1.25Cr-0.5Mo material

I’m also confused about this and really want to understand it; is there anyone who can provide a systematic explanation?

1.25Cr0.5Mo is a type of steel plate used for boiler and pressure vessel applications. The 1.25Cr-0.5Mo steel plates used for cylinders and heads (including the base layer of composite steel plates), in addition to meeting the requirements specified below, must also comply with the other relevant requirements outlined in ASMESA387/SA387M Gr11 Class 2. 1.25Cr-0.5Mo steel should be produced using an electric furnace or an oxygen converter with vacuum degassing and refining processes; it should be a naturally fine-grained killed steel. Chemical composition: C: ≤0.15, Si: 0.44–0.86, Mn: 0.35–0.73, P: ≤0.10, S: ≤0.007, Cr: 0.94–1.56, Mo: 0.40–0.70, Ni: ≤0.25, Cu: ≤0.20, Sb: ≤0.0030, Sn: ≤0.015, As: ≤0.016; impurities: ≤3 ppm. Mechanical properties: Tensile strength at room temperature (MPa): 515–690; Yield strength at room temperature (MPa): ≥310; Elongation at room temperature (%): ≥18; Reduction of area at room temperature (%): ≥45. Charpy impact energy at -20°C (V-notch J): The average value of three specimens should be ≥54, with one specimen being allowed to have a value of ≥47. Yield strength at high temperatures of 475°C: σ0.2 at 475°C ≥185.5 MPa, and σb ≥348 MPa. Corresponding national standard steel grade: 14Cr1Mo