When processing medium and heavy plates, the thickness generally ranges from 8 to 60 mm, with hot rolling as the main method of manufacture. The materials usually employed are Q235, Q345, various high-strength steels, and similar ones. To reduce cutting-induced defects in the cross-section, shearing is performed at high temperatures, typically between 400°C and 700°C. Four Core Challenges in Heavy-Duty Shearing of Knives 1. High Temperature: When the temperature is high, the martensite in the tool undergoes tempering and breaks down into ferrite and large carbides, causing the matrix to become softer. At 400°C, cementite (Fe3C) begins to coarsen and lose effectiveness; as a result, the blade loses hardness and fails. 2. Oxide Scale: The presence of iron oxide scale on the surface of hot-rolled plates results in increased abrasive wear of the tool. The knife's cutting edge gradually rounds off, thereby losing its sharpness, which in turn unintentionally increases the tool clearance and leads to larger shearing burrs on the steel plate. 3. Fatigue: The hardness of the oxide scale on the surface of the plate is considerably greater than that of the base metal; it is brittle and abrasive and thus acts as the main reason for shearing tool wear and failure. At the same time, thermal-cycling shearing conditions increase fatigue effects. 4. Impact Load: When it comes to impact load, the thickness of hot-rolled plates is usually not uniform, and the brittle oxide scale breaks apart on impact, resulting in local stress peaks at shearing edges; under repeated impacts, the microscopic cutter edge defects grow so that small pieces of the surface material flake off from the knife and knife edge chipping occurs. Shearing Targets for Heavy Plates. Within the above demanding operational conditions, steel mills encounter considerable challenges in achieving the specified shearing criteria: 1.Shearing burr within < 3%–5% of plate thickness. 2.The length tolerance of the plate sheet after cutting is within plus or minus 0.5 to 1 mm, and the cut must be perpendicular. 3.Clean cross-section free from tearing, nodulation, or edge collapse. 4.Blade lifespan capable of supporting batch production with low tool-change frequency. Alloy Composition and Performance of H13 Tool Steel To address the challenging problems associated with heavy plate shearing, LCKNIFE chose H13 (1.2344, 4Cr5MoSiV1) tool steel for its advantageous composition. 1.Carbon (C: 0.32–0.45%): Contributes to the matrix quenching hardness and basic wear resistance; the medium carbon content ensures toughness of the knife without causing brittleness. 2.Silicon (Si: 0.80–1.25%): Improves the hardenability of knife steel and enhances oxidation resistance and thermal fatigue resistance. · 3.Manganese (Mn: 0.20 to 0.60%): Helps the tool’s hardenability. 4.Chromium (Cr: 4.75–5.50%): Gives excellent hardenability, forms chromium carbides, and has good resistance to oxidation at high temperatures in a knife. 5....