WELDING & JOINING No.6(360),2003


CONTENTS

Feature Article
  INVESTIGATION AND RECENT PROGRESS OF FORMATION MECHANISM OF BLOWHOLE IN STAINLESS STEEL WELD
  Taiyuan University of Technology Sun Xian
 Abstract: The object studied in this paper is the weld of rutile type Cr-Ni austenitic stainless electrode. Based on the theory of blowhole emersion velocity, recent progress of mechanism investigation of blowhole formation, including the influence theory of moisture in electrode covering, the influence theory of non-metallic inclusions in droplets, the influence theory of solidification mode of weld metal and the influence theory of droplet transfer pattern, are introduced, which provides the basis for necessary theory of further investigating and engineering application. 
 Key words: blowhole, stainless steel weld, formation mechanism, recent progress

Research Papers
1ӢREMOTE SYSTEM OF WELDING NUMERICAL SIMULATION BASED ON B/S
Tsinghua University Liang Chenjian, Wu Aiping, Zou Guisheng
Abstract: In this paper, based on B/S mode and EJB technology, a remote welding simulation system is outlined, which combines the technologies of Internet and welding numerical simulation, and three layers structure, including application layerӢpresentation layer and execution layer, and the solutions of the key technologies which include development standard Ӣdata baseӢintellect modeling and solution of FEM in the system research are presented. It's an exploration of the application of computer and network technologies in welding.
Keywords: network, agile manufacture, welding numerical simulation

2ӢEFFECTS OF POSTWELD HEAT TREATMENT IN VACUUM ON PROPERTIES OF LASER WELDED JOINT OF BT20 TITANIUM ALLOY
Beijing Aeronautical Manufacturing Technology Research Institute Yao Wei£¬Gong Shuili£¬ Chen Li
Abstract: In this paper, the effects of postweld heat treatment in vacuum on properties of laser welded joint of BT20 titanium alloy were studied. It showed that the tensile strength and the elongation of CO2 laser and YAG laser welded joint of BT20 titanium alloy without heat treatment were equivalent to those of the base metal respectively, but the microhardness was higher than that of the base metal. Postweld heat treatment in vacuum could obviously decrease the residual stress and improve the distribution of the residual stress of laser welded joint, and the effects on properties of welded joint were not obvious. In addition, the effects of postweld heat treatment on properties of YAG laser welded joint were more sensitive than that of CO2 laser welded joint because of greater effect on acicular martensite a in YAG laser weld.
Key words: titanium alloy, laser welding, postweld heat treatment in vacuum, properties of welded joint

3ӢCONSTANT-CURRENT CONTROL SYSTEM OF RESISTANCE SPOT WELDING BASED ON FUZZY LOGIC
Shanghai Jiaotong University Du Quanying, Chen Shanben
Wuhan Science and Technology University YU Yousheng

Abstract: The article studies a fuzzy logic control system for the resistance spot welding. The system adopting the single-chip microcomputer of intel80C196KC as the core tool and fuzzy logic as the adjusting way can compensate for the all kinds of influences on the welding current and make the current constant in the welding process, thus it can guarantee the quality of the welding. Using the difference between the effective value of current and preset value of current as well as the variation of the difference as two input variables, the controller outputs the adjusting angle of thyristor which is in the welding main return circuit. The results of the experiments show that the system, compared with the general PID controller, is more stable and can keep the current constant in the welding process, and then guarantees the quality of the welding.
Keywords: resistance spot welding, single-chip microcomputer of intel80C196KC, fuzzy control

4ӢNUMERICAL SIMULATION OF STRESS FIELD OF MEDIUM-HIGH CARBON STEEL SPECIMEN DURING SURFACING COOLING PROCESS
Yanshan University Yang Qingxiang, Cai Dayong, Yao Mei
Abstract: The temperature and residual stress field of medium-high carbon steel during surfacing cooling process are measured by adoption of thermal infrared imager and X-ray stress gauge. By use of experimental data and the physicalӢmechanical parameters of materials, the stress field model of FEM is established. According to this model, the stress of medium-high carbon steel during surfacing cooling process was analyzed in this paper. The simulation results show that the compressive stress will be appeared on the surface of the specimen during following cooling process when martensitic transformation occurs, and the great tensile stress will be appeared on the surface of the specimen and hold to room temperature with the increase of the time.
Keywords: medium-high carbon steel, surfacing, process stress, numerical simulation

