Hardened steel mechanical properties

Hardened Steel is extremely resistant to wear and abrasion. This is one of the main benefits when producing components that need to withstand regular abuse or heavy loads without failure or damage. It is also able to combat rust and corrosion better than standard steel.

When tools begin to reach the end of their lifecycle, or when an event has impacted them, the wear on the tool can create specific wear effects. These effects influence the quality of the parts produced, the efficiency of the equipment, or the downtime associated with operator intervention. The importance of understanding the effects of tool wear is that they can be used to develop thresholds and algorithms for detecting and preventing tool wear in the future.

For the ultimate performance on Hardened Steel, look no further than YG-1’s flagship X5070 Blue milling cutters. Dedicated for ultra-high performance machining of Hardened Steel up to 70HRC, these cutters can cope with extreme heat up to 1,400°C. The nanograin carbide substrate combined with YG-1’s unique silicon-based coating means nothing cuts Hardened Steel faster or for longer than X5070 Blue. The range includes a wide range of sizes from just 0.1mm diameter and a host of geometries including long neck, corner radius, ball nose and 6-8 flute finishing tools.

Depending on end-use, metal feedstock in workpieces used in CNC machining will vary in purity. When impurities exist, they can result in a build-up of edge fragments. These fragments can abrade the tool, reducing its sharpness and effectiveness over time. Abrasion is a mechanical form of wear that occurs most often at low spindle speed.

At Cutwel, we speak to many people about the difficulties of machining Hardened Steel and how we would advise best to machine this particular material. In this article I have summarised all the common questions I get asked and also provided a bit of background information to help you on your way.

As wear occurs, the accuracy of the part decreases. There will be acceptable tolerances for any workpiece. But a single type of tool wear can increase to the point that the part goes out of spec for that cutting activity, causing loss of the part. Multiple types of wear can coincide, cascading the deformation and, therefore, the accuracy of the part. This can create a major quality issue as parts will either need to be scrapped or reworked. Effectively manaing tool wear and understanding when failure will occur is an important part of maintaining high quality in an efficient manner.

As tools impact the work face at high speed, chips form and damage the tool's rake face. This chip flow across the face leaves a divot, or crater, like a scar. The formation of craters is a typical type of tool wear that may not impact the tool quality unless it directly deforms the cutting surface. Crater wear generally occurs near the cutting edge.

4G Mills from YG-1 are ideal for Hardened Steels up 55HRC. This range boasts a huge selection of sizes including micro tools from just 0.03mm diameter and a huge range of geometries including standard, ball nose, 6 flute finishers and reduced neck options. Despite the majority of 4G mills being made from a premium micrograin carbide, the unique tool geometry and coating allow them to machine up to 1200°C with outstanding wear resistance making them suitable for Hardened Steel up to 55HRC. There are also a select few series made from a nanograin carbide substrate for higher-performance machining.

Traditionally, machining Hardened Steel has always been a slow and time-consuming process. This was down to low cutting speeds and feeds being used, plus there was always a risk of deep stepped tool marks being formed on the workpiece due to the large cutting depths used, particularly when roughing. EDM (Electric discharge machining) can also be used on Hardened Steel which could end up being a very time-consuming and costly process.

When the tool contacts the workpiece's shoulder, the rubbing of the two pieces can create a chemical reaction on the tool. The result creates both abrasion and adhesion and can lead to flank wear. If the wear is excessive, it may lead to complete tool failure.

On the lower end of the budget, general-purpose coated carbide cutters such as K2 Carbide, NC Mills or Mammut Carbide can machine Hardened Steel up to 45HRC, but depending on your setup and machining capabilities, we would advise you to progress to a higher performing range such as 4G Mills or X-Power Pro to get the best results.

Plastic deformation is a thermal issue when the material in the cutting tool is softened. If the workpiece material grade is higher than the tool's, the tool can change shape or lose sharpness. This damage can be avoided by understanding the tool hardness in relation to the material hardness and its inherent performance characteristics.

Also on harder materials, thermal shock can occur, therefore air jet cooling, oil mist or air mist can be used. Jet cooling is the best option however as it eliminates any requirements for the tool to withstand rapid and severe temperature changes.

Failure of tools due to tool wear is typical, but can be analyzed and addressed with tool monitoring. The wear generally occurs over time and is a gradual failure in a cumulative process that affects tool life. Tool wear will also vary depending on tool shape, depth, cutting fluid, and cutting speed. This impacts the sharpness and effectiveness of the tool and means that some tools can subtly change shape.

What is hardened steel used for

CBN (Cubic Boron Nitride) is the 2nd hardest material, only surpassed by diamond, therefore CBN tooling is also commonly used in Hardened Steel applications due to its superior wear resistance and toughness.

