The change characteristic of drillability and hardness of a rock under different thermal situations is a fundamental problem that must be clarified in deep engineering. In order to study the effect of high temperature on the drilling rate and hardness of a rock, the micro-drilling, indentation hardness and Leeb hardness tests were carried out on the sandstone samples that were preheated to different temperatures. The microstructure of the samples was observed by scanning electron microscope (SEM) to reveal the physical essence of changes in drilling rate and hardness. The results showed that the drilling rate increases gradually with temperature increase. The fastest increase rate was between 300 °C and 500 °C, and the increase rate was lower when the temperature exceeded 500 °C. The indentation hardness and Leeb hardness both had a decrease and then an increase with the increase in temperature, and the inflection point was around 700 °C. According to SEM images, the changes in drilling rate and hardness of samples treated below 700 °C were induced by the development and expansion of cracks (mainly intergranular cracks), which is a quantitative change process. The change in drilling rate and hardness above 700 ℃ was controlled by melting, which became a qualitative change process. The samples’ drilling rate, indentation hardness and Leeb hardness showed excellent linear correlations with their P-wave velocity and linear or local linear relationships with uniaxial compressive strength (UCS).

岩石在不同热工况下的可钻性和硬度变化特征是深部工程必须明确的基本问题。为研究高温对岩石钻孔速度和硬度的影响，对预热至不同温度的砂岩样品进行了显微钻孔、压痕硬度和里氏硬度试验。通过扫描电子显微镜（SEM）观察样品的微观结构，揭示钻孔速度和硬度变化的物理本质。结果表明，随着温度的升高，钻孔速率逐渐增加。300～500℃之间增幅最快，超过500℃时增幅较低。压痕硬度和里氏硬度均随温度升高先下降后上升，拐点在700℃左右。根据 SEM 图像，700 ℃以下处理的样品的钻孔速率和硬度的变化是由裂纹（主要是晶间裂纹）的发展和扩展引起的，这是一个量变过程。700℃以上的钻孔速度和硬度的变化是由熔化控制的，变成了质变过程。样品的钻孔速率、压痕硬度和里氏硬度与它们的 P 波速度和单轴抗压强度 (UCS) 的线性或局部线性关系显示出极好的线性关系。700℃以下处理的试样钻孔速度和硬度的变化是由裂纹（主要是晶间裂纹）的发展和扩展引起的，这是一个量变过程。700℃以上的钻孔速度和硬度的变化是由熔化控制的，变成了质变过程。样品的钻孔速率、压痕硬度和里氏硬度与它们的 P 波速度和单轴抗压强度 (UCS) 的线性或局部线性关系显示出极好的线性关系。700℃以下处理的试样钻孔速度和硬度的变化是由裂纹（主要是晶间裂纹）的发展和扩展引起的，这是一个量变过程。700℃以上的钻孔速度和硬度的变化是由熔化控制的，变成了质变过程。样品的钻孔速率、压痕硬度和里氏硬度与它们的 P 波速度和单轴抗压强度 (UCS) 的线性或局部线性关系显示出极好的线性关系。