What is qst?

QST rebars:The acronym 'QST' stands for 'Quenched & Self Tempered' reinforcement steel bars.

In hot rolling mills the steel bar is passed through a high pressure water quenching system whereby only the peripheral temperature is drastically reduced while the core remains largely unaffected. On leaving the specially designed quenching system, the core heat tempers the peripheral martensite that was formed during quenching. This results in a rebar with a soft core and a uniform hardened tempered martensite periphery - a rebar with high yield strength but with extremely good ductility. Such rebars are ideal for use in high hazard seismic areas.

These bars are produced in bar rolling mills by use of the globally proven and accepted THERMEX Quenching System and Technology of M/s HSE Germany.

In the Indian Region comprising India, Nepal, Bhutan, Bangladesh, Myanmar, Pakistan and Sri Lanka, M/s H&K Rolling Mill Engineers Pvt. Ltd., Mumbai (H&K India) have been given perpetual exclusive rights by HSE Germany to Licence, sell, market, install and commission the unique THERMEX Quenching Systems. As on 1 April 2013, H&K India has received orders for nearly 200 Thermex Systems to be set up in rolling mills - of which about 29 were under excecution. The installed capacity of Thermex QST rebars in India alone is over 14 million tonnes (65% market share). Each Thermex Licensee in Indian Region is subject to strict quarterly audit. Qualified QST engineers visit each Licensee to ensure that the rebar properties are as per the strict standards laid down by HSE Germany and H&K India besides meeting the Standrards of the country.

The Thermex 500 QST rebar meets most global standards and codes and is widely accepted by leading users of rebars because of the uniform properties obtained from the various Thermex Licensees.

In India, the registered trade mark/name THERMEX is owned by H&K India as per permission given by HSE Germany.

Unfortunately, in India, these QST rebars are incorrectly referred to as 'TMT' bars. 'TMT' is an acronym for Thermo-Mechanically Treatment even though no mechanical treatment is involved in the process. This has lead to a number of improper 'TMT' rebars being sold in India with non-uniform tempered martensite periphery at the rebar cross-section - encouraged by this non-uniformity "not being a ground for rejection" as per latest rebar code IS:1786-2008!

For further information you may contact R. K. Markan at handk.india@gmail.com