Questions You Should Know about hot rolled steel bar

Not a stupid question at all. In fact many makers have been sorely disappointed in steel because of not knowing the difference. 416 stainless for instance can be had both ways. The surface looks better in cold rolled. I use it because it cleans up a little better in the milling vice. You have to be really careful with 440-c for instance. Hot rolled bar, is uglier on the surface. But is good stuff. There is a lot of sheared 440-c out there from cold rolled plate. It can have a very strong tractor tire tread grain when trying to finish. Seems that hot rolled is just a bit more dense. In steel going to be used forging, it probably doesn't matter. You can improve on the grain in cold rolled by forging, but hot rolled is damed good just as it comes form the mill. There is a lot of talk about grain refinement. It is mostly BS. You can get a shape that you want by forging with less metal that stock removal, But the grain refinement comes from the heat treating. Not from forging. Such things as edge packing, and breaking up the molecules is pure smoke and mirrors. Sells well to the UN educated. But is nothing more than Flem-flam at it's best. Mike "How it is made", prolly the best show ever made for gearheads,
had a segment on how they make steel. Wuz most excellent indeed.

Oftentimes you see a blacksmith forging a bar (making, say,
damascus), working with something like 1"x1"x10" bar.

Now, imagine that bar is 15 feet x 15 feet x 20 feet, being forged
by a gian press, while being held in giant tongs. That's what it looks
like.

Before that happens, they smelter iron and additives in a giant
smelter, with 3 giant electrodes. Must be megaAmps of current
doing the job. As the metal melts, they add alloying elements and
frequently check the resulting "mix" for proper percentages, adjusting
as needed. As they pour, filters will catch larger debri. Of course,
to qualify for NASA, this process needs to be pretty darn clean. It might
have to be repeated few times, to get progressively cleaner, better steel.


Some metals, like brass, can be hardened by "working" it . Steel doesn't
exhibit this feature. Still, when they roll, a lots of stress ends up in the
metal . Also, when hot rolling, exterior layers loose carbon and other alloying
elements. Nasty, hard scale forms. It has to be removed - this makes steel
"decarb" free and it also brings it down to exact dimensions (precision-ground) or just slightly oversized (called just that). Another way to remove the scale is to pickle the steel in acid, but of course it is not precise at all.

When using hot roll for removal-method knifes, one has to be careful not to end up with a warped blade, again due to the stress of hot-rolling being hidden in the metal bar. At best, you will have to spend lots of time orrecting it. Ok this was just on history channel and a while back how its made.

When steel is heated up the molecules align in to what they called a matrix. This becomes a stronger steel. In cold rolling they start with a huge billet of steel and run it throguh rollers compressing the steel. In cold roll steel youll have the same matrix as you did in the original billet (for the most part its really less change to the matrix). Cold rolling also uses many more rollers and or passes to get the stock to the final size and shape this is why it will tend to have a nicer looking finish.

With hot rolled steel the matrix will change become more dense and well aligned. In stock removal this is a good thing as it will grind and file etc smoother for us (more consitancy) than cold rolled. In the end though if your heat treating is good other than the ease of finishing both will end up the same or very close to the same in hardness grain structure etc.

Remember on raw hot rolled youll need to remove a portion of the mettal from top bottom and both esdges to get past the scale layer.

OT sort of but intresting. You know that alluminum foil you use to wrap your lunch in? Well it is a multi layer or damascus alloy. To get foil they use hot roller to thin out a very huge billet of aluminum. Once its at a given thickness it is folded in half and ran through the rollers again to increase its strength. Depending on how heavy a duty its to be used for it may be folded again and again ran through the rollers. So you heavy duty foil is folded twice giving a 4 layer damscus aluminum foil

Just a fun little fact i picked up watchign how its made heheh

Business owners and makers have thousands of steel varieties on the market to choose from. With such an array of metal options, selecting the correct type, grade, and finish of your building material can be tedious. Pennsylvania Steel Co. offers a vast assortment of premium steel products in Pennsylvania, Ohio, the Southeast, and New England. Plus, our online resources help our clients build the best projects possible.

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Today, we&#;re breaking down hot rolled vs cold rolled steel to help you understand which is better for your application.

