 carbides were employed in the wear-resistant part by changing the amount of chromium and molybdenum. In the alloys containing
a large amount of chromium, a number of large hexagonal-shaped primary carbides and fine eutectic carbides were formed. These
large primary carbides were so hard and brittle that they easily fractured or fell off from the matrix, thereby deteriorating
the wear resistance and fracture toughness. In the alloys containing a smaller amount of chromium, however, a network structure
of eutectic carbides having a lower hardness than the primary carbides was developed well along solidification cell boundaries
and led to the improvement of both wear resistance and toughness. The addition of molybdenum also helped enhance the wear
resistance by forming additional M2C carbides without losing the fracture toughness. Under the duocasting conditions used in the present study, the appropriate
compositions for wear resistance and fracture toughness were 17 to 18 pct chromium and 2 to 3 pct molybdenum. 相似文献
2.
Sunghak Lee Seong-Hun Choo Nack J. Kim Eung-Ryul Baek Sangho Ahn 《Metallurgical and Materials Transactions A》1996,27(12):3881-3891
A correlation is made of microstructure and fracture toughness in hypereutectic high-chromium white iron hardfacing alloys.
In order to investigate the matrix effect of these alloys, in particular, four different matrices such as pearlite, austenite,
and a mixture of pearlite and austenite were employed by changing the ratio of Mn/Si, while the total volume fraction of carbides
was fixed. The hardfacing alloys were deposited twice on a mild steel plate by the self-shielding flux-cored arc-welding method.
Fracture toughness was increased by increasing the volume fraction of austenite in the matrix, whereas hardness and abrasion
resistance were nearly constant.In situ observation of the fracture process showed that cracks initiated at large primary carbides tended to be blocked at the austenitic
matrix. This suggested that fracture toughness was controlled mainly by the amount of austenite in the matrix, thereby yielding
the better toughness in the hardfacing alloy having the austenitic matrix. Considering both abrasion resistance and fracture
toughness, therefore, the austenitic matrix was preferred for the high-chromium white iron hardfacing alloys. 相似文献
3.
Yu. G. Gurevich A. P. Kuz'micheva D. E. Dorfman 《Powder Metallurgy and Metal Ceramics》1994,32(9-10):857-860
A process has been developed for hardening powder steel by surface coating with white cast iron. The electrical and chemicothermal parameters have been determined theoretically. Formulas are derived that define the heating conditions and cooling rate. Structural features of the hardened layers have been examined. Electrocontact melting raises the resistance to wear in SP60 powder steel under conditions of dry friction and lubricated friction by a factor six by comparison with hardened high-speed steel. 相似文献
4.
The influence of a range of austenitizing and subcritical (tempering) heat treatments on the high-stress abrasion resistance
and fracture toughness of four commercially significant grades of alloy white cast iron was investigated. Complementing an
earlier study[1] on the influence of a more limited range of heat treatments on the gouging abrasion performance of the same alloys, the results
showed that the effect of austenitizing temperature on high-stress abrasion pin test weight loss differed for each alloy.
With increasing austenitizing temperature, these results ranged from a substantial improvement in wear performance and retention
of hardness through to vir-tually no change in wear performance and substantial falls in hardness. Fracture toughness, however,
increased markedly in all alloys with increasing austenitizing temperature. Tempering treatments in the range 400 °C to 600
°C, following hardening at the austenitizing temperature used commonly in industrial practice for each alloy, produced significant
changes in both hard-ness and wear performance, but negligible changes in fracture toughness. Most importantly, the data showed
that selection of the correct temperature for subcritical heat treatment to reduce the retained austenite content for applications
involving repeated impact loading is critical if abrasion resistance is not to suffer. 相似文献
5.
