Issue 75

A. Casaroli et alii, Fracture and Structural Integrity, 75 (2026) 104-123; DOI: 10.3221/IGF-ESIS.75.09

[%]

C

Cr

Ni

Mn

Si

S

P

Cu

Mo

Ti

Nb

N

AISI 304 ASTM A240: AISI 304 304 mod. Limit values for 304 mod. AISI 430 ASTM A240: AISI 430 AISI 441 ASTM A240: AISI 441

0.04

18.05

8.02

1.72

0.37

<0.01

0.04

0.04

0.21

-

0.03

0.06

<0.08

18-20

8-11

<2.00

<0.75

<0.03 <0.045

-

-

-

-

<0.10

0.05

18.06

9.56

1.46

0.35

<0.01

0.03

0.03

0.15

-

0.03

0.03

9 10.50

<0.05

18-18.75

<2.00

<0.75

-

-

-

-

-

-

-

0.05

16.19

0.55

0.47

0.33

<0.01

0.04

0.04

0.02

-

0.03

0.05

<0.12

16-18

<0.75

<1.00

<1.00

<0.03

<0.04

-

-

-

-

-

0.03

17.87

0.4

0.33

0.58

<0.01

0.04

0.04

0.04

0.25

0.45

0.01

0.1

0.57 0.9

<0.03

17.5-19.5

<1.00

<1.00

<1.00

<0.03

<0.04

-

-

<0.03

0.5

Table 1: Experimental chemical composition of the sheets used for the experimentation compared to the limit values. AISI 304 is similar to EN X5CrNi18-10. 304 mod. is characterized by a chemical composition compatible with the AISI 304 limits, compared to which it establishes lower maximum chromium and higher minimum nickel contents. AISI 430, similar to X6Cr17. AISI 441, similar to X2CrTiNb18. AISI 441 is characterized by a very limited carbon content and the addition of small amount of titanium and niobium to stabilize the ferrite and prevent the precipitation of chromium carbides. Tensile tests For each type of stainless steel, nine tensile specimens were obtained, three of which were machined parallelly (L), three perpendicular (T) and three at 45° (Q) with respect to the rolling direction. The results, expressed as the mean value of the three replicates, are summarized in Tab.4. Each tensile test was carried out according to the ISO 6892 standard at a deformation rate of 0.005 s -1 until the elongation of 2%, then it was increased to 0.05 s -1 until failure. From each test, the values of the yield strength, R p0.2 , the ultimate tensile strength, R m , the percentage plastic extension at maximum force, A g %, and the percentage elongation after fracture, A% (L 0 = 25 mm) were determined. Moreover, the strain hardening exponent was calculated according to ISO 10275, in the engineering strain range 4%-15%, while the strain ratio was estimated according to ISO 10113, using the slope, m r , of the true plastic width strain vs. true plastic length strain line. The true plastic width strain, ε b , and the true plastic length strain, ε l , were measured at the engineering strains of 2%, 4%, 8% and 12%. Then, from the r values measured in the three investigated directions the normal (r̄ ) and the planar anisotropy ( Δ r) coefficients were obtained. The strain ratio value is defined by Eqn. (3), whereas the normal and the planar anisotropy coefficients were determined according to Eqns. (4) and (5).

m

r, 0-90-45

r

=-

(3)

0-90-45

1+m

r, 0-90-45

m

r, 0-90-45

r

=-

(4)

0-90-45

1+m

r, 0-90-45

m

r, 0-90-45

r

=-

(5)

0-90-45

1+m

r, 0-90-45

where r 0-90-45 are the strain ratios in the longitudinal, transversal and 45° directions, ε w,0-90-45 and ε t,0-90-45 are the strains in the width and the thickness direction for the three specimens series.

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