The ultra-wide square plate forging for shield cutter heads features a special structure characterized by large width and small thickness. The ultra-wide thin-plate cutter head square plate forging manufactured this time, with dimensions of 5750 mm × 5750 mm × 380 mm, belongs to the field of extreme manufacturing. It presents extremely high difficulty in width expansion and imposes stricter requirements on grain size and molten steel purity control. The traditional process route of "upsetting and drawing + wide-anvil flat drawing + 90° rotary drawing" is very difficult to control. Through process innovation, a new process scheme of "dimension-controlled preforming + rotary anvil-feeding width-expansion drawing + four-side flattening" is proposed. By strengthening the control over smelting and heat treatment processes, the production trial has been successfully completed.
The problem of Grade 4 network carbides and a small amount of eutectic carbides in Cr5 forged steel caused by improper post-forging heat treatment design can be solved by optimizing the heat treatment process. High-temperature normalizing is adopted to dissolve most carbides into the matrix, followed by rapid cooling using water-based or oil-based quenching media to ensure full austenite transformation, reduce precipitation of secondary carbides, thereby sufficiently refining the microstructure and avoiding the formation of network carbides. Ultimately, zero defect echoes and favorable bottom echoes are achieved in testing.
Prior to roll quenching and tempering, appropriate heat treatment processes can improve the grass-like echo defects of roll blanks. Aiming at the grass-like echo defects detected by ultrasonic testing in 70Cr5Mo steel roll blanks, this paper adopts post-forging heat treatment processes such as normalizing and spheroidizing annealing to refine the microstructure morphology of 70Cr5Mo steel blanks, obtain favorable microstructural features, and reduce or eliminate grass-like echoes in the blanks, so as to ensure no adverse effects on inspection and service performance.
