Market pressures have forced many manufacturers to look beyond traditional materials and push for innovation in their product categories.
This recent development is related to converging factors such as conservation and energy inputs, environmental concerns, using standard materials in new unconventional ways and implementing value-added processes to upgrade current materials to meet more stringent regulations and end-use requirements. Whatever the reason, it has become an opportunity for innovation in the heat-treatment process. This article will explore recent developments and global trends where heat treatment plays an important role.
Lightweighting Initiatives by Automotive Manufacturers
Producers of automobiles today have been faced with the challenges associated with meeting the U.S. Department of Transportation’s Corporate Average Fuel Economy (CAFE) regulations.
These pressures have forced automobile engineers to seek out new designs that improve fuel-consumption efficiencies. This includes substituting materials used in the manufacture of vehicles with stronger and lighter alternatives. A major component to improving a vehicle’s fuel economy is weight reduction. The lighter a vehicle is, the less power it requires to accelerate and maintain speeds. Lightweighting technologies have been a main concern of automakers since the 1975 oil embargo. They are today because of the concern over the prospect of global climate change.
Since the mid-1970s, the automotive industry has successfully reduced the weight of automobiles, primarily through downsizing of the vehicle. Although past strategies have been very successful, there are restrictions to downsizing. These restrictions have forced automakers to seek out weight reductions through new methods that include plastics, composites, new lightweight aluminum, carbon fiber and magnesium materials for automotive body and structures instead of plain-carbon steels. A car with a lighter body can be paired with lighter secondary components (e.g., engine, suspension and structures). These secondary weight-savings benefits are significant since they roughly double the benefit of a lighter body structure.
Innovative New Approach
The introduction of new lightweight automotive body and structure components has created opportunities and challenges for supply-chain professionals, material engineers and product designers (Fig. 1). Great work has gone into formulating the optimal combination of lightweight materials that allow for acceptable joining and forming technologies to be used in the manufacture of the automobile while also providing the required strength, corrosion and physical properties. A recent example of this combination is by Ford Motor Company, which has introduced aluminum into the 2015 F-150 line of pickup trucks. Ford claims that its use of aluminum in the body and bed reduces the truck’s weight by up to 700 pounds.
The demand for lighter automotive body and structural components has had a trickledown effect on the secondary processes used to manufacture them. This trickledown effect has impacted the methods and equipment used for the thermal processing or heat treatment of these components. The introduction of aluminum alloy use in automotive body and structural components has led to additional challenges for thermal processes and equipment that improve the components’ strength and ductility characteristics.
These new demands have created opportunities for designers of thermal-processing equipment to develop new concepts specifically tailored for the processing of lightweight aluminum automotive bodies and structures. They are unique to these specialized components and have forced designers to reconfigure their designs of the past to new models that will be used in future.
Examples of requirements for today’s heat-treatment systems for lightweight aluminum automotive body and structures include:
• Process and product flexibility to operate random product types under a common recipe
• Lean manufacturing features that reduce work in process/product inventories
• Furnace-system designs that reduce energy consumption and emissions
• Furnace designs that integrate component geometry features to maximize processing uniformity and dimensional stability
• Individual-component process-data collection and archiving capability
• Simulation and modeling capabilities of heating and precision air quenching (PAQ™)
• Development of hybrid equipment designs that allow for future capacity increases
Industrial-furnace engineers leveraged existing technologies to form a modernized system for handling these new components while also addressing their unique requirements. These innovative lightweight aluminum automobile body and structure component heat-treatment systems are unique and do not resemble the traditional aluminum automotive-product heat-treatment systems first introduced in the early 1980s. The introduction of these new systems demonstrates the evolution that is taking place within the automotive and thermal-processing industries. Furthermore, this evolution points out that the systems and processes that were implemented over 40 years ago during the first oil crisis and the resultant lightweighting initiatives are a thing of the past and have been replaced with newer technologies that will continue to grow and change in the future.
In the automotive world, the battle between steel and aluminum is being fought one part at a time. While aluminum in automobile production is getting considerable attention due to the fact that it weighs approximately one-third that of comparable steel components, the steel industry has become creative at finding alternative materials for use in automotive structural applications.
Specifically, in the past 15 years there has been replacement of traditional non-heat-treated steel components with light-gauge, high-strength microalloyed steel heat-treated components for items such as door intrusion beams, A/B pillars, etc. Blank materials that were traditionally cold formed are now heated in industrial furnaces (roller hearths, walking beams, batch slot furnaces) to 1750°F (954°C), sometimes in the presence of a N2 atmosphere. As a minimum, an indirect-heated system is necessary.