Steel Manufacturing, Summarized

Not to be mistaken with the four main types of steel, the general steel manufacturing process falls into two main categories: hot-rolled and cold-rolled. This process starts with the extreme heating and consequent oxidation of mined steel ore. Basically, pieces of large, rectangular metal called billets are heated and flattened into sizable rolls. 

From there, the steel will either be hot rolled or cold rolled for its finalized design. &#;Rolling&#; refers to the vital step in the manufacturing process that involves forming the metal by using a series of rollers in an attempt to reshape it or enhance its properties. This formation method (hot or cold rolling) will determine the material&#;s ultimate function.

Once steel is heated past its recrystallization temperature (over º F) it can be easily formed and sized. If the material isn&#;t processed further at room temperature, it&#;s considered hot-rolled. The steel that goes through further refinement processes is categorized as cold-rolled. Explore further metal rolling methodology differences, capabilities, and tolerances below!

Hot-Rolled Steel

As hot-rolled steel cools, it tends to shrink and form asymmetrically, allowing for more variation in shape and size. For this reason, hot-rolled steel is used in projects where the finished product doesn&#;t have specific dimensional requirements.

For example, one of the most commonly recognized forms of hot-rolled steel is sheet metal, which is frequently used in creating air ducts and motor vehicles. In these applications, surface finish and proportions don&#;t need to be precise.

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As a result, hot-rolled steel is typically cheaper in price simply because it doesn&#;t involve any further processing. Since it doesn&#;t require any reheating, production costs for hot-rolled steel are much lower.

Cold-Finished Steel

That being said, cold-rolled steel needs reheating to further refine its structural properties. In order to achieve more exact dimensions and surface quality, the metal is re-rolled at a lower temperature. This supplemental rolling results in more specified attributes including exterior finish, durability, and dimensional parameters. 

PA Steel, for example, carries a variety of cold-finished bars in a range of grades and finishes for businesses all over the eastern United States. This equipment is used for creating products such as furniture, garages, and home appliances.

Although it&#;s typically up to 20% more durable than hot-rolled, cold-finished steel is limited to basic square, round, and flat shapes. Despite its improved resistance, the additional processing performed on cold-rolled metals may make it more susceptible to internal stress. Finalized materials need to be stress relieved prior to grinding or cutting to avoid potentially volatile warping or distortion.

Frequently Asked Questions

What are the environmental implications or sustainability factors associated with hot-rolled and cold-finished steel production processes?

The environmental implications of hot-rolled and cold-finished steel production processes differ significantly. Hot-rolled steel production generally consumes more energy due to the high temperatures involved, leading to higher greenhouse gas emissions. On the other hand, cold-finished steel may require more processing steps, potentially consuming more resources, but it can offer energy savings by not needing the extreme heat of hot rolling. Sustainability factors can vary depending on factors such as energy efficiency, material wastage, and water usage in each process.

How do the mechanical properties, such as strength, ductility, and toughness, differ between hot-rolled and cold-finished steel products?

The mechanical properties of hot-rolled and cold-finished steel products vary due to the different manufacturing processes. Hot-rolled steel typically has a rougher surface finish and less precise dimensions compared to cold-finished steel. Cold-finished steel tends to have improved dimensional accuracy, smoother surfaces, and higher tensile strength. Cold-finished steel may also exhibit better ductility and toughness compared to hot-rolled steel, making it more suitable for applications requiring precise dimensions and enhanced mechanical properties.

Are there specific industries or applications where cold-finished steel is preferred over hot-rolled steel and vice versa?

The preference for either cold-finished or hot-rolled steel in specific industries or applications depends on various factors. Cold-finished steel is often favored in industries requiring tight tolerances, excellent surface finish, and precise dimensional control, such as automotive manufacturing, aerospace, and construction. Hot-rolled steel is commonly used in structural applications where exact dimensions are less critical, such as in building construction, shipbuilding, and general fabrication. Understanding the requirements of the application, including factors like cost, aesthetics, and mechanical properties, helps in choosing the most suitable steel type for a particular industry or project.

Contact us to discuss your requirements of cold rolled round bar. Our experienced sales team can help you identify the options that best suit your needs.