What Is 31CrMo12 (1.8515) Steel? Chemical Composition, Mechanical Properties & Industrial Uses
By Jiangsu Liangyi Technical Team15 min read · 3,200 wordsLast reviewed: May 2025
31CrMo12 (material number 1.8515) is a high-performance chromium-molybdenum alloy steel standardized under EN 10083-3:2006. This complete technical reference covers its exact chemical composition, full mechanical property tables by section size, heat treatment parameters, international equivalent grades across DIN, BS, and AFNOR standards, and documented real-world applications in wind energy, mining, cement, oil & gas, and heavy engineering — authored by engineers with 25+ years of production experience with this grade.
2.80–3.30%Chromium (EN 10083-3)
0.30–0.50%Molybdenum Content
250 mmMax Through-Hardening
58–62 HRCCase Surface Hardness
880–1230 MPaTensile Strength Q&T
Quick Answer — What Is 31CrMo12?
31CrMo12 (EN material number 1.8515) is a high-alloy, heat-treatable chromium-molybdenum steel per EN 10083-3:2006. It contains 0.28–0.35% C, 2.80–3.30% Cr, and 0.30–0.50% Mo. Its defining characteristic is through-hardenability in sections up to 250 mm, achieved by its high chromium content — more than double that of 42CrMo4. After quenching and tempering, it achieves Rm 880–1230 MPa and Yield Strength ≥675–835 MPa depending on section size. It is used for large forged gear shafts, crusher shafts, crankshafts, and rolled rings in wind energy, mining, cement, and oil & gas industries.
Section 01 — Overview
What Is 31CrMo12 Steel? Definition & Key Characteristics
31CrMo12 is a high-alloy, heat-treatable chromium-molybdenum (CrMo) alloy steel standardized under EN 10083-3:2006 — the European standard for quenched and tempered steels. Its unique EN material number is 1.8515, used as a shorthand identifier across all European engineering specifications and material certificates.
The grade designation directly encodes its chemical composition following the DIN/EN naming convention: 31 represents nominal carbon content of approximately 0.31%, Cr is chromium, Mo is molybdenum, and 12 represents chromium content multiplied by one-quarter (×4 ≈ 3% Cr). This makes the alloy content immediately legible to engineers across Europe.
Key Distinction from 42CrMo4
What separates 31CrMo12 from the more common 42CrMo4 is its exceptionally high chromium content of 2.80–3.30% — more than double the 0.90–1.20% in 42CrMo4. This critical difference enables through-hardening in sections up to 250 mm versus approximately 100 mm for 42CrMo4, making 31CrMo12 the correct choice for large, heavily loaded forgings where consistent mechanical properties from surface to core are non-negotiable.
JL
Jiangsu Liangyi Materials Engineering Team
"31CrMo12 is specified when 42CrMo4 is simply not enough — either because the section exceeds 100mm, the surface must achieve 58+ HRC after case hardening, or the fatigue life requirement exceeds what lower-alloy steels can deliver. We have produced this grade continuously since 1997."
ISO 9001:2015 Certified · Established 1997 · Jiangyin City, Jiangsu, China
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Primary Standard
EN 10083-3:2006. Also covered under DIN 17200 and compatible with ASTM A788 forging requirements.
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Product Forms
Open die forgings, seamless rolled rings (OD to 5000mm), forged bars, gear shafts, hollow parts, crankshafts.
30 kg to 30,000 kg per piece. Max ring OD 5000 mm. Max shaft length 12,000 mm. Max bar diameter 1200 mm.
Section 02 — Chemical Composition
31CrMo12 (1.8515) Chemical Composition — EN 10083-3:2006
The chemical composition of 31CrMo12 is precisely defined by EN 10083-3:2006. The high chromium and molybdenum content are its two defining characteristics, responsible for all its performance advantages over lower-alloy grades.
