Case-Hardened Gear Forgings
Forged SCR420 gear blank components for automotive and industrial gearbox applications requiring a carburized, wear-resistant tooth surface over a tough core capable of absorbing bending and impact load without cracking.
JIS G4104 SCR420
Chromium Case-Hardening (Carburizing) Alloy Steel
SCr Series, No Mo Addition
Distinct From SCM Cr-Mo Through-Hardening Family
SAE 5120-Comparable Chemistry
Cr-Alloyed Case-Hardening Grade Role
EN 10204 3.1/3.2
Full Material Certification & Traceability
SCR420's Role Within JIS Alloy Steel: Chromium for Hardenability, Not Through-Hardening
SCR420 occupies a specific position within JIS's alloy steel grade system that's easiest to understand by contrast with the site's existing coverage of two related JIS families: the S-C series (JIS G4051, covering plain carbon structural steels like S45C) and SCM440 (JIS G4053, a chromium-molybdenum grade functionally equivalent to SAE 4140, used for through-hardened shafts and structural components). SCR420 sits in a third JIS family — the SCr series, chromium alloy steels without molybdenum addition — and its low carbon content (roughly 0.18-0.23%) combined with chromium alloying (roughly 0.9-1.2%) is deliberately formulated not for through-hardening bulk strength the way SCM440 is, but for carburizing: the chromium content raises hardenability enough to develop a genuinely hard, wear-resistant carburized case reliably through heat treatment, while the low base carbon content keeps the core material soft and tough after the carburizing and quench-harden cycle, exactly the property combination a case-hardened gear tooth or wear pin needs — hard where it contacts and wears, tough where it needs to absorb impact and bending load without cracking. SCR420 functions as a cost-effective middle ground within JIS's case-hardening grade options: it delivers meaningfully better hardenability and case quality than a plain low-carbon S-C series grade like S15C or S20C would provide for demanding carburized components, without the added alloying cost of molybdenum-bearing case-hardening grades like SCM420 or SCM415, which push hardenability and core strength further for applications with heavier sections or higher core-strength requirements than SCR420 is intended to serve.
SCR420 Forged Products
Shaft and Pin Forgings for Carburizing
Forged shaft and pin blank components in SCR420, sized for carburizing heat treatment to develop a hard wear surface at bearing and contact points while retaining core toughness through the component's cross-section.
Cam and Follower Component Forgings
Forged SCR420 cam and follower component blanks for automotive and machinery applications requiring a hard, wear-resistant contact surface developed through case hardening, matched to the cyclic contact loading these components experience.
Custom Components to Japanese OEM Drawings
Forged components manufactured directly to Japanese and Asian OEM drawings referencing SCR420 material and carburizing heat treatment callouts, supporting customers sourcing to JIS-based engineering documentation.
Heat Treatment, Testing and Certification for SCR420 Supply
Carburizing and Case Hardening to Specified Depth
Carburizing heat treatment developing SCR420's specified case depth and surface hardness, with quench and temper parameters controlled to achieve the target case-to-core hardness transition the application's wear and fatigue duty requires.
Core Hardness and Toughness Verification
Mechanical property verification confirming the carburized component's core retains the ductility and toughness SCR420's low base carbon content is specifically formulated to provide, distinct from the case hardness developed at the surface.
Case Depth Measurement
Metallurgical case depth verification confirming the carburized layer meets the drawing's specified depth requirement, since case depth that's too shallow wears through prematurely and case depth that's excessive can compromise core toughness.
EN 10204 3.1/3.2 Certification
Material test certificates per EN 10204 3.1 as standard, with 3.2 third-party witnessed certification available for customer quality system and Japanese/Asian OEM documentation requirements.
SCR420's Role Within JIS Alloy Steel: Chromium for Hardenability, Not Through-Hardening
Case-hardening steel selection within the JIS alloy steel framework follows a logical progression that mirrors the broader industry pattern seen in SAE and DIN case-hardening grade families: plain carbon low-carbon grades at the economical end, chromium-alloyed grades offering improved hardenability and case consistency in the middle, and molybdenum-bearing chromium grades at the higher-performance end for the most demanding core-strength and section-size requirements. SCR420 occupies that middle position specifically, and understanding where it sits relative to its JIS family relatives — S-C series carbon steels on one side, SCM chromium-molybdenum grades on the other — is what allows correct grade selection for a given carburized component rather than defaulting to whichever grade happens to be most familiar.
