GB/T 9943-2025 in English

In-depth Interpretation of the GB/T9943-2025 High-Speed Tool Steel Standard

The release and implementation of the national standard GB/T9943-2025 "High-Speed Tool Steel" marks a new stage in the technical specifications of high-speed tool steel in my country. This standard integrates and replaces the three standards GB/T9943-2008, GB/T9941-2009, and GB/T36708-2018, achieving unified specifications for the technical requirements of high-speed tool steel bars, steel plates, and pre-hardened steel.

Analysis of Key Changes in the Standard Revision

Compared with the 2008 version of the standard, the main technical changes in the 2025 version are reflected in multiple dimensions:

In-depth analysis of chemical composition system

The new standard includes 20 high-speed steel grades, which are divided into two categories according to the alloy system:

Tungsten high-speed steel: represented by W18Cr4V and W12Cr4V5Co5, traditional tungsten steel has excellent thermal stability and red hardness, but carbide segregation is serious and the processing performance is relatively poor.

Tungsten-molybdenum high-speed steel: Including 18 grades such as W6Mo5Cr4V2 and W9Mo3Cr4V. By partially replacing tungsten with molybdenum, the carbide distribution is improved, and the toughness and thermoplasticity are enhanced, making it the mainstream choice for modern high-speed steel.

The three newly added grades, W6Mo5Cr4V2Co2, W10Mo2Cr4V5Co8 and W7Mo7Cr4V7Co11, are all high-performance cobalt high-speed steels with extremely high red hardness and wear resistance, and are suitable for processing difficult-to-cut materials.

Heat treatment process technical requirements

The standard specifies the heat treatment process parameters for various types of high-speed steel in detail:

Organization and performance quality control requirements

Carbide unevenness control

The standard stipulates strict carbide unevenness qualification levels based on product dimensions:

• Nominal size

Control of Bulk Carbides

For tungsten and tungsten-molybdenum steel bars of different sizes, the standard specifies corresponding acceptable levels of bulk carbides to ensure the uniformity of the material structure and performance.

Control of Non-Metallic Inclusions

For the first time, the acceptable levels of non-metallic inclusions are clearly defined. The requirements for electroslag remelted steel are higher than those for non-electroslag remelted steel, reflecting the high emphasis on purity.

Technical Specifications for Pre-hardened High-Speed Steel

A major highlight of the new standard is the detailed specifications for pre-hardened high-speed steel bars:

Hardness Requirements: The hardness of pre-hardened steel is negotiated between the supplier and buyer, with the hardness deviation within the same batch no greater than 1.5 HRC, ensuring product consistency.

Decarburization Layer Control: Strict decarburization layer depth requirements are specified for different diameters, and no decarburization layer is permitted in pre-hardened, ground steel bars.

Metallographic Structure: The required structure is tempered martensite plus carbides, with an overheating level no greater than Level 1 and a tempering level no greater than Level 2.

Dimensional Accuracy: Pre-hardened steel bars are produced to H10 accuracy, while pre-hardened, ground steel bars are produced to H9 accuracy, meeting the requirements of precision machining.

Application fields and selection guide

According to the main characteristics and uses of each grade provided in Appendix A, the application of high-speed tool steel can be summarized as follows:

Testing Methods and Quality Control

The standard specifies a complete testing system:

Chemical Composition Analysis: Standard methods such as GB/T223 and GB/T4336 are used to ensure accurate control of element content. Hardness Testing: Use a Rockwell hardness tester, Brinell hardness tester, or Vickers hardness tester, selecting the appropriate method based on the specific condition. Microstructure Examination: This includes macrostructure, eutectic carbide heterogeneity, and bulk carbides, graded using a metallographic microscope and other equipment. Decarburization Layer Detection: Follow the methods specified in GB/T224 to ensure surface quality meets requirements. Implementation Recommendations and Precautions: Material Selection Recommendations: 1. Select the appropriate grade based on the material characteristics: For ordinary steel, choose W6Mo5Cr4V2; for difficult-to-machine materials, choose cobalt-containing high-performance high-speed steel. 2. Consider processing requirements: For precision machining, choose pre-hardened, ground steel bars; for general machining, choose hot-rolled, annealed steel. 3. Focus on dimensional accuracy: For precision tool manufacturing, choose H9 grade accuracy; for general tools, choose H10 grade accuracy.

Heat Treatment Process Control

1. Perform heat treatment strictly within the temperature range specified in the standard to avoid overheating or underheating.

2. Pay attention to preheating, especially when heating in a salt bath furnace. Sufficient preheating is essential.

3. The tempering process must be thorough, generally using three tempering cycles to ensure complete microstructural transformation.

Key Quality Inspection Points

1. Strengthen incoming product inspection, especially focusing on key indicators such as chemical composition and hardness.

2. Pay attention to microstructural inspection. Carbide unevenness and large carbides directly affect tool life.

3. Surface quality inspection cannot be neglected. The depth of the decarburized layer affects the ultimate performance of the tool.

Technical and Economic Significance of the Standard Implementation

The implementation of GB/T9943-2025 will have a profound impact on the high-speed tool steel industry:

Technical Improvement: Unified technical specifications promote product quality improvements and drive technological progress in the industry.

Resource Optimization: A reasonable grade system avoids resource waste and improves material utilization efficiency.

International Integration: Appendix C provides a comparison of domestic and foreign grades, which is conducive to international trade and technological exchanges.

Application Expansion: The newly added high-performance grades meet the modern manufacturing industry's demand for high-end cutting tools.

As a basic technical specification in the field of high-speed tool steel, this standard provides a comprehensive technical basis for tool manufacturers and will surely promote the development of my country's tool steel industry towards high quality.