A number of steels, such as USIBOR, have aluminum coatings to protect the component surface from corrosion once inside the car structure. The magic of these microalloyed steels, which have additions of Ti, B and Cb, is that they are able to develop nearly full as-quenched hardness in a water-cooled die during the forming process. The new technology, generally referred to as hot stamping, allows steel parts 1-4 mm thick to be cooled sufficiently fast in the water-cooled die to develop 35-40 HRC. No subsequent tempering is employed (Fig. 2).
North American Energy Independence Drives Search for Nonconventional Sources
The U.S. has recently surpassed Russia as the largest producer of natural gas in the world. This nearly unthinkable achievement was possible due to hydraulic fracturing combined with horizontal-drilling techniques. Both of these technologies require large amounts of API 5CT-certified heat-treated pipe that has been quench and tempered to meet specific yield-strength characteristics. The most common grades are L80, P110 and Q125, which represent 80,000, 110,000 and 125,000 psi yield-strength levels. Specific casing diameters of 4.5, 5.5, 7.0 and 9.625 inches make up the majority of industry needs in lengths up to 44 feet long.
Houston, Texas, represents the epicenter of OCTG (oil country tubular goods) production in North America with many recent pipe quench-and-temper facilities established, but the Northeast U.S. and Canada have also seen additional new capacity. Pipes for OCTG applications are generally heat treated in either continuous tunnel furnaces or walking-beam furnaces, combined with ID/OD spray quenching and forced convective tempering. Most facilities combine downstream processing to include one or more of the following: hydrotesting (welded pipe), ultrasonic inspection, surface inspection, end threading, bucking and capping. With individual quench-and-temper furnace line capacities ranging from 50,000-500,000 tons/year, there is an incredible amount of heat-treated pipe going into ever-demanding downhole applications (Fig. 3).
Updates to Regulations Create New Standards for Railcar Manufacturing
The July 2013 Lac Megantic rail tank-car disaster in Quebec will have long-term implications for the railcar industry for years to come. A substantial number of railcars in the North American fleet do not meet current standards and must be replaced. As the pipeline on wheels continues to grow for new shale oil not serviced by existing pipe networks, rail tank cars are playing an increasingly vital role in both the U.S. and Canada for the transportation of crude to the U.S. Gulf Coast and eastern-Canadian refineries.
New manufacturers have entered the rail tank-car production business, and demand is at record levels. Heat treatment plays an important role in stress relieving the welded tank-car structure, which generally consists of a series of formed and welded rings that make up the cylinder. This cylinder is closed on either end by formed dished heads. The entire tank-car assembly (minus the lower undercarriage assembly) is stress relieved in large car-bottom furnaces at temperatures of ~1200°F (650°C) for times prescribed in the AAR standards. Some furnace configurations are for single tanks, and others are designed for double-wide, or two tanks at a time (Fig. 4).
Reducing Costs, Creating a Premium Product for the Mining Industry
Whether it’s grinding rods or grinding balls (Fig. 5), improved material properties lead to increased life and reduced operating costs for the mining industry. It’s no secret that the various forms of heat treatment are typically a necessary or value-added process required to modify or improve a product’s mechanical and metallurgical properties. Consumables in the mining industry are no exception. Heat treating improves quality and differentiates it from cheaper offshore suppliers.
The sheer volume of aggregate processed to obtain the minimal amount of the mineral/ore being mined is staggering. Literally, tons of aggregate are pulverized in large tumblers, known as ball mills or rod mills (depending on the process/type of grinding media being used), in order to begin the process of separating minerals from ore. This inherently harsh environment combined with the tendency of “as rolled” or “as forged” products supplied in the less-than-ideal normalized or annealed condition lends itself well to a quench-and-temper process.
Quenching and tempering the grinding media significantly improves the hardness and toughness of the media, providing for excellent impact and wear performance. The quenching portion of the process involves bringing the product to an austenitizing temperature (where the solid solution of iron and carbon is achieved by heating above the upper critical temperature) –
generally between 1550°F and 1750°F – and holding it for a period of time until the crystalline structure is achieved before rapidly cooling the product in water or polymer. Tempering involves reheating the previously hardened or quenched steel to a temperature below the lower critical temperature (300-1200°F/150-650°C), depending on the desired properties, holding for a period of time and cooling to ambient temperature.
Ever-increasing product demands require steel and aluminum materials with enhanced mechanical and metallurgical properties to meet the challenge of 21st-century manufacturing processes. Heat treatment in all its forms will play a vital role in the growth and sustainability of new technologies.
For more information: Julie Bond, marketing coordinator, CAN-ENG Furnaces International Ltd., 6800 Montrose Road, Niagara Falls, ON, Canada L2E 6V5; tel: 905-356-1327; fax: 905-356-1817; e-mail: email@example.com; web: www.can-eng.com