An article from PeterSmith.net.nz, written by
www.petersmith.net.nz/boat-anchors/steel-and-materials.php

Steel Grades & Qualities For Anchors

A comment from the designer of the Rocna anchor

The shanks on all galvanized Rocna anchors use a type of plate formed from high strength low alloy (HSLA) steel.

There has been much confusion resulting from discussion of the precise steel grades used. A problem for customers has been a conflation, in much of the online and printed discourse, of the two primary properties that define a steel’s strength:

  1. yield strength, and
  2. ultimate tensile strength.

Both properties are measured in terms of pressure. The former defines the points at which a material will begin to deform plastically, and is always less than the tensile strength. In calculations of bending moments, “bending strength” is directly proportional to the yield figure.

The steel for the Rocna shank was referenced in literature and elsewhere as a “grade 800” steel, which referred to a HSLA steel characterized by a tensile strength of at least 760 MPa and a yield strength of 690 MPa. This reference inherited from the steel first used in Rocna shanks produced in New Zealand and Canada, specifically Bisplate 80 and Algoma QT100 respectively.

The Rocna in current production uses in its shank a steel called “Q620”. This numerical name refers to a grade with a minimum yield of 620 MPa. The average actual yield of all tested samples of this steel is 688 MPa.

In some online sources, as well as printed articles, there have been misleading or erroneous statements comparing the yield of Rocna shank steel to the “grade 800” tensile strength of the advertised steel or other anchors. For example, it has been common to see deliberate attempts to confuse readers with comments talking about “620 vs 800”. This is an entirely invalid comparison. The average tensile strength of all tested samples of steel used in current Rocna production has actually been 788 MPa.

For context, the reader should consider that “mild” or low carbon steel features a yield strength of about 250 MPa.

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