Acceptance Standards for Different Cast Iron Parts

The acceptance standards for different cast iron parts vary depending on their application scenarios, material requirements, performance indicators, and customer needs. Below is a categorized explanation of the key acceptance criteria for common cast iron parts (e.g., gray iron, ductile iron, malleable iron):

1. Categories of Acceptance Standards for Cast Iron Parts

(1) International and National Standards

ISO International Standards:

ISO 185: Classification and performance requirements for gray cast iron.

ISO 1083: Performance standards for ductile iron castings.

Chinese National Standards:

GB/T 9439: Technical requirements for gray cast iron parts.

GB/T 1348: Technical requirements for ductile iron parts.

GB/T 5612: Technical requirements for malleable iron castings.

GB/T 6414: Dimensional tolerances and machining allowances for castings.

(2) Industry Standards

Certain industries, such as automotive, shipbuilding, and construction machinery, may use specialized industry standards like JB/T or YB/T.

Company-specific standards based on contracts may also define detailed acceptance criteria.

(3) Customer-Specific Requirements

Some cast iron parts require unique acceptance criteria (e.g., geometric precision, performance, surface quality) tailored to the customer’s specifications.

2. Main Contents of Acceptance Standards for Cast Iron Parts

(1) Chemical Composition

Gray Cast Iron: The content of carbon, silicon, manganese, phosphorus, and sulfur must meet the standards (e.g., GB/T 9439).

Example: HT200 typically requires 3.0%–3.5% carbon and 1.8%–2.5% silicon.

Ductile Iron: Magnesium and rare earth elements must be controlled to ensure nodularity.

Example: QT500-7 must have a nodularity of ≥80%.

(2) Mechanical Properties

Gray Cast Iron: Acceptance is based on tensile strength, e.g., HT200 requires tensile strength ≥200 MPa.

Ductile Iron: Must meet tensile strength and elongation requirements.

Example: QT450-10 requires tensile strength ≥450 MPa and elongation ≥10%.

Malleable Iron: Tested for impact toughness and plasticity.

(3) Dimensional and Shape Tolerances

GB/T 6414 defines the dimensional tolerance levels and machining allowances for castings.

Typical tolerance levels are CT6–CT10, depending on machining requirements.

Parting line deviation, hole position tolerance, and flatness must comply with design drawings.

(4) Surface Quality

Surface Roughness: Depending on the casting method (e.g., sand casting, investment casting, die casting), Ra values typically range from 6.3 to 25 μm.

Surface Defects: No cracks, porosity, cold shuts, sand inclusions, or shrinkage cavities are allowed.

Gate and Riser Cleaning: Must be properly cleaned without affecting assembly or performance.

(5) Internal Quality

Defect Inspection:

Ultrasonic Testing: For internal cracks and delaminations.

X-Ray Inspection: For porosity, inclusions, and shrinkage cavity distribution.

Magnetic Particle Inspection: For surface and subsurface cracks.

Density Requirements: Critical areas must be free of defects affecting mechanical performance.

(6) Heat Treatment Status

Verification of whether the casting has undergone heat treatment (e.g., annealing, normalizing, quenching).

Ductile iron may require annealing to improve ductility, while gray iron may benefit from normalizing for uniform microstructure.

(7) Machining Allowances

Ensuring the casting has adequate machining allowance and that dimensions comply with design drawings.

(8) Dimensions and Weight

Dimensional deviations must follow design drawings and standards. Weight deviations should meet contractual requirements (usually ±5%).

3. Acceptance Procedures

Visual Inspection: For cracks, gate and riser cleaning, and surface defects.

Dimensional Measurement: Using calipers, coordinate measuring machines (CMM), etc., to check critical dimensions.

Performance Testing: Tensile, hardness, and impact tests as required.

Non-Destructive Testing: Ultrasonic or X-Ray testing for internal quality.

Document Verification: Checking material reports, mechanical performance test reports, and process records.

4. Specific Requirements for Different Types of Cast Iron Parts

Gray Cast Iron Parts

Used for components requiring excellent vibration damping, such as machine tool beds. Focus is on graphite morphology and distribution.

Limited porosity is acceptable but must not concentrate or occur in stressed areas.

Ductile Iron Parts

Used for components requiring high strength and toughness, such as automotive suspension parts. Requires nodularity and microstructure inspection.

High-grade products often require no defects (no cracks or porosity).

Malleable Iron Parts

Used for pressure-bearing components, tested for toughness and strength.

Consistency in microstructure after annealing is critical.

Summary

The acceptance standards for cast iron parts are usually defined by a combination of international standards, national regulations, and customer requirements. The key aspects include chemical composition, mechanical properties, dimensional accuracy, surface and internal quality, and compliance with machining and heat treatment conditions. The exact acceptance criteria vary depending on the type of cast iron part, its application, and industry-specific considerations.