Large-size diesel exhaust valve and manufacturing method thereof

A manufacturing method of a large-size diesel exhaust valve, comprising the following steps:

• pretreatment:
• subjecting a 3J40 alloy bar to a solution treatment at 1,000° C. to 1,050° C. for 50 min to 70 min to obtain a first intermediate material, and oil-cooling the first intermediate material to obtain a second intermediate material, wherein a thickness of a single lamella of a α-Cr lamellar phase is controlled at less than 150 nm and a diameter of a nickel-lean Cr—Al—Ce particle phase is controlled at no more than 10 μm;
• electric upsetting process:
• forming the second intermediate material through electric upsetting at a low strain rate to obtain a first billet, wherein throughout the electric upsetting process, an electric upsetting temperature is controlled at 1,150° C. to 950° C. and an electric upsetting strain rate is controlled at 0 s−1 to 0.05 s−1;
• supplemental heating treatment:
• conducting supplemental heating on a head of the first billet at 1,000° C. to 1,050° C. for 20 min to 25 min to obtain a second billet;
• heat preservation treatment:
• holding the second billet at 1,000° C. to 1,050° C. for 20 min to 25 min to obtain a third billet, wherein a total time of a supplemental heating time and a heat preservation time is 45 min or less;
• die forging process:
• forging the third billet at one time to produce a first initial exhaust valve with a disc portion and a rod portion;
• and
• post-treatment:
• subjecting the first initial exhaust valve to an aging treatment at 770° C. to 790° C. for 16 h to 18 h to obtain a second initial exhaust valve, and air-cooling the second initial exhaust valve,
• wherein the thickness of the single lamella of the α-Cr lamellar phase is controlled at less than 140 nm and the diameter of the nickel-lean Cr—Al—Ce particle phase is controlled at no more than 10 μm.