{"id":4820,"date":"2019-11-25T14:05:40","date_gmt":"2019-11-25T12:05:40","guid":{"rendered":"https:\/\/fractory.com\/?p=4820"},"modified":"2024-01-26T16:18:42","modified_gmt":"2024-01-26T14:18:42","slug":"heat-affected-zone-causes-effects-reduction","status":"publish","type":"post","link":"https:\/\/fractory.com\/heat-affected-zone-causes-effects-reduction\/","title":{"rendered":"Heat Affected Zone – Causes, Effects and How to Reduce It"},"content":{"rendered":"

The heat affected zone (or simply HAZ) is something that occurs when metal is subject to high temperatures. It has a negative impact on the design and structure of the metal. This article discusses those effects and how to reduce them.<\/p>\n

Some manufacturing procedures that produce the HAZ are mechanical cutting, thermal cutting and welding<\/a>.<\/p>\n

With mechanical cutting, the shear strength of the metal has to be surpassed. The majority of the energy converts into heat that influences both the life span of the tools and the metal being cut.<\/p>\n

Thermal cutting methods, like laser cutting<\/a> and plasma cutting<\/a>, actually use heat for cutting. Again, the same structural and aesthetic changes take place.<\/p>\n

Welding, similarly to thermal cutting, uses very high temperatures to either add molten metal or melt the parts themselves.<\/p>\n

As the formation of the heat affected zone has a considerable effect on the quality of the final product, it is good to understand the different aspects of it.<\/p>\n

What is the Heat Affected Zone?<\/h2>\n

During metal cutting or metal welding, the metal absorbs the generated heat. This heat transmits away from the cutting edge through the metal body, as metal is a good heat conductor.<\/p>\n

A zone is formed between the melted metal and the unaffected base metal called the heat affected zone (HAZ). In this zone, the metal is not melted but the heat has led to changes in the metal\u2019s micro-structure. These changes in structure can reduce the metal\u2019s strength.<\/p>\n

The HAZ is identifiable by a series of brightly coloured bands between the cutting\/welding interface and the unaffected base metal. The colours range from light yellow to purple as shown in the table below.<\/p>\n

It is very important to understand that the HAZ accounts for reduced strength to design safe applications. The weakest sections of a structure<\/strong> exist in the HAZ.<\/p>\n

A structure is as strong as its weakest point. Therefore, recognising the HAZ may be the difference between the success and failure of a particular part.<\/p>\n

What Does the Colour Tell?<\/strong><\/h2>\n

As a result of using different temperatures during manufacturing processes, a variety of tints are present in the HAZ. These tints range from light yellow to dark blue in increasing order of the temperature.<\/p>\n

The band colours in order of temperature progression are:<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n
Colour<\/strong><\/td>\nCutting temperature<\/strong><\/td>\n<\/tr>\n
Light yellow<\/td>\n290\u00ba C<\/td>\n<\/tr>\n
Straw yellow<\/td>\n340\u00ba C<\/td>\n<\/tr>\n
Yellow<\/td>\n370\u00ba C<\/td>\n<\/tr>\n
Brown<\/td>\n390\u00ba C<\/td>\n<\/tr>\n
Purple brown<\/td>\n420\u00ba C<\/td>\n<\/tr>\n
Dark purple<\/td>\n450\u00ba C<\/td>\n<\/tr>\n
Blue<\/td>\n540\u00ba C<\/td>\n<\/tr>\n
Dark blue<\/td>\n600\u00ba C<\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n

Factors that further affect the formation of these heat tints are:<\/p>\n