5ӢCHARACTERISTICS OF HARMFUL STRUCTURE IN ADJACENT-WELD ZONE OF W9MO3CR4V/45 STEEL WELDED JOINT BY FRICTION WELDING AND ITS INFLUENCE ON THE QUALITY
Changchun Uiversity of Technology Zhou Zhenhua, Li Jun , Huo Yanqiu, Lu Xiaofeng
Abstract: W9Mo3Cr4V high speed steel(HSS)( ¦µ45 heat rolling bars with friction diameters of ¦µ40 and ¦µ20) was friction welded to 45 steel, and followed by annealing”¢quenching and tempering. The structure in the adjacent-weld zone was examined with optical and scanning electronic microscope. The results showed that in the adjacent-weld zone of the ¦µ40 HSS, overheated structure and a small amount of ledeburite were found. These were considered to be formed under too high friction linear speed and comparatively serious carbide segregation in the side of HSS. The harmful structure could not be eliminated by annealing and quenching, and when the quenching temperature is comparatively high, it tends to crack in the adjacent-weld zone along the weld.
Key words: high speed steel, friction welding, heat treatment, overheated structure, ledeburite

6”¢WELDING PROCEDURE OF SA-387M GR22CL2 STEEL USED IN REFORMING REACTOR 
Daqing Oil Field Building Material Manufacturing & Setting Co.Ltd 
Harbin Welding Institute Li Juanjuan Jiao Wei
Abstract: Based on the weldability characteristic of ASME SA-387M GR22CL2 steel, the welding material and procedure are studied to prevent cold crack, temper brittleness and to assure the mechanical properties of welded joint to meet designing requirement. The results show that the welding procedure are used successfully in practice.
Key words: reforming reactor, pearlitic heat resistanting steel, weldability, welding procedure

7ӢWELDING PROCEDURE OF X20CrMoV121 STEEL USED IN THICK-WALLED MAJOR DIAMETER PIPE CONNECTING MAIN STEAM
Neijinang General Power Plant Leng Zhengao
Abstract: X20CrMoV121 is the heat-resistant steel produced in accordance with Germany industry standard- DIN17175. The maximum available temperature is 650”ę and it is applied broadly to the imported high pressure and temperature set. This paper gives the application of X20CrMoV121 steel in a certain power station engineering in Sichuan province, analyses its welding property, introduces in detail the welding and heat treatment procedure
Key words: X20CrMoV121 steel, high pressure and temperature, welding procedure

8ӢDOUBLE ARC PHENOMINON OF VARIABLE POLARITY PLASMA ARC WELDING PROCEDURE IN WDLDING OF ALUMINUM
Beijing University of technology Lع Yaohui, Chen Shujun, Han Yongquan, Yin Shuyan
Abstract: In variable polarity plasma arc welding of aluminum, the stability and strained condition of variable polarity plasma arc were affected significantly by pilot arc. In DCEP time, large part of main current formed free arc between the pilot source and the nozzle through pilot arc power source, so double arc happened. At the same time, the force and penetration of plasma arc decreased because of the double arc..
Key words: plasma arc, variable polarity, pilot arc

Practical Essays
1”¢Repair welding of crack in clad steel plate head after machine-shaping”­”­”­”­”­”­”­”­”­”­”­.Zhang Lixin
2”¢Submerged arc welding of steel structure heelpost of high-rise building”­”­”­”­”­Bi Bo et.al
3”¢MAG welding of torque tension bar”­”­”­”­”­”­”­”­”­”­”­”­”­”­Nie Rong 
4”¢Sample explanation on cause and countermeasure of electric shock accident in shielded metal arc welding £ØSMAW£©”­”­”­”­”­”­”­”­”­”­”­”­”­Tao Tao
5”¢Testing method of shunting current in resistance spot welding of stainless steel”­”­”­”­”­”­”­”­”­”­”­”­”­”­”­”­”­”­”­”­”­”­”­”­”­Chen Yu et.al

Welding Train
Rudiment and practice of welding procedure qualification”­”­”­”­”­Xu Shiping et.al