Element
Symbol
Content Range (wt.%)
Function in Steel
Carbon
C
0.28 – 0.35
Core hardness and strength after quenching; controls hardenability depth
Silicon
Si
≤ 0.40
Deoxidizer during steelmaking; minor solid-solution strengthening
Manganese
Mn
0.40 – 0.70
Secondary hardenability contributor; improves toughness and machinability
Phosphorus
P
≤ 0.025
Controlled impurity — limits grain boundary embrittlement at elevated temperatures
Primary hardenability agent — enables through-hardening to 250mm; improves wear and corrosion resistance
Molybdenum ★
Mo
0.30 – 0.50
Prevents temper brittleness in Cr steels; enhances elevated temperature strength and creep resistance
Why High Chromium (2.80–3.30%) Is the Defining Feature
Chromium increases hardenability by slowing carbon diffusion during the quench, allowing the austenite-to-martensite transformation to occur deeper into the cross-section before the cooling rate becomes too slow. At 2.80–3.30% Cr, 31CrMo12 achieves uniform through-hardening in sections up to 250 mm thick — a capability that 42CrMo4 (0.90–1.20% Cr) cannot replicate beyond approximately 100 mm.
This is the fundamental reason 31CrMo12 is specified for large forged gear shafts in wind turbine gearboxes, eccentric shafts in gyratory crushers, and pinion shafts in cement rotary kilns — all applications where a soft, under-hardened core in a lower-alloy steel would lead to premature fatigue failure or unacceptable property variation.
The Role of Molybdenum (0.30–0.50%)
Molybdenum in chromium steels serves two critical functions. First, it suppresses temper brittleness — a phenomenon where chromium steels cooled slowly through the 350–550°C range become severely embrittled at their grain boundaries. Without Mo, thick chromium steel forgings risk brittle fracture after Q&T heat treatment. Second, Mo contributes to elevated temperature strength and creep resistance, making 31CrMo12 suitable for applications like cement kiln pinion shafts operating at moderately elevated temperatures.
Certification Note: Jiangsu Liangyi performs and documents full chemical composition spectroscopic analysis for every heat (melt batch) of 31CrMo12. Results are included in the EN 10204 Type 3.1 material certificate. EN 10204 Type 3.2 certification (with accredited third-party inspection body countersignature) can be arranged on request for projects that require it.
Section 03 — Mechanical Properties
31CrMo12 Mechanical Properties After Quenching & Tempering (Q&T)
All values below are after standard quenching and tempering (Q&T) heat treatment per EN 10083-3:2006. Properties decrease with increasing section size — a fundamental consequence of the cooling rate gradient during quenching, even in a highly alloyed steel like 31CrMo12.
Section Thickness
Tensile Strength Rm (MPa)
Yield Strength Re (MPa)
Elongation A (%)
Impact Energy KV at 20°C (J)
16 – 40 mm
1030 – 1230
≥ 835
≥ 10
≥ 20
40 – 100 mm
980 – 1180
≥ 785
≥ 11
≥ 20
100 – 160 mm
930 – 1130
≥ 735
≥ 12
≥ 20
160 – 250 mm
880 – 1080
≥ 675
≥ 12
≥ 20
31CrMo12 vs. 42CrMo4 — Performance Comparison
Through-Hardenability — Max uniform section depth
31CrMo12
250 mm
42CrMo4
~100 mm
Surface Hardness after case hardening
31CrMo12
58–62 HRC
42CrMo4
54–58 HRC
Chromium content (direct hardenability driver)
31CrMo12
~3.05% Cr
42CrMo4
~1.05% Cr
Hardness Summary by Heat Treatment Condition
Condition
Hardness
Notes
Soft Annealed
≤ 248 HB
For machining; maximum deliverable hardness
Quenched & Tempered (Q&T)
280 – 350 HB
Standard condition; EN 10083-3 properties apply
Case Hardened (carburize + quench)
58 – 62 HRC surface
Tough core retained; case depth per specification
Nitrided
900 – 1050 HV
Minimal distortion; best for precision ground gears
Section 04 — Heat Treatment
Heat Treatment Parameters for 31CrMo12 (1.8515)
Correct heat treatment is essential to achieve the EN 10083-3 mechanical property requirements. All parameters must be confirmed for the specific part geometry and section size. Jiangsu Liangyi uses computer-controlled furnaces with documented temperature–time curve logs for every batch.
