本发明公开了一种油气田用马氏体不锈钢圆管坯，其包括下述成分，以质量百分数计：C：0.16～0.21％，Si：0.15～0.35％，Mn：0.3～0.5％，P≤0.015％，S≤0.002％，Cr：12.6～13.0％，Mo：0.05～0.1％，N：0.02～0.04％，余量为Fe及其它杂质。本发明还公开了一种油气田用马氏体不锈钢圆管坯的制造方法，其包括以下步骤：铁水预处理、K‑OBM‑S粗炼、VOD精炼、LF精炼、浇铸、初轧开坯、修磨、径锻、退火、检验、车光打孔及交库。本发明通过成分优化设计和控制工艺过程中的关键参数，解决了气体含量高、夹杂物级别难控制、钢质纯净度差、探伤缺陷等质量问题，确保制造出的圆管坯钢质纯净、气体含量低、大幅度减少缺陷，满足后续制管生产及成品管在油气井中的使用要求。

The invention discloses a martensitic stainless steel round pipe blank for oil and gas fields, which comprises the following components, in terms of mass percentage: C: 0.16～0.21%, Si: 0.15～0.35%, Mn: 0.3～0.5%, P≤ 0.015%, S≤0.002%, Cr: 12.6-13.0%, Mo: 0.05-0.1%, N: 0.02-0.04%, the balance is Fe and other impurities. The invention also discloses a method for manufacturing martensitic stainless steel round pipe billets for oil and gas fields, which includes the following steps: hot metal pretreatment, K-OBM-S roughing, VOD refining, LF refining, casting, blooming, Grinding, diameter forging, annealing, inspection, turning and drilling and delivery. The invention solves the problems of high gas content, difficult control of inclusion levels, poor steel purity, flaw detection defects and other quality problems by optimizing the design of the composition and controlling the key parameters in the process, and ensures the purity of the produced round tube billet steel. The gas content is low, the defects are greatly reduced, and the requirements for subsequent pipe production and the use of finished pipes in oil and gas wells are met.