Chrome Moly 25CrMo4 Alloy Steel Bars

Product Description

25CrMo4 (standardized as W.Nr. 1.7218 under EN 10083-3) is a low-carbon variant within the Chromium-Molybdenum (Chrome Moly) alloy steel family. When specified in bar stock, it occupies a highly specialized niche: it bridges the gap between high-strength structural steels and highly weldable fabrication steels.

Unlike its higher-carbon relative 42CrMo4 (AISI 4140), 25CrMo4 drops the carbon level to achieve outstanding impact toughness and excellent weldability while preserving the signature heat-resistance and fatigue limits of a true chrome moly grade.

1. Chemical Composition (EN 10083-3 / W.Nr. 1.7218)

The deliberate reduction of carbon paired with targeted chromium and molybdenum levels defines its mechanical character:

2. Mechanical Profile vs. Dimensional Cross-Section

When ordered in the standard Quenched & Tempered (+QT) condition, 25CrMo4 bars show excellent yield-to-tensile ratios. However, due to its lower carbon content and absence of nickel, its mechanical thresholds scale based on the bar diameter ($d$):

• Small Bars ($\le$ 16 mm): Tensile strength registers at 900 – 1100 MPa with a minimum yield strength of 700 MPa.

• Medium Bars (16 mm – 40 mm): Tensile strength shifts to 800 – 950 MPa with a minimum yield of 600 MPa.

• Large Bars (40 mm – 100 mm): Tensile strength measures 700 – 850 MPa with a minimum yield strength of 450 MPa.

• Massive Bars (100 mm – 160 mm): Tensile strength tracks at 650 – 800 MPa with a minimum yield strength of 400 MPa.

3. High-Temperature Capability (Creep Resistance)

A major engineering advantage of 25CrMo4 is its behavior at elevated thermal thresholds. Thanks to the molybdenum additions, components machined from these bars resist continuous mechanical stress without stretching or suffering thermal relaxation at temperatures ranging from $450^\circ\text{C}$ up to $530^\circ\text{C}$. This makes it an ideal fit for steam-line and boiler assemblies.

4. Key Delivery States

• Quenched & Tempered (+QT): Pre-treated to typical working bands ($\sim 220$ to $280\text{ HBW}$). This allows direct machining into final components without the dimensional distortion risks associated with a post-fabrication quench line.

• Soft Annealed (+A): Normalized/annealed down to a maximum hardness of 212 HBW. This is the mandatory choice for complex machining, high-speed turning, or deep gundrilling to extend tool life.

• Treated for Shearability (+S): Softened to a maximum of 255 HBW to safely permit cold-shearing or cold-heading operations without fracturing the bar edges.

5. Direct Global Equivalents

If you are matching international drawings or evaluating material test certificates (MTCs), 25CrMo4 maps directly to:

• USA: AISI 4130 / SAE 4130 (The closest chemical and behavioral equivalent)

• Japan: JIS SCM420 / SCM430

• France (AFNOR): 25CD4

• United Kingdom: BS 708M25 / 708A25

• China: GB 30CrMo

• Russia: GOST 20KHM (20ХМ) / 30KHM (30ХМ)

6. Fabrication Guidelines: Welding and Machining

⚠️ Technical Comparison

• Superior Weldability: Unlike 42CrMo4 (AISI 4140) which is highly prone to cold cracking, 25CrMo4 can be successfully welded due to its lowered carbon window. It still requires a moderate preheat ($150^\circ\text{C} - 200^\circ\text{C}$) depending on the cross-sectional thickness, followed by controlled cooling to safeguard the heat-affected zone (HAZ).

• Machining: In its annealed state, it chips beautifully and leaves an exceptionally clean surface finish. If machining in the +QT state, standard carbide tooling with rigid setups is recommended.