5 Need-to-Know Case Hardening Processes - Page 32 of ...

Your parts need heat treated to herculean surface hardness but with a soft, ductile core. That is to say, you are looking at case hardening processes, most likely one of these: gas carburizing, low-pressure carburizing, carbonitriding, gas nitriding, and ferritic nitrocarburizing.

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Mike Harrison at Gasbarre Thermal Processing Systems brings us a Technical Tuesday article about what case hardening is and how five of the most common processes vary by (1) comparing the specific guidelines for each temp and time, (2) identifying equipment used to perform each process, and (3) providing a chart (at the end!) to understand different process considerations.

Case hardening falls into a class of heat treatment processes that typically involve the addition of carbon and/or nitrogen to the material through solid-gas reactions at the surface followed by diffusion. These processes are performed for any number of reasons that generally include increasing strength and wear resistance, but in all cases the end result is a harder, higher-strength surface with a softer, more ductile core.

Case hardening processes can be divided into two subsets: those that include quenching to harden, such as gas carburizing, low-pressure carburizing (LPC), and carbonitriding; and those that do not include quenching, such as gas nitriding and ferritic nitrocarburizing (FNC). This article will provide a brief look into each process, the types of equipment used, and considerations for implementation.

Diffusion + Quenching Processes

These processes involve heating the workload to austenitizing temperature, which is above the upper critical temperature for the material in question, then supplying and allowing the desired element(s) to diffuse into the part surface, followed by rapid cooling (quenching) to create a phase change to martensite that strengthens the material. Tempering is then performed to create a material that has the desired final strength and ductility properties. The result is a high concentration of added elements on the surface that continually decreases through diffusion until eventually matching the same concentration as the base material; this gradient similarly produces a hardness that is higher at the surface, gradually diminishing until reaching the core. Higher alloyed steels may also see a microstructural change in the core from quenching that produces a core with higher hardness than the previously untreated material, but lower than the surface hardness produced.

Atmosphere Gas Carburizing

Gas carburizing is a process where carbon is added to the material&#;s surface. The process is typically performed between -°F, with carburizing times commonly between 2-8 hours; of course, these values can vary depending on the material, process, and equipment. The most common atmosphere used for atmosphere gas carburizing is endothermic gas with additions of either natural gas or propane to increase the carbon potential of the furnace atmosphere. Common case depths achieved are around 0.005-0.040&#;, with deeper cases possible through a combination of longer treatment times and/or higher temperatures.

The atmosphere gas carburizing process can be performed both in batch and continuous equipment. On the batch side, traditionally an integral quench (IQ) furnace is used (Fig. 1); it consists of a heating chamber where the workload is heated and exposed to the carburizing atmosphere, then the workload is transferred to an attached quench tank for cooling. The entire furnace system is sealed and under protective atmosphere to preserve the part surface and maintain safe control of any combustible gases. For batches of large product, a pit furnace can be used for carburizing with the workload being transferred via an overhead crane into and out of the furnace to a quench tank.

For continuous processing, a belt furnace can be used. The product is placed on a belt and then progresses through the furnace at the desired temperature and atmosphere composition; the carburizing time can be varied by adjusting the belt speed through the furnace. At the end of the furnace, the parts drop off the belt into the quench tank. Then, a conveyor pulls the parts out of the tank and drops them on another belt to be washed and tempered. For continuous processing of heavier loads pusher furnaces, rotary retort, rotary hearth, and roller hearth furnaces can be used.

To achieve a carburizing atmosphere endothermic gas is typically used, which is produced by an endothermic gas generator (Fig. 2) that heats a combination of natural gas and air to create a mixture that is approximately 40% hydrogen, 40% nitrogen, and 20% carbon monoxide. This mixture is generally considered carbon-neutral, meaning it will neither add nor deplete carbon from the surface. To increase the carbon concentration the endothermic gas needs to be enriched with a gas (typically natural gas or propane) that will help produce additional carbon monoxide, which will &#;boost&#; the carbon potential and drive carbon diffusion into the material.

A less common carburizing atmosphere comes from a nitrogen-methanol system, where nitrogen gas and liquid methanol are combined and injected into the furnace. Upon exposure to the high furnace temperature the methanol will decompose to hydrogen and carbon monoxide. Natural gas or propane additions are still required in order to provide carbon for absorption into the surface of the steel.

