Weldability of Dual Phase Steel Containing Boron

Carbon steel containing boron-dual phase was produced by casting and were heated to 1200 °C for hot forging to produce plates of 10 and 6 mm thick. The plates produced were heated to the inter-critical annealing temperature for 15 min. and then water quenched followed by tempering process. The microstructure of the produced steel is ferrite with islands of martensite. Welding was done to the heat treated steel plates (6mm) using SMAW process and applying AWS-E11016 electrode and as a result an over-tempered region in the heat affected zone was formed with a significant reduction of the ultimate tensile strength of the welded joint. Reduction of heat input resulted in an increase in the joint strength. Welding of the hot rolled plates with a subsequent heat treatment resulted in formation of homogenous joint with good mechanical and metallurgical properties. Application of Electron Beam Welding to this dual phase steel resulted in a welded joint with good mechanical properties comparable to that of the base metal. The results were discussed based on microstructure analysis and hardness distribution of the welded joints.

Formation and stabilization of reverted austenite in supermartensitic stainless steel

The formation and stabilization of reverted austenite upon inter-critical annealing was investigated in a X4CrNiMo16-5-1 (EN 1.4418) supermartensitic stainless steel by means of scanning electron microscopy, electron backscatter-diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy and dilatometry. The results were supported by thermodynamics and kinetics models, and hardness measurements. Isothermal annealing for 2 h in the temperature range of 475 to 650 °C led to gradual softening of the material which was related to tempering of martensite and the steady increase of the reverted austenite phase fraction. Annealing at higher temperatures led to a gradual increase in hardness which was caused by formation of fresh martensite from reverted austenite. It was demonstrated that stabilization of reverted austenite is primarily based on chemical stabilization by partitioning, consistent with modeling results.