440MPa级新型高强度烘烤硬化钢的组织与性能研究

Study of Microstructure and Properties of a New 440 MPa Grade High Strength Bake Hardening Steel

采用OM和TEM等仪器对440MPa级新型高强度烘烤硬化钢的组织与性能进行了分析，研究了其强化机制与烘烤硬化机理。结果表明，试验用钢的显微组织为铁素体与少量珠光体的混合组织，随着氮元素含量增加与卷取温度的下降，铁素体晶粒变得更加细小；低氮钢630，600℃卷取下铁素体晶粒平均尺寸分别为8．34，7．89μm，由细晶强化引起的屈服强度增量分别为190，196MPa；高氮钢630，600℃卷取下铁素体晶粒尺寸分别为6．93，6．71μm，由细晶强化引起的屈服强度增量分别为209，212MPa。烘烤硬化热处理后屈服强度与抗拉强度均呈现出上升的规律，在相同的预应变下，晶粒尺寸越小，氮含量越高，抗拉强度上升值越大；高氮钢在10％预应变下BHT值均在70MPa以上，抗拉强度达到500MPa以上。

The microstructure and properties of a new 440 MPa grade high strength bake hardening steel were analyzed by OM and TEM. The strengthening mechanism and bake hardening mechanism were studied. The results showed that the microstructure of the test steel was a mixture of ferrite and a small amount of pearlite. With the increase of N content and the decrease of the coiling temperature, the ferrite grains became finer. The average ferrite grain size of the low N steel was 8.34 μm and 7.89 μm when the coiling temperature was 630 ℃ and 600℃, respectively, and the yield strength increment caused by fine grain strengthening was 190 MPa and 196 MPa, respectively. The average ferrite grain size of the high N steel was 6.93 μm and 6.71 μm when the coiling temperature was 630 ℃ and 600 ℃, respectively, and the yield strength increment caused by fine grain strengthening was 209 MPa and 212 MPa, respectively. The yield strength and tensile strength both showed an ascending rule after bake hardening treatment. Under the same prestrain, the smaller the grain size was and the higher the N content was, the more the tensile strength increased. The BHT value of the high N content steel at 10% prestrain was above 70 MPa and the tensile strength was above 500 MPa.