Low-Pressure Carburizing

Low-pressure carburizing (LPC), or vacuum carburizing, is a variation of carburizing performed in a vacuum furnace. Instead of the atmospheres mentioned previously, a partial pressure of hydrocarbon gas (such as propane or acetylene) is used that directly dissociates at the part surface to provide carbon for diffusion. After LPC, the workload is transferred to a quench system that could use oil or high-pressure gas, typically nitrogen. LPC with gas quenching can be an attractive option for distortion prone complex geometries as the cooling rates are slower than oil quenching; however, given the slower cooling rate, it becomes very important to choose a higher alloyed steel that will achieve the desired hardness.

LPC typically provides faster carburizing times when compared to traditional gas carburizing. This can be attributed to a more efficient reaction of the hydrocarbon gas used and to the option of using higher carburizing temperatures, typically up to °F. This is made possible by the type of internal furnace construction of vacuum furnace design, although care must be taken at higher temperatures to avoid undesirable grain growth in the material. LPC also has the benefit of eliminating the potential for intergranular oxidation, since it is running in a vacuum system.

LPC is typically performed in a single-chamber vacuum furnace, with oil quenching or high-pressure gas quenching done in a separate chamber (Fig. 3). Continuous vacuum furnaces can also be used in applications that require increased throughput (Fig. 4).

Carbonitriding

Despite its name, carbonitriding is more closely related to carburizing than it is to nitriding. Carbonitriding is a process where both carbon and nitrogen are added to the material surface. This process is typically performed in a range of -°F and generally produces a shallower case depth than carburizing. Carbonitriding is used instead of carburizing for plain carbon steels that do not contain enough alloying content to respond well to quenching, as the added nitrogen can provide a higher hardenability in the case to allow for proper hardness development.

Atmosphere carbonitriding can be performed in the same equipment as is used for carburizing. The furnace atmosphere is still typically endothermic gas-based and includes the addition of ammonia to provide the nitrogen. Vacuum carbonitriding with both hydrocarbon and ammonia additions can also be performed in the same equipment as used for vacuum hardening and low pressure carburizing.

Diffusion Only Processes

These processes involve heating the workload to a temperature below the austenitizing temperature, allowing the desired element(s) to diffuse into the part surface, then slow cooling. The increase in hardness at the material surface comes only from the addition of the diffused element(s), and not from a phase change due to quenching. As these processes are performed below the lower critical temperature (i.e., below the austenitizing range), the desired core hardness and microstructure need to be developed through a separate heat treatment prior to case hardening. Generally, the process temperature selected should be at least 50°F below any prior treatment temperatures to avoid impact to the core properties.

Gas Nitriding

Gas nitriding is a process where nitrogen is added to the material surface. The process is typically performed between 925-°F; cycle times can be quite long as the diffusion of the nitrogen is slow at these temperatures, with nitriding times typically ranging from 16 - 96 hours or more depending on the material and case depth required. Nitriding can be performed in either a single or two-stage process and has the potential to produce two types of case, the first being a nitrogen-rich compound layer (or &#;white layer&#;) at the surface that is extremely hard and wear-resistant but also very brittle. This compound layer depth is dependent on processing time. In the more traditional two-stage process, the case depth produces a gradient of hardness from surface to core that commonly ranges from 0.010-0.025&#;, with minimal white layer, typically between 0-0.&#;. Nitriding is typically performed on higher alloyed steels or steels specifically designed for the nitriding process (e.g., Nitralloy®) as it relies on the formation of nitrides to create the increased hardness, which is achieved through the use of nitride-forming alloys such as aluminum, molybdenum and chromium. Pre and post oxidation treatments can be incorporated into the cycle to achieve certain benefits. Since the process does not require quenching to harden, it has the potential of producing a product that is more dimensionally stable and may not require any post-process finishing.

This process is most commonly performed in batch equipment; while it is possible to use a continuous furnace, keeping the ends of furnace sealed to contain the atmosphere can be challenging. Traditionally, pit furnaces have been used for nitriding as they can accommodate larger load sizes and can be easier to seal as gravity helps keep the lid sealed; however, horizontal designs have gained in popularity in recent years (Fig. 5). In either case, the furnaces are usually a single-chamber design with the load sealed inside an Inconel or stainless steel retort.

