Current status of heat treatment standards for titanium and titanium alloys in china

The classification of heat treatment of titanium and titanium alloys is introduced, and the common standards of heat treatment of titanium and titanium alloys at home and abroad are summarized; This paper analyzes the problems existing in the understanding and application of heat treatment system in titanium and titanium alloy processing enterprises in China at the present stage, and looks forward to the development trend of heat treatment standards for titanium and titanium alloy in the future.

Titanium is an important structural metal developed in the 1950s. It has low density, high specific strength, corrosion resistance, high temperature resistance, non-magnetic and other excellent properties, as well as four major functions of shape memory, superconductivity, hydrogen storage, and biocompatibility. It is widely used in aviation, aerospace, ships, weapons, nuclear, chemical, seawater desalination, medical equipment, environmental protection and other fields, It plays an important role in national economic development and national defense industry [1].
In order to optimize the structure and properties of titanium and titanium alloys, heat treatment is considered as a key process in titanium production. The martensitic transformation of titanium and titanium alloys during heat treatment will not cause significant changes in the alloy and may cause brittleness ω It is difficult to refine grains through phase and allotropic transformation, with poor thermal conductivity and high chemical activity β Large phase transition temperature difference β When the phase area is heated β The heat treatment of titanium and titanium alloys must be carried out in combination with chemical composition and historical processing technology to obtain the required structure and properties. The selection of appropriate heat treatment standards and processes for titanium and titanium alloys has become an important link for titanium and titanium alloy products to obtain the best matching relationship between the structure and properties to meet the use.

1. Classification of titanium and titanium alloy heat treatment

The heat treatment of titanium and titanium alloys is mainly divided into three categories: heat treatment, surface heat treatment and diffusion heat treatment to improve the structure and comprehensive properties. See Table 1 for details.

2. Current situation and development trend of titanium and titanium alloy heat treatment standards

2.1 Current status of titanium and titanium alloy heat treatment standards

The titanium industry in China started relatively late, and the corresponding titanium and titanium alloy systems were established mainly by copying foreign materials and making them domestically. Therefore, the heat treatment system for titanium and titanium alloys in practical application was gradually explored and determined on the basis of relevant foreign materials, combined with the actual heat treatment equipment status and application needs in China, and then gradually realized the embryonic form of standardization of titanium and titanium alloy heat treatment through specifications. Compared with the development of titanium and titanium alloy products, the established special heat treatment standards for titanium and titanium alloys involve few brands and cover incomplete application fields of products, resulting in that the heat treatment system used for titanium and titanium alloys is mainly the heat treatment system recommended in the standards for titanium and titanium alloy products. At present, the heat treatment system and basis selected for titanium and titanium alloy products in China are mainly Chinese national standards, American standards and Russian standards. See Table 2 for the main special standards for heat treatment involved; See Table 3 for heat treatment system of typical alloy; See Table 4 for general basic standards of heat treatment.
The establishment of the titanium and titanium alloy system in the United States is mainly aimed at the aviation and aerospace industries, and has formulated special titanium and titanium alloy heat treatment standards. The heat treatment of titanium and titanium alloy grades involved in the United States is included in its heat treatment standards, and the standards are updated rapidly; At the same time, the heat treatment system and requirements specified in the American Aerospace Standard AMS and other product standards are matched to meet the heat treatment requirements of special and general titanium and titanium alloy materials.
Table.1 Classification of heat treatment of titanium and titanium alloys

