Understanding the Ductile Iron Alternative to Steel

Recent skyrocketing oil prices shifted buying patterns for large fuel guzzling vehicles towards more fuel efficient vehicles. Even though gasoline prices have decreased, consumers and carmakers have recognized that the volatile situation could easily change, so alternate fuel vehicles have received a lot of attention. The situation in the steel industry is surprising similar. Even though pricing has lost some volatility engineers are increasingly attracted to an alternative material that complements steel grades by offering a substance that can heat-treat like 4140, wear like 8620 and machine like 12L14. In this case, the alternative is continuous-cast ductile iron, an engineered metal product called Dura-Bar.

Available in as-cast rounds, tubes, rectangles and squares in sizes up to 20-inch diameter and 25-inch wide, Dura-Bar is stocked in over 100 metal service center locations around North America. In addition, rounds are available centerless turned, and stocked rectangles and squares are available milled in over 30 sizes.

Processing and Performance Advantages

Potential users who have not experienced the ease of substituting Dura-Bar for steel may not realize continuous cast iron is not plagued by the same foundry defect issues as static castings or the weak and brittle properties of"gray" iron. In fact the data shows the ductile grades match up well with low and medium carbon steel grades. Furthermore, popular Dura-Bar grades such as 65-45-12 and 80-55-06 meet ASTM A536 ductile iron specifications. In these ratings, the first two digits represent the tensile strength in psi/ksi/1000, the second two are the yield strength in psi/ksi/1000 and the third two digits are the elongation in percent. A comparison of these two materials to popular hot rolled steels that they frequently replace is shown in the table below.

One of the keys to Dura-Bar’s performance is the carbon embedded throughout the matrix. During the casting process, the carbon forms graphite nodules. The graphite content provides improved machinability by acting as a chip breaker, dissipating heat during machining and reducing friction between the insert edge and the work piece. This results in increased tool life and higher machining speeds and increased throughput. In addition, graphite nodules strengthen Dura-Bar giving it increased ductility. In the application, this means improved wear performance. Also, the graphite eliminates the carborizing process, required by many steel grades priorto heat treating, without comprising performance. The tradeoff of slightly lower hardness than the steel is usually offset in the application by improved wear characteristics. A significant advantage in using Dura-Bar is the ability to machine parts faster, with less insert wear.Additionally, if weight in the end application is a consideration, ductile iron is approximately 8 percent lighter than steel.

One final consideration involves whether the application in question involves operation in cold weather which is important for hydraulics applications – especially those that operate in frozen tundra areas. Testing for cold weather performance by an independent lab showed superior stress creep over steel.

Improved Expectations

Maybe not now but at some time in the future, the steel situation could endanger either profitability or delivery. However, even if this does not occur, Dura-Bar ductile iron offers many advantages that can provide improved throughput, performance and reliability. Come to Dura-Bar for the availability and stay for the performance improvements and cost savings.