Alfred Dhooge

New Generation 21/4Cr Steels T/P 23 and T/P 24 Weldability and High Temperature Properties

Creep resistant steels for high temperature service are a vital part in the construction of power stations. The possibilities to increase steam parameters of new boilers are restricted if pressure and temperature in the membrane water-walls cannot be simultaneously increased. The increase of steam parameters requires the development of new high strength and creep resistant materials. This paper gives data on weldability, mechanical properties, toughness and high temperature behaviour (creep) of new materials T/P 24 (7CrMoVTiB10-10) which have been developed by Vallourec & Mannesmann Tubes, and T/P 23 (7CrWVMoNb9–6). It is the outcome of a research project of the Belgian Welding Institute in collaboration with Laborelec and with industrial partners. Both base metals and weldments in tubes and thick walled pipes have been investigated.

Plasma Arc Welding of Modified 12% Cr Stainless Steel

This article deals with the plasma arc welding properties of 6 mm thick modified X2CrNi12 stainless steel conforming to the grades EN 1.4003 and UNS S 41003 with carbon content below 0.015% to improve the weldability. The butt welds produced without filler metal and with AISI 316L austenitic type of consumable were subjected to tensile and bend tests as well as Charpy impact toughness testing. Examinations including fractography, metallography, chemical analysis of the weld metal, ferrite content, grain size, and hardness analyses were carried out. Sound plasma arc welded joints of modified 12 Cr revealed the microstructure-property relationship, such as high ferrite content (≥ 70%) resulting in ferrite grain coarsening mainly at the high temperature heat-affected zone (HTHAZ) has no adverse effect on tensile or bend properties, but has negative effects on low temperature toughness. Enhanced toughness was provided in case of the low temperature heat affected zone (LTHAZ) with finer grained microstructure. The increase at the weld metal hardness in Weld 2 is related to the austenitic type of filler used.

High temperature properties of improved 9% Cr steel weldments

Abstract A small research program has been performed on a Modified 9% Cr 1% Mo steel (T91-ASTM A213) base material and weldments to establish the most fruitful lines along which a larger project could develop. The as-received base material was characterised by isostress and isothermal creep tests. In order to identify the influence of heat treatment, creep tests were performed on non-standard austenitised material. Weldments were produced on as-received and half-tempered base material. The creep test results indicate a limited loss of creep strength of the weldments compared to the base material due to the existence of a weak intercritical heat affected zone.

New friction welding process for pipeline girth welds : parameter optimization

Abstract A promising new welding method for fully automatic welding of pipelines has been developed. The proposed welding procedure, called friction with an ‘explosive’ forge force (FRIEX), is a new variant of the well-known friction welding process. In the first part of the present paper, the working principles of the FRIEX welding process are described. Subsequently, a brief overview is given of small-scale experiments that have been conducted in order to demonstrate the practical feasibility of this welding process. The optimization of the shape of the welding ring is discussed. Finite element models have been developed which are able to predict the process behaviour under varying process parameters. Results of numerical simulations showed good agreement with experimental observations.

Influence of deceleration phase on properties of friction welded pipelines using intermediate ring

Abstract A new welding method for fully automatic welding of pipelines has been developed. The proposed welding procedure is a new variant of the well known friction welding process. An intermediate ring is rotated in between the pipes to be welded to generate the required heat to realise the weld. In the first part of the present paper, the working principles of the new welding process are briefly described. Since a literature survey revealed that the deceleration phase has an influence on the mechanical properties and heat affected zone microstructure of friction welds, the enhancement of the mechanical properties by controlling the deceleration was investigated for the welding process. The influence of the deceleration phase on the properties of the welds is discussed. The pipes used were 3 in. pipes (outer diameter: 88˙9 mm) with a wall thickness of 7˙6 mm, made of the pipeline steel API-5L X42. Three welding ring materials were used: a thermomechanically rolled steel, a quenched and tempered steel and a normalised fine grained steel. The parameters studied were the duration of the deceleration and the rotation speed at which forging is performed.

Submerged arc welding of thick ferritic martensitic 12Cr stainless steel with a variety of consumables

Abstract Modified X2CrNi12 stainless steel, conforming to EN 1·4003 and UNS S41003 grades, has been designed with less carbon (<0·015%) and impurities to improve the weldability and mechanical properties. The present paper deals with submerged arc welding (SAW) of 30 mm thick plates of this steel with austenitic and duplex stainless steel consumables. Several samples extracted from the welded joints were subjected to mechanical testing by means of tensile, bend, Charpy impact and crack tip opening displacement (CTOD) fracture toughness tests. Microstructural examination including grain size analysis, hardness and ferrite measurements was carried out. Salt spray and blister tests as corrosion testing were applied. Considering all data obtained, it can be recommended to use austenitic filler metals as an economic alternative for SAW of this steel in the areas where impact is anticipated and adequate atmospheric corrosion resistance is needed since the weld made with austenitic wires exhibited very encouraging low temperature impact toughness properties related with finer grained microstructure and adequate strength and corrosion properties.