Classification		Definition [3,5]
Heat treatment for improving structure and comprehensive properties	Thermomechanical treatment	For pure titanium and titanium alloy a β Titanium alloy heated to β No fine equiaxed crystal structure can be obtained only by heat treatment above the phase transformation point, β The titanium plate is heated to β The grain will also grow rapidly above the phase transition point. In order to obtain fine grains, it is necessary to conduct hot or cold working to strain them before heat treatment and recrystallization.
	Stress relief annealing	Heat treatment that reduces the residual stress of crystallization without causing recrystallization of the structure. When titanium is worked, its plasticity will be reduced due to work hardening. Heat treatment that softens titanium by eliminating strain hardening, recrystallization or precipitation accumulation caused by work.
	Annealing	When titanium is worked, its plasticity will be reduced due to work hardening. Heat treatment that softens titanium by eliminating strain hardening, recrystallization or precipitation accumulation caused by work.
	Recrystallization annealing	Annealing heated above recrystallization temperature depends on recrystallization to eliminate work hardening or adjust microstructure.
	β annealing	Taijin β Chasing at appropriate temperature above the transition point.
	Isothermal reflow	A heat treatment to stabilize the alloy structure. stay β Heating at a certain temperature below the transition point is cooled in the furnace or converter to the specified temperature and kept at this temperature for a certain time before air cooling to room temperature.
	Double annealing	Heat treatment with air cooling in two stages. In the first stage, the metastable phase is retained during air cooling, while in the second stage, the metastable phase is decomposed during heat preservation.
	Triple annealing	The heat treatment of triple annealing. During triple annealing, the first time is solution treatment, which is mainly used to adjust the primary phase A and transformation β Ratio between phases. The second treatment was to obtain stable tissue. The third time is aging strengthening treatment. The effect of stabilizing the structure and increasing the strength can be obtained simultaneously by triple annealing.
	Fixation	Heat treatment in which the alloy is heated to an appropriate temperature and kept at this temperature for a sufficient time to make the soluble components completely dissolve into the solid solution and maintain an unstable state after quenching. about β Titanium alloy is used to heat the alloy to β Above the phase transition point, a phase disappears and becomes β single-phase. a+ β Titanium alloy is generally heated. reach β The temperature at a slightly lower phase transition point β The proportion of phases increases.
	Quench	The process of contacting the heated alloy with the cooling medium and cooling it from a certain temperature at a speed fast enough to retain part or all of the soluble components in the solid solution.
	Prescription	After solution treatment, it shall be kept at an appropriate temperature for enough time to precipitate the second phase from the unstable solid solution, which results in a strengthened heat treatment. It can also make the precipitation of intermetallic carbides in the alloy reach high strengthening.
	Vacuum heat treatment	To remove hydrogen or prevent oxygen and nitrogen The pollution of hydrogen and other harmful gases makes titanium and titanium alloys undergo heat treatment under vacuum conditions, such as vacuum annealing.
Surface heat treatment		The surface chemical or physical heat treatment of titanium alloy final product parts mainly improves the surface wear resistance, and the chemical vapor deposition (CVD), physical vapor deposition (PVD) and other coating technologies for corrosion resistance, oxidation resistance and other properties are also included.
Diffusion heat treatment		In order to improve the strength of diffusion welding and to eliminate the solidification segregation and homogenize it after sintering in powder metallurgy, the diffusion between atoms should be promoted through heat treatment.

Russia inherits the titanium and titanium alloy system established by the former Soviet Union and mainly serves the aviation, aerospace, ship and nuclear industries. Due to the difference in design concept, the standard system of materials and heat treatment established by Russia is different from the standard system of titanium and titanium alloy heat treatment established by the United States. It is mainly used in the former Soviet Union and countries that introduced Russian titanium and titanium alloy systems. Generally, there is no separate heat treatment system involved in product standards, and the established heat treatment system for titanium and titanium alloys is complete and versatile; Specific process and good operability; Both principle and process practice [6].

