How are High Tensile bolts like 10.9 and 12.9 grades made?

The code is comprised of two numbers separated by a dot. This dot is not a decimal marker but is merely a means of separating the two parts of the code. The number to the left of the dot when multiplied by 100 provides an indication of the ULTIMATE STRENGTH in Mega Pascals while the number to the right when multiplied by 10 times the preceeding number gives YIELD STRENGTH (Mega Pascals - MPa) or STRESS at 0,2% PERMANENT SET (MPa) depending on the strength grade; e.g. 8.8 Ultimate Strength: 8 x 100 = 800 MPa Yield Strength or Stress at 0,2% Permanent Set: 8 x 8 x 10 = 640 MPa How are they made? See the link belowhttp://www.m-d.co.za/images/M&DTechnicalData.pdf