A series of twelve Cr-Mo white irons varying in carbide volume from 7 to 45 pct were tested for dynamic fracture toughness
and wet sand abrasion resistance. Carbon content was varied from 1.4 to 3.9 pct. Two matrix microstructures were employed,
and the compositions (copper and chromium content) were varied to assure constant matrix compositions. Chromium was varied
from 11.6 to 25.7 pct. In addition, one composition of white iron was subjected to thirty different heat treatments to define
the effect of matrix microstructure on dynamic fracture toughness and abrasion resistance. It was shown that for the abrasive
wear system used, a carbide volume of about 30 pct represented an optimum quantity, above which abrasion resistance decreased.
Martensitic irons provided consistently better abrasion resistance than austenitic irons. Dynamic fracture toughness decreased
with carbide volume, as expected. Higher toughness values were obtained with predominantly austenitic matrix microstructures
than with predominantly martensitic matrix microstructures. Considering both abrasion resistance and fracture toughness, it
was shown that heat treated irons could provide an optimal combination of these properties.
Formerly Visiting Research Metallurgist, Climax Molybdenum Co. Research Laboratory. 相似文献
6.
The unlubricated sliding wear test of high chromium white cast irons (HCCIs) was conducted using a pin-on-disc configuration under different heat treatments and different hardnesses of the counterface. With the increase of counterface hardness (20?HRC–47?HRC–54?HRC), the mass loss of the sample first increases then decreases. When the counterface hardness is 20?HRC, adhesion wear mainly takes place between the high chromium cast iron and the surface of 1045 steel. When the hardness is 47 or 54?HRC, first HCCI’ matrix wear takes place, then carbide bump flakes under alternating stress. The mass loss of the counterface decreases with the increase of hardness for the same sample. The mass loss of quenching, once tempering and twice tempering sample decreases gradually for the same counterface hardness, but fluctuation of the samples’ surface increased. The disc material is always softer than the pin material and results in a severe wear regime operation. 相似文献
7.
B. V. Cockeram 《Metallurgical and Materials Transactions A》2002,33(1):33-56
Nickel-base wear materials are typically used as weld hardfacing deposits, or as cast or hot isostatically pressed (HIP) inserts
that provide the needed wear resistance to a base material with the desired mechanical properties. Most nickel-base wear materials
contain high levels of chromium, silicon, carbon, and boron, which results in complex microstructures that are comprised of
high volume fractions of silicide, carbide, and/or boride phases. The volume fraction of nickel-phase dendrite regions typically
ranges from 40 to 70 pct, and these dendrite-phase particles are individually isolated by a matrix of silicide, carbide, and
boride phases. The continuous matrix of brittle silicide, carbide, and boride phases results in a low damage tolerance for
nickel-base wear materials, which is a concern in applications that involve high stresses, thermal transients, or shock loading.
Fatigue crack growth (FCG) and fracture toughness (K
IC) testing in accordance with ASTM E399 methods has been used to quantify the damage tolerance of various nickel-base wear
materials. Fractographic and microstructure examinations were used to define a generic toughening mechanism for nickel-base
wear materials. The toughness of nickel-base wear materials is primarily controlled by the plastic deformation of the nickel-phase
dendrites in the wake of a crack moving through the matrix of brittle silicide, carbide, and/or boride phases, i.e., crack bridging. Measured K
IC values are compared with calculated K
IC values based on the crack-bridging model. Microstructure examinations are used to define and confirm the important aspects
of the crack-bridging model. This model can be used to predict the toughness values of nickel-base wear materials and direct
processing methods to improve the K
IC values. 相似文献
8.
