Where RINA E620 Sits in the Hull Steel Family
RINA E620 is an extra high strength shipbuilding steel plate grade approved under the rules of RINA, the Italian classification society for ships, offshore units and marine structures. In the grade designation, 620 is the minimum yield strength in MPa and the letter E fixes the Charpy V-notch impact test temperature at −40 °C. It belongs to the top of the strength ladder used for hull structural steel, above the more common 355 and 460 MPa classes.
Plate of this class is produced as a low alloy steel in the quenched and tempered condition, so that the strength requirement is met by heat treatment rather than by heavy alloying. That combination is what allows the material to be welded in a shipyard while still delivering the high load carrying capacity expected from a 620 MPa grade.
Chemical Composition and Crack Sensitivity
The table below gives the maxima normally applied to RINA E620 plate in the quenched and tempered condition. Residual elements are limited so that toughness at −40 °C and weldability are preserved.
| Element | Requirement | Element | Requirement |
|---|---|---|---|
| C | 0.20 % max | Ni | 0.40 % max |
| Si | 0.10–0.55 % | Cr | 0.20 % max |
| Mn | 1.70 % max | Mo | 0.08 % max |
| P | 0.030 % max | Cu | 0.35 % max |
| S | 0.030 % max | Al | 0.020 % min |
| Nb | 0.02–0.05 % | V | 0.05–0.10 % |
| Ti | 0.007–0.05 % |
Two calculated parameters are used to judge the risk of cold cracking in the heat affected zone. The crack sensitivity index is Pcm = C + Si/30 + Mn/20 + Cu/20 + Ni/60 + Cr/20 + Mo/15 + V/10 + 5B, expressed in percent. The carbon equivalent is Ceq = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15, also in percent. Low values of both support welding without excessive preheat; the actual limits are agreed with the classification society for the thickness and joint design concerned.
Mechanical Properties
Values are typical of the property table applied to the grade in the quenched and tempered condition.
| Grade | Thickness (mm) | Yield strength min (MPa) | Tensile strength (MPa) | Elongation min (%) | Impact energy min at −40 °C |
|---|---|---|---|---|---|
| RINA E620 | 8–260 | 620 | 720–890 | 15 | 41 J |
The narrow spread between the minimum yield strength and the specified tensile range leaves little margin for a producer, which is why the quenched and tempered route and a documented heat treatment cycle are essential. Impact energy is verified on Charpy V-notch specimens at the cold test temperature, together with shear area and lateral expansion, to confirm that the plate will not behave in a brittle manner in service.
Dimensions and Delivery Range
Thickness: plates are rolled in the range covered by the property table, typically 8 mm to 260 mm according to mill capability.
Width: plates up to about 4800 mm wide are produced for hull and offshore fabrication.
Length and edge condition: cut to order with sheared or flame cut edges, and ultrasonic examination available on request.
Supplementary requirements: through-thickness testing, Charpy testing at additional temperatures, and third-party inspection can be agreed before rolling.
Welding, Forming and Fabrication
Welding consumables must be matched to the 620 MPa strength class of the parent plate; undermatching consumables reduce joint efficiency.
Preheat and interpass temperature should be derived from the measured carbon equivalent and the plate thickness, not from a default value.
Heat input and cooling rate influence the toughness of the weld heat affected zone and should be controlled within the qualified procedure.
Flame cutting and machining are straightforward, but edges of thick plate should be inspected and any hardening layer removed before welding.
Cold forming of thick plate requires care because of the high yield strength; forming limits are best verified by trial rather than assumed.
Applications
The grade is used where high strength and low temperature toughness are both needed, and where reducing plate thickness helps to lower structural weight. Typical applications include hull structures of large vessels, deck and bottom plating in highly stressed regions, primary support members, offshore structural components and heavy marine equipment exposed to cold climates.
Frequently Asked Questions
Q: What does RINA E620 mean?
RINA identifies the classification society whose rules apply, 620 is the minimum yield strength in MPa, and the letter E means the Charpy impact test is carried out at −40 °C.
Q: What are the mechanical properties of RINA E620 plate?
The grade is specified with 620 MPa minimum yield strength, 720–890 MPa tensile strength, 15 % minimum elongation and a minimum impact energy of 41 J at −40 °C.
Q: Why is the plate supplied quenched and tempered?
Quenching and tempering develop the required strength while retaining toughness; the treatment also keeps alloying additions modest, which protects weldability.
Q: What is the crack sensitivity index used for?
The Pcm and carbon equivalent formulas estimate how readily the heat affected zone may harden and crack, and they guide the preheat temperature used during welding.
Q: Can RINA E620 plate be welded?
Yes, using a qualified procedure with strength matched consumables, controlled heat input and a preheat level derived from the carbon equivalent of the actual heat.
Q: Which applications suit this grade best?
Large ship hull structures, offshore components and heavy marine fabrications where weight saving, high load capacity and cold temperature toughness are all required.
