GB/T 9808 ZT380 (DZ40) / ZT490 (DZ50) / ZT520 (STM-R780) / ZT540 (DZ55) / ZT590 (DZ60) Thick-Wall Seamless Steel Tubes for Drilling

GB/T 9808 seamless steel tubes for drilling are engineered for geological core drilling, water-well drilling, hydrogeological drilling, and engineering drilling. The current standard in force is GB/T 9808-2023, implemented on July 1, 2024, and it covers seamless tubes used for casing stock, core tube stock, coupling stock, ordinary drill rod stock, drill collar stock, and related drilling components. For the grade combination in your title, the practical supply range spans legacy DZ strength classes and the newer ZT designation system, including the JIS-aligned STM-R780 / ZT520 strength level.

Specifications

Main Features

1. Clearly defined strength ladder for drilling service: widely used market references show minimum yield / tensile / elongation levels of ZT380: 380/640 MPa/14%, ZT490: 490/690 MPa/12%, ZT520: 520/780 MPa/15%, ZT540: 540/740 MPa/12%, and ZT590: 590/770 MPa/12%. This gives buyers a straightforward progression from conventional geological drilling to higher-load deep-hole service.
2. Thick-wall seamless construction for combined axial, torsional, and wear loading: drilling tubes work under tension, compression, bending, torsion, impact, and abrasive mud/rock contact, which is why higher hardenability Mn-B, Mn-Mo-B, and Mn-V-B substrate chemistries are commonly selected for the upper strength classes.
3. Updated compliance basis under the current Chinese national standard: GB/T 9808-2023 replaced GB/T 9808-2008 and remains the active national standard, which matters for procurement files, inspection plans, and mill test certificate wording after July 1, 2024.
4. Cross-standard purchasing flexibility: ZT520 corresponds well to the STM-R780 strength level under JIS G 3465, with 520 MPa proof stress, 780 MPa tensile strength, and 15% elongation, which is helpful when buyers compare Chinese and Japanese drilling-tube specifications.

Our Advantages

1. How do we avoid outdated standard references in quotations and MTCs?
   We align quotations to GB/T 9808-2023, the current active edition, rather than relying only on older GB/T 9808-2008 wording still common in market listings. This reduces documentation mismatch during project approval and third-party inspection.
2. How do we clarify the chemistry behind DZ / ZT strength classes?
   Professional buyers often ask whether a strength class corresponds to a single chemistry. In practice, legacy drilling grades such as DZ40, DZ50, DZ55, and DZ60 are commonly associated with representative substrate steels such as 45MnB / 50Mn, 40Mn2 / 40Mn2Si, 40Mn2Mo / 40MnVB, and 45MnMoB. We therefore confirm both the strength class and the actual steelmaking chemistry on the order and MTC, which is far more useful for machining, heat treatment review, and failure analysis.
3. How do we control drilling reliability in thick-wall tube supply?
   GB/T 9808 covers technical requirements, test methods, inspection rules, and NDT-related references such as eddy current testing and ultrasonic testing. For procurement, that means buyers can require dimensional verification, heat-treatment traceability, and nondestructive examination suitable for thick-wall drilling stock rather than buying only by nominal strength.

Execution Standards

Application Field

Mineral exploration wireline core drilling rods — especially where the drilling string requires higher collapse resistance, torsional stability, and reliable core recovery in medium-depth to deep-hole geological exploration. This is particularly suitable for the ZT520 / STM-R780 and ZT590 / DZ60 strength classes.

Chemical Composition

Note: legacy DZ / ZT strength classes are often supplied through representative substrate steels rather than a single universal chemistry. The table below therefore lists the commonly associated and technically relevant steel grades used to realize the strength levels in your title. For STM-R780, the accessible JIS data in the public source explicitly gives P and S limits; the full heat analysis is typically confirmed on the mill certificate or by the producing mill’s JIS route.

* Residual limit in the referenced GB alloy-steel data source.

Mechanical Properties

Note: the table below combines the market-recognized minimum drilling-tube strength classes in your title with the publicly accessible representative substrate-steel data where useful for technical review. ZT/DZ values are the most relevant for finished drilling-tube purchasing; substrate-steel values help buyers assess heat-treatment potential and machinability.