A. Neville F. Reza S. Chiovelli T. Revega 《Metallurgical and Materials Transactions A》2006,37(8):2339-2347
Erosion-resistant high-chromium white cast irons (CWIs) are widely used in hydrotransport components, particularly in oil-sand
operations. Due to the acceptance that corrosion processes can accentuate material degradation by erosion processes andvice versa, it is important to understand the corrosion resistance of these materials in the environments in which they are used. Three
CWI alloys with different chemical compositions—chromium (26 to 40 wt pct) and carbon (2.5 to 4.3 wt pct)—were investigated
in this study. Electrochemical DC potentiodynamic polarization and potentiostatic tests were carried out in a solution of
1000 ppm Cl− at a pH of 8.5 (obtained by adding NaOH) that simulates a recycle cooling water. A detailed characterization of the microstructures
was also performed. There are significant effects of microstructural features and alloy composition on the corrosion behavior
of CWIs. Two key factors have been shown to determine the corrosion behavior: the primary carbide area fraction and the amount
of chromium as well as other elements in the matrix. The corrosion resistance of the CWI alloys strongly depends on the ratio
of chromium content in the M7C3 carbide to that in the matrix (CrM7C3/Crmatrix). 相似文献
9.
Crack extension behavior and fracture toughness of ductile cast iron were examined by three-point bend tests, where various
detection methods of crack initiation under static and dynamic loading conditions were adopted. Loading on the specimens was
interrupted at various displacement points, and the final fracture surfaces of the specimen were observed via scanning electron
microscopy (SEM). Crack-tip opening displacement (CTOD) obtained under the dynamic loading condition was smaller than that
under the static loading condition in ferritic ductile cast iron, and CTOD additionally decreased with increasing pearlite
content in the matrix. The relationship between J (ΔC) obtained by the compliance changing rate method and J(R) established
by the intersection of the crack extension resistance curve and the theoretical blunting line varied with pearlite content.
The average value of .J(ΔC) and J(R), that is J (mid), was proposed to define the fracture toughness of ductile cast iron;
J (mid) was considered to be a reasonable measure for the fracture toughness of ductile cast iron, irrespective of loading
condition and the pearlite content in the matrix. 相似文献
10.
运用扫描电镜观察Cr5钢在不同淬火温度下的显微组织,通过洛氏硬度计和摩擦磨损试验机分析淬火温度对Cr5钢摩擦磨损性能的影响。结果表明:Cr5钢淬火后的基体组织是马氏体,基体上会分布有未溶碳化物。随着淬火温度提升,未溶碳化物逐渐减少,淬火组织逐渐均匀化,但淬火温度达到一定值(1 050~990 ℃)时,碳化物基本溶解完全,组织较均匀,硬度值最大,为54.7HRC,磨损失重量最小,磨损表面相对较平整,耐磨性相对较好;继续升高淬火温度,马氏体组织粗大化,使得硬度有所降低,耐磨性下降。 相似文献
11.
12.
Effects of alloying elements on microstructure,hardness, and fracture toughness of centrifugally cast high-speed steel rolls 总被引:15,自引:0,他引:15
Chang Kyu Kim Yong Chan Kim Jong Il Park Sunghak Lee Nack J. Kim Jung Seung Yang 《Metallurgical and Materials Transactions A》2005,36(1):87-97
A study was made of the effects of alloying elements on the microstructure, hardness, and fracture toughness of centrifugally
cast high-speed steel (HSS) rolls. Particular emphasis was placed on the role of hard carbides located along solidification
cell boundaries and the type of the tempered martensitic matrix. Microstructural observation, X-ray diffraction analysis,
hardness and fracture-toughness measurements, and fractographic observations were conducted on the rolls. The constitution
and morphology of carbides observed within the intercellular boundaries varied depending upon the predominant alloying elements
that comprised them. These massive carbide formations strongly influenced the bulk material hardness and fracture toughness
due to their high hardness. The effects of alloying elements were analyzed on the basis of the liquidus-surface diagram which
and indicated that the proper contents of the carbon equivalent (CE), tungsten equivalent, and vanadium were 1.9 to 2.0, 10
to 11, and 5 to 6 pct, respectively. The roll material, containing a small amount of intercellular carbides and lath-type
tempered martensitic matrix, had excellent fracture toughness, since carbides were well spaced. Therefore, it was suggested
that the optimization of alloying elements was required to achieve the homogeneous distribution of carbides. 相似文献
13.
