Out of the 5 books I have about welding, not one of them ever mentions a distinction between "cold rolled" and "hot rolled" steel. Is there anyone who can explain the differences between them, in terms of the manufacturing process and subsequent strength? I have heard that cold rolled is stronger, but I cannot locate it anywhere! Even my local steel mill does not supply this stuff. If cold rolled is so great, why is it that nobody stocks it? Also, would it even be considered acceptable to fabricate leaf-spring hangers out of .25" hot rolled steel plate? Is hot rolled really that weak? And one final question. Isn't your typical angle-iron, square-tube, and rectangular tube steel all hot rolled??? I see people using all this stuff for vital suspension brackets, and it does not seem to raise concern.....
The terms hot rolled and cold rolled are generic. In order to really know the differences in strengths you need the actual grade designations.
Hot rolled is normally structural type steel that was heated and squeezed through a series of rollers to form the shape. There is mill scale all over it and the actual size and cross section are not very precise. As an example, a flat bar will have rounded corners, a round rod may actually be somewhat oval. HR works fine for most applications as long as the grade/strength is adequate and you don't mind some minor irregularities.
Cold rolled started out hot, was squeezed to rough form, then cold finished to final shape & size. The surfaces are normally shiny and smooth and have more precise dimensions and sharper corners. Round rods are going to actually be round (at least for normal uses). Strength varies according to type and grade. 1018 is less expensive and is usually an ASTM A-108 material. From there you go up the scale on a wide range to more exotic alloys that are not as easily welded and the lower grades.
I do not know what leaf spring hangers are made from. Others on this forum can answer that better than I can, I simply am pointing out that the hot rolled, cold rolled terminology don't tell you much without more info.
Chet Guilford
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