Papers by Keyword: Hypereutectoid Steel

Abstract: In the present study an investigation has been carried out for spheroidization of 100Cr6 bearing steel used in forging industry. Three different spheroidization processes were considered. The first one was the annealing of normalized steel under A_c1 temperature for a long time. The second one was the annealing of normalized steel above A_r1 temperature after heating between A_c1 and A_cm for one hour. The third one was the annealing of hardened steel under A_c1 temperature for a long time. For evaluation of cold workability with different spheroidization annealing periods, the yield strength and percentage of reduction in area in uniaxial tension were recorded. The present results indicate that low alloyed carbon bearing steels can be easily processed to achieve unique microstructures and properties.

Abstract: Three different Fe-C alloys were prepared in vacuum using the arc melting method: hypereutectoid (1.4% C), eutectoid (0.76% C) and hypoeutectoid (0.4% C). Unlike commercial steels, which they always contain Mn and other impurities, our samples were prepared by using high quality powders (99.999 wt.%). The samples were heat-treated and then observed with optical and scanning electronic microscopy (Zeiss EVO MA10). Selected samples were tested by microidentation (microhardness test). After isothermal transformation at 350 °C fine bainite nanostructures were observed in the hypoeutectoid sample, the mean size of which was found to be 50 nm. With the eutectoid sample, following different heat treatment procedures different micro-and nanostructures were measured: pearlite lamellar spacing, spheroidized cementite particles, and martensite needles, whose mean size is 145 nm, 290 nm and 200 nm respectively. The nanostructure of hypereutectoid sample after isothermal transformation at 650 °C, reveals the eutectoid and proeutectoid cementite lamellas with a mean spacing of 390 nm. X-ray diffraction pattern of eutectoid sample indicated the existence of cementite (Fe₃C) content which is also confirmed by carbon mapping of pearlite colonies performed with Energy Dispersive X-ray Spectroscopy. The Vickers hardness of the samples compares well to the one of corresponding commercial steels.

Abstract: Influence of modifying with silicocalcium (SiCa) on the structure and friction properties of the hypereutectoid steel alloyed with 8.85 wt. % of Cu was studied. SiCa modifying of the copper alloyed hypereutectoid steel, led to the formation of the vermicular graphite distributed in the indendritic space instead of cementite. Coefficient of friction reduction and increased wear resistance were marked in the copper alloyed hypereutectoid steel due to the presence of graphite and cupric inclusions in the steel structure. The wear resistance of the graphitized hypereutectoid steel alloyed with 8.85 wt. % of Cu was almost 5 times higher compared to the wear resistance of bronze BrA9J3L and 75% higher compared to the wear resistance of antifriction cast iron AChS-1.

Abstract: This work studies the formation of cast structures in hypereutectoid steel modified by alloying modifiers (Fe30Si55Mg7Ca2REM4, Fe34Si55Mg9Ca2 and Fe63Ni30Mg7) together with inoculants Fe20Si60Ba20. It is found that at spheroidizing by 0.7 % Fe63Ni30Mg7 and inoculation by 1.5 % Fe20Si60Ba20 causes the formation of inclusions of nodular graphite with nodularity exceeding 90 % and a structurally-free cementite structure is obtained. The mechanical properties of the steel with nodular graphite modified by Fe63Ni30Mg7 and Fe20Si60Ba20 are as follows: tensile strength (σb) 660-680 МPа, yield strength (σ0.2) 520-540 МPа, percent elongation (δ) 5-8 %, impact strength (КС) 15-35 J/cm2, Brinell hardness (НВ) 241-255. After ferritic annealing these parameters were found to be σb =530-560 МPа, σ0.2=400-430 МPа, δ =20-24 %, КС=160- 180 J/cm2, 150-162 НВ.

Abstract: Microstructure evolution and mechanical properties of hypereutectoid steel with the microduplex (α+θ) structures formed by hot deformation of undercooled austenite were investigated by hot uniaxial compression tests in a Gleeble-1500 simulation test machine, and the effects of subsequent annealing and the addition of Al were analyzed. The results indicated that at the beginning of hot deformation of undercooled austenite the formation of proeutectoid cementite was retrained and only lamellar pearlite was produced. With further strain, dynamic spheroidization of pearlite took place, leading to the formation of microduplex (α+θ) structure consisting of ultrafine ferrite matrix and dispersed cementite particles. In comparison with the normal microstructure consisting of lamellar pearlite and proeutectoid cementite, the microduplex (α+θ) structure presented higher strengths with similar ductility. Subsequent annealing could make the microduplex (α+θ) structure more uniform, which demonstrated better balance between strength and ductility. The addition of Al is disadvantageous to the formation of microduplex (α+θ) structure, but can result in the further refinement. With the addition of Al, the strength of microduplex (α+θ) structure was improved and the ductility was not deteriorated markedly.

Abstract: The relationship between mechanical properties and pearlite microstructure was investigated using various heat treatments on a hypereutectoid steels containing 1% carbon with different levels of vanadium and silicon. Specimens were heat treated at various temperatures ranging from 900 to 1200°C and transferred to salt bath conditions at 550, 580 and 620°C to examine the structural evolution of pearlite. The results show that the thickness of the cementite network increases with increasing reheat temperature. This is likely due to the larger austenite grain size reducing the grain boundary area available for proeutectoid cementite nucleation. It was found that the vanadium and silicon additions increased the strength of hypereutectoid steels through refinement of the microstructure and precipitation strengthening.