Dr. Arvind Thekdi, an Energy Expert for the U.S. Department of Energy, routinely conducts energy assessments to improve energy efficiency of process heating systems at industrial plants. During the assessments, he often encounters questions that indicate confusion about how process heating systems operate. In this article, Dr. Thekdi provides some basic information about process heating systems, and offers solutions for reducing heat losses to increase efficiency.
“While some heat treatments are used to soften the material or improve its machinability, most are processed to obtain strengthened or hardened properties. The majority of heat treatments apply to metallic materials and, typically, the techniques include annealing, normalizing, quenching, tempering, precipitation strengthening, surface hardening, and case hardening. Heat treatment is so critically important that we can safely say a part undergoing extensive manufacturing processes such as melting, rolling, forging, and other related machining is of little or no value without the necessary and appropriate heat treatment.”
Steel is primarily iron with up to 1% carbon, plus other alloying additions (generally totalling less than 5%).
A steel composition can be thought of as a recipe; different amounts of each ingredient make up your final product. In steel these ingredients are known as alloying additions and can affect the steel in different ways. We can affect the:
Properties of steels.
strength
hardness
toughness
ductility
fatigue
formability
machinability
weldability, and
corrosion resistance.
The addition of carbon to iron is probably the most important addition in steels which makes ‘The Iron Carbon Equilibrium Diagram’ very useful. Equilibrium means that enough time has been allowed on heating and cooling for any reactions to fully complete.
Typical Iron Carbon Diagram
In a steel <723°C, different structures are present and depending on the carbon content we can have at <0.8% Carbon – ferrite and pearlite, at 0.8% carbon – pearlite and >0.8% carbon – pearlite and cementite.
While the iron carbon diagram describes the structures of steel under equilibrium conditions, two further diagrams can be used when faster cooling rates are used; these are the CCT (continuous cooling transformation) diagram and the TTT (time temperature transformation) diagram. Both of these diagrams are helpful in selecting the optimum steel and process parameters.
When we cool a steel at faster cooling rates we can achieve additional structures, these can be bainite and martensite. CCT and TTT help determine the structures achieved.
In metallurgy the hardenability of a steel is a key parameter and when we talk about hardenability in steels we are often describing how deep into the steel we can achieve hardening. If a steel is described as having a low hardenability this will mean that the steel will produce a shallower depth of hardness. Hardenability is not to be mistaken for hardness; when describing the hardness we are often looking at the microstructure achieved during cooling. For a given steel it can be assumed that the quicker the cooling rate the greater the chance of achieving a harder structure and if that steel has a high hardenability this hard structure will be present deeper into the thickness.
In metals there are atomic defects called dislocations, these dislocations reduce the strength of the metal. The principle of strengthening mechanisms is to reduce the ability of these dislocations to move through the metal, this can be achieved by:
Atomic dislocations within the metal potentially reduce the metal’s strength.
Grain Size; the grains can interact with the dislocations preventing further movement. If we reduce the grain size we can increase the number of grains interacting with the dislocations, preventing movement and thus strengthening the metal.
Cold work introduces a large amount of strain into the metal; this strain interacts with the dislocations strain field, impeding the movement of the dislocations.
Solid solution strengthening is applied when we add other chemical elements to a metal. Addition of these elements can either be called interstitial or substitutional solid solution strengthening and will cause distortion in the atomic structure, restricting the dislocation movement and strengthening the steel.
Dispersion or precipitation strengthening is highly related to the structure of the metal and takes place when a phase is finely precipitated through a softer matrix. This precipitate acts as a barrier to dislocation movement.
The next in the series will be Steel Making and Casting.
WATERLOO, IA—Advanced Heat Treat Corp. (AHT) recently announced that it has received a Federal Firearms License (FFL) issued by the U.S. Department of Justice, Bureau of Alcohol, Tobacco, Firearms and Explosives at their facility in Monroe, Michigan. AHT now has licenses at all four of the company’s locations in Iowa, Alabama and most recently, Michigan. All licenses are available to view or download on the Quality section of their website: www.ahtcorp.com under the “About” section.
“While we are no stranger to processing firearms, the addition of this license will allow us to better serve those customers whose parts require an FFL,” stated Gary Sharp, President and CEO. “Our firearm customers have recently experienced better lubricity and corrosion resistance with one of our trademarked processes, UltraOx®, so we wanted to be better equipped to handle all of their parts for aesthetics and consistency. We are excited to now be able to expand that offering to our Michigan customers.”
