1. Introduction
Gray cast iron is one of the most widely used casting materials, with excellent casting properties and wide applications. The release and implementation of the new standard GB/T 9439-2023 “Gray Iron Castings” is of great significance for promoting the development and quality improvement of the gray iron casting industry. This article will comprehensively analyze and discuss the key changes and impacts of this standard.
2. Key Changes in the Standard
2.1 Normative Reference Documents
The new standard lists 19 normative reference documents, with 6 added and 4 deleted compared to the old standard. These changes reflect the updated requirements and advancements in the field of gray iron casting technology. The specific added and deleted standards are shown in the following table:
| Added Standards | Deleted Standards |
|---|---|
| GB/T223.72 Steel and alloy – Determination of sulfur content – Gravimetric method | GB/T231.2 Metallic materials – Brinell hardness test – Part 2: Verification and calibration of hardness testers |
| GB/T223.86 Steel and alloy – Determination of total carbon content – Infrared absorption method after combustion in an induction furnace GB/T9443 Cast steel and cast iron – Penetrant inspection GB/T20123 Steel – Determination of total carbon and sulfur content – Infrared absorption method after high-frequency induction furnace combustion (routine method) | GB/T231.3 Metallic materials – Brinell hardness test – Part 3: Calibration of reference blocks |
| GB/T38441 Pig iron and cast iron – Determination of chromium, copper, magnesium, manganese, molybdenum, nickel, phosphorus, tin, titanium, vanadium and silicon – Inductively coupled plasma atomic emission spectrometric method | GB/T7233.1 Steel castings – Ultrasonic examination – Part 1: Castings for general use |
2.2 Gray Iron Casting Grades
The chapter on gray iron casting grades in the new standard has been adjusted. The grades named by hardness level have been moved from the “Technical Requirements” chapter to the “Gray Iron Casting Grades” chapter. The new standard’s grades are in full correspondence with the ISO 185 standard. There are two naming methods for gray iron casting grades: by material strength level and by hardness level. Both the new and old standards specify 14 grades, with 8 grades named by strength level and 6 grades named by hardness level. The following table shows the tensile strength of gray iron casting samples named by strength level:
| Material Grade | Casting Main Wall Thickness/mm | Tensile Strength/MPa | Material Grade | Casting Main Wall Thickness/mm | Tensile Strength/MPa | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Single Cast Test Bar or Parallel Test Bar | Attached Cast Test Block | Single Cast Test Bar or Parallel Test Bar | Attached Cast Test Block W | |||||||||
| V | ≤ | ≥ | Newly Added ≤ | V | > | A | W | Newly Added ≤ | ||||
| HT100 | 5 | 40 | 100 | 200 | 5 | 10 | 250 | 350 | ||||
| HT150 | Newly Added 2.5 | 5 | 250 | 10 | 20 | |||||||
| 5 | 10 | 20 | 40 | 210 | ||||||||
| 10 | 20 | HT250 | 40 | 80 | 190 | |||||||
| 20 | 40 | 150 | 125(120) | 80 | 150 | 170 | ||||||
| 40 | 80 | 110 | 150 | 300 | 160 | |||||||
| 80 | 150 | 100 | HT275 | 10 | 20 | 275 | 375 | |||||
| 150 | 300 | 90 | 20 | 40 | 230 | |||||||
| HT200 | Newly Added 2.5 | 5 | 200 | 40 | 80 | 210(205) | ||||||
| 5 | 10 | 300 | 80 | 150 | 190 | |||||||
| 10 | 20 | 150 | 300 | 180(175) | ||||||||
| 20 | 40 | 170 | HT300 | 10 | 20 | 300 | 400 | |||||
| 40 | 80 | 155(150) | 20 | 40 | 250 | |||||||
| 80 | 150 | 140 | 40 | 80 | 225(220) | |||||||
| 150 | 300 | 130 | 80 | 150 | 210 | |||||||
| HT225 | 5 | 10 | 325 | 150 | 300 | 190 | ||||||
| 10 | 20 | 225 | HT350 | 10 | 20 | 350 | 450 | |||||
| 20 | 40 | 190 | 20 | 40 | 290 | |||||||
| 40 | 80 | 170 | 40 | 80 | 260 | |||||||
| 80 | 150 | 155 | 80 | 150 | 240(230) | |||||||
| 150 | 300 | 145 | 150 | 300 | 220(210) |
For gray iron castings named by material strength level, the new and old standards have the following differences:
- The expected tensile strength Rm(min) value of the casting body has been deleted and transferred to the informative appendix C.
