Development of non-annealing cold heading steel 10B21 hot rolled wire rod

The cold heading wire rods for fasteners are used to spheroidizing annealing or softening annealing before drawing to reduce strength and increase plasticity.However,the annealing process consumes energy and time,which not only increases costs but also pollutes the environment.For this reason,the non-annealing cold heading steel 10B21 wire rod with excellent cold workability was developed.Firstly,the composition of cold heading steel 10B21 was optimal designed.Under the premise of ensuring hardenability,the boron content is increased,and the carbon and manganese content were reduced,and the range of w(Ti)/w(N) was controlled in 4.0~4.5 to ensure the effective boron yield.Secondly,wire rod was produced by controlled rolling and controlled cooling process.In the slow cooling phase transition process,an appropriate amount of boron phase of M₃(C,B)+M₂₃(C,B)₆ was generated at the interface of α/γ to accelerate the deposition of carbon and form the best structure for cold heading.Meanwhile,due to the reduction of carbon and manganese content,the hardness of the steel was significantly reduced.Finally,a high plastic cold heading steel with excellent cold workability was obtained.The hot rolled wire rod could be directly drawn and cold heading without annealing,and could be used for making 8.8 grade high strength fasteners with large deformation such as flange bolts.