When turning Hardened Steel, one option to opt for are CBN turning inserts. These ground inserts offer vastly improved cutting speeds, tool life and surface finish compared to standard carbide inserts. They are specifically designed for turning Hardened Steel between 50-70HRC. We offer a range of grades for various applications including continuous or intermittent Hardened Steel turning.

X- Power Pro milling cutters from YG-1 are exceptional for dry high-speed cutting of Hardened Steel. Made from an ultrafine micrograin carbide, X-Power Pro is ideal for many Hardened Steel applications such as mold & die, tool making or high-precision machining. The range includes micro diameters from just 0.4mm and has a range of geometries including standard, corner radius, long neck, ball nose and 6-8 flute finishing tools.

Similar to Stainless Steel, Exotics (or Heat Resistant Super Alloys) are preferred where corrosion resistance is required. Not only that but Exotics also have a higher temperature resistance than Hardened Steel.

In CNC machining, the reality is that metal meeting metal results in tool wear. Metal cutting, grinding, drilling, boring, and other tasks are all part of machining. And as these activities are all “metal-on-metal,” at some point, something must give.

Hardened steel grades

In this section, I will advise in general what to consider when choosing the correct tools for Hardened Steel machining. However, if you require specific tooling recommendations for dedicated Hardened Steel machining then please see here.

The insights and analysis offered by the software can deliver immediate benefits for optimizing processes, addressing undetected problems, and prescribing solutions to reduce cost, increase quality, and ramp-up capacity. To find out how MachineMetrics can deliver solutions to help you manage and control tool wear and get the best out of your tooling and equipment, book a demo today.

Detecting tool wear may be done manually by the observation of machinists and operators or in an automated fashion, using a tool monitoring system. Historically, tool wear has been identified only after it’s impact has been noticed, such as the realization that the tool is producing poor quality parts. However, with the development of automated software solutions, stakeholders are better able to identify tool wear and tool failure as soon as it occurs, or even predict and prevent it from happening altogether. Some of the approaches for detecting tool wear include:

In Mold and Die, Hardened Steel is commonly used to construct the molds themselves. Despite its higher cost, it is chosen over other materials (such as Aluminium) due to the longer life span which outweighs the initial investment over a larger number of parts.

Hardened Steel Price

Hardened Steel is a more wear-resistant and durable carbon steel that has been specially treated to offer improved hardness and strength over softer steels.

The main advantage of Stainless Steel over Hardened Steel is its corrosion resistance. Particularly because Hardened Steel is prone to cracking.

BC Machining, a manufacturer of fabricated metal parts, was producing such large quantities of scrap that they were forced to run their machines at 200% capacity just to hit their production goals. With no insight into when tools were worn or about to break, BC Machining accumulated significant costs from producing scrap and replacing broken tooling. To prevent scrap production and maximize tool life, they partnered with MachineMetrics. Read our case study to learn how BC Machining virtually eradicated scrap from tool wear, significantly reduced their changeover times, and saved $72k per machine annually. Read the complete case study.

Should you need advice on machining Hardened Steel then please look no further than our expert technical team who boast a wealth of experience across a range of industries. We will be able to advise on tool selection, set up and machining methods to help you get the best from your Hardened Steel applications.

If the correct high-performance tool is selected, then the geometry of the flutes can be relied upon to control the heat, form the chips correctly and evacuate the swarf. This negates the requirement for coolant.

It is made by heating carbon steel to a higher temperature and then rapidly cooled. This process is called quenching. Because of quenching, the steel becomes extremely hard but also brittle. A solution to reducing brittleness without affecting the hardness, the material is reheated again and then left to naturally cool. This is called tempering. A combination of quenching and tempering results in Hardened Steel that can still be machined but without the risk of cracking.

Tool run-out is quite important when machining Hardened Steel because if the runout is greater than 0.01mm, the tool life can be greatly reduced. This is particularly relevant on some small-diameter tools where the chip load can also be doubled if the runout is too big. This makes choosing the right toolholder for your application an absolute priority. High-precision chucks negate the impact of tool runout. Please contact me or the Cutwel Technical Team for advice on choosing the right toolholder for machining Hardened Steel.

Flank wear occurs parallel to the cutting edge and can result in cutting edge failure. As workpieces encounter abrasive and adhesive wear, high temperatures form and impact the tool and performance characteristics of the workpiece. As flank wear increases, the speed of the cut must be increased as well.

When using coolant on Hardened Steel applications thermal shocking can occur due to the major temperature differences involved, which can cause breakages. If you need an alternative method for swarf evacuation, we would advise air or mist coolant instead.

With so much heat being transferred from the chip flyoff, the proper type and amount of cutting fluid must be used to remove the chips and help direct the excess heat away. Understanding the material of the workpiece and tool and the specifications, speed, and feed rate will determine the application rate of coolant during cutting.

