Case-Hardened Forged King Pins for Heavy Trucks, Buses & Agricultural Equipment
Shivam Forge manufactures hot-drop forged king pins for heavy truck steering axles, buses, semi-trailers, agricultural tractors, and off-highway equipment at our Shapar GIDC facility in Rajkot. Produced in 20MnCr5, EN36, and EN24T, case-hardened to 58–62 HRC on the pin surface, and OD-ground to h6/g6 tolerance, our king pins are built for safety-critical steering duty with full 100% MT inspection.
In a heavy truck's steering axle, the king pin is the vertical pivot about which the stub axle rotates for steering. It carries the entire corner weight of the vehicle as a bending load — on a loaded 40-tonne truck, that can be 5–8 tonnes per front corner. The king pin runs in bronze or nylon bushings in the steering knuckle, which means its surface hardness, OD tolerance, and surface finish directly determine the wear life of the whole steering assembly. A worn or cracked king pin is a catastrophic safety failure on a vehicle doing highway speeds. This is why commercial vehicle OEMs and axle manufacturers worldwide specify drop-forged case-hardened king pins — not ground bar, not cast components.
King pins for rigid front steering axles of two-axle and three-axle heavy trucks, and TAG (tridem axle group) steering axles on multi-axle vehicles. Typical OD range 30–60 mm, length 150–250 mm. 20MnCr5 or EN36 grade, case depth 1.0–1.5 mm, surface 60–62 HRC.
City buses, intercity coaches, and articulated buses use king pins in the steering axle. Coach king pins often specify tighter OD tolerance and lower Ra surface finish than truck versions because coach steering geometry is more sensitive. We grind to g6 tolerance and Ra 0.4 μm for coach applications.
The semi-trailer coupling kingpin (sometimes called a fifth-wheel kingpin or turntable kingpin) is a different component from the steering axle king pin — it is a large-diameter (50 mm or 90 mm SAE) solid steel pin that locks into the truck's fifth-wheel coupling. We produce these in EN24T through-hardened to 38–42 HRC per SAE J133.
Tractor front steering axles — both beam axle and suspended axle designs — use king pins in the steering knuckles. Agricultural king pins see lower absolute loads than truck pins but must tolerate heavy contamination (mud, water, abrasive soil) and infrequent lubrication. Case-hardened 20MnCr5 with generous case depth (1.2–1.5 mm) for durability.
Motor graders, wheel loaders, and rigid dump trucks use oversize king pins in their articulated or conventionally steered axles. These are high-load, low-speed applications with severe contamination exposure. We produce king pins up to 80 mm OD and 400 mm length in EN36 or EN24T for off-highway OEM applications.
Large mining trucks (100+ tonne payload) use custom king pins well beyond commercial vehicle standards — 100–150 mm OD in some designs. We produce custom oversize king pins from drawing, in EN24T or SAE 4340, through-hardened or case-hardened depending on the customer's specification.
King pin dies are designed to produce the correct forging envelope — sufficient machining stock on the pin OD (3–5 mm for grinding allowance) and on end faces. Our tool room conducts a tolerance study before die manufacture to confirm that forging-to-finish machining stack-up meets the finished OD specification and concentricity requirement.
King pin blanks are heated in a gas-fired rotary hearth furnace to 1150–1250°C and forged in closed dies on 300T to 600T drop hammers or friction screw presses. Multi-blow sequence ensures full die fill. Forged pin OD is 3–5 mm above finish size. Flash trimmed hot.
King pin forgings in 20MnCr5 and EN36 are loaded into our pit-type or sealed-quench furnace for gas carburising at 920–940°C, followed by controlled cooling or direct oil quench. Case depth is targeted at 0.8–1.5 mm effective case (50 HRC endpoint) depending on OEM specification. Carbon profile is tested by micro-hardness traverse on witness samples.
After case hardening, every king pin batch is tested for surface hardness (58–62 HRC target) and core hardness (30–40 HRC target for 20MnCr5). Core must retain toughness to resist bending fracture even if the case is fully stressed. Both Rockwell surface readings and Vickers cross-section traverses are used to verify the hardness profile.
Case-hardened king pin blanks are cylindrically ground on our centreless or between-centres grinding machines to achieve OD tolerance h6 (interference-to-transition fit in bearing bush) or g6 (clearance fit) per the OEM's specification. Surface finish Ra 0.4–0.8 μm. Grinding parameters controlled to prevent rehardening or tempering damage to the case.
Every king pin is 100% wet fluorescent magnetic particle inspected per ASTM E1444, focusing on the OD surface and end-face transitions. Any linear indication is cause for rejection. Final dimensional report covers OD diameter, length, straightness, and end-face perpendicularity. Records retained for warranty and field investigation purposes.
20MnCr5 (IS 4432 equivalent, also SAE 5120) is the workhorse grade for case-hardened king pins in India. Carburises readily to 1.0–1.5 mm case depth, achieves 60–62 HRC surface, and retains a 28–34 HRC core for adequate toughness. Used by all major Indian commercial vehicle OEMs for truck and bus king pins.
EN36 (655M13, nickel-chromium case-hardening steel) for applications requiring higher core strength than 20MnCr5 can deliver in large section sizes. Core tensile strength 800–1100 MPa after case hardening. Used for oversized off-highway king pins and heavy truck applications with very high bending loads.
SAE 8620 (0.2% C, Ni-Cr-Mo alloy case-hardening steel) for king pins specified by US or European OEMs with American material standards. We source 8620 from established billet suppliers and produce king pins to AMS or ASTM standards with appropriate material certification.