- The tensile strength value of the parallel test bar has been added, which is the same as that of the single cast test bar.
- The casting main wall thickness of 2.5 – 5 mm and the corresponding tensile strength values for grades HT150 and HT200 have been added.
- The maximum tensile strength value of each grade of single cast test bar or parallel test bar has been increased.
- The minimum tensile strength values of some main wall thickness attached cast test blocks have been changed, and the values in the table with parentheses are the old standard values, which are 5 – 10 MPa higher than the old standard.
- The maximum and minimum tensile strength values of single cast test bars and parallel test bars are mandatory. For attached cast test blocks, in the old standard, the minimum tensile strength value is a mandatory value except for the casting main wall thickness of 150 – 300 mm, which is a guidance value; in the new standard, it is required that “with the consent of both the supplier and the purchaser, the tensile strength value of the attached cast test block representing the main wall thickness of the casting can also be a mandatory value”.
- The regulation of test bar types has been added. If the type of test bar is specified, a “/” should be added after the grade, followed by a letter to represent the type of test bar: /S represents single cast test bar or parallel test bar, /A represents attached cast test bar, /C represents body test bar. When the tensile strength is used as the acceptance index, the type of sample should be specified in the ordering agreement. If not specified in the ordering agreement, the supplier can decide on its own.
- The application of grade HT100 has been added, which is suitable for materials requiring high shock absorption and high thermal conductivity.
For gray iron castings named by hardness level, the new and old standards have the following differences:
- The grade representation method is different. The new standard consists of the cast iron code HT, the Brinell hardness symbol HBW, and the maximum hardness value of the casting with a main wall thickness of 40 – 80 mm; while the old standard consists of the symbol H and the maximum hardness value of the casting with a main wall thickness of 40 – 80 mm.
- The casting main wall thickness of 2.5 – 5 mm and the corresponding Brinell hardness values for grades HT – HBW155 and HT – HBW175 have been added.
- The regulation that “the Brinell hardness difference at a specific position of the casting is not greater than 40 HBW, which is only applicable to mass-produced castings. With the consent of both the supplier and the purchaser, the fluctuation range of the hardness value can be appropriately increased” has been added.
- The annotation that “at a position of the casting agreed upon by both the supplier and the purchaser, the hardness difference of the casting can be controlled within the 40 HBW hardness value range” has been deleted.
2.3 Technical Requirements
- The acceptance index of the mechanical properties of the casting: In the old standard, it should be clearly specified in the ordering agreement. In the new standard, it is that “if the acceptance items are not clearly specified in the ordering agreement, the supplier should take the tensile strength as the main acceptance basis”.
- The content in the “Note” of “Table 2 Hardness Grades and Casting Hardness of Gray Iron” in the old standard, such as “The relationship between hardness and tensile strength is shown in Appendix B, and the relationship between hardness and wall thickness is shown in Appendix C”, has been promoted to the standard text.
- The sampling position of the casting body: In the new standard, it is required to be agreed upon by both the supplier and the purchaser, and the content such as “If the purchaser has specific requirements, it should meet the purchaser’s drawings and technical requirements” and “If the purchaser requires sampling from the casting body but does not specify the sampling position of the body, the supplier can decide the sampling position according to the casting structure and stress condition” has been deleted.
- The detection frequency and quantity of tensile strength and hardness have been adjusted from the “Technical Requirements” chapter to the “Sample Preparation” chapter, and a subsection of “Detection Frequency and Quantity” has been listed separately to emphasize its importance. It is required that “the sampling frequency of the sample representing the casting material should be consistent with the quality control requirements of the supplier or agreed upon by both the supplier and the purchaser”.
- Two notes have been added: Note 1: The body performance values of the casting cannot be unified because they are closely related to factors such as the complexity of the casting, the wall thickness of the casting, and the cooling rate. Note 2: The tensile properties of the casting body sample are not only affected by the material properties but also by the defects at the sampling position.
- The test conditions for measuring Brinell hardness have been added: “Unless otherwise specified, HBW indicates the Brinell hardness measured under the test condition of 10/3000”.
