1、J.Mater.Sci.Technol.,2011,27(4),369-376.Semi-hot Stamping as an Improved Process of Hot StampingMalek Naderi1),Mostafa Ketabchi1),Mahmoud Abbasi1)and Wolfgang Bleck2)1)Department of Mining and Metallurgy,Amirkabir University of Technology,Tehran,Iran2)Department of Ferrous Metallurgy,RWTH-Aachen Uni
2、versity,Aachen,GermanyManuscript received December 5,2010,in revised form February 11,2011Reducing the forming load,deletion of springback,increasing the formability of sheets as well as producinghigh strength parts are the main reasons to apply hot stamping process.Hot stamping process and 22MnB5st
3、eels are the state of the art process and grades,respectively;however novel processes and steel gradesare under considerations.In the current research,behavior of the steel grade MSW1200 blanks under semiand fully hot stamping processes was characterized.During semi-hot stamping process,the blank wa
4、s firstlyheated to a temperature of about 650C and then formed and quenched in the die assembly,simultaneously.Microstructure and mechanical properties of semi and fully hot stamped blanks were studied and the resultswere compared with those of normally water/air quenched blanks.The hot stamped blan
5、ks attained thestrength values as high as water quenched blanks.The highest ductility and consequently,the best formabilitywere achieved for the blank which had been semi-hot stamped.It was concluded that for the mentioned steel,semi-hot stamping process could be considered as an improved thermo-mec
6、hanical process which not onlyguaranteed a high formability,but also led to ultra high strength values.KEY WORDS:Semi-hot stamping;Hot stamping;MSW1200 steel;Mechanical properties1.IntroductionTo optimize the fuel consumption of cars,theweight reduction of cars is intensively required inthe automobi
7、le industry.Hence,application of highstrength steel sheets in automobile bodies would be agood solution to reduce the weight of cars1.How-ever,the use of high strength steel sheets usuallyleads to some disadvantages like high impact on thetools,reduced formability and the increased tendencyto spring
8、back2.To improve the formability charac-teristic and reduce or avoid the springback of highstrength steel sheets,hot stamping process has beenused widely.During this process,not only the flowstress is largely reduced by preheating the sheets,but also due to simultaneous occurrence of formingand quen
9、ching,forming load and springback decreaseand formability increases3.Hot stamping is de-Correspondingauthor.Tel.:+982164542949;Fax:+98 21 66405846;E-mail address:m.abbasiaut.ac.ir;ab-(M.Abbasi).fined as the process in which the blank is heated tothe temperature of the austenite stabilization region,
10、i.e.about 900C,for definite time and then formedand quenched simultaneously4.Many attempts havebeen done on the hot stamping process of steel sheetsespecially on quenchable boron-alloyed steels.It is re-ported that boron enhances hardenability and retardsand postpones thermally activated transformat
11、ions,e.g.ferrite and pearlite transformations3.Merkleinand Lechler2used 22MnB5 steel as material andstudied its hot stamping process.They showed thathot stamping process can result in production of com-ponents with tensile strength more than 1500 MPadue to changes in microstructure.Naderi et al.5an-
12、alyzed the microstructural and mechanical propertiesof different B-bearing steels after being hot stamped.Microstructures of the hot stamped blanks were com-posed of martensite.The resulted microstructuresprovided the yield strengths of 6501370 MPa and thetensile strengths of 8502000 MPa.The disadva
13、ntageof the hot stamping is remarkable oxidation on thesurface of products6.Thesheets are heatedat370M.Naderi et al.:J.Mater.Sci.Technol.,2011,27(4),369376Table 1 Chemical composition of the investigated steel(mass%)CSiMnCrNiAlTiCeq0.140.121.710.550.060.020.0020.258about 900C to attain the martensit
14、ic transformationinduced by the die quenching,and the oxide scalesare generated at this temperature.The oxidation be-comes remarkable due to contact with air after takingthe sheet out of the furnace.The shot blasting is usedto remove the oxide scales of stamped products orthe aluminum and zinc coate
15、d sheets are employed toprevent the oxidation during the hot stamping.Butthe shot blasting and coating are costly.Mori andIto7evaluated the effect of the oxidation preventiveoil on oxidation of quenchable steel sheets in a hothat-shaped bending experiment.They found that theoxidation was prevented b
16、y using coating.Schielet al.8analyzed corrosion behavior of coated andnon-coated steels after being hot stamped and notifiedthat high temperature austenization could damagethe coatings.Innovation of a stamping process thatbrings advantages of hot and cold stamping processesall together not only will result in low forming loadand minimizing of springback but also may preservethe coating properties properly and save time andcost.Semi-hot stamping process is a reply to thisrequest.During the semi-h
