When you need to order cold rolled or hot rolled steel for your next fabrication project, it&#;s important to buy the right kind to match the job. Not only are there four major types or groups of steel (carbon, alloy, stainless, and tool steel), the World Steel Association has identified over 3,500 different grades of steel, each with unique characteristics and properties.
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While most of the differences between steel grades have to do with their compositions&#;what percentages of carbon and other alloying materials are in the mix&#;how the steel is processed also contributes to the distinctiveness of a particular grade. One very common processing technique is rolling, which involves passing the steel through pairs of rolls at high pressure. This procedure can impart specific mechanical properties to the resulting steel stock along with making it uniform in thickness. It is estimated that nearly 90% of produced steel goes through the rolling process.
Rolling is divided into two general categories&#;cold rolling and hot rolling. All steel is created with heat, of course, and then allowed to cool. Cold rolled steel is generally processed around room temperature, while hot rolled steel is heated above the material&#;s recrystallization temperature before processing. The atoms of metals are nearly always arranged in a crystalline lattice structure. That structure gets deformed through physical processing, which can strengthen the metal, since the rearranged atoms can&#;t move as freely. When a metal reaches its recrystallization temperature&#;around one-third to one-half of its melting point&#;the atoms become more mobile and then reorient themselves into the original crystalline pattern of the material.
The two types of rolled steel can be readily distinguished from each other. Cold rolled steel has a smooth surface with an oily finish and appears dark gray, while hot rolled steel has a non-oily surface with a somewhat rough and scaly finish and a blue-gray appearance. They can also be differentiated by an examination of the edges of bar stock that is square or rectangular, since cold rolled steel will have sharp edges and hot rolled steel will have rounded ones.
It is important to understand the benefits and drawbacks of cold and hot rolled steel to properly gauge which material is better for specific projects.
Hot rolling is a common method of &#;hot working&#; a metal, which can also include other processes that are performed above the recrystallization temperature, such as drawing, extrusion, and forging. Working steel while it is hot enough to recrystallize keeps it from strain hardening, giving it different properties than cold rolled steel.
Some of the advantages of hot rolled over cold rolled steel include:
Disadvantages of hot rolled steel:
Applications that use hot rolled steel include:
When close tolerances and exact shapes aren&#;t needed, hot rolled steel is ideal for the project.
Processing steel through the cold working method of cold rolling puts the metal under mechanical stress, imparting a change to its crystalline structure.
Some of the advantages of cold rolled over hot rolled steel include:
Disadvantages of cold rolled steel:
Applications that use cold rolled steel include:
When closer tolerances and better surface finishes are needed, cold rolled steel is ideal for the job.
While cold rolled steel might generally be regarded as &#;better&#; than hot rolled steel, the key consideration is the end goal of the fabrication project. Savings in cost and ease of working must be weighed against the strength and precision required of the finished part.
A fabrication shop should establish a good relationship with a reputable steel service center or other metal supplier who can advise them on the best material for any given job, while providing fast delivery and a fair price. Likewise, having a connection with a trusted and qualified machinery consultant can assist a fabricator in finding the right equipment to complete any metalworking endeavor.
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If you have a big&#;or even small&#;project in the works and want to make sure you have the perfect machine to match your metal, please give Revolution Machine Tools a call today for a competitive quote and a free consult to make sure the job gets done accurately and on time.
Last month we showed you the ways precision ground bar can save you money! This month, as we continue highlighting this new product, we are answering five questions you may have when determining if precision ground bar is right for you.
1. How can I apply the bar?
If the end will be used in a rotational application (i.e. pistons, pins, gears, shafts, drills, etc.) there is a good chance there will be additional processing steps to the bar&#;meaning there is a great need for precision.
2. How can PGB help my current machining process or operation flow?
Depending on the additional processing steps your business completes, we have a variety of options to suit you. If you are using a CNC machine, bar feeder, or swiss machine, the machine will be optimally utilized with a precision ground product. Alternatively, if you are grinding the material internally to a finished diameter, we can save your business time and money with our finished product.
3. What if there are specific mechanicals my bar needs to meet?
We know some customers need certain mechanicals or heat treatment. We can easily meet these requirements for you, saving you money!
4. What if I have required finish tolerances?
Once you let us know the application of the bar, this can help give us an idea of the tolerances you need. Of course, we will confirm this with you! Often, customers purchase a turned, ground, & polished product (TG&P), but require either a bearing shaft quality (BSQ) or pump shaft quality (PSQ) tolerance. Our experienced team can offer you guidance when determining which is right for you.
5. What if I require a surface finish?
A surface finish is something we can easily accommodate. This is often measured in average roughness (RA), and the lower the number, the better or smoother the finish. For a precision ground bar, 32 RA is standard, while 63 RA is standard for cold finished bar. We realize not all applications require a smoother surface, but it is always important to us to clarify and confirm the different finishes you desire. O&#;Neal Steel will partner with you and present the best options for improving your operational efficiency.
Are you interested in learning more about cold rolled round bar? Contact us today to secure an expert consultation!