Development and Quality Control of 600 MPa Steel Bar for Bolt Applied to Seam Gateway Support

Abstract：According to the present status of the bolt bar steel long term with a low strength and poor safety performances,a low yield strength ratio and high tough plasticity bolt bar steel with a yield strength of 600 MPa was researched and developed for the seam gateway support.The paper stated the design ideas of the chemical compositions,micro material structure and the production technique route.The paper had a deep research on the influence factors to the low yield strength ratio and high impact toughness under the hot-rolling technique.The production control technique of the pureness could be improved with the reduction of the dynamic recrystallization zone to reduce the mixed crystal,the cooling controlled fined crystal particle and the clean steel rout and could have an excellent plastic toughness.Also with the controlled multi phase steel formation F（ferrite,53%）＋P（pearlite）＋M（martensite）/A（austenite） and the second phase nanoparticles（10~30 nm）,the intensified tensile strength was calculated,the F size was about 10~15 μm and the yield strength ratio reached the designed requirement not over 0.72.An evaluation on the actual controlled level of the inclusions in the steel and the performance index was conducted.