Large cast iron platform made of HT250 cast iron

How to distinguish whether the material of a cast iron platform is HT200 or HT250?
As an essential foundational tool in industrial manufacturing, the material properties of a cast iron platform directly affect machining accuracy and equipment lifespan. HT250, as a high-strength cast iron grade, features good wear resistance, high compressive strength (250MPa), and excellent machinability, making it widely used in applications such as machine tool bases and inspection platforms. So, how can one accurately determine whether a cast iron platform is made of genuine HT250 material? The following provides identification methods from six dimensions.

1. Physical Performance Testing Method
1. Hardness Test: The Brinell hardness range of HT250 is typically between 180-250 HB. Use a portable hardness tester to take multiple measurements at different locations on the platform. If the values are below 170 HB, it may be a lower-grade cast iron; if above 260 HB, it could be alloy cast iron or specially treated.
2. Acoustic Identification: Tap the platform with a metal rod. HT250 will produce a clear, resonant metallic sound that lasts longer, while lower-grade cast iron will produce a dull, short sound. Experienced personnel can preliminarily judge the material based on sound frequency differences.
2. Chemical Composition Analysis Method
Using a spectrometer to detect key element content can determine the material:
Carbon equivalent (CE) should be controlled between 3.9%-4.3%
Carbon content (C) 2.9%-3.3%
Silicon content (Si) 1.4%-2.0%
Manganese content (Mn) 0.6%-1.2%
3. Metallographic Structure Observation Method
Observe the sample under a 100x microscope:
HT250 should exhibit fine lamellar pearlite (≥95%)
Graphite morphology should primarily be Type A (uniformly distributed)
Graphite length should be controlled at grades 4-6
If a large amount of ferrite or Type D graphite is found, the strength does not meet standards. According to one inspection statistic, 30% of "HT250" platforms are actually HT200, with pearlite content only around 85%.
4. Mechanical Performance Verification Method
1. Bending Strength Test: The bending strength of a standard HT250 test bar under a 300mm span should be ≥450 MPa. Request the supplier to provide test reports for accompanying test bars.
2. Elastic Modulus Measurement: The elastic modulus of HT250 is 105-130 GPa, which can be measured non-destructively using the vibration frequency method. One production line once experienced excessive robot repeatability errors due to insufficient platform elastic modulus.
5. Surface Feature Identification Method
1. Machining Mark Observation: After machining, HT250 surfaces appear uniformly gray-white, with chips being curly; inferior cast iron may show "chill" or "pitting."
2. Casting Mark Identification: Reputable manufacturers will cast "HT250" markings on non-working surfaces and provide material certificates. Be cautious of products with ground or painted-over markings.
Mastering these identification methods can help avoid the risk of inferior material substitution. It is recommended that users adopt a "initial inspection + re-inspection" dual process during acceptance, combining physical testing and chemical analysis to ensure the cast iron platform meets the genuine performance requirements of HT250. For platforms used in critical workstations, material performance should be rechecked every two years to ensure long-term stability.
Weiyue Machinery, Ms. Xie, 15350773479