外文翻譯 --關(guān)于經(jīng)旋壓成型生產(chǎn)的高強(qiáng)度薄壁鋼管缺陷發(fā)展的研究(英文）

1、69 Practical Failure Analysis Volume 1(5) October 2001An Investigation of the Development of Defects During Flow Forming of High Strength Thin Wall Steel TubesK.M. Rajan and K. Narasimhan(Submitted 12 June 2001; in revis

2、ed form 6 August 2001)Flow forming technology has emerged as a promising, economical metal forming technology due to its ability to provide high strength, high precision, thin walled tubes with excellent surface finish.

3、This paper presents experimental observations of defects developed during flow forming of high strength SAE 4130 steel tubes. The major defects observed are fish scaling, premature burst, diametral growth, microcracks, a

4、nd macrocracks. This paper analyzes the defects and arrives at the causative factors contributing to the various failure modes.Keywords: metal forming, inclusions, expert system, microstructure, surface finishPFANF8 (200

5、1) 5:69-76 © ASM InternationalIntroductionFlow forming is a promising, economical metal forming technology that can meet the challenging requirements of high specific strength, close dimen- sional tolerances, and ex

6、cellent surface finish de- manded by the defense and aerospace industries. The relatively low tooling cost and remarkable material utilization due to chipless metal forming provide economic drivers, while the ability to

7、achieve high strength finished product from low strength starting material is due to strain hardening.Flow forming is an incremental forming process that uses a 3-D variation of basic rolling processes and combines rolli

8、ng, shearing, and bending into one operation. It is similar to neither upsetting nor swag- ing. Essentially a point deformation metal forming process, flow forming results in a part having a highly deformed microstructur

9、e. Significant increases in yield strength, ultimate tensile strength, and hard- ness, and a corresponding reduction in ductility, accompany the flow forming process.Conventionally, tubes are produced by hot extru- sion

10、followed by drawing or pilgering. However, it is not practical to hot extrude thin wall tubes beyond a specified limit. Drawing is an easier and less expen- sive process than extrusion; therefore, a thick wall tube is co

11、ld extruded and finished on a draw bench or pilger mill. The drawing process is essentially a tensile process. Microcracks and other defects inside the material tend to propagate during the draw, leading to failure. The

12、area reduction is typicallylimited to 10% for each draw of a hard material, and the total reduction may require a number of anneal- ing cycles.[1] An increase in the number of drawing/ annealing cycles increases the cost

13、 of production. It is obviously very expensive to use drawing operations to produce components from hard-to-work mater- ials. However, if dimensional tolerances are not critical, it is advisable to use cheap conventional

14、 cold drawn steel (CDS) tube. Flow forming, therefore, offers several advantages over conventional tube making methods.The Flow Forming ProcessFlow forming is used to produce a seamless tube with tight dimensional tolera

15、nces. Seamless tubing, theoretically, may represent the ultimate in reliabil- ity.[2] A metal blank or preform is formed over a rotating mandrel. The metal blank and the mandrel (which are locked together) rotate, and th

16、e forming roller follows the mandrel at a preset that has been programmed into a CNC flow forming machine. The preform metal is plasticized by the local ap- plication of heavy compressive forces exerted by coni- cal roll

17、ers. The deformed metal takes the shape of the mandrel, and proper wall thickness is achieved by control of the gap between the rollers and the mandrel.Flow forming can be divided into two distinct processes: forward flo

18、w forming and reverse flow forming. In forward flow forming, roller feed and deformed material movement are in the same direc- tion. The formed material is under tension, and theK.M. Rajan, Armament Research and Developm

19、ent Establishment, Pune-411 021, India. K. Narasimhan, Department of Metallurgical Engineering and Materials Science, IIT, Bombay-400 076, India. Contact e-mail: nara@met.iitb.ac.in.71 Practical Failure Analysis Volume 1

20、(5) October 2001hardness and percentage thickness reduction assoc- iated with each pass are shown in Table 1. The flow formed tube, after undergoing a total percentage thickness reduction of about 88%, was trimmed, and t

21、ensile test samples were taken from a fully formed extra length of the tube as per ASTM A 370 (Fig. 3). The specified and achieved mechanical properties and dimensional accuracies are presented in Table 2.Proof Pressure

22、TestingTubes that satisfied the specified mechanical prop- erties and dimensional accuracy requirements were subjected to 100% hydraulic testing. The tubes were subjected to a pressure 10% above the maximum expected oper

23、ating pressure for about one min, then checked for permanent set, if any, and premature failure. No testing in induced failure or permanent set was accepted. After passing this test, the tubes were subjected to burst tes

24、ting.Burst Pressure TestingOne tube out of each group manufactured from the same heat of steel and lot of processed preforms was randomly selected and subjected to burst pressure testing. The burst pressure test confirms

25、 the margin of safety over the maximum expected operating pressure. A few burst tubes are shown in Fig. 4.DefectsDefects in the flow formed tubes may cause failure in the proof or the burst tests. The types of defectsand

26、 associated failures can be categorized as micro- cracks, macrocracks, diametral growth, ovality, fish scaling, and premature bursting.The flow forming process occasionally introduces waviness or bulges on the outer-face

27、 of tubes. Such defects occur only under certain working conditions. This phenomenon is called “plastic flow instabil- ity.”[5] Kobayashi[7] analyzed instability in cone spin-Table 2 Mechanical properties and dimensional

28、 tolerances of flow formed tubeMechanical Properties Dimensional TolerancesUTS 0.2% yield strength %EI Ovality Straightness Surface roughness (MPa) (MPa) (mm) (mm) CLA (µm)Specified 1200 (min) 900 (min) 6 (min) 0.2

29、(max) 0.15 (max) --Actual 1250-1350 950-1100 7-8 0.15-0.20 0.1-0.15 N5-N6Table 1 Flow forming sequence with thickness and hardness variations in each passPass No. Initial thickness Final thickness Initial hardness Final