High Strength Low Alloy Steels

High-strength low-alloy (HSLA) steels are designed to provide better mechanical properties and/or greater resistance to atmospheric corrosion than conventional carbon steels. They are not considered to be alloy steels in the normal sense because they are designed to meet specific mechanical properties rather than a chemical composition (HSLA steels have yield strengths greater than 275 MPa, or 40 ksi). The chemical composition of a specific HSLA steel may vary for different product thicknesses to meet mechanical property requirements. The HSLA steels have low carbon contents (0.05 to ~0.25% C) in order to produce adequate formability and weldability, and they have manganese contents up to 2.0%. Small quantities of chromium, nickel, molybdenum, copper, nitrogen, vanadium, niobium, titanium, and zirconium are used in various combinations. The types of HSLA steels commonly used include:

• Weathering steels, designed to exhibit superior atmospheric corrosion resistance

• Control-rolled steels, hot rolled according to a predetermined rolling schedule designed to develop a highly deformed austenite structure that will transform to a very fine equiaxed ferrite structure on cooling

• Pearlite-reduced steels, strengthened by very fine-grain ferrite and precipitation hardening but with low carbon content and therefore little or no pearlite in the microstructure

• Microalloyed steels, with very small additions (generally <0.10% each) of such elements as niobium, vanadium, and/or titanium for refinement of grain size and/or precipitation hardening

• Acicular ferrite steel, very low carbon steels with sufficient hardenability to transform on cooling to a very fine high-strength acicular ferrite (low-carbon bainite) structure rather than the usual polygonal ferrite structure

• Dual-phase steels, processed to a microstructure of ferrite containing small, uniformly distributed regions of high-carbon martensite, resulting in a product with low yield strength and a high rate of work hardening, thus providing a high-strength steel of superior formability

Table 3 lists chemical compositions for various HSLA steels.

Table 3 Compositional limits for HSLA steel grades described in ASTM specifications

ASTM specification

Type or

designation

Heat compositional limits, %(a)

grade

C

Mn

P

S

Si

Cr

Ni

Cu

V

Other

A 242

Type 1

K11510

0.15

1.00

0.45

0.05

0.20 min

A 572

Grade 42

0.21

1.35(b)

0.04

0.05

0.30(b)

■ (c) min

(d)

Grade 50

0.23

1.35(b)

0.04

0.05

0.30(b)

■ (c) min

(d)

Grade 60

0.26

1.35(b)

0.04

0.05

0.30

■ (c) min

(d)

Grade 65

0.23(b)

1.65(b)

0.04

0.05

0.30

■ (c) min

(d)

A 588

Grade A

K11430

0.100.19

0.901.25

0.04

0.05

0.150.30

0.400.65

0.250.40

0.020.10

Grade B

K12043

0.20

0.751.25

0.04

0.05

0.150.30

0.400.70

0.250.50

0.200.40

0.010.10

Grade C

K11538

0.15

0.801.35

0.04

0.05

0.150.30

0.300.50

0.250.50

0.200.50

0.010.10

Grade D

K11552

0.100.20

0.751.25

0.04

0.05

0.500.90

0.500.90

Zr

Grade K

0.17

0.51.20

0.04

0.05

0.250.50

0.400.70

0.40

0.300.50

0.10 Mo, 0.0050.05 Nb

ASTM specification

Type or grade

designation

Heat compositional limits, %(a)

C

Mn

P

S

Si

Cr

Ni

Cu

V

Other

A 606

0.22

1.25

0.05

A 607

Grade 45

0.22

1.35

0.04

0.05

■ (c) min

(d)

Grade 50

0.23

1.35

0.04

0.05

■ (c) min

(d)

Grade 55

0.25

1.35

0.04

0.05

■ (c) min

(d)

Grade 60

0.26

1.50

0.04

0.05

■ (c) min

(d)

Grade 65

0.26

1.50

0.04

0.05

0.20 min(c)