Process
Temperature Range
Cooling Method
Result & Purpose
Hot Forging
900 – 1100°C
Air or slow cool
Shape forming; grain refinement via plastic deformation
31CrMo12 has limited weldability. Its carbon equivalent (CE ≈ 0.85–1.0) creates significant cold cracking risk without proper precautions. When welding is required: preheat to 200–350°C, use matched or over-alloyed filler wire, and perform post-weld stress relief at 600–650°C. In practice, most 31CrMo12 forgings are designed to avoid welding — they are forged to near-net shape. Engineers requiring a more readily weldable grade should consider 18CrNiMo7-6 or 34CrNiMo6 instead.
Engineers working across different national standards frequently need to identify the correct local equivalent of 31CrMo12. The following cross-reference covers the most widely used national standards. Critical warning: Always verify the chemical composition limits against the target standard's published data — grade names alone are not sufficient for procurement or engineering specification.
1.8515EN Material No.
31CrMo12EN 10083-3 (EU)
32CrMo12DIN 17200 (DE)
722M24BS 970 (UK)
30CD12AFNOR NF (FR)
25H3MPN/GOST (PL/RU)
Standard
Grade Designation
C (%)
Cr (%)
Mo (%)
Equivalence
EN 10083-3
31CrMo12 / 1.8515
0.28–0.35
2.80–3.30
0.30–0.50
Primary
DIN 17200
32CrMo12
0.29–0.36
2.80–3.30
0.30–0.50
Direct
BS 970
722M24
0.20–0.28
2.90–3.40
0.30–0.50
Near
AFNOR NF
30CD12
0.27–0.34
2.80–3.20
0.30–0.50
Direct
ASTM
No direct equivalent
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Verify
Procurement Guidance: When sourcing 31CrMo12 forgings from China for European projects, explicitly specify the EN 10083-3:2006 chemical composition limits and mechanical property requirements in your purchase order. Do not rely on the grade name alone. Request EN 10204 Type 3.1 material certificate as a contractual deliverable. For pressure equipment projects requiring PED compliance, specify Type 3.2 with third-party inspection body countersignature in your purchase order.
Section 06 — Manufacturing Process
How 31CrMo12 Forgings Are Made: Step-by-Step Manufacturing Process
The quality of a 31CrMo12 forging is determined by the precision of every manufacturing step — not just chemical composition. Understanding this process enables buyers to ask informed questions during supplier qualification and audit.
Electric arc furnace (EAF) smelting, followed by ladle furnace (LF) refining and VD/VAD vacuum degassing, achieves low sulfur (≤0.035%), phosphorus (≤0.025%), and dissolved hydrogen/nitrogen. For projects requiring the highest cleanliness grade, ESR (electro-slag remelting) can be specified and sourced. This step locks in the chemical composition verified against EN 10083-3 limits.
02
Ingot Casting & Uniform Pre-Heating to 900–1100°C
Cast into steel ingots, then soaked uniformly in a furnace to forging temperature, ensuring consistent plasticity throughout the section and preventing surface cracking or internal tearing during deformation.
03
Open Die Forging — Minimum Forging Ratio ≥ 3:1
Hydraulic presses rated 2000T to 6300T apply multiple upsetting (compression) and elongation passes, achieving a forging ratio of ≥3:1. This breaks down the as-cast columnar grain structure, closes internal shrinkage porosity, refines grain size, and dramatically improves mechanical properties, impact toughness, and UT inspectability over the original ingot.
04
Seamless Ring Rolling (for annular components)
Annular parts — gear rings, slewing bearing races, flange blanks, riding rings — are hot-rolled on CNC ring rolling machines with 1M to 5M rolling capability. This produces seamless rings with circumferential fiber flow aligned with the principal stress direction, giving superior fatigue life over flame-cut or welded ring alternatives.
05
Computer-Controlled Quenching & Tempering (Q&T)
Austenitized at 840–870°C then oil or polymer quenched, followed by tempering at 540–660°C in computer-monitored heat treatment furnaces. Temperature–time curves are recorded and archived for each batch. This is the critical step for achieving EN 10083-3 tensile strength, yield strength, and impact energy requirements.
06
CNC Machining — Rough, Semi-Finish, and Precision Finish
Three-stage machining: rough machining after forging (removes scale, establishes reference surfaces), semi-finish after Q&T (prepares surfaces for final dimensions), and precision finish machining using CNC lathes, milling centers, gear hobbing machines, and grinding machines — all to customer drawing dimensions and tolerances.
