Low pressure carburizing (LPC) is a proven, robust case hardening process whose potential is only limited by the style and size of vacuum furnace. Today, LPC is typically used in horizontal vacuum furnaces where the opportunity to carburize large parts is limited. In this paper we present a new adaptation of the technology in large pit type vacuum furnaces, capable of opening to air at elevated temperature. This underscores the potential of LPC to carburize larger, more massive parts in a clean, effective and efficient process. The result is quality casehardened parts without the undesirable side effects of atmosphere gas carburizing such as the use of a flammable atmosphere, reduced CO and NOx emissions, no intergranular oxidation, and limited retort life. Another significant advantage is decreased process time. The case study presented here shows that eliminating furnace conditioning and increasing process temperature can significantly reduce cycle durations by nearly three times and cut utility costs in half. Under these conditions, a return on investment (ROI) is in the neighborhood of 1 – 2 years is possible, making LPC in a pit style furnace a cost-effective solution than traditional atmosphere gas carburizing technologies.

This paper examines the latest developments in energy management in heat treatment with a specific focus on electrical heating and tighter integration between the power supply and furnace control to maximize energy efficiency. It also discusses the use of IGBT (insulated-gate bipolar transistor) and SCR (silicon-controlled rectifier) based power supplies as energy-efficient alternatives to variable reactance transformers (VRTs) for powering electric vacuum furnaces.

This paper compares and contrasts heat treat processes and equipment typically used to harden gears. It discusses the basic design and operation of vacuum, controlled atmosphere, and hybrid furnaces and process techniques such as carburizing, carbonitriding, nitriding, nitrocarburizing, and neutral hardening. It also includes information on operating and maintenance costs, using batch integral quench furnaces as the base case for comparison. A discussion on when to consider continuous furnace types is included as well.

This paper presents four case studies documenting the time and money that heat treaters have saved with the help of predictive maintenance tools. In one case, a heat treater avoided potential catastrophic melting of a heating element and several hangers when predictive maintenance software guided the operator to a broken ceramic in a specific heating zone. In another case, a commercial heat treater was alerted to a low kW reading, indicating a heater failure on a diffusion pump, which would have led to the contamination of a vacuum furnace if not addressed in a timely manner. Situations involving a failing motor on a quench tank and the degradation of furnace insulation are also discussed. Cost comparisons, with and without predictive maintenance, are included in three of the four studies.

This paper discusses the growing use of automation in heat treating and some of the benefits that have been realized in early applications. It provides examples showing how articulated robots are used to load and unload parts on fixtures, how inline 3D cameras facilitate dimensional and distortion control, and how test coupons placed by robots at strategic locations throughout a load are weighed before and after heat treatment to determine if parts in different areas of the load are likely to be carburized to the same degree. It also includes an example of an automatically generated report and explains how binary codes on base trays can be used to automatically upload recipes for specific heat treatments.

This paper presents the results of a study examining the cooling rates of two vacuum high-pressure gas quenching furnaces: a large 10-bar furnace equipped with a 600-hp blower motor and a smaller 10-bar furnace with a 300-hp motor. In comparing critical cooling temperatures for H13 in the 1850°F to 1300°F range, the furnace that is almost three times larger in volume (110 vs. 40 ft 3 of hot zone) cooled the same workload almost identically to smaller unit. The test results clearly show that gas flow, or velocity, is more meaningful than pressure when it comes to cooling rate.

This paper reviews several recent advancements in high pressure gas quenching technology along with the impact of new higher hardenability steels. With design upgrades and improved gas flow and heat removal, a wider variety of materials, part geometries, and load sizes can now be gas quenched.

Today’s competitive environment requires that you do more with less – to make equipment last longer and run more efficiently. With the industry becoming more demanding, there has never been a better time to ask the question: “Where, and in what, do I invest my money with aging equipment?" This paper offers a close-up look at what is possible when weighing different options for upgrading an aging vacuum furnace, focusing on the many factors that go into choosing the right upgrades and repairs for both your equipment and process requirements.

