GB/T 42851-2023
1517MPaMJ threaded bolts (English Version)
- Standard No.
- GB/T 42851-2023
- Language
- Chinese, Available in English version
- Release Date
- 2023
- Published By
- General Administration of Quality Supervision, Inspection and Quarantine of the People‘s Republic of China
- Latest
- GB/T 42851-2023
- Scope
- The structure, dimensions and technical requirements of 1517MPaMJ threaded bolts (hereinafter referred to as bolts) are applicable to the design, manufacture and acceptance of MJ threaded bolts with strength grades of 1~517MPa.
- Introduction
Analysis of the core content of the standard
Technical dimension GB/T 42851-2023 requirements Comparison of conventional bolt standards Material specification PH13-8Mo stainless steel (GB/T 20878) Usually alloy steel such as 30CrMnSiA is used Tensile strength 1515-1620MPa 800-1200MPa Thread process Cold/warm rolling after heat treatment (315-427℃) Machining before heat treatment Fatigue life ≥65,000 times (average value) No mandatory requirement usually
Detailed explanation of key technical requirements
1. Materials and heat treatment
The standard stipulates that PH13-8Mo precipitation hardening stainless steel should be used, and its solution treatment should be kept at 927℃±14℃ for 30-40 minutes, and then quickly cooled to below 16℃ within 1 hour. The aging temperature is selected in the range of 510-621℃ according to the hardness requirement, and the duration is ≥4 hours.
2. Thread manufacturing process
MJ threads need to be rolled in one go after the final heat treatment, and the following must be strictly controlled:
- Rolling temperature ≤427℃ (duration time <90 seconds when exceeding 315℃)
- Face roughness Ra≤0.8μm
- Thread correction tolerance see standard table A.1
3. Mechanical performance indicators
Diameter (mm) Minimum tensile strength (kN) Double shear load (kN) Fatigue test load (kN) 5 23.913 - The upsetting process must be completed before heat treatment
- The cold rolling deformation of the lower fillet of the head is ≤0.05mm (diameter ≤10mm)
- Strictly monitor the aging temperature deviation (±10℃)
2. Quality Inspection Scheme
A three-level inspection system is recommended:
- Incoming inspection: 100% hardness inspection (HRC42-48)
- Process inspection: Metallographic inspection of 5 pieces per batch (grain flow line, overburning, etc.)
- Outgoing inspection: Sampling according to GB/T 2828.1 Level II
3. Response to special working conditions
For stress corrosion environment:
- Vacuum solution treatment is preferred
- 1500h alternating immersion test is mandatory
- Surface MoS2 coating thickness ≥0.005mm
Standard Evolution Analysis
This standard incorporates ISO 5855-2 (MJ thread) is combined with HB 5800 (aerospace tolerance). The innovations include:
- Cold rolling strengthening process for the fillet under the lead-in head
- Specified grain flow density requirements for the threaded part
- Added stress durability test (96h stable load)
GB/T 42851-2023 Referenced Document
- GB/T 20878 Stainless steels——Designation and chemical composition*， 2024-07-24 Update
- GB/T 230.1 Metallic materials.Rockwell hardness test.Part 1:Test method
- GB/T 2828.1 Inspection procedure by count sampling part 1: Lot by lot inspection sampling plan retrieved by acceptance quality limit (AQL)
- GB/T 90.2 Fasteners--Marking and packaging
GB/T 42851-2023 history
- 2023 GB/T 42851-2023 1517MPaMJ threaded bolts
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