07
Full NDT Inspection, Dimensional Check & Certificate Issuance
Every batch undergoes: UT per EN 10228 / ASTM A388 (internal flaws), MT per ISO 9934 (surface cracks), Brinell hardness survey, full dimensional inspection to drawing, and mechanical property testing from representative test coupons heat-treated alongside the production parts. EN 10204 Type 3.1 material certificate issued for every batch. NDT inspection is performed by qualified operators.
Section 07 — Industrial Applications
Where Is 31CrMo12 (1.8515) Used? Applications & Specific Components
31CrMo12 is selected for the most demanding mechanical environments across global heavy industry. Its combination of large section through-hardenability, high surface hardness after case hardening, good impact toughness, and elevated temperature stability makes it irreplaceable for specific applications where lower-alloy steels have proven inadequate.
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Wind & Hydro Energy
Critical transmission components requiring 20+ year service life under continuous cyclic loading. 31CrMo12 is widely used for wind turbine gearbox components. Whether a specific forging meets ISO 6336-5 MQ material quality grade depends on the part dimensions, heat treatment condition, and test results — this is confirmed per order.
High-impact, continuous-duty applications in iron ore, copper, and coal mining. Shafts must survive repeated shock loads without fatigue crack initiation — the tough core of Q&T 31CrMo12 is essential.
Rotary kiln and grinding mill drive systems run 24/7 under combined high torque and moderate temperature. DIN 3990-5 and similar gear quality standards are commonly referenced for these applications.
Drilling equipment under high pressure, alternating torsional loads, and H₂S-containing environments. Full material traceability and NDT documentation are required for these applications.
Large-section crankshafts, gearbox components, and power transmission shafts across diverse industries where 42CrMo4 cannot provide adequate through-hardening or surface hardness.
Decision Guide: When to Specify 31CrMo12 Instead of 42CrMo4
Specify 31CrMo12 over 42CrMo4 when any of the following engineering conditions apply:
Section thickness exceeds 100 mm and consistent through-hardening to the core is required by design
High-cycle fatigue loading — gear tooth root bending stress in wind turbine or industrial gearboxes
Surface hardness after case hardening must exceed 58 HRC with a defined effective case depth
Part requires compliance with gear material quality standards such as ISO 6336-5 MQ or ML — confirmed per test results on each batch
Wear life is a key maintenance cost driver and replacement costs or downtime penalties are high
Operating temperature reaches 350–400°C — as in cement kiln pinion shafts or gas compressor cranks
Corrosion resistance is a secondary but relevant requirement (Cr content provides marginal improvement over low-Cr grades)
For a full product specification, available dimensions, and pricing for custom 31CrMo12 forged components — including open die forgings, seamless rolled rings, and precision-machined shafts — contact our technical team directly.
Section 08 — Quality & Certification
Quality Inspection Standards & EN 10204 Material Certification
Specifying the correct material grade is only the first step. Verifying conformance through documented third-party testing and traceable certification is what differentiates reliable forgings from risky ones. The following standards govern inspection at Jiangsu Liangyi for all 31CrMo12 production.
Inspection Category
Applicable Standards
What It Confirms
Chemical Composition
ASTM A751 / EN 10083-3
Full spectroscopic elemental analysis per heat — confirms grade and composition limits
Tensile Test
ASTM A370 / ISO 6892-1
Rm, Re, elongation (A), reduction of area (Z) — verified against EN 10083-3 table by section
Charpy Impact Test
ISO 148-1 / ASTM A370
KV impact energy at 20°C — confirms toughness requirement ≥20J
Complete batch traceability from steel heat number to finished forging delivery
Every production batch of 31CrMo12 forgings ships with an EN 10204 Type 3.1 material certificate issued by Jiangsu Liangyi's quality department, covering chemical composition, mechanical test results, heat treatment records, and dimensional inspection. EN 10204 Type 3.2 certification — requiring countersignature by an accredited independent third-party inspection body — can be arranged on request for projects that require it. All inspection records are archived for a minimum of 10 years for full production traceability.
For full details on available sizes, supply conditions, lead times, and downloadable certification documentation, see our 31CrMo12 forging product page.
