Ultrahigh Carbon Research Articles

Cleavage fracture under tension with constraint

A Fe-3%Si/UHCS metal laminated composite with individually discrete Fe-3%Si and ultra high carbon steel (UHCS), can be studied for the fracture behavior of Fe-3%Si under constraint environment. This paper offers some insights about the condition when materials fracture brittlely or yield to exhibit ductility. Also the familiar rule of mixture, which intuitively averages component's strengths and ductilities to predict those for their composite, may not apply in some cases as will be shown in this paper.

Superplastic forming of ultrahigh carbon alloyed PM steels: K. Peichi et al (R. Zapp Werkstofftechnik, Düsseldorf, Germany)

Superplastic forming of ultrahigh carbon alloyed PM steels: K. Peichi et al (R. Zapp Werkstofftechnik, Düsseldorf, Germany)

Impact properties of a laminated composite based on ultrahigh carbon steel and brass

Notch impact test of composites laminated with ultrahigh carbon steel (UHCS) containing five different interleaf materials indicate that a UHCS-brass combination provides the best impact properties at low temperature. This is because brass does not exhibit a ductile-brittle transition temperature and thereby contributes to blunting of propagating notches.

Impact Properties of a Laminated Composite Based on Ultrahigh Carbon Steel and a Ni-Si-Steel

A laminated composite consisting of an ultrahigh carbon steel (UHCS) and an 8Ni-2Si iron interleaf material can be selectively heat treated without carbon diffusion between adjacent layers. This desirable attribute leads to a low ductile-brittle transition temperature (DBTT) of about 163K ( − 110°C) after selective heat treatment. This result is a consequence of notch blunting from the presence of the sharp interlayer boundary and the tough interleaf material. Based on Charpy notch impact results of selectively heat-treated UHCS composites containing 8Ni-2Si iron and other interleaf materials, it is concluded that the DBTT is principally a function of the notch-toughness of the interleaf material.

Fracture behavior of a laminated steel-brass composite in bend tests

A 35-layer laminated metal composite, consisting of alternating ultrahigh carbon steel (UHCS) and brass layers, was evaluated for its plasticity and fracture characteristics in bending. The unnotched composite achieved remarkable ductility exhibiting a 0T bend ( i.e. bent upon itself) without failure. Voids were formed in the tension and compression regions of the UHCS layers and were associated with elongated carbide particles. Even with initial notches on the surface, the composite can be bent without failure. Delamination and crack tip blunting in the brass layer inhibited crack propagation and prevented total failure. Propagation of cracks occurs at about 45° to the maximum tensile stress direction. In contrast, laminated polymer-base composites fracture at 90° to the maximum tensile stress direction.

Microstructural studies of a roll-bonded laminated ultrahigh carbon steel bar

The microstructure and hardness of a metal matrix laminated composite, containing an ultrahigh carbon steel and medium carbon steel, is examined and evaluated. The composite, in the form of a round bar, is made by a novel method using a helical radial-shear rolling process developed in the Soviet Union. The as-hot-rolled laminate is shown to have a high hardness of HV = 500 in the ultrahigh carbon steel region, which is attributable to the fine microstructure consisting of eutectic carbides, a discontinuous network of proeutectoid carbides, and ultrafine pearlite.

Elevated temperature mechanical behaviour of an ultrahigh carbon steel/brass laminated composite

The mechanical properties of a laminated metal composite ( lmc) based on ultrahigh carbon steel and brass were investigated from 710 to 840°C. A high strain rate sensitivity exponent, m, of about 0.5 was observed at low strain rates and decreased to about 0.15 at high strain rates. The strain rate vs. flow stress behaviour for the composite at low strain rates correlates well with predicted behaviour based on the isostrain concept. The expected superplastic behaviour in the m=0.5 region was not realized because of severe cracking in the brass layers.

Superplastic behaviour of rapidly solidified ultrahigh carbon alloy tool steel X380 CrVMo 25 9 3

This paper describes the superplastic properties of the rapidly solidified (RS) ultrahigh carbon alloy tool steel X380 CrVMo 25 93. By application of a specific production route, a microcrystalline structure can be produced which consists of a ferritic matrix (grain size d ≤ 3·8 μm) and fine dispersed carbides (d=1–3 μm). At test temperatures T of about 1050°C the tool steel can be deformed superplastically. Maximum tensile elongations are limited by cavity formation at the austenite/carbide interfaces. Compression tests reveal clearly that the cavity volume is decreased compared with that found in tensile tests. The mechanism for accommodation of grain boundary sliding is discussed in the light of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations. To demonstrate the potential of the tool steel X370 CrVMo 25 93 for the production of near net shape components some samples were precision forged in the superplastic regime.MST/1378

