ASTM A453 Grade 660 Class D (660D) Specification

ASTM A453 Grade 660 Class D (660D) is solution treated at 1650 ± 25 °F [900 ± 14 °C] for 2 h min or 1800 ± 25 °F [980 ± 14 °C] for 1 h min and liquid quenched, then aged at 1325 ± 25 °F [720 ± 14 °C] for 16 h and air cooled, with a second age at 1200 ± 25 °F [650 ± 14 °C] for 16 h if needed to reach the properties (A453/A453M-17 Table 4). Table 5 requires up to 2½ in. [63.5 mm]: 130 ksi [895 MPa] tensile and 105 ksi [725 MPa] yield; over 2½ in. [63.5 mm]: 120 ksi [825 MPa] tensile and 95 ksi [655 MPa] yield; 15 % elongation, 18 % reduction of area and 248 to 321 HB (24 to 35 HRC) in both size ranges; A453/A453M-17 added the separate large-size limits. Class D does not require a stress-rupture test and is stamped NR in addition to the other required markings (8.2.1, 9.1). Unlike Class A, B and C, Class D has a 105 ksi [725 MPa] minimum yield up to 2½ in., a 321 Brinell maximum instead of 341 (approximately 35 HRC instead of 37 HRC), and no stress-rupture test. API 6A (21st edition) 8.2.3.2 sets the same 35 HRC maximum and 725 MPa / 655 MPa yield split for 660D bolting, and ISO 15156-3 (NACE MR0175) also limits UNS S66286 to 35 HRC. API 20F covers Grade 660 Class D for BSL-2 and BSL-3 bolting. NORSOK M-630:2020 MDS S39 Rev. 1 covers A453 Gr. 660 Class D studs, bolts and nuts with Charpy V testing at -101 °C: 27 J average, 20 J single, 0.38 mm lateral expansion. ASTM A453 Grade 660 Class D bolting to MDS S39 is manufactured at TorqBolt.

Data sheets for every product form: ASTM A453 Grade 660 PDF Data Sheets.

Source: ASTM A453/A453M-17; API 6A 21st edition; API 20F; ISO 15156-3; NORSOK M-630:2020 MDS S39 Rev. 1. Last reviewed 20 October 2026.

Table Of Contents

Properties
Chemical Composition
Mechanical Properties
Offshore Service Caution
Annealing & Ageing Cycles
Continuous Heat Treatment Charge Sizes
Lot / Batch Sizes
Marking Requirements
Bolting Threading Types
Product Range

ASTM A453 Grade 660 Class D Properties

Chemical Composition

Grade	ASTM A453 Grade 660 Class D
UNS Number	S66286
Elements	Content, %	Product Analysis Variation, Over or Under, %
Carbon (C)	0.08 max	0.01 over
Manganese (Mn)	2.00 max	0.04
Phosphorus (P)	0.040 max	0.005 over
Sulfur (S)	0.030 max	0.005 over
Silicon (Si)	1.00 max	0.05
Nickel (Ni)	24.0-27.0	0.2
Chromium (Cr)	13.5-16.0	0.2
Molybdenum (Mo)	1.00-1.50	0.05
Titanium (Ti)	1.90-2.35	0.05
Aluminum (Al)	0.35 max	0.05 over
Vanadium (V)	0.10-0.50	0.03
Boron (B)	0.001-0.010	0.0004 under to 0.001 over

Mechanical Properties

Grade		ASTM A453/A453M Grade 660
Class		D (≤2 1 / 2 in. [63.5 mm])	D (>2 1 / 2 in. [63.5 mm])
Tensile Strength,min	ksi	130	120
Tensile Strength,min	MPa	895	825
Yield Strength(0.2 % Offset), min	ksi	105	95
Yield Strength(0.2 % Offset), min	MPa	725	655
Elongation in 4× Diam, min, %		15	15
Reduction of Area, min, %		18	18
Brinell Hardness Number		248-321	248-321
Approximate Rockwell Hardness,B and C	min	24 HRC	24 HRC
Approximate Rockwell Hardness,B and C	max	35 HRC	35 HRC
Hardness as per API 20F BSL2 & BSL3*		35 HRC	35 HRC
(*) 100% Hardness Mandatory

Offshore Service Caution (API 6A 8.2.3.6)

API 6A (21st edition) 8.2.3.6 states that ASTM A453/A453M Grade 660D solution-treated and age-hardened bolting should not be used on pressure containing and high load bearing connectors in the following situations :

wet/dry offshore and coastal applications in the presence of salt air;
where it is routine to clean/wash equipment with untreated/raw seawater.
NOTE 1 - Environmentally assisted cracking, such as stress corrosion cracking (SCC), may result from the presence or accumulation of Chlorides from deposited salt on highly stressed austenitic stainless steel bolting, such as Grade 660D .
NOTE 2 - API 6ACRA addresses alternative, higher-strength CRA materials suitable for sour exposure .

Annealing & Ageing Cycles

Grade Symbol	Class	Solution Treatment	Hardening Treatment
ASTM A453/A453M Grade 660	D	1650 ± 25 °F [900 ± 14 °C], hold 2 h min, and liquid quench or 1800 ± 25 °F [980 ± 14 °C], hold 1 h min, and liquid quench	1325 ± 25 °F [720 ± 14 °C], hold 16 h, air cool If necessary to achieve properties, second age: 1200 ± 25 °F [650 ± 14 °C] hold 16 h, air cool
(A) Times refer to the minimum time material is required to be at temperature.

Continuous Heat Treatment Charge Sizes

Diameter, in. [mm]	Weight, lb [kg]
To 1³/₄ [44]	3000 [1400]
Over 1³/₄ [44] to 2¹/₂ [63]	6000 [2700]
Over 2¹/₂ [63]	12000 [5400]

Lot / Batch Sizes

Diameter, in. [mm]	Maximum Lot Size, lb [kg]
1¹/₂ [38] and under	200 [90]
Over 1¹/₂ [38] to 1³/₄ [44], incl	300 [140]
Over 1³/₄ [44] to 2¹/₂ [63], incl	600 [270]
Over 2¹/₂ [63]	20 pieces

Marking Requirements

Grade	Marking
ASTM A453 Grade 660 Class D	TB 660D M1/M2/R1/R2 NR
ASTM A453 Grade 660 Class D BSL2	TB NR 660D API 20F2 Heat No.
ASTM A453 Grade 660 Class D BSL3	TB NR 660D API 20F3 Heat No.