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September 27, 2019

How to select the best grade of steel for the application

Many grades of steel can fulfill the same application requirements, but the environment, designed product life, safety factors and cost will help to narrow down the options. This quick overview from our metallurgist, Kyle Rackers, can help get you started choosing the right grade of steel for your application.

What is the best steel for a given application? 

Choosing steel grades can be quite an ominous task. There is a myriad of choices for today’s engineers and who is to say what is “right” for a given application. Many grades of steel can fulfill the same application requirements, but the environment, designed product life, safety factors and cost will help to narrow down the options. Typically you would first consider mechanical requirements like strength, hardness, toughness and hardenability; then review the service environment requirements like corrosion resistance or the need to withstand extreme temperatures. Hardenability is crucial when working with thick cross-sections or when machining will expose surfaces that were buried within the heat-treated cross-section.

Next, the manufacturing processes need to be taken into account when selecting grades of steel. Is the component designed as a casting, fabrication or forging? Is the engineer considering converting to a forged solution? Does the component need to be subsequently welded? What heat-treatment configuration will be required to meet optimal properties? If nondestructive testing is required at what point in the process should it be performed? All of these considerations will impact the type of elements added to improve the quality of steel to ensure the grade of steel can withstand the application requirements. 

Generally, the first consideration for alloy elements is carbon. Carbon provides steel strength, hardness and wear-resistance, so you want to select a grade of steel with just enough carbon to meet the desired property levels. Grades that have lower carbon percentages are softer and easier to machine and form and have the ability to be welded. Conversely, high-carbon steel increases tensile strength, abrasion resistance and depth of hardening, but decreases in toughness and could possibly increase manufacturing costs due to reduced machinability, higher tempering temperatures and greater risk of quench cracking. Other alloying elements contribute to strength and hardness, but on a smaller degree than carbon and vary greatly element to element. 

Your specifications for toughness and hardenability will direct the next set of element decisions. For superior toughness, the steel residual elements, like phosphorus, sulfur, tin, lead, etc., can be driven to very low limits. Unfortunately, reaching toughness requirements this way can greatly increase material costs. There are ways to gain toughness by adding the appropriate alloy elements like manganese, nickel, chromium and molybdenum, but how they are used varies greatly depending on the product specifications.

To enhance hardenability for all steel grades and greatly increases toughness for low-carbon (less than 0.10 wt%) steel, manganese is a useful, cost-effective addition. You should, however, consider using manganese carefully as it can segregate in large ingots creating inconsistent material properties. To improve toughness, especially at lower operating temperatures, nickel is a good option that also mildly boosts hardenability in steel. The drawback to nickel is that it is one of the most expensive alloying elements. Molybdenum offers increased hardenability, hot hardness, toughness and even acts as a sort of booster for any other elements that are present. And, if your application requires some corrosion resistance chromium will do just that also adding to hardenability and to a small degree toughness. 

Potential applications for:
•    High strength steel like grade 4140 or grade 4340: pinion gears and shafts, dies and tooling.
•    Low carbon steel like grade 1008 or grade A-350 LF2: structural components that require weldability
•    Moderate strength and good toughness steel like grade 8630 or grade 4330: Demanding structural components that need low-temperature toughness
•    Moderate wear resistance when toughness is not required in steel like grade 1045: bearing rollers, wheels, some ring and pinions

Knowing steel grade applications can certainly help you select the right steel to meet your project’s requirements, but working with a metal-and-forging expert who understands steel properties is the best way to ensure you are finding the right steel that fits within the budget of your project. At Scot Forge, our metallurgy specialists can help you pick or tailor an alloy to meet your specific needs. Currently, we have a raw material inventory that includes: stainless steel, alloy steel, tool steel, aluminum, nickel, brass, bronze and copper. With more than 300 grades in this inventory, you can expect a quick turnaround time on forged products including both simple and custom shapes. 
 
Contact us today for an expert who will support you from ingot to finish component delivery.

Watch for future blogs on stainless steels and non-ferrous materials.