1.7131 or 1.6587? Selecting Case-Hardening Steel for Gears

A hard tooth is not enough: the core, distortion and size also decide

Gear size, tooth-root load, required case depth, core toughness, distortion control and inspection determine whether 1.7131 or 1.6587 is the better route.

16MnCr5 / 1.7131 and 18CrNiMo7-6 / 1.6587 are both case-hardening steels, yet they serve different section and duty ranges. The case resists contact and wear while the core carries bending, impact and structural load; selection must control both systems.

This guide is intended for designers, buyers, heat-treatment teams and workshops supplying parts across Iran. It translates a familiar market enquiry into requirements that can be checked before payment, cutting, machining or furnace work.

Quick decision map

Identity, standard and the real engineering question

1.7131 is a practical choice for many small and medium components with a qualified carburizing route. Nickel-chromium-molybdenum 1.6587 offers greater hardenability and core-toughness potential for larger or more highly loaded gears, but it does not remove process risk.

For compact gears with moderate section, 16MnCr5 often provides an efficient balance of availability, machining and carburizing response. For thick roots, wide faces or demanding loads, 18CrNiMo7-6 may provide a more robust core when properly processed.

Gear size and tooth-root load

Sets the required core response and failure margin. Record Module, face width, effective section and duty spectrum before commercial comparison begins. If this field remains verbal, purchasing, production and inspection can each interpret the same requirement differently.

Case requirement

Surface hardness alone does not define fatigue performance. The order should therefore require Effective case depth, hardness profile and reference limit. Catalogue data becomes useful only after product form, section and test condition are made comparable.

Section, process and delivered condition

Section size changes cooling rate, property distribution, sampling position and sometimes the applicable property range. Product form also matters: bar, plate and forging may share a grade name but follow different dimensional, testing and delivery requirements.

Specify effective case depth by test method and hardness limit, not by a vague request for a hard surface. Final grinding allowance must preserve the useful case, and retained austenite, intergranular oxidation or grinding damage may require project-specific control.

Inspection evidence that closes the decision

Evidence should answer a defined question. An MTC records heat identity and declared results; a process record proves the route used; a supplementary test report proves a result at a stated location. None of them should be treated as a substitute for the other two.

Core property

Supports the case under bending, shock and overload. Define Core hardness, strength or impact requirement at a stated location and identify the point where production must stop if the evidence is missing or outside the agreed range.

Distortion and inspection

Carburizing, quenching and grinding can change geometry and surface integrity. Release should be based on Stock allowance, datum plan, profile check and crack inspection, attached to the same heat and piece identity. A valid test report has limited conformity value after traceability has been lost.

A defensible purchase specification

State material number, product form and condition, gear geometry, carburized and final dimensions, effective case-depth definition, surface and core requirements, distortion allowance, test coupon and final NDT.

Grade/material number: [complete]; standard and edition: [complete]; form and dimensions: [complete]; delivery condition: [complete]; quantity and cutting tolerance: [complete]; MTC type: [complete]; supplementary test and acceptance rule: [complete]. Topic-specific requirement: State material number, product form and condition, gear geometry, carburized and final dimensions, effective case-depth definition, surface and core requirements, distortion allowance, test coupon and final NDT.

Ordering checklist for Tehran, Tabriz, Isfahan and Yazd

• Write the recognised market term, but place 1.7131 or 1.6587 and the documented designation on the same enquiry.
• Close Gear size and tooth-root load with Module, face width, effective section and duty spectrum.
• Close Case requirement with Effective case depth, hardness profile and reference limit.
• Define Core property before irreversible processing.
• Keep Distortion and inspection traceable through cutting, storage and loading.
• State destination, required dispatch date, packaging, piece count and who authorises release.

Related encyclopaedia pages and guides

• 16mncr5 1 7131
• 18crnimo7 6 1 6587
• Previous Week-01 technical guide
• Next Week-01 technical guide
• Alloy-steel encyclopaedia
• Evidence and calculation methodology
• Contact Shaygan Steel

Frequently asked questions

Is 1.7131 always enough for a small gear?

Not automatically. Load, tooth root, case depth, material quality and process capability still control acceptance.

Does 1.6587 eliminate distortion?

No. It can support demanding cores, but distortion remains a process and geometry issue.

Does high surface hardness prove gear quality?

No. Case depth, hardness profile, core support, cracks, retained austenite and final geometry also matter.

Sources and method

This article uses the official references below as technical orientation and translates them into a procurement workflow for the Iranian market. A producer data sheet applies to the product and conditions it states; it does not replace the current purchase standard, drawing or MTC for the delivered heat.

• Ovako Steel Navigator — official technical reference
• Ovako Steel Navigator — official technical reference
• Steel-Iron-List — official technical reference

Conclusion and next step

Select 1.7131 or 1.6587 by the required case-core system and the process capability for the real gear, not by a single hardness value or the assumption that more alloy is always better.

For an enquiry, send material number, form, raw and final dimensions, quantity, delivery condition, inspection needs and destination in one message. Shaygan Steel can then review the evidence for current stock before proposing a supply route.