Jinsun Liao

Toughness investigation on simulated weld HAZs of SQV-2A pressure vessel steel

Abstract In order to get detailed information about weld HAZs toughness of SQV-2A steel and determine the optimum welding and heat treatment parameters, the toughness of simulated CGHAZs (coarse grained heat affected zone) and CGHAZs (intercritically reheated CGHAZ) were systematically investigated. The influence of tempering thermal cycles on weld ICCGHAZs toughness was clarified. The effect of post weld heat treatments (PWHT) on weld CGHAZs toughness was also determined. The results showed that high toughness (absorbed energy >200 J) of weld HAZs could be achieved by selecting the optimum welding and PWHT parameters (cooling time Δ t 8/5 : 6–40 s, PWHT: 893 K, 3.6–7.2 ks). Tempering thermal cycles with peak temperature of above 573 K could remarkably improve the toughness of deteriorated ICCGHAZs and reduce the hardness, when cooling time Δ t 8/5(2) of the reheating thermal cycle was 6 s, which implies that welding of SQV-2A without PWHT is possible, provided that low heat input welding is adopted and welding procedure is correctly arranged. Metallography and fractography revealed that M–A constituents in weld HAZs played an important role in controlling weld HAZ toughness.

Effect of cooling time on HAZ toughness and microstructure: Simulated HAZ toughness of low‐alloy SQV‐2A pressure vessel steel (1st report)

Summary This paper describes an investigation of the microstructure and Charpy impact energy of the simulated weld HAZ of low‐alloy SQV‐2A steel with particular reference to the effect of the formation of M‐A constituent and its morphology. Weld HAZ thermal cycles having cooling times ?t8/5 from 6 to 1000 sec, which reflect various welding heat inputs, were simulated with a Gleeble 1500 thermal/mechanical simulator. The formation of M‐A constituent and its morphology were examined by TEM and SEM. The M‐A constituent of this steel forms at cooling times ?t8/5 above 20 sec. With an increasing cooling time, the M‐A constituent forms not only near the grain boundaries, but also in the grain interiors (transgranularly) and changes from an elongated to a massive shape. Both elongated and massive M‐A constituents appear to impair the HAZ toughness of SQV‐2A steel. The M‐A constituent acts as a microcrack initiation site inducing toughness loss, but the toughness appears to be affected not only by the M‐A constit...

Weld HAZ Toughness and Its Improvement of Low Alloy Steel SQV-2A for Pressure Vessels. (Report 1). Effect of Cooling Time on the Weld HAZ Toughness and Microstructure.

The microstructure and Charpy impact energy of simulated weld HAZs of low alloy steel SQV-2A have been investigated with particular reference to the effect of the formation of M-A constituent and its morphology. Weld HAZ thermal cycles having cooling times Δt8/5, from 6 to 1000 s, which reflect various welding heat inputs, were simulated with Gleeble 1500 thermal/mechanical simulator. The formation of M-A constituent and its morphology were examined with TEM and SEM. For this, steel, the M-A constituent formed at cooling times Δt8/5 more than 20s. With increasing cooling time, the M-A constituent formed not only near the grain boundary but also in bulk region, and changed from elongated shape to massive shape. Both enlongated and massive M-A constituents seem to impair the HAZ toughness of SQV-2A steel. The M-A constituent acts as the initiation site of microcracking to induce the toughness loss, but the toughness may be affected by not only M-A constituent but also the matrix, because the matrix itself seems to become brittle with increasing cooling time.