Decarburisation Effect on Hardened Strip Steel Fastening Components

Medžiagotyra. 2016;22(1):148-152 DOI 10.5755/j01.ms.22.1.7467

 

Journal Homepage

Journal Title: Medžiagotyra

ISSN: 1392-1320 (Print); 2029-7289 (Online)

Publisher: Kaunas University of Technology

Society/Institution: KTU

LCC Subject Category: Technology: Mining engineering. Metallurgy

Country of publisher: Lithuania

Language of fulltext: English

Full-text formats available: PDF, HTML

 

AUTHORS

Karli JAASON (Tallin University of Technology)
Priidu PEETSALU
Mart SAARNA
Priit KULU
Jüri BEILMANN

EDITORIAL INFORMATION

Peer review

Editorial Board

Instructions for authors

Time From Submission to Publication: 48 weeks

 

Abstract | Full Text

<span lang="EN-US">Heat treatment is widely used for high reliability fastening components such as buckles and brackets. The current study focuses on mass production of safety components which are fineblanked from sheet metal, austempered and chromium electroplated. Electroplating together with stamping defects may lead to unexpected brittle failure of the component. It is widely known that during austenitisation, decarburisation could avoid brittle failure and, therefore, slight decarburisation is recommended. There is little information how much mass production is influenced by decarburisation and where the limits are. The current study has two goals. The first one focuses on the extent of decarburisation effect on the part properties, and the second aims to find the optimum furnace setting for the product type used in the study. Also, it is necessary to choose a reliable decarburisation control method for austempered components. The effect on material grades was analyzed by using three steel alloys with carbon content of 0.37 wt.%, 0.47 wt.% and 0.62 wt.%. The specimens were austempered to hardness 45<sup> </sup>–<sup> </sup>51 HRC under endothermic protective atmosphere. To gain different decarburisation levels, two gas set-ups were used. Infrared gas analyzer was used to measure CO and CO<sub>2</sub> content in the furnace gas. Three characteristics of the specimens were evaluated: hardness, rupture strength and brittleness. The depth of the decarburisation was determined by three different approaches according to standard EN ISO 3887. Based on the results, the spectrographic method is the most reliable for determining the depth of decarburisation. This study reveals that higher surface decarburisation has a positive effect on the ductility and no effect on the rupture strength of the component. The material with carbon content of 0.62 wt.% is the most sensitive to decarburisation. During mass production, the inaccuracy of hardness measuring raises which results in the inaccuracy of salt bath temperature regulation. For the used thermal cycle, the furnace gas carbon potential 0.30<sup> </sup>–<sup> </sup>0.40 has to be used to ensure expected performance of fastening products.</span>