This standard specifies the spheroidization grade assessment and technical requirements for low-carbon structural steel, low-carbon alloy structural steel, medium-carbon structural steel, medium-carbon alloy structural steel and free-cutting structural steel. This standard is applicable to the organization rating of cold heading, cold extrusion, cold bending and automatic machine tool cutting and other industrial steels. JB/T 5074-1991 Spheroidization rating of low and medium carbon steel JB/T5074-1991 Standard download decompression password: www.bzxz.net

Mechanical Industry Standard of the People's Republic of China
JB/T 504---1991
Rating of Spheroidized Body of Low and Medium Carbon Steel
Published on June 11, 1991
Implementation by the Ministry of Machinery and Electronics Industry of the People's Republic of China on July 1, 1992
Mechanical Industry Standard of the People's Republic of China
Rating of Spheroidized Body of Low and Medium Carbon Steel
1 Subject Content and Scope of Application
JB/T5074—1991
This standard specifies the spheroidized body grade assessment and technical requirements for low carbon structural steel, low carbon alloy structural steel, medium carbon structural steel, medium carbon alloy structural steel and free-cutting structural steel.
This standard is applicable to the organization rating of steel for cold heading, cold extrusion, cold bending and automatic machine tool pre-cutting processing. 2 Reference standards
GB7232 Terminology of metal heat treatment processes
3 Terminology
Point-shaped spheroidization
The spheroidized particles of carbides in pearlite are fine, and are dot-shaped when observed under a microscope (400~500 times), and spherical when observed at high magnification. 4 Technical requirements
4.1 Organization rating of cold shock, cold extrusion and cold bending 4.1.1 Low-carbon structural steel may not be inspected for pearlite structure; low-carbon alloy structural steel must be rated as agreed upon by both the supply and demand parties. 4.1.2 For medium-carbon structural steel and medium-carbon alloy structural steel, deformation ≤80%, 4~6 grades are qualified: deformation >80%, 5~6 grades are qualified. 4.2 Organization rating of steel for automatic machine tools
4.2.1 For free-cutting structural steel, the organization is 1~4 grades. 4.2.2 Low carbon structural steel, low carbon alloy structural steel, medium carbon structural steel and medium carbon alloy structural steel, 1~3 levels are qualified. 5 Test specimens
5.1 The test specimens shall be selected from representative parts of the heat treatment furnace, and generally 3~5 samples shall be selected according to the effective heating zone size of the furnace. 5.2 During the cutting and preparation process of the metallographic specimens, there shall be no phenomenon of structural changes caused by heat. 5.3 After the metallographic specimens are ground and polished, they shall be corroded with 2%~5% nitric acid alcohol. Select more than 3 representative fields for evaluation. 6 Spheroidization classification
6.1 The evaluation of the spheroidization grade shall be comprehensively evaluated based on the morphology, quantity, size and distribution of its organization. The magnification is generally 400 times.
6.2 The classification instructions are shown in Table 1 and Figure 1, Table 2 and Figure 2, Table 3 and Figure 3 respectively. 6.3 The classification of the spheroidization of free-cutting structural steel shall be evaluated according to its chemical composition in accordance with Article 6.2. Approved by the Ministry of Machinery and Electronics Industry on June 11, 1991 and implemented on July 1, 1992
JB/T5074-1991
Table 1 Spheroidized body classification group of low carbon structural steel and low carbon alloy structural steel
Pearlite + ferrite
Pearlite and a small amount of spheroidized body + ferrite
Spheroidized body and pearlite + ferrite
Spheroidized body and a small amount of pearlite + ferrite
Point-shaped spheroidized body and a small amount of pearlite + ferrite Spheroidized body + ferrite
Figure 1—Grade 11
Figure 1—Grade 33
Figure 122 grade
Figure 1-44 grade
Figure 1--55 grade
JB/T5074-1991
Figure 1-66 grade
Figure 1 Spheroidized body classification diagram of low carbon structural steel and low carbon alloy structural steel 400x
Table 2 Spheroidized body classification of medium carbon structural steel
Pearlite + ferrite
Pearlite and a small amount of spheroidized body + ferrite
Pearlite and spheroidized body + ferrite
Point-shaped spheroidized body and a small amount of pearlite + ferrite Point-shaped spheroidized body and a small amount of spheroidized body + ferrite Uniformly distributed spheroidized body + ferrite Rope
Figure 211 grade
Figure 2-22 grade
Figure 2-33 grade
Figure 2-
JB/T5074-1991
Figure 2-44 grade
Figure 2-66 grade
Figure 2 Spheroidal body classification diagram of medium carbon structural steel: 400×Table 3 Spheroidal body classification of medium carbon alloy structural steel
Pearlite + ferrite
Pearlite and a small amount of spheroidized body + ferrite
Spheroidized body and pearlite + ferrite rope
Point-shaped spheroidized body and a small amount of pearlite + ferrite Spheroidized body and point-shaped Spheroidized body + ferrite
Uniform distribution Spheroidized body + ferrite
Figure 3-11 grade
Figure 3-33 grade
JB/T5074-1991
Figure 3-22 grade
Figure 3-44 gradewww.bzxz.net
Additional explanation:
Figure 3-55 grade
JB/T5074-1991
Figure 3 Spheroidized body classification diagram of medium carbon alloy structural steel Figure 3-66 grade
This standard was proposed by the National Technical Committee for Heat Treatment Standardization and is under the jurisdiction of the Beijing Electromechanical Research Institute of the Ministry of Machinery and Electronics Industry. This standard was drafted by the Beijing Electromechanical Research Institute of the Ministry of Machinery and Electronics Industry, the First Automobile Manufacturing Plant, the Second Automobile Manufacturing Plant, and the Wuhan Automobile Standard Parts Factory.
The main drafters of this standard are Zhao Deyin, Jing Liyuan, Cao Aofang, Zhang Shumei and Gao Xiangsheng.
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