Introduction: Why Steel Grade Selection Is the Most Important Specification Decision
India uses thousands of tonnes of steel in manufactured components every year. Shafts, gears, structural frames, housings, brackets, pins, and hundreds of other component types are made from steel in grades ranging from simple mild steel to exotic high-alloy tool steels and stainless grades.
The wrong steel grade is one of the most common and expensive specification errors in manufacturing. A gear made from mild steel when EN36 case-hardening steel was required will wear to failure in months. A shaft made from SS304 when SS416 martensitic stainless was required cannot be hardened to the required surface hardness. A bracket made from 4140 alloy steel when EN8 mild steel was sufficient adds cost with no benefit.
Nathan Engineering, as a steel components manufacturer in India with experience across the full steel grade spectrum, uses this guide to explain the most important steel grades, their applications, and how heat treatment changes their properties — giving designers and buyers the knowledge to specify correctly.
Category 1: Mild Steels — General Purpose Structural Grades
IS2062 / ASTM A36 — General Structural Steel
The most widely used structural steel globally. Adequate strength for most structural applications, excellent weldability, and the lowest cost of any engineering steel. Yield strength approximately 250 MPa. Used for welded frames, fabricated structures, general brackets, and non-critical machined components.
Nathan Engineering uses IS2062/A36 for the majority of welded sheet metal frame fabrications and general structural machined components where strength and hardness are not critical requirements.
EN8 (C45 / AISI 1045) — General Engineering Medium Carbon Steel
Significantly stronger than mild steel (yield strength 430–580 MPa depending on condition), and can be surface hardened by flame or induction hardening to HRC 55–60. Good machinability in normalised condition. Widely used for shafts, keys, studs, and general engineering components where mild steel is insufficient.
CRCA (Cold Rolled Close Annealed) — Sheet and Plate
The standard sheet metal material for pressed and fabricated components. IS513 CR4 grade is the most common, offering good formability and surface quality suitable for painting or powder coating. Nathan Engineering’s sheet metal fabrication uses CRCA as the default material for enclosures, panels, and structural sheet components.
Category 2: Alloy Steels — High Strength and Heat-Treatable Grades
EN24 (4340 / AISI 4340) — Nickel-Chromium-Molybdenum Alloy Steel
One of the most widely used high-strength alloy steels. Heat treated to very high tensile strength (1000–1100 MPa typical in T condition) with good toughness and fatigue resistance. Suitable for large cross-sections without loss of through-hardness.
Used for high-stress shafts, connecting rods, gears, crankshafts, and any structural component where very high strength is required. Nathan Engineering regularly machines EN24 for industrial machinery, defence, and aerospace structural component applications.
EN19 (4140 / AISI 4140) — Chromium-Molybdenum Alloy Steel
The most widely used medium-high strength alloy steel. Good balance of strength, toughness, and machinability. Heat treated to 700–900 MPa tensile strength. Lower cost than EN24 and suitable for most applications where maximum strength is not required.
Used for: shafts, gears, bolts, hydraulic cylinder bodies, machine tool components, and general high-strength machined parts. Nathan Engineering’s most common alloy steel for CNC machined components.
EN36 (AISI 8620) — Nickel-Chromium Case-Hardening Steel
Designed for case-hardening (carburising): the part is machined from EN36, then carburised and quenched to produce a hard case (HRC 58–62) over a tough, ductile core. Used where surface wear resistance and fatigue strength are required with impact toughness — gears, camshafts, pins, and splined shafts.
H13 Tool Steel — Hot Work Die Steel
The standard material for aluminium die casting dies and moulds operating at elevated temperatures. Excellent resistance to thermal fatigue cracking (heat checking) and good toughness at operating temperature. Nathan Engineering specifies H13 for aluminium die casting tool inserts, cores, and slides.
Heat Treatment: How the Same Steel Can Have Completely Different Properties
Annealing
Heating to above the transformation temperature and slow cooling. Produces the softest, most machinable condition. Used to prepare steel for machining before hardening, or to relieve machining stresses in complex components.
Normalising
Heating to above transformation temperature and air cooling. Produces a uniform, relatively fine-grained microstructure with moderate strength. The standard supply condition for EN8 and structural alloy steels.
Through-Hardening (Quenching and Tempering)
Heating to hardening temperature, rapid quenching in oil or water, then tempering to the required hardness and toughness combination. Used for EN24, EN19, and EN36 to develop high strength. Nathan Engineering supplies components in Q&T condition with hardness test certification.
Case Hardening (Carburising and Quenching)
The part is exposed to a carbon-rich atmosphere at elevated temperature, allowing carbon to diffuse into the surface layer. After carburising, the part is quenched to produce a hard case (HRC 58–62) with a tough core. Case depth is typically 0.5 mm to 2.0 mm depending on application. Used for gears, pins, and splined components.
Induction Hardening
A high-frequency electromagnetic coil heats only the surface of the component, which is then immediately quenched. Produces hard surface with no change to the core properties. Ideal for selective hardening — hardening only the bearing journal of a shaft, for example, while leaving the rest of the shaft in its softer, tougher condition.
Steel Components Nathan Engineering Manufactures
- CNC-turned shafts — EN8 through EN24, normalised to Q&T, in diameters 10 mm to 200 mm
- Machined housings and bearing pedestals — EN8 and cast iron with precision-bored bearing seats
- Gear blanks — EN36 and EN24 rough-turned blanks ready for gear hobbing
- Hydraulic cylinder bodies — EN19 or EN24 honed bores in thick-walled tubes
- Structural fabrications — IS2062 and CRCA welded frames, guards, and enclosures
- Stamped steel components — CRCA and high-strength low alloy (HSLA) stampings for automotive
- Heat-treated components — Q&T and case-hardened parts with hardness certification
Contact Nathan Engineering for Steel Components
- Email: nathan@nathanengineering.co.in
- Phone: +91 93601 75927
- Website: www.nathanengineering.in
Submit your drawings with material and heat treatment requirements for a detailed quotation within 24–48 hours.
