Fundamentals of cold rolled steels

Cold rolled steels provide excellent press  formability,  surface  finish, thickness and flatness tolerances. Steel companies manufacture three groups of  low-  or  ultra-low-carbon  grades  to meet  a  variety  of  customer  formability requirements:  CS  Type  B,  DS  Type  B, EDDS,  and  EDDS+. They  also  produce HSLA steels and structural steel grades for those  applications  that  require  specified strength levels.

Cold rolled steels can also be specified as  dent  resistant  or  bake  hardenable  for applications  that  require  dent  resistance after forming and painting. Each grade can be processed with several surface finishes depending  on  customer  requirements. Lubricants  can  be  applied  to  enhance formability and to avoid at-press lubrication.

Cold rolled steels have the following features:

● Excellent Surface Appearance-Cold Rolled Steels have manufacturing controls in place assuring consistent surface quality to satisfy customer requirements.

● Formability-Cold Rolled Steels can be used to produce parts containing simple bends to parts with extreme deep drawing requirements.

● Paintability- Due to stringent surface roughness controls, Cold Rolled Steels are readily paintable using essentially any paint system.

● Weldability- Cold Rolled Steels can be joined using virtually any accepted welding practice.

Standard grades for cold rolled steels are:
● Commercial Steel (CS Type B)- May be moderately formed; a specimen cut in any direction can be bent flat on itself without cracking.

● Drawing Steel (DS Type B)-DS Type B is made by adding aluminium to the mol steel and may be used in drawing applications.

● Extra Deep Drawing Steel (EDDS)-Interstitial Free (I-F) steels are made Drawing Steel by adding titanium and/or niobium to the molten steel after vacuum degassing and offer excellent drawability.

●  Extra  Deep  Drawing  Steel  Plus (EDDS+)-Interstitial Free (I-F) steels are made by adding titanium and/or niobium to the molten steel after vacuum degassing and offer excellent drawability.

Surface finish
Cold  rolled  steels  are  manufactured with a matte finish obtained by rolling with specially roughened rolls on the cold mill and the temper mill. This finish helps to maintain effective lubrication during metal forming and improves the appearance of painted surfaces. Non-standard matte finishes can be provided that optimise the opposing effects of surface roughness on painted part appearance and lubrication during press forming.

Surface protection and lubrication
To prevent rusting in transit and storage, cold rolled steels can be supplied with a rust protective oil film or press forming lubricants. A  pre-applied  press  forming  lubricant provides uniform lubrication and eliminates the housekeeping problems.

A dry film (acrylic/polymer) lubricant can also be supplied by further processing the cold rolled product through a coil coating facility. These specialty organic coatings are easily removed with a mild alkaline cleaner.

Formability, mechanical properties
The formability of all steel products is a result of the interaction of many variables, the main ones being the mechanical properties of the steel, the forming system (tooling) used to manufacture parts, and the lubrication used during forming.

Tight control over chemical composition, hot  rolling  parameters,  amount  of  cold reductNike Zoom Kobe IV