The type of steel that best fits your project’s need will vary depending on how the steel will be applied. Understanding different steel types will allow you to pick a steel that performs best for your application. For example, hot rolled and cold rolled steel manufacturing methods create two very different end products.

We believe by understanding the distinctions between these two methods you will save your company time, raw materials costs, and additional processing. We will review the distinctions between hot rolled and cold rolled steel and how each has its advantages and limitations.

*Note: Hot-rolling and cold-rolling does not imply different grades of steel. Steels of different grades can be produced as hot-rolled or cold-rolled.

Hot-Rolled steel

 Hot-Rolled steel is the product produced after the steel is made and slabs are cast. Integrated Mills will reheat slabs for rolling and Mini Mills will roll slabs directly after slabs are cast. Slabs are reheated or stabilized to temperatures above 1200* and sent through the “Hot Strip Mill” that usually consists of a descaler, roughing stand and a minimum of 5 sets of very large high force computer controlled sets of rolls that gradually reduce the slab thickness to the desired finished thickness.

Hot Rolled coil products can be supplied as rolled and may be referred to any one of the following, “HR Black” – “Black Band” “Black Iron”—These products are used where the remaining surface scale is not detrimental to the application of the steel. For example, racking systems, heavy gauge tanks, structural beams and pipe products are good examples for HR Black applications.

In many cases Hot Rolled Black is taken to a secondary Pickling operation to remove the remaining scale left over from the Hot Rolling process.  In the Pickling operation, coils are loaded onto a payoff reel where they are uncoiled and sent through a series of tanks from acid to rinse then oiled and recoiled. Some Pickle lines are set up to apply other lube products and others may have in line leveling or shape correction equipment. Pickled products are used in applications that require the removal of the Hot Mill scale, most all Hot Rolled steel used to produce Automotive parts are Pickled. Pickled products are called out as Hot Rolled Pickled & Oiled or “HRPO”.

Hot Rolled Surface, Flatness and Gauge control vary between producers and generally are not as good as Cold Rolled products.

Hot Rolled products are available in Low Carbon, Structural Steel, High Strength Low Alloy  and Advanced High Strength Steel

Hot-Rolled steel’s properties make it popular for structural components and applications in which precise shapes and tolerances aren’t critical. These include things such as:

Cold-Rolled steel

Cold Rolled steel is produced by further reducing the Hot Rolled Pickled products at room temperature. There are two main types of “Cold Mills”, a Tandem Mill is as it implies a series of rolls or stands similar to a Hot Mill. Many Tandem Cold Mills are 5 stands with high force computer control rolls the gradually reduce the thickness.  A Reversing Mill is usually one set of rolls where the steel is pulled back and forth reducing the thickness until the final thickness is achieved.

The first product off of a Cold Mill is what is called “Full Hard”, there are applications for Full Hard however the majority of Cold Rolled parts are specified to require annealing or further processing to recrystallize the grain structure for improved formability.

With all of this further processing, Cold Rolled products are usually improved over Hot Rolled products. Cold Rolled typically has better Shape or Flatness, Surface, Gauge Control and in some cases better Formability.

Cold Rolled products are available in Low Carbon, Structural Steel, High Strength Low Alloy and Advanced High Strength Steel all the way up to materials that exhibit tensile strength in excess of 1700 Mpa.

Typical uses for cold-rolled steel include:

  • Automotive parts
  • Home appliances
  • Metal furniture
  • Aerospace structural members
  • Roof and wall systems
  • HVAC
  • Electric Motors

Should I use hot-rolled or cold-rolled steel for my project?

Comparing the products below may help you decide.

Cost

  • CR is almost always more expensive due to the further processing.
  • HR is almost always less expensive.

Surface

  • CR is usually better and can be refined to the point where it has a mirror like finish such as an Electric Stove burner bowl. This is accomplished by using certain roll texture in the Cold Rolling process.
  • HR is still readily paintable and is used in some semi exposed applications—Automotive Steel Wheels.

Thickness Control

  • CR is normally better, tight tolerances can be achieved with extra care and cost above typical CR—CR Strip Products are marketed to be very precise. On the high side of thickness CR becomes a specialty product above .130” thick.
  • HR gauge control varies between producers and is suitable for many applications. HR is limited to roughly .050” minimum thickness—below .050 usually requires CR material.

Shape / Flatness

  • CR is normally better
  • HR can be suitable for more stringent flatness requirements when further processed through a leveling device. These options should be explored before going to CR for Flatness.

Formability

  • In Low Carbon products CR is generally more formable due to the processing, this advantage is diminished in higher strength products.
  • HR material can be produced to manufacture demanding dimensional parts. This is especially true with HSLA products-HR is almost always as good or better with respect to formability.

In Summary 

For projects that require large, structural components we recommended going with hot-rolled steel for the parts manufacturing. If the project requires more precise dimensional components, cold-rolled steel is the way forward. A key determining factor for using hot-rolled or cold-rolled is the final thickness. Typically cold-rolled is used for thinner gauges and hot-rolled for thicker gauges, mostly defined by the process per se. There is an overlapping area in which both cold-rolled and hot-rolled can be produced in the same thickness, in which case cost and surface conditions will be the determining factors for which product to choose.

National Material Mexico is capable of providing both of these products and we have a long track record working closely with companies on producing both hot-rolled and cold-rolled steel for their projects. If you have any additional questions, please visit our contact page.

About National Material L.P. – Since its founding in 1964, National Material Limited Partnership has grown to over 30 business units and is now one of the largest suppliers of steel in America. The National Material group of industrial businesses consists of the Steel Group, Stainless and Alloys Group, Raw Material Trading Group, Aluminum Group, and Related Operations. Visit National Material: http://www.nationalmaterial.com or call (U.S.) 847-806-7200