The invention discloses an improved 21 / 4Cr-1Mo-1 / 4V steel 
forging which is characterized by comprising the following components in percent by weight: 0.11-0.15 percent of carbon, not more than 0.10 percent of 
silicon, 0.30-0.60 percent of 
manganese, not more than 0.01 percent of 
phosphorus, not more than 0.01 percent of 
sulfur, 2-2.5 percent of 
chromium, 0.9-1.10 percent of 
molybdenum, not more than 0.20 percent of 
nickel, not more than 0.15 percent of 
copper, 0.25-0.35 percent of 
vanadium, not more than 0.30 percent of 
titanium, not more than 0.002 percent of 
boron, not more than 0.07 percent of 
niobium, not more than 0.015 percent of 
calcium and the balance of iron. The invention also discloses an automatic temperature-control inflation three-dimensional circulating water rapid cooling 
thermal treatment method of the steel 
forging, which comprises the steps of: 1, an after-
forging thermal treatment process: normalizing at a temperature of 890-990 DEG C, air-cooling after constant temperature is not less than 1h / 100mm, 
tempering at a temperature of 680-720 DEG C, furnace-cooling after constant temperature, and cooling at a limited speed at a temperature of below 400 DEG C; 2, a thermal refining process: 
quenching at a temperature of 900-980 DEG C, carrying out constant temperature with 1h / 100mm, rapidly cooling and 
quenching and 
tempering at a temperature of 680-720 DEG C, carrying out constant temperature with 1h / 100mm and air-cooling thickness of the forging, wherein the 
water temperature of thickness of the forging is not more than 10 DEG C; and 3, adopting a three-dimensional 
automatic control circulating water periphery inflation method. The forging has higher tension strength, temper 
brittleness resistance, 
hydrogen damage resistance and lower long-term high-temperature damage sensitivity.