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.Molybdenum (Mo: 1.10–1.75%): Stops the cutter knife temper softening and acts as the main element for secondary hardening. · Vanadium (V: 0.80 to 1.20%): Forms stable, tiny VC carbides in slitter knives. It makes grains smaller and helps steel resist wear at high temperatures.

H13 hot-work die steel in the shearing application incorporates a balanced ratio of 5% Chromium, 1.5% Molybdenum, and 1% Vanadium. This alloy composition provides the knife tool exceptional hardenability and resistance to thermal checking. At temperatures up to 600°C, H13 knives retain a hardness above 48 HRC. The wear resistance of the knife is three to five times greater than that of conventional knife cutter tool steels, and post-heat treatment impact toughness can exceed Ak 50J, achieving an optimal balance between hardness and impact resistance.

Key Reasons for H13's High-Temperature Strength

1. Secondary Hardening Peak: When H13 steel is quenched, it develops a high-hardness martensite; on tempering at a temperature between 500 and 600°C, molybdenum and vanadium cause nanoscale alloy carbides (Mo2C and VC) to precipitate out of the supersaturated martensite, the fine particles acting to pin the grain boundaries and as a result hardness recovers or even increases while in other steels the hardness decreases.

2. Stable high-temperature carbides: Vanadium carbide (VC) has an extremely high melting point and does not tend to coarsen even at 700°C; unlike ordinary cementite (Fe3C), which begins to coarsen at 400°C, the H13 strengthening particles maintain the knife’s hardness below 400–650°C.

3. Grain refinement stability: Cr and Mo prevent movement of grain boundaries in the shearing knife and thus inhibit grain growth at high temperatures; a finer grain structure increases a shear knife tool’s resistance to high-temperature softening.

4. Resistance to oxidation and decarburization: Significant reductions in cutting tool hardness are caused by decarburization. Chromium and silicon form a dense, protective oxide film on the knife surface, which reduces surface burning and decarburization.

Common H13 Blade Applications

H13 tool steel is commonly used in the manufacture of metallurgical products.

Typical applications involving cutting include:

Heavy plate shearing,Hot-rolled coil slitting,Cut-to-length line shearing,Crocodile shearing,High-strength plate shearing,Concave-convex shearing,Arc shearing,Flying shears,Gantry shears,Scrap metal shearing,Hydraulic cylinder shearing.

H13 shear tools Heat Treatment Process

1. Material Selection: Choose Electro-Slag Remelted (ESR) H13 and then shape it into the required knife tool blanks by forging.

2. Annealing: Heat the knife raw material to a temperature between 860 and 890°C and keep it for 2 hours; then cool to a temperature between 740 and 760°C for an isothermal hold of 4 hours; afterward, furnace-cool to about 500°C before air cooling.

3. Preheating: carry out two stages of preheating (at 600–650°C and at 800–850°C) before quenching in order to reduce thermal stress of the shear knife.

4. Quenching: When making toughness-oriented tools, heat the shear knife to a temperature between 1020 and 1050°C and then oil-cool it until they reach a hardness of 54 to 58 HRC. For tools where hardness is the main concern, heat the shear knife to 1050-1080°C, then oil-cool it to achieve a hardness of 56-58 HRC.

5. Tempering: at temperatures of 500–530°C the hardness of the knife is 51–54 HRC, at 530–560°C the hardness is 48–52 HRC, and at 560–580°C the hardness is 47–49 HRC.

6. Triple Tempering: After having carried out two tempering cycles of the shear knife, test the Rockwell hardness, and then carry out a third tempering at 550 to 560°C in order to eliminate the retained austenite and relieve the internal stress.

7. Cryogenic Treatment: Cryogenic treatment of the shear knife should be carried out between quenching and the first tempering stage to convert the retained austenite into martensite, thus enhancing the microstructural uniformity, hardness, and dimensional stability.

Core Shearing Process Parameters

1.The shearing method is mainly made up of cross-cutting (transverse) and slitting (longitudinal).

2.Cutter knife gap: The blade clearance (side gap) is dynamically adjusted to about 8 percent of the plate thickness, and bigger gaps are employed in the case of high-strength steel.

3.Transverse Rake Angle: The transverse rake angle is between 0.5° and 3°; in the case of thicker and higher-strength plates, a greater rake angle is required to reduce the peak shearing force.

4.Shearing Force: The shearing force for heavy-duty sizing shears can have a peak value of 1000 to 2000 kN, leading to cyclic impact fatigue.

5.Line Speed: · In the case of hydraulic shears used individually, the feeding is carried out at a low speed in an intermittent manner; for cut-to-length operations, the speed ranges from 5 to 30 m/min (lower speeds are used when thicker plates are being processed). · 6.Clamping Condition: In the clamping condition, high-pressure hydraulic cylinders clamp the plate during the entire process to prevent it from flipping or sliding and to ensure that the cut is perpendicular.

7.Plate Shape Condition: Handles irregularities such as camber, uneven heads/tails, and internal stress that cause warping or shifting.

Maintenance Guidelines for H13 Cutter Tools

1. Match Hardness: When it comes to match hardness, LCKNIFE will choose the appropriate hardness resulting from the heat treatment depending on whether cold or hot shearing is involved, the yield strength of the plate sheets, and plate thickness.

2. Preheat Tools: Preheat the cutter blades to bring the tool temperature in line with the initial working conditions. Preheat the blades before use to avoid premature cracking due to thermal shock.

3. Control Clearance: Keep blade gaps at the right size to stop iron scale from getting into the spaces at the edge.

4. Secure clamping: Make sure the plates are tightly clamped in order to reduce sliding friction and prevent scratching of the surface.

5. Optimize Cooling: Improve cooling by using a specialized cutting fluid while processing to ensure adequate and stable lubrication and heat dissipation, so that extreme temperature differences that cause the cutter blade thermal fatigue cracking are avoided.

6. Check the wear: frequently regrind the trimmer knife edges to eliminate any micro-cracks and fatigue layers.

7. Rust Prevention: To prevent the cutter tools from rusting, apply an industrial anti-rust oil uniformly when storing the cutter knives.

Maanshan Licheng Blade Manufactory specializes in producing industrial shearing knives and tools by professionally selecting highly suitable materials for the specific metal sheet cutting situations. Advanced heat treatment processes, including vacuum, cryogenic, and salt-bath treatments, are employed to maximize the cutter blade performance for different shear applications. Rigorous quality control and precise manufacturing standards ensure that these knife tools can be fully trusted by partners worldwide.