Study and prevention of cracking during weld-repair of heat-resistant cast steels

International audienceHeat-resistant cast steels are highly sensitive to cracking as they are weld-repaired because of their very low ductility. To prevent weld-repair cracking of three different heat-resistant cast steels used for the manufacturing of superplastic forming (SPF) dies, the effect of various welding parameters, such as the choice of the filler material, the number of weld passes and the pre-heating temperature has been investigated. The choice of an appropriate filler metal and the pre-heating to 400 °C of the material prior to welding drastically lower the propensity to cracking, but remain unable to eliminate cracks entirely. To further reduce weld-repair cracking and hopefully prevent it completely, a buttering technique has been developed. Buttering of the base metal surface with nickel alloys before weld-repair has been shown to prevent cracking of the base metal, but results in some hot-cracking of the buttering layer itself. On the other hand, buttering with Ni-Fe alloys, less sensitive to hot-cracking, results in crack-free weld repairs

Experimental and numerical investigation of the weld repair of superplastic forming dies

Issu de : AMPT 2003 - International conference on advances in materials and processing technologies, Dublin, IRELAND, July 8-11, 2003International audienceSuperplastic forming process (SPF) is an advanced process conducted at high temperature using moderate strain rates, typically used for shaping TAW sheets for aerospace applications. Thermomechanical stresses on the forming dies due to successive forming cycles may result in the earl), degradation and even fracture of SPF tools through fatigue crack propagation. To reduce cost and extend service life. dies are generally weld-repaired and subsequently re-used in the typical severe conditions of SPF. The implementation of robust, easy processing welding techniques resulting in high quality repair able to sustain cumulative thermomechanical stresses is of utmost concern to SPF parts manufacturers. The paper focuses on the development of an automated TIG technique to weld repair high nickel, high chromium heat resistant alloys based on a complementary approach including thermal instrumentation, numerical simulation using Sysweld(TM) and metallurgical investigation: this former being performed on either as-received, repaired and repaired plus damaged materials

Rechargement par soudage d'aciers réfractaires moulés (application à la réparation des matrices de formage superplastique)

TOULOUSE3-BU Sciences (315552104) / SudocALBI-ENSTIMAC (810042301) / SudocSudocFranceF

A microstructural and low-cyle fatigue investigation of weld-repaired heat-resistant cast steels

The multi-pass weld-repair of heat-resistant cast steels is carried out using an automated shielded metal arc welding (SMAW) process, with various filler materials and pre-heating at 400°C. Specimens weld-repaired with a filler material more resistant than the heat-resistant cast steel (over-matching) generally crack within the base metal following the tenth filling pass, whereas specimens buttered with a soft alloy prior to welding remain free of cracks. The high temperature strain-controlled fatigue lifetime of material weld-repaired without buttering is lower than that of bulk initial material. This is due to an increase of the stress amplitude as a result of the so-called over-matching. In the case of material welded following a prior buttering, the fatigue lifetime is reduced because of the stress tri-axiality generated in the thin soft layer which prevents its plastic flow. As a consequence, it is concluded that even though buttering prevents cracking efficiently during welding, it is not acceptable as far as fatigue performance, especially lifetime, is concerned

A microstructural and low-cycle fatigue investigation of weld-repaired heat-resistant cast steels

International audienceThe multi-pass weld-repair of heat-resistant cast steels is carried out using an automated shielded metal arc welding (SMAW) process, with various filler materials and pre-heating at 400 degrees C. Specimens weld-repaired with a filler material more resistant than the heat-resistant cast steel (over-matching) generally crack within the base metal following the tenth filling pass, whereas specimens buttered with a soft alloy prior to welding remain free of cracks. The high temperature strain-controlled fatigue lifetime of material weld-repaired without buttering is lower than that of bulk initial material. This is due to an increase of the stress amplitude as a result of the so-called over-matching. in the case of material welded following a prior buttering, the fatigue lifetime is reduced because of the stress tri-axiality generated in the thin soft layer which prevents its plastic flow. As a consequence, it is concluded that even though buttering prevents cracking efficiently during welding, it is not acceptable as far as fatigue performance, especially lifetime, is concerned

Micro transition to model cracking phenomenas during multipasses welding processes

The nucleation of cracks during welding process is of main importance in order to assess the lifetime prediction of the component that is made. Due to the complexity of the loading of the material during the process, a two scale numerical model is developped. The two scales are (i) the structural level and (ii) the microstructural level. A macroscopic criteria is developped and a simultion is performed to look at the influence of the process parameters (initial temperature, input energy, thermal boundary conditions,...). Then a microstructural ¯nite element model is developped

Etude expérimentale et numérique du soudage-rechargement : prévision du risque de fissurations à froid d'un acier austénitique réfractaire

Non renseign

Influence of the mechanical properties of filler materials on weld repair quality of SPF tools

In superplastic forming (SPF) of titanium alloy sheets, the thermomechanical stresses due to successive forming cycles are likely to provoke early degradation and even fracture of dies. For economic reasons, dies are generally weld-repaired in order to extend their service life. A weld repair technique was developed for high nickel high chromium heat resistant alloys using shielded metal arc welding process. This paper focuses on the influence of the preheating and the buttering with a low strength filler metal on the quality of the welded zones in order to optimise the procedure of SPF tool repair. A double approach including numerical simulation using SysweldTM and experimental investigations is proposed

Rechargement T.I.G. d'outillages de formage superplastique -essais et simulation

National audienc