E. Pagounis V. K. Lindroos M. Talvitie 《Metallurgical and Materials Transactions A》1996,27(12):4183-4191
The influence of the matrix structure on the mechanical properties of a hot isostatic pressed (hipped) white iron matrix composite
containing 10 vol pct TiC is investigated. The matrix structure was systematically varied by heat treating at different austenitizing
temperatures. Various subsequent treatments were also employed. It was found that an austenitizing treatment at higher temperatures
increases the hardness, wear resistance, and impact toughness of the composite. Although after every different heat treatment
procedure the matrix structure of the composite was predominantly martensitic, with very low contents of retained austenite,
some other microstructural features affected the mechanical properties to a great extent. Abrasion resistance and hardness
increased with the austenitizing temperature because of the higher carbon content in martensite in the structure of the composite.
Optimum impact energy values were obtained with structures containing a low amount of M (M7C3+M23C6) carbides in combination with a decreased carbon content martensite. Structure austenitized at higher temperatures showed
the best tempering response. A refrigerating treatment was proven beneficial after austenitizing the composite at the lower
temperature. The greatest portion in the increased martensitic transformation in comparison to the unreinforced alloy, which
was observed particularly after austenitizing the composite at higher temperatures,[1] was confirmed to be mechanically induced. The tempering cycle might have caused some additional chemically induced transformation.
The newly examined iron-based composite was found to have higher wear resistance than the most abrasion-resistant ferroalloy
material (white cast iron). 相似文献
14.
The effects of additions of 0.6 to 2.0% Cr on the temper embrittlement behaviour of 0.25 C–1.0 Si–1.3 Mn cast steel under several hardening conditions were studied. The susceptibility to temper embrittlement, transgranular and intergranular fracture were increased as the chromium content increased when the steels were tempered at 350°C and slowly cooled from 550°C. The impact toughness and abrasion resistance of the steels were found to depend to a great extent on the Cr-content and tempering temperature. 相似文献
15.
The effect of heat treatment on the gouging abrasion resistance of alloy white cast irons 总被引:2,自引:0,他引:2
A series of heat treatments was employed to vary the microstructure of four commercially important alloy white cast irons,
the wear resistance of which was then assessed by the ASTM jaw-crusher gouging abrasion test. Compared with the as-cast condition,
standard austenitizing treatments produced a substantial increase in hardness, a marked decrease in the retained aus-tenite
content in the matrix, and, in general, a significant improvement in gouging abrasion resistance. The gouging abrasion resistance
tended to decline with increasing austenitizing tem-perature, although the changes in hardness and retained austenite content
varied, depending on alloy composition. Subcritical heat treatment at 500 ° following hardening reduced the retained austenite
content to values less than 10 pct, and in three of the alloys it caused a significant fall in both hardness and gouging abrasion
resistance. The net result of the heat treatments was the development of optimal gouging abrasion resistance at intermediate
levels of retained aus-tenite. The differing responses of the alloys to both high-temperature austenitizing treatments and
to subcritical heat treatments at 500 ° were related to the effects of the differing carbon and alloying-element concentrations
on changes in theM
s
temperature and secondary carbide precipitation. 相似文献
16.
Microstructure and its effect on toughness and wear resistance of laser surface melted and post heat treated high speed steel 总被引:2,自引:0,他引:2
Leif Åhman 《Metallurgical and Materials Transactions A》1984,15(10):1829-1835
High speed steel hacksaw blade blanks were laser surface melted and rapidly solidified along one edge. The laser melting resulted
in complete carbide dissolution. By subsequent machining and heat treatments saw teeth were manufactured with a refined internal
structure of the edges and corners. The structure was fully martensitic with a uniform and dense dispersion of small primary
carbides. Sawing tests in quenched and tempered steel showed that blade life was somewhat improved, as compared to conventionally
heat treated blades. The increased wear resistance is believed to be due to improved toughness along with high hardness caused
by the refined carbide structure. Sawing tests in austenitic stainless steel did not give any significant improvement in performance.