The underlying metallurgical logic is the same principle that governs case-hardening steel selection across every national standard system: carburizing introduces carbon into a component's surface layer specifically to allow that surface to harden significantly during the subsequent quench, while the component's low-carbon core remains relatively soft and tough because it never absorbs enough additional carbon to harden the same way. Alloying additions like chromium don't change this fundamental mechanism, but they do improve hardenability — the material's ability to actually achieve full hardness through the carburized case depth during quenching, particularly for components with more complex geometry or where a more reliable, consistent case hardness result matters more than a plain carbon grade can dependably deliver.
SCR420's specific chromium-only alloying, without molybdenum, reflects a deliberate cost-versus-performance positioning within this framework: it delivers a genuine, measurable hardenability improvement over plain low-carbon S-C series case-hardening grades, making it the appropriate choice for gears, pins, and cam components with moderate section size and wear duty, while avoiding the added material cost molybdenum alloying introduces for applications that don't actually need the further hardenability and core-strength improvement molybdenum-bearing grades like SCM420 provide. Getting this grade selection right — rather than over-specifying an unnecessarily alloyed grade or under-specifying a plain carbon grade for a genuinely demanding wear application — is a meaningful cost and performance decision for high-volume automotive and machinery component production.
For manufacturers sourcing forged case-hardening steel components to Japanese or Asian OEM drawings specifying SCR420, Shivam Forge supplies forgings with controlled carburizing heat treatment, case depth verification, and full mechanical property certification. Contact our engineering team at +91-9265772827 or sales@shivamforge.com with your component drawing and specified case depth requirement to discuss manufacturability and quotation.
Frequently Asked Questions
How is SCR420 different from SCM440, which the site also covers?
SCM440 is a chromium-molybdenum alloy steel formulated for through-hardening bulk strength, functionally equivalent to SAE 4140, used for shafts and structural components requiring deep, uniform hardness through the section. SCR420 is a chromium-only alloy steel (no molybdenum) with lower carbon content, formulated specifically for carburizing — developing a hard case over a tough core — and is not intended for through-hardening applications the way SCM440 is.
How is SCR420 different from JIS G4051's S-C series carbon steel grades?
S-C series grades like S45C are plain carbon steels without significant alloying, generally lower in hardenability. SCR420's chromium addition raises hardenability meaningfully above plain carbon case-hardening grades like S15C or S20C, delivering more consistent, reliable case quality during carburizing heat treatment, particularly for components with more demanding wear duty or larger cross-sections.
Why choose SCR420 instead of a molybdenum-bearing grade like SCM420?
SCR420 offers a cost-effective middle ground — better hardenability and case quality than plain carbon case-hardening grades, without the added alloying cost molybdenum-bearing grades like SCM420 or SCM415 carry. For components with moderate section size and core-strength requirements, SCR420 is often the more economical choice; heavier sections or higher core-strength demands may justify moving to a molybdenum-alloyed case-hardening grade instead.
What is SCR420 comparable to in the SAE/AISI system?
SCR420's chromium-alloyed, low-carbon case-hardening chemistry is broadly comparable in role to SAE 5120, a chromium case-hardening grade within the American system. As with other JIS-to-SAE comparisons, minor chemistry range differences exist between the two standards, which we verify against your specific drawing requirement.
What case depth can be achieved with SCR420?
Achievable case depth depends on the carburizing cycle time and temperature applied, and we develop the heat treatment cycle to hit your drawing's specified case depth and surface hardness requirement rather than a single fixed value. Share your target specification and component geometry and we can confirm feasibility.
Why Choose Shivam Forge
Trusted forging manufacturer — Rajkot, Gujarat
Shivam Forge delivers precision hot-forged components from our integrated Shapar, Rajkot facility — covering forging, CNC machining, heat treatment, and quality inspection under one roof.
- Hot forging from quality alloy steel billets (42CrMo4, C45, EN8, SS316L)
- In-house CNC/VMC machining to drawing — ±0.05mm tolerances
- Heat treatment — normalizing, hardening, tempering, annealing
- CMM inspection and full EN 10204 3.1 material certification
- Custom OEM forging from customer drawings — PPAP/ISIR available
- Fast export from Mundra Port — CIF worldwide, FOB India
- Export expertise — Europe, Middle East, Americas, Asia-Pacific