The requirements and standards for spare parts in mechanical equipment are becoming higher and higher, and the scenarios and scope of use are becoming wider and wider, which requires the use of composite heat treatment processes when processing metals. Various types of composite combinations of processes such as strengthening treatment, surface alloying, surface heat treatment, surface functional plating, and deformation strengthening have greatly improved the performance of mechanical parts.

The meaning of composite heat treatment is to rationally combine multiple heat treatment processes to more effectively improve the performance of the workpiece, tap the material potential to a greater extent, save energy as much as possible, reduce costs, and improve production efficiency. Since the temperatures of various processes are different and the resulting properties are different, the order of combination must be considered during implementation. Composite heat treatment is not a combination of general preliminary heat treatment and final heat treatment, but a combination of final heat treatment processes.

Composite heat treatment processes currently used

Combination of multiple heat treatment processes: quenching after chemical heat treatment such as nitriding; combination of several chemical heat treatments, chemical heat treatment after quenching and tempering, etc.

Combination of plating and heat treatment: overall or surface hardening + surface functional coating (plating) coating.

Combination of pressure processing and heat treatment, that is, deformation heat treatment, is a new process that combines phase-change strengthening with deformation strengthening.

Combination of overall or surface strengthening and surface deformation strengthening (rolling, shot peening).

Composite Heat Treatment of Metal Surfaces in Auto Parts

Composite heat treatment is an advanced metallurgical process used to improve the surface properties of metal components in automotive applications. It involves combining different heat treatment techniques to achieve specific enhancements, such as increased surface hardness, improved wear resistance, enhanced corrosion protection, and better thermal stability. Automotive parts that undergo composite heat treatment are often subject to extreme stress, friction, and harsh environmental conditions, making this process crucial for optimizing performance and extending the lifespan of these components.

This article will explore the various auto parts that benefit from composite heat treatment, explain how this process improves their functions, and discuss the advantages it offers in automotive engineering.

Auto Parts That Benefit from Composite Heat Treatment

Several critical automotive parts require composite heat treatment to perform optimally, especially those involved in power transmission, engine operation, and braking systems. Some of the key components include:

Engine Components:

Camshafts: Camshafts regulate the opening and closing of engine valves, making them vital to the internal combustion process. Camshafts are subject to continuous contact with cam followers, and composite heat treatment improves their wear resistance and fatigue strength.

Crankshafts: Crankshafts convert the linear motion of pistons into rotational motion, driving the vehicle. The surfaces of crankshaft journals and bearings are treated to improve their fatigue resistance and wear performance.

Pistons and Piston Rings: Pistons move at high speeds within engine cylinders, while piston rings seal the combustion chamber. These components require heat treatment to enhance their resistance to friction, wear, and high temperatures.

Transmission Components:

Gears: Gears transmit power from the engine to the wheels, enduring high loads, friction, and rotational forces. Composite heat treatment improves their surface hardness and wear resistance, ensuring smooth operation and preventing premature failure.

Clutch Plates: Clutch plates engage and disengage the engine from the transmission. Heat treatment ensures the plates maintain their frictional properties and durability, even under heavy load conditions.

Brake System Components:

Brake Rotors (Discs): Brake rotors are subjected to extreme friction and heat during braking. Heat treatment processes, such as nitriding, enhance the wear resistance and thermal stability of brake rotors, reducing the risk of warping or cracking under high-stress conditions.

Brake Pads Backing Plates: These plates support the friction material in the brake pads. Composite heat treatment improves their structural integrity and resistance to corrosion, ensuring reliable performance over time.

Suspension and Steering Components:

Ball Joints and Control Arms: Suspension and steering components, such as ball joints, control arms, and tie rods, must endure constant stress and movement. Composite heat treatment increases their fatigue strength and resistance to wear, allowing for smoother handling and longer service life.

Drive Shafts and Axles:

Constant Velocity (CV) Joints: CV joints allow for smooth transmission of power to the wheels while the vehicle is turning. These joints undergo composite heat treatment to enhance their wear resistance and durability.

Drive Shafts: Drive shafts transfer power from the transmission to the wheels. Heat treatment improves their resistance to fatigue and torsional stress, preventing premature failure under heavy loads.

How Composite Heat Treatment Improves Functionality

Increased Surface Hardness:

One of the primary benefits of composite heat treatment is the significant increase in surface hardness, which protects the metal parts from wear and abrasion. Processes like carburizing, nitriding, and carbonitriding are commonly used to introduce carbon or nitrogen into the surface of the metal, forming a hardened layer. This hardened layer resists the mechanical stresses of friction, reducing the rate of wear on critical components like gears, camshafts, and brake rotors.

Enhanced Wear Resistance:

Wear resistance is a crucial property for auto parts that are subjected to constant friction and contact, such as gears, pistons, and brake system components. Composite heat treatment increases the wear resistance of these parts by refining their surface microstructure and increasing their hardness. This reduces the likelihood of surface degradation over time, ensuring that the parts can withstand prolonged use without excessive wear.

Improved Fatigue Strength:

Fatigue is a common cause of failure in automotive components that experience repeated cyclic stresses, such as drive shafts, crankshafts, and suspension parts. Composite heat treatment processes like induction hardening or tempering increase the fatigue strength of these parts by optimizing their grain structure and improving their resistance to crack initiation and propagation. This allows the parts to endure high levels of stress and load cycling without succumbing to fatigue damage.

Corrosion Resistance:

Corrosion can significantly impact the longevity and performance of automotive components, especially those exposed to moisture, road salts, and chemicals. Composite heat treatment processes like plasma nitriding or nitrocarburizing improve the corrosion resistance of metal surfaces by forming a protective layer of nitrides or oxides on the surface. This is particularly important for brake system components and suspension parts that are regularly exposed to harsh environmental conditions.

Thermal Stability and Resistance:

Components like pistons, brake rotors, and camshafts are regularly exposed to high temperatures during engine operation or braking. Composite heat treatment enhances the thermal stability of these parts, allowing them to maintain their mechanical properties and dimensional stability even at elevated temperatures. Processes such as quenching and tempering improve the ability of metal parts to resist thermal deformation, ensuring that they function reliably even in high-temperature environments.

Composite Heat Treatment Processes Used in Auto Parts Manufacturing

Carburizing:

Carburizing is a heat treatment process that introduces carbon into the surface of steel components, forming a hard outer layer while maintaining a tough core. This process is commonly used for gears, crankshafts, and other power transmission components. The hardened surface is highly resistant to wear and fatigue, while the softer core ensures that the part can absorb impact without fracturing.

Nitriding:

Nitriding is a process that diffuses nitrogen into the surface of metal components to create a hard, wear-resistant layer. This process is often used on camshafts, crankshafts, and hydraulic components. Nitriding offers excellent wear and fatigue resistance without the need for post-treatment machining, as it doesn’t cause dimensional distortion.

Induction Hardening:

Induction hardening involves heating the surface of a component using electromagnetic induction and then rapidly cooling it to increase surface hardness. This process is frequently used for drive shafts, CV joints, and gears to improve their wear resistance and durability.

Carbonitriding:

Carbonitriding is similar to carburizing but also introduces nitrogen into the surface layer. This process enhances both the hardness and corrosion resistance of components. It is particularly useful for parts like brake components and pistons that need to resist both wear and corrosive environments.

Quenching and Tempering:

Quenching involves rapidly cooling a heated metal part to lock in its hardness, followed by tempering to reduce brittleness. This composite heat treatment process is often applied to suspension components, axles, and drive shafts to increase their strength and toughness while maintaining flexibility.

Conclusion

Composite heat treatment is a vital process in the automotive industry, ensuring that critical components like gears, camshafts, pistons, brake rotors, and suspension parts can withstand the demanding conditions of modern vehicles. By improving surface hardness, wear resistance, fatigue strength, and corrosion resistance, composite heat treatment significantly enhances the functionality and longevity of auto parts.

As automotive technologies evolve and vehicles become more powerful and efficient, the importance of composite heat treatment in optimizing performance and durability will continue to grow. Manufacturers rely on these advanced treatment processes to produce parts that meet the rigorous demands of modern automotive engineering, ensuring that vehicles remain reliable, safe, and efficient for years to come.