Cutting insert, cutting edge-replaceable rotary cutting tool and rotary cutting method

A cutting insert having a plate shape centered on an insert center axis, the cutting insert comprising:

• a front surface and a back surface facing each other in an insert axial direction that is a direction in which the insert center axis extends;
• an outer peripheral surface extending from the front surface to the back surface;
• and
• a cutting edge formed at an intersecting ridge line between the front surface and the outer peripheral surface,
• wherein the outer peripheral surface comprises a flank surface extends from the cutting edge toward the back surface,
• wherein the flank surface inclines toward the insert center axis as the flank surface extends from the cutting edge toward the back surface,
• wherein the front surface comprises a flat surface and a peripheral area surrounding the flat surface,
• wherein the peripheral area comprises an inclined surface and a rake surface,
• wherein the inclined surface has a first edge coupled to the flat surface and a second edge opposite the first edge, and is angled with respect to the flat surface so that the second edge is located away from the insert center axis and the back surface,
• wherein the second edge of the inclined surface has a first portion that is coupled to the outer peripheral surface and a second portion coupled to the rake surface,
• wherein the rake surface extends from the second portion of the second edge to couple to the cutting edge, and is angled with respect to the inclined surface so that the rake surface extends away from the insert center axis and toward the back surface,
• wherein the cutting edge comprises a main cutting edge portion, and
• wherein, when viewed from a cutting edge length direction of the main cutting edge portion, a first angle between the back surface and the rake surface is 4° or more, and a second angle between the insert center axis and the flank surface is 2.5° or more.