不同锰含量冷作强化非调质钢的微观组织和力学性能

Microstructure and mechanical properties of cold hardening microalloyed steel with different manganese contents

研究两种Mn含量的低碳Mn-B-Ti系冷作强化非调质钢的微观组织和力学性能。结果表明,当Mn含量偏低(B8钢,1.60%Mn)时,其微观组织为铁素体+粒状贝氏体+珠光体的混合组织;而当Mn含量较高(B6钢,2.02%Mn)时,可获得全低碳粒状贝氏体组织。两种钢的微观组织和拉伸性能随拉拔减面率γ的变化规律基本一致,但B6钢的屈强比明显低于B8钢。经300℃时效处理后,B6钢的强度可达到10.9级螺栓,而B8钢仅满足9.8级螺栓的要求。这表明,控制钢中的Mn含量以获得强塑性配合较好的低碳粒状贝氏体组织是10.9级螺栓用冷作强化非调质钢的基本条件。

Microstructure and mechanical properties of low carbon Mn-B-Ti series cold hardening microalloyed steels with two different manganese contents were studied.The results show that mixed microstructure which consists of ferrite,granular bainite and pearlite is obtained for steel B8 with a lower manganese content of 1.60%,whereas full low carbon granular bainite is obtained for steel B6 with a higher manganese content of 2.02%.The variations of both microstructure and tensile properties with drawing reduction for the two test steels are almost consistent,however,the yield strength ratio of steel B6 is obvious lower than that of steel B8.After aging treatment at 300 ℃,the strength of steel B6 meets the requirement of 10.9 grade bolt,while the strength of steel B8 just meets the requirement of 9.8 grade bolt.It is suggested that manganese content should be strictly controlled to obtain a full low-carbon granular bainitic microstructure to meet the requirement of cold hardening microalloyed steel for 10.9 grade bolt.