Effect of the t8/5 Cooling Time on the Properties of S960MC Steel in the HAZ of Welded Joints Evaluated by Thermal Physical Simulation

Abstract

The heat input into the material during welding significantly affects the properties of high-strength steels in the near-weld zone. A zone of hardness decrease forms, which is called the soft zone. The width of the soft zone also depends on the cooling time t8/5. An investigation of the influence of welding parameters on the resulting properties of welded joints can be performed by thermal physical simulation. In this study, the effect of the cooling rate on the mechanical properties of the heat-affected zone of the steel S960MC with a thickness of 3 mm was investigated. Thermal physical simulation was performed on a Gleeble 3500. Three levels of cooling time were used, which were determined from the reference temperature cycle obtained by metal active gas welding (MAG). A tensile test, hardness measurement, impact test with fracture surface evaluation, and microstructural evaluation were performed to investigate the modified specimen thickness. The shortest time t8/5 = 7 s did not provide tensile and yield strength at the minimum required value. The absorbed energy after recalculation to the standard sample size of 10 × 10 mm was above the 27 J limit at −40 °C. The hardness profile also depended on the cooling rate and always had a softening zone.

Influence of Welding Parameters and Filler Material on the Mechanical Properties of HSLA Steel S960MC Welded Joints

“…This limit assumes a correlation between the hardness and the strength. In previous experiments on a Gleeble device [18], S960MC steel samples were exposed to different temperatures and thermal cycles, and the mechanical properties were evaluated. According to the hardness and strength values, the limit value of hardness (90% of base material) was determined, at which the steel reached the required yield strength.…”

“…Depending on the temperature reached, softening is divided into transformation softening (if the temperature has exceeded Ac1) and tempering softening (below Ac1) [8,14]. The phenomenon of softening has been the subject of several studies, which include excess heat input and a low cooling rate as the key issues of the decrease in strength [9,[14][15][16][17][18][19][20][21][22]23]. With an increasing maximum temperature and a decreasing cooling rate, changes in the HAZ properties are more pronounced.…”

Numerical Verification of Tests on the Influence of the Imposed Thermal Cycles on the Structure and Properties of the S700MC Heat-Affected Zone

“…The reduction of sheet thickness produced in thermo-mechanical rolling processes (TMCP) for the needs of the automotive, shipbuilding, oil industry while maintaining all existing operational parameters allows to achieve significant savings resulting from lower expenditure on material processing and lower transport costs. Alternative materials with respect to modern steel grades still have many limitations associated with high manufacturing costs, limited resistance to elevated temperatures and difficult joining processes [5][6][7][8][9][10].…”

Assessing MMA Welding Process Stability Using Machine Vision-Based Arc Features Tracking System

“…Considering the highly nonlinear and time-varying complex welding process with a high number of degrees of freedom MMA is not often a subject of research. Several methods utilizing one or more sources of information about the welding process condition and stability was elaborated for different welding techniques [ 8 , 9 , 10 ].…”