A new high strength and energy efficient graphite board (HEFVAC) was introduced in fall 2016 as a vacuum furnace insulation package, which has evolved with the goal of further reducing power consumption. The unique features of the HEFVAC material offer a new approach to the design and construction of a vacuum furnace hot zone. Our presentation will document the thermal advantages of the HEFVAC board as well as introduce a new hot zone design that integrates the board into a self-supporting structure. This new design offers greatly improved thermal efficiency, resulting in reduced power usage compared to current vacuum furnace hot zones.

A review of vacuum processing in a multiple-chamber vs. single-chamber vacuum furnace and the advantages and disadvantages of both design concepts will be presented. Cycle calculations will be shown to illustrate the differences in the floor-to-floor time, heating energy required to process and cooling power to quench a normalized load. Additionally, the presentation will discuss the differences in residual atmosphere for a given vacuum level for the two furnace concepts. Differences in operation and maintenance between the two concepts and appropriate processes to run in each will also be discussed.

An advanced nickel alloy with a specially designed chemistry to provide maximum oxidation resistance at the most extreme temperatures and controlled precipates to maximize creep strength. A leading vacuum furnace supplier has selected this alloy as a suitable material for bar baskets in their most demanding application, 2300 F and pressure quenching. Baskets fabricated from all other alloys tested lasted between 5 and 10 cycles before requiring extensive, labor intensive straightening. The new alloy baskets have been used for over 30 cycles, with minimal distortion. This extended life eliminates several straightening cycles and the high labor costs associated with manual straightening and reassembly.

Low pressure carburizing (LPC) in a vacuum furnace is increasingly the preferred method of case hardening for aerospace gears, and acetylene is often one of the gases used in the process. Selective case hardening is common with gears, where certain sections of a part are “stopped off” or “masked” to prevent carburization at those locations. For aerospace parts, the masking used is typically copper electroplating. The low pressures and high temperatures used in LPC lead to copper evaporation, which contaminates the vacuum furnace hot zone and components. In a worst-case scenario, deposited copper can lead to short-circuiting of power feedthroughs. This study looks at the effect of vacuum and partial pressure gases on copper evaporation and its application in production processes.

Hardening and case hardening are among the most common types of heat treatment processes, which can be performed in either atmosphere or vacuum furnaces. These processes, followed by oil quenching, are carried out in batch sealed quench and continuous furnaces such as pusher, roller, or rotary hearth types. Atmosphere heat treatment technology and equipment was developed more than 60 years ago with little new product innovation or change since. However, in this time period the needs of manufacturing have changed dramatically, driven by global competitiveness and the drive for lower unit cost. As such the heat treatment solutions must be capable of achieving higher productivity (through shorter cycle times), increased flexibility (with respect to material and process/cycles) and meet higher product quality standards. In addition, today’s manufacturing requires absolute process reproducibility and integration with other manufacturing processes, all done using energy efficient and environmentally friendly equipment. The solution to this situation is modern vacuum furnace technology and vacuum equipment that easily adapts to stringent specifications and changing industry standards. In this discussion, two case studies of this technology are presented. The first includes a two-chamber sealed oil quench vacuum furnace to case harden a SAE 5120 component to a surface hardness of 61 HRC using a Low - Pressure Carburizing (LPC) process. The result was a 30% savings over traditional atmosphere carburizing integral quench furnace owned by a commercial heat treater. The second study involves the use of a three-chamber sealed oil quench vacuum furnace to case harden SAE 5115 steel automotive steering components to an effective case depth of 0.9 mm minimum and a minimum surface hardness of 60 HRC. Using LPC these parameters were easily achievable. By, using a three-chamber sealed oil quench furnace, the potential for up to 600 kg/hr throughput was demonstrated, while maintaining costs comparable to a traditional atmosphere style integral quench furnace. Together, both studies show that sealed oil quench vacuum furnaces can improve process time and quality over a traditional atmosphere integral quench furnace while maintaining the process costs needed to remain competitive.

