High-hardness Rebar Cutting Blades Chipping and Performance Requirements
High-hardness rebar cutting blades are not necessarily prone to chipping. Whether or not chipping occurs depends primarily on the balance between hardness and toughness, not simply the hardness value itself. Moreover, the durability of rebar cutting blades does not rely on pursuing high hardness; instead, it is determined by the chemical composition of the blade material. In fact, excessively high hardness will make the blade more brittle. If only high hardness is pursued while neglecting toughness, the blade will become brittle, significantly increasing the risk of chipping. This is a common cause of chipping in such blades.
The core requirement for rebar cutting blades is "hard but not brittle, tough and wear-resistant." For the shearing conditions of rebar (especially high-strength deformed steel), qualified blades achieve a balance of properties through heat treatment processes (such as quenching + low-temperature tempering), and their hardness varies with the chemical composition of the material:
Hardness: Ensures the wear resistance of the blade, coping with the hard texture of rebar and high-frequency shearing. The Rockwell hardness of qualified blades varies according to their material composition: conventional blades made of common alloy materials typically have a Rockwell hardness of HRC55~60, while blades made of high-performance alloy materials designed for high-strength rebar can reach HRC50~55;
Toughness: Counteracts the impact load during rebar shearing (the rigid shearing of rebar generates instantaneous impact force), preventing chipping and breakage of the blade edge.
Main reasons for chipping in high-hardness blades (not due to hardness itself):
Process defects: Heat treatment without proper toughness matching, or low material purity (containing impurities, segregation), leading to high internal stress and coarse grains in the blade, resulting in a sharp decrease in toughness at high hardness;
Improper material selection: Using ordinary high-carbon steel (such as T8, T10) instead of specialized alloy tool steel (such as Cr12MoV, D2) / H13. These materials cannot simultaneously achieve both high hardness and high toughness;
Improper working conditions: Shearing oversized rebar, improper adjustment of the gap between the blade and the cutting machine, lateral force caused by rebar misalignment during feeding, or forcibly cutting with a dull blade will cause the edge of the high-hardness blade to bear extra impact/stress and chip;
Poor processing accuracy: The blade edge is ground too sharp, without a transition chamfer, causing stress to concentrate at the edge, making it prone to cracking at the edge under high hardness.
Key Practices to Prevent Chipping of High-Hardness Rebar Cutting Blades:
Select qualified materials and processes: Prioritize alloy tool steel blades such as Cr12MoV and H13, which have undergone proper quenching and tempering treatment. The supplier should provide hardness test reports;
Standardize usage and adjustment: Strictly match the blade specifications to the rebar diameter, adjust the cutting machine blade gap (usually 0.1~0.3mm), and avoid off-center cutting and hard cutting; sharpen the blades promptly after blunting, maintaining a slight bevel on the cutting edge (0.1~0.2mm) to reduce stress concentration;
Perform daily maintenance: Before cutting, clean the rebar surface of hard slag and welding scars to prevent hard foreign objects from damaging the cutting edge; after stopping the machine, apply rust prevention to the blades to prevent material embrittlement.