Impact of a Multi-step Heat Treatment on Different Manufacturing Routes of 18CrNiMo7-6 Steel

Paranjayee Mandal,Laurie Da Silva,Himanshu Lalvani,Maider Olasolo

doi:10.1007/s11661-020-05728-x

Paranjayee Mandal, Laurie Da Silva + Show 2 more

Open Access

https://doi.org/10.1007/s11661-020-05728-x

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Abstract

Effect of an optimized multi-step heat treatment routine on conventional (machining from wrought bar stock) and alternate manufacturing routes (hot forging and cold rotary forging) for producing flat cylindrical-shaped machine drive components from 18CrNiMo7-6 steel was investigated. The microstructure and mechanical properties of the final component manufactured using these three different routes were analyzed using optical microscopy, electron backscatter diffraction (EBSD), hardness testing, electro-thermal mechanical testing (ETMT), and rotary bending fatigue testing (RBFT) before and after implementing the multi-step heat treatment. It was found that the multi-step heat treatment transformed the as-received microstructure into the tempered martensitic microstructure, improving hardness, tensile, and fatigue properties. The heat treatment produced desired properties for the components manufactured by all three different routes. However the cold rotary forging, which is the most material utilizing route over the others, benefited the most from the optimized heat treatment.

Highlights

THE case-hardened 18CrNiMo7-6 steel is widely used in the field of transportation, energy generation, and general mechanical engineering due to its three key characteristics—high wear resistance, good fatigue strength, and cost-efficiency
The tempering at Step5 maintained the martensitic microstructure and high hardness values irrespective of the different manufacturing routes
The deformation texture after the heat treatment showed no prominent BCC texture fibers or components for both hot forging and cold rotary forging routes, but a clear evolution of c-fibre was observed for the machining route

Summary

Introduction

THE case-hardened 18CrNiMo7-6 steel is widely used in the field of transportation, energy generation, and general mechanical engineering due to its three key characteristics—high wear resistance, good fatigue strength, and cost-efficiency. The typical applications include gears of all kinds, camshafts, heavy-duty axles and arbors, bushings, wear pins, bearings, sprockets, metal rolling equipment, machine tools, universal joints, link components, etc.[1,2] This steel is typically supplied in the annealed condition followed by a multi-step heat treatment that develops a hard wear-resistant case (hardness of up to 60 HRC) on a relatively soft core material. Alloying the base material with chromium, molybdenum or nickel enhances the hardenability and impact toughness of the core material, whereas the quenching and tempering treatments increase the strength of core material by developing a martensitic microstructure.

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