To achieve a nitriding atmosphere, ammonia (not nitrogen) is used to supply the atomic nitrogen necessary for diffusion. At the process temperatures used, ammonia does not readily dissociate on its own; rather, it dissociates when exposed to a heated steel surface (iron acting as a catalyst) into atomic nitrogen and hydrogen. To control the amount of nitrogen available for nitriding, the dissociation rate of the ammonia can be measured with high dissociation rates (high hydrogen content) providing a lower nitriding potential and low dissociation rates (low hydrogen content) leading to more nitriding potential. The depth of the compound layer can be varied through control of the nitriding potential, with higher nitriding potentials producing a thicker compound layer.

For more precise atmosphere control, an ammonia dissociator can be used to provide gas to the furnace that has already been split to dilute the atmosphere with hydrogen to more quickly achieve a high dissociation rate in the furnace. The ammonia dissociator is a heated box with a small retort inside; the ammonia is passed through this retort that contains a catalyst to promote the dissociation of the ammonia, and the resulting gas mixture is cooled and then injected into the furnace.

Ferritic Nitrocarburizing

In the author&#;s opinion, just like with carbonitriding, ferritic nitrocarburizing (FNC) is named incorrectly as it is more closely related to nitriding than it is with carburizing. FNC is a process that is still mostly nitrogen-based but with a slight carbon addition as well. The added carbon helps promote compound layer formation, particularly in plain carbon and low alloy steels that do not contain significant nitride-forming alloys. This process is typically performed in a range of -°F with cycle times much shorter than nitriding, typically 1-4 hours. The compound layer produced is usually much deeper than nitriding at 0.-0.&#;, with case depths reaching up to 0.025&#;, although in many applications a case depth may be difficult to measure. FNC is usually performed instead of nitriding in applications where the deeper compound layer is needed to increase wear resistance, but the added strength of a deep case depth is not as critical.

FNC can be performed in the same equipment used for nitriding, as long as a hydrocarbon gas is available to the furnace such as carbon dioxide or endothermic gas. FNC can also be performed in an IQ furnace using a mixture of ammonia and endothermic gas; for cooling, the parts can be oil quenched or slow cooled in a top cool chamber (if equipped).

Considerations

Case hardening processes are some of the most common heat treatments performed, but each process has its own unique needs. The table below provides a summary of the considerations that need to be made when selecting the optimum process. This list is by no means exhaustive; it is encouraged to work with a furnace manufacturer familiar with each process to help select the correct process and equipment needed.

Graphic: System hardening is all about protecting your server or workstation.

Did you know that the U.S. government allocated an estimated $18.78 billion for cybersecurity spending in ?

The reason why is made clear in the U.S. Department of Defense's Cyber Strategy Report:

Competitors deterred from engaging the United States and our allies in an armed conflict are using cyberspace operations to steal our technology, disrupt our government and commerce, challenge our democratic processes, and threaten our critical infrastructure.

As such, many companies supporting and selling servers and workstations to the DoD are turning to advanced system hardening tools and best practices to improve the security of their servers and other computer systems, oftentimes as a prerequisite for doing business with the DoD.

In this blog post, we'll discuss system hardening, its importance, the types of system hardening, how system hardening is achieved, and more. By the end, you should know what steps to take to begin or expand upon your system hardening processes and procedures.

Graphic: System hardening involves reducing a server's or workstation's attack surface.

What does system hardening mean?

System hardening is the process of securing a server or computer system by minimizing its attack surface, or surface of vulnerability, and potential attack vectors. It&#;s a form of cyberattack protection that involves closing system loopholes that cyberattackers frequently use to exploit the system and gain access to users&#; sensitive data.

One official definition of system hardening, according to the National Institute of Standards and Technology (NIST), is that it&#;s &#;a process intended to eliminate a means of attack by patching vulnerabilities and turning off non-essential services.&#;

Part of the system hardening elimination process involves deleting or disabling needless system applications, permissions, ports, user accounts, and other features so that attackers have fewer opportunities to gain access to a mission-critical or critical-infrastructure computer system's sensitive information.

