How Slab Induction Quenching and Tempering Machine Solves Uneven Hardness of Thick Steel Blanks

Uneven hardness has long been a prominent quality defect plaguing the heat treatment of thick steel slabs processed by traditional gas furnaces and box-type quenching lines. Thick steel blanks ranging from 50mm to 150mm thick easily suffer from inconsistent surface and core temperature, asymmetric cooling speed, partial overheating or undercooling, resulting in scattered hardness values across slab surfaces, unstable hardened layer depth and unqualified mechanical performance. The newly upgraded steel plate induction heat treatment equipment fundamentally addresses this industry pain point through segmented multi-zone induction heating, closed-loop temperature monitoring, balanced spray quenching and integrated online tempering technology, delivering consistent hardness for heavy thick steel blanks.

The root cause of uneven hardness in conventional thick slab processing lies in slow, non-directional radiant heating. Gas-fired furnaces heat the surrounding air first, so slab surface temperature rises far faster than the core. For ultra-thick blanks, the temperature gap between surface and center can exceed 80°C after holding, leading to incomplete austenitization inside the slab and excessive grain growth on the outer layer. This creates an obvious hardness gradient from edge to core after quenching. By contrast, the steel slab induction hardening heat treatment machine relies on eddy current internal heating: alternating electromagnetic fields generate heat synchronously inside the steel blank, realizing inside-out uniform heat conduction and eliminating temperature stratification of thick workpieces at the source.

Integrated online induction tempering further stabilizes hardness consistency after quenching. Untempered quenched steel carries massive residual thermal stress, which will trigger spontaneous hardness drifting after natural cooling. Immediately after quenching, thick slabs directly enter the tempering induction coil without secondary transfer, receiving low-temperature uniform reheating to transform brittle martensite into stable tempered martensite. The continuous linear tempering structure avoids temperature dead zones existing in static box tempering furnaces, relieves internal stress evenly across the whole slab and locks unified finished hardness without local hardness attenuation.