ASTM A1008 (CR) vs. ASTM A1011 (HR) 1

[GMIracing]

We use HSLAS for most of our applications due to our tradeoff criteria for applied stress, mass, cost, and formability. Currently, I would say our most commonly purchased is grade 340 or 410. So, with all of this in mind, I believe that we are mostly limited to ASTM A1008 (CR) or ASTM A1011 (HR) for the NAFTA production region.

My question, when only looking at these two ASTM standards and given the same grade 410 HSLAS-F for both, what is the benefit of Cold Rolled vs. the Hot Rolled equivalent?

Analysis of the two standards shows a 2% better min elongation percentage (18% for CR and 20% for HR), and both would meet our specifications for forming. The chemical composition limits are the same for both standards. The min Inside Radius for Cold Bending is the same for both standards (1 1/2t for HSLAS-F).

What should one expect regarding a difference regarding performance between the two standards? Would one give better forming tolerances, fatigue strength, tool wear rates, weld HAZ properties, welding/brazing distortion rates, or etc? Is the difference between the two really only the superior surface finish properties with the Cold Rolled specification? (When keeping YS and TS the same)

I appreciate if anyone had some recommendation for references on sheet steels in machine design applications it would be a great help to me.

 

[CoryPad]

Improved flatness, reduced thickness variation, reduced roughness variation are expected benefits of cold rolled steel.

Reduced cost is an expected benefit of hot rolled steel.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[metengr]

Additional information, see below;

Hot-rolled steel is rolled to its final thickness in an elevated-temperature process. The finishing temperature is determined by the composition of the steel and the desired properties. In the as-hot-rolled condition, the steel has a dark-gray oxide coating on its surface, which offers limited corrosion protection as long as it is undisturbed. However, the oxide flakes off during forming and may be undesirable around the press. Because the oxide coating also interferes with steel surface lubricants, it should be removed before the final finishing of most formed parts. Hot-rolled steel may be ordered pickled (using either hot sulfuric or hydrochloric acid to remove the oxide) and oiled to inhibit in-transit rusting. Hot-rolled steel in the as-pickled condition will show stretcher strains or Lüders lines on the surface after forming. Whenever surface appearance is important, the steel should be ordered with a temper-rolled surface (skin pass of less than 2% cold reduction) to reduce this tendency. If aging is a problem because of storage requirements, special-killed hot-rolled steel should be ordered.

There is no preferred grain orientation providing high r values in hot-rolled steel, but improved grain size and resistance to longitudinal splitting may be attained by closely controlling chemical composition, which differs between commercial- and drawing-quality hot-rolled steel. Higher strength levels (when necessary for the part being formed) are obtained by alloy additions and processing controls to develop improved structure. Because higher strength is associated with forming problems such as lower ductility, increased springback, and longitudinal bend failures, only high-strength low-alloy steels designed for improved formability should be used in structural parts made by press operations. Mechanical properties of several types of hot-rolled sheet are given in Table 1.

Cold-rolled steel sheet forming is produced by the cold reduction of hot-rolled pickled coils, followed by annealing and possibly additional processing, such as temper rolling. Class 1 (E, exposed) should be ordered when a controlled surface finish is required. Class 2 (U, unexposed) is intended for applications in which surface appearance is not of primary importance. Both classes are available as commercial-quality, drawing-quality, or drawing-quality special-killed cold-rolled steel. Mechanical properties of cold-rolled steel sheet are given in Table 2.

Most cold-rolled steels exhibit yield point elongation in the as-annealed condition. This appears as Lüders lines, or stretcher strains, on the surface of formed parts (for example, flat areas near the corners of pan-shape draws) that have been subjected to moderate forming operations. The yield point elongation may be removed by temper rolling the annealed coils. Because temper coiling strengthens the steel and reduces its ductility, it is usually limited to 0.5 to 1.5% elongation of the strip. Temper rolling under tension is more effective than flex rolling or roller leveling for eliminating yield point elongation because the steel is more uniformly strained through the thickness. These latter methods are sometimes used the plants of fabricators because the equipment is less expensive and because it permits the use of aged coils of rimmed steels that may show strain on the surface of formed parts.

In addition to many as-processed surface finishes, cold-rolled sheet may be ordered with a metallic coating that provides corrosion protection or a decorative finish that reduces the manufacturing costs of parts such as appliances or building panels.

Source;
ASM Handbook, Volume 1

 

[GMIracing]

thanks for the information guys.

 

[MSUKeith]

There is only a small range of gauges available where the HR and CR products overlap therefore if you have a specific gauge in mind it may only be available in one form and only from certian mills. Some mills are more capable than others, such as the continious anneal line at ArcelorMittal (formally Inland) which was designed for this product.

Do not neglect the differences in formability - the ability to stamp/stretch/draw will be better and more consistent with the CR product and certain shapes may only be manufacturable from CR. R value, total elongation and n value will all be better with CR.

Fatigue properties will also be different depending on high cycle or low cycle - see SAE J1099 for examples.

 

[GMIracing]

MSUKeith Quote:
"There is only a small range of gauges available where the HR and CR products overlap therefore if you have a specific gauge in mind it may only be available in one form and only from certian mills. Some mills are more capable than others, such as the continious anneal line at ArcelorMittal (formally Inland) which was designed for this product."

I was under the impression that both CR and HR HSLAS are available in the standard US Gauges and also the usual metric flavors, is this not the case? Is there an ASTM norm that lists the standard available thicknesses produced?

We currently purchase what I would consider to be a large volume of coiled steel sheets. A conservative estimate would put it at about 5000 metric tonnes of one grade and thickness, and about 6000 metric tonnes of another for our high volume program. I assumed that if you were purchasing coils in large enough quantities, a steel mill would be able to make thicknesses tailored to our wishes. Again, I only can assume as I have had only limited contact with the mills we purchase steel from.

Thanks for the SAE J1099 reference. Although I only gave it a quick glance, I think it is going to be an interesting read for me.

 

[MSUKeith]

GMIracing,

A rough estimate of the available gauges for a HSLA grade would be CR: 0.65 - 2.0 mm and HR: 1.7 - 10 mm; hence the small overlap. This due to the available power, reduction and cooling rates of the hot mills on HR product and will vary depending on width, mill etc. On the CR side the design and capability of the cold mill and anneal line comes into play. Some mills have different 'sweet spots' for gauge/width/grade combinations than others and will charge extras or no quote if you are to far outside this. See the online price books for the various mills for more information.

 

[DannyEQS]

Another consideration is if your parts are going to be galvanized or used bare. You will have many more mills to choose from if you want CR+galv compared with HR+galv.

And I agree with MSUKeith's comments, except that I think some of the newer minimills might be able to go a bit thinner on the HR (although I don't know if they do the combo of strength and desired width).

 

[TVP]

MSUKeith,

I am a little surprised at the upper limit of 2.0 mm for cold-rolled HSLA. I was thinking that this type of product would be available up to 3 or 4 mm thick at least, from large producers like US Steel or Mittal. It's kind of difficult to know exactly when you are an end-user and your stamping suppliers buy everything from processors and not the mills directly.

 

[NickE]

I've seen HRPO that has been skin passed for improved gauge control and surface condition. This also reduces the formability somewhat.

A large amount of the time there is a huge disconnect between what is called out on prints for low carbon steel automotive parts and what is actually required to make the part. This is often brought together through the cooperation of the stamping supplier, steel supplier, and Tier 1 customer. (and can take days of work sometimes)


Nick
I love materials science!