Table.2 Heat treatment standards of titanium and titanium alloys

Standard	Brand involved	Type of heat treatment involved
GB/T 37584-2019	TAl、TA2、TA3、TA7、TA11、TA15、TA18、TA19 、TA21、TC1、TC2、TC4、ZTC4、TC6、TC10、 TC11、TC16、TC17、TC18、TC19、TC21、 ZTC3、ZTC5、TB2、TB3、TB5、TB6	Ordinary annealing, double annealing, isothermal annealing β  Annealing, stress relief annealing, solution, aging
GJB 3763A-2004	TA0、TA0-1、TA1、ZTA1、TA2、TA3、TA5 、TA6、TA7、ZTA7、TA7ELI、TA9、TA10、 TA11、TA12、TA13、TA15、TA15-1、TA15-2、 TA16、TA18、TA19、TA20、TA21、TC1、TC2、 ZTA5、ZTA15、TC3、TC4、ZTC4、TC6、TC9、 TC10、TC11、TC16、TC17、TC18、ZTC3、 ZTC5、TB2、TB3、TB5、TB6、TB8	Ordinary annealing, double annealing, isothermal annealing β  Annealing, stress relief annealing, solution, aging
HB/Z 137-2014	TA1-1、TA1、TA2、TA3、TA4、TA5、TA6 、TA7、TA7ELI、TA9、TA10、TA11、TA12、 TA13、TA15、TA15-1、TA15-2、TA16、TA18、 TA19、TA20、TA21、TC1、TC2、TC3、TC4、 TC4-DT、TC6、TC9、TC10、TC11、TC16、 TC17、TC18、TC21、TB2、TB3、TB5、TB6、 TB8、TB12、ZTA2、ZTA3、ZTA4、ZTA7、 ZTA15、ZTC3、ZTC4、ZTC5、ZTC6	Ordinary annealing, full annealing, double annealing, isothermal annealing, triple annealing β  Annealing, leveling β  Annealing, stress relief annealing, solution, aging, vacuum heat treatment
HB/Z 419-2017	Ti40、Ti55、Ti70、Ti-5Al-2． 5Sn、Ti-5Al-2． 5Sn ELI、Ti-8Al-1Mo-1V、Ti-3Al-2． 5V、Ti-6Al-2Sn 4Zr-2Mo、Ti-6Al-4V、Ti-6Al-4VELl、Ti-6Al-6V-2Sn、Ti-6Al-2Sn-4Zr-6Mo、Ti-15V-3Al-3Cr-3Sn、Ti-10V-2Fe-3Al	Ordinary annealing β  Annealing, stress relief annealing, solution, aging
AMS-H-81200D	Commercially Pure Titanium ( All grades) 、5Al-2.5Sn、6Al-4V、13V-11Cr-3Al、5Al-2.5Sn ELI、6Al-4VELI、3Al-8V-6Cr-4Mo-4Zr、6Al-2Cb-1Ta-0.8Mo、6Al-6V-2Sn、15V-3Al-3Cr-3Sn、8Al 1Mo-1V、3Al-2.5V、10V-2Fe-3Al、6Al-2Sn-4Zr-2Mo、6Al-2Sn-4Zr-6Mo、6Al-2Sn-2Zr-2Mo-2Cr 0.25Si、5Al-2Sn-2Zr-4Mo-4Cr、11Sn-5Zr-2Al-1M	Ordinary annealing β  Annealing, recrystallization annealing, double annealing, stress relief annealing β  Solution treatment, two-phase solution, aging
AMS 2801 B	Commercially Pure Titanium ( All grades) 、6Al-4V( ELI) 、3Al-8V-6Cr-4Mo-4Zr、3Al-2.5V、6Al 6V-2Sn、13V-11Cr-3Al、5Al-2.5Sn、6Al-2Sn-4Zr-2Mo、10V-2Fe-3Al、8Al-1Mo-1V、6Al-2Sn-4Zr 6Mo、15V-3Al-3Cr-3Sn、6Al-4V	Annealing, stress relief, aging, over aging, cold working+aging β  Solution treatment+overaging, solution treatment β  Solution treatment, solution treatment+aging, solution treatment+overaging
No.685-76	BT3-1、OT4-1、OT4、BT6C、BT14、BT16、BT20、IIT-7M	Annealing, quenching and aging
BAC 5613	Commercially Pure Titanium ( All grades) 、Ti-6Al-4V、Ti-4Al-3Mo-1V、Ti-6Al-6V-2Sn、Ti-7Al 4Mo、Ti-8Al-1Mo-1V、Ti-13V-11Cr-3Al	Annealing, solution, aging, stress relief β  annealing

Table.3 Typical TC4 titanium alloy heat treatment system

Standard	Country	Grade	Nominal composition	Product type	Heat treatment system (ordinary annealing)
GB/T 2965-2007	China	TC4	Ti-6Al-4V	Bar	700-800 ℃, heat preservation for 1-3h, air cooling.
GJB 1538A-2008	China	TC4	Ti-6Al-4V	Bar	700-800 ℃, heat preservation for 1-4h, air cooling.
GJB 2219A-2008	China	TC4	Ti-6Al-4V	Wire and bar	700-850 ℃, heat preservation 0.5-2h, air cooling or furnace cooling.
GJB 3763A-2004	China	TC4	Ti-6Al-4V	Wire, bar, forging	700-850 ℃, heat preservation for 1-2h, air cooling or slower cooling.
GB/T 37584-2019	China	TC4	Ti-6Al-4V	Bars and forgings	705-790 ℃, heat preservation for 1-2h, air cooling or slower cooling.
HB/Z 137-2014	China	TC4	Ti-6Al-4V	Bars and forgings	700-850 ℃, heat preservation for 1-2h, air cooling or slower cooling.
AMS 4928W	U.S.A	6Al-4V	Ti-6Al-4V	Wire rods – Bars, forgings	704-788 ℃, heat preservation not less than 1h, cooling as required.
AMS-H-81200D	U.S.A	6Al4V	Ti-6Al-4V	Wire, bar, forging	705-790 ℃, heat preservation for 1-2h, air cooling.
No.685-76	Russia	BT6	Ti-6Al-4V	Bars and forgings	750-900 ℃, based on section thickness, air cooling.
BS 3TA11	Britain	BS TA11	Ti-6Al-4V	Bar	700-800 ℃, heat preservation not less than 1h, air cooling or furnace cooling.

Japan’s titanium and titanium alloy systems mainly serve the civil market, such as chemical industry, building materials and other fields. The system has obvious uniqueness, mainly consisting of corrosion resistant materials, mostly pure titanium and low alloy titanium alloys. The heat treatment standards are mostly formulated within the enterprise, and are matched with titanium and titanium alloy processing material systems.