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But at its core, system hardening is a method for protecting a system against attacks perpetrated by cybercriminals. It involves securing a computer system&#;s software mainly but also its firmware and other system elements to reduce vulnerabilities and a potential compromise of the entire system.

Now you know why system hardening exists, but you might be wondering about its practical purpose and why businesses and organizations implement system hardening practices.

The basic purpose of implementing system hardening techniques and practices is to simply minimize the number of potential entryways an attacker could use to access your system and to do so from inception. This is oftentimes referred to as following a secure-by-design philosophy.

Graphic: There are a few different types of system hardening, but they're all interrelated.

What are the types of system hardening?

System hardening involves securing not only a computer&#;s software applications, including the operating system, but also its firmware, databases, networks, and other critical elements of a given computer system that an attacker could exploit.

There are five main types of system hardening:

• Server hardening
• Software application hardening
• Operating system hardening
• Database hardening
• Network hardening

It&#;s important to note that the types of system hardening are broad enough to be universal and translate well across different server and computer system configurations; however, the methods and tools used to practically achieve a hardened or secure-by-design state vary widely.

But for now, let&#;s review the purpose of each type of system hardening.

Server hardening

Server hardening is a general system hardening process that involves securing the data, ports, components, functions, and permissions of a server using advanced security measures at the hardware, firmware, and software layers.

These general server security measures include, but are not limited to:

• Keeping a server&#;s operating system patched and updated
• Regularly updating third-party software essential to the operation of the server and removing third-party software that doesn&#;t conform to established cybersecurity standards
• Using strong and more complex passwords and developing strong password policies for users
• Locking user accounts if a certain number of failed login attempts are registered and removing needless accounts
• Disabling USB ports at boot
• Implementing multi-factor authentication
• Using self-encrypting drives or AES encryption to conceal and protect sensitive information
• Using firmware resilience technology, memory encryption, antivirus and firewall protection, and advanced cybersecurity suites specific to your operating system, such as Titanium Linux

Software application hardening

Software application hardening, or just application hardening, involves updating or implementing additional security measures to protect both standard and third-party applications installed on your server.

Unlike server hardening, which focuses more broadly on securing the entire server system by design, application hardening focuses on the server&#;s applications, specifically, including, for example, a spreadsheet program, a web browser, or a custom software application used for a variety of reasons.

At a basic level, application hardening involves updating existing or implementing new application code to further secure a server and implementing additional software-based security measures.

Examples of application hardening include, but are not limited to:

• Patching standard and third-party applications automatically
• Using firewalls
• Using antivirus, malware, and spyware protection applications
• Using software-based data encryption
• Using CPUs that support Intel Software Guard Extensions (SGX)
• Using an application like LastPass to manage and encrypt passwords for improved password storage, organization, and safekeeping
• Establishing an intrusion prevention system (IPS) or intrusion detection system (IDS)

Operating system hardening

Operating system hardening involves patching and implementing advanced security measures to secure a server&#;s operating system (OS). One of the best ways to achieve a hardened state for the operating system is to have updates, patches, and service packs installed automatically.

OS hardening is like application hardening in that the OS is technically a form of software. But unlike application hardening&#;s focus on securing standard and third-party applications, OS hardening secures the base software that gives permissions to those applications to do certain things on your server.

Oftentimes, operating system developers, such as Microsoft and Linux, do a fine and consistent job of releasing OS updates and reminding users to install these updates. These frequent updates -  and we&#;ve all ignored them - can actually help keep your system secure and resilient to cyberattacks.

Other examples of operating system hardening include:

• Removing unnecessary drivers
• Encrypting the HDD or SSD that stores and hosts your OS
• Enabling and configuring Secure Boot
• Limiting and authenticating system access permissions
• Limiting or eliminating the creation and logging in of user accounts

Database hardening

Database hardening involves securing both the contents of a digital database and the database management system (DBMS), which is the database application users interact with to store and analyze information within a database.

Database hardening mainly involves three processes:

1. Controlling for and limiting user privileges and access
2. Disabling unnecessary database services and functions
3. Securing or encrypting database information and resources

Types of database hardening techniques include:

• Restricting administrators and administrative privileges and functions
• Encrypting in-transit and at-rest database information
• Adhering to a role-based access control (RBAC) policy
• Regularly updating and patching database software, or the DBMS
• Turning off needless database services and functions
• Locking database accounts if suspicious login activity is detected
• Enforcing strong and more complex database passwords

Network hardening

Network hardening involves securing the basic communication infrastructure of multiple servers and computer systems operating within a given network.