Once you have selected the right type of tool you then need to consider what cutting data (speeds and/or feeds) you should use. Where possible, always follow the supplier or manufacturer’s recommended cutting data. If you are unsure of what speeds or feeds to use when machining Hardened Steel please do not hesitate to contact me or any member of the Cutwel technical team for more advice.

Hardsteel composition

Due to the heat produced when machining Hardened Steel, you will require tools with a thermal barrier coating. In addition to this, cobalt content can also improve heat resistance and strength. Negative rake angle tools should also be adopted to protect the cutting edge against the hardness of the material.

Different metal feedstocks for workpieces may have different performance characteristics. They may be softer or harder depending on the metal. When the metal is softer, an annealing effect can occur where the soft, semi-melted metal adheres to the cutting tool. If the edge builds up too much, the tool can fail. Proper speed and fluid can reduce or eliminate this issue.

Managing tool life is always important and when machining Hardened Steel you may experience high cutting temperatures which can reduce how long a tool will optimally perform. We recommend using small cut depths when machining Hardened Steel because of the increased time the tool is exited from the cutting process. It results in the cutting edge being cooled, thus increasing its tool life.

First off, it is not possible to use HSS or standard Carbide tooling when milling Hardened Steel, especially above 50HRC. We would always recommend a superior grade of carbide such as Ultrafine or Nanograin. These substrates are much denser which results in a harder-wearing tool with extremely high heat resistance.

For tapping Hardened Steel we would always recommend our high-resistance range of machine taps. These Italian made ultra-high quality powder metal machine taps from UFS also contain high cobalt and vanadium content for the ultimate wear resistance. The short flute design and 15° helix angle provide exceptional strength when tapping hard steels.

Should you need to ream a Hardened Steel drilled hole, we also have a range of Carbide reamers for Hardened Steel up to 67HRC from Karnasch.

Fortunately, reducing and managing tool wear can be automated quickly and efficiently with MachineMetrics Tool Monitoring system. Settings can be monitored to a degree not possible with human intervention, and variations are reported through intuitive dashboards that display machine conditions accurately. MachineMetrics can even analyze the frequency of signals within the machine to predict tool failure.

Tool selection is critical and should include sharpness, tool geometry, coating, and function considerations. This selection also requires understanding equipment types and age and tool holding capabilities, depending on feedstock.

This "give" comes in the form of tool wear, where regular operation means that tools will lose surface, sharpness, and temper over time. If equipment and processes are monitored and optimized, this wear is gradual and predictable. If it is not, tool wear can result in part quality problems and broken tooling.

Despite some of the pros of using Hardened Steel, it should be taken into consideration that despite its hardness it is unable to cope with sharp impacts. Also, you should be careful when subjecting the material to high temperatures due to the quenching and tempering processes which can lead to a reduced melting point.

Because tools and workpieces are in constant contact with severe friction and rubbing, tools become stressed over time. This stress is the result of metal-to-metal contact and high stress and pressure. It is also subject to very high temperatures.

High temperature in a metal-to-metal machining process is inevitable. But temperature management is critical. If done correctly, most of the heat is removed with the chip fly off.

One major thing to look out for, which is key to maintaining tool life and machining quality, is maintaining a constant chip load on the tool’s cutting edge. In milling, for instance, the chip load equals feed rate divided by spindle speed, multiplied by the number of cutting flutes.

Hardened steel vs stainless steel

Chipping occurs on the cutting face and creates a rough or marred cutting edge. It may result from an improper machine setup or because the tool holder isn't correctly secured. This can also occur in larger workpieces where chips may be carried up to a half rotation before being impacted by fluid.

Metal-to-metal friction from cutting, drilling, and other tasks within the CNC machine will always create high temperatures. If the cutting fluid is too low or not the correct type, a higher temperature can result. Temperature can also rise if the cutting depth is too severe or if the feed is too high. Finally, higher speed can also contribute to even more heat.

The chip load varies widely, if the load is too low or too high it will cause them to wear out too fast, chip or break. Lots of high speed and feed cuts with small depths is the best method for ensuring a quality product.

As discussed above, there are many types of tool wear. Some are mechanical; others can be created through equipment settings or operator error. And some, such as temperature management, require a skilled dance to create the best environment to reduce wear. It is critical that operators know the types of tool wear and that each can be caused by different circumstances that occur alone or in combination.

Hardened steel properties

Failure occurs when the tool breaks or fractures altogether. Preventing tool breakage and even catastrophic failure are possible by ensuring the proper speed settings, cutting depth, and force. It also requires using the appropriate fluid. Failure can also be detected when abnormal vibration or noise is present, indicating a tool holder or setting out of spec.

