The effect of quenching temperature on hardness and grain size in 22Cr2Ni4MoV steel is a critical factor in determining its mechanical properties. In this study, diesel was used as the quenching cooling medium. It was observed that the quenching temperature significantly influences both hardness and grain size. The optimal performance was achieved at a quenching temperature range of 850–900°C, where the hardness reached a maximum of 47 HRC, and the grain size was approximately 8–15. However, as the quenching temperature increased beyond this range, both hardness and grain size decreased substantially. Therefore, 850–900°C was selected as the ideal quenching temperature for this steel grade. Subsequent tests were conducted using 850°C quenching followed by diesel cooling.
The effect of tempering temperature on hardness and impact toughness was also investigated. For Cr2Ni4MoV steel, during low-temperature tempering (below 250°C), both hardness and impact toughness decreased gradually. However, once the tempering temperature exceeded 250°C, the hardness dropped more rapidly with increasing temperature. Meanwhile, the impact toughness decreased sharply after 250°C, reaching a minimum value of 35 J at around 480°C. After 500°C, the impact toughness began to increase linearly with further temperature rise. A temper brittleness zone was observed between 300–550°C, which can affect the material's overall toughness.
In addition, the influence of tempering temperature on strength and plasticity was studied. The tensile strength and yield point of 22Cr2Ni4MoV steel decreased linearly as the tempering temperature increased. However, the elongation and reduction in area showed a slight dip within the 250–500°C range, aligning with the brittle zone identified earlier.
The steel exhibits excellent hardenability, allowing the formation of a martensite structure even through air cooling. Sample 'a' shows the martensite structure obtained after forging and air cooling. Sample 'b' represents the ferrite + pearlite microstructure after normalization at 920°C followed by tempering at 680°C. Sample 'c' displays a martensite plus trace residual austenite structure after oil quenching at 850°C. Sample 'd' illustrates tempered martensite with a small amount of residual austenite after quenching at 850°C and tempering at 200°C. Sample 'e' presents a tempered sorbite structure after quenching at 850°C and tempering at 480°C. Finally, sample 'f' shows a martensite structure with distinct grain boundaries formed by quenching at 975°C.
In the discussion, it is noted that 22Cr2Ni4MoV is a high-hardenability low-carbon alloy steel. After forging, it tends to form a martensite structure, which has high hardness but coarse grain size (approximately grade 2). To achieve a more ductile microstructure suitable for subsequent processing, normalization and tempering are recommended. This treatment results in a ferrite + pearlite structure (as shown in sample 'b'), with hardness reduced to about 22–24 HRC and grain size improved to approximately 8 grades. This preparation ensures better machinability and workability for further applications.
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