Advances and trends in plastic forming technologies for welded tubes

With the implementation of environmental protection, sustainable development and conservation-oriented policies, components and parts of thin-walled welded tubes have gained increasing application in the aircraft and automotive industries because of their advantages： easily achieving forming and manufacturing process at low cost and in a short time. The current research on welded tube plastic forming is mainly concentrated on tube internal high-pressure forming, tube bending forming, and tube spinning forming. The focuses are on the material properties and char- acterization of welded tubes, finite element modeling for welded tube forming, and inhomogeneous deformation behavior and the mechanism and rules of deformation coordination in welded tube plastic forming. This paper summarizes the research progress in welded tube plastic forming from these aspects. Finally, with a focus on the urgent demand of the aviation, aerospace and automotive industries for high-strength and light-weight tubes, this paper discusses the development trends and challenges in the theory and technology of welded tube plastic forming in the future. Among them, laser tailor-welded technology will find application in the manufacture of high-strength steel tubes. Tube-end forming technology, such as tube flaring and flanging technology, will expand its appli- cation in welded tubes. Therefore, future studies will focus on the FE modeling regarding how to consider effects of welding on residual stresses, welding distortions and microstructure, the inhomo- geneous deformation and coordination mechanism of the plastic forming process of tailor-welded tubes, and some end-forming processes of welded tubes, and more comprehensive research on the formin~ mechanism and limit of welded tubes.

Determination of continuous constitutive relationship of weld zone of high-strength steel rectangular welded tube

For QSTE700 high-strength steel rectangular welded tube,the mechanical properties of the weld zone vary with the distancefrom the centerline of the weld.Therefore,the accurate description of constitutive relationship of the weld zone is of greatsignificance for the study of formability of QSTE700 rectangular welded tube.Firstly,the mechanical properties of parentand mixed specimens containing weld zone and parent zone were obtained by uniaxial tensile test.And based on the micro-hardness test,the width and the microhardness distribution of the weld zone were determined.Secondly,by subdividingthe weld zone into several small areas,and combining with the rule of mixtures and nanoindentation test,the continuous functional relationships of strength coefficient K,hardening coeffecient n and elastic modulus E were obtained,and then,the continuous constitutive relationship of QSTE700 rectangular welded tube was established.Finally,the validity and reliability of the continuous constitutive relationship of welded tube were verified by nanoindentation fest and rotary drawbending of rectangular welded tubc.Besides,it was found that the finite element model of rotary draw bending of QSTE700 rectangular welded tube established by using the continuous constitutive relationship can well simulate the cross sectiondeformation and wall thickness variation.

Effect of Rare Earth on the Corrosion-Resisting Performance of Zinc-Based Alloy Coatings

The corrosion behavior of coatings of pure zinc and Zn-Al,Zn-Al-RE alloys in NaCl solu- tions was studied by salt-spray experiments,even corrosion experiments and electrochemical measurements of bi-directional polarization curves and a.c.impedance in weak polarization region consistent regularities were obtained by these different methods,viz.,the corrosion resistance of Zn could be enhanced by alloying it with Al,and particularly with Al-RE.The causes of enhancement of corrosion resistance by RE were also discussed.

Product development of Baosteel HFW 610 Mill

Baosteel's high-frequency electric resistance welded(HFW) 610 longitudinal seam mill(8 5/8″-24″, the yearly output 300000 t) and UOE 1422 longitudinal submerged arc welding(SAW) mill(20' -56',the yearly output 500000 t) are established in 2005 and 2008,respectively.Product specification covers whole of API 5CT standard and most of API 5L standard,terminating the history of manufacturing the medium and large size pipes at Baosteel.The yearly output increased from 1,200000 t to nearly 2000000 t.HFW 610 mill is oriented at mid size pipes,which are mainly linepipe and welded casing.The designed yearly output of HFW mill is 300000 t,including casing of 90000 t,linepipe of 180000 t,round structural pipe of 15000 t and rectangle structural pipe of 15000 t. The yearly output of oil casing line supporting the welding line is 120000 t,among which including welded casing and seamless casing of 30000 t.Baosteel's HFW 610 longitudinal seam mill was established on October 27,2005. After the equipment trial run In October,2005 - March,2006 and equipment function examination In April,2006 - June,2006,mass production started in July 2006.And in December 2006,monthly designed capacity was achieved,reaching to 30496.644 t in welding pipe and 28 349.939 t in finished pipe.The output of 2006,2007, 2008 and 2009 was 117 067 t,223 554 t,255 791 t,and 204 424 t,with the comprehensive yield ratio 79.4%, 87.8%,90.80%and 91.92%respectively.This study introduces Baosteel HFW 610 Mill which is the world class,energy conservation and environmental protection enterprise,including product orientation,process and new product development.

Study of Magnetically Impelled Arc Butt Welder for Tube to Sheet Welding

Magnetically impelled arc butt welder is mainly used in the automotive industry for butt welding tubes.To extend the range of the welding applications,a new type of magnetically impelled arc butt welder for tube to plate welding had been developed.The welder consisted two parts of mechanical device and electrical control system,in which the mechanical device with an appropriate clamping,location and upsetting control was specially designed for simple operation.The electrical control system involved the power supply,magnetic field and logic control of the welding.So the starting and rotating behaviour of the arc in the welding region of tube and sheet can be accurately controlled for the quality of tube to sheet joints.As a result,the welder for tube to sheet welding could generate a stable rotating arc by adjusting the welding parameters,and had a constant high-quality joint.