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High Temperature Nitriding of Stainless Steel : How Furnace Brazing in N2 Atmosphere Affects Steel Types 316L and 310S

Palmqvist, Klara LU (2025) KASM10 20251
Centre for Analysis and Synthesis
Abstract
Austenitic steels are one of the most used stainless steels due to their good properties such as
high strength and corrosion properties making them suitable for a material making brazed heat
exchangers. Under the brazing process of the heat exchangers, the austenitic steels are
unavoidable heat treated by the brazing atmosphere. Which is why the brazing furnaces use an
“inert” environment such as argon or nitrogen gas. However, brazing in nitrogen can cause an
unwanted effect of chromium nitride precipitation decreasing the corrosion and oxidation
resistance of the material. On the other hand, it can have a positive effect if solid solution
nitrogen is formed, causing an increasing hardness and corrosion performance.

The aim of... (More)
Austenitic steels are one of the most used stainless steels due to their good properties such as
high strength and corrosion properties making them suitable for a material making brazed heat
exchangers. Under the brazing process of the heat exchangers, the austenitic steels are
unavoidable heat treated by the brazing atmosphere. Which is why the brazing furnaces use an
“inert” environment such as argon or nitrogen gas. However, brazing in nitrogen can cause an
unwanted effect of chromium nitride precipitation decreasing the corrosion and oxidation
resistance of the material. On the other hand, it can have a positive effect if solid solution
nitrogen is formed, causing an increasing hardness and corrosion performance.

The aim of this study was therefore to investigate the relationship between nitrogen pressure,
temperature, and chromium nitride precipitation by heat-treating stainless-steel types 316L and
310S. As well as examine how high temperature nitriding affect the hardness, corrosion and
oxidation performance of the material. It was also studied how this correlate to thermodynamic
calculations using the thermodynamic software Thermo-Calc.

This study resulted in that a brazing atmosphere conducting nitrogen will cause the formation
of Cr2N precipitates on both steel types at temperatures above 900 °C. However, it was also
found that even if there was some precipitation, there seemed to be some nitrogen in solid
solution. This influenced both hardness and other properties, as both the precipitation and solid
solution nitrogen enhanced hardness while the formation of chromium nitrides affected the
general corrosion negatively. Finally, even if 310S had a more severe nitridation, it seemed to
still have a better corrosion and oxidation performance compared to 316L. (Less)
Please use this url to cite or link to this publication:
author
Palmqvist, Klara LU
supervisor
organization
course
KASM10 20251
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Austenite, Brazing, Chromium Nitrides, High-Temperature Nitriding, Solid Solution Nitriding, Materials Chemistry
language
English
id
9199818
date added to LUP
2025-06-16 15:44:10
date last changed
2025-06-16 15:44:10
@misc{9199818,
  abstract     = {{Austenitic steels are one of the most used stainless steels due to their good properties such as
high strength and corrosion properties making them suitable for a material making brazed heat
exchangers. Under the brazing process of the heat exchangers, the austenitic steels are
unavoidable heat treated by the brazing atmosphere. Which is why the brazing furnaces use an
“inert” environment such as argon or nitrogen gas. However, brazing in nitrogen can cause an
unwanted effect of chromium nitride precipitation decreasing the corrosion and oxidation
resistance of the material. On the other hand, it can have a positive effect if solid solution
nitrogen is formed, causing an increasing hardness and corrosion performance.

The aim of this study was therefore to investigate the relationship between nitrogen pressure,
temperature, and chromium nitride precipitation by heat-treating stainless-steel types 316L and
310S. As well as examine how high temperature nitriding affect the hardness, corrosion and
oxidation performance of the material. It was also studied how this correlate to thermodynamic
calculations using the thermodynamic software Thermo-Calc.

This study resulted in that a brazing atmosphere conducting nitrogen will cause the formation
of Cr2N precipitates on both steel types at temperatures above 900 °C. However, it was also
found that even if there was some precipitation, there seemed to be some nitrogen in solid
solution. This influenced both hardness and other properties, as both the precipitation and solid
solution nitrogen enhanced hardness while the formation of chromium nitrides affected the
general corrosion negatively. Finally, even if 310S had a more severe nitridation, it seemed to
still have a better corrosion and oxidation performance compared to 316L.}},
  author       = {{Palmqvist, Klara}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{High Temperature Nitriding of Stainless Steel : How Furnace Brazing in N2 Atmosphere Affects Steel Types 316L and 310S}},
  year         = {{2025}},
}