| With the rapid development of modern industry,there is a growing demand for high-performance forklift trucks in logistics,warehousing,machinery manufacturing and other industries.Therefore,the development of high-performance gantry mounting structural steel for forklift is particularly urgent.At present,the high-performance gantry mounting structural steel with yield strength up to 500 MPa has not been reported.In this paper,a kind of 500 MPa grade gantry mounting structural steel with C-Mn-Nb-V-Cr-N composition system has been developed,which is mainly used in the production of J150a,J160b,C220b and so on.By means of microalloying and controlled rolling,the mechanical properties of the test steel can reach the indexes of yield strength?500 MPa,tensile strength?610 MPa,elongation?17%,impact energy at-20?? 27 J.According to the requirements of mechanical properties,a reasonable chemical composition was designed,and a series of basic research and rolling technology research were carried out on the test steel in the laboratory.The main research results were as follows.(1)Through the austenite coarsening test,the austenite growth behavior of the test steel at different austenitizing temperature(1000?1200?,every 50?)and holding time(15,30 min)was studied.The results showed that in a certain range,the austenite grain size increases with the increase of temperature and holding time,and the optimal austenitizing temperature is about 1150?.(2)Through the single pass compression experiment,the stress-strain relationship of the test steel under different deformation temperature(850?1050?,every 50?)and deformation rate(0.01,0.1,1,10 s-1)was studied,and the true stress-strain curvea were drawn.In a certain range,the higher the deformation temperature,the lower the deformation rate,then the easier dynamic recrystallization occurred.According to the experimental results,the recrystallization activation energy of the test steel was calculated to be Qd=358.9 kJ/mol,and the thermal deformation equation of the test steel was deduced to be?=1.94×1014[sinh(0.0069?p)]6.7exp(-358900/RT),the deformation resistance model of the test steel was.(3)Through the thermal simulation test,the continuous cooling transformation law of austenite was studied,and the dynamic and static CCT curves of the tested steel were drawn.The results showed that the cooling rate and the corresponding transformation products were:F+P at 0.1 ?/s,F+ P+B at 0.5 ?/s,F+ B at 1?5 ?/s,F+ B+M at 10 ?/s,B+M at 20?35?/s under the condition of undeformed.The cooling rate and corresponding transformation products were:F+P at 0.1?0.5 ?/s,F+P+B at 1?2 ?/s,F+ B+M at 5 ?/s,F+ B+ M at 10?/s,B+ M at 20?35?/s under the condition of deformed.The main structure of the test steel after air cooling is F+P.(4)Through the high temperature tensile test,the high temperature thermoplasticity of the test steel was studied.The results showed that when strain rate were 0.05 s-1 and 0.005 s-1,the temperature range of the third brittle zone were 685?716 ? and 611?896? respectively.The third brittle zone should be avoided when straightening the test steel to avoid the generation and propagation of cracks.(5)Through several times of rolling process research,the gantry mounting structural steel with mechanical properties up to the target was obtained,and it was successful in industrial trial production.The main chemical composition is:content of C is 0.17?0.19%,content of Mn is 1.4-1.6%,content of Nb is 0.03?0.04%,content of V is 0.07?0.09%,content of Cr is 0.3?0.4%,content of N is 0.011?0.013%.Main rolling process:heating temperature is 1150?,initial rolling temperature is 950?970?,final rolling temperature is 860?880?. |
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