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GB/T 38720-2020 English PDF (GBT38720-2020)

GB/T 38720-2020 English PDF (GBT38720-2020)

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GB/T 38720-2020: Microstructure examination of medium-carbon steel and medium-carbon alloy structural steel after quenching

This Standard specifies raw materials and requirements, inspection requirements, quenching microstructure grade and evaluation for common medium-carbon structural steel and medium-carbon alloy structural steel. This Standard is applicable to inspection and evaluation of microstructure after parts quenching and tempering of medium-carbon structural steel and mediumcarbon alloy structural steel.
GB/T 38720-2020
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 25.200
J 36
Microstructure examination of medium-carbon steel
and medium-carbon alloy structural steel after
quenching
ISSUED ON: MARCH 31, 2020
IMPLEMENTED ON: OCTOBER 01, 2020
Issued by: State Administration for Market Regulation;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Terms and definitions ... 5
4 Raw materials and requirements ... 5
5 Inspection requirements ... 6
6 Quenching structure level and microstructure evaluation ... 7
7 Inspection report ... 13
Annex A (informative) Standard spectrum of microstructure level after
quenching + medium temperature tempering (450??C) ... 14
Annex B (informative) Standard spectrum of microstructure level of quenching + high temperature tempering (600??C) ... 21
Microstructure examination of medium-carbon steel
and medium-carbon alloy structural steel after
quenching
1 Scope
This Standard specifies raw materials and requirements, inspection
requirements, quenching microstructure grade and evaluation for common
medium-carbon structural steel and medium-carbon alloy structural steel. This Standard is applicable to inspection and evaluation of microstructure after parts quenching and tempering of medium-carbon structural steel and medium- carbon alloy structural steel.
This Standard is not applicable to evaluation of microstructure that contains decarburization, over-burning as well as microstructure under isothermal quenching after parts quenching and tempering of medium-carbon structural steel and medium-carbon alloy structural steel.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 699, Quality carbon structure steels
GB/T 1979, Standard diagrams for macrostructure and defect of structural steels
GB/T 3077, Alloy Structure Steels
GB/T 6394, Metal - Methods for estimating the average grain size
GB/T 7232, Terminology of metal heat treatment
GB/T 10561, Steel - Determination of Content of Nonmetallic Inclusions - Micrographic Method Using Standards Diagrams
Fine series ???2.5 ???2.0 ???1.5 ???2.0
???2.0 Coarse
series ???2.0 ???1.5 ???1.0 ???1.5
4.5 The raw material band structure is tested according to GB/T 34474.1. The band structure in Cr-Mo, Cr-Ni-Mo steels shall not be greater than level 3. For other steels, it shall not be higher than level 2.
4.6 The acid-leaching microstructure of raw materials shall be tested according to GB/T 1979. There shall be no visually visible residual shrinkage holes, bubbles, cracks, inclusions, skinning, white spots, interaxial cracks. The level of ingot segregation, center segregation, center looseness and general
looseness shall not be greater than 2.
5 Inspection requirements
5.1 Inspectors shall undergo professional training and obtain corresponding employment certificates. At the same time, they shall have basic knowledge of metal materials and heat treatment, as well as the preparation and use of corrosive agents, inspection quality and other knowledge, in accordance with relevant requirements of GB/T 34895.
5.2 The temperature, humidity, vibration, and noise of the testing environment shall meet the requirements for the use of metallographic inspection equipment, including sample preparation equipment, and related safety requirements. 5.3 In general, the test specimens shall be prepared by mechanical methods under the cold conditions of the representative service area. If prepared by hot cutting method, the heat affected zone shall be completely removed. The effective wall thickness, chemical composition, state before heat treatment and heat treatment batch of the specimen shall be able to characterize the tested parts.
5.4 The metallographic examination of sample preparation, grinding and
polishing shall be carried out in accordance with the provisions of GB/T 34895. During the preparation process, there shall be no phenomenon of tissue change due to heat. The etching agent is 4% nitroethanol solution. The waste liquid generated during the inspection process shall be disposed of after
neutralization and centralized disposal.
5.5 Quenching and tempering test specimens are randomly observed at 500 times magnification for more than 5 representative fields of view. Compare with the standard spectrum to determine the structure level.
5.6 The optical microscope shall meet the requirements of testing accuracy.

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