GB/T 10051.2-2010 is Part 2 of the lifting hook series standard, specifically addressing the material heat treatment and dimensional tolerance requirements for forged hooks.

Scope and Application of the Standard

GB/T 10051.2-2010 is Part 2 of the GB/T 10051 "Lifting Hooks" series. This part sets forth the general technical specifications for forged hooks, covering design calculation basis, material selection principles, heat treatment process requirements, and dimensional tolerance standards. The standard is applicable to the manufacturing technical conditions of die-forged and free-forged hooks used in lifting appliances, with a rated lifting capacity range of 0.1 to 500 t. It covers the technical parameters of both straight-shank and ring-type hook configurations. Building on the general requirements of Part 1, this standard imposes more specific technical requirements on the forging process, heat treatment, and quality inspection of forged hooks.

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Material and Heat Treatment Requirements

The standard specifies detailed requirements for the material and heat treatment of forged hooks: hooks must be die-forged from high-quality carbon structural steel or alloy structural steel, with common material grades being DG20 (No. 20 hook-specific steel) and DG34CrMo (alloy steel hook-specific grade). Carbon content must be ≤0.25%, with P and S contents ≤0.025%. After forging, hooks must undergo normalizing followed by tempering: normalizing at 850–900°C with air cooling, and tempering at 550–650°C with air or furnace cooling. The metallographic structure after heat treatment must be uniform ferrite + pearlite (DG20) or tempered sorbite (DG34CrMo), with a grain size rating of no less than Grade 6. Surface hardness of the hook body: HB 140–187 for DG20 material and HB 210–270 for DG34CrMo material.

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Dimensional and Geometric Tolerances

The standard defines tolerances for the key dimensions of forged hooks: hook opening size deviation of ±2 mm (≤100 t) or ±3 mm (>100 t). Thickness deviation of the curved hook section: ±1.5 mm. Hook neck diameter tolerance: h9 grade. Hook thread tolerance: 6g grade (mating with the hook nut). Inner corner radius R deviation of the curved hook section: ±1 mm. Coaxiality between the hook centerline and thread centerline: Φ0.5 mm. Hook tip deflection (within the hook mouth plane): ≤3 mm. Surface roughness of the hook body: Ra≤6.3 μm (non-mating surfaces) or Ra≤3.2 μm (mating surfaces and threads). All dimensional and geometric tolerance inspections must be performed after heat treatment (deformation caused by heat treatment must remain within tolerance limits).

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Forging Process Specifications

The standard imposes strict requirements on the forging process: hooks must be die-forged with a forging ratio of no less than 3:1, ensuring the metal flow line runs continuously along the hook profile (flow lines must not be interrupted at critical sections). Forging temperature range: initial forging temperature 1150–1200°C, final forging temperature ≥850°C. After forging, hooks must be slowly cooled in air to room temperature (rapid cooling is prohibited). The forged surface must be free of cracks (confirmed by visual inspection plus Magnetic Particle Inspection), folds, overheating, and heavy scale. Flash must be removed before heat treatment, and the trimmed area must be ground smooth. Each forged hook must undergo visual inspection, dimensional inspection, and hardness inspection upon completion.

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Inspection Rules and Routine Tests

The standard requires that each forged hook undergo visual inspection, dimensional inspection, hardness inspection, and a static load test before delivery. At least one hook from each batch (same heat number, same heat treatment state) must be subjected to tensile and impact tests. The static test load is 2 times the rated lifting capacity (for general-purpose hooks) or 2.5 times (for hooks used in lifting and transporting molten metal), with a holding time of ≥5 min. After the test, the residual deformation of the opening must not exceed 0.25% of the original opening size. The Factory Certificate must indicate the hook model, rated lifting capacity, material grade, heat treatment state, and test load value. Kelude forged hooks are manufactured and inspected strictly in accordance with the technical requirements of GB/T 10051.2.

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Forged Hook Heat Treatment Comparison Table

The comparison table below lists the core parameter configurations for forged hook heat treatment, for reference by selection and operating personnel.

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