| Cord steel has good elasticity,high strength and impact resistance.It is the representative product of super clean steel and the iconic product of steel wire production level.Cord steel is drawn step by step by wire,the diameter is generally 0.15～0.38 mm,any slightly larger size of hard inclusion,segregation,unconventional organization,internal and surface defects may cause wire breakage.In addition,cord steel bars have very strict requirements for chemical composition,diffusion hydrogen content,decarburization layer,inclusion type,size and quantity.Taking SWRH77A,SWRH77B and SWRH82B cord steel produced by Liugang Group as experimental materials,the effects of air relative humidity on diffusion hydrogen content of cord steel,heat treatment parameters on decarburization layer of cord steel,refractory material on cleanliness of cord steel and slag washing on refining effect of cord steel were studied.The inclusions and their microstructure in cord steel were analyzed and the Ca O-Si O2-Al2O3ternary low melting point plastic zone was determined.The main results are as follows:（1）The diffusive hydrogen content,hydrogen pore size and microhardness values all increase with the increase of air relative humidity.By implementing RH vacuum hydrogen removal method in liugang production line,the hydrogen content in the steel decreased from 8～10 ppm before refining to less than 1 ppm.（2）A heat treatment decarburization protective material with Bayer red mud as the main raw material was developed.The red mud protective coating has a good protective effect on the test steel when the heating temperature is lower than 950℃.（3）The inclusions in cord steel are mostly below 20μm,and the inclusions are mainly A sulfides and C silicate.The Mn S inclusions will deform along the rolling direction of the test steel after rolling deformation,which belongs to plastic inclusions,while the inclusions containing Ba do not deform and belong to non-deformed inclusions.The undeformed structure of cord steel is mainly layered Sorbite.After rolling deformation,the whole structure is gradually fibrous,and the lamellar spacing of layered Sorbite decreases gradually.After de-stress annealing treatment,the flake cementite in the tissue was broken and spheroidized gradually.Spherical cementite does not have plastic deformation,only arranged with rolling direction,which is not suitable for drawing.So lead bath quenching or water bath quenching should be carried out.（4）The composition range of low melting point plastic zone of Ca O-Si O2-Al2O3ternary system is:Si O2content is 40%～60%,Al2O3content is10%～20%,Ca O content is 25%～40%,melting point is lower than 1400℃.SWRH82B cord steel has the best corrosion resistance after reacting with alumina magnesia brick.A dense Al2O3oxide film was formed on the surface to prevent the reaction.（5）The high melting point red mud slag can be modified into low melting point refining slag by adding 60%silicon oxide and 48%calcium oxide.The slag washing process has a good refining effect on SWRH82B cord steel with more Al2O3inclusions. |
