BS 4882

Table 4. Nuts in ferritic, austenitic and precipitation-hardenable alloys complying with BS 1506 and BS 3076

Nut grade identification marks Material designation
(from BS 1506)		 Alloy type Limiting ruling section of nut Heat treatment and cold working condition (1)(6)(7) Hardness Charpy V-notch impact strength (4)
Metric series Inch series Metric series Inch series HB HV Test temperature Mean of three values
Ferritic steels mm in °C J
M2H 2H 162 Carbon steel 63 2½ Harden 830°C to 860°C OQ(9), Temper 450°C (min.) 248 to 352 261 to 371
M2HM (5) 2HM (5) Harden 830°C to 860°C OQ, Temper 620°C (min.) 159 to 235 168 to 247
M4 M14 4L4 253 C¼%Mo 38 1½ Harden 880°C to 910°C OQ or WQ, Temper 550°C (min.) 248 to 352 261 to 371 -100 27
M4M (5) 4M (5) 63 2½ Harden 880°C to 910°C OQ or WQ, Temper 600°C (min.) 159 to 235 168 to 247
ML9 L9 509-650 9%Ni 75 3 Normalize 880°C to 930°C AC, 770/870°C AC 187 to 248 197 to 261 -196 40
ML9A L9A 509-690 9%Ni 100 4 Harden 770°C to 820°C OQ or WQ, Temper 540°C to 660°C 207 to 255 217 to 268 -196 40
M7 ML7 7L7 630-860 1%Cr¼%Mo 63 2½ Harden 850°C to 880°C OQ, Temper 600°C (min.) 248 to 331 261 to 348 -100 27
M7M ML7M (5) 7M L7M (5) 630-690 63 2½ Harden 850°C to 880°C OQ, Temper 620°C (min.) 201 to 235 211 to 247 -100 27
M7A 7A 631-850 1%Cr½%Mo 200 8 Harden 850°C to 900°C OQ or WQ, Temper 600°C (min.) 248 to 302 261 to 318
M16 16 670-860 1%Cr½Mo¼%V 100 4 Harden 930°C to 970°C OQ, Temper 650°C (min.) 248 to 302 261 to 318
M16B 16B 671-850 1¼%CrMoV 200 8 Harden 930°C to 970°C OQ or AC, Temper 650°C (min.) 248 to 302 261 to 318
M6 6 410S21-760 12%Cr 100 4 Harden 950°C to 1020°C OQ or AC, Temper 600°C (min.) 228 to 269 240 to 283
M6K M6K M (2) 6K 6KM (2) M 410S21-690 200 8 Harden 950°C to 1020°C OQ or AC, Temper 620°C (min.) (2) 201 to 235 211 to 247
M8 M8A (3) 8 8A (3) 304S31 18Cr10Ni Solution treated 1000°C to 1100°C (3) -196 27
M8X 8X See table 2 Solution treated before cold working 320 max. 337 max. -196 27
M8M M8MA (3) 8M 8MA (3) 316S31 18Cr12Ni2Mo Solution treated 1000°C to 1100°C (3) -196 27
M8MX 8MX See table 2 Solution treated before cold working 320 max. 337 max. -196 27
M8T M8TA 8T 8TA 321S31 18Cr10NiTi Solution treated 1000°C to 1100°C -196 27
M8TX 8TX See table 2 Solution treated before cold working 320 max. 337 max. -196 27
M8C M8CA (3) 8C 8CA (3) 347S31 18Cr10NiNb Solution treated 1000°C to 1100°C (3) -196 27
M8CX 8CX See table 2 Solution treated before cold working 320 max. 337 max. -196 27
Precipitation-hardenable alloys
M17B ML17B 17B L17B 286S31 15Cr25NiMoVTiAlB 200 8 Solution treated 970°C to 990°C 248 to 341 261 to 360 -196 20
M17BM ML17BM (8) 17BM L17BM (8) Precipitation hardened 710°C to 760°C, 16h min. AC 248 to 321 261 to 339 -196 20
M80A ML80A 80A L80A BS 3076 – Grade NA20 Ni20Cr 399 12 Solution treated 1080°C, soak up to 8h AC or quench; precipitation 850°C 24h, AC; 700°C 16h AC 286 to 360 300 to 380 -196 20

(1) Cold working austenitic stainless steel, bar material properties see table 2 which details effect of bar size.
(2) 12% Cr steel (grades M6KM and 6KM) for sour gas service, nuts should be double tempered, first treatment should be above 620 °C, second at a lower temperature at or above 620 °C.
(3) Austenitic stainless steel for sour gas (sulphide stress cracking resistance) all nuts should be solution treated after all forming and machining are completed, designated ‘A’ condition, and maximum hardness HB 235, HV 247.
(4) Charpy V-notch impact tests:
(a) where stated on enquiry and order,
(b) average of three tests minimum individual value to be not less than 70 % of specified average (minimum) value.
(5) Ferritic steels: (designated ‘M’ grade, 2HM, 4M, 7M etc.) for sour gas service nuts should be heat treated after all forming and machining are completed.
(6) Information extracted from BS 1506 and given for guidance. Austenitizing at temperatures outside this range may significantly effect stress rupture values.
(7) Minimum tempering temperatures are mandatory.
(8) Nuts for sour gas service.
(9) Oil quench (OQ); water quench (WQ); air cool (AC).