Section 09 — FAQ
Frequently Asked Questions About 31CrMo12 (1.8515) Steel
What is 31CrMo12 (1.8515) steel?
31CrMo12 (EN material number 1.8515) is a high-alloy, heat-treatable chromium-molybdenum steel per EN 10083-3:2006. Its composition — 0.28–0.35% C, 2.80–3.30% Cr, 0.30–0.50% Mo — gives it outstanding through-hardenability in sections up to 250mm, high wear resistance after case hardening (58–62 HRC), and good impact toughness. It is used for large forged gear shafts, crusher eccentric shafts, crankshafts, and seamless rolled rings in wind energy, mining, cement, and oil & gas industries globally.
What is the difference between 31CrMo12 and 42CrMo4 steel?
The key difference is chromium content: 31CrMo12 has 2.80–3.30% Cr versus 0.90–1.20% in 42CrMo4. This gives 31CrMo12 through-hardening capability to 250mm sections (vs. ~100mm for 42CrMo4) and higher surface hardness after case hardening (58–62 HRC vs. 54–58 HRC). 31CrMo12 also has longer fatigue life under cyclic loading and better elevated temperature stability. 42CrMo4 is more economical for smaller sections and moderate loads. Choose 31CrMo12 when sections exceed 100mm, surface hardness above 58 HRC is needed, or ISO 6336-5 MQ gear quality grade must be met.
What are the international equivalent grades for 31CrMo12 (1.8515)?
International equivalents for 31CrMo12 (1.8515) include: 32CrMo12 per DIN 17200 (Germany) — direct match; 722M24 per BS 970 (United Kingdom) — near match (slightly lower C); 30CD12 per AFNOR NF (France) — direct match; 25H3M per PN/GOST (Poland/Russia); material number 1.8515 as the universal EN designation. No direct ASTM equivalent exists — verify chemical composition limits when cross-referencing to American standards for any engineering application.
What heat treatment does 31CrMo12 require?
Standard Q&T heat treatment: austenitize at 840–870°C, oil or polymer quench, then temper at 540–660°C. For soft annealing before machining: 650–700°C slow furnace cool (max 248 HB). For case hardening: carburize at 900–950°C + quench + low temper achieves 58–62 HRC surface. For nitriding: 500–550°C gas nitriding achieves ~900–1050 HV surface with minimal distortion. Hot forging is performed at 900–1100°C. Computer-controlled furnaces with logged temperature–time curves are required for batch traceability.
What material certification is required for 31CrMo12 forgings in European projects?
For most European industrial applications: EN 10204 Type 3.1 material certificate (issued by manufacturer's own quality department) — documents chemical composition, mechanical test results, heat treatment records, and dimensional inspection. For pressure equipment under PED 2014/68/EU: EN 10204 Type 3.2 with countersignature by an accredited independent third-party inspection body is mandatory — this must be specified in your purchase order. Additional project-specific certification requirements should be discussed during the inquiry stage.
What is the lead time and minimum order for custom 31CrMo12 forgings?
Standard lead time is 20–35 working days from confirmed drawing and order, covering steel melting, forging, heat treatment, machining, and inspection. Parts requiring case hardening, nitriding, or third-party inspection may require 40–50 days. Minimum order is 30 kg per piece. Maximum single-piece weight is 30,000 kg. Jiangsu Liangyi supports both one-off sample production and large-volume repeat orders with an annual capacity of 120,000 tons.
Is 31CrMo12 steel suitable for PED 2014/68/EU pressure equipment?
31CrMo12 forgings can be manufactured to meet the material and documentation requirements applicable to pressure equipment projects. PED 2014/68/EU conformance for the finished equipment is ultimately the responsibility of the equipment manufacturer and the relevant notified body. As a material supplier, Jiangsu Liangyi can provide EN 10204 Type 3.1 material certificates as standard, and EN 10204 Type 3.2 (with accredited third-party inspection body countersignature) can be arranged on request. Please discuss your specific PED documentation requirements during the inquiry stage.
Need Custom 31CrMo12 (1.8515) Forgings?
Send your drawings and technical requirements. Our engineering team reviews and responds with a detailed quotation within 24 hours. ISO 9001:2015 certified. EN 10204 Type 3.1 material certificate provided with every order. 50+ countries served since 1997.