Table.4 Typical basic standards for heat treatment of titanium and titanium alloys

Standard No	Standard name
GB/T 6611-2008	Terminology and metallography of titanium and titanium alloys.
GB/T 7232-2012	Terminology of metal heat treatment process.
GB/T 8121-2012	Terminology of heat treatment process materials.
GB/T 9452-2012	Measuring method for effective heating zone of heat treatment furnace.
GB/T 12603-2005	Classification and code of metal heat treatment process.
GB/T 13324-2006	Terminology of heat treatment equipment.
GB 15735-2012	Safety and health requirements for metal heat treatment production process.
GB/T 17358-2009	Calculation and measurement method of power consumption in heat treatment production.
GB/T 23603-2009	Detection method for surface contamination layer of titanium and titanium alloy.
GB/T 27946-2011	Limit of harmful substances in the air of heat treatment workplace.
GB/T 30822-2014	Technical requirements for environmental protection of heat treatment.
GB/T 30825-2014	Heat treatment temperature measurement.
GB/T 32541-2016	Heat treatment quality control system.
GB/T 34895-2017	General rules for metallographic examination of heat treatment.
GB/T 34647-2017	Status code of titanium and titanium alloy products.
GB/T 36561-2018	Technical requirements and evaluation system for clean and energy-saving heat treatment equipment.
GJB 509B-2008	Quality control of heat treatment process.
JB/T 6955-2008	Technical requirements for quenching medium commonly used in heat treatment.
JB/T 13026-2017	Oil based quenching medium for heat treatment.

2.2 Development trend of titanium and titanium alloy heat treatment standard system

The heat treatment standard of titanium and titanium alloy is a technical document for strict production process conditions, which is a powerful measure to achieve comprehensive management of heat treatment production. The preparation and revision of heat treatment standards in major titanium producing countries in the world have the following development trends:

• 1) Basic standard for heat treatment of strengthened titanium and titanium alloys. Establish a perfect heat treatment standard system from the perspectives of heat treatment equipment, instrument and instrument temperature control accuracy, heat treatment medium quality, heat treatment quality inspection, unified heat treatment terminology, and economic experience process system matching with the process.
• 2) Emphasize the technical level of personnel, and formulate corresponding personnel qualification standards.
• 3) Pay attention to management level. Evaluate whether the existing management level meets the requirements of titanium and titanium alloy heat treatment according to the continuous heat treatment quality management data (such as temperature, hardness, waste rate statistics, etc.).

3. Problems

With the rapid increase of titanium consumption in aviation, aerospace, chemical and other industries, domestic titanium processing material manufacturers have focused on the heat treatment of titanium and titanium alloys as the focus of product quality control, but there are still many problems.

• 1) There is a big gap between the manufacturing level of heat treatment equipment and that of developed countries, which hinders the overall improvement of heat treatment quality of titanium and titanium alloys.
• 2) The popularity of advanced heat treatment processes (such as surface heat treatment processes) is low, and there is no support of relevant standards, leading to unstable service life and reliability of key titanium parts.
• 3) The technology and management standards supporting the heat treatment of titanium and titanium alloys need to be improved.
• 4) The domestic special standards for heat treatment of titanium and titanium alloys contain few brands, are slow to update, and cannot cover the heat treatment system and types in the product standards. It is necessary to further integrate resources and improve the applicability and universality of the standards.
• 5) In China, titanium and titanium alloys are mostly imported or imitated from abroad, lacking basic research on heat treatment and process matching; At the same time, China’s industrial grade sponge titanium has a trend of chasing low impurity content, which leads to that in the past decade, some pure titanium processing products are in line with product standards, and the heat treatment system is gradually breaking through the early experience temperature range.

4. Outlook

The special standards and general basic standards for heat treatment of titanium and titanium alloys that have been established in China provide rules for the implementation of total quality management of heat treatment of titanium and titanium alloys, and lay a foundation for the quality of heat treatment to reach the international level. However, there are still some difficulties, such as lack of basic research on titanium and titanium alloy heat treatment, few standardization personnel, long standard updating cycle, and incomplete heat treatment quality detection methods. The following work needs to be carried out in the future:

• 1) Strengthen the basic research on the influence of heat treatment of titanium and titanium alloys on the structure and properties of materials.
• 2) Accelerate the adoption of international standards and advanced foreign standards. Timely revise the heat treatment standards for titanium and titanium alloys with too long standard age to meet the market demand.
• 3) Strengthen the implementation of basic standards for heat treatment, and promote the establishment of a standard system for heat treatment of titanium and titanium alloys that integrates production, safety, environment, health and quality.
• 4) Further promote and implement the standards, train more heat treatment standardization staff, and promote the development of the industry.

Author: Hu Zhijie, Feng Junning, Ma Zhongxian, Xie Chen
Source: China Titanium Flanges Manufacturer: www.titaniuminfogroup.com
Reference:

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