A surface microstructure strengthening process for alloy steel used in hard rock drilling tools

By controlling the flow rate and temperature of the cooling medium, an interwoven structure of martensite and lower bainite is formed on the surface of the alloy steel of the hard rock drilling tool. This solves the problem of softening of the alloy steel surface under high temperature environment, improves hardness retention and impact toughness, and extends the service life of the tool.

CN122303541APending Publication Date: 2026-06-30QIDONG COUNTY FENGSU DRILLING TOOLS CO LTD
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Patent Information

Authority / Receiving Office
CN · China
Patent Type
Applications(China)
Current Assignee / Owner
QIDONG COUNTY FENGSU DRILLING TOOLS CO LTD
Filing Date
2026-05-20
Publication Date
2026-06-30

AI Technical Summary

Technical Problem

The alloy steel surface of existing hard rock drilling tools is prone to softening under high temperature conditions, resulting in poor hardness stability and difficulty in maintaining cutting edge life.

Method used

By controlling the flow rate and temperature of the cooling medium, the Reynolds number of the heat transfer boundary layer is kept in the laminar flow range of 1800 to 2200. The latent heat of phase transformation drives the local turbulent transformation, forming an interwoven structure of martensite and lower bainite. Alloying elements are precipitated in situ at the phase interface through segmented tempering treatment to construct a tough phase skeleton.

Benefits of technology

It achieves a high-density in-situ interwoven structure on the surface of alloy steel, which improves hardness retention and impact toughness, prevents softening during secondary tempering, and extends the service life of tools.

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Abstract

This invention relates to the field of heat treatment technology for high-performance tunneling machine tool steel, and discloses a surface microstructure strengthening process for alloy steel used in hard rock drilling tools. The process includes: heating the alloy steel workpiece to the austenitizing temperature, injecting a cooling medium into the quenching zone and setting the initial Reynolds number of the heat transfer boundary layer to be in the critical laminar flow range, using the latent heat of phase transformation released by the microstructure transformation to instantaneously reduce the kinematic viscosity of the cooling medium at the contact interface, driving the heat transfer boundary layer to transform from laminar to local turbulent flow to dissipate the latent heat of phase transformation, suppressing microstructure coarsening, forming an interwoven structure of martensite and lower bainite, and sequentially employing isothermal treatment and two-stage segmented tempering. This invention constructs a dynamic compensation mechanism that utilizes the latent heat of phase transformation to induce a self-correcting flow field, thereby offsetting local temperature rise in real time, eliminating soft spots caused by heat conduction lag, and enabling the strengthened layer microstructure to possess extremely high thermal stability and hardness.
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