Chemical composition and mechanical properties of Q420R, a Chinese grade of low-temperature pressure vessel steel.
Q420R Approximate Grade Lookup Table

Table 1  Chemical Composition

Grade Chemical Composition(Quality Fraction)/%
C Si Mn Cu Ni Cr Mo Nb V Ti Altb P S Others
Q420R ≤0.20 ≤0.55 1.2~1.60 ≤0.30> 0.20~0.50 ≤0.30 ≤0.08 0.015~0.050 ≤0.100 ≤0.030 　 ≤0.020 ≤0.010 Nb+V+
Ti≤0.22
Cu+Cr+
Mo≤0.45

7.1.4 According to the buyer's requirements, the nitrogen content of Q420R steel plates should not exceed 0.020% and 0.025%, respectively.
7.1.6 The content of residual elements chromium, nickel, and copper should not exceed 0.30% each, and molybdenum should not exceed 0.080%, with the total content of these elements not exceeding 0.70%. Analysis is not required if the supplier can guarantee this.
7.1.7 According to the buyer's requirements, the carbon equivalent of the Q420R grade can be specified, and the value shall be determined through negotiation between the supplier and the buyer.
7.1.8  The permissible deviation of the chemical composition of finished steel products shall comply with the provisions of CB/T 713.1.
7.1.9  For a comparison of similar grades with relevant international standards, please refer to Appendix A.

Table 2  Mechanical properties and processing properties

Grade Delivery status Thickness mm Tensile test Impact test 180°Bending test b=2a
Tensile strength Rm/MPa Lower yield strength ReL/MPa Elongation after fracture A/% Temperature/℃ Impact absorption energy KV2/J
≥ 　 ≥
Q420R Normalizing or Normalizing＋Tempering >60～100 510～610 330 20 -20 47 D=3a
6～20 590～720 420 18 -20 60 D=3a

Note: D is the diameter of the bending indenter; b is the width of the sample; a is the thickness of the sample.
When the yielding phenomenon is not obvious, the specified plastic elongation strength Rp0.2 can be used instead.

Table 3  High temperature mechanical properties

Grade Thickness/mm Test temperature/℃
100 150 200 250 300 350 400 450 500
ReLᵃ  (or Rp0.2)/MPa,≥
Q420R >6～20 380 355 330 305 280 255 240 　 —
>20～30 365 340 315 290 270 245 230 　 　

ᵃ When the yielding phenomenon is not obvious, the specified plastic elongation strength Rp0.2 can be used instead.