The London-based metals trading and manufacturing company Liberty House Group (LHG) has launched a metal recycling business called Liberty Metal Recycling (LMR), which it says is a step toward it achieving its Greensteel vision to create a competitive and sustainable steel sector in the United Kingdom.
IHEA’s Fundamentals of Industrial Process Heating Online Learning Course is scheduled to begin on Oct. 17, 2016. This course is ideal for students who wish to take the course at home or work in a flexible web-based distance-learning format. It’s an affordable alternative to campus-based classes and allows students to go at their own pace. The course offers an indispensable tool to industrial process heating operators and users of all types of industrial heating equipment. In the instructor-led, interactive online course, students learn safe, efficient operation of industrial heating equipment, how to reduce energy consumption and ways to improve your bottom-line.
This class provides an overview of the fundamentals of heat transfer, fuels and combustion, energy use, furnace design, refractories, automatic control, and atmospheres as applied to industrial process heating. Students will gain a basic understanding of heat transfer principles, fuels and combustion equipment, electric heating, and instrumentation and control for efficient operation of furnaces and ovens in process heating. For complete course description, visit www.ihea.org and click the Events tab to find the class. Students will also earn PDH’s for passing the course.
This course is led by industry expert, Max Hoetzl, retired Vice President of Surface Combustion. Max brings more than 40 years’ experience in the combustion industry to IHEA’s online course.
This is a 6-week online course beginning on Oct. 17th. Registration fee includes course instruction, live interaction with the trainer, class forums to interact with other students, plus an electronic copy of IHEA’s Fundamentals of Process Heating Course Handbook. Registration is open now through Oct. 14th, 2016 at www.ihea.org. Click the Fundamentals of Industrial Heating Online Course button on the right side of the homepage. Cost for IHEA members is $700 and non-members is $875.
To meet Schafer Gear Works’ growing demand for high-precision commercial aviation shafts and gears, the company recently moved its Fort Wayne, Ind., operations to its larger production facility in South Bend, Ind. “Acquisition of new, state-of-the-art equipment at our South Bend plant and the ability to better leverage our gear manufacturing expertise led to the transfer,” said Paresh Shah, operations manager for the South Bend facility. The transition was seamless and the plant now produces precision-critical shafts and small-diameter gears with tolerances to 0.0004” and microfinishes to 16 RMS.
Shah said moving the small-diameter gear production 90 miles west to Schafer Gear Works South Bend will improve design and manufacturing efficiencies as well as customer support. By centralizing the facility’s small- and medium-diameter gear engineering, production and quality control expertise, the company is expanding its presence in the aerospace and automotive industries as well as with medical instruments, light and heavy industrial products, recreation vehicles, and material handling companies. Its efforts to reduce tool costs and downtime keep pricing competitive and delivery among the fastest in the gear-making industry. Because of the South Bend facility’s continuous equipment improvements and stringent quality standards, it has earned ISO 9001-2008 and AS9100 certification.
Schafer Gear Works manufactures one of the widest ranges of custom-engineered, precision-cut gears for off-highway markets. In addition to the small-diameter gears and precision components, the South Bend plant produces 1.5- to 10-inch diameter spur, internal and helical gears as well as shafts.
Total lifecycle cost of running a piece of equipment can be significantly reduced if the right end-user/OEM cooperation can be established. This article helps captive heat- treaters think through the process of establishing a profitable partnership with their equipment’s original manufacturer.
“The hardening of materials by laser is a specialized and fast-growing field as it offers improved wear resistance, expansion of component life, and increased strength and fatigue limits of the material.”
Source: Reliable Plant
To meet Schafer Gear Works’ growing demand for high-precision commercial aviation shafts and gears, the company recently moved its Fort Wayne, Ind., operations to its larger production facility in South Bend, Ind. “Acquisition of new, state-of-the-art equipment at our South Bend plant and the ability to better leverage our gear manufacturing expertise led to the transfer,” said Paresh Shah, operations manager for the South Bend facility. The transition was seamless and the plant now produces precision-critical shafts and small-diameter gears with tolerances to 0.0004” and microfinishes to 16 RMS.
