16 04, 2018

Complex Phase Steel: An Introduction

2018-04-16T23:30:52+00:00 April 16th, 2018|News Blog, NMC Media|

WHAT IS COMPLEX PHASE STEEL?

Complex Phase steel (CP steels) is a part of the Advanced High-Strength Steel (AHSS) family.

Complex Phase steels gain their strength through extremely fine grain size and micro structure containing small amounts of martensite, pearlite and retained austenite embedded in a ferrite-bainite matrix. High grain refinement is achieved by precipitation of micro alloying elements such as Nb, Ti or V or retarded recrystallization.

Complex Phase steel is being produced as both hot-rolled and cold-rolled which can be hot dipped galvanized for corrosion protection. Hot-rolled products are available in the higher thickness ranges needed to produce structural type parts.

The chemistry and microstructure of CP steels is similar to Trip Steels, except for the addition of some quantities of the Nb, Ti and or V to cause a precipitation strengthening effect.

The bainite complex phase microstructure exhibits improved strain hardening and strain capacity over the bainite structure alone.

Properties of CP steel

CP steels have a higher minimum yield strength in comparison with dual phase steels of identical tensile strengths of 800 Mpa and greater. When compared to DP steels, CP steels have a much higher yield strength to tensile strength ratio.

CP steels have high work hardening capability at low strain, high fatigue strength, high energy absorption, wear resistance and bake hardening potential.

Heat treatment of hot-rolled CP steels at 500-700 C can further increase the yield point of the material by up to 100 MPa.

CP steels are readily welded to itself or other common grades of steel, spot welders for other lower strength grades can be used with the appropriate adjustments.

Current and developmental strength grades range from 780 to 1470 Mpa minimum tensile strength with 5-30% total elongation.

Formability

With high uniform elongation and continuous yielding CP steels have excellent formability and are suitable for stretch forming, roll-forming, bending and hole expansions.

Applications of CP steel

Due to CP steels high capability to absorb energy during a collision they are particularly well suited for weight saving manufacturing of cold formed crash relevant parts in automobiles. There are several automotive applications in body structure, suspension and chassis components.

Current production grades of CP steels and examples of automotive applications:

  • CP 600/900 Frame rails, B pillar reinforcements, tunnel stiffener
  • CP 680/780 Frame rails, chassis components, cross members
  • CP 800/1000 Suspension brackets, fender beams
  • CP 1000/1200 Frame rail reinforcements, rocker panel supports
  • CP 1050/1470 Bumper beams, side sills

To summarize complex phase steels’ properties:

  • Tensile strengths that meet and exceed 800 MPa
  • High ratio of yield to tensile strength
  • Great for cold forming, bending, and hole expansion
  • Strong bake-hardening qualities
  • High durability and wear resistance
  • High crash energy absorption
  • Good weldability

About National Material L.P. With more than 3,000 employees from a multinational portfolio of companies, NMLP provides engineered metal products, which include steel processing, aluminum extrusion and stainless steel rolled product companies, to automotive, aerospace, construction, defense, electrical, and industrial markets.

Visit National Material: http://www.nationalmaterial.com or call (U.S.) 847-806-7200, Diana Pulido

4 04, 2018

The Differences Between Hot and Cold Rolled Steel

2018-04-04T18:33:39+00:00 April 4th, 2018|News Blog, NMC Media|

hot and cold rolled steel

When approaching your project, it is crucial to know the type of steel that is best suited for your needs. Different types of steel manufacturing can produce material that performs better for the specific applications. The hot and cold rolled steel manufacturing methods specifically have a great effect on the overall performance of the steel.

Prior knowledge of distinctions between the two methods can help your company save on time, raw material cost, and additional processing. This article aims to explain the differences between hot and cold rolled steel and discuss the advantages (and limitations) of each.

NOTE: Hot-rolling and cold-rolling should not be mistaken for different grades of steel. Steels of different grades can be produced as hot-rolled or cold-rolled.

HOT-ROLLED STEEL

Hot-rolling refers to a mill process in which you roll the steel at a temperature above its recrystallization temperature; a heat that typically exceeds 1000° F.

When steel is heated past its recrystallization point, it becomes more malleable and can be properly formed and shaped. It also allows for the ability to produce larger quantities of steel. The steel is then cooled at room temperature, which “normalizes” it, eliminating the worry for stresses in the material arising when quenching or work-hardening.

When the steel cools off, it will shrink non-uniformly, which gives slightly less control on the overall size and shape of a finished hot-rolled product.

Hot-rolled steel typically has a scaly surface finish. For situations in which the appearance of the material is a concern, the scales can be removed by several techniques: pickling, grinding, or sand-blasting.

These properties make hot-rolled steel most suitable for structural components and other applications where incredibly precise shapes and tolerances are of less importance, such as:

  • Railroad tracks
  • I-beams
  • Agricultural equipment
  • Sheet metal
  • Automotive frames

COLD-ROLLED STEEL

As you might suspect, the manufacturing process behind cold-rolled steel is a bit different. Despite the name, this process refers to steel that is pressed with the pressure of a roller at room temperature.

Compared to hot-rolled steel, cold-rolled steel has a nearly 20% increase in strength through the use of strain hardening. It’s through a series of breakdown, semi-finishing, sizing, semi-roughing, roughing, and finishing that cold-rolled steel shapes can be created.

Cold-rolling steel allows for the creation of very precise shapes. Since the process is performed at room temperature, the steel will not shrink as it cools, as it does in the hot-rolled process.

The exterior finish of cold-rolled steel is very desirable when aesthetics and visual appeal are a priority in your project.

However, the applications of cold-rolled steel are somewhat limited to a couple of shapes – square, round, flat, and variations thereof.

Typical uses for cold-rolled steel:

  • Strips
  • Bars
  • Rods
  • Home appliances
  • Roof and wall systems
  • Metal furniture
  • Aerospace structural members

HOT AND COLD ROLLED STEEL. WHICH DO I NEED?

If you require large structural components, you will most likely need the hot-rolled steel process to create the parts. For smaller parts that require more precise and durable qualities, then the cold-rolled steel process is the way to go. If you have questions about which mill process you need for your project, feel free to call National Material at 847-806-7200 and ask for one of our skilled customer representatives.