Additive manufacturing, popularly known as 3-D printing, is the newest manufacturing technology which is taking the world by storm. Additive manufacturing is a process whereby a digital model is converted into a metallic three dimensional part by layering powders or wrought feed stock into a near net or a dimensionally complete part. There are many people in the world who claim additive manufacturing will never replace machining, otherwise known as subtractive manufacturing. On the other hand many believe additive manufacturing will someday change the world. As is so often the case this author believes that reality lies somewhere in between the skepticism and hype.

There are many inherent advantages with utilizing two-chamber, or multiple chamber vacuum furnaces. These include energy efficiency, reduced processing time, and a plethora of processes. Design of multiple chamber vacuum furnaces will be discussed including heating, cooling, and maintenance.

Vacuum furnaces are expensive to purchase and operate. By using creative fixture solutions, manufacturers, commercial heat treaters and overhaul & repair facilities can safely increase the number of parts heat treated or brazed per batch, increasing productivity while lowering the cost per unit.

A study was conducted on a set of H13 steels to enhance their performance as matrices and pins. The steels were austenitized in a high-pressure vacuum furnace at 1015 °C for 180 minutes, followed by nitrogen quenching in a high vacuum (2 bar). Two tempering treatments were applied: one at 540 °C and another at 580 °C, each for 180 minutes, with subsequent nitrogen cooling to room temperature. The nitrocarburizing process was carried out in a liquid bath salt furnace at 580 °C for varying durations of 45, 60, 90, 120, 150, and 180 minutes to assess the impact of treatment time on the quality of the nitrocarburizing layer. Post quenching and tempering, the steels exhibited hardness values ranging from 550 to 570 HV. After nitrocarburizing, the surface hardness increased to between 740 and 810 HV, with a nitrocarburizing layer thickness of less than 14 μm. The microstructural evolution of the compound layer was analyzed using scanning electron microscopy and X-ray diffraction. The characterization revealed a continuous nitrocarburizing ε-Fe 2–3 (C,N) layer. Specimens treated for 45 to 60 minutes demonstrated superior wear performance compared to those treated for 90 to 180 minutes.

A recently introduced new vacuum furnace design allows the total integration of heat treatment into the manufacturing line. This compact unit can be implemented into the heart of the production chain and provides heat-treatment processes which can be fully synchronized with the green and hard machining-operations. When performing case hardening, the components are low pressure carburized at high temperatures (1050°C) followed by gas quenching. Using this technology, the components are treated in most cases in a single layer of parts (“2D-treatment”) which allows for an easy automated loading and unloading of the fixture-trays. Furthermore this “small batch – treatment” leads to an optimum in quality regarding quench homogeneity and distortion control. By using the small batch concept, a continuous flow of parts can be established. There is no need to wait until enough parts are collected to build a large batch with multiple layers (“3D-batch”). Therefore excessive costs are avoided for inventory, part storage and transportation within the plant. Typical components for this technology come from the automotive, aerospace and tool industry. The paper shows several new results from case hardening applications.

Titanium use in aerospace and medical applications continues to grow. Alpha case formation is a diffusion reaction that occurs at the surface of titanium when processing at elevated temperature in atmospheres containing oxygen, nitrogen, and/or carbon, with oxygen being the prominent element associated with alpha case. Oxygen is solution strengthening at low concentrations, but greatly decreases ductility and forms alpha case at higher concentrations. Thus, alpha case is brittle and has a detrimental effect on part performance and longevity. Higher temperatures increase alpha case depth. Temperatures less than 550°C (1022°F) limit oxygen mobility and keep case depth from increasing. Above 480°C (896°F), air or water vapor will start to produce alpha case.

Historically, this carburizing has been performed in an endothermic gas consisting of CO 2 , CH 4 , CO, etc, but carburizing in low pressure with the proper gas mixture changes the landscape. Using C 2 H 2 , the process is no longer endothermic as C 2 H 2 is a catalytically decomposable hydrocarbon and dissociates in the presence of an iron catalyst. LPC is a recipe driven in contrast to the constant monitoring of the carbon potential in atmospheric gas carburizing, and with the wide acceptance of simulation programs, recipes are no longer created by trial and error. Introduction of nitrogen to the steel, followed by carbon with higher temperatures, can dramatically reduce cycle times and still control grain growth.