经新型Q-P-T工艺处理后Q235钢的组织与性能

MICROSTRUCTURE AND PROPERTIES OF Q235 STEEL TREATED BY NOVEL Q-P-T PROCESS

研究了最低屈服强度为235 MPa的Q235钢经新型淬火-分配-回火(Q-P-T)工艺处理后的力学性能和焊接性能.结果表明,经Q-P-T处理后的Q235钢(QPT235钢)强度得到了大幅度的提升:屈服强度和抗拉强度分别达到435和615 MPa.采用相同焊料和焊接工艺,QPT235钢焊接接头的力学性能比Q235钢显著提高,前者的抗拉强度约为532 MPa,延伸率约为16.7%,而后者的抗拉强度约为414 MPa,延伸率约为12.4%.显微组织观察揭示了QPT235钢性能改善的原因:QPT235钢焊接热影响区中铁素体晶粒和珠光体层片显著细化,并避免了魏氏组织的大量出现;在QPT235钢的母材和热影响区中均存在硬相马氏体、贝氏体和软相残留奥氏体的复合组织,取代了Q235钢中部分的铁素体和珠光体.

This paper presents the mechanical properties and welding properties of Q235 steel with minimum yield strength of 235 MPa treated by a novel quenching-partitioning-tempering （Q P- T） process. The experiments indicate that the strengths of Q-P-T treated Q235 steel （briefly called QPT235 steel） markedly raise compared with Q235 steel, and its yield strength and tensile strength are 435 and 615 MPa, respectively. In addition, the mechanical properties of the welding joint of QPT235 steel are markedly improved compared with Q235 steel when the same welding solder and process are performed for the steel with the two treatments, and the tensile strength and elongation of the former are about 532 MPa and 16.71%, respectively, while those of the latter are about 414 MPa and 12.4%. The microstructural characterization reveals two main factors resulting in the mechanical properties of QPT235 steel superior to those of Q235 steel： the grains of ferrite and interlamellar spacing of pearlite are both refined in the welding heat affected zone （HAZ）, and a lot of widmanstatten structures in the welding joint of Q235 steel is avoided for QPT235 steel; there is a mixed microstructure of hard phases of martensite and bainite as well as remained austenite as soft phase in both base metal and HAZ, which replace parts of ferrite and pearlite in Q235 steel.