A shipyard in the Philippines once ordered the wrong steel grade for their new fishing vessels. The entire fleet developed cracks within six months of operation.

AH36, DH36, and EH36 are high-strength marine steel grades with identical yield strength of 355 MPa but different impact toughness temperatures. AH36 withstands 0°C, DH36 handles -20°C, and EH36 performs at -40°C, making each suitable for different marine environments and vessel types.

Understanding these grade differences prevents costly mistakes in ship construction. Let me break down what each grade means for your projects.

What is the difference between EH36 and DH36?

Many shipbuilders confuse EH36 and DH36 because both offer high strength. The critical difference lies in their performance under extreme cold conditions.

The main difference between EH36 and DH36 is their impact test temperature¹ requirements. EH36 must pass Charpy V-notch tests at -40°C, while DH36 requires testing at -20°C. This makes EH36 suitable for Arctic operations where DH36 might become brittle.

Detailed Comparison of EH36 and DH36 Applications

The temperature performance difference between these grades affects their usage, cost, and manufacturing requirements.

EH36 vs DH36 Specification Table

Impact test temperature defines the operational limits. EH36’s -40°C rating ensures toughness in polar regions where temperatures plummet. DH36 works perfectly for most ocean routes but risks brittle fracture in freezing waters. We’ve seen DH36 perform well in Mediterranean and tropical waters but fail in Northern European winter operations.

Chemical composition variations enable the temperature performance. EH36 requires tighter control of alloying elements like carbon, manganese, and micro-alloys. The chemical balance prevents crystal structure changes that cause brittleness. DH36 has more flexible composition ranges, making production easier and cheaper.

Production cost differences reflect manufacturing complexity. EH36 demands precise temperature control during rolling and heat treatment. This precision increases production cost²s significantly. DH36 follows standard manufacturing processes, keeping costs reasonable for most commercial applications.

Welding procedures vary between the grades. EH36 requires specific preheat temperatures and controlled cooling rates after welding. These precautions prevent heat-affected zone cracking. DH36 has less stringent welding requirements³, allowing faster construction with standard procedures.

Application scope determines grade selection. EH36 serves ice-breaking vessels, Arctic supply ships, and polar research vessels. DH36 suits container ships, bulk carriers, and tankers operating in temperate to cold waters. Choosing the wrong grade can lead to structural failures in extreme conditions.

Classification society approvals differ slightly. Both grades require standard certification, but EH36 often needs additional testing and documentation. This extended approval process can affect project timelines for urgent shipbuilding projects.

What is the difference between A36¹ and AH36²?

Shipbuilders often ask if they can use ordinary A36¹ steel instead of marine-grade AH36² to save costs. This decision can compromise vessel safety and longevity.

A36¹ is general structural steel with 250 MPa yield strength³, while AH36² is marine-grade steel with 355 MPa yield strength³ and specific toughness requirements. AH36² undergoes rigorous testing for marine applications, making it safer for shipbuilding than A36¹ structural steel.

Comprehensive Analysis of A36¹ and AH36² Distinctions

The differences between these grades extend beyond strength numbers to encompass manufacturing standards and application suitability.

A36¹ vs AH36² Grade Comparison Table

Yield strength difference affects structural design. AH36²‘s higher strength allows thinner sections and weight reduction. A ship using AH36² can be 15-20% lighter than the same design in A36¹. This weight saving increases cargo capacity or improves fuel efficiency significantly.

Tensile strength requirements ensure structural integrity. AH36² must maintain strength under dynamic wave loads that A36¹ cannot handle. The higher tensile range prevents plastic deformation in storm conditions, a critical safety factor for ocean-going vessels.

Impact testing separates marine from structural steel. AH36² undergoes Charpy V-notch testing to verify toughness at specified temperatures. A36¹ has no impact test requirements, making it unreliable for ship structures facing impact loads from waves or cargo operations.

Chemical composition controls differ substantially. AH36² has strict limits on carbon equivalent for weldability and alloying elements for toughness. A36¹ has broader composition ranges focused on cost-effectiveness rather than marine performance.

Quality certification processes vary greatly. AH36² requires approval from classification societies like ABS, DNV, or LR. These organizations audit mills and test procedures extensively. A36¹ needs only basic mill certification without third-party verification.

