Study On Microstructures&Properties Of Heat-affected Zone Of X100Pipeline Steels

In this paper, the microstructures and properties of heat-affected zone (HAZ) of X100pipeline steel in the welding process were studied by welding thermal simulation techniques,mechanical properties test and microstructure analysis, and the weakest area in HAZ ontoughness was found. Microstructure and properties of Coarse-Grained HAZ (CGHAZ) in X100Pipeline Steel were discussed under different heat input. In order to make the toughness ofCGHAZ to the best, suitable heat input range was put forward.Welding thermal cycle was one of the key factors that affect microstructure and propertiesof HAZ in X100Pipeline Steel, the toughness of different areas of HAZ were lower than baesmetal and they decreased along with the increase of peak temperatue.Among the different areasof HAZ, toughness of CGHAZ decreased42.6%compared with base metal and only reached163.8J, this phenomenon is called CGHAZ local embrittlement. Because of coarse grain andcoarse M-A constituents between grains, CGHAZ was the weakest area in HAZ on toughness.The toughness of CGHAZ of X100pipeline steel were lower than baes metal and theydecreased when peak temperatue increased. Toughness loss of CGHAZ was30percentage lessthan base metal when heat input in the range of10to20KJ/cm; The toughness of CGHAZdecreased significantly when heat input was more than25KJ/cm, particularly, the toughness lossof CGHAZ was96.1percentage less than base metal when heat input reached50KJ/cm, thisphenomenon is called serious CGHAZ local embrittlement.In CGHAZ with smaller grain size there exist slender bainitic ferrite lathes, thismicrostructure insure the CGHAZ with better strength and toughness when heat input changes inthe range of10to20KJ/cm; when heat input changes in the range of25to50KJ/cm, size ofCGHAZ was larger and long stripe M-A constituents、quasi-polygonal ferrite and degeneratedpearlite appear in the grains, so the toughness of CGHAZ decreased sharply. Based on thisanalysis, recommended range of heat input for X100pipeline steel changes between10and20KJ/cm. Results of this paper are not only helpful to establish the relationship between weldingtechnology、microstructure and properties, but also helpful to make welding technology on pipe manufacture welding and field welding of X100pipeline steel.