高强钢增强韧性的在线淬火技术开发与应用

Development and application of online quenching technology for enhancing toughness of high strength steel

近年来,广泛应用于中厚板高强钢生产的在线淬火工艺是一种绿色、短流程制造工艺,然而与离线淬火工艺相比,普遍存在强度偏高而冲击韧性较低的问题,阻碍了这种工艺的推广应用。研究发现,产生此类问题的原因是因为轧制过程中奥氏体组织调控不当,使得轧制后钢板的奥氏体晶粒主要呈现出扁平状,这种形态的奥氏体在随后的直接淬火过程中容易形成贯穿原始奥氏体晶粒的马氏体板条,并且取向较为一致,不利于阻止裂纹的拓展。以奥氏体组织调控为基础,钢板轧制后形成细小等轴状态的奥氏体晶粒,并保留部分塑性变形过程的位错,在随后的淬火过程中,形成取向各异的马氏体板条束,这种组织有利于阻止裂纹拓展,从而可有效提升钢材的冲击韧性,不添加昂贵的微合金元素也可实现550 MPa级高强钢的生产,在强度相同的情况下,-20℃冲击韧性大幅度提升到200 J以上,达到离线淬火相当的水平,同时,提高了机组产量;相比于离线淬火,这种工艺下的微合金元素可较多固溶于奥氏体中,随后淬火过程中保留于马氏体中,在回火过程中增强微合金碳氮化物析出强化作用,进一步提高产品的强度,最终采用该工艺所制造的690 MPa级高强钢性能与离线淬火韧性相当且强度略高,为工艺进一步推广应用拓展了新思路。

In recent years,the online quenching process widely used in the production of high-strength steel for medium and thick plates,which is a green and short process manufacturing process.However,compared with the offline quenching process,the problem of high strength and low impact toughness,which hinders the promotion and application of this process.It is found that the reason for this problem is the austenite grain of the rolled steel plate mainly presents a flat shape due to the improper control of the austenite structure during rolling.In the subsequent direct quenching process,this form of austenite is easy to form martensite lath through the original austenite grain,and the orientation is relatively consistent,which is not conducive to preventing the expansion of cracks.In this paper,based on the control of austenite structure,the rolled steel plate forms fine equiaxed austenite grains,and retains some dislocations during plastic deformation.In the subsequent quenching process,martensite lath with different orientations are formed.This structure is conducive to preventing crack propagation,thus improving the impact toughness of the steel effectively.The production of 550MPa high strength steel can be achieved without adding expensive microalloying elements,the impact toughness at-20℃has been significantly increased to over 200J,reaching the equivalent level of offline quenching,while also increasing the production of rolling line.Compared with offline quenching,the microalloyed elements under this process can be more solidly dissolved in austenite,and then retained in martensite during quenching.The precipitation strengthening effect of microalloyed carbonitride is enhanced during tempering.Finally,the 690MPa high strength steel produced by this process has the same performance and slightly higher strength as offline quenching,which expands a new idea for further promotion the process.