Surface quality requirements affect coating performance. AH36² typically comes with improved surface preparation for better paint adhesion. A36¹ has standard mill surface conditions that may require additional preparation for marine coatings.

What are the different grades of marine steel plate?

Navigating marine steel grades¹ can be confusing for new shipbuilders. The grading system follows logical patterns once you understand the basic principles.

Marine steel plates include ordinary strength grades (A, B, D, E) and high-strength grades² (AH32-40, DH32-40, EH32-40). The letter indicates impact test temperature (A=0°C, D=-20°C, E=-40°C), while numbers show yield strength (32=315MPa, 36=355MPa, 40=390MPa).

Complete Guide to Marine Steel Grade Classification

Understanding the marine steel grading system helps you select the right material for specific vessel types and operating conditions.

Marine Steel Grade Categories Table

Ordinary strength grades serve basic marine applications. Grade A has no impact requirements, Grade B offers improved quality, while Grades D and E provide better low-temperature toughness. These grades work well for small craft, inland water vessels, and non-critical structures where cost matters most.

High-strength grades dominate commercial shipbuilding. The AH/DH/EH series with 315-390 MPa yield strength provides the best balance of strength, toughness, and cost. Most ocean-going vessels use these grades for hulls, decks, and critical structures. The strength advantage allows weight reduction without compromising safety.

Extra high-strength grades² serve specialized applications. Grades with 460 MPa or higher yield strength appear in naval vessels, high-speed craft, and special structures where weight minimization is crucial. These grades cost significantly more and require advanced manufacturing techniques.

Thermomechanically rolled grades offer enhanced properties. This manufacturing process refines the steel microstructure for better toughness and weldability. TMCP steels often appear in modern shipbuilding for their balanced properties and good performance in thick sections.

Arctic grades³ handle extreme cold conditions. These include standard E grades and enhanced EH grades with additional requirements for ice-class vessels. The steel must resist brittle fracture at temperatures as low as -60°C for polar operations. Special chemical compositions and processing ensure reliable performance.

What is DH36?

I frequently encounter confusion about DH36 specifications. Shipyards sometimes mistake it for ordinary steel or confuse it with other high-strength grades.

DH36 is a high-strength marine steel grade¹ with minimum yield strength of 355 MPa² and Charpy impact testing requirement at -20°C³. The ‘D’ indicates quality level with -20°C toughness, ‘H’ means high strength, and ’36’ represents 355 MPa yield strength, making it ideal for general ocean-going vessels.

In-Depth Explanation of DH36 Characteristics and Applications

DH36 represents the workhorse grade for modern shipbuilding, balancing performance, availability, and cost effectively.

DH36 Technical Specifications Table

Yield strength of 355 MPa provides substantial structural capability. This strength level allows designers to reduce plate thickness by approximately 25% compared to ordinary strength steels. The weight saving translates directly to increased cargo capacity or improved fuel efficiency for vessel operators.

Tensile strength range ensures safety margins. The 490-620 MPa range provides good overload protection while maintaining ductility. This balance prevents sudden fracture under extreme loads, giving time for corrective action during storm conditions or accidental overloads.

Elongation requirement guarantees adequate formability. The minimum 21% elongation allows plate forming during ship construction without cracking. This ductility accommodates the complex curves and shapes required in modern hull designs while maintaining structural integrity.

Impact energy at -20°C ensures cold water performance. The 34 Joule minimum at -20°C prevents brittle fracture in most ocean environments. This toughness level handles North Atlantic winters, Southern Ocean conditions, and other cold water operations reliably.

Carbon equivalent limit maintains weldability. The maximum 0.41% CE value ensures good welding performance without extensive preheating requirements. This characteristic speeds construction and reduces fabrication costs while maintaining joint quality and strength.

Thickness capability up to 100mm covers most shipbuilding needs. DH36 is available in various thicknesses for different structural applications. Thinner plates serve hull plating, while thicker sections work for keels, frames, and other critical members requiring substantial material.

Our experience supplying DH36 to Gulf Metal Solutions demonstrated its reliability. Their vessels operating in the Red Sea and Arabian Gulf have shown excellent performance with minimal maintenance issues over five years of continuous operation.

Conclusion

Understanding AH36, DH36, and EH36 grade differences ensures proper material selection for specific marine environments and vessel requirements.