(d)

Grade 70

0.26

1.65

0.04

0.05

■ (c) min

(d)

A 618

Grade Ia

0.15

1.00

0.15

0.05

0.20 min

Grade Ib

0.20

1.35

0.04

0.05

■ (e) min

Grade II

K12609

0.22

0.851.25

0.04

0.05

0.30

0.02 min

Grade III

K12700

0.23

1.35

0.04

0.05

0.30

■ (f) min

A 633

Grade A

K10802

0.18

1.001.35

0.04

0.05

0.150.30

0.05 Nb

Grade C

K12000

0.20

1.151.50

0.04

0.05

0.150.50

0.01-0.05 Nb

Grade D

K02003

0.20

0.70-1.60(b)

0.04

0.05

0.150.50

0.25

0.25

0.35

0.08 Mo

Grade

K12202

0.22

1.15-

0.04

0.05

0.15-

Nb(c),

ASTM specification

Type or

designation

Heat compositional limits, %(a)

grade

C

Mn

P

S

Si

Cr

Ni

Cu

V

Other

E

1.50

0.50

0.11

0.01-0.03 N

A 656

Type 3

0.18

1.65

0.025

0.035

0.60

0.08

0.020 N, 0.0050.15 Nb

Type 7

0.18

1.65

0.025

0.035

0.60

0.0050.15

0.020 N, 0.0050.10 Nb

A 690

K12249

0.22

0.600.90

0.080.15

0.05

0.10

0.400.75

0.50 min

A 709

Grade 50, type 1

0.23

1.35

0.04

0.05

0.40

0.0050.05 Nb

Grade 50, type 2

0.23

1.35

0.04

0.05

0.40

0.010.15

Grade 50, type 3

0.23

1.35

0.04

0.05

0.40

(g)

0.05 Nb max

Grade 50, type 4

0.23

1.35

0.04

0.05

0.40

(h)

0.015 N max

A 715

0.15

1.65

0.025

0.035

V, Ti, Nb added as necessary

A 808

0.12

1.65

0.04

0.05 max or 0.010 max

0.150.50

0.10

0.02-0.10 Nb, V + Nb = 0.15 max

A 812

65

0.23

1.40

0.035

0.04

0.150.50®

V + Nb = 0.020.15

0.05 Nb max

80

0.23

1.50

0.035

0.04

0.150.50

0.35

V + Nb = 0.020.15

0.05 Nb max

A 841

0.20

(j)

0.030

0.030

0.15-

0.25

0.25

0.35

0.06

0.08 Mo, 0.03 Nb,

ASTM specification

Type or grade

designation

Heat compositional limits, %(a)

C

Mn

P

S

Si

Cr

Ni

Cu

V

Other

0.50

0.02 Al total

A 871

0.20

1.50

0.04

0.05

0.90

0.90

1.25

1.00

0.10

0.25 Mo, 0.15 Zr, 0.05 Nb, 0.05 Ti

(a) If a single value is shown, it is a maximum unless otherwise stated.

(b) Values may vary, or minimum value may exist, depending on product size and mill form.

(c) Optional or when specified.

(d) May be purchased as type 1 (0.005-0.05 Nb), type 2 (0.01-0.15 V), type 3 (0.05 Nb, max, plus 0.02-0.15 V) or type 4 (0.015 N, max, plus V > 4N).

(e) If chromium or silicon are each 0.50% min, the copper minimum does not apply.

(f) May be substituted for all or part of V.

(h) Nitrogen with vanadium content of 0.015% (max) with a minimum vanadium-to-nitrogen ratio of 4:1.

(i) When silicon-killed steel is specified.

(j) For plate under 40 mm (1.5 in.), manganese contents are 0.70 to 1.35% or up to 1.60% if carbon equivalents do not exceed 0.47%. For plate over 40 mm (1 to 5 in.), ASTM A 841 specifies manganese contents of 1.00 to 1.60%.

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