Typically Hardened Steels rank on the Rockwell scale between 40HRC and 70HRC. Materials between 55-70HRC would generally be classed as high Hardened Steels. To compare all the different types of Steel and where Hardened Steels rank on the Rockwell scale, please see a summary below:

Metals have vastly different performance characteristics. Hardened metals can create greater temperature and require more force, while softer metals with lower melting points can have a higher built-up edge. Knowing the performance characteristics of the feedstock, the quality and characteristics of the tool, and even the age and capabilities of the machine can help you choose the right tool for the suitable metal.

Different types of tool wear, the differential hardness between tooling and workpiece, and repeatedly high to low temperatures can cause reduced tool life. These factors can be managed based on experience and training and an operator's knowledge of the workpiece and tool material. But they can also be monitored by advanced tool monitoring software from MachineMetrics. Decreased tool life is a controllable issue with the correct automated monitoring in place.

For instance, in the automotive industry (as well as mechanical and plant engineering), Hardened Steel is often used to create parts such as gears, bolts, cardan shafts and coupling parts. The hardness and strength make the material have a high strength-to-weight ratio, which supports any applications that are subjected to shock loads or wear and tear.

Tool wear depends on many variables. Type of equipment, hardness of blank feedstock, number of operations performed on the part, force applied for each task, and other variables will contribute to tool wear. Because of these variables, tool wear will take many forms, including:

Because tools and workpiece friction cause high temperatures, adhesion wear can occur. Here, chips flowing over the face of the tool may bond with the tool face itself, like a spot-welding effect. This may also impact the dimensional accuracy of the workpiece itself. Adhesion wear may occur more often if the wrong fluid or wrong amount of fluid is used.

Worn tools will exhibit observable and predictable behavior in many but not all instances. Temperature-increased cutting force and other wear factors may create signs that manifest as vibration or noise. Learning these signs can help operators adjust to reduce wear.

We have several Hardened Steel carbide drills from YG-1, Karnasch and Kennametal that are dedicated for high-performance drilling of 50-70HRC. They all have a lower helix angle than standard carbide drills which maximise rigidity.

In the modern day, high-speed Hardened Steel tooling technologies now allow small cutting depths with large feed rates. These are increasingly becoming more prominent and replacing the older, more time-consuming methods.

As tool wear builds, increased cutting force may be required to compensate. There will be acceptable tolerance increases for both the tool and the workpiece. But if the wear is significant, the force could exceed acceptable tolerance and require changing.

Tool wear is the gradual breakdown of machine tools as a result of cutting operation, eventually leading to tool failure.

Cutting and machining are expensive production technologies. The high cost of equipment, operator training, high-quality tooling, and proper material selection of workpiece feedstock can be impacted by tool wear. Each life span reduction of a tool and each scrapped workpiece adds cost to the run and reduces profit margin. And worn tools are also a danger to the operator and machine, risking even higher repair costs.

This all depends on what tool you are using, but in most cases, tool life will be higher and more consistent when cutting dry. Flood coolant should certainly be avoided on Hardened Steel, it can reduce tool life considerably.

Traditionally, tool wear was experiential. In a machining operation, operators had to undergo years of training to learn by "feel" and observation when a tool was experiencing excessive wear. And many settings and parameters were determined experimentally or were simply accepted based on schedules provided by machine tool OEMs. But, this approach is highly inaccurate, resulting in poor quality parts, unused tool life, and excessive downtime.

Despite Hardened Steel potentially being brittle or prone to cracking, Cast Iron is particularly more so (except for malleable cast iron).

A more cost effective option, but at the sacrifice of tool life, would be to go down the route of ceramic turning inserts. As a last resort, PCD Turning Inserts can also be used because the base of the material is made from Diamond which is the hardest in the world.

Sometimes, the increased cutting forces between the tool and the workpiece can be too great to overcome. This force causes the sudden and complete loss of the tool and damage to the workpiece and perhaps the machine itself. Causes for a fracture may lie in settings for depth of cut, speed, or feed of material. Hot spots along the workpiece can also cause fracture by dulling the tool until it fails. Preventing tool breakage avoids safety concerns and avoids downtime events.

Hardened steel material list

CNC machined pieces generate excessive heat between the tool and the workpiece. Managing this heat ensures the correct speed, proper tool set up for tool holders, and the correct amount of fluid. If the heat generated is too high or too low, or if temperature variations swing quickly from cut to cut, it can affect the performance characteristics of the workpiece metal. This can cause the formation of cracks that are evenly spaced and perpendicular to the turning tool’s cutting edge.

The more critical the tool wear, the greater the impact on the surface finish. Dull tools may cause uneven or jagged cut faces on the workpiece. And drilling or cutting may cause surface build-up or increases in wear land, contributing to chipping and cratering, affecting the surface finish. Especially in high precision machining, this can develop severe quality issues, meaning pieces will either need to be re-worked or scrapped.