Cold drawn steel bars are made by forcing hot rolled steel through a die, reducing its size and changing its shape. This process, known as plastic deformation, results in a stronger, more precise, and smoother steel product.
Compared to hot rolled steel, cold drawn bars are known for their superior strength, dimensional accuracy, smooth finish, and straightness, which make them ideal for a variety of applications.
Let’s take a closer look at the cold drawing process, the advantages of using cold drawn steel, and the many ways this material is used in manufacturing and construction.
The cold drawing process
Drawn bars are made using a process called cold drawing.
Initial material: hot rolled steel
The process often starts with hot rolled steel bars, which are finished at very high temperatures (1600° F to 2200° F).
The cold drawing procedure
In cold drawing, the steel is first cleaned and then pulled through a carbide die. The die has a smaller opening than the bar, so as the steel is drawn through, the cross-sectional area is reduced and the bar is shaped.
After drawing, the bars are straightened, and can be heat treated at this point, if desired. Finally, they’re cut to length and inspected.
Resulting improvements
Cold drawing results in bars with improved dimensional tolerances and straightness, and an enhanced surface appearance.
Key Advantages of Cold Drawn Steel Bars
Cold drawn steel bars offer several advantages over hot rolled steel, making them a great choice for certain applications.
Superior Mechanical Properties
Cold drawing increases the strength of the steel. Cold drawn bars have greater tensile and yield strengths than hot rolled steel, sometimes making heat treatment unnecessary. For example, a 1045 grade of steel might have a yield strength of 50,000 PSI and a tensile strength of 75,000 PSI if it’s hot rolled. If it’s cold drawn, the yield strength can increase to 75,000 or even 100,000 PSI, and the tensile strength can exceed 100,000 PSI.
Dimensional Accuracy and Straightness
Cold drawn steel offers tighter tolerances than hot rolled steel. A 4″ diameter 1018 HR bar might have a size tolerance of +.063″ / -0″, while a cold drawn bar of the same dimensions and grade would have a tolerance of +0″ / – .005″. Cold drawn bars also have superior straightness, measuring 1/16″ in any 5 ft for a 1018 bar over 15′ long.
Improved Surface Finish
The surface finish of cold drawn steel is smoother than that of hot rolled steel, eliminating the need for extra machining to remove scale.
Enhanced Machinability
Cold drawn steel offers better machinability and chip formation, leading to faster and more efficient machining.
Types and Applications of Cold Drawn Steel Bars
Cold drawn steel bars come in a wide range of shapes and sizes, so it’s easy to find one for your project.
Common Shapes and Sizes
- Rounds
- Flats
- Squares
- Hex bars
Cold drawn bars typically come in sizes from 1″ to 6″.
Material Grades and Specifications
The steel grades most often used in cold drawing are 1018, 1045, 10V45, 1050, 1117, 1141, 1144, 12L14, 1215, 4130, 4140, 4150, and 8620.
Manufacturing processes adhere to industry standards, meeting ASTM specifications that include AISI, SAE, JIS, and DIN.
Typical Applications
You’ll find cold drawn steel bars used across many industries and for many purposes, including:
- Screw machines
- CNC lathes
- Hydraulic fittings
- Gears
- Fasteners
Cold drawn vs. hot rolled steel bars
Cold drawn steel bars and hot rolled steel bars have different characteristics that make them suited for different applications. Here’s a quick comparison:
- Strength and hardness. Cold drawing generally makes for stronger and harder steel.
- Dimensional tolerances and straightness. Cold drawn steel is more uniform in its dimensions and straighter than hot rolled steel.
- Surface finish. Cold drawn steel has a smoother surface.
- Cost. Cold drawn steel is generally more expensive to produce than hot rolled steel.
Frequently Asked Questions
What is bar drawing?
Bar drawing is a metalworking process used to reduce the diameter of a metal bar by pulling it through a die. It’s a cold working process that improves the bar’s surface finish, dimensional accuracy, and mechanical properties like tensile strength and yield strength.
What are the three types of steel bars?
While there are many ways to categorize steel bars, three common types are hot-rolled steel bars, cold-finished steel bars, and alloy steel bars. Hot-rolled bars are formed at high temperatures, while cold-finished bars undergo further processing for improved precision and surface finish. Alloy steel bars contain specific elements to enhance properties like strength or corrosion resistance.
What is a drawn bar?
A drawn bar is simply a metal bar that has been produced using the bar drawing process. This process results in a bar with tighter dimensional tolerances, a smoother surface finish, and improved mechanical properties compared to hot-rolled bars. The term “drawn” refers to the pulling action through the die.
What is a bright drawn bar?
A bright drawn bar is a type of drawn bar that undergoes additional processing to achieve a particularly smooth and shiny surface finish. This is often achieved through specialized drawing techniques, polishing, or other surface treatments. Bright drawn bars are often used in applications where aesthetics are important, or where a very precise surface is required.
Summary
Cold drawn steel bars offer a range of advantages, including exceptional strength, accurate dimensions, a smooth surface, and good machinability.
Choosing the right steel bar is critical for any project. Before you decide on a particular type, think about how you plan to use it and what qualities are most important. Consider size, straightness, surface smoothness, mechanical properties, and how easily it can be machined.
Drawn bars are available in a variety of standard sizes and grades. If you need a custom steel bar, most suppliers can provide custom grades upon request.