For example, consider 4# and 5# national standard angle steel; the standard thicknesses are 40404 and 50505, with a tolerance of within 6% (i.e., within 6 points). Angle steel with thinner thicknesses is classified as non-standard angle steel.
It is important to note that not all non-standard angle steel is of inferior quality. Some large manufacturers produce non-standard angle steel with deviations controlled within a certain range, such as 40403 angle steel and 50504 angle steel, which are of relatively good quality and widely used.
However, non-standard angle steel processed by some small factories often has uneven material quality with many impurities. The carbon content is generally higher, making the surface hard and less ductile, prone to breaking under stress, and the deviation cannot be controlled within a certain range. It is not suitable for critical or main components. Additionally, mass production generally does not recommend using such steel materials. For instance, a 40404 angle steel in non-standard quality might actually measure 38393.5, 36373.0, or 38353.2. Therefore, product quality cannot be reliably controlled.
