►Heat Treatment Methods
Various heat treatment methods can be chosen based on specific objects and objectives.
Quenching and Tempering Steel: High-temperature tempering (500-650°C).
Spring Steel: Medium-temperature tempering (420-520°C) after quenching.
Carburizing Steel: Carburizing quenching followed by low-temperature tempering (150-250°C).
The strength of low carbon and medium carbon (alloy) steels decreases while plasticity and toughness increase with higher tempering temperatures after martensitic quenching. However, the influence of tempering temperature varies due to different carbon content in low and medium carbon steel. To achieve favorable overall mechanical properties, the following approaches can be adopted:
(1) Choose low carbon (alloy) steel and temper it at a temperature below 250°C after quenching to obtain low carbon martensite. Surface carburizing, which increases the carbon content of each surface layer, can improve the surface wear resistance of this type of steel, commonly known as carburized structural steel.
(2) Utilize high carbon steel, followed by quenching and tempering at high temperatures (500-650°C) to maintain sufficient strength while retaining high plasticity. This type of steel is generally referred to as quenching and tempering steel. If high strength with reduced plasticity and toughness is desired, low-temperature tempering of low carbon steel containing gold can be employed, resulting in "ultra-high-strength steel."
(3) For medium carbon and high carbon steel (e.g., 60,70 steel) and some high carbon steel (e.g., 80,90 steel) used in spring manufacturing, quenching and tempering are used to ensure high elastic limit, yield limit, and fatigue limit.
►Heat Treatment Process of Titanium Alloys
(1) Stress Relief Annealing: This process aims to eliminate or reduce residual stress generated during processing. It provides protection against chemical erosion and reduces deformation in corrosive environments.
(2) Full Annealing: The objective is to achieve good toughness, improve processing performance, facilitate reprocessing, and enhance dimensional stability and structural integrity.
(3) Solution Treatment and Aging: While α titanium alloys and stable β titanium alloys cannot be strengthened through heat treatment alone, they undergo annealing during production. α+β titanium alloys and metastable β titanium alloys containing a small amount of α phase can be further strengthened by solution treatment and aging.
Furthermore, to meet specific workpiece requirements, the industry employs additional metal heat treatment processes such as double annealing, isothermal annealing, β heat treatment, and deformation heat treatment.