The effect of the altered microstructure on performance is likely to be more or less pronounced depending on application,
tool and work material. 相似文献
17.
Yoshiyuki Tomita 《Metallurgical and Materials Transactions A》1987,18(8):1495-1501
A modified heat treatment has been suggested whereby lower temperature plane-strain fracture toughness (K
IC) of 4340 ultrahigh strength steel is dramatically improved in developed strength and Charpy impact energy levels. The modified
heat-treated 4340 steel (MHT-4340 steel) consists of a mixed structure of martensite and about 25 vol pct lower bainite which
appears in acicular form and partitions prior austenite grains. This is produced through isothermal transformation at 593
K for a short time followed by an oil quench (after austenitizing at 1133 K and subsequent interrupted quenching in a lead
bath at 823 K). The mechanical properties obtained at room temperature (293 K) and 193 K have been compared with those achieved
using various heat treatments. Significant conclusions are as follows: the MHT-4340 steel compared to the 1133 K directly
oil-quenched 4340 steel increased theK
IC values by 15 to 20 MPa • m1/2 at increased strength and Charpy impact energy levels regardless of the test temperature examined. At 193 K,K
IC values of the MHT-4340 steel were not less than those of the 1473 K directly oil-quenched 4340 steel, in whichK
IC values are significantly enhanced at markedly increased strength, ductility, and Charpy impact energy levels. The MHT-4340
steels compared to austempered 4340 steels at 593 K, which have excellent Charpy impact properties, showed superiorK
IC values at significant increased strength levels irrespective of test temperatures. The lower temperature improvement inK
IC can be attributed to not only the crack-arrest effect by acicular lower bainite but also to the stress-relief effect by the
lower bainite just ahead of the current crack. 相似文献
18.
Effects of carbon and chromium additions on the wear resistance and surface roughness of cast high-speed steel rolls 总被引:7,自引:0,他引:7
Yong Jung Kang Jun Cheol Oh Hui Choon Lee Sunghak Lee 《Metallurgical and Materials Transactions A》2001,32(10):2515-2525
The effects of carbon and chromium additions on the wear resistance and surface roughness of five high-speed steel (HSS) rolls
manufactured by a centrifugal casting method were investigated in this study. High-temperature wear tests were conducted on
these rolls to experimentally simulate the wear process during hot rolling. The wear-test results revealed that the wear resistance
increased with increasing carbon content because of the increased total carbide fraction. In the HSS roll containing a smaller
amount of chromium, the wear resistance was improved because it contained a number of very hard MC carbides. However, it showed
a very rough roll surface because of the preferential removal of the matrix and the sticking of the rolled material to the
roll surface during the wear process. Rolls containing a higher chromium content had very low surface roughness, because of
the formation of a larger amount of M7C3 carbides of slightly lower hardness and homogeneous wear of the matrix and carbides. In order to improve wear resistance
with consideration of surface roughness, the increase in the chromium content, i.e., the increase in the amount of M7C3 carbides, which can result in a low surface roughness, was suggested. 相似文献
19.
20.
Saied Azab El-Ghazaly 《国际钢铁研究》1993,64(2):136-141
A series of six Cr-, Cr + Mo-, Cr + Mo + V cold work cast tool steels were produced and investigated for microstructure, impact toughness and both experimental and industrial abrasive wear. Grain refinement of the steel matrix even in as-cast condition was obtained on using 2.3 % Mo + 0.9 % V and that ensured increasing impact toughness and abrasion resistance. An optimum impact toughness of about 85 J-cm?2 was obtained in air quenched (970°C) and tempered (450°C) Mo + V containing steels in which area fraction of carbides reached 38 %. The abrasion resistance improved in case of steels tempered at 250°C and had fine grain structure. 相似文献