Two of the main ways that network hardening is achieved are through establishing an intrusion prevention system or intrusion detection system, which are usually software-based. These applications automatically monitor and report suspicious activity in a given network and help administrators prevent unauthorized access to the network.

Network hardening techniques include properly configuring and securing network firewalls, auditing network rules and network access privileges, disabling certain network protocols and unused or unnecessary network ports, encrypting network traffic, and disabling network services and devices not currently in use or never in use.

Using these techniques in combination with an intrusion prevention or intrusion detection system reduces the network&#;s overall attack surface, and thus, bolsters its resistance to network-based attacks.

Photo: The NIST maintains one of several system hardening standards.

What are some system hardening standards?

Several industry standards and guidelines for system hardening exist. The National Institute of Standards and Technology (NIST), the Computer Information Security (CIS) Center for Internet Security, and Microsoft, for example, all maintain standards for system hardening best practices.

For example, system hardening best practices outlined by the NIST in Special Publication (SP) 800-123, a document focused entirely on system hardening, include:

• Establishing a system security plan
• Patching and updating the OS
• Removing or disabling unnecessary services, applications, and network protocols
• Configuring OS user authentication
• Configuring resource controls appropriately
• Selecting and implementing authentication and encryption technologies

Another example of a system hardening standard is CIS Benchmarks, an expansive collection of more than 100 system hardening configuration guidelines addressing vendor-specific desktops and web browsers, mobile devices, network devices, server operating systems, virtualization platforms, the cloud, and commonly used software applications.

The CIS Center's system hardening standards are accepted by government, business, industry, and academia. Relevant CIS benchmarks are available for download free of charge on the organization&#;s Free Benchmarks PDFs webpage.

How can I harden my system?

System hardening is a dynamic and variable process. One of the best ways to begin or expand upon the system hardening process is to follow a system hardening checklist or a system hardening standard, such as those published by the NIST or CIS Center.

Generally, how you harden your system depends on your server&#;s configuration, operating system, software applications, hardware, among other variables.

The system hardening standards and guidelines published by the NIST and CIS Center for Internet Security, for example, discuss system hardening techniques specific to Microsoft Windows, Unix, and Linux.

So, if you&#;re curious about how to begin the system hardening process, reading the NIST&#;s Special Publication 800-123 and the CIS Center for Internet Security&#;s free benchmark PDFs is a good place to start. You can then, if necessary, consult with an experienced cybersecurity professional on how to move forward with implementing these standards&#; recommended processes and best practices within your business or organization.

There are some common and transferrable system hardening practices of which you should be aware, however. We've put a few best practices in the checklist below.

A good system hardening checklist usually contains the following action items:

1. Have users create strong passwords and change them regularly
2. Remove or disable all superfluous drivers, services, and software
3. Set system updates to install automatically
4. Limit unauthorized or unauthenticated user access to the system
5. Document all errors, warnings, and suspicious activity

Photo: Trenton Systems' 3U BAM Server, a hardened, cyber-resilient rugged server.

Conclusion: Trenton Systems hardens its servers from inception.

Trenton Systems partners with leading cybersecurity companies and is able to make changes to its server hardware, firmware, and software in an effort to further secure, or harden, its servers and workstations.

The 3U BAM Server is our most recent shining example of trusted computing and system hardening. The BAM is secured by Intel PFR, Intel SGX, and Intel TME, and we can even make changes to its ports, further secure its BIOS, among other enhancements, to ensure that your BAM server is as cyber-resilient as possible.

In addition, Star Lab, a Wind River company and Trenton Systems software technology partner, offers the Titanium Security Suite for Linux operating systems. Through our partnership with Star Lab, we can incorporate this suite for customers upon request. We can also incorporate FUTURA Cyber's self-encrypting drive security manager to assist with the management of FIPS 140-2 SEDs.

For more information about acquiring a secure, hardened rugged server or workstation, reach out to us. Our in-house cybersecurity experts and cybersecurity technology partners are here to assist you every step of the way.

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