- The content related to hardness in the old standard, such as “Note 1: The hardness grade classification is applicable to castings whose machinability and wear resistance are the main performance requirements” and “Note 2: For castings with a main wall thickness of t ≥ 80 mm, they are not classified by hardness”, has been promoted to the standard text.
- The hardness detection position has been modified from “If the purchaser has specific requirements for the test position and hardness value of the casting body, it should meet the purchaser’s drawings and technical requirements” to “Both the supplier and the purchaser should agree on the main wall thickness and the position of hardness detection, and clearly specify them in the ordering agreement. The hardness can also be detected on the sample”.
- The acceptance rule of hardness in the new standard does not distinguish the type of test bar, and the “Table 3 Tensile Strength and Hardness Values of Single Cast Test Bars” in the old standard has been deleted. The acceptance rule of hardness is the same for both the casting body and the single cast test bar.
- The metallographic structure has been revised from “The test method and test items of the metallographic structure should comply with the provisions of GB/T 7216” to “The graphite morphology of gray iron castings is mainly A-type graphite, with A-type graphite greater than 90%, and the total amount of carbides and phosphide eutectics in the matrix structure should be less than 1%”.
- The requirement of “The casting should comply with the purchaser’s protection, packaging, and storage and transportation specifications during the delivery process” in the surface quality has been deleted, and the “Special Requirements” section has been deleted. Nondestructive testing is a must.
2.4 Inspection Rules
- The sections of “Inspection Rights” and “Inspection Location” have been deleted.
- Regarding the batch division, the content has been changed from “The maximum weight of each sampling batch is 2000 kg of castings after cleaning. With the consent of both the supplier and the purchaser, the sampling batch can be changed” to “A total mass of 2000 kg of castings is a sampling batch”.
- The number of tensile strength tests has been changed from “At least one tensile test should be carried out for each sampling batch” to “One tensile test should be carried out for each sampling batch”.
- “Hardness test” has been added, that is, the hardness test can be carried out on the casting body, the tensile sample, or the hardness test block. One hardness test should be carried out for each sampling batch.
- Regarding the preservation of test data, both the new and old standards require the preservation of all complete original records of tests and inspections. However, the old standard does not specify the preservation period, while the new standard requires “The preservation period shall not be less than five years or in accordance with the period required by the customer”.
3. Impact on the Casting Industry
3.1 Standardization of Production
The implementation of the new standard will further standardize the production process of gray iron castings. The clear regulations on various aspects such as casting grades, technical requirements, sample preparation, and test methods provide a unified standard for enterprises, which 有助于 improve the consistency and stability of product quality. This is conducive to promoting the healthy development of the industry and enhancing the overall competitiveness of domestic gray iron casting products in the international market.
3.2 Quality Improvement
The new standard has made a series of adjustments and improvements to the technical requirements and test methods, which will promote enterprises to pay more attention to the quality control of products. For example, the stricter requirements for the tensile strength and hardness of castings, as well as the more detailed regulations on the metallographic structure, will encourage enterprises to optimize the production process, improve the quality of raw materials, and strengthen the quality inspection links, 从而 effectively improve the quality and performance of gray iron castings.
3.3 Technological Innovation
The changes in the standard also pose certain challenges to enterprises, which will prompt them to carry out technological innovation. For example, the development of new casting processes and technologies to meet the requirements of higher strength and thinner wall thickness of castings; the research and application of new testing methods and equipment to improve the accuracy and efficiency of testing. Technological innovation will not only help enterprises better comply with the new standard but also 推动 the continuous progress and development of the entire casting industry.
3.4 Market Access and Trade Facilitation
The new standard is more in line with international standards, which will facilitate the export trade of gray iron castings. Enterprises that comply with the new standard can more easily enter the international market and expand their business scope. At the same time, the unified standard also 有助于 reduce trade barriers and promote the smooth progress of international trade in the casting industry.
4. Conclusion
The release and implementation of GB/T 9439 – 2023 “Gray Iron Castings” is a major event in the casting industry. The standard has made a series of important changes and improvements, which will have a profound impact on the production, quality, technology, and market of gray iron castings. Enterprises should actively understand and master the new standard, strengthen technological innovation and quality management, and promote the sustainable development of the gray iron casting industry.