EN24T (817M40T, SAE 4340 equivalent) through-hardened to 38–42 HRC is an alternative to case-hardened king pins for applications where uniform through-section properties are preferred — notably semi-trailer 5th-wheel kingpins per SAE J133, which require through-hardening rather than surface case.
Some OEMs specify proprietary steel grades — 20NiCrMo2, 16MnCr5, or specific chemical limits within a grade window. We work from the OEM's material specification document and source billet accordingly. Composition verification by spectrometer at goods-inward is standard on all OEM-specified grades.
King pins typically have threaded ends for the castellated retaining nut (IS 6094 or DIN 71802 specification). We cut threads after grinding to ensure thread axis is concentric with the ground OD. Thread profile — M-metric or UNF — and nut retention method per OEM drawing or IS 6094 standard.
The king pin is one of those components that most people have never heard of but that every heavy truck depends on. It is the vertical pivot pin through the steering knuckle of the front axle — the element that physically allows the front wheel to turn left and right. In a loaded 40-tonne truck, each front corner carries 5–8 tonnes. That load is transmitted to the king pin as a bending force, which is why king pin fatigue life is a real engineering concern. Commercial vehicle OEMs spend considerable effort on king pin design — specifying case depth, core hardness, OD tolerance, surface finish, and material grade — because they know that a worn or cracked king pin is a steering failure on a vehicle doing 80 km/h on the highway.
Shivam Forge at Shapar GIDC, Rajkot has manufactured king pin forgings for Indian and export commercial vehicle applications for over two decades. Our manufacturing sequence is: closed-die hot forging on 300T–600T presses, then gas carburising in our pit-type furnaces at 920–940°C to 0.8–1.5 mm case depth, oil quenching to lock the martensite structure, low-temperature tempering at 150–180°C, and centreless or between-centres OD grinding to h6 or g6 tolerance. The end product is a king pin with 58–62 HRC surface hardness, 28–40 HRC core (depending on grade and section size), Ra 0.4–0.8 μm surface finish, and concentricity within 0.03 mm on the ground OD.
Grade selection matters significantly for king pins. 20MnCr5 (IS 4432 / SAE 5120) is the standard choice for Indian commercial vehicle OEMs — it carburises predictably, achieves the required surface hardness in standard section sizes, and is cost-effective given India's production volumes. EN36 (655M13, nickel-chromium case-hardening steel) delivers higher core strength in large-section king pins for heavy-duty off-highway applications. For semi-trailer 5th-wheel kingpins per SAE J133, EN24T through-hardened to 38–42 HRC is the correct specification — these are not case-hardened components. Shivam Forge produces all three variants and will recommend the grade based on your application and OD size.
Quality control on safety-critical king pins is not optional. Our quality regime: 100% wet fluorescent magnetic particle inspection per ASTM E1444 on the pin OD after grinding, which detects surface and near-surface cracks introduced during forging, heat treatment, or grinding burn. Dimensional report from CMM or checking fixtures for OD, length, straightness, and end-face perpendicularity. Case depth verification by micro-hardness traverse on witness samples from each furnace load. Surface and core Rockwell hardness on every lot. These records are available for customer review and are part of our standard inspection documentation.
If you are an axle manufacturer, commercial vehicle OEM, or maintenance and repair organisation looking for king pin forgings in India, Shivam Forge is one of the specialist manufacturers in Rajkot's Shapar GIDC forging cluster. We supply to Indian OEMs and export to aftermarket customers in the Middle East, Africa, and Southeast Asia. Lead time for standard dimensions: 2–3 weeks from order. New tooling: 5–7 weeks including die manufacture and first article. Call +91-9265772827 or email info@shivamforge.com with your drawing — we will confirm capability and provide a detailed quotation within 48 hours.
Yes. We manufacture hot-drop forged, case-hardened, and OD-ground king pins at Shapar GIDC, Rajkot for heavy trucks, buses, semi-trailers, tractors, and off-highway equipment. Grades: 20MnCr5, EN36, 8620, and EN24T. 100% MT inspection on every piece.
20MnCr5 (IS 4432) is the standard choice for most Indian commercial vehicle OEMs — it carburises well, achieves 60–62 HRC surface, and the core remains tough at 28–34 HRC. EN36 (655M13) is used for heavy-duty applications requiring higher core strength in large section sizes.
We target 0.8–1.5 mm effective case depth (50 HRC endpoint) for king pins, depending on OEM specification. Case depth is verified by micro-hardness traverse on a witness sample from each furnace load. The carbon profile is controlled by furnace atmosphere carbon potential and carburising time.
Surface hardness is checked by portable Rockwell hardness tester on the pin OD at three or more axial positions per piece. Results are logged and compared to the 58–62 HRC acceptance criterion. Core hardness is checked on the trimmed end face after grinding.
Our centreless and between-centres grinding can hold h6 or g6 OD tolerance as required — typically ±0.008–0.013 mm on 35–60 mm diameter pins. Surface finish Ra 0.4–0.8 μm. Straightness within 0.05 mm per 200 mm length.
Yes. We supply king pins for heavy truck rigid and TAG steering axles, city buses, intercity coaches, and articulated buses. Coach specifications typically call for tighter OD tolerance and finer surface finish than truck pins — we accommodate both.
For standard dimensions with existing die tooling: 100 pieces minimum. For new dimensions requiring die manufacture: 200–500 pieces minimum to amortise tooling cost. Prototype quantities (5–20 pieces) available using adaptable tooling at higher per-piece cost.
Send your drawing with OD tolerance, case depth, surface HRC, length, grade specification, and quantity to info@shivamforge.com or call +91-9265772827. We respond with tooling cost (if new die required), piece price, and lead time within 48 hours.
Why Choose Shivam Forge
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.
