What are the characteristics of B-2 Hastelloy - Knowledge

1. What are the characteristics of B-2 Hastelloy?

Hastelloy B-2® (UNS N10665) is a nickel-molybdenum (Ni-Mo) based superalloy renowned for its exceptional corrosion resistance in severe reducing environments. It is a low-carbon variant of the earlier Hastelloy B, optimized to avoid intergranular corrosion. Its core characteristics are as follows:

1.1 Outstanding Corrosion Resistance

It excels in reducing acids such as hydrochloric acid (HCl), sulfuric acid (H₂SO₄, low concentration), phosphoric acid (H₃PO₄), and acetic acid. It maintains stability even at high temperatures and concentrations of these acids.

It has strong resistance to pitting corrosion and crevice corrosion in chloride-containing solutions, making it suitable for environments with high chloride ion concentrations (e.g., chemical processing wastewater).

Note: It performs poorly in oxidizing environments (e.g., nitric acid, chromic acid) or mixed acids with oxidizing agents (e.g., HCl + Fe³⁺/Cu²⁺), as oxidizing ions can cause rapid corrosion of the alloy.

1.2 Microstructural and Processing Characteristics

It has a single-phase austenitic structure with extremely low carbon and silicon contents. This structure avoids the precipitation of brittle intermetallic phases (e.g., Ni₃Mo) during heat treatment or service, ensuring good toughness.

It has excellent weldability and can be welded using common methods (e.g., TIG, MIG). However, post-weld heat treatment (solution annealing) is required to restore corrosion resistance and eliminate welding stress.

Its cold working performance is moderate. Cold working (e.g., rolling, drawing) can improve its strength, but intermediate annealing is needed to prevent work hardening.

1.3 Application Scenarios

It is widely used in the chemical industry, such as equipment for hydrochloric acid production, pickling tanks, and reaction vessels for organic synthesis.

It is applied in the oil and gas industry, including downhole tools and pipelines for sour gas (high H₂S content) extraction.

It is used in the pharmaceutical and food processing industries for equipment handling corrosive media (e.g., acid cleaning systems).

2. What is the mechanical strength of B-2 Hastelloy?

The mechanical strength of Hastelloy B-2 is mainly reflected in its tensile strength, elongation, and hardness, which vary slightly with product form (e.g., plate, tube, forging) and heat treatment state. The following data are based on the solution-annealed state (the most common state for corrosion-resistant applications), in compliance with ASTM B333 (for tubes) and ASTM B335 (for plates/sheets):

Mechanical Property	Test Temperature	Typical Value	Minimum Requirement
Tensile Strength	Room Temperature	750 MPa	690 MPa
Elongation	Room Temperature	45%	40%
Brinell Hardness	Room Temperature	190 - 220 HB	No mandatory requirement
Tensile Strength	500°C	580 MPa	550 MPa
Elongation	500°C	48%	42%

Key notes:

At temperatures above 600°C, the tensile strength of B-2 Hastelloy decreases significantly. Therefore, it is rarely used in structural components for long-term service at temperatures exceeding 600°C.

After cold working, its tensile strength can increase by 20% - 30% (e.g., tensile strength up to 900 MPa after heavy cold rolling), but elongation will decrease accordingly.

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3. What is the yield strength of B-2 Hastelloy?

Yield strength (σ₀.₂, 0.2% offset yield strength) is a critical indicator of the alloy's resistance to plastic deformation. Similar to mechanical strength, the yield strength of B-2 Hastelloy is affected by temperature and heat treatment state. The following are typical values and standard requirements:

3.1 Yield Strength at Different Temperatures (Solution-Annealed State)

Test Temperature	Typical Yield Strength	Minimum Requirement
Room Temperature	320 MPa	275 MPa
200°C	290 MPa	250 MPa
300°C	270 MPa	230 MPa
400°C	250 MPa	210 MPa
500°C	230 MPa	190 MPa

3.2 Key Notes on Yield Strength

Heat Treatment Impact: Solution annealing (typically 1060 - 1100°C, rapid cooling) ensures uniform microstructure, which helps maintain stable yield strength. If the cooling rate is too slow, the yield strength may decrease slightly due to grain growth.

Cold Working Impact: Cold working significantly improves yield strength. For example, after 30% cold rolling, the room-temperature yield strength can reach 550 - 600 MPa, which is nearly twice that of the solution-annealed state.

Standard Reference: ASTM standards (e.g., ASTM B335) specify the minimum yield strength for B-2 Hastelloy to ensure its structural reliability in load-bearing applications (e.g., pressure vessels, structural parts).