Semi-solid processing using cooling plate technique was developed to produce a high quality ultrahigh-carbon steel (UHCS) components. Microstructure and mechanical properties were investigated as a function of fraction of solid. The microstructure of UHCS was improved using semi-solid processing. A unique homogenized microstructure comprised of fine particles grain size (200–100 μm) was obtained which totally differs from that obtained by ordinary UHCS casting (520 μm particle grain size). Tensile strength of as-cast and heat treated semi-solid processed UHCS is relatively high compared with ordinary one. Both the tensile strength and elongation closely connect with the particle grain size and cementite network changed with fraction of solid. Increasing fraction of solid increases hardness values, which is attributed to the fine and homogenous structure by semi-solid processing.

Semi-solid processing of ultrahigh-carbon steel castings

An ultrahigh-carbon steel containing 1.6 wt.% carbon (UHCS-1.6C) was processed to obtain ultrafine spheroidized ferrite, pearlite and tempered martensite, respectively. The tensile properties of these structures were evaluated at room temperature. The ultimate tensile strengths of UHCS-1.6C ranged from 930 to 1570 MPa, elongations to failure from 4.4 to 19%, and yield ratios from 0.65 to 0.92. The fracture mechanisms of these structures were clarified based on an examination to the fracture surfaces. The present results indicate that ultrahigh-carbon steels can be easily processed to achieve unique microstructures and properties.

Processing and properties of ultrahigh-carbon (1.6%C) steel

In this study, effect of modification treatment via Fe–Si–Mg–Ca–RE modifier on microstructure of ultrahigh carbon steel containing 1.5 wt% C was investigated. Microstructure characterization was performed by optical microscopy. It was found that as-cast proeutectoid carbide network tend to break after the modification treatment, and the carbides changed to discontinuous and spherical shape and uniformly distributed in matrix. Also, grain size, porosity and inclusions content decreased by modification treatment.

Microstructure of Cast Ultrahigh Carbon Steel (UHCS) Modified via Fe–Si–Mg–Ca–RE

Spray Deposition and Coating Processes

The tribological behavior of 1.41 wt% C ultrahigh-carbon steel (UHCS-1.41C) was investigated in comparison with a GCr15 bearing steel with a pin-on-disk and a two-disk tribometer at varying applied loads in ambient conditions. The wear surfaces of the specimens were examined with an optical microscope, EDX, and SEM. The retained austenite was measured by XRD. The results show that the friction coefficient of UHCS-1.41C is higher than that of GCr15 at a low load (6 N); however, it becomes lower than that of GCr15 at higher loads (10 N, 20 N). The wear rate of UHCS-1.41C is always lower than that of GCr15 according to the results of the two-disk test. UHCS-1.41C exhibits a stronger work hardening ability, which results in a higher resistance to wear than that of GCr15 during the two-disk test.

Tribological Behavior of 1.41 wt% C Ultrahigh-carbon Steel With Quenching and Low-temperature Tempering Treatment

The microstructure and mechanical properties of the spray formed 1.25C–3.0Si–1.5Cr ultrahigh-carbon steel (UHCS) were described. The 1.25C–3.0Si–1.5Cr UHCS was processed by spray forming to break up carbide networks. The fine pearlites with average interlamellar spacing of 0.20 μm was observed in the as-sprayed microstructure. The ultimate tensile strength and the pearlite spacing can be related by the Hall–Petch equation. The as-sprayed 1.25C–3.0Si–1.5Cr UHCS consisting of fine lamellar pearlites has been shown to exhibit superplastic behavior at elevated temperature. The dramatic change of microstructure from fine lamellar pearlites to equiaxed grains stabilized by spheroidized particles during superplastic deformation has been observed. The estimation on the basis of thermodynamics shows that the content of chromium of 1.54 wt.% is needed to inhibit graphite formation in the 1.25C–3.0Si–1.5Cr UHCS.

Microstructure and mechanical properties of spray formed ultrahigh-carbon steels

Spray forming UHCS-1.6Al material has a refined equiaxed pearlitic structure, which was necessary for high-train-rate superplasticity. During deformation, the cementite particles pin the grain boundaries and prevent the grains growing up. As a result it exhibited excellent high-strain-rate superplasticity, with a peak ductility of 187% occurring at a strain rate of 5*10-3s-1.

Jun Wang

Papers

Microstructure and mechanical properties of spray formed ultrahigh-carbon steels

High-Strain-Rate Superplasticity of Big Grains in Spray Forming Ultrahigh Carbon Steel Contain 1.6wt.%Al(UHCS-1.6Al)