Tensile Properties of Laminated Composites Based on Ultrahigh Carbon Steel

Laminated composites based on ultrahigh carbon steel (UHCS) have been prepared by roll bonding in three systems: UHCS/304 stainless steel, UHCS/Hadfield manganese steel, and UHCS/Fe-3%Si alloy. Tensile properties of these laminates were evaluated after various conditions of selective heat treatment. From these data, it is shown that the yield strength of the laminated composites follows the law of mixtures. The law of mixtures does predict the ductility of the laminated composites when the ductilities of the two components are similar, but does not predict the ductility for cases where the component ductilities are greatly dissimilar.

Superplasticity and Newtonian-viscous flow in fine-grained class I solid solution alloys.

Elevated temperature (1 023 to 1 193 K) tensile properties are described for a fine (6 μm) and coarse (100 μm) grained ultrahigh carbon (1.25 %) steel containing 10 % aluminum. The coarse-grained steel exhibits Class I solid solution alloy behavior wherein a stress exponent of three is noted. The fine-grained steel exhibits exceptionally low stress exponents, where a stress exponent of two is observed at low strain rates and decreases to as low as 1.35 with an increase in strain rate. A creep model is developed to explain these rersults based on grain boundary sliding accommodated by two different dislocation processes. When n=2, the accommodation process is attributed to dislocation climb and when n is less than 2, dislocation solute-dragged glide becomes the important accommodation process. The model predicts ideal Newtonian-viscous flow (n=1) will occur in Class I solid solution alloys at sufficiently high temperatures and at fine-grain sizes. It is shown that the superplastic alloys Al-Mg-Cu, Ti-6Al-4V and Mg-33Al exhibit the predicted fine-grained Class I solid solution alloy behavior, whereas the superplastic alloys Ni-39Cr-10Fe-7.5Ti-1Al, Cu-39.4Zn, Fe-26Cr-6.5Ni-0.05Al, Fe-1.6C and Ag-28Cu exhibit the predicted fine-grained Class II solid solution behavior.

Superplasticity of steels and ferrous alloys

Numerous reports are now available showing the occurrence of superplastic deformation in high and ultrahigh carbon steels, low carbon low alloy steels, austenitic stainless steels, and duplex stainless steels or alloys. In this review we tabulate the more significant results in this area and examine in detail the current status of structural superplasticity in steels and ferrous alloys.

Economical low alloyed steel for surface hardening

Fe–1.4C–0.65Si–0.85Mo ultrahigh carbon steel was liquid phase sintered in 10%H2–90%N2 at 1300 °C from Höganas Astaloy 85 Mo HP base iron, fine graphite and silicon carbide powders mixed with polypropylene glycol. The microstructure then comprised fine pearlite and grain boundary cementite networks and the density increased from ∼6.8 g cm−3 to ∼7.7 g cm−3. A group of specimens then underwent austenitisation, isothermal quenching/autotempering at M(10%) temperature, followed by cooling to room temperature. This produced a crack-free martensitic microstructure, which transformed to ferrite plus fine spheroidised carbides by annealing for 3 h at 750 °C. To attain full density and well-distributed submicron carbides, these specimens were warm forged at 700–750 °C. To ascertain if some processing steps can be discarded, as-sintered and quenched samples were similarly thermo-mechanically processed. The required stresses and resultant microstructures depended on temperature and strain rate, with optimum microstructure, for Bähr processing at 775 °C of quenched material, fully comparable with that of prior spheroidised specimens. Microstructures and hardness values are presented for all processing routes.

MULTILAYERED COMPOSITES BASED ON ULTRAHIGH CARBON STEEL AND BRASS

ABSTRACT Thermal and mechanical processing procedures were developed to prepare unique metal matrix laminated composites (MMLC) based on a combination of ultra high carbon steel (UHCS) and brass. The MMLC material, of 50 volume percent of each component, was processed at about 700°C to large strains by a combination of rolling and press-bonding. Discrete interlayer boundaries were retained until layer thicknesses of less than 10 μm were reached. At this stage brass penetrated the UHCS material and became the continuous component, The UHCS/brass laminated composites can be selectively heat-treated with no interdiffusion between the layers. Exceptional ductility was obtained in the laminated composite in bend and tensile tests at room temperature.

