Study On Microstructure And Microhardness Of Heat-affected Zone Of Quenched And Tempered Steel In Open Arc Swing Bead Welding

Squeeze roller is the core components of the crucial large-scale pressequipment in the dry-process cement production line. Surfacing strengtheningof the new squeeze roller and surfacing repair of damaged squeeze roller arethe main methods to extend the roller press life. The cement plant stronglyincline to repair the old squeeze roller on-line using high current building up inwinter, however, this is limited by the lower toughness of heat-affected zone.The relationship between the microstructures and mechanical properties of theweld zone and heat-affected zone of the45quenched and tempered steel underdifferent heat input and cooling down with ice in single and dual-channelsurfacing were investigated in this paper.The heat inputs of different processes increase in accordance with the3,6,9,2,5,8,1,4,7process number sequence. The ice cooling has little influenceon the t8/5of different processes, but has great influence on the t8/3. Among thet8/3data, the7thprocess is greater than70s, about30s more than the1stand3rdprocesses.The microstructures of fusion zone and coarse grain heat affected zone(CGHAZ) of one-pass bead weld samples mainly consists of net-like ferrite,troostite/sorbite and a small amount of widmanstatten and M-A island. Theheat input has no obvious influence on the composition of microstructures offusion zone and overheated zone, but has significant influence on theproportion of the above phases, especially the amount and size of M-A andwidmanstatten. In addition, the heat input has no obvious effect on the amountand size of ferrite of softening zone.For one-pass bead weld processes, the1Asample has good formability. Its average dilution ratio and forming coefficient are0.443and23.5, respectively. Compared with the others samples, the finestgrain was obtained in the fusion and coarse grain zones of1A sample, whichare5.07and5.40ASTM grade, respectively. The volume percentage of M-A inthe above zones is2%-3%, which is the least amount compared with those ofthe others. The microhardness fluctuation in its heat-affected zone is the least,of which the range is32HV0.3.The microstructures of the regions, which is the weld zones in first-pass building up welding and is reheated up to a temperature higher than AC1in thesecond pass, and the heat-affected zones in first-pass, and reheated up to a atemperature higher than1400℃in second pass, mainly consists of equiaxedgranular bainite and a small amount of net-like ferrite. The microhardness ofthe said regions is almost the same as that of the weld zones of single pass. Themicrostructures of the regions, which is the quenching zone in the two passes,and the soft zones of first-pass, and reheated up to a temperature in range ofAc1~1400℃in the2ndpass, chiefly include in sorbite/troostite, M-A massivestructure and a little amount of net-like ferrite. Compared with thecoarse-grained of single pass, the grains of the above regions become finer, themicrohardness distribution curves are the peak shape, which has no obviousdifference with those of the Ⅱ zones of one pass samples of. The regions,which is the quenching zone or the soft zone in the single pass and reheated upto a temperature in range of temper temperature~Ac1in the second pass, arebelong to tempering soft zones; the microhardness in IIC and IIIC zones areslightly different.The amount of M-A massive structure in the critical coarse-grainedheat-affected zone of the4B sample of double passes is the least and the sizeof M-A is the smallest. The microhardness fluctuation range of4B sample is85.4HV0.3, however, the differential value of the others between maximumand minimum are greater than100HV0.3.Combined consideration the formability of bead weld layer,microstructure homogeneity of weld zone, grain size, M-A volume percentageand microhardness in fusion and coarse grain zones, The optimized build-upwelding process parameters are as follows:For single pass welding, the electric current, voltage, moving velocity ofblowtorch and weld width are300A,29V,60mm/min and60mm, respectively.For double pass welding, the electric current, voltage, moving velocity ofblowtorch and weld width are340A,30V,70mm/min and60mm, respectively.