Possibilities and Limitations to Improve the Weldability of Low Carbon 12Cr Ferritic Stainless Steel for Expanded Industrial Applications

Ferritic stainless steel X2CrNi12 (EN 10088) is generally appreciated for its relatively low cost and good resistance to wet abrasion and mild environments, but unfortunately its weldability is restricted. Typical applications up to now include railway wagons for coal and iron ore, mining and mineral process and transport equipment, bus frames and chassis, silos, etc. This steel grade nowadays can be fabricated cost effectively with low carbon and impurity levels appreciably improving both the weldability and mechanical properties. In this case, long-term maintenance costs of assemblies produced using this ‘clean’ X2CrNi12 stainless steel will be low, with a suitable coating providing sufficient protection for several decades. For other applications, the use of weldable X2CrNi12 is also more economical than higher alloyed stainless steels. Moreover, joining the steel by laser welding without filler metal should be considered. The present paper provides an overview of results of a research project initiated by the Belgian Welding Institute investigating the possibilities of this modified low carbon ferritic stainless steel. The main objective of this work was to demonstrate that it offers great application ranges for constructing purposes which should expand its application field substantially. In the near future broadening this steel family with even higher mechanical properties allowing further reduction of plate or wall thickness and of production costs will be explored.

Friction stir welding and hybrid laser welding applied to 6056 alloy

Innovative welding processes are continuously gaining industrial interest. Both friction stir welding (FSW) and hybrid laser welding (HLW) are automated welding processes which allow achieving high quality joints in aluminium alloys, in combination with a high productivity. The EN AW-6056-T4 alloy is a relatively recent high strength weldable AlMgSiCu alloy, which is used in aviation. This alloy was subjected to FSW and HLW. The optimisation procedures which were used for FSW and HLW to assess the most appropriate welding parameters are discussed. A comparison is made between the mechanical properties in the as-welded and in the T78 post-weld heat treated (PWHT) temper. Concerning the friction stir welds, the PWHT only caused a decrease of the elongation after fracture; the thermal treatment had no effect on the minimal hardness zones of the weld, hence the tensile strength did not change. The hybrid laser welds however showed a significantly higher tensile strength after PWHT, but this was also accompanied by a ductility loss. Fatigue testing was performed on the PWHT welds. Friction stir welds clearly possessed better fatigue properties than hybrid laser welds.

New 12% Cr-steel for tubes and pipes in power plants with steam temperatures up to 650°C

Abstract Nowadays, intense efforts are made to increase efficiency and thereby minimize harmful emissions of power plants. This can be achieved by increasing operating pressure and temperature to ultrasupercritical conditions. Presently martensitic 9% Cr-steels, e.g. P91, E911 and P92 are used for power plants with advanced steam parameters. Whilst these materials have the highest creep rupture strength values of ferritic steels, their oxidation resistance is lower than 12% Cr-steels, such as X20CrMoV12-1. With increasing steam temperature (target: 650°C) the lifetime of components made of 9% Cr-steel becomes limited not only by creep but also by oxidation. The present paper reports a new 12Cr martensitic steel developed by Vallourec & Mannesmann, which is designed for use at temperatures up to 650°C. It is the outcome of a normative research project of the Belgian Welding Institute in collaboration with Laborelec and with industrial partners (Carnoy Industrial Piping, Cockerill Mechanical Industries, Fabricom, Stork Mec, Böhler Thyssen Welding Germany, Vallourec & Mannesmann Tubes, AIB-Vinçotte, VCL, Tractebel and WTCM). Base metal properties (creep strength, toughness, reheat cracking susceptibility, oxidation behavior…), welding and high temperature behavior of the new 12% Cr-steel, and welds are addressed.

12.2 – A New Potential for Welded Structures in Modified X2CrNi12: Characterization of Dissimilar Arc Weld with S355 Steel

In this study, modified X2CrNi12 ferritic stainless steel conforming in composition to grades UNS S41003 (ASTM A240) and Wr. Nr. 1.4003 (EN 10088-2 and EN 10028-7) has been welded to non-alloy S355 steel by means of flux cored arc welding (FCAW) process. A dissimilar butt welded joint was subjected to a series of tests in order to investigate all aspects of the weld properties. Mechanical testing was carried out by means of Charpy impact, tensile and bend tests. Microstructural examinations including hardness surveys, ferrite content measurements and grain size analyses of various weld regions were realised. Salt spray and blister tests were also applied as exposure testing. Rather promising results have been obtained yielding a correlation between microstructure and impact toughness.