Comparison Between High-Alloy Steel and Ordinary Alloy Steel

I. Definitions and Classification Criteria: The Critical "10%" Threshold
There are clear standards regarding chemical composition for the classification of alloy steels. Based on the total mass fraction of alloying elements, alloy steels are categorized into three tiers:

Low-alloy steel: Total alloying element content < 5%. Common examples include 16Mn and 15CrMo.

Medium-alloy steel: Total alloying element content between 5% and 10%. Example: Cr4W2MoV.

High-alloy steel: Total alloying element content > 10%. Typical examples include Cr12, 12Cr1MoVG, and stainless steels with very high chromium content (such as 3Cr13).
II. Performance Comparison: The "Overwhelming Superiority" of High-Alloy Pipes
1. High-Temperature and Creep Resistance
This is the area where the two differ most significantly. Because high-alloy steel pipes contain substantial amounts of elements such as chromium (Cr), molybdenum (Mo), and tungsten (W), they maintain stable crystal structures and mechanical properties even at high temperatures. For instance, high-alloy grades like T91 and T92 are frequently used in boiler superheaters and reheaters; they offer tensile strengths exceeding 585 MPa and are capable of long-term service in environments around 600°C. In contrast, ordinary low-alloy pipes (such as 20G) are markedly inferior in terms of high-temperature rupture strength and oxidation resistance, with service temperatures typically remaining below 540°C.

2. Corrosion Resistance
Chromium is a key element for enhancing the corrosion resistance of steel. High-alloy steel pipes (especially those with chromium content exceeding 10%) can form a dense, chromium-rich oxide film on their surface, exhibiting excellent corrosion resistance against acids, alkalis, and high-temperature, high-pressure sulfur-containing media. Ordinary alloy pipes, due to their limited content of elements like chromium and nickel, rely primarily on surface coatings or specialized treatments for corrosion resistance; consequently, their service life in highly corrosive media falls far short of that of high-alloy pipes.

3. Mechanical Strength
High-alloy steel pipes generally possess higher yield strength and tensile strength. Taking the ASME SA213 standard as an example, T92 high-alloy pipes require a tensile strength of at least 620 MPa, whereas standard SA210A-1 pipes require only 415 MPa. This superior strength allows high-alloy pipes to withstand higher internal pressures, making them suitable for use in supercritical and ultra-supercritical power generation units.
III. Manufacturing Process and Cost: Why High-Alloy Pipes Come at a Premium
The high performance of high-alloy steel pipes comes at a high manufacturing cost.

Material Costs: The addition of rare alloying elements—such as nickel, molybdenum, vanadium, and titanium—results in raw material costs for high-alloy pipes that are far higher than those for standard alloy pipes, which contain only small amounts of manganese and silicon.

Processing Complexity: High-alloy steels exhibit high resistance to deformation and have a narrow hot-working temperature range. Consequently, the processes for rolling, cold drawing, and heat treatment are extremely demanding (requiring, for instance, annealing and tempering steps with precise temperature control). In contrast, the manufacturing processes for standard alloy pipes are mature, offering higher production efficiency and product yields.

Price Disparity: Overall, the market price of high-alloy steel pipes is typically several times—or even dozens of times—higher than that of standard alloy pipes of the same specifications.