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.

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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.
 

What is the axis?

The shaft is one of the very important elements used in the machine. They are used to support rotating parts such as pulleys and gears, which are supported by bearings located in rigid machine housings. Gears and pulleys on the shaft help transmit motion. Many other rotating elements are keyed to the shaft. They are subjected to bending moments and torsional moments due to the reaction forces of the members supported by the shafts and the torque generated by the power transmission. Shafts always have a circular cross-section and can be hollow or solid.

Features of shaft parts

1. Shaft parts are characterized by rotating body parts, whose length is greater than the diameter, and are generally composed of the outer cylindrical surface, conical surface, inner hole, thread and corresponding end surface of the concentric shaft.

2. According to different structural shapes, shaft parts can be divided into optical shaft, stepped shaft, hollow shaft and crankshaft. When processing, attention should be paid to the surface roughness of the parts, mutual position accuracy, geometric shape accuracy, ruler accuracy, etc.

Basic machining route of shaft parts

The main machining surfaces of shaft parts are the outer circular surface and the common special-shaped surface, so the most suitable machining method should be selected for various accuracy grades and surface roughness requirements. Its basic processing routes can be summarized into four.

1. The processing route from rough turning to semi-finishing turning to finishing turning is also the most important process route selected for the needle outer circle machining of shaft parts of commonly used materials.

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2. From rough turning to semi-finishing, to rough grinding, and finally to fine grinding, the processing route requires high precision for ferrous materials, small surface roughness requirements and parts that need to be hardened. is the best choice because grinding is its most ideal follow-up process.

3. From rough turning to semi-finishing turning to fine turning and diamond turning, this processing route is specially used to process non-ferrous metal materials. Because non-ferrous metals have low hardness, it is easy to block the gaps between sand grains. It is easy to obtain the required surface roughness, and the finishing and diamond turning processes must be used; the last processing route is from rough turning to semi-finishing, and then to rough grinding and fine grinding.

4. Finishing processing. This route is a processing route that is often used for parts that have been hardened for ferrous metal materials, and have high requirements on precision and low surface roughness values.

Turning Technology of Shaft Parts

1. Lathe tool post shaft machining

When the processed parts are batch or single-piece production, the process route is: forging, normalizing, rough turning, large end diameter and end face, drilling center hole, rough turning, small end diameter and end face, drilling center hole, fine turning, and outer surface. Circular and end face all grooves - threading - turning plane craft groove - acceptance - pliers drilling - acceptance - cylindrical grinding - acceptance - blackening - storage.

2. Analysis of turning process program

(1) The blanks used in mass production are die forgings, and their advantages are mainly high forging accuracy. The machining allowance is small, but the uneven structure and the appearance are produced.

A hard layer appears on the surface. In order to improve the cutting performance, normalizing is invited. If it is a single piece production, the raw material is directly used as bar material, but the machining allowance is relatively small.

Large, it will affect production efficiency and material utilization.

(2) The third process is to turn the end face first, then drill the center hole, and then use the top support to wait for turning the outer circle, which is conducive to the firm installation and improved performance.

The amount of cutting can ensure the coaxiality of one end.

(3) The seventh process is that the precision and roughness requirements are guaranteed by grinding for the positioning of the measuring center.

3. Processing of steering knuckle shaft

(1) Processing route

Forging, normalizing, scribing, drilling center hole, rough turning, outer circle, threading, fine turning, outer circle, acceptance, scribing, planing, gear opening, rough and fine turning, coarse and fine turning, tapered hole, plug-in slot, and drilling One tapping, one acceptance, one storage.

(2) Step analysis of scribing method

First, according to the blank allowance of each processing part, mark the position of the center hole at both ends of the shaft end, and drill the center hole, and use the two-center clamping method to rough and finish the outer circle of each gear of the shaft end. Then use this journal as the benchmark to draw the line with the auxiliary speed.

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