An Historical Mullite Fiber-Reinforced Ceramic Composite: Characterization of the ‘Wootz’ Crucible Refractory

AbstractSince at least the sixteenth century, the ‘wootz’ ultra-high carbon white cast-iron ingot was produced in India by melting or carburising iron in a crucible. This ingot was forged into sword blades of so-called ‘Damascus’ steel. The charged crucible was fired in a long (24 hour) single cycle at high temperature (1150-1250°C) in a strongly reducing atmosphere. Raw materials for the refractory vessel are clay and ‘coked’ rice husks. At high temperatures, two phases reinforce the glassy matrix - cristobalite relics of rice husks and a network of mullite crystals. This paper characterizes the microstructure and chemistry of the mullite network in the glassy matrix by means of a combination of techniques: optical microscopy, XRD, SEM, TEM with EDS, and HREM.

Superplasticity of Ultra-High Carbon Steels Containing 3-5%Aluminum

ABSTRACTTo study the effect of Al on superplasticity of ultra-high carbon steel (UHCS), 3–5%Al was added to the UHCS, and superplastic behavior was measured at 700–800°C. To produce the fine and superplastic microstructure, an isothermal rolling at 700°C was used, and the grain size of ferrite was less than about 2μm in diameter after the process.Significant improvement in superplasticity was observed; the strain-rate sensitivity was high upto a strain-rate of 10−2 s−1, and 402% elongation was measured at 750°C and at an engineering strain-rate of 5000%/min(i.e., 8.3×10−2s−1). It has been determined that the Al-addition leads to a finer grain size, which, in turn, improved the superplastic properties of the ultra-high carbon steels.

Factors Influencing the Fatigue Behavior of Ferrous Laminates

Laminates based on ultrahigh carbon steel were prepared and found to exhibit enhanced fatigue life as compared to a monolithic reference material. This result was achieved through the insertion of weak interlaminar regions of copper into the layered material during preparation of the laminates. The presence of these regions allowed for the operation of a delamination mechanism in advance of the propagating fatigue crack. The result was interlaminar separation and associated crack blunting. Stress-life curves show that an increase in life by as much as a factor of four is achieved for these materials when compared to monolithic specimens of similar processing history.

巨大共晶炭化物を含む超高炭素鋼の疲労き裂進展抑制機構

Superior resistance to the stage II fatigue crack growth was obtained on an ultra high carbon steel containing massive eutectic carbide extended in the direction perpendicular to the original crack growth direction by forging. The fatigue crack growth rate obtained in this study was about 1/4 times as low as that of general mild steel without eutectic carbides. Microscopic observations revealed that the fatigue crack path was bent or branched when it encountered the massive carbide. Taking the actual crack configurations affected by the carbide into consideration, the “Effective stress intensity factor (SIFeff)” for fatigue crack growth was estimated, in which significant reduction of the SIFeff was obtained.An analytical study showed that the SIFeff of the bent crack would decrease significantly with increasing the angle θ between the carbide extention direction and the loading direction. The relation between the growth rate and SIFeff was examined on various specimens that have different carbide orientation on the basis of the above analysis. It was found that the growth rate drastically changed in accordance with θ and also found that the dependense of the growth rate on θ was in good agreement with the SIFeff-θ relation. It was made clear that crack growth retardation was due to the reduction of SIFeff resulting from the complicated crack morphology affected by massive carbide.

Superplasticity of a stainless steel clad ultrahigh carbon steel

Superplasticity of a stainless steel clad ultrahigh carbon steel

Development of ferrous laminated composites with unique microstructures by control of carbon diffusion

A novel method is described for preparing ferrous laminated composites, containing ultrahigh carbon steel as one of the components, which results in hard and soft layers bounded by sharp and discrete interfaces. The method is based on increasing the activity of carbon in iron by silicon addition; in this manner, the carbon is made to segregate into specific layers by heat treatment at low temperatures (∼770 °C). The results are ferrous laminated composites with discrete and sharp interfaces that consist of hard layers containing spherical carbide particles embedded in a matrix of ultrafine martensite or ferrite adjoining soft layers of a coarse grained iron alloy. In addition, the high activity of carbon is shown to result in total depletion of carbon in a silicon containing UHC steel ribbon bonded to mild steel.

Ultrahigh Carbon Steels

Recent studies and results on ultrahigh carbon (UHC) steels suggest that major development efforts on these steels are timely and that programs to evaluate prototype structural components should be initiated. These recent results include: the development of economical processing techniques incorporating a divorced eutectoid transformation, the improvement of room temperature strength and ductility by heat treatment, the enhancement of superplastic properties through dilute alloying with silicon, and the attainment of exceptional notch impact strength in laminated UHC steel composites manufactured through solid state bonding. The unique mechanical properties achieved in UHC steels are due to the presence of micron-size fer-rite grains and ultrafine spheroidized carbides.