TOKYO — When a roll of aluminum produced at a Kobe Steel factory fell short of customers’ exacting demands for qualities like strength, plant managers were supposed to make a painful but necessary decision: Start again and make a new, better roll of metal, even if it cost the company time and money.

But for at least a decade, according to an internal company report released on Friday, those managers took an easier way out, manipulating test data on some products to avoid expensive do-overs.

The report by the Japanese steel maker is its first public accounting of the causes of a data falsification scandal that has shaken the company and prompted around 500 of its customers around the world — including manufacturers of cars, trains and aircraft — to scramble to verify their products’ safety.

The report, produced by Kobe Steel without input from regulators or other outside parties, concluded that the company had erred by elevating the pursuit of short-term profit over the maintenance of scrupulous quality standards. That failing, it said, was exacerbated by lax oversight by senior executives and an “insular” corporate culture that discouraged employees from questioning improper but long-established practices.