Metallic materials are fundamental in modern industries for their mechanical strength, electrical and thermal conductivity, used from aerospace to daily utensils.
Metallurgical engineering involves extensive work in the extraction, processing, and performance optimization of metal materials.
Heat treatment alters metal microstructure through heating and cooling to control hardness, strength, toughness, and wear resistance.
Traditional heat treatments like quenching and tempering remain common but face limits in meeting modern industry’s advanced performance demands.
This article reviews heat treatment in metallurgy, its challenges, and future trends to improve metal processing.
Current Status of Metal Material Heat Treatment Processes
Metal heat treatment has long evolved, with annealing, normalizing, quenching, and tempering well established.
As requirements for material performance continue to rise, traditional processes have been continuously optimized and improved.
Advanced heating equipment enables precise temperature and speed control, improving heat treatment effectiveness.
New cooling media and methods reduce cracks and deformation, boosting yield rates.
New heat treatments like induction quenching and laser technology enhance metal surface wear, corrosion, and fatigue resistance.
However, current metal material heat treatment processes still face numerous challenges.
Existing processes struggle to precisely control microstructure and performance in complex-shaped metals with special requirements.
Traditional heat treatment can’t ensure uniform microstructure in large turbine disks, affecting reliability and lifespan.
On the other hand, energy consumption and environmental pollution issues are prominent in heat treatment processes.
Traditional heating wastes energy and some chemical treatments harm the environment.
Despite its flaws, metal heat treatment in metallurgy is rapidly advancing with new technologies emerging.
Future heat treatments will enhance materials and promote energy saving and emission reduction.
Important Role of Metal Material Heat Treatment Processes
As metallurgy advances, metal processing—especially heat treatment—gains importance.
In metallurgy, heat treatment controls improve metal properties; quenching and tempering boost steel strength and toughness.
annealing, on the other hand, reduces material hardness while enhancing ductility and machinability.
Heat treatment also modifies physical properties like conductivity, magnetism, and thermal expansion, crucial for special alloys’ functions.
Refined heat treatment creates finer, uniform grains and fewer defects, improving material performance.
normalizing treatment helps refine grains, eliminate internal stress, and improve machining performance.
Heat treatment uses phase changes to improve materials; for example, quenching turns steel’s austenite into hard, strong martensite.
Stress-relief annealing and similar heat treatments release internal stresses, ensuring dimensional stability and accuracy.
Heat treatment maintains precision parts’ shape and dimensional stability, preventing deformation from temperature changes.
Advanced heat treatments speed up processes, boost efficiency, recycle scrap, and cut production costs.
Shortcomings of Traditional Heat Treatment Processes for Metal Materials
High Energy Consumption
Traditional metal heat treatments in metallurgy no longer meet modern needs, with high energy consumption a major issue.
Heat treatment equipment typically requires long preheating and heating times—often lasting several hours—to achieve uniform temperatures in workpieces.
Traditional heaters use indirect heating with low efficiency, causing significant heat loss.
Long holding times and inadequate insulation in conventional processes lead to increased energy consumption due to significant heat loss.
Traditional cooling is slow and wastes heat, especially in liquid cooling where heat isn’t effectively recovered.
Severe Environmental Pollution
While traditional heat treatment processes enhance the performance of metallic materials, they also cause significant environmental pollution.
Oil-based cooling media used in processes such as quenching and tempering produce volatile organic compounds at high temperatures.
These substances not only pollute the environment but also pose health risks to humans.
Fossil-fuel heating furnaces emit significant nitrogen oxides during combustion.
Coal- or gas-fired heating equipment emits smoke and fine particles that harm air quality if untreated.
Heat treatment cleaning and acid washing generate toxic wastewater, needing strict treatment to avoid pollution.
Poor Precision and Consistency
Traditional heat treatments enhance metal performance but often lack precision and consistency in practice.
Traditional heat treatment relies on manual or basic automation, limiting precise temperature control.
This can result in uneven temperature distribution between the surface and interior of the workpiece, affecting the final heat treatment outcome.
Traditional processes rely on manual control of key parameters, causing variations from operator skill differences.
In large workpieces, uneven temperature changes between center and edges during holding hinder uniform consistency.
Traditional cooling methods like oil, water, or air lack flexibility for specific workpiece needs.
Cooling media and workpiece shape affect cooling rates, causing uneven microstructure and performance.
Traditional heat treatment processes often rely on the experience of operators, lacking scientific data analysis and optimization methods.
This approach makes it difficult to ensure consistent results in each processing cycle.
Analysis of Heat Treatment Processes for Metallic Materials
Induction Heating Surface Hardening of Metallic Materials
Induction surface hardening uses electromagnetic induction to generate eddy currents that rapidly heat and cool metal surfaces.
Since the current is concentrated on the surface of the workpiece (skin effect), the heating primarily affects the surface layer of the workpiece.
Induction heating offers rapid heating, often completed in seconds.
Immediate cooling is performed after heating to achieve the desired microstructure and properties.
Induction hardening heats faster, saving time and ensuring precise, uniform layers.
Concentrated heating cuts thermal stress and deformation, enabling automated mass production.
Induction heating surface hardening starts with cleaning the workpiece to remove oil, rust, and impurities for effective heating.
Next, choose an inductor matching the workpiece shape and size to ensure uniform magnetic field coverage.
Next, determine key parameters such as heating frequency, power density, heating time, and cooling medium to achieve optimal hardening results.
Finally, place the workpiece into the inductor, activate the power supply, and begin heating.
Monitor temperature to stay below limits; after heating, quickly spray coolant to form martensite.
Post-hardening tempering at 150–250°C reduces stress and boosts toughness and fatigue resistance.
Laser Heat Treatment Technology for Metal Materials
Laser heat treatment is a thermal processing method that uses high-energy-density laser beams to rapidly heat and cool the surface of metal materials.
By rapidly heating localized areas, laser processing allows precise control over depth and uniformity through adjustments in power, speed, and spot size.
Laser processing does not require direct contact with the workpiece, reducing the risk of mechanical wear and deformation.
Small heating area and short time cause rapid cooling, forming fine, uniform microstructures like martensite or amorphous phases.
Laser quenching heats metal surface above critical temperature, then rapidly cools to form hard martensite.
Powders or wires are melted onto the substrate through cladding, creating a durable and specialized alloy coating.
Laser annealing refines microstructure and relieves stress with low-power laser heating, improving ductility without overheating.
Laser shock peening uses pulsed lasers to induce compressive stress, boosting fatigue and corrosion resistance.
Ion nitriding treatment of metal materials
In metallurgical engineering, ion nitriding enhances metal performance by introducing nitrogen atoms into surfaces.
Ion nitriding uses active nitrogen ions in plasma to diffuse into metal surfaces at high temperatures, forming a hard nitride layer.
Operating at 400–600°C, ion nitriding uses lower temperatures than gas nitriding, reducing workpiece deformation.
High nitrogen ion concentration speeds up nitriding, achieving desired depth quickly.
The plasma uniformly covers the entire workpiece surface, ensuring consistency in the thickness and composition of the nitrided layer.
Ion nitriding first cleans and dries the workpiece surface to remove oil and oxides, ensuring quality.
Next, the workpiece is placed in an ion nitriding furnace where vacuum pumping removes oxygen and moisture to avoid reaction interference.
Next, inert gas is introduced, and high-voltage DC causes glow discharge, ionizing gas into positive ions and electrons.
Finally, nitrogen or ammonia gas is introduced, decomposing into nitrogen ions and hydrogen atoms under glow discharge.
Nitrogen ions bombard the workpiece surface, activating atoms and promoting nitrogen diffusion inside.
After nitriding, power and gas are stopped, and the workpiece cools naturally or forcibly before removal.
Future Development Trends in Metal Material Heat Treatment Processes
Advances in technology and industry drive metal heat treatment toward higher efficiency, precision, and eco-friendliness.
Sensors, AI, and big data enable real-time heat treatment control; machine learning ensures optimal parameters and consistent quality.
Robots integrated with heat treatment handle loading, unloading, and transfer, reducing labor and boosting efficiency.
New heat treatments use ultra-short lasers for precise micro/nano processing, adding functions and broadening applications efficiently.
New surface methods combine electrochemical reactions and heat treatment to create high-performance coatings.
Green manufacturing improves furnace design with efficient combustion and waste heat recovery, cutting energy use.
promoting the use of clean energy to reduce carbon emissions.
Conclusion
In summary, metallurgical heat treatment has advanced, enhancing materials and driving progress through optimized and new methods.
This article reviews recent advances in metal heat treatment, focusing on induction hardening, laser treatment, and ion nitriding.
Future metal heat treatments will evolve toward greater efficiency, precision, and sustainability amid new materials and diverse market demands.