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Research carried out by the University of Cardiff in Wales for ILZRO (International Lead Zinc Research Organization) project took an in-depth look at the problem of silicon reactivity and included phosphorous as a reactive element also. The researchers varied the weight percentage of silicon and phosphorous and then assessed the reactivity of the steel at different galvanizing temperatures. This work led to a table of reactivity classifications for silicon and phosphorous content.

ILZRO Classifications of Sandelin Steels
Class Silicon Weight (%) Phosphorous
Weight (%)
Steel Reactivity Coating Appearance
1. Normal / Hypo-Sandelin 0.000 - 0.035 0.000 - 0.025 Generally Normal But
Occasionally Low
Few Defects
2. Semi-Sandelin 0.000 - 0.040 0.025 - 0.035 Normal Localized Defects Due to
Outbursts of Zeta Alloy
3. Non-Classical Sandelin 0.000 - 0.040 > 0.035 High, Especially with High
Phosphorous Content
Pronounced Surface Defects
(e.g. 'Tree Bark'): High Tendency
to Flake
4a. Sandelin (Low Phosphorous) 0.040 - 0.135 < 0.010 Moderate, Increasing With
Silicon Content
May Appear Normal With
Few Defects
4b. Sandelin (High Phosphorous) 0.040 - 0.135 > 0.010 High Generally Few Defects
5a. Hyper-Sandelin (Low Phosphorous) 0.135 - 0.350 < 0.030 High, But Generally Thinner
Coatings Than On Class 5b
May Appear Normal With
Few Defects
5b. Hyper Sandelin (High Phosphorous) 0.135 - 0.350 > 0.030 High Tendency to Flake, Especially
With High Phosphorous Content
6. Extreme Hyper-Sandelin > 0.350 > 0.000 High, & Increasing With Silicon Content Tendency to Flake, Increasing
With Phosphorous Content

For more information on steel selection and the impact of silicon and